Dysfunctional neuro-muscular mechanisms explain gradual gait changes in prodromal spastic paraplegia.

BACKGROUND: In Hereditary Spastic Paraplegia (HSP) type 4 (SPG4) a length-dependent axonal degeneration in the cortico-spinal tract leads to progressing symptoms of hyperreflexia, muscle weakness, and spasticity of lower extremities. Even before the manifestation of spastic gait, in the prodromal phase, axonal degeneration leads to subtle gait changes. These gait changes - depicted by digital gait recording - are related to disease severity in prodromal and early-to-moderate manifest SPG4 participants. METHODS: We hypothesize that dysfunctional neuro-muscular mechanisms such as hyperreflexia and muscle weakness explain these disease severity-related gait changes of prodromal and early-to-moderate manifest SPG4 participants. We test our hypothesis in computer simulation with a neuro-muscular model of human walking. We introduce neuro-muscular dysfunction by gradually increasing sensory-motor reflex sensitivity based on increased velocity feedback and gradually increasing muscle weakness by reducing maximum isometric force. RESULTS: By increasing hyperreflexia of plantarflexor and dorsiflexor muscles, we found gradual muscular and kinematic changes in neuro-musculoskeletal simulations that are comparable to subtle gait changes found in prodromal SPG4 participants. CONCLUSIONS: Predicting kinematic changes of prodromal and early-to-moderate manifest SPG4 participants by gradual alterations of sensory-motor reflex sensitivity allows us to link gait as a directly accessible performance marker to emerging neuro-muscular changes for early therapeutic interventions.

Functional MRI in Parkinson's disease with freezing of gait: a systematic review of the literature.

BACKGROUND: Freezing of gait (FOG), a common and disabling symptom of Parkinson's disease (PD), is characterized by an episodic inability to generate effective stepping. Functional MRI (fMRI) has been used to evaluate abnormal brain connectivity patterns at rest and brain activation patterns during specific tasks in patients with PD-FOG. This review has examined the existing functional neuroimaging literature in PD-FOG, including those with treatment. Summarizing these articles provides an opportunity for a better understanding of the underlying pathophysiology in PD-FOG. METHODS: According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we performed a literature review of studies using fMRI to investigate the underlying pathophysiological mechanisms of PD-FOG. RESULTS: We initially identified 201 documents. After excluding the duplicates, reviews, and other irrelevant articles, 39 articles were finally identified, including 18 task-based fMRI studies and 21 resting-state fMRI studies. CONCLUSIONS: Studies using fMRI techniques to evaluate PD-FOG have found dysfunctional connectivity in widespread cortical and subcortical regions. Standardized imaging protocols and detailed subtypes of PD-FOG are furthered required to elucidate current findings.

[Study on gait symmetry based on simulation and evaluation system of prosthesis gait].

A software and hardware platform for gait simulation and system evaluation for lower limb intelligent prosthesis is proposed and designed, in order that the wearable symmetry effect of the intelligent knee prosthesis can be quantitatively analyzed by machine test instead of human wear test. The whole-body three-dimensional gait and motion analysis system instrument, a device to collect gait data such as joint angle and stride of adults, was used for extracting simulated gait characteristic curve. Then, the gait curve was fitted based on the corresponding joint to verify the feasibility of the test platform in the experiment. Finally, the developed artificial knee prosthesis was worn on the prosthetic evaluation system to quantitatively analyze the gait symmetry effect. The results showed that there was no significant difference in gait symmetry between the developed knee joints at different speeds, which could reach more than 88%. The simulation and evaluation of the prosthetic gait have good effects on the functional simulation and evaluation of the lower limb intelligent prosthesis.

Development and validation of a novel ankle joint musculoskeletal model.

An improved understanding of contact mechanics in the ankle joint is paramount for implant design and ankle disorder treatment. However, existing models generally simplify the ankle joint as a revolute joint that cannot predict contact characteristics. The current study aimed to develop a novel musculoskeletal ankle joint model that can predict contact in the ankle joint, together with muscle and joint reaction forces. We modelled the ankle joint as a multi-axial joint and simulated contact mechanics between the tibia, fibula and talus bones in OpenSim. The developed model was validated with results from experimental studies through passive stiffness and contact. Through this, we found a similar ankle moment-rotation relationship and contact pattern between our study and experimental studies. Next, the musculoskeletal ankle joint model was incorporated into a lower body model to simulate gait. The ankle joint contact characteristics, kinematics, and muscle forces were predicted and compared to the literature. Our results revealed a comparable peak contact force and the same muscle activation patterns in four major muscles. Good agreement was also found in ankle dorsi/plantar-flexion and inversion/eversion. Thus, the developed model was able to accurately model the ankle joint and can be used to predict contact characteristics in gait.

Increasing midtarsal joint stiffness reduces triceps surae metabolic costs in walking simulations but has little effect on total stance limb metabolic cost.

The human foot's arch is thought to be beneficial for efficient gait. This study addresses the extent to which arch stiffness changes alter the metabolic energy requirements of human gait. Computational musculoskeletal simulations of steady state walking using direct collocation were performed. Across a range of foot arch stiffnesses, the metabolic cost of transport decreased by less than 1% with increasing foot arch stiffness. Increasing arch stiffness increased the metabolic efficiency of the triceps surae during push-off, but these changes were almost entirely offset by other muscle groups consuming more energy with increasing foot arch stiffness.

Influence of Isolated Talonavicular and Subtalar Joint Arthrodesis on Hindfoot Kinematics and Range of Motion During Cadaveric Gait Simulation.

BACKGROUND: Isolated subtalar and talonavicular joint arthrodeses have been associated with adjacent joint arthritis and altered hindfoot kinematics during simplified loading scenarios. However, the effect on kinematics during dynamic activity is unknown. This study assessed changes in subtalar and talonavicular kinematics after isolated talonavicular (TNiso) and subtalar (STiso) arthrodesis, respectively, during stance simulations. METHODS: Fourteen midtibia specimens received either a TNiso or STiso arthrodesis, with 7 randomized to each group. A 6-degree-of-freedom robot sequentially simulated the stance phase for the intact and arthrodesis conditions. Bootstrapped bias-corrected 95% CIs of the talonavicular and subtalar joint kinematics were calculated and compared between conditions. RESULTS: The TNiso decreased subtalar inversion, adduction, and plantarflexion in late stance (P < .05). The subtalar range of motion in the sagittal and coronal planes decreased by 40% (P = .009) and 46% (P = .002), respectively. No significant changes in talonavicular joint kinematics were observed after isolated subtalar arthrodesis; however, the range of motion was reduced by 61% (P = .007) and 50% (P = .003) in the coronal and axial planes, respectively. CONCLUSION: In this model for arthrodesis, changes in subtalar kinematics and motion restriction were observed after isolated talonavicular arthrodesis, and motion restriction was observed after isolated subtalar arthrodesis. Surprisingly, talonavicular kinematics did not appear to change after isolated subtalar arthrodesis. CLINICAL RELEVANCE: Both joint fusions substantially decrease the motion of the reciprocal adjacent joint. Surgeons should be aware that the collateral costs with talonavicular fusion appear higher, and it has a significant effect on subtalar kinematics during the toe-off phase of gait.

Peroneus Brevis to Longus Tendon Transfer in the Treatment of Flexible Progressive Collapsing Foot Deformity: A Cadaveric Study.

BACKGROUND: Although operative treatment of the flexible progressive collapsing foot deformity (PCFD) remains controversial, correction of residual forefoot varus and stabilization of the medial column are important components of reconstruction. A peroneus brevis (PB) to peroneus longus (PL) tendon transfer has been proposed to address these deformities. The aim of our study was to determine the effect of an isolated PB-to-PL transfer on medial column kinematics and plantar pressures in a simulated PCFD (sPCFD) cadaveric model. METHODS: The stance phase of level walking was simulated in 10 midtibia cadaveric specimens using a validated 6-degree of freedom robot. Bone motions and plantar pressure were collected in 3 conditions: intact, sPCFD, and after PB-to-PL transfer. The PB-to-PL transfer was performed by transecting the PB and advancing the proximal stump 1 cm into the PL. Outcome measures included the change in joint rotation of the talonavicular, first naviculocuneiform, and first tarsometatarsal joints between conditions. Plantar pressure outcome measures included the maximum force, peak pressure under the first metatarsal, and the lateral-to-medial forefoot average pressure ratio. RESULTS: Compared to the sPCFD condition, the PB-to-PL transfer resulted in significant increases in talonavicular plantarflexion and adduction of 68% and 72%, respectively, during simulated late stance phase. Talonavicular eversion also decreased in simulated late stance by 53%. Relative to the sPCFD condition, the PB-to-PL transfer also resulted in a 17% increase (P = .045) in maximum force and a 45-kPa increase (P = .038) in peak pressure under the first metatarsal, along with a medial shift in forefoot pressure. CONCLUSION: The results from this cadaver-based simulation suggest that the addition of a PB-to-PL transfer as part of the surgical management of the flexible PCFD may aid in correction of deformity and increase the plantarflexion force under the first metatarsal. CLINICAL RELEVANCE: This study provides biomechanical evidence to support the addition of a PB-to-PL tendon transfer in the surgical treatment of flexible PCFD.

Role of Robotic Gait Simulators in Elucidating Foot and Ankle Pathomechanics.

Testing with cadaveric foot and ankle specimens began as mechanical techniques to study foot function and then evolved into static simulations of specific instances of gait, before technologies were eventually developed to fully replicate the gait cycle. This article summarizes the clinical applications of dynamic cadaveric gait simulation, including foot bone kinematics and joint function, muscle function, ligament function, orthopaedic foot and ankle pathologies, and total ankle replacements. The literature was reviewed and an in-depth summary was written in each section to highlight one of the more sophisticated simulators. The limitations of dynamic cadaveric simulation were also reviewed.

A hip disarticulation prostheses test system to simulate gait for prostheses evaluation.

BACKGROUND: The limited number of hip prostheses users makes it less feasible to conduct amputee tests for prosthesis development in the clinic, which restricts the development efficiency of the intelligent prostheses. OBJECTIVE: This study proposes a hip disarticulation prostheses test system (HDPTS) to supplement the amputee tests for hip disarticulation prosthesis (HDP) evaluation, which would potentially facilitate the prosthesis evaluation safety and development efficiency. METHODS: The hip trajectory of an individual with normal gait was acquired and reproduced by calculating the corresponding movement joint angle of a manipulator. Then, an HDP was fit on an amputee and on the HDPTS respectively to obtain the hip and knee joint angles of the HDP during walking. Comparing the root mean square error (RMSE) of the expected and planned trajectory, the joint angles between the amputee test and HDPTS test, to verify the feasibility and accuracy of the HDPTS for prosthesis evaluation. RESULTS: The RMSE between the expected and planned trajectory value was less than 1.20 mm (< 0.19%). The RMSE of the joint angles between the amputee test and HDPTS test were 2.18∘ (1.8%) and 3.13∘ (5.92%) for hip and knee joint respectively. CONCLUSION: The HDPTS was found accurate in hip trajectory reproduction and feasible in gait simulation for the prosthesis evaluation, which could potentially supplement the amputee test for prosthesis design thus improving prosthesis test safety and development efficiency.

Hindfoot Arthrodeses and the Order of Joint Fixation Influence Tibiotalar Kinematics During Simulated Stance.

BACKGROUND: Although hindfoot arthrodeses relieve pain and correct deformity, they have been associated with progressive tibiotalar degeneration. The objective was to quantify changes in tibiotalar kinematics after hindfoot arthrodeses, both isolated subtalar and talonavicular, as well as double arthrodesis, and to determine if the order of joint fixation affects tibiotalar kinematics. METHODS: Hindfoot arthrodeses were performed in 14 cadaveric mid-tibia specimens. Specimens randomly received isolated fixation of the subtalar or talonavicular joint first, followed by fixation of the remaining joint for the double arthrodesis. A 6-degree-of-freedom robot sequentially simulated the stance phase of level walking for intact, isolated, and double arthrodesis conditions. Tibiotalar kinematic changes were compared for the intact and arthrodesis conditions. A subsequent analysis assessed the effect of the joint fixation order on tibiotalar kinematics. RESULTS: Isolated and double hindfoot arthrodeses increased tibiotalar plantarflexion, inversion, and internal rotation during late stance. Tibiotalar kinematics changes occurring after isolated arthrodesis remained consistent after the double arthrodesis for both the subtalar- and talonavicular-first conditions. The order of joint fixation influenced tibiotalar kinematics through some portions of stance, where the talonavicular-first double arthrodesis increased tibiotalar plantarflexion, eversion, and internal rotation compared to the subtalar-first double. CONCLUSION: Tibiotalar kinematics were modestly altered for all conditions, both isolated and double hindfoot arthrodeses. Changes in tibiotalar kinematics were consistent from the isolated to the double arthrodesis conditions and varied depending on which isolated hindfoot arthrodesis was performed first. Further research is needed to assess the clinical implications of the observed changes in tibiotalar kinematics, particularly as it pertains to the development of adjacent joint arthritis. CLINICAL RELEVANCE: These findings may correlate with clinical research that has cited hindfoot arthrodesis as a risk factor for adjacent tibiotalar arthritis. Once either the subtalar or talonavicular joint is fused, avoiding the arthrodesis of the second joint may not necessarily protect the tibiotalar joint.

The Foot and Ankle Kinematics of a Simulated Progressive Collapsing Foot Deformity During Stance Phase: A Cadaveric Study.

BACKGROUND: Progressive collapsing foot deformity (PCFD) is a complex pathology associated with tendon insufficiency, ligamentous failure, joint malalignment, and aberrant plantar force distribution. Existing knowledge of PCFD consists of static measurements, which provide information about structure but little about foot and ankle kinematics during gait. A model of PCFD was simulated in cadavers (sPCFD) to quantify the difference in joint kinematics and plantar pressure between the intact and sPCFD conditions during simulated stance phase of gait. METHODS: In 12 cadaveric foot and ankle specimens, the sPCFD condition was created via sectioning of the spring ligament and the medial talonavicular joint capsule followed by cyclic axial compression. Specimens were then analyzed in intact and sPCFD conditions via a robotic gait simulator, using actuators to control the extrinsic tendons and a rotating force plate underneath the specimen to mimic the stance phase of walking. Force plate position and muscle forces were optimized using a fuzzy logic iterative process to converge and simulate in vivo ground reaction forces. An 8-camera motion capture system recorded the positions of markers fixed to bones, which were then used to calculate joint kinematics, and a plantar pressure mat collected pressure distribution data. Joint kinematics and plantar pressures were compared between intact and sPCFD conditions. RESULTS: The sPCFD condition increased subtalar eversion in early, mid-, and late stance (P < .05), increased talonavicular abduction in mid- and late stance (P < .05), and increased ankle plantarflexion (P < .05), adduction (P < .05), and inversion (P < .05). The center of plantar pressure was significantly (P < .01) medialized in this model of sPCFD and simulated stance phase of gait. DISCUSSION: Subtalar and talonavicular joint kinematics and plantar pressure distribution significantly changed with the sPCFD and in the directions expected from a PCFD foot. We also found that ankle joint kinematics changed with medial and plantar drift of the talar head, indicating abnormal talar rotation. Although comparison to an in vivo PCFD foot was not performed, this sPCFD model produced changes in foot kinematics and indicates that concomitant abnormal changes may occur at the ankle joint with PCFD. CLINICAL RELEVANCE: This study describes the dynamic kinematic and plantar pressure changes in a cadaveric model of simulated progressive collapsing foot deformity during simulated stance phase.

Orthosis and Foot Structure Affect the Fifth Metatarsal Principal Strains During Simulated Level Walking.

BACKGROUND: Fractures of the proximal fifth metatarsal bone are common injuries in elite athletes and are associated with high rates of delayed union and nonunion. Structural features of the foot may increase fracture risk in some individuals, emphasizing the need for intervention strategies to prevent fracture. Although orthotic devices have shown promise in reducing fractures of the fifth metatarsal bone, the effect of orthosis on fifth metatarsal strains is not well understood. PURPOSE: To quantify the effects of different foot orthotic constructs on principal tensile strains in the proximal fifth metatarsal bone during cadaveric simulations of level walking. An additional purpose was to investigate the relationships between structural features of the foot and corresponding strains on the fifth metatarsal bone during level walking. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 10 midtibial cadaveric specimens were attached to a 6 degrees of freedom robotic gait simulator. Strain gauges were placed at the metaphyseal-diaphyseal junction (zone II) and the proximal diaphysis (zone III) during level walking simulations using 11 different foot orthotic configurations. Images of each specimen were used to measure structural features of the foot in an axially loaded position. The peak tensile strains were measured and reported relative to the sneaker-only condition for each orthotic condition and orthotic-specific association between structural features and principal strains of both zones. RESULTS: In total, 2 of the 11 orthotic conditions significantly reduced strain relative to the sneaker-only condition in zone II. Further, 6 orthotic conditions significantly reduced strain relative to the sneaker-only condition in zone III. Increased zone II principal strain incurred during level walking in the sneaker-only condition showed a significant association with increases in the Meary's angle. Changes in zone III principal strain relative to the sneaker-only condition were significantly associated with increases in the Meary's angle and fourth-fifth intermetatarsal angle. CONCLUSION: The use of orthotic devices reduced principal strain relative to the condition of a sneaker without any orthosis in zone II and zone III. The ability to reduce strain relative to the sneaker-only condition in zone III was indicated by increasing values of the Meary's angle and levels of the fourth-fifth intermetatarsal angle. CLINICAL RELEVANCE: Clinicians can use characteristics of foot structure to determine the proper foot orthosis to potentially reduce stress fracture risk in high-risk individuals.

The implications of non-anatomical positioning of a meniscus prosthesis on predicted human knee joint biomechanics.

Despite all the efforts to optimize the meniscus prosthesis system (geometry, material, and fixation type), the success of the prosthesis in clinical practice will depend on surgical factors such as intra-operative positioning of the prosthesis. In this study, the aim was therefore to assess the implications of positional changes of the medial meniscus prosthesis for knee biomechanics. A detailed validated finite element (FE) model of human intact and meniscal implanted knees was developed based on a series of in vitro experiments. Different non-anatomical prosthesis positions were applied in the FE model, and the biomechanical response during the gait stance phase compared with an anatomically positioned prosthesis, as well as meniscectomized and also the intact knee model. The results showed that an anatomical positioning of the medial meniscus prosthesis could better recover the intact knee biomechanics, while a non-anatomical positioning of the prosthesis to a limited extent alters the knee kinematics and articular contact pressure and increases the implantation failure risk. The outcomes indicate that a medial or anterior positioning of the meniscus prosthesis may be more forgiving than a posteriorly or laterally positioned prosthesis. The outcome of this study may provide a better insight into the possible consequences of meniscus prosthesis positioning errors for the patient and the prosthesis functionality. Graphical abstract.

Calibration of the shear wave speed-stress relationship in in situ Achilles tendons using cadaveric simulations of gait and isometric contraction.

It has been shown that shear wave speed is directly dependent on axial stress in ex vivo tendons. Hence, a wave speed sensor could be used to track tendon loading during movement. However, adjacent soft tissues and varying joint postures may affect the wave speed-load relationship for intact tendons. The purpose of this study was to determine whether the proportional relationship between squared wave speed and stress holds for in situ cadaveric Achilles tendons, to evaluate whether this relationship is affected by joint angle, and to assess potential calibration techniques. Achilles tendon wave speed and loading were simultaneously measured during cadaveric simulations of gait and isometric contractions performed in a robotic gait simulator. Squared wave speed and axial stress were highly correlated during isometric contraction at all ankle postures (R2avg = 0.98) and during simulations of gait (R2avg = 0.92). Ankle plantarflexion angle did not have a consistent effect on the constant of proportionality (p = 0.217), but there was a significant specimen-angle interaction effect (p < 0.001). Wave speed-based predictions of tendon stress were most accurate (average RMS error = 11% of maximum stress) when calibrating to isometric contractions performed in a dorsiflexed posture that resembled the posture at peak Achilles loading during gait. The results presented here show that the linear relationship between tendon stress and squared shear wave speed holds for a case resembling in vivo conditions, and that calibration during an isometric task can yield accurate predictions of tendon loading during a functional task.

Anteroposterior Translational Malalignment of Ankle Arthrodesis Alters Foot Biomechanics in Cadaveric Gait Simulation.

Tibiotalar arthrodesis is a common surgical treatment for end-stage ankle arthritis. Proper ankle alignment is important as malalignment can lead to complications that may require revision surgery. This study aimed to determine how anteroposterior (AP) translational malalignment of ankle arthrodesis affects distal foot joint kinematics and plantar pressure. Ankle arthrodesis was performed on 10 cadaveric foot specimens using a custom fixture that could fuse the ankle neutrally and induce discrete malalignments (3, 6, and 9 mm) anteriorly and posteriorly. Gait was simulated under each alignment with a robotic gait simulator, and foot bone motion and plantar pressure were quantified. AP translational malalignment did not substantially affect plantar pressure or joint range of motion, but there were several significant differences in joint position throughout stance phase. Differences were seen in five joints (talocalcaneal, talonavicular, calcaneocuboid, fifth tarsometatarsal, and first metatarsophalangeal) and in the position of the first metatarsal relative to the talus. The most extreme effects occurred when the talus was displaced 6 mm or more posteriorly. In vivo, this may lead to aberrant joint loading, which could negatively impact patient outcomes. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:450-458, 2020.

Modeling and simulation of musculoskeletal system of human lower limb based on tensegrity structure.

In this paper, a mechanical model of the skeletal muscle of human lower limb system is established by using the Hill muscle model and kinetic equation of the movement of lower extremities according to the attachment positions of skeletal muscle. State vector and neural control are delineated by the direct configuration method. Changes of gait and skeletal muscle stress during walking process are analyzed with energy consumption as objective function. Results illustrate that simulation data are in good agreement with actual walking gait data. Feasibility and correctness of the designed model and control behavior of skeletal muscle tension structure are also verified.

Augmented Ligament Reconstruction Partially Restores Hindfoot and Midfoot Kinematics After Lateral Ligament Ruptures.

BACKGROUND: Altered kinematics and persisting ankle instability have been associated with degenerative changes and osteochondral lesions. PURPOSE: To study the effect of ligament reconstruction surgery with suture tape augmentation (isolated anterior talofibular ligament [ATFL] vs combined ATFL and calcaneofibular ligament [CFL]) after lateral ligament ruptures (combined ATFL and CFL) on foot-ankle kinematics during simulated gait. STUDY DESIGN: Controlled laboratory study. METHODS: Five fresh-frozen cadaveric specimens were tested in a custom-built gait simulator in 5 different conditions: intact, ATFL rupture, ATFL-CFL rupture, ATFL-CFL reconstruction, and ATFL reconstruction. For each condition, range of motion (ROM) and the average angle (AA) in the hindfoot and midfoot joints were calculated during the stance phase of normal and inverted gait. RESULTS: Ligament ruptures mainly changed ROM in the hindfoot and the AA in the hindfoot and midfoot and influenced the kinematics in all 3 movement directions. Combined ligament reconstruction was able to restore ROM in inversion-eversion in 4 of the 5 joints and ROM in internal-external rotation and dorsiflexion-plantarflexion in 3 of the 5 joints. It was also able to restore the AA in inversion-eversion in 2 of the 5 joints, the AA in internal-external rotation in all joints, and the AA in dorsiflexion-plantarflexion in 1 of the joints. Isolated ATFL reconstruction was able to restore ROM in inversion-eversion and internal-external rotation in 3 of the 5 joints and ROM in dorsiflexion-plantarflexion in 2 of the 5 joints. Isolated reconstruction was also able to restore the AA in inversion-eversion and dorsiflexion-plantarflexion in 2 of the joints and the AA in internal-external rotation in 3 of the joints. Both isolated reconstruction and combined reconstruction were most successful in restoring motion in the tibiocalcaneal and talonavicular joints and least successful in restoring motion in the talocalcaneal joint. However, combined reconstruction was still better at restoring motion in the talocalcaneal joint than isolated reconstruction (1/3 for ROM and 1/3 for the AA with isolated reconstruction compared to 1/3 for ROM and 2/3 for the AA with combined reconstruction). CONCLUSION: Combined ATFL-CFL reconstruction showed better restored motion immediately after surgery than isolated ATFL reconstruction after a combined ATFL-CFL rupture. CLINICAL RELEVANCE: This study shows that ligament reconstruction with suture tape augmentation is able to partially restore kinematics in the hindfoot and midfoot at the time of surgery. In clinical applications, where the classic Broström-Gould technique is followed by augmentation with suture tape, this procedure may protect the repaired ligament during healing by limiting excessive ROM after a ligament rupture.

A fast inverse dynamics model of walking for use in optimisation studies.

Computer simulation of human gait, based on measured motion data, is a well-established technique in biomechanics. However, optimisation studies requiring many iterative gait cycle simulations have not yet found widespread application because of their high computational cost. Therefore, a computationally efficient inverse dynamics model of 3D human gait has been designed and compared with an equivalent model, created using a commercial multi-body dynamics package. The fast inverse dynamics model described in this paper led to an eight fold increase in execution speed. Sufficient detail is provided to allow readers to implement the model themselves.

Cadaveric gait simulation reproduces foot and ankle kinematics from population-specific inputs.

Cadaveric gait simulation allows researchers to directly investigate biomechanical consequences of surgeries using invasive measurement techniques. However, it is unclear if foot and ankle kinematics that are population-specific are reproduced using these devices. Therefore, we assessed foot and ankle kinematics produced in a cadaveric gait simulator during the stance phase of gait in a set of five cadaveric feet. Tibial motions and ground reaction forces previously collected in vivo in a group of healthy adults were applied as inputs parameters. In vitro foot and ankle kinematics were acquired and directly compared to population-specific in vivo kinematics of the same healthy adults from which input parameters were acquired. Analyses were completed using cross correlation to determine the similarities in kinematic profiles and joint ranges of motion were calculated to determine absolute differences in kinematics. Ankle, subtalar, and talonavicular in vitro joint kinematics were positively correlated to in vivo joint kinematics (rxy = 0.57-0.87). Further, in vivo and in vitro foot and ankle kinematics demonstrated similar amounts of within-group variability (rxy = 0.50-0.85 and rxy = 0.72-0.76, respectively). Our findings demonstrate that cadaveric gait simulation techniques reproduce population-specific foot and ankle kinematics, providing a valuable research tool for testing surgical treatments of foot and ankle maladies. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1663-1668, 2016.

A device for characterising the mechanical properties of the plantar soft tissue of the foot.

The plantar soft tissue is a highly functional viscoelastic structure involved in transferring load to the human body during walking. A Soft Tissue Response Imaging Device was developed to apply a vertical compression to the plantar soft tissue whilst measuring the mechanical response via a combined load cell and ultrasound imaging arrangement. Accuracy of motion compared to input profiles; validation of the response measured for standard materials in compression; variability of force and displacement measures for consecutive compressive cycles; and implementation in vivo with five healthy participants. Static displacement displayed average error of 0.04 mm (range of 15 mm), and static load displayed average error of 0.15 N (range of 250 N). Validation tests showed acceptable agreement compared to a Houndsfield tensometer for both displacement (CMC > 0.99 RMSE > 0.18 mm) and load (CMC > 0.95 RMSE < 4.86 N). Device motion was highly repeatable for bench-top tests (ICC = 0.99) and participant trials (CMC = 1.00). Soft tissue response was found repeatable for intra (CMC > 0.98) and inter trials (CMC > 0.70). The device has been shown to be capable of implementing complex loading patterns similar to gait, and of capturing the compressive response of the plantar soft tissue for a range of loading conditions in vivo.