Introduction

We recently developed a non-invasive technique for measuring in vivo tendon stress [1] which could be used to assess rehabilitation of tendon injuries. The technique is based on a simple tensioned beam model for tendon, which predicts that shear wave speed squared is proportional to axial stress at functional loads [1]. We have previously shown that our model is valid for ex vivo tendons loaded in a mechanical testing machine [1]. Additionally, we have applied the technique to measure in vivo tendon stresses during dynamic activities, e.g., the Achilles tendon during walking [1]. However, there is no non-invasive gold standard measure for tendon stresses in vivo. Thus, an in vitro validation technique is more viable. Here we present pilot data for in vitro validation of the proportional relationship between wave speed squared and tendon stress.

Methods

We simulated gait [2] on one fresh-frozen cadaveric lower limb specimen: 1) a 6-DOF robot moved a force plate relative to the plantar surface of the foot to mimic relative tibia-to-ground motion and ground reaction forces observed during normal gait; 2) tendon forces were concurrently modulated using PID control to prescribe dynamic force profiles estimated from the literature. Gait simulations were performed at 1/6^th physiologic speed and at 50% body weight. We synchronously measured Achilles and tibialis anterior tendon wave speeds using a novel surface-mounted sensor [1] comprised of: 1) a piezoelectric-actuated (Thorlabs PK4JQP1) tapping device that induces shear waves, and 2) a pair of miniature single-axis accelerometers (Piezotronics 352C23) aligned in series along the tendon. After each tap (50 taps/s), the induced wave sequentially passes the two accelerometers. Wave speed is calculated from a time delay determined by cross-correlation of the two acceleration signals. Tendon wave speed and force data were collected for each tendon during three simulated gait cycles.

Results

Ensemble averaged Achilles tendon wave speed squared and force (see figure) were highly correlated for both the Achilles (r² = 0.94 ± 0.01) and tibialis anterior (r² = 0.94 ± 0.01) tendons.

Discussion

Although more data are needed, these results show that in vitro Achilles and tibialis anterior tendon squared shear wave speeds are directly proportional to axial loading during functional activities. Thus, our non-invasive technique can provide highly sought after estimates of in vivo tendon loading. Future validation work (n=10 cadaveric specimens) will consider possible inter-specimen and inter-tendon differences in the wave speed-stress relationship, and will address the potential need for subject-specific calibration.

Acknowledgements

NSF GRFP (DGE-1256259, DGE-1747503), NIH (HD092697).

References

1. Martin, J.A., et al. Nat Commun, in revision

Introduction
    Early training for Achilles tendon ruptures (ATRs) can yield positive results [1], but the possibilities of re-rupture are also added [2].

Methods

Results
Eqs. 1-4 were used to design a gait pattern for early training of ATRs, i.e. to delay stance phase from the uninjured side, to reduce step length from the injured side and to control walking speed. A 50-year-old ATR patient and his doctor agreed to adopt our early training gait pattern three days after his cast was removed. VGRFs from the uninjured and injured side of 24 tests from a 98-week follow-up study of this patient were shown below. Fig. A – X: results from 24 tests, where W-number referred to the testing week, red VGRF of the injured side, green that of the uninjured side, black square dot line the resultant force of both sides, grey bar the double support time, and blue dash line the weight. VGRF was normalized by weight. The results showed that the peak values of the injured side’s VGRF were close to the weight at the early training period.

Discussion
When walking is prescribed as part of rehabilitation training program [3], it is necessary to design a gait pattern to best recover while preventing further injury [4]. The case study showed the effectiveness of our designed gait pattern - to delay stance phase from the uninjured side, reduce step length from the injured side and control walking speed so as to reduce the peak values of the injured side’s VGRF close to the weight. It can be applied to develop early rehabilitation training program for ATRs.

Acknowledgements
National Natural Science Foundation of China (Grant Number 11172073) 

References
[1] Schepull, et al, Am J Sport Med 2013; 41:2550-2557
[2] Soroceanu et al J Bone Joint Surg Am 2012;94:2134-2143
[3] Tejwani, et al, Am J Orthopsychiat 2014;43:E221-5;
[4] Fan et al, Gait Posture 2016;47:31-36.

Knee-Ankle-Foot Orthoses are used for reproducing the extension of the knee joint and dorsiflexion in the ankle joint to improve the walking pattern of patients with muscular weakness in quadriceps or pretibial muscles. In most passive orthoses, the hamstring or calf muscles are used to compensate for the weakness of the quadriceps or pretibial muscles, respectively. Therefore, strengthening these muscles is essential in order to correct the walking pattern in patients. Using a non-circular cam and a linear spring, a non-linear rotation mechanism that is capable of producing any torque value at different angles of rotation is designed. By designing a patient specific mechanism, the moment needed to correct the walking pattern in proportion to the muscle weakness of the patient is applied in any desired number of stages to the hamstring and calf muscles. This leads to the strengthening of these muscles in the long term and does not exert sudden pressure on them. Exerting sudden pressure on the hamstring or calf muscles to correct walking patterns in order to compensate for the weakness in these muscles may damage them. Damaging hamstring or calf muscles in these patients is results in locking their joints because none of their extension and flexion muscles have the ability to apply the necessary torque. Therefore, in order to maintain the stability of patients, it is necessary to hold their knee and ankle joints steady.

Introduction

Accurate reduction of the syndesmosis is a significant predictor of functional outcomes following syndesmotic fixation^1-5. The purpose of this study was to compare the reliability and accuracy of 16 existing computed tomography (CT) methods to measure the distal tibiofibular syndesmosis in uninjured, paired cadaveric specimens and in simulated malreduction models. It was hypothesized that there exists a repeatable method that can accurately discern each specific malreduction based on the native anatomy of the contralateral side.

Methods

Computed tomography scans of twelve pairs of fresh-frozen lower leg specimens were collected, and 3D models were used to establish a joint coordinate system according to the ISB standard⁶.  The CT images were then re-sliced along the proximal/distal axis. A literature review identified 16 methods comprised of 35 measurements for analyzing the syndesmosis on CT scans. Each measurement was performed on the 24 native ankle CTs in a custom Matlab program by three independent raters, one of whom performed the measurements twice. The 24 intact CTs were then digitally malreduced (Fig1A) and re-measured by the primary rater. The malreduced states included 1) 2mm of lateral fibular translation 2) 2mm of posterior tibial translation 3) 7 degrees of external tibial rotation 4) 1,2 and 3 combined. Standardized response mean (mean difference divided by standard deviation of differences) between each simulated malreduced state and its contralateral intact state was calculated for each of the measurements. On the intact state measurements, the intraclass correlation coefficient (ICC) was calculated to assess inter- and intra-rater measurement reliability, and Pearson correlation coefficients were calculated to assess side-to-side correlation.

Results

The most responsive (highest standardized response mean) measurements for detecting isolated and combined malreduction (Fig1B) were Mendelsohn Center Tibio-Fibular Distance, Phisitkul Medial/Lateral Translation and Prior Diastasis for lateral translation, Davidovitch Direct Translation for posterior translation, and Nault Angle for external rotation of the fibula. Additionally, these measurements were highly repeatable (inter-rater ICCs>0.6) and displayed variable intact side to side correlation (range:0.102–0.508).

Discussion

Reliable, predictive CT measurement techniques to assess isolated lateral and posterior translation, isolated external rotation, and combined syndesmosis malreduction were identified. The best methods were selected based on high responsiveness to a specific malreduction, even when confounded by additional translations or rotations. Computer-simulated injuries can be used to assess diagnostic tools in a resource-efficient manner. Additionally, this study can help establish a gold standard syndesmosis assessment method for improved clinical diagnosis. 

References

1. Leeds, Foot Ankle International.1984;66(4):490-503.
2. Pettrone, JBJS American Volume.1983;65(5):667-677.
3. Sagi, Journal of Orthopaedic Trauma.2009;23(3):213-220.
4. Van Vlijmen, Orthopedics.2015;38(11):e1001-1006.
5. Weening, Journal of Orthopaedic Trauma.2005;19(2):102-108.
6. Wu, Journal of Biomechanics.2002;35(4):543-548.

Introduction

One of the current approaches for treatment of anterior or posterior compartmental leg weakness is a mechanical brace called an ankle foot orthosis (AFO). This type of device has shown clinical benefit for numerous populations [1], including people with cerebral palsy and multiple sclerosis. This benefit is significantly influenced by AFO torsional stiffness [2]. However, the current approach to AFO fitting and selection mainly relies on clinician observation and lacks quantitative performance assessment. We propose the use of an emulator, consisting of a powered exoskeleton controlled by off-board motors, to actively mimic the behavior of different AFOs, thereby allowing patients to ‘try on’ and evaluate candidate devices [3]. To do this it is necessary to first develop an appropriate representation of passive AFO parameters. Here we examine this representation and its use by an emulator system.

Methods

The dynamic, ankle stiffness curve of different AFOs was measured using a custom-built device inspired by [4]. The stiffness data (averaged from multiple cycles) was fitted with piecewise-linear regressions, fitting plantarflexion and dorsiflexion portions separately. The fitting algorithm iteratively searches for the appropriate number of segments, using a heuristically-determined stopping criterion based on regression error. The algorithm was tested with six AFOs spanning multiple manufacturing methods and materials.  

To emulate a particular AFO, a potentiometer attached on an exoskeleton measures ankle angle, which is then used to look up the reference torque from the piecewise-linear stiffness curve. A proportional gain feedback controller applies the desired torque to the exoskeleton. Control is achieved by modulating motor speed to pull a Bowden cable, attached via a series-spring to a footplate at the exoskeleton heel. A load-cell, placed posteriorly at the heel, measures total ankle torque.

Results and Discussion

The piecewise-linear fitting algorithm maintains the hysteretic properties of the AFO torsional stiffness curves, which are neglected by common linear-stiffness approximations. Moreover, the algorithm can generate regressions without the manual input previously needed [3], which facilitates the creation of large candidate device databases. This new stiffness representation marks the first step towards passive device emulation for patient-centric design and advancing candidate device evaluation for improving patient outcomes.  

Future work will involve validation of torque tracking with a human subjects trial. Additionally, the performance of the haptic emulation will be evaluated by comparing user movement under physical and emulated AFO conditions.

Acknowledgements

NSF PFI #1534003 and NIDILRR #90RE5012. Thanks to Darren Bolger, CPO for his aid in exoskeleton construction and understanding AFO fitting.

References

1. Rubin, G., et al., (1988). Clin Podiatr Med Surg, 5(3) p695
2. Kobayashi, T., et al., (2016). Clin Biomech, 35 p81
3. Caputo, J.M., et al., (2015). IEEE ICRA, p6445
4. Bregman, D.J.J., et al., (2009). Gait Posture, 30(2) p144

Introduction

Gait is one of the basic and important movements in human daily life [1], and there are various gait patterns. Abnormal foot placement in horizontal plain (toeing) during stance phase of gait may induce musculoskeletal disorders of lower limbs. Toeing abnormality includes excessive in-toeing and out-toeing, as compared to normal-toeing. Although it is possible to distinguish abnormal walking from offline analysis of gait data [2], real-time classification is difficult. Plantar pressure may be used for the real-time classification of abnormal gait. We hypothesized that the pressure distribution in the forefoot area is associated with the toeing angle. Therefore, we aimed to investigate the mediolateral pressure distribution in abnormal toeing gaits, as compared to the normal toeing gait.

Methods

Ten young male adults with no history of musculoskeletal surgery participated (age: 23.8 ± 1.5 yrs, weight: 70.8 ± 5.8 kg). Pressure sensors were mounted on the insole of shoes (F-scan, Tekscan Inc., South Boston, MA). Subjects were instructed to walk in three toeing patterns: out-toeing, normal, and in-toeing for 10 m at the comfortable walking speed. Foot progression angle (FPA) was derived from the 3D kinematic data measured by Vicon. Forefoot area was divided into three parts, i.e., center, lateral, and medial regions. The peak pressure in each region was extracted and the mediolateral difference in peak pressure was analyzed. The pressure difference was compared among toeing patterns by ANOVA and post-hoc pairwise comparisons (Tukey’s HSD).

Results

Fig. 1 shows representative patterns of peak pressure (a) and the mediolateral pressure difference (medial pressure-lateral pressure) (b) in three different toeing gaits. The medial peak pressure was greater than lateral region in case of out-toeing, and vice versa for in toeing (Fig. 1a). Accordingly, mediolateral pressure difference was the greatest for out-toeing and the least for in-toeing (Fig. 1b).

        (a) peak pressure distribution         (b) mediolateral difference in peak pressure

Fig. 1 Pressure distribution and pressure difference (difference=medial pressure - lateral pressure);  *: p<0.05, **: p<0.01, ***: p<0.001

Discussion

We confirmed that the forefoot pressure distribution varies in different toeing gaits. The asymmetry in peak pressure may be the result of relative concentration of foot pressure near the progression line in push-off phase. It suggests that the medial forefoot and lateral forefoot perform the main “push-off” for out-toeing and in-toeing, respectively. The results of this study would be useful for the realtime detection of toeing abnormality.

Acknowledgements

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education and the Ministry of science. (2017R1A2B2010062, 2015M3A9D7067390).

References

1. Perry J, (1992). NJ: Slack Inc., p431

2. M. simic et al., (2013). Osteoarthritis and cartilage 21, p1272

Introduction: Lateral ankle sprains, caused by rapid ankle inversion, and noncontact anterior cruciate ligament (ACL) knee injuries, caused by excessive knee loading, are common lower extremity injuries that occur during dynamic tasks, such as cutting. Ankle braces are commonly used in athletics to prevent lateral ankle sprains by reducing ankle inversion while allowing full sagittal plane range of motion. However, there is limited and conflicting research about how an ankle brace affects other joints, such as the knee, during cutting movements. It is also not known if sex differences exist during a cutting task when an ankle brace is present. Therefore, the purpose of this study was to determine the effects of an Ultra Zoom® hinged ankle brace and sex on three-dimensional (3D) ankle and knee kinematics, ground reaction forces (GRF), and vertical loading rate (VLR) during a 45° cutting maneuver.

Methods: Eighteen recreationally active adults (10 males: height=1.81±0.07m, mass=85.43±10.20kg, 8 females: height=1.66±0.03m, mass=68.07±5.61kg) volunteered. Participants completed 45° sidestep cutting trials with and without an Ultra Zoom® ankle brace on their dominant foot, defined as their preferred kicking leg. 3D ankle and knee kinematics and GRF were collected. Dependent variables included initial contact (IC) and peak knee flexion, knee abduction, knee internal rotation, ankle dorsiflexion, and ankle inversion angles. Peak vertical, posterior, and medial GRF were also identified and normalized to body weight (BW). Finally, VLR was calculated by dividing peak vertical force by time to peak value (BW×s^-1). Separate 2×2 (sex × brace condition) repeated measures ANOVAs were used to detect differences for all dependent variables (p≤0.05).

Results: Significant brace condition differences were found for IC ankle dorsiflexion angle (p=0.011), peak ankle inversion angle (p<0.001), and VLR (p=0.040). Participants demonstrated 3.4° greater IC ankle dorsiflexion, 5.7° less peak ankle inversion, and 2.15 BW×s^-1 greater VLR in the brace condition compared to the no brace condition. Significant sex differences were found for IC knee flexion angle (p=0.019) and peak knee flexion angle (p=0.023). Females demonstrated 7.0° less IC knee flexion, as well as 7.7° less peak knee flexion compared to males. No other significant differences were found.

Discussion: The use of an ankle brace during a cutting maneuver restricted frontal plane ankle movement while not affecting dorsiflexion range of motion. Furthermore, the only significant changes in knee mechanics were due to sex differences, which has been well documented. These findings indicate that the use of an Ultra Zoom® hinge brace is suitable for sports, reduces the risk of lateral ankle injuries, and does not alter knee mechanics, potentially decreasing the risk of ACL injury.

Introduction

Neuromuscular disorders and injuries such as cerebral palsy and stroke often result in foot-drop which caused a great difficulty in walking [1]. Ankle foot orthosis have been prescribed to control ankle position, provide stability, and assist limb clearance. However, the pre-cut traditional of anterior ankle foot orthoses (AAFOs) could only be used for patients with less plantar spasticity, and some of them occurred AAFOs fracture within two months [2]. Currently, 3D-printing technique can be applied to patients with different conditions. Finite element analysis can be used to predict the stiffness and weak point [3]. Therefore, this study will conduct 3D-printing to fabricate AAFO and estimate its stiffness using finite element method.

Methods

A healthy subject was recruited to this study. This study made five traditional (Figure. 1) and 3D-printed (Figure. 2) AAFOs. We obtained the geometry of lower extremity by using 3D scanner, and created an AAFO model. Five AAFOs were printed by fused deposition modeling method in 3D-printing machine with PLA material. We compared the stiffness in 20 degrees of plantarflexion and data were collected by mechanical test between five traditional AAFOs and five 3D-printed AAFOs. With the AAFO model, the finite element analysis using ANSYS workbench is applied for simulation at 15 degrees of plantarflexion and find out the weak point of AAFO. The weak point part of AAFO will be strengthened in different thickness (Figure. 3) by a software ANSYS workbench.

Results

 Under the same constant rate (20N/min), the angle-moment curve shows the 3D-printed AAFOs (K=1.5) are more stiff than the traditional AAFO (K=0.5) as shown in the Figure 4. While the AAFO were applied the same force the FEA result showed as the stiffness of 3D-printed AAFO is increased with raised the thickness around the neck of AAFO as shown in Figure 5.

Discussion

The results of this study shows that the 3D-printed AAFOs were stiffer than the traditional AAFOs due to material properties difference. Therefore, 3D-printed AAFOs can bear more stress in walking than the traditional AAFOs. The more thickness around the neck of 3D-printed AAFO, the more stiffness was shown in the result. In conclusion, 3D-printed AAFOs can be used for patients with higher spasticity, and the strengthened AAFO can get a higher stiffness than the conventional AAFO.

Reference

1. Halar, E.,et al., (1987), AM J Phys Med Rehab, 1: p. 45-66.
2. Lai, H. J., et al., (2010), Medical engineering & physics, 32(6), 623-629.
3. Syngellakis S., et al., (2000), Proc Inst Mech Eng H., 214(5):527–39. 


Introduction

Gait in patients with calf muscle weakness is characterized by excessive ankle dorsiflexion and a diminished ankle power during push-off, which leads to an increased walking energy cost (EC). In rehabilitation care, these patients are provided with various types of ankle foot orthoses (AFOs), who are effective in reducing ankle dorsiflexion but generally do not support the ankle power, which limits their effect on EC. Spring-like AFOs are promising to support the push-off, but their effect on ankle power and other gait measures depends on the AFO’s stiffness and patient’s characteristics. Individually optimizing the stiffness of spring-like AFOs may improve their effectiveness. We therefore studied if stiffness-optimized AFOs are more effective in reducing walking EC and improving gait biomechanics compared to regular non-optimized AFOs in patients with calf muscle weakness.

Methods

We included 37 patients with calf muscle weakness (age: 56.9±15.5, 12 unilateral affected) who already used an AFO for lower limb muscle weakness. Participants were provided with a new custom made spring-like AFO of which the stiffness could be varied. Walking EC (assessed during a 6-minute walk test) and gait biomechanics (assessed with a 3D gait analysis) were assessed for five stiffness configurations of the spring-like AFO (stiffness range: 2.8 to 6.6 Nm/degree) and the patients’ own regular AFO. Based on the EC and gait biomechanics outcomes, three assessors selected the optimal AFO stiffness for each patient. Using paired t-tests, the stiffness-optimized AFO was compared with the regular AFO for walking EC, and maximal ankle dorsiflexion angle, knee extension moment and ankle power (all during stance). The optimized AFOs’ contribution to ankle power was calculated using its stiffness, deflection angle and angular velocity.

Results

Stiffness-optimized AFOs significantly reduced walking EC by 11.3% compared to regular AFOs (4.58±0.89 vs 4.07±0.77, p<0.001). Furthermore, the optimized AFO increased external knee extension moment (0.15±0.25 vs 0.21±0.21 Nm/kg, p=0.019) and ankle power (1.27±0.83 to 1.43±0.57 W/kg, p<0.028), where the spring-like properties of the optimized AFO supported ankle power with 0.51±0.29 W/kg, i.e 35%. No effect on ankle dorsiflexion angle was found (p=0.300).

Discussion

This study in patients with calf muscle weakness showed that stiffness-optimized AFOs significantly and meaningfully reduce walking EC and improve gait biomechanics compared to regular non-optimized AFOs. The reduction in EC may be explained by the increased ankle power, which reduces the energy losses at heel-strike, and the power generated by the AFO, which, partly, took over ankle power. In conclusion, stiffness-optimized AFOs substantially improve gait compared to non-optimized AFOs regularly provided to patients with calf muscle weakness, which emphasizes the necessity to individualize AFOs in this patient group.

The human inferior member anatomy mainly ensures the relative rotation motions between the trunk and the femoral, leg and foot regions due to the hip, knee and ankle joints.

The paper deals with a new original mechanical system (mechanism) with three loops and three degrees of mobility, respectively four degrees of freedom.

 The mechanism may simulate the human member functioning. Its structural solution allows as well the simultaneous motion of all leg regions as each part or various two of them.

The femoral region may have a variable rotation motion of maximum 100 degrees relative to the trunk. The leg part may similarly ensure a variable oscillating rotation of maximum 75 degrees relative to its femoral part. The foot region may also oscillate relative to its leg part with 90 degrees.

Due to the mechanical system structure all rotation motions may be adjustable.  

For composing the equation of motion for foot, there is a nonlinear term which is the ankle stiffness. Ankle stiffness has not a constant value. It is linear proportional to the absolute value of applied joint torque [1]. So the ankle rehabilitation exoskeleton cannot be controlled with a linear controller. So in this paper, Sliding mode control is used for nonlinear system and it is simulated and validated with Simulink(The MathWorks, Inc.) considering the actuator’s performance.

Equation of motion for foot was composed. There are 3 kinds of terms when the equation of motion is written about ankle joint torque.
M_az={(r_dx-r_py)F_x+(r_dy-r_px)F_y}+{r_pyma_x+r_pxm(g-a)}+I_zα_z (1)
First one is caused by ground reaction forces, second one is caused by linear acceleration of foot mass, and the last one is caused by moment of inertia of foot. Effect of Ground reaction force to ankle joint force is very little, so it can be deleted [2]. And the second term has also very little value compared to total ankle joint torque [3].
k=a|Τ| (2)
So it can also be deleted. After that, by putting the variable ankle stiffness and actuator force term, complete the equation of motion for controlling the ankle rehabilitation exoskeleton robot.
Sliding surface with n=2 was composed and block diagram in Simulink was designed and simulated.

Results

With the value of gains [κ=1, λ=1], there are gap between reference angle and controlled angle. When gain is increased to [κ=1, λ=10], error tracking was done at 0.8 seconds when the total gait cycle period is 2 seconds. And when gain is increased to [κ=1, λ=10], error tracking was done at 0.2 seconds and error stays 0 after then. But it has a chattering in the controlled input, so instead of sign function, saturation function was used. Then chattering was gone but error tracking performance was decreased.

For simulating, size of the controlled input does not matter. But in the real robot control, the performance of actuator should be considered for designing the controlled input. So the future work is adjusting the gain value for reducing the controlled input size. And putting the controller to our ankle rehabilitation exoskeleton robot, do the gait cycle experiment and validation with the surface EMG sensors.

This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIP) (No. 2017M1A3A3A02016507).

References

[1] P.L.WEISS, et al., (1988). Journal of Biomechanics, 21(7) p539-544
[2] H. Okada, et al., (2007). Journal of Biomechanics, 40(2) pS511
[3] David A. Winter, The BIOMECHANICS and MOTOR CONTROL of HUMAN GAITS

Introduction

Locomotion can be affected by lesions or neurological diseases like strokes and spinal cord injuries. This diseases have a high prevalence in the world and can generate secondary conditions like heart or renal affections that decrease the quality of life[1][2]. A new mechanism of rehabilitation aim to recovery the human gait based on the use of exoskeleton devices[3]. However, there isn’t a standard protocol for the assessment of lower limbs exoskeletons, hence, the objective of this study is to perform a gait analysis protocol based in a literature review in a healthy population sample under two conditions: without exoskeleton device and with exoskeleton device in passive mode; and compare different parameters to characterize the human gait.

Methods

A literature review was performed and the most common parameters and tasks used were selected. An experimental protocol was developed with healthy males between 18 and 30 years old, with hight between 168 cm and 190 cm. Two different sessions are performed, (i) without exoskeleton device, motion cameras are used with Davis Heel protocol for lower limbs; (ii)then, the  protocol is adapted to use the exoskeleton device with clusters and parallel bars with reflective markers, which replace various markers in hip, knee and ankle region (Figure 1). Two force plates are used to record the reaction force and evaluate the gait symmetry and electromyography is registered in eight muscles, two in lumbar region and six in the lower limbs. Parameters like cadence, stride length, percentage of phases in gait and, RMS and percentage of activation in electromyography are evaluated.

Figure 1.  Experimental set up and marker's adaptations

Results

10 patient’s parameters were recorded without exoskeleton and with exoskeleton device. The cinematics parameters like ranges of movements of joint, velocity, and stride length are expected to decrease, furthermore, time of cycle gait could increase and is expected that percentage of each phase of cycle changes. Finally, in electromyography preliminary results show  that rectus femoris activity increase while muscular activity in gastrocnemius decrease.

Discussion

The exoskeleton used allows the flexion/extension of hip, knee and ankle, and abduction/adduction of hip, but, hinders rotation movement. Furthermore, center joints of device can generate an extra load in lower limbs of user (in passive mode). For this reason, the range of movement can be affected decreasing the velocity and stride length and conversely, increasing the duration time of cycle gait. 

 References

[1]         World Health Organization, “WHO | Spinal cord injury: as many as 500 000 people suffer each year,” 2013.

[2]         Federation World Heart, “Stroke,” 2017.

[3]         B. Chen et al., “Recent developments and challenges of lower extremity exoskeletons,” J. Orthop. Transl., vol. 5, pp. 26–37, 2016.

Introduction

Effectively assisting human locomotion with exoskeletons is much harder than it may seem, due, in large part, to the complexity of the neuromusculoskeletal system, the broad range of responses different users can have to the same assistance strategy, and the time-varying dynamics that users exhibit as they learn to walk with exoskeleton assistance. Human-in-the-loop optimization, which systematically varies device behavior in response to measured changes in the user so as to maximize human performance, can overcome many of these challenges [1], but there is still room for improvement. Our goal was to develop a human-in-the-loop control strategy that addresses some limitations of current approaches by slowly and continuously responding to changes in biomechanical outcomes thought to encode the user’s needs, thereby enabling co-adaptation between the device and the user.

Methods

We developed a heuristic-based algorithm that uses online measurements of muscle activity and joint kinematics to guide the evolution of a desired ankle exoskeleton torque profile. The driving heuristics were: 1) soleus muscle activity, which acts cooperatively with the exoskeleton, indicates the user wants more torque; 2) tibialis anterior muscle activity, which acts antagonistically to the exoskeleton, indicates the user wants less torque; and 3) a lack of reduction in average soleus muscle activity and significant deviations from nominal ankle kinematics indicate the user is having trouble adapting, therefore torque growth should slow or stop.

We conducted an experiment to evaluate the effectiveness of the algorithm at discovering torque profiles that improve whole-body locomotor economy. Ten able-bodied participants walked with bilateral exoskeletons on a treadmill at 1.25 m·s^-1 for 30 minutes while torque evolved based on the described heuristics. We measured soleus muscle activity and whole-body metabolic rate. 

Results

The algorithm led to evolved torque profiles that significantly reduced soleus muscle activity and metabolic rate (Fig. 1). Metabolic rate was, on average, 22% below that measured during walking with the exoskeletons in a zero-torque mode (p = 1·10^-4, Fig. 1B).

Figure 1. (A) Average exoskeleton torque (top) and soleus muscle activity (bottom) in the zero-torque (left) and adaptive (right) conditions. (B) Metabolic rate across walking conditions.

Discussion

The discovered pattern of exoskeleton torque was effective at reducing whole-body metabolic rate through the intermediate step of supplanting a significant portion of soleus muscle activity. Torque grew relatively slowly, which may be beneficial for motor learning, while still seeming to converge quickly. The control strategy can discover any pattern of torque governed by measured muscle activity, making it generalizable to other joints, and it likely scales well, providing the framework for a full lower-limb exoskeleton assistance strategy.

Acknowledgments

This material is based upon work supported by Panasonic Corporation.

References

[1] Zhang, J., et al., (2017). Science. 356, pp.1280-1284.

Introduction

Hydrogels closely mimic natural living tissue, more than any other class of synthetic biomaterials [1]. It is beneficial to include soft-tissue substitutions in the form of cushioning materials when prescribing orthoses for diabetic patients, since diabetes causes the fat pad under the heel and forefoot to become thinner and less effective in reducing pressure [2]. In this work, poly acrylic acid based hydrogel material was developed with better pressure relieving ability for diabetic insoles.

Methods

Poly acrylic acid based double network hydrogels were synthesized in stages to optimize the mechanical properties; firstly by varying the first network crosslinker mole percentage relative to monomer concentration from 1 to 9. Next, the crosslinker mol % of first network solution was locked and second crosslinker was changed from 0 to 0.1, 0.5, 1.0 and 2.0 mol %. In the third step, the compressive strengths were measured at different swelling percentages. All hydrogel samples were triplicated and average stress- strain behavior were considered for stiffness calculations.  Hydrogels under compression was modelled successfully using a finite element software to better understand the mechanism of load transfer within the insole and to compare the pressure relieving ability under static load with commercially available insoles.

Results

The required stiffness can be achieved by first network solution with 1M Acrylic acid, 4 mol% crosslinker and second network solution with 1M Acrylic acid and 0.1 mol% crosslinker at 50% swelling (Fig.1A). The finite element modeling (FEM) results showed that hydrogel insoles are more effective in distributing pressure, compared to the commercial polymer ‘gel’ materials.

Fig.1: (A) Variation of stiffness with crosslinker mol% at 50% swelling. (B) The von Mises stress of poroelastic hydrogel material (MPa) (C) The von Mises stress of hyperelastic material (MPa)

Discussion

The hydrogel samples were compression tested between two porous plates in a deionized water container to expel extra water due to poroelastic behavior caused by the water movement within the hydrogel and to mimic the viscoelastic behavior of polymeric network. The Fig 1 (A) shows the variation of stiffness of hydrogel with crosslinker percentage within the expected compression ratio of 30% to 50%.  Both experimental and finite element analysis showed a better stress relaxation in hydrogel samples than commercially available polymer gel materials. In order to model the rate-dependent fracture behavior of hydrogel, the solid and fluid contributions were split and visualized separately. The lower von Mises stress of hydrogel compared to hyperelastic material is shown in Fig.1 (B) and (C) respectively .

Acknowledgement

This work is supported by NSF grant RPHS/2016/DTM 02.

References

1. Peppas,N.A., et al (2000),European Journal of Pharmaceutics and Biopharmaceutics,  50(1) p27-46

2. Huppin, L., (2012, September). Retrieved from https://podiatrym.com/pm/Huppin912.pdf.

Introduction

Prosthetic foot is a lower limb rehabilitation device required to biomimic the human ankle-foot complex. The need for improvement of the design of a prosthetic foot has been highlighted to eliminate bilateral asymmetry in the gait of prosthesis users [1]. Among the technical parameters of a prosthetic foot, the roll-over shape (ROS) is critical in defining the characteristics of the gait. ROS is defined as the effective rocker the lower limb system forms during the stance phase of walking [2]. This parameter had always been experimentally evaluated for a prosthetic foot. Here, a numerical framework based on the finite element method is proposed to evaluate the ROS of a prosthetic foot.

Methods

The rocker based inverted pendulum model of human walking was employed to evaluate the roll-over geometry. CAD models of the prosthetic foot with the keel and the foot shell were developed. Linear elastic material model was opted for the keel and a hyperelastic model was chosen for the foot shell. The numerical analysis was performed using the commercial finite element software, Ansys Workbench 18.2 (Ansys Inc.). The large deformation analysis was performed with contact behaviour formulated using the Augmented Lagrange formulation at the frictional contact interfaces. Multi-point constraint formulation was incorporated at the bonded contact regions and a surface projection technique was used to evaluate the norm of the nodal penetration at the contact interfaces. The interface treatment was set to “adjust to touch” to offset initial clearance to avoid global search for contact [3]. The domain was discretized with non-overlapping elements consisting of both tetrahedrons and hexahedrons. Appropriate boundary conditions were employed and the non-linear algebraic equations obtained were solved using the Newton Raphson method. A mesh convergence study was conducted and the solution obtained was used for the evaluation of the ROS.

Results

Plot of the deformed configuration of the prosthetic foot during the terminal stance is as shown in Figure.1A. The ROS calculated from the converged solution is as illustrated in Figure.1B. Critical parameters such as the radius of curvature, centre of curvature and the effective foot length ratio were evaluated from the plot to further study the performance of the prosthetic foot.

Discussion

The a priori evaluation of the roll-over geometry has been executed with the finite element model of the prosthetic foot. The material and the geometric properties of the prosthetic foot will be iteratively varied and the roll-over shape will be evaluated with the objective of achieving an improved design for a prosthetic foot.

References

1. Knox, E.H., (1996). PhD Thesis, Biomedical Engineering. Northwestern University, Evanston, IL.
2. Hansen, A.H. et al., (2004). Clin. Biomech. 19(4), p407.
3. Wriggers. P., (2008). Nonlinear Finite Element Methods. Springer.

Musculoskeletal disorders refer to diseases that occur in the nervous system, muscular system and body tissues when repeated labor movements or excessive posture are applied to the musculoskeletal system. In the industrial field where musculoskeletal diseases are constantly developing, exoskeletal aids are being actively studied as a method for preventing musculoskeletal diseases. However, the present study is focused on developing the performance of the exoskeleton assist device so is not widely used in industry due to the inconvenience of the wearer. Therefore, it is necessary to design the optimal exoskeleton design considering not only the performance of the exoskeleton assist device but also compatibility with the human body and mobility. In this study, we simulated the lifting action with attaching a non - powered exoskeleton assist device to figure out the most wearable one. We selected the lifting motion, which is general and easily tired, based on Posture, Activity, Tools and Handling(PATH), the work posture analysis system. The motion analysis test was performed with the selected lifting action. The age of the selected subjects was the early 20s, average height of 174.3cm, average weight of 70kg. Vicon Motion Capture System was used as the motion analysis software. As a analysis tool, AnyBody Modeling System was used and inverse dynamics analysis was performed by AnyBody Modeling System using 6 different motion analysis data. The momentum of erector spinae, the hamstring and the Gestrocnemius muscles were compared and the moments of the knee and hip joints were also compared. As a results of analysis, the exotendon attached to the back of the knee and hip had less muscle momentum than the other parts. In addition, the muscle momentum was less when the two exotendons were attached than when one was attached, and the muscle momentum was lowest when the cross type was attached. The results of this analysis will enable the wearer to design a lighter, more efficient and customized non - powered exoskeleton assist device.

Acknowledgment

This work was supported by Institute for Information & communications Technology Promotion(IITP) grant funded by the Korea government(MSIP) (No. 2016-0-00452,Development of creative technology based on complex 3D printing technology for labor, the elderly and the disabled)

[Introduction]

 In recent years, the number of patients with osteoarthritis increase with aging. One of the therapies has Total Ankle Arthroplasty (TAA). If the alignment before deformation of the ankle can be estimated, it is possible to plan TAA following bones of the foot and ankle joint before progress. However, the rear foot part bone alignment of osteoarthritis has not been fully elucidated. This study investigated the rear foot part bone alignment of osteoarthritis.

[Methods]

Five joints from patients who did not show symptoms or deformation on CT images were treated as a control group (normal and stage 1 group). In patients group, stage 2 group, stage 3A group, stage 3B group, and stage 4 group were, 2, 3, 5, and 2 joints respectively. The three-dimensional bone models were reconstructed from CT images of all joints. The loading plane reference coordinate systems embedded to the ankle joint was defined as follows; malleolus (medial/lateral) direction was X axis, second toe direction was Y axis, tibial axis into knee direction was Z axis, and origin set on the contact surface. The relative position of talus and calcaneus with respect to the contact surface were calculated and evaluated in 3D using Go-ICP [1].

[Results]

　Figure1,2 show the relationship between the alignment of talus/calcaneus and stages of the disease in the loading plane reference coordinate system, respectively. Significant differences in the 3B group were observed in talus and calcaneus compared to control group. Average rotation angle of talus/calcaneus in Y-axis direction were -31.6 [deg] (p<0.05) and -15.2 [deg] (p<0.05), respectively. Also, one in Z-axis direction were -12.5 [deg] (p<0.05) and 14.3 [deg] (p<0.05), respectively.

Figure 1. Results of talus and calcaneal rotation y direction in the coordinate system. The asterisk (*) indicates significant differences between stages(p<0.05)

Figure 2. Results of talus and calcaneal rotation z direction in the coordinate system. The asterisk (*) indicates significant differences between stages(p<0.05)

[Discussion]

 The rotation in the Y-axis direction indicates inversion (positive) and eversion (negative) in talus and calcaneus. The 3B group (talus and calcaneus) significantly rotates inversion compare to the control group. Although the subtalar joint attempts to compensate for the deformity of the medial malleolus [2], the compensatory function failed and the large rotation occurred. In addition, our method can obtain the talus/calcaneus were significantly rotated in the Z-axis direction, which is difficult to investigate in X-ray and CT.  

[Reference]

1. Jiaolong Yang et al., Go-ICO: A Globally Optimal Solution to 3D ICP Point-Set Registration, IEEE TRANSACTIONS ON PATTERNANALYSIS AND MACHINE INTELLIGENCE, No.11, vol.38, pp.2241-2254, 2016.
2. Takakura et al., (1995) Low tibia osteoarthritis of the ankle Result of a new operation in 18 patients, pp.50-54.

Introduction

The aim of this work is to design a low-cost, passive prosthetic foot using the lower leg trajectory error metric (LLTE) [1]. Many people in developing countries require low-cost prostheses that enable close to able-bodied gait patterns to expand their capabilities and avoid social stigma. The LLTE is a novel metric that quantitatively predicts the biomechanical response of a prosthetic foot given its mechanical design and evaluates that response against able-bodied kinematics. The smaller the LLTE, the closer the predicted response is to able-bodied kinematics. Using the LLTE as a design objective, a single part, compliant prosthetic foot, which could be manufactured at low cost, was optimized to enable close to able-bodied kinematics.

Methods

The foot design consisted of a C-shape described by a set of nine parameters (Fig.1a) and was constrained to fit within a volume shaped like a human foot [2]. The LLTE was calculated for a given design using FEA analysis to determine how it would deform in response to able-bodied ground reaction forces. A genetic algorithm found which set of parameters yielded the lowest LLTE (0.186). This optimized foot was manufactured and tested with a universal testing system (Instron, Norwood, MA, USA), which measured the deflection of the foot in response to several load conditions to characterize its mechanical behavior. This prosthesis was then tested with six transtibial subjects at Bhagwan Mahaveer Viklang Sahayata Samiti (BMVSS) in Jaipur, India for qualitative feedback with their informed consent.

Results & Discussion

The optimized prototype foot is shown in Fig.1b and can be manufactured for under $10. Instron testing showed that the measured vertical deflection differed from the vertical deflection predicted by FEA by less than 3 mm (Fig.1c), indicating that the foot performed as designed. From testing at BMVSS (Fig.1d), qualitative feedback indicated that younger, more active users liked the spring-like response of the foot, while older, less active users felt it was less stable. One subject commented that he could run with the prototype, unlike his usual prosthesis. Many of the subjects liked the lighter weight of the prototype compared to the Jaipur foot, another low-cost prosthetic foot. However, all the subjects preferred the appearance of the Jaipur foot over the prototype.

The results have helped us better identify our target user population, and demonstrate the need for adding a cosmetic cover to our design. In the future work, the kinematics of subjects using the prototype will be measured to evaluate the accuracy of the LLTE predictions.

[1] Olesnavage and Winter, “LLTE: A novel optimization parameter for designing passive prosthetic feet,” IEEE-ICRR, 2015.

[2] Olesnavage, Prost, Johnson, and Winter, “Passive Prosthetic Foot Shape and Size Optimization Using LLTE,” JMD, 2017 (In Review).

Introduction
The sports performance level for amputees has improved by the development of sports prosthesis. Although studies have been conducted on prosthesis for short distance runners, prosthesis for long jumper has not yet been investigated. Our research group is developing a sports prosthesis for long jump, which is optimized by motion simulation [1]. However, in the motion simulation, fully evaluating the material strength of the proposed prosthesis is difficult. The purpose of this study is to investigate the material strength property of the prosthesis by using a finite element model and trial products; hence, we are propose a processing method for strength prosthesis.

Methods
A trial prosthesis product was fabricated out of approximately 40 pre-proof sheets of carbon fiber reinforced plastics (CFRPs). CFRP is a composite material comprising carbon fiber and a resin. The CFRPs were laminated on top of a mold using aluminum. In this study, the surface profile of the mold represented the optimal shape of the prosthesis, calculated by the motion simulation. The strength of the fabricated prosthesis was investigated by a compression test.
The finite element analysis was performed as follows. Based on the dimensions of the prosthesis obtained from the simulation, a computational model was created by three dimensional (3D) computer aided design (CAD). Then, the model was imported into a finite element software for analysis. The model was divided into 41,984 elements by using a hexahedral secondary mesh. The analysis conditions were as close as possible to those of the compression test.

Results
The results obtained by finite element analysis revealed that the prosthesis had a strain of approximately 0.7% with a load of 3,000 N. Since the limit value of the CFRP strain was approximately 1%, the prosthesis was not broken. However, the results of compression test showed that the trial product of the prosthesis could not endure more than 3,000 N. By comparing the strains of the finite element analysis to the experimental results, the error was determined to be approximately 5%. Therefore, the two results were found to be roughly in agreement.

Discussion
The reason for the destruction of the prosthesis was delamination. When delamination occurred, the rigidity around the prosthesis rapidly decreased, buckling occurred, and the prosthesis was destroyed. It is believed that the cause of delamination was the weak crimping force and that air or foreign matter might have been mixed between the CFRP layers.

Reference
1. Hase, K., Murata, S., Obinata, G., (2016) Simultaneous optimization of long jump technique and sports prosthesis, Proceedings of the 8th Asian Conference on Multibody Dynamics

Partial forefoot amputation leads to limited mobility with negative impact on the patient's health status. It reduces the forefoot lever, resulting in an instable and asymmetric gait. The conventional treatment with a silicone prosthesis offers only a cosmetic aspect, but is not able to transfer the push-off forces necessary for sportive activities. To solve this issue, a patient-specific carbon fiber prosthesis was developed and then optimized with an anisotropic carbon Finite Element Model (FEM) based on the individual patient parameters body weight, degree of mobility and amputation level.

The first step in the development of the carbon prosthesis consists of modelling a patient-specific prosthesis CAD shell model. The dimensions of the affected limb of the patient were recorded using 3D scanning (Eva-Scanner, Artec Europe, Luxemburg). The CAD model derived from the scan was then used as the basis for performing the carbon modeling. The second step was the simulation of the gait cycle and thus loading the carbon model under physiological forces. By splitting the prosthesis into three functional sections, the specification of an individual stiffness for each section was possible. The third step was the optimization of the overall model with respect to the required stiffness and strength.The limits of the failure analysis in the FEM were set using a reverse factor of 0 (no failure) and 0.875 (total failure including a safety factor).

The simulation was applied on a prosthesis of a left side amputated patient (body weight: 93 kg, sportive activities: walking). The force value applied to the prosthesis was linked to the body weight and the performed activity (in this case: walking à 1.6x body weight). In total two different types of carbon fabrics were used: bidirectional, and unidirectional carbon fabrics. The shaft of the prosthesis was layered with 16 unidirectional carbon fabrics. Due to high shear stresses and rotational loads during the gait process, the area around the ankle has been reinforced with ten bidirectional layers. Four unidirectional carbon fabrics were layered in the sole part of the prosthesis in order resist the loads occurring during the gait cycle and to restore the lost lever arm. After the simulation has shown a maximum reserve factor of 0.8, the prosthesis was provided to the patient.

The approach presented allowed the analysis of a patient-specific prosthesis using a FEA and design the carbon model with respect to the loading specifications by optimizing the carbon fiber layers and fiber orientation. Design rules based on systematic analysis studies will be derived in the future leading to a meta-model and replacing the need for individual finite element analysis. The meta-model shall be the basis for a design tool for the orthopedic technician, in the production of the patient specific prosthesis.

    People with mobility impairments tend to be highly dependent on devices such as sticks or wheelchairs. Such reliance may lead to the degeneration of their lower limbs. Hence, doctors would prescribe orthoses, which can help improve the performance of lower limbs. However, orthosis prescription today is mainly based on doctors’ experiences and often mismatched with patients’ needs as they progress [1]. Therefore, we developed an assisted prescribing system to help doctors prescribing orthoses in a more objective way.

    This assisted prescribing system was established by estimating the lower limb functionalities, assortments and characteristics of orthoses. It was developed to provide an algorithm indicating which types of orthoses can be applied in each movement control or rehabilitation state. Four patients with ambulatory difficulties were recruited to validate our assisted prescribing system. Subjects were asked to wear the orthoses prescribed by our developing system for more than three months. Stance duration, cadence of the affected leg, and symmetry of stance duration as well as cadence were then obtained by measuring level walking of the subject with and without the prescribed orthosis.

    Figure 1 presents the results of one of the four subjects participating in the study (a 56-year-old patient with stroke). By our developed system, she was prescribed with a KAFO, assembled with free type of knee orthosis and anterior ankle foot orthosis. As time passing by, the value of her stance duration is closer to 60%, which is commonly perceived as the performance of a healthy person. And the value of her cadence also has the trend going upward. There is no difference in the symmetry of cadence between trials with and without KAFO, but slight tendency of increase can be observed in the symmetry of stance duration.

    The subject’s stance duration approaching 60% reveals that she gained more confidence to support herself with the affected leg through the aid of the orthosis, and the stability was also improved. This case can convey the truth that our assisted prescribing system met patients’ expectations successfully. It has been proved to provide proper orthoses, and hence offer a relatively objective standard to support clinical prescriptions.

Acknowledgements

    The authors would like to thank Taiwan Ministry of Science and Technology for financial support (Grant# NSC 102-2218-E-009-015 & MOST 103-2218-E-009-005 & MOST 104-2218-E-009-005).

References

Introduction:

Ankle-foot orthoses (AFOs) are commonly used to help patients diagnosed with cerebral palsy or stroke to correct postures or assist gaits [1]. Common designs use only a single specific posture to obtain body geometry from the user for fabricating AFOs. However, this would cause the discomfort when the user performed activities of daily living (ADLs) due to body geometry change. Thus, the users would reduce their willingness to wear AFOs. The purpose of this study, therefore, was to establish a procedure incorporating multiple postures according to the characteristics of the lower extremities to make AFOs that are comfortable and enhancing the wearing willingness.

Methods:

        We recruited 16 healthy young subjects (22-25 yrs.), three healthy older subjects (54-71 yrs.), and two older stroke subjects (56 and 65 yrs.) with hemiplegia in this study. In order to establish the procedure, we developed an algorithm by the characteristics and the geometric parameters from ADLs of the healthy subjects to acquire the margin and thickness of AFOs which are primary factors affecting comfort and strength of the devices. The procedure is as follows. First, subjects were asked to perform ADLs such as sitting, standing, squatting and standing on one leg, and we used a 3-D scanner to capture the surface dimensions of the lower extremities. After scanning, we imported the data into a modelling software and applied our proprietary algorithm to design customized AFOs. Finally, we used a 3-D printer to manufacture AFOs and had the subjects wear the AFOs for ADLs. Subjects’ feedbacks and gait data were obtained to validate comfort and effectiveness of our AFOs.

Results:

After the stroke subjects have worn the AFOs for a few months (3-6 months), we analyzed the stance duration and cadence. Both of them had improvements on their gait. Fig.1A shows the stance duration of one of the stroke patients with right-side hemiplegia. The stance duration was approaching to the value of an intact person (60%) as the wearing time went by. Fig.1B shows the increase in the cadence over time while wearing AFO. The feedbacks from both subjects indicated that the comfort of our AFOs was better than their previous devices fabricated based on a single posture.

Conclusion:

We developed a procedure with algorithm to make AFOs based on multiple postures to provide better fitting and functionality. This can also be extended to other types of orthoses such as KAFOs, KOs, or HKAFOs.   

Acknowledgements

Partial financial support from Taiwan Ministry of Science and Technology grants MOST-102-2218-E-009-015, MOST-103-2218-E-009-005, MOST-104-2218-E-009-005

Reference:

1. Paneth, N., et al. (2006). "The descriptive epidemiology of cerebral palsy." Clinics in Perinatology 33(2): 251-267.

Introduction: Flatfoot patients have a collapsed medial longitudinal arch, which is associated with dysfunction of muscle. Previously, Levinger et al. measured the kinematics in the flatfoot and normal subjects using a skin marker-based method [1]. However, the talus motion cannot be measured using skin markers in intact foot. This study aims to investigate the kinematics in the Chopart's joint in normal and flatfoot subjects during stance phase of normal walking using a bi-planar fluoroscopic (BPF) system and to quantify the differences in their arthrokinematics.                     

Method: Eighteen normal and five flatfoot subjects participated in the study. The study was approved by Chung-Ang University IRB. An informed consent was obtained from each subject. Three-dimensional (3D) bone models of talus, calcaneus, navicular and cuboid were reconstructed from computed tomography images. Subjects walked at self-selected normal walking speed and their BPF images of the foot were captured. The Chopart's joint kinematics were calculated by registering bone models to BPF images using a 2D to 3D manual registration method. Surface relative velocity vectors (SRVVs) were calculated on articular surfaces in the talonavicular and calcaneocuboid joints [2]. Average relative speed (ARS) based on SRVVs was calculated for every 10% of stance phase. The kinematics differences between normal and flatfoot subjects were quantified using independent samples t-tests with 0.05 significant level.

Result: The SRVVs were calculated for normal and flatfoot subjects from heel strike (0%) to terminal stance (90%) (Figure 1A). The average ARS was around 20 mm/s early and terminal stance and less than 12 mm/s at mid-stance of normal walking in both talonavicular and calcaneocuboid joints. In normal subjects, the ARS was relatively low in calcaneocuboid joints during mid-stance compared to the early stance and terminal stance, while it was not the case in flatfoot subjects. The flatfoot subjects showed significantly larger ARS at 40, 50 and 80% of stance phase in the talonavicular joint and mostly from 20 to 70% of stance phase in the calcaneocuboid joint (Figure 1B) than those of normal subjects.

Discussions: The flatfoot subjects shown more movement than the normal subjects during mid-stance of normal walking, which would explain the more stability of the normal foot than the flatfoot subjects. The large movement in flatfoot during mid-stance was not contribute to natural motion as normal subjects. Arthrokinematics provides a more detailed interaction of the Chopart's joint.

Acknowledgements: This study was supported by Basic Science Research Program through the NRF (NRF-2017R1A2B2010763) and Projects for Research and Development of Police Science and Technology through CRDPST and KNPA (PA-C000001) funded by the Ministry of Science, ICT and Future Planning.

References:

1. Levinger, P., et al. Gait & posture 32.4 (2010): 519-523.

2. Anderst, W.J., et al. J Biomech. 43.5 (2010): 994-997.

INTRODUCTION

Walking constitutes a large component of the day-to-day activity of underground coal miners. It is therefore imperative that miners’ boots protect their feet from undesirable external stimuli and meet the demands placed on their lower limbs while they walk on challenging surfaces. Underground coal miners, however, experience a high incidence of work-related lower limb injuries with sprains and strains caused by slips being highly prevalent. Interactions among the walking surface, boot and human body create a three-part system whereby changes in work boot design can influence lower limb motion at initial contact when walking, thereby influencing slip risk. Although substantial research has documented how different non-work related footwear types influence walking, research quantifying how work boots influence walking biomechanics at initial contact is sparse. This study aimed to investigate the effects of systematic variations to shaft stiffness and sole flexibility in work boots when participants walked across simulated underground coal mining surfaces.

METHODS

Twenty males (aged 36±13.8 years) completed a functional circuit before walking across two surfaces (uneven and soft) under four mining boot conditions (stiff shaft + stiff sole, stiff shaft + flexible sole, flexible shaft + flexible sole, flexible shaft + stiff sole). Shank and thigh muscle activity; plantar pressures; ankle, knee and hip joint motion; and ratings of perceived comfort were recorded during each trial. Repeated measures ANOVA and t-tests determined whether any of the gait variables were significantly (p≤0.05) affected by boot shaft type, sole type and/or walking surface.

RESULTS

There were significant main effects of both boot shaft and sole type on muscle activity and plantar pressures, although these main effects were surface specific (see Figure 1). Despite these differences in gait caused by both shaft and sole type, there were no significant differences in the comfort ratings reported by the participants between the boot conditions. A boot with a flexible shaft and stiff sole, however, was the boot type preferred by the participants.

DISCUSSION

Although the shaft and sole of underground coal mining work boots significantly influenced gait it did not influence perceptions of comfort when the participants walked on surfaces typically encountered by underground coal miners. However, because the effects of variations in shaft and sole stiffness were moderated by walking surface, manufacturers must consider the walking surface when designing work boots for underground coal miners. Manufacturers also need to consider the interaction of the shaft and sole when designing underground coal mining work boots in order to optimise movement of the lower limb and allow controlled foot-to-ground to minimise slip risk.

Introduction:
Pressure measurement technology has progressed substantially since its inception in the late 1800’s and many scientific reports have provided insight into foot-ground surface interaction.  There is, however, a scarcity of research on how load is transferred between consecutive steps. The aim of this study was to therefore present a method of quantifying regional load transfer between consecutive footsteps in typically developed (TD) children to determine the effect of the proceeding step on foot-ground pressures during the subsequent step.

Methods:
Six TD children between 4-16 years of age, without a history of lower limb injury were recruited. An EMED-XL pressure platform (Novel_GmbH; 88x188 capacitive sensors (4sensors/cm2); 100Hz) was positioned in a 10-camera, motion-capture laboratory (10x Vicon V16 Vantage cameras; 2000Hz) to collect synchronous marker trajectory and pressure data. Reflective markers were attached according to the Oxford Foot Model (OFM), before participants performed 12-14 walking trials at a self-selected speed. A dedicated Matlab code was developed to automatically re-align the reference systems [1, 2], superimpose markers onto the footprints, identify five regions of interest (ROIs) [1], and process the extracted parameters associated with both the single steps and whole gait cycle. The procedure to optimize the matching between marker configuration at midstance and maximum pressure footprint was further developed from previous studies [1, 3], by taking into account the lowest marker motion along the three axes.

Results:
Eight load transfer phases (i.e. double foot contact) were included for each participant (4 R-L and 4 L-R), and were normalised to body mass. For the rear foot, medial forefoot forces (72.8% of body weight) at the end of the stance phase were consistently larger than lateral forefoot forces (28.5%) across all participants (see figure). For the front foot, medial and lateral hindfoot forces were similar at heel strike with the medial hindfoot forces being generally higher during the initial loading phase (36.1% medial and 30.1% lateral at 50% of load transfer) - although this varied across participants (see figure).

Conclusion:
The present findings provide preliminary data regarding load transfer in young typically developed children. For the participants in the current study, normalised forces show a common load transfer pattern for selected walks in a typically developed cohort. Reviewing the load transfer phase of subsequent steps will assist in determining if, and to what extent, plantar forces in one step influence the next step. Future work will analyse irregular load transfers from the current cohort to explore strategies used to correct abnormal or off-balance steps, and compare with gait kinematics and kinetics.

References:

1. Stebbins JA, et al., Gait Posture. 22(4):372–376, 2005.
2. Giacomozzi C., Stebbins J.A. Gait Posture. 53:1131-138, 2016
3. Bertsch C, et al., Gait Posture. 19:235-242, 2004.

Introduction

Ankle injuries, with the most common being the ankle sprain, can lead to the failure of several anatomic structures, including the ligaments: The diagnosis is, in an initial phase, done by inspection, palpation and instability tests. However, the anterior drawer test, which was designed to indirectly evaluate the integrity of the anterior talofibular ligament (the first to be injured in acute lateral sprains) and considered the most clinically relevant, presents a great dispersion of results. The introduction of methods to give quantifiable measure of the injury level, discarding the subjectivity of the examiner, will be a significant improvement for the clinical practice. Several devices have been developed to replicate clinical instability testing and providing more accurate and objective results. However, the problems inherent in traditional tests remain, especially the inter-individual variation [1]. Having this goal in mind, in this work a novel device for ligament injuries diagnose was developed where the movement of the talus with respect to the tibia is characterized by the amplitude of the rotations in the three anatomical planes: coronal, sagittal and horizontal.

Methods

The prototype device quantifies the rotations in the three anatomical planes rather than the linear displacement of the talus in relation to the tibia as usual (anterior drawer test) or the amount of tilt made by the foot (talar tilt test). The device permits to immobilize the tibia allowing only the movement of the foot. The foot is placed in a position with a preset amount of plantarflexion and internal rotation. Then, forcing a varus movement of the talus with respect to the tibia the correspondent rotations are measured using a three axis gyroscope and accelerometer. The values read by this sensor, rigidly connected to the Talus, are registered through a computer interface developed for usage of an Arduino microcontroller. The device was tested using 11 cadaver’s feet and the amplitude of rotations were measured for the intact foot and for successive cuts on the on the ligaments (see figure 1).

Results and Discussion

The development of this prototype aims a better and more reliable diagnosis of ankle ligament injuries. The device is able to evaluate the amplitude of movement, to assess the ligaments integrity. The interface developed helps the visualization of the data and helps to keep track of different studies enabling an easy use of the results for statistical analysis. Results of the tests in cadavers show the viability of the device to quantify the ankle injury with obtained results within the range of expectable values.

Acknowledgements

To the project UID/EMS/50022/2013 (IDMEC-LAETA).

References

[1] Lynch SA, “Assessment of the Injured ankle in the Athlete”, J. Athletic Training, (2002).

Figure 1 – Testing the device on a cadaver’s foot.

Introduction

Upper and lower motor neuron lesions such as stroke and peripheral neuropathies often result in drop-foot which caused walking difficulties. Ankle foot orthoses (AFO) can assist in controlling position and motion of the ankle and in providing stability. Anterior AFO (AAFO) is commonly used in Asia because of its convenience in wearing [1]. Recently, 3D printing in medical applications is expanding rapidly, and additive manufacturing of custom AAFO may have significant potential for development.  To evaluate the 3D printed AAFO, the kinematics between conventional and 3D printed AAFO was compared through motion analysis.

Methods

The subject was recruited to fabricate a conventional AAFO and obtained a geometry of 3D printed AAFO using a 3D scanner (Artec 3D, Luxembourg). The AAFOs were printed with polylactic acid (PLA) and nylon filament, respectively. Data were recorded by inertial measurement unit (IMU) sensors (APDM, USA), which were placed on subject’s pelvis, thigh, shank, and foot. Four walking conditions were included in the conventional AAFO, 3D-printed nylon AAFO, 3D-printed PLA AAFO, and barefoot (no AFO) condition. The range of motion (ROM) of hip, knee, and ankle joint were calculated by Matlab (Mathworks, USA).

Results  

In the knee flexion, the peak value with AAFO conditions was smaller than that without AAFO as shown in the Figure 1.  The first wave of nylon AAFO was 5° greater than that of the others. In ankle joint, ROM of conventional AAFO was smaller than that of PLA AAFO and Nylon AAFO. However, the pattern in nylon AAFO exhibited a similar tendency as the pattern in barefoot condition.

Fig. 1: (A) Hip, (B) knee and (C) ankle joint angles in gait cycle (degree).

Discussion

For the nylon AAFO, it revealed a similar trend with the normal condition, and had better shock absorber at first wave of knee motion. For the PLA AAFO, it showed similar motion pattern in knee and hip joint as compared with other groups, but not rigid as conventional AAFO in ankle joint. In conclusion, 3D-printed AAFO showed a better performance in ROM of ankle joint but demonstrated a similar performance as conventional AAFO in ROM of hip and knee joint. The effect of different AAFO types on walking kinematic may relate to the difference of material properties.

References

1. Chen, C.C., et al., (2010). Arch Phys Med Rehabil, 91(12) p1862-1868

Introduction: Footwear designs constantly change and while debates over minimalist, zero-drop, stiff or cushioned shoes occur there is little overall consensus. If an individual wishes to have a stiff shoe in some instances and a more compliant shoes in others two separate shoes would be needed. If shoe stiffness could be altered a single shoe could be used, but it would be important to understand how balance and mobility would be impacted, especially if the use had impaired mobility. Therefore the purpose of this study was to assess impact forces, loading rate and joint motions using modifiable footwear (stiff vs. compliant soles) to barefoot control trials.

Methods: 19 healthy females (40.8±14.5 yr; 69.1±15.7 kg; 1.6±.34m) were fitted with a modified Plug-in-Gait marker set (including thigh and shank clusters) and Therafit^TM Arielle shoes and asked to walk on a force instrumented treadmill at a self-selected speed (1.33±.09m/s) across three footwear conditions [barefoot (BF), compliant shoe (COMPL), stiff shoe (STIFF)] in a random order for three minutes each. From the final minute initial contact and peak joint angles during stance were calculated at the hip, knee, and ankle in the sagittal plane as well as peak ground reaction force. Repeated measures ANOVAs were performed. α = 0.05.

Results: Significantly smaller peak GRF (p=.007), max knee flexion angle (p<.001), plus impact (p=.001) and peak dorsiflexion (p<.001) angles were revealed for BF vs. shod conditions. BF walking resulted in lower horizontal braking forces than COMPL (p=.026) but not the STIFF shoe (p=.071). Additionally, knee flexion at impact (p<.001) increased across all three conditions from COMPL-STIFF-BF conditions.

Discussion: Shoes, regardless of sole stiffness, resulted in larger impact forces along with greater peak knee flexion and dorsiflexion angles. However, unlike previous research [1] greater knee flexion occurred at initial contact when BF than the STIFF shoe which in turn was greater than the COMPL shoe. Also depending on shoe stiffness there was an increase in breaking forces when wearing the less stiff COMPL shoe. These findings demonstrate the influence of shoe stiffness on gait and indicate that while mechanics were altered when shod (e.g., harder landing, larger peak ankle and knee flexion), difference as a function of shoe compliancy did alter the knee flexion (more extended) at initial contact and altered the amount of frictional forces utilized during walking. Future studies should determine the influence of sole stiffness on muscle activation patterns and in mobility impaired individuals potentially at risk for falling.

References:

1. Morio C, Lake MJ, Gueguen N, Rao G, Baly L: The influence of footwear on foot motion during walking and running. J Biomech. 2009, 42: 2081-2088.

Introduction

The human foot has evolved to support bipedal locomotion [1]. The bone arrangement that constructs the medial longitudinal arch (MLA) has been described as one of the most important structural characteristic with the function to support the human body [2]. The examination of footprints gives insight about the MLA [3]. Differences in plantar pressure patterns between left and right foot are interesting from a clinical [4] as well as from a footwear manufacturing point of view. Therefore, the objectives of this study are to determine the reliability of measuring arch indices with a pressure mat and to determine the correlation between left and right arch indices during static and dynamic trials.

Methods

Fifty healthy, physically active males (mean ± standard error, age: 25.73 ± 0.75 years, height: 174.98 ± 0.84 cm, weight: 72.22 ± 0.79 kg) were recruited for this study. Static and dynamic arch indices of both feet were measured using a plantar pressure mat. Intraclass correlation coefficients were calculated to determine the reliability. Pearson’s r and the coefficient of determination (R²) were calculated to describe the relationship between left and right arch indices.

Results

The reliability for static and dynamic measurements of arch indices was excellent (ICC: 0.967 (0.947,0.981) and 0.914 (0.863, 0.948)). A strong correlation between left and right arch indices was found for the static (r = 0.703, R² = 0.50) and the dynamic (r = 0.749, R² = 0.56) trials (Fig.1).

Fig.1:      Correlation between the arch index in left and right foot during the dynamic trial.

Discussion

A strong correlation between left and right arch indices was found in static and dynamic trials, however, the goodness of fit is moderate. The model accounts for 50% and 56% of the variance in the static and dynamic trials, respectively. As a result, conclusions about the contralateral foot when measuring only one foot should be handled with caution. Differences of up to 0.18 in static and 0.14 in dynamic were found between left and right arch indices.

References

1. Franklin, S., Grey, M. J., Heneghan, N., Bowen, L., Li, F. Barefoot vs common footwear: A systematic review of the kinematic, kinetic and muscle activity differences during walking. Gait & Posture, 42 (3) (2015)

2. McKeon, P., Hertel, J., Bramble, D., Davis, I. The foot core system: a new paradigm for understanding intrinsic foot muscle function. Br J Sports Med, 49 (290) (2015)

3. Cavanagh, P. R. & Rodgers, M. M. The arch index: A useful measure from footprints. J. Biomechanics 20 (5) (1987)

4. Goonetilleke, R. S. The Science of Footwear. CRC Press (2012)

Diabetic polyneuropathy (DPN) is present in 50-70% of older people with diabetes¹. In later stage DPN, sensory and motor dysfunction occurs and muscle weakness develops¹. This decline in strength is associated with slower walking speed and increased risk of disability and falls². Of concern, neuropathic patients have been found to have a 41% reduction in the ankle strength, with atrophy being most pronounced in the distal muscles³.

Despite evidence that resistance training can improve muscle strength, no study has investigated whether a training program can improve foot muscle strength in people with DPN.  Therefore, this pilot aimed to determine the effectiveness an exercise intervention to increase toe strength in people with DPN.

Methods

26 participants diagnosed with type two diabetes and presenting with PN were randomised into either a 12-week supervised foot strengthening program (n=15)⁴ or a control group (n=11). Toe flexor strength was assessed while each participant stood on an emed pressure platform (Novel_gmbh). During each trial, participants were instructed to push down as hard as possible onto the platform under two conditions: i) using their lesser toes (2-5), or ii) using only their hallux. Maximum force under the hallux and lesser toes were calculated and then normalised to body mass (%BW).  Participants completed the test at baseline and again 12 weeks later and compared using a RM ANOVA.

Results

20 participants returned to the laboratory for retesting (77%). For hallux strength, although there was no significant interaction (p =0.35), there was an increase in hallux strength from pre- to post-intervention for the exercise group (Mdiff = 1.3 %BW), but no change across time for the Control group (Mdiff = 0.03 %BW). However, a significant time x group interaction effect was found for lesser toe strength (p ≤ 0.05). For the intervention group, lesser toe strength increased from 5.4 %BW to 5.7%BW after performing the exercises, whereas toe strength decreased in the control group from by 0.8%BW.

Discussion

This study has provided good pilot data to suggest that a foot strengthening exercise program may be suitable for people with diabetic neuropathy. Following 12-weeks of a progressive-resistance exercise program, toe strength increased, however, it is probably that the small sample size resulted in this not being statistically significant for the hallux.  Further research is warranted to determine whether interventions designed to strengthen and mobilise the toe muscles and joints may be effective in reducing forefoot plantar pressures in individuals with diabetes at risk of ulceration.

References

1.            Kirkman, et al. Diabetes Care. 2012;35:2650-64.

2.            Latham, et al. J Gerontol A Biol Sci Med Sci. 2004;59A:48-61.

3.            Andersen, et al. Diabetologia. 1997;40:1062-9.

4.            Mickle, et al. Clin Biomech. 2016;40:14-9.

Introduction: Individuals with chronic ankle instability (CAI) demonstrate deficits in balance control and current evidence shows that gluteal muscles play important roles in distal ankle injuries. The purpose of this study was to investigate if the training of gluteal muscles would influence the balance control in individuals with CAI. Methods: Twenty college students (20.6 ± 1.9yrs, 168.6 ± 9.3cm, 64.5 ± 15.8) with CAI were recruited in this study. All of them were divided into two groups: rehabilitation group (RG, n=10) and control group (CG, n=10). The RG completed 6-week gluteal muscle rehabilitation while the CG did not receive any treatment. The participants went through balance test with Y balance test (YBT) and limits-of-stability (LOS) test using Biodex balance system before and after intervention. A two-way mixed design ANOVA, with the treatment group (RG vs CG) as the between-subjects independent variable and time (baseline and 6 weeks) as the within-subjects independent variable, was used. Results: Significant group by time interaction were found for three directions in the YBT and overall scores in LOS test. The reach distances in anterior (ANT), medial-lateral (ML) and posterior-lateral (PL) directions were significantly increased in RG in post-test while no significant change was found in CG after training. Also, there was significant difference between groups in the reach distances of YBT in ML and PL directions in post-test. The overall scores in level 10 in LOS test was significantly improved in RG after training. Conclusions: It is concluded that 6-week gluteus muscle training enhances balance control in individuals with CAI.

Introduction. An ankle-foot orthosis (AFO) is a medical device that provides passive support during gait. An important metric for the AFO is stiffness, or compliance, about the ankle axis [1].  Typically, stiffness is adjusted by the shape of the trimline, material, and thickness of the AFO. Traditionally, the AFO is fabricated by thermoforming a plastic sheet around a mold of a patient’s limb. Three-dimensional printing techniques such as Material Extrusion (MEX) are allowing for the mass customization of complex parts. With MEX, AFOs can be fabricated quickly, repeatably, and with regional stiffness [2]. This study compares traditional and MEX AFO stiffness and aims to show that AFOs with comparable stiffness produce similar gait patterns.

Methods. The right foot and leg of a healthy subject was scanned (Omega, WillowWood, OH), and the scan was modified (Standard Cyborg, CA) to create both the adjusted positive model and the 3D model of the AFO. From the adjusted positive model, a foam model was created. A standard 4.75mm polypropylene sheet was thermoformed around this model, and trimlines were cut to create the traditional AFO device. From the 3D model, a MEX machine (Fortus, Stratasys, MN) was used to fabricate a 4mm thick, nylon AFO. Both AFOs were subjected to a stiffness test (Fig. 1a) using a custom mechanical testing device. This device measures angular deflection and torque about the AFO ankle axis.  Average stiffness of the AFO is obtained by applying a linear fit to the torque-deflection curve (Fig. 1b). Under an IRB approved protocol, a healthy subject walked with regular shoes and with the two AFOs while gait parameters were recorded using inertial measurement units (IMUs) (Legsys, BioSensics, MA). A Fisher Pairwise Method for one-way ANOVA was used to determine statistical difference (P<0.05) between the three conditions. 

Results. Average stiffness of both AFOs were similar – 3.8 N-m/deg – compared to cited ranges [3]. Gait analysis demonstrated that stride length, right-side knee angle at contact, and left and right-side knee flexion during swing were statistically similar between AFOs but different from the regular shoe condition. However, the AFOs performed statistically differently in step length and left and right-side stride duration.  In a survey, the subject revealed the printed AFO better limited the foot’s motion during gait. 

Discussion. MEX of AFO has been shown to produce statistically similar gait results in a healthy subject compared with traditionally manufactured AFO. Further studies with pathological subjects need to be performed to compare the correcting ability of the AFOs.

Acknowledgements

NSF PFI #1534003; NIDILRR #90RE5012

References

[1]      Kobayashi, T, et al., (2015) Clin. Biomech., 30(8), (775–780)

[2]      Shih, A., et al., (2017) Procedia CIRP 63 (156-160).

[3]      Singerman, R. et al., (1999) , J. Prosthetics Orthot., 11.

The provision of Ankle Foot Orthosis (AFO) to promote mobility is a very common intervention in clinical practice. Typical application area consists of patients with neurological diseases (like cerebral palsy or stroke) or neuromuscular diseases, suffering from muscle paresis. Despite  its frequent clinical use, levels of evidence are low, and many studies even show conflicting evidence. It seems that  some patients are strong responders, while others are not.

The AFO is a mechanical device, that interacts with ankle biomechanics, aiming to support or compensate muscle functions about the ankle, but will restrain remaining function at the same time. So in order to maximally support gait performance, provision of an AFO requires an optimal match between its mechanical characteristics and the pathological neuromechanics about the ankle of a particular patient.

The AFO mechanics can be considered as a spring in many cases. So a match between its mechanics and the patient’s needs, requires tuning of the neutral angle (AFO angle in the unloaded situation) and its stiffness. First I will present a versatile instrument to measure these parameters. Furthermore gait analysis is required to measure ankle function (with and without the AFO) in the patient and an outcome measure to quantify overall gait performance, like the walking speed or the energy cost of walking.

From computational modelling I will present that a theoretical optimum of stiffness is present. Too flaccid behaviour is not able to store energy , while a rigid behaviour will fully restrain the motion. Based on this I will present 3 comprehensive studies in 3 different groups of patients (Cerebral Palsy, Stroke, and post-polio). The studies have focussed on the Energy Cost of Walking as outcome of gait performance, and studying the role of ankle mechanics within the global optimisation

The results of the 3 studies generally confirm the theoretical findings, but biological variability, especially in cerebral palsy, makes it complex to forecast results in the individual case. We will discuss what further studies it would take to arrive at a clinical practise of precision orthotics, guided by biomechanical based diagnostics.

Recently, there has been a resurgence of interest in powered wearable robots including powered exoskeletons for human assistance. Because they are worn, the actuators for such machines must be exceptionally small and exceptionally light, while still being able to deliver substantial power and force. It is an ideal application for fluid power because fluid power has unsurpassed force and power density compared to electric motors. Fluid power, which includes hydraulics and pneumatics, has traditionally been used in large machines such as punch presses, excavators and motion bases for full-scale flight simulators. Bringing fluid power to the small scale required for wearable robots comes with interesting engineering challenges that include control and efficiency considerations. This presentation will describe modeling and simulation results that can be used to predict the size, weight and efficiency of the small-scale hydraulics that can drive next-generation lightweight wearable robots, and will propose design guidelines that can help the engineering designer optimize small scale hydraulics. An application of small-scale hydraulics will be presented, which is a hydraulic powered ankle-foot orthosis that has exceptional torque yet is still small and light. Two versions have been developed and bench tested, one for adults that can produce up to 90 Nm of active torque, and an even smaller child-size version that is being tested for technical feasibility as an emulator for the plastic AFO commonly prescribed for children with cerebral palsy.

High energy traumatic lower extremity injuries often have wide ranging negative effects. Impaired gait, disability, depression and reduced quality of life are frequently observed[1]. Ankle foot orthoses, external devices which interface with the lower leg and foot to support and protect the lower limb, can significantly improve limb function following lower extremity trauma[2]. Although ankle foot orthoses come in many shapes, sizes and materials, robust carbon fiber custom dynamic orthoses (CDOs) are better able to compensate for decreased limb function than widely-used thermoplastic alternatives or off-the-shelf carbon fiber devices. CDOs have a proximal cuff below the knee to support and transfer force to the limb, a posterior carbon fiber dynamic strut to store and return energy, and a full-length rigid foot plate that supports the foot and acts as a lever to allow strut deflection. The objective of this presentation is to synthesize the findings from recent efforts to enable data driven design of custom carbon fiber CDOs.

Several research studies were conducted to investigate the effects of specific design parameters on one specific type of CDO, the Intrepid Dynamic Exoskeletal Orthosis (IDEO). Young military service members with impaired lower limb function due to injury participated in a series of biomechanical gait studies using well established methods[3]. We examined the relative effect of strut stiffness[4, 5], strut bending point[6], heel wedge properties[7], and alignment[8] on lower limb function.

Selective laser sintering was used to systematically modify the stiffness and bending point of the posterior strut; heel wedge height and durometer were methodically modified; and sagittal alignment was adjusted using a wedge at the distal strut attachment point.

Device design significantly influences limb loading, device and limb motion and subsequent muscle activation. Modifications to heel wedge properties and alignment produced the largest and most systematic effects.

We will compare and contrast the relative effects of each design parameter, with an eye toward applying the lessons learned from research on the IDEO to other CDOs, and the development of objective guidelines for their prescription. Knowledge of the specific effects of design parameters on device function and patient response can be used to tune devices to meet individual patient needs.

Acknowledgement: Center for Rehabilitation Sciences Research. The views expressed herein are those of the authors and do not reflect the official policy or position of any federal organizations or the U.S. Government.

References:  1)Doukas-J Bone Joint Surg Am, 2013. 2)Bedigrew-Clin Orthop Relat Res, 2014. 3)Wilken-Gait Posture, 2012. 4)Haight-Gait Posture, 2015. 5)Harper-Clin Biomech , 2014. 6)Ranz- Clin Biomech, 2016. 7)Ikeda-Prosthet Orthot Int, 2017. 8)Brown-J Biomech, 2017.

Introduction

Ankle sprains are well known to be among most common sports-related injuries. Lateral ankle sprains affect nearly a half of all ankle sprains and have a reported recurrence rate of more than 70%. In lateral ankle sprains and accompanying lesions of the lateral ligaments orthoses are used for the functional treatment by protecting the ligaments from excessive stresses and reinjury since a previous injury history may be one of the most important risk factors for an ankle sprain. They are furthermore applied in conservative and post-surgical treatment, but also in injury prevention. Despite their common application in clinical routine, there is very little biomechanical evidence on the efficacy of various orthoses to restrict inversion and internal rotation and on the stabilizing effect on ankle joints with existing lateral instability. Therefore the aim of the present study was to biomechanically evaluate and quantify the isolated stabilizing abilities of commonly prescribed semi-rigid ankle orthoses in a simulated reoccurring inversion trauma.

Methods

Twelve anatomic lower leg specimens were tested in plantar flexion and hindfoot inversion in a simulated inversion trauma in a quasi-static and dynamic (at 50°/s) mode. Tests were performed on intact specimens, specimens with the ruptured anterior talofibular ligament (ATFL) (simulating an existing ankle sprain injury), followed by stabilization with 5 different semi-rigid orthoses (AirGo Ankle Brace (DJO, LLC; Vista, CA, USA), Air Stirrup Ankle Brace (DJO, LLC; Vista, CA, USA), Dyna Ankle 50S1 (Otto Bock HealthCare GmbH; Duderstadt, Germany), MalleoLoc (Bauerfeind AG; Zeulenroda-Triebes, Germany), Push Aequi (Push, Maastricht-Airport; Netherlands)). The stabilizing effect was quantified by the reinforcement of internal rotation moment between tibia and calcaneus compared to the injured and unprotected state.

Results

Only two orthoses (AirGo and Air Stirrup) reinforced the ankle joint during inversion compared to the uninjured and unprotected state in quasi-static and dynamic modes (Figure 1a and 1b).

Both orthoses consist of two separate large, a medial and lateral, plastic shell elements, which provide their high stability. Additional preinflated and cushioned aircells in both orthoses allow sufficient adhesion on the skin. Aequi showed internal rotation moment in the magnitude of intact ankle joints. Dyna Ankle 50S1 and MalleoLoc provided less than 2.5% resistance to applied internal rotation compared to ankle joint with ruptured ATFL. Their design should be reconsidered. Testing in quasi-static and dynamic mode delivered valid and comparable results.
Discussion

In conclusion ankle orthoses varied significantly in their ability to stabilize the ankle joint during an inversion trauma. Presented objective data on passive stabilization may assist clinicians when prescribing adequate orthoses.

Acknowledgments

We acknowledge the people, who have selflessly donated their body for medical research and ORMED GmbH (Freiburg, Germany) for the donation of orthoses.

Cerebral palsy (CP) is a pathology that results from an irreversible and non-progressive injury of the immature brain. In Brazil, CP is the most common motor deficiency during childhood, with an occurrence of around 35,000 cases per year. Spasticity is a major impairment in children with CP and the equinus foot is a common gait abnormality resulting from spasticity of the ankle plantar flexor. The ankle-foot orthosis (AFO) is used in the effective conservative treatment for preventing the progression of equinus deformities. The use of AFO limits ankle plantar flexion and provides passive stretching for the tight soft tissues. The traditional method for AFO manufacturing involves plaster casting, an imperfect process producing non-repeatable results and is highly dependent on skilled labor. Additive manufacturing (AM) methods and 3D scanning technologies shave been proposed as alternatives to the traditional approach. The objective of this research was to develop a methodology for production of AFO orthoses based on photogrammetry and computational simulation. Sixty photos were taken with a smartphone around the foot of an adult in three different angles with image overlap and distance of 20 cm. The free softwares ReMake and Meshmixer (Autodesk) were used for photogrammetry and modeling respectively. The 3D image obtained was treated with mesh closure and smoothing. The AFO orthosis was modeled according to the anatomical position of the ankle, foot, plantar fascia, malleoles and with determined height up to the head of the fibula. After the modeling, an offset function with distance of 5 mm and thickness of 3 mm was applied. The computational simulation using finite element method was performed for two AFO with different materials (acrylonitrile butadiene styrene (ABS) and polypropylene (PP)) using the software Abaqus. Photogrammetry proved to be a fast, practical and low-cost technique compared with laser scanning. The 3D scanning with Kinect showed to be a possible methodological alternative presenting a mesh difference of 0.06 mm when compared to photogrammetry. This approach allows adjustment through the customization of several parameters (thickness, angulation and material) and it can be modified according to the clinical evaluation. The computational analysis showed higher tensions in the AFO in the forefoot and ankle region, and when comparing the materials, the ABS model showed a tension of 26% in relation to the PP model. The combination of photogrammetry and computational simulation allowed designing more efficient orthoses in all three planes with different materials. This approach can be an option to reduce time and hard work in the production, with greater adaptability to the patient.

Many wearable sensors and algorithms have been investigated for gait event detection; however, with increasing number of sensors and algorithms, gait estimation system complexities increase. This study investigated the minimum sensor configuration (individual or pair) to achieve the simplest cost-effective configuration for robust gait event estimation for a powered AFO.

Five sensors were attached to the Portable Powered Ankle-Foot Orthosis (PPAFO) [1]. Two force sensitive sensors (FSR) (SEN-09376 ROHS, SparkFun) were embedded between the sole and tread and used for detecting foot heel or ball contact. A linear magnetic potentiometer (MagnetoPot; Spectra Symbol) measured linear translation of two parallel pneumatic actuators, which converted directly to ankle angle through a gear train at the ankle joint. Two inertial measurement units (IMU) (MPU9250; InvenSense) were attached to the foot and shank segments (dorsal surface and anterior shin) to track segment kinematics.

To assess performance of single or double sensor configurations, sensor-based estimates were compared to “true” values through event-based and state-based approaches in terms of gait event detection timing (ms) and gait state estimation (% gait cycle), respectively [2]. Five healthy male subjects walked on an instrumented treadmill (Bertec) wearing the PPAFO and motion markers (Vicon) on the right foot for five one-minute trials each. Gait cycles were divided into 101 states (0%-100% GC) using eight signals to define “true” gait states (ankle and shank angle from motion capture data, bilateral vertical ground reaction forces, and their derivatives). For the five sensors, gait events were detected through a combination of local maxima, minima and threshold-crossing methods; then the detected events were used to perform gait state estimation [2]. Mean absolute error between “true” and estimated values quantified sensor configuration performance.

Using direct and derived signals, ten gait events representing initiation or mid-point of the eight gait cycle sub-phases could be detected from the sensors. Individually, each FSR detected two different events, while the potentiometer, foot IMU and shank IMU detected four, six, and eight, respectively. All sensor configurations had errors less than 3.5% GC. Configurations that included an IMU had better performance than non-IMU configurations. The single IMU configurations (on the shank or foot) both outperformed all other configurations (mean state estimation error: < 2% GC; mean event detection timing error: < 23ms). Since more detectable events could improve system robustness (i.e., adjusting to variable speeds) by updating estimation more frequently, a single shank IMU configuration was recommended. As a failsafe feature, a heel FSR can be included to increase event detection redundancy.

Acknowledgements

NSF Engineering Research Center for Compact and Efficient Fluid Power #0540834

References

[1] Wang, Z and Hsiao-Wecksler, ET, J Med Devices 10(3):030963, 2016

Hybrid orthoses have become a powerful rehabilitation tool for gait disorder that combine a powered exoskeleton that actuates lower limb joints, with functional electrical stimulation (FES) that induce contraction in the denervated muscles. Nevertheless, as a consequence of the synchronous activation and recruitment of fast-twitch muscle fibers during artificial stimulation, a trade-off between FES and electromechanical actuation must be considered to reduce fatigue and therefore, to increase rehabilitation training periods. The strategies to control both command signals are mainly based in dynamic models for walking or predictive cooperative models to obtain a functional movement. The main drawback is the lack of physiological information to develop the controller. In this work we propose a physiologically based criteria to control both the active orthosis and the FES device. The idea is to tune a fatigue dynamic block included in a modification of the Hill-type muscle model that accounts for artificial stimulation. In this way, for each subject wearing the hybrid orthosis, it is possible to compute fatigue and recovery times based on that model, and therefore to adapt stimulation and electromechanical actuation times to reduce fatigue.  To do so, a battery of stimulation tests were carried out to obtain subject’s specific parameters for the muscle model. In particular, as knee flexion was the movement to be induced, a stimulation of the quadriceps group was carried out, and the motion of the leg was recorded. To tune the fatigue dynamics block, the divergences between muscle forces in forward dynamics, and in inverse dynamics were studied. On the one hand, muscle stimulation profiles were used as inputs in the artificially activated muscle model to obtain muscle forces. On the other hand, the measured motion was used as input in the inverse dynamic approach to obtain the muscle forces that produce that motion. A system identification approach was then used to obtain the dynamics that accounts for the divergences in muscle forces calculated by inverse and forward dynamics. Once identified the fatigue dynamics, the time to fatigue and the recovery time were obtained and used to adapt the robotic-FES combined actuation. The design of rehabilitation routines for hybrid orthoses must consider on the one hand the desired kinematics and, on the other hand, the muscle physiology, as part of the movement is performed under artificial activation. The proposed approach includes both conditions, and it is expected to be useful in the elaboration of training programs for subjects with gait disabilities.