The tibiofemoral articulating surfaces bear primary load in the B-P Hinge Knee rather than the hinge element, as in other hinge knee designs. This enables the use of a small hinge that only needs to withstand shear forces rather than the much greater compression forces. This knee's tibiofemoral articulating surfaces are fully congruent in all phases of flexion, resulting in extremely low contact stress for all activities.Pappas saw a need for a condylar bearing hinge knee prosthesis that made use of the bearing arrangement. The bearing arrangement is used in this combination to transfer the majority of the loading from the femur to the tibial via the condylar surfaces of the femoral and tibial components. The hinge is only used for knee stabilisation rather than load transfer, this allows for the use of relatively small hinge elements, resulting in a lighter weight device that requires far less bone removal than traditional hinge load bearing knee replacements. It is preferable to keep as much bone as possible because implant fixation is often improved when more bone is retained. BP Hinge Knee Assembly :. A rod is used to stabilise a mating tibial platform in the tibia, with the bearing translating on the platform in the posterior-anterior directions in response to knee flexion and extension. The bearing bears the full extension load on congruent articulating contact regions with the condylar surfaces and lesser flexion loads via incongruent articulating contact. A hinge assembly is pinned to the femoral condylar component via a head with a depending shaft fixed to a UHMWPE tapered bearing that is axially floating and rotatably movable in a tibia platform component mating cavity. The head passes through the bearing and stops the bearing translations at the extreme posterior and anterior. Wedges: There are options for distal, posterior, and tibial wedges, metallic implants are used to compensate for bone loss, there are six sizes and two thicknesses of distal femoral augments available (5 and 10 mm). Posterior Femoral Augments are available in six different sizes and three different thicknesses (5, 10, and 15 mm).Tibial augments are available in six different sizes and three different thicknesses (5, 10 and 15 mm).
