抄録
Experimental results are described to clarify the relation between the stance phase control function of an external prosthetic knee joint and mechanical characteristics exerted on the prosthesis in level walking, and to establish a clear standard for selecting an external prosthetic knee joint for trans-femoral prostheses. The stance phase control functions of prosthetic knee joints are (1) preventing sudden knee flexion at heel strike, (2) decreasing movement of center of gravity by small knee flexion (double knee action) in middle stance phase, and (3) shifting smoothly to swing phase at the end of stance phase. In this paper, functions (1) and (2) are examined to clarify the effect of improving the prosthetic gait. Gaits of three normal subjects using a knee-disarticulation prosthesis for experience and three trans-femoral amputees were measured by a pylon load cell installed in the shank of the prosthesis to get six force quantities, and flexible electro-goniometers made of electroconductive rubber placed on the side of ankle, knee, and hip joint. The angular displacement and joint moments of the hip, knee, and ankle were measured. Normal subjects are used to examine the experimental process for preliminary evaluation of the function of various knee joints. Prosthetic knee joints used in the experiment were 3 R 20 (solid knee joint), 3 R 15 (weight-stabilizing knee joint), Total Knee (six-bar linkage knee joint), 3 R 60 (five-bar linkage knee joint), and 3 R 49 (non-friction knee joint). The prosthetic foot used was a single axis foot, in which ankle joint stiffness was changed from hard to soft. Before the experiment, each subject was instructed how to effectively use each knee joint and experienced walking with the knee joint for a long period. Knee joints were selected from the series of 3 R 20, 3 R 15, Total Knee, 3 R 60, and 3 R 49, in which the amount of voluntary control changes from small to large. From the data for prosthetic gait in level walking, the following results are obtained. 1) The extension moment of the hip joint of trans-femoral amputees became large when the non-friction knee joint was used. The non-friction knee joint has no function to prevent knee flexion in stance phase. 2) The knee joint of trans-femoral amputees flexed about ten degrees in the middle of stance phase when the Total Knee and 3 R 60 were used. The angular displacement pattern was very close to that of normal gait, and decreased movement of the center of gravity. This knee flexion relates to the angular displacement and the moments of the hip and knee joints in the stance phase. 3) The stance phase control function of the prosthetics knee joint was significantly influenced by the stiffness of plantar flexion of the prosthetic foot. As the stiffness of plantar flexion of the prosthetic ankle joint decreased, the amount of voluntary control decreased in the case of the free knee (3 R 49), and function was impaired in the case of the other knee joints except the solid knee (3 R 20).
