title: All-polyethylene patellar components are not the answer.
abstract: Recent reports of the high incidence of polyethylene failure of metal-backed patellar components have rekindled the interest in cemented, all-polyethylene designs. One hundred four retrieved patellar components of metal-backed and all-polyethylene designs were analyzed for wear. Additionally, patellofemoral contact stress as a function of flexion angle was measured for unused components using pressure-sensitive Fuji film. Significant wear (2+ on a 0-3 scale) was seen in 65% of metal-backed designs and in 78% of all-polyethylene components. Severe wear (3) was seen in 44% of all-polyethylene components and in 39% of metal-backed devices. The incidence of severe wear (3) of congruent designs was statistically significantly lower than that of the noncongruent designs. Contact stress analysis confirmed that dome-type geometries typically resulted in stresses that exceed the yield strength of the polyethylene, whereas the more congruent geometries generated significantly reduced stress levels.
authors.affiliation: Dartmouth Biomedical Engineering Center, Thayer School of Engineering, Dartmouth College, Hanover, NH 03755.
authors.forename: J P
authors.initials: JP
authors.lastname: Collier
authors.forename: J L
authors.initials: JL
authors.lastname: McNamara
authors.forename: V A
authors.initials: VA
authors.lastname: Surprenant
authors.forename: R E
authors.initials: RE
authors.lastname: Jensen
authors.forename: H P
authors.initials: HP
authors.lastname: Surprenant
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D007720:Knee Prosthesis; D009068:Movement; D011095:Polyethylenes; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013314:Stress, Mechanical
chemical_list: D011095:Polyethylenes