The effects of prosthetic alignment on the stability of the knee in above knee amputees
The components and alignment of a prosthesis have a large influence on the gait of an above knee amputee. The present criteria for determining the optimum alignment are mainly subjective, based on visual observation of the amputee's gait and by considering his/her comments. These comments however, are not always helpful. It has been reported that a range of alignments is acceptable to the patient and to the prosthetist, and it is believed that the optimum alignment can be selected from the range of acceptable alignments using biomechanical analysis. The socket is an important component in an above knee prosthesis and can affect the gait of the amputee. While the conventional socket is the quadrilateral, several problems have been reported with this type of socket. These include instability in the coronal plane, discomfort and restriction of the stump muscles causing limitations in the function of the prosthesis. In an attempt to overcome these problems the ischial containment (IC) socket was introduced in 1985. The biomechanical characteristics of the IC socket have, however, not been objectively assessed and compared with those of the quadrilateral socket. In this study, the effect of alignment adjustments on the gait variables for eight above knee amputees wearing quadrilateral sockets was investigated. Three of these amputees were also tested wearing IC sockets. The alignment of the prosthesis was systematically changed at the ankle, knee and socket. The primary aim of this project was therefore, to systematically vary the alignment of the prosthesis and to study the effects on the gait, and to compare the performance of amputees wearing IC and quadrilateral sockets. The ultimate goal of this research work is to provide a method for the determination of the optimum alignment from a range of acceptable alignments. A socket axis locator and a coordinate measuring system were used for measuring the prosthetic alignment accurately. Three TV cameras and two Kistler force plates were operated simultaneously and synchronously at a rate I of 50 Hz to acquire the displacements of the body segments and the ground reaction forces. All angular movements at the joints, moments and the temporal-distance parameters were calculated for both the prosthetic and the sound legs of the amputees, and for the right and left legs of ten normal subjects. The movement of the upper body was also recorded. Computer programs were developed to calculate and graphically present the above parameters in three dimensions. It was found that alignment changes affected the gait parameters of the whole body. At the prosthetic joints, certain changes in the alignment of the prosthesis resulted in specific alterations in the gait pattern. These effects were repeatable. The anterior-posterior (AP) joints moments and the fore-and-aft ground reaction force were found to be the most sensitive variables to alignment changes. The trunk rotations in the AP and medio-lateral planes, and the torso rotation in the transverse plane were also found to be sensitive to alignment changes, and the trunk was the main compensating element for any misalignment. At the sound side, the alignment changes resulted in noticeable changes in the AP joints moments and fore-and-aft ground reaction force. In the coronal and transverse planes, changes in the gait patterns that were analysed were not always consistent. These changes mainly depend on the method of compensation which is adopted by the patient. The IC socket showed improvements in the patient's performance in terms of higher speed of walking, comfort, improved symmetry in the two legs and the gait parameters are more comparable with those of normals.