Background: Stair ascent can be difficult for individuals with transfemoral amputation because of the loss of knee function. Most individuals with transfemoral amputation use either a step-to-step (nonreciprocal, advancing one stair at a time) or skip-step strategy (nonreciprocal, advancing two stairs at a time), rather than a step-over-step (reciprocal) strategy, because step-to-step and skip-step allow the leading intact limb to do the majority of work. A new microprocessor-controlled knee (Ottobock X2 ® ) uses flexion/extension resistance to allow step-over-step stair ascent. Questions/Purposes: We compared self-selected stair ascent strategies between conventional and X2 ® prosthetic knees, examined between-limb differences, and differentiated stair ascent mechanics between X2 ® users and individuals without amputation. We also determined which factors are associated with differences in knee position during initial contact and swing within X2 ® users. Methods: Fourteen individuals with transfemoral amputation participated in stair ascent sessions while using conventional and X2 ® knees. Ten individuals without amputation also completed a stair ascent session. Lower-extremity stair ascent joint angles, moment, and powers and ground reaction forces were calculated using inverse dynamics during self-selected strategy and cadence and controlled cadence using a step-over-step strategy. Results: One individual with amputation self-selected a step-over-step strategy while using a conventional knee, while 10 individuals self-selected a step-over-step strategy while using X2 ® knees. Individuals with amputation used greater prosthetic knee flexion during initial contact (32.5°, p = 0.003) and swing (68.2°, p = 0.001) with higher intersubject variability while using X2 ® knees compared to conventional knees (initial contact: 1.6°, swing: 6.2°). The increased prosthetic knee flexion while using X2 ® knees normalized knee kinematics to individuals without amputation during swing (88.4°, p = 0.179) but not during initial contact (65.7°, p = 0.002). Prosthetic knee flexion during initial contact and swing were positively correlated with prosthetic limb hip power during pull-up (r = 0.641, p = 0.046) and push-up/early swing (r = 0.993, p < 0.001), respectively. Conclusions: Participants with transfemoral amputation were more likely to self-select a step-over-step strategy similar to individuals without amputation while using X2 ® knees than conventional prostheses. Additionally, the increased prosthetic knee flexion used with X2 ® knees placed large power demands on the hip during pull-up and push-up/early swing. A modified strategy that uses less knee flexion can be used to allow step-over-step ascent in individuals with less hip strength. Level of Evidence: Level II, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.
CITATION STYLE
Aldridge Whitehead, J. M., Wolf, E. J., Scoville, C. R., & Wilken, J. M. (2014). Does a Microprocessor-controlled Prosthetic Knee Affect Stair Ascent Strategies in Persons With Transfemoral Amputation? Clinical Orthopaedics and Related Research, 472(10), 3093–3101. https://doi.org/10.1007/s11999-014-3484-2
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