Performance of conventional and X2® prosthetic knees during slope descent.

Background: Individuals with transfemoral amputation often have difficulty descending sloped surfaces due to increased lower extremity range of motion and torque requirements. The X2®, a new microprocessor-controlled prosthetic knee, claims to improve gait over sloped terrain. The aim of this study was to evaluate how experienced prosthesis users descended a sloped surface using the X2®, compared to a conventional knee, either mechanical (MECH) or microprocessor (MP).

Methods: Descent technique and biomechanics were assessed in 21 service members with unilateral transfemoral amputation as they descended an instrumented 10° slope at a self-selected walking velocity.

Findings: Use of the X2® in the MECH group resulted in greater hill assessment scores (8.5 to 11.0, P=0.026), due primarily to decreased reliance on handrail use. The use of the X2® in the MP group increased prosthetic knee flexion to a median of 6.4° at initial contact (P=0.002) and 73.7° in swing (P=0.005), contributing to longer prosthetic limb steps (P=0.024) and increased self-selected velocity (P=0.041). Additionally, the use of the X2® in the MP group increased prosthetic limb impact peaks (11.6N/kg, P=0.004), improving impact peak symmetry to -1.3% (P=0.004).

Interpretation: Decreased reliance on handrail use as MECH users descended in the X2® indicate improved function and perhaps greater confidence in the device. Additional biomechanical improvements for existing MP users suggest potential longer-term benefits with regard to intact limb health and overuse injuries.