The effects of prosthetic alignment on gait biomechanics

In clinical settings, trans-tibial prosthetic alignment is a primarily subjective procedure that is based on: the clinical experience and judgment of prosthetists; and amputee feedback regarding comfort, stability and performance, which can be unreliable. This highlights the need for a more objective understanding of prosthetic alignment which would lead to better guidance and tools for prosthetists to assess and modify prosthetic alignment; thus facilitating comfortable ambulation, aesthetic gait appearance, and low energy cost of walking for amputees 7 ' 16 ' 25 . Previous research studies have the advantage of presenting objective and quantitative knowledge which cannot be obtained from subjective observations. However, most of these studies have only considered the relationships between fairly limited sets of biomechanical characteristics and prosthetic alignment settings. Furthermore, amputee comfort has not usually been addressed within the same studies. Therefore, the study reported in this thesis considers the effects of alignment changes on both biomechanical measures and comfort. The goals of the study were: 1) to investigate the effects of alignment changes on the kinematics and kinetics of trans-tibial amputee gait; and 2) to assess the feasibility of a new objective approach for predicting amputee comfort by measuring both the forces and moments at the socket/pylon interface using inverse dynamics calculations based on captured kinematic and kinetic data. Because this pilot study involved only one subject, the findings should be treated with caution. However, it is possible to make tentative conclusions with regard to possible objective alignment criteria. For example, based on the results, socket flexion versus extension appears to involve a trade-off between: a) achieving foot flat effectively whilst maintaining a good first GRF peak (not too extended); b) providing sufficient dorsi-flexion resistance during single stance (not too flexed); c) providing sufficient push-off (not too flexed); and d) avoiding pelvis obliquity (not too extended). Interestingly, it appears possible to make these judgments with just a force-plate and a coronal plane observation of obliquity