Abstract
There are many designs of friction lock knees which resist the tendency of the knee to flex by a braking action during the stance phase. These knees are good for elderly or feeble amputees, but might interfere with the gait of young and active above-knee amputees, because knee flexion should begin late in the stance phase. He also will not be able to "jack-knife" down stairs and may have difficulty supporting his weight on the prosthesis while lowering himself to a sitting position. Therefore, we need prescription criteria for selection of the knee mechanism. Before preparing the criteria, we need to know the following details-mechanical characteristics of the knees, the gait pattern of the above-knee amputees and the results of the actual use of the knees of above-knee amputees. 1. Physical testing of friction lock knees A testing device which measures the relation between the load and brake moment of the knee mechanism was made. The knees used in the study were Bock 3 R 15 Knee, Bock 3 P 23 Knee, LAPOC Friction Lock Knee and Kolman Safety Knee. All knees except 3 R 15 showed remarkabe constant friction when the weight-bearing brake was adjusted to a sufficiently high level. 2. Pylon study with simulated prosthesis A potentiometer was mounted on the prosthetic knee joint. Tape switches were attached on the sole of both shoes. Strain gauges were attached on the pylon for detecting axial load and knee moment. "Incomplete" knee collapse of the simulated prosthesis was recorded both when the person walked on a leveled floor without a friction lock with reduced alignment stability and when on descending ramps without a friction lock with regular alignment stability. The friction lock knee prevented an "incomplete" knee collapse in both cases above and a substantial level of knee moment was simultaneously recorded, which indicates the working of the friction lock knee.
