Short and Longer Term Changes in Amputee Walking Patterns Due to Increased Prosthesis Inertia

Abstract

The purpose of this study was to quantify the time course of changes in walking patterns among unilateral, transtibial amputees whose prosthesis inertia properties were substantially altered to match with those of their intact limb. Four unilateral transtibial amputees completed three test sessions on days 1, 2, and 8 of an 8-day protocol. Walking kinetics were computed from overground trials; temporal characteristics were collected during treadmill walking. Assessments were initially performed on day 1 without additional mass on the prosthesis. Mass was then added to the distal aspect of the prosthesis such that the mass and moment of inertia of the prosthetic leg were matched with those of the intact shank and foot. This added mass remained attached to the prosthetic limb for the next 7 days. Gait assessments were completed immediately and after 5, 10, 15, 30, and 60 minutes of exposure to the altered inertia. Amputees returned to the laboratory on days 2 and 8 for additional assessments. Measures of gait symmetry between the intact and prosthetic legs changed within 5 minutes of exposure to altered prosthesis inertia and remained in this altered state until the load was removed on the eighth day, at which time symmetry indices returned to their original state. Matching the inertia properties between legs exacerbated stance time and swing time asymmetries but improved peak knee moment symmetry during swing termination. The increased joint kinetic symmetry, however, required greater muscular efforts, particularly on the prosthetic side. In conclusion, substantial alteration of the inertia properties of the prosthesis immediately altered temporal and joint kinetic symmetry between intact and prosthetic legs, both when mass was added to the prosthesis and when that mass was removed. Because of our small sample size, caution should be exercised when generalizing these outcomes to all lower limb amputees. (J Prosthet Orthot. 2011;23:114 –123.) KEY INDEXING TERMS: gait, rehabilitation, symmetry, prosthesis design, inertia manipulation