Prosthetic Components and Stability in Amputee Gait

Most of what is known about how amputees walk and how the properties of prosthetic components affect their gait has been discovered through sagittal plane observations while amputees walk back and forth along a straight line. Abnormal limb loading, thought to be a principal factor in the occurrence of residual limb pain which in turn may cause instability and limit mobility, can certainly occur while walking in a straight line. However, the incidence of abnormal limb loading is likely amplified when performing more complex gait activities, such as turning or avoiding obstacles; activities that are so very common in everyday life. The specific aims of this investigation are to: 1. discover the biomechanical strategies used and the stability of both intact individuals and trans-tibial amputees walking along a circular trajectory and 2. explore the effects of a prosthetic intervention on turning biomechanics, stability, comfort, and mobility. We propose to investigate three sets of hypotheses: The first set of hypotheses addresses the fundamental biomechanical mechanisms associated with walking along a circular trajectory, how intact subjects differ from amputees, and the effect of a rotation adaptor pylon. We will conduct experiments to test three hypotheses related to achieving a change of heading, orientation, and balancing of centripetal forces necessary to walk along a circular trajectory. The second set of hypotheses seeks to identify whether trans-tibial amputees with a rigid pylon are more unstable during a turning task than non-amputees and whether or not the rotation adaptors enhance stability. We will conduct experiments to calculate an index of dynamic stability that measures the rate at which a person can respond to a perturbation and return to a stable gait pattern. The third set of hypotheses addresses how the rotational properties of the prosthetic pylon can influence comfort and mobility during daily activities. To measure comfort and mobility, we will solicit questionnaire responses and step count measures from amputees after a one-month period of wearing a rigid pylon and after a one-month period of wearing a transverse plane rotation adaptor (within-subject comparison). In addition to these field measurements, we will also compare the distance traveled during a six-minute walk. Patient opinions about their prosthesis and mobility measures over long periods of time can play a significant role in prosthesis evaluation. For veteran amputees who experience discomfort and increased risk for residual limb skin problems, it seems reasonable to suppose that these problems might occur when walking along a curved trajectory rather than just a straight line. The joint forces and moments of turning may differ significantly from those exhibited while walking in a straight line. The proposed research will create a new knowledge base with which to understand prosthetic intervention effectiveness. The immediate clinical impact for the trans-tibial amputee is the determination if transverse plane rotational adapter pylons can improve their comfort, mobility, and stability.