Conventional 4-bar linkage knee mechanisms: a strength-weakness analysis

The purpose of this article is to inform clinicians of the relevant knowledge gained from research in the field of prosthetics. From a biomechanical point of view, clinicians need relevant knowledge in order to properly prescribe a lower limb prosthesis, including prosthetic components. In this context, and due to the lack of data regarding their utility, a strength-weakness analysis of 8 types of 4-bar linkage knee mechanisms has been carried out. Free-moving knees are intrinsically stable in the stance phase of walking when the O degrees center of rotation is behind the femur head to heel line. This was found in 5 of the 8 knees. Furthermore, bending the knee at toe-off requires force. The hip-flexion-torque required is smaller when the O degrees center of rotation is closer to the femur head to toe line and is dependent on the measure of axial load. Comparatively, however, much energy is usually still necessary. This can be improved. The maximal axial residual limb load, the maximal hip-moment, and the energy required are, on investigation of the knees, approximately the same in relation to the walking speed during the swing phase of gait. Friction influences the swing characteristics of the prosthetic lower limb considerably. In this context, little is yet known about swing phase knee control units. The present 4-bar linkage knees-with-lock are a derivation of the free-moving knees. Their movement characteristics, and often heavy construction, are of no relevance when walking with a fixed knee. In proportion, much energy is required. Therefore, there is a demand for a simple knee mechanism that moves freely during the swing phase, locks at the beginning of the stance phase, and unlocks at the end of it.