Evaluation of impulsive wave transmission through total knee joint prothesis

The most significant advancement in orthopaedics in the last 50 years has been the evolution of practical total knee joint replacement. However, in the presence of all these successes, there is a note of “gloom” to a small percentage of patients in which loosening of the prosthesis occur, with the attendant pain and restricted mobility. At present, attempts to reduce the incidence of failure have been directed primarily at redesigning hip and knee implants, and research towards understanding the mechanics of impact force transmission across normal and prosthetic joints is practically nonexistent. The present study is an attempt to evaluate the differences between “normal” and prosthetic joint mode of impact wave transmission. Using cadaveric skeletal remains, an abbreviated (cut at the lower tibia and upper femur ends) lower extremity specimen is suspended vertically by long steel wires. The upper (femur) end is subjected to a 150‐lb load (to simulate body weight) and the lower tibia end rests on a 100‐lb shaker. The skeletal system is subjected to a 3‐g impulsive load at a frequency range of 1–3 Hz to simulate brisk walking and jogging. The procedure is repeated twice; first with the original knee joint intact, and again with the knee joint portion replaced with a prosthesis. Preliminary results reveal that there are significant differences in the mode of impulsive wave transmission across the “normal” and prosthetic knee joints. Prosthetic joints appear to reduce impulsive peaks along both the tibia and femur as compared with “normal” joints. The effects of viscoelastic shoe inserts in the propagation of impact waves across the two types of joints (normal and prosthetic) is also being investigated.