Transfemoral amputee intact limb loading and compensatory gait mechanics during down slope ambulation and the effect of prosthetic knee mechanisms.

Background: Intact limb knee osteoarthritis is a prevalent secondary disability in transfemoral amputees. Walking down a ramp may increase this risk due to excessive limb loading. We sought to determine whether intact limb loading differed between transfemoral amputees and controls during down slope ambulation, and the compensatory strategies transfemoral amputees used to modify intact limb loading. Secondarily, we sought to determine the effect of prosthetic knee type.

Methods: Five unilateral transfemoral amputees and five non-amputee controls walked down a ramp and the following outcome measures were compared between amputees and controls and across prosthetic knee type (C-leg versus Power Knee): step length, walking speed, leading limb ground reaction forces, and trailing and leading limb ankle and knee energy absorption. Linear mixed effects regression was used to test for association between gait variables and limb.

Findings: There were no significant differences in intact limb loading between amputees and controls or between prosthetic knee types. Transfemoral amputees walked slower (C-leg - control = -0.29 m/s; P = 0.008, Power Knee - control = -0.38 m/s; P < 0.001) with a shorter intact limb step length (C-leg - control = -0.12 m/s; P < 0.001, Power Knee - control = -0.16 m/s; P < 0.001). The prosthetic trailing limb ankle absorbed less energy throughout stance than the trailing limb in controls (C-leg-control = -0.22 J/kg; P < 0.001, Power Knee - control = -0.22 J/kg; P < 0.001).

Interpretation: Intact limb loading in transfemoral amputees is equivalent to controls during down ramp ambulation, in spite of reduced prosthetic trailing limb energy absorption. The primary compensatory strategies include a reduced ambulation speed and intact limb step length, which reduces center of mass velocity at heel contact.