An Attempt to Improve Stance Mechanics of Trans-Tibial Amputee Gait by the Design of a Modular Ankle Joint Prosthetic

Background: A-priori research shows that trans-tibial (TT) amputees display poor gait parameters when walking with low-cost ankle-foot prosthetics (here referred to as baseline AFP’s). This has drastic implications for the amputee populations in the developing world specifically, as they have limited access to advanced prosthetic technologies. Low-cost AFP’s are unable to adequately replicate natural stance mechanics, and reliance on these devices results in increased energy expenditure, osteoarthritis and lower-limb joint deterioration. Methodology: This project details the design of a novel ankle joint prosthetic (AJP) that serves as an attachment to baseline AFP’s, with the aim of facilitating better stance mechanics via the restoration of ankle joint mechanisms. The work is presented in three core sections: Part 1 explains the rationale as to why adequately replicating natural stance mechanics is an appropriate need; Part 2 presents the design of the modular low-cost AJP that utilises only simple mechanical elements; and Part 3 presents the experimental quantification of the impact the AJP has on stance mechanics of a baseline AFP (Otto Bock 1D10) in a simulation of the TT amputee walking gait cycle, via the use of three able-bodied participants and a pseudo-prosthesis. Results: The results indicate that the AJP significantly improves the stance mechanics of the baseline AFP. During forefoot rollover a stable joint moment and an increase in joint range of motion (RoM) was observed, yielding a decrease in ankle stiffness. During initial weight acceptance of early stance, an increase in joint RoM displays the restoration of controlled plantarflexion, which indicates an improved transition from heelstrike to footflat. This is a critical mechanism that facilitates stability control during weight acceptance, and the results suggest that the designed AJP is performing better in this regard than its closest functional competitor. However, equipment errors limited the ability to accurately report on ankle stiffness of this phase. Conclusions: Overall the final conclusions are that the designed AJP improves rollover shapes of the baseline AFP, eases phase transitions, and facilitates stability control and forward tibial progression. In combination with the low cost price (±50 USD), its ease of assembly and modular design, the AJP is thus a preferable option for low-income amputees in developing countries. Finally, there is significant evidence of functional and mechanical reliability, and therefore testing of the device can progress to a clinical study involving amputee participants

A neuromechanics-based powered ankle exoskeleton to assist walking post-stroke: a feasibility study

Background: In persons post-stroke, diminished ankle joint function can contribute to inadequate gait propulsion. To target paretic ankle impairments, we developed a neuromechanics-based powered ankle exoskeleton. Specifically, this exoskeleton supplies plantarflexion assistance that is proportional to the user’s paretic soleus electromyography (EMG) amplitude only during a phase of gait when the stance limb is subjected to an anteriorly directed ground reaction force (GRF). The purpose of this feasibility study was to examine the short-term effects of the powered ankle exoskeleton on the mechanics and energetics of gait. Methods: Five subjects with stroke walked with a powered ankle exoskeleton on the paretic limb for three 5 minute sessions. We analyzed the peak paretic ankle plantarflexion moment, paretic ankle positive work, symmetry of GRF propulsion impulse, and net metabolic power. Results: The exoskeleton increased the paretic plantarflexion moment by 16% during the powered walking trials relative to unassisted walking condition (p \u3c .05). Despite this enhanced paretic ankle moment, there was no significant increase in paretic ankle positive work, or changes in any other mechanical variables with the powered assistance. The exoskeleton assistance appeared to reduce the net metabolic power gradually with each 5 minute repetition, though no statistical significance was found. In three of the subjects, the paretic soleus activation during the propulsion phase of stance was reduced during the powered assistance compared to unassisted walking (35% reduction in the integrated EMG amplitude during the third powered session). Conclusions: This feasibility study demonstrated that the exoskeleton can enhance paretic ankle moment. Future studies with greater sample size and prolonged sessions are warranted to evaluate the effects of the powered ankle exoskeleton on overall gait outcomes in persons post-stroke

Changes in ankle muscle force and power during walking in patients with peripheral artery disease

Background: Patients with peripheral artery disease (PAD) have significantly reduced lower extremity muscle strength compared with healthy individuals as measured during isolated, single plane joint motion by isometric and isokinetic strength dynamometers. The objective of this study was to understand the contribution of the ankle muscles during walking in patients with PAD and compared to healthy older individuals. Methods: A total of 12 patients diagnosed with Fontaine stage II PAD and 10 healthy older controls were recruited for the study. Each subject walked across a 10-meter pathway with reflective markers placed on specific anatomical locations on lower limbs while the marker coordinates were recorded using a 12-high speed infrared camera system. Gait simulations were performed in OpenSim software (version 4.0). The muscle force and power for individual muscles at ankle and as a group of ankle plantar flexor muscles were exported from OpenSim. Results: There was a significant reduction in ankle muscle power in patients with PAD during propulsion phase (p \u3c 0.05). There were significant reductions in lateral and medial gastrocnemius muscle forces and power during propulsion in patients with PAD (p \u3c 0.05). However, soleus muscle force and power were not altered during stance phase. Conclusions: Our simulation findings identified important information about PAD gait mechanics, specifically altered ankle muscle force and power contribution during stance phase

THE EFFECTS OF AN OVER-THE-COUNTER ORTHOTIC ON LOWER EXTREMITY KINEMATICS IN RECREATIONAL RUNNERS

Abnormal foot mechanics during the stance phase of running may affect the kinematics of the lower extremities and predispose an individual to injuries of the foot, ankle, and knee. Custom made foot orthotics are often prescribed to correct abnormal mechanics during running by restoring dynamic stability to the closed chain of the lower extremity. However, custom made orthotics are expensive and must be made by a specially trained professional. An alternative to custom made orthotics are several brands of over-the-counter orthotics. However, there has been no research done to examine the efficacy of using an over-the-counter orthotic to correct abnormal gait mechanics. The purpose of this study was to examine the effects of an over-the counter orthotic on ankle and knee joint kinematics during running in individuals identified as excessive pronators

Biomechanical demands of the 2-step transitional gait cycles linking level gait and stair descent gait in older women

Stair descent is an inherently complex form of locomotion posing a high falls risk for older adults, specifically when negotiating the transitional gait cycles linking level gait and descent. The aim of this study was to enhance our understanding of the biomechanical demands by comparing the demands of these transitions. Lower limb kinematics and kinetics of the 2-step transitions linking level and descent gait at the top (level-to-descent) and the bottom (descent-to-level) of the staircase were quantified in 36 older women with no falls history. Despite undergoing the same vertical displacement (2-steps), the following significant (p<.05) differences were observed during the top transition compared to the bottom transition: reduced step velocity; reduced hip extension and increased ankle dorsiflexion (late stance/pre-swing); reduced ground reaction forces, larger knee extensor moments and powers (absorption; late stance); reduced ankle plantarflexor moments (early and late stance) and increased ankle powers (mid-stance). Top transition biomechanics were similar to those reported previously for continuous descent. Kinetic differences at the knee and ankle signify the contrasting and prominent functions of controlled lowering during the top transition and forward continuance during the bottom transition. The varying musculoskeletal demands encountered during each functional sub-task should be addressed in falls prevention programmes with elderly populations where the greatest clinical impact may be achieved. Knee extensor eccentric power through flexion exercises would facilitate a smooth transition at the top and improving ankle plantarflexion strength during single and double limb stance activities would ease the transition into level gait following continuous descent

Inferring muscle functional roles of the ostrich pelvic limb during walking and running using computer optimization

Owing to their cursorial background, ostriches (Struthio camelus) walk and run with high metabolic economy, can reach very fast running speeds and quickly execute cutting manoeuvres. These capabilities are believed to be a result of their ability to coordinate muscles to take advantage of specialized passive limb structures. This study aimed to infer the functional roles of ostrich pelvic limb muscles during gait. Existing gait data were combined with a newly developed musculoskeletal model to generate simulations of ostrich walking and running that predict muscle excitations, force and mechanical work. Consistent with previous avian electromyography studies, predicted excitation patterns showed that individual muscles tended to be excited primarily during only stance or swing. Work and force estimates show that ostrich gaits are partially hip-driven with the bi-articular hip–knee muscles driving stance mechanics. Conversely, the knee extensors acted as brakes, absorbing energy. The digital extensors generated large amounts of both negative and positive mechanical work, with increased magnitudes during running, providing further evidence that ostriches make extensive use of tendinous elastic energy storage to improve economy. The simulations also highlight the need to carefully consider non-muscular soft tissues that may play a role in ostrich gait

An Innovative Testing Protocol to Study Foot and Ankle Kinetics during Early Stance Phase of Gait

The objective of this study was to improve upon existing testing platform limitations with respect to foot and ankle mechanics in the sagittal plane during dorsiflexion and plantar flexion. The intent was to develop a multi-loading protocol that simulated aspects of early stance phase of walking gait. This data were used to evaluate the influence an Achilles load has on the kinematic profile of the ankle complex. Also, resulting kinematic profile data can be used to evaluate ligament/tendon effects, ankle arthroplasty, and various surgical techniques. A pair of cadaveric human feet, from the same donor, 50 years of age were dissected and potted for testing. A pure moment protocol was developed to determine the path of least resistance or lowest energy state to rotate the tibia about the ankle complex. This protocol utilized a 4-degree of freedom robot coupled with a two 6-axis load cells. Positional data was used to calculate the instantaneous axis of rotation (IAR) of the ankle complex. The data was then normalized with respect to the widest distance across the tibia. Results from this work include a repeatability study of the robotic testing platform (RTP), validation of protocol, calculation of the IAR, and a study of the effect an Achilles load has on ankle kinematics. The repeatability study used a modified version of the protocol to reduce setup effects. A repeatability analysis was conducted comparing repeated test runs for dorsiflexion and plantar flexion (one way repeated measures ANOVA with a Bonferroni test) and found no significant difference between the data sets for (P\u3c0.05). The IAR results with and without a passive Achilles load were significantly different (P\u3e0.05), using same statistical approach. Future work is to actively drive the Achilles load and add a push-off condition were the rotation is about the distal end of the first and second metatarsals. Along with that, the upper limit of the vGRF is to be increased to simulate the later part of the stance phase of gait where the Achilles load is larger

3-D kinematic comparison of treadmill and overground running.

Studies investigating the mechanics of human movement are often conducted using the treadmill. The treadmill is an attractive device for the analysis of human locomotion. Studies comparing overground and treadmill running have analyzed discrete variables, however differences in excursion from footstrike to peak angle and range of motion during stance have yet to be examined. This study aimed to examine the 3-D kinematics of the lower extremities during overground and treadmill locomotion to determine the extent to which the two modalities differ. Twelve participants ran at 4.0m/s in both treadmill and overground conditions. 3-D angular kinematic parameters during the stance phase were collected using an eight camera motion analysis system. Hip, knee and ankle joint kinematics were quantified in the sagittal, coronal and transverse planes, then compared using paired t-tests. Of the parameters analyzed hip flexion at footstrike 12° hip range of motion 17°, peak hip flexion 12.7°, hip transverse plane range of motion 8° peak knee flexion 5° and peak ankle excursion range 6.6°, coronal plane ankle angle at toe-off 6.5° and peak ankle eversion 6.3° were found to be significantly different. These results lead to the conclusion that the mechanics of treadmill locomotion cannot be generalized to overground

Biomechanical demands differentiate transitioning vs. continuous stair ascent gait in older women

Background Stair ascent mechanics change with age, but little is known about the differing functional demands of transitioning and continuous ascent. Work investigating the risky transition from gait to ascent is sparse, and the strategies that older adults adopt to achieve these demanding tasks have not been investigated. Methods This study compared the biomechanics of a 2-step transitional (floor-to-step2) and continuous ascent cycle (step1-to-step3) and investigated the role of limb preference in relation to dynamometer-derived knee strength during this transition. A biomechanical analysis of 36 women (60–83 years) ascending a 3-step staircase was conducted. Findings The 2-step transitioning cycle was completed quicker, with a larger range of motion, increased forces, larger knee flexor and dorsiflexor moments and ankle powers (P ≤ 0.05), but reduced hip and knee flexion, smaller hip extensor moments and hip and knee powers compared to continuous ascent. During the transition, 44% of the participants demonstrated a consistent limb preference. In these cases large between-limb extensor strength differences existed (13.8%) and 71% of these participants utilised the stronger limb to execute the 2-step transitional cycle. Interpretation The preferential stronger-limb 2-step transitioning strategy conflicts with previous recommendations of a stronger lead limb for frail/asymmetric populations. Our findings suggest that most healthy older women with large between-limb differences utilise the stronger limb to achieve the considerable propulsion required to redirect momentum during the 2-step transition. The biomechanical demands of ascent, relative to limb strength, can inform exercise programmes by targeting specific muscle groups to help older adults maintain/improve general functioning

Multi-segment foot kinematics and plantar fascia strain during treadmill and overground running

Although physiologically beneficial, running is known to be associated with a high incidence of chronic injuries. Excessive coronal and transverse plane motions of the foot segments and strain experienced by the plantar fascia are linked to the development of a number of chronic injuries. This study examined differences in multi-segment foot kinematics and plantar fascia strain during treadmill and overground running. Twelve male recreational runners ran at 4.0 m.s-1 in both treadmill and overground conditions. Multi-segment foot kinematics and plantar fascia strain were measured using an eight-camera motion analysis system and contrasted using paired samples t-tests. The results showed that plantar fascia strain was significantly greater in the overground condition (8.23 ± 2.77) compared to the treadmill (5.53 ± 2.25). Given the proposed relationship between excessive plantar fascia strain and the etiology of injury, overground running may be associated with a higher incidence of injury although further work is necessary before causation can be confirmed