Length-Actuated Transfemoral Prosthesis Increases Hip Flexion/Extension Symmetry for Users

Introduction:: The goal of a prosthesis for unilateral transfemoral amputees is to restore proper gait biomechanics and minimize the compensatory actions caused by limb asymmetries^1,2. These prosthesis users rely heavily on hip movements and femoral flexion to control prosthetic function and gait mechanics, that lead to increased muscle activity and metabolic energy expenditure, and an increased incidence of falling due to poor balance, toe clearance and knee buckling ^3,4. Femoral movement and associated changes in leg-length in transfemoral amputees are poorly understood. The aim of this study was to test the hip flexion/extension symmetry between a previously developed length-actuated prosthesis from our lab and a habitual prosthesis. We hypothesize that a straight-leg prosthesis that can actively lengthen and shorten will assist in the optimization of toe clearance and propulsion forces, and thus improve dynamic hip movement symmetry (and compensatory mechanisms) of prosthesis users.

Materials and Methods:: Following approval from Clemson University’s Institutional Review Board (IRB2022-0496), two persons with transfemoral amputation (P1= M, 64, K3, Ottobock C-Leg (microprocessor); P2 = F, 55, K2, Ossur Total Knee (passive)) were recruited from local clinical network to participate in this study. To be eligible, persons were required to have a unilateral transfemoral amputation, be categorized under the MFCL of K2 or K3. The study consisted of three visits to take anthropometric data, tune the prosthesis, and take final biomechanical data for the prosthesis while participants walked. Gait was performed by the participant on a dual belt instrumented treadmill (Bertec®, Columbus, OH) surrounded by a fourteen-camera motion capture system (Vicon, Culver City, CA). Participants were markered with a PlugIn Gait marker set and additional markers on the prosthesis for tracking. During the final visit, prosthesis users walked with both their habitual prosthesis and the tuned length-actuated prosthesis while biomechanical data was collected to compare the user with both devices. The participants walked with both prostheses for an accommodation period of at least five minutes to reach a desired speed of 0.67 m/s (1.5 mph), and data was collected after five minutes of walking. They were given a ten-minute break between tests to change into the length-actuated prosthesis and for final adjustments to be made to the prosthetic leg and socket. Data for hip flexion/extension was calculated in Visual3D^TM with the pipeline function around the x-axis.



Results, Conclusions, and Discussions:: A qualitative analysis of the kinematics for hip flexion/extension (Figure 1) showed qualitatively normal measures for both prosthetic devices. While using the habitual prosthetic knee, both participants had an early peak prosthetic side hip extension during late stance and earlier and longer hip flexion during terminal swing, which was not present while using the length-actuated prosthesis. The extended periods of hip flexion and increasing velocities near late swing show that there may be less confidence in secure knee extension during late stance when users used their habitual knees, and comparatively more comfort and confidence in hip motion and the ability to avoid knee buckling using the length-actuated prosthesis. In addition, participants exhibited (qualitatively) higher hip flexion moments during pre-swing with their prosthetic side while using their habitual knee compared to the length-actuated prosthesis.

Conclusions: The decreased hip flexion moments show that prosthetic users exhibited a higher confidence in the length actuated prosthesis, which helped show that the length-actuated prosthesis could be successful at providing a stable support during stance, but participants still displayed typical gait compensations to achieve to clearance. Users were confident in the device not buckling under weight and started to become confident in the overall motion for push-off and toe clearance but need more time and research towards the adaptation to the device and retraining to reduce compensatory mechanisms during swing.



Acknowledgements (Optional): :

References (Optional): : References: ¹Harandi VJ, et al. Med Eng Phys. 2020;77:95-106. ²De Pauw K, et al. Clin Biomech. 2020;71(October 2019):59-67. ³Kark L, et al. Gait Posture. 2012;35(2):238-243. ⁴Wentink EC, et al. Neuroeng Rehabil. 2013;10(1). ⁵Hutchison RE, et al. Proc Inst Mech Eng Part H J Eng Med. 2019;233(7):723-734.