Conformity in condylar replacement knee prosthesis

Abstract

Experiments were carried out to determine the optimum conformity between the femoral and tibial condyles in condylar replacement knee prostheses. Wear tests and observations from removed prostheses indicated that both high and low conformity produced characteristic abrasion and fatigue. Partly conforming condyles provided stability under load-bearing but allowed laxity to occur. Fixation to resist the various forces on the tibial components was enhanced by a short central intramedullary peg. Partial conformity is proposed as the optimum configuration between femoral and tibial components.

Polyethylene wear in unicondylar knee prostheses

“…This is due to the differences in contact area and congruity between tibial and femoral components which determine the contact stresses. Previous studies have indicated that contact stresses in the knee often exceed the yield strength of UHMWPE (Walker and Hsieh 1977, Walker 1988.…”

The ‘Sliding Meniscus’ Knee Prosthesis: Design Concepts

“…An interposition between the femoral and tibial components appears theoretically to be more attractive than partially constrained prostheses because contact stresses arising from rolling of the femoral condyle on the conforming meniscal components are reduced (Walker and Hsieh, 1977) as the meniscal component is not fixed, but slides on the tibial component, the T-slot in the tibial component just serving as a locator. The number of degrees of freedom is larger than in the constrained prostheses, the greater the constraints the greater the shear forces at the cement/bone junction, leading to an increased likelihood of loosening.…”

The design and pre-clinical evaluation of knee replacements for osteoarthritis

“…Having proposed that a peg would provide superior fixation to other contemporary methods, an experimental model was constructed to test out the hypothesis. The model consisted of a 6-channel knee simulating machine where cyclic loads and motions were applied to different components affixed to cadaveric tibias and tested over millions of cycles (Walker and Hsieh, 1977). The onepiece pegged components were clearly superior in fixation.…”