EFFECTS OF PROSTHESIS INERTIA ON THE MECHANICS AND ENERGETICS OF AMPUTEE LOCOMOTION

Open Access
Author:
Smith, Jeremy Douglas
Graduate Program:
Kinesiology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 19, 2007
Committee Members:
  • Philip Martin, Committee Chair
  • John Henry Challis, Committee Member
  • Stephen Jacob Piazza, Committee Member
  • Robert L Sainburg, Committee Member
  • Henry Joseph Sommer Iii, Committee Member
Keywords:
  • transtibial
  • biomechanics
  • loading
Abstract:
Amputees are often prescribed prosthetic limbs with inertia properties far less than those of the limb they replace, and as a result an inertia asymmetry between legs is created. This inertia asymmetry has been suggested to contribute to the asymmetrical walking patterns often exhibited by unilateral amputees. Unilateral, transtibial amputees also typically expend 20% to 30% more metabolic energy than non-amputees walking at the same speeds. Reasons for these higher costs are not fully understood. This dissertation consists of four studies designed to better understand the influence of prosthetic leg inertia on the mechanics and energetics of amputee locomotion. Studies 1 and 2 investigated the process by which individuals adjust their gait patterns to accommodate an inertia manipulation of the lower extremity over a short term (over the first hour) and a longer term (eight days). In both unilateral, transtibial amputees and non-amputees, temporal and joint kinetic descriptors of gait changed within five minutes of exposure to an additional mass added distally to one leg. Over the course of the next eight days, these measures showed no further changes. The return to baseline values was equally rapid upon removal of the mass on the eighth day. Adjustment to the inertia change was nearly immediate, rather than a slow and gradual adjustment process. In study 3, the effects of multiple prosthetic leg inertia configurations on metabolic costs, kinematic symmetry, and temporal symmetry were investigated. In general, metabolic costs, kinematic asymmetries, and temporal asymmetries increased systematically with increasing prosthetic inertia. The lowest metabolic cost and most symmetrical walking patterns were observed when amputees walked without mass added to their prosthetic leg, (i.e., walked with their normal prosthesis). Thus, the use of a lightweight prosthesis appeared to minimize gait asymmetries and metabolic costs during walking. Study 4 addressed the effects of multiple prosthetic leg inertia configurations on intersegmental dynamics and lower extremity muscle excitations during walking. With respect to the prosthetic leg, absolute angular impulses of the muscle, interaction, and gravitational moments of the hip and knee increased systematically during swing. During stance of the prosthetic leg, absolute angular impulses of the interaction and gravitational moments at the hip and knee also increased systematically with increasing inertia, whereas the muscle moments were unaffected. Intersegmental dynamics of the intact leg during the entire gait cycle were minimally affected by increases in prosthetic leg inertia. In general, these results suggested increases in prosthesis inertia increased demands on the musculature during the swing phase of the prosthetic leg. EMG data did not support our finding of increased muscle demand on the prosthetic leg during swing. Results of studies 3 and 4 provide no indication that the current practice of using of lightweight prostheses is contraindicated or can be improved upon substantially. Unilateral, transtibial amputees appear to gain the most benefit by using a below-knee prosthesis whose inertia properties are far less than those of the limb it replaces. Increasing the inertia properties of below-knee prostheses is not recommended.