Lead limb loading during a single-step descent in persons with and without a transtibial amputation in the trailing limb

Background: Decreased mechanical work done by the trailing limb when descending a single-step could affect load development and increase injury risk on the leading limb. This study assessed the effect of trailing limb mechanics on the development of lead limb load during a step descent by examining individuals with unilateral transtibial amputations who are known to exhibit reduced work in the prosthetic limb. Methods: Eight amputees and 10 able-bodied controls walked 5m along the length of a raised platform, descended a single-step of 14cm height, and continued walking. The intact limb of amputees led during descent. Kinematic and kinetic data were recorded using integrated motion capture and force platform system. Lead limb loading was assessed through vertical ground reaction force, and knee moments and joint reaction forces. Sagittal-plane joint work was calculated for the ankle, knee, and hip in both limbs. Findings: No differences were found in lead limb loading despite differences in trail limb mechanics evidenced by amputees performing 58% less total work by the trailing (prosthetic) limb to lower the centre of mass (P=0.004) and 111% less for propulsion (P<0.001). Amputees descended the step significantly slower (P=0.003) and performed significantly greater lead limb ankle work (P=0.017). After accounting for speed differences, initial loading at the knee was significantly higher in the lead limb of amputees versus controls. Interpretation: Increasing lead limb work and reducing forward velocity may be effective compensatory strategies to limit lead limb loading during a step descent, in response to reduced trailing limb work.