Non-uniformity of contact stress on polyethylene inserts in total knee arthroplasty

This study examined tibiofemoral contact stresses in 15 commercially available TKR designs, using digitally imaged pressure-sensitive film. The objectives were (1) to determine the correlation between minimization of spatial mean contact stress and minimization of the amount of overloaded (> 10 MPa) polyethylene contact area, and (2) to ascertain the difference in contact stresses for machined versus moulded polyethylene inserts. The data showed that there was no statistically significant (design rank-order) correlation of spatial mean contact stress with overloaded polyethylene area. The data also showed that machining cutter preparation of the polyethylene insert caused substantial local contact stress non-uniformities that corresponded to the pattern of grossly visible machining marks.