Bilateral patellar component shear failure of highly cross-linked polyethylene components: report of a case and laboratory analysis of failure mechanisms.

A case of bilateral patellar component failure due to fatigue fracture of the all-polyethylene fixation pegs in a highly cross-linked ultra-high-molecular-weight polyethylene design is presented. To recreate this failure mode, a novel test method was developed to investigate the effects of peg orientation and cement technique on patella fatigue strength under cyclic compression and shear loading. Patellar peg orientation had a minor effect on shear strength, whereas lack of cement in the backside patellar groove had a substantial effect.