The influence of prosthetic foot alignment on trans-tibial amputee gait

An optimally aligned prosthesis, as accomplished by the subjective judgment of the prosthetist, guarantees the best quality of gait. Yet, amputees can adapt to a large variety of geometrical configurations of the prosthetic components. Different external rotation angles of the foot in trans-tibial (TT) prostheses were investigated. The study tried to identify (a) the relationship between foot angle and other gait parameters and (b) the compensating pattern of the amputees to excessive external rotation of the foot. Eight (8) TT amputees, fitted with an identical type of prosthesis, were investigated during ambulation. The prosthetic foot was externally rotated as follows: optimal angle (10.94 x degrees +/- 5.21 degrees), optimal angle plus another 18 degrees, and optimal angle plus another 36 degrees. Analysis of gait was performed with the aid of an electronic walkway. Speed of gait, stance and swing time, and foot angle were monitored in 4 runs for each of the three foot angles. Speed of gait remained almost constant in the three tests. Stance and swing time, as well as step length, significantly changed when 36 degrees were added to the optimal foot angle. This foot position significantly influenced inter-legs time difference and symmetry between the legs. During ambulation, prosthetic foot external rotation was decreased by internal rotation of the limb at the hip joint level. It is concluded that TT amputees can maintain an efficient speed of gait even when the prosthetic foot is malpositioned in excessive external rotation. Although such a malalignment significantly influences other gait parameters during walking, amputees are able to adapt themselves by internal rotation of the hip joint in the amputated leg.