Advancing Exoskeleton Development: Validation of a Robotic Surrogate to Measure Tibial Strain.

Bone stress injuries are prevalent among athletes and military recruits and can significantly compromise training schedules. The development of an ankle-foot orthosis to reduce tibial load and enable a faster return to activity will require new device testing methodologies capable of capturing the contribution of muscular force on tibial strain. Thus, an actuated robotic surrogate leg was developed to explore how tibial strain changes with different ankle-foot orthosis conditions. The purpose of this work was to assess the reliability, scalability, and behavior of the surrogate. A dual actuation system consisting of a Bowden cable and a vertical load applied to the femur via a material testing system, replicated the action-reaction of the Achilles-soleus complex. Maximum and minimum principal strain, maximum shear strain, and axial strain were measured by instrumented strain gauges at five locations on the tibia. Strains were highly repeatable across tests but did not consistently match in vivo data when scaled. However, the stiffness of the ankle-foot orthosis strut did not systematically affect tibial load, which is consistent with in vivo findings. Future work will involve improving the scalability of the results to match in vivo data and using the surrogate to inform exoskeletal designs for bone stress injuries.

Upper Extremity Amputation and Prosthetics Care Across the Active Duty Military and Veteran Populations.

The hand and arm are exceptionally dexterous, exquisitely sensitive, and proficient in performing tasks and functions. Given the invaluable functions of the upper extremity in daily life, replacement of a missing limb through prosthetic substitution is challenging. Prosthetic and rehabilitation needs of injured Service members from recent military conflicts have brought upper extremity amputation to the forefront, which has led to an increase in attention and resource allocation. This article provides an overview of the care of the upper extremity amputee including surgical considerations, prosthetic design and fitting, and preprosthetic and post-prosthetic rehabilitation considerations.

Marker-based method to measure movement between the residual limb and a transtibial prosthetic socket.

BACKGROUND: Limb movement between the residuum and socket continues to be an underlying factor in limb health, prosthetic comfort, and gait performance yet techniques to measure this have been underdeveloped. OBJECTIVES: Develop a method to measure motion between the residual limb and a transtibial prosthetic socket. STUDY DESIGN: Single subject, repeated measures with mathematical modeling. METHODS: The gait of a participant with transtibial amputation was recorded using a motion capture system using a marker set that included arrays on the anterior distal tibia and the lateral epicondyle of the femur. The proximal or distal translation, anterior or posterior translation, and angular movements were quantified. A random Monte Carlo simulation based on the precision of the motion capture system and a model of the bone moving under the skin explored the technique's accuracy. Residual limb tissue stiffness was modeled as a linear spring based on data from Papaioannou et al. RESULTS: Residuum movement relative to the socket went through ~30 mm, 18 mm, and 15° range of motion. Root mean squared errors were 5.47 mm, 1.86 mm, and 0.75° when considering the modeled bone-skin movement in the proximal or distal, anterior or posterior, and angular directions, respectively. CONCLUSION: The measured movement was greater than the root mean squared error, indicating that this method can measure motion between the residuum and socket. CLINICAL RELEVANCE: The ability to quantify movement between the residual limb and the prosthetic socket will improve prosthetic treatment through the evaluation of different prosthetic suspensions, socket designs, and motor control of the prosthetic interface.

Effectiveness of force production in persons with unilateral transtibial amputation during cycling.

BACKGROUND: Few published reports exist regarding the control of the human/prosthesis interface in persons with unilateral transtibial amputation. OBJECTIVE: To investigate strategies employed by prosthetic users in controlling the human/prosthesis interface to highlight challenges associated with either the amputation or the design of the prosthesis. STUDY DESIGN: Randomized controlled trial. METHODS: Cycling was used as the locomotor task to allow for better control of task mechanics compared to walking. A group of nine cyclists with intact limbs were compared to eight cyclists with transtibial amputation (CTA) during a simulated cycling time trial. The CTA group pedaled with a stiff and flexible prosthetic foot. Reaction forces between the foot and the pedal were measured using an instrumented pedal system. The force effectiveness (FE) ratio was used as the measure of task performance. The FE ratio is the force component normal to the bicycle crank arm divided by the resultant force for both limbs and is commonly used to analyze pedaling technique. RESULTS: The CTA group was equally as effective at applying forces as the intact group. CONCLUSIONS: These data suggest that individuals with lower limb loss are able to compensate for their amputation to utilize a similar pedaling technique for locomotor performance. As global strategies, e.g. force effectiveness, appear similar between groups future research should focus on local strategies, e.g. individual joint kinematics and kinetics.