Review Question - QID 707

Adding a polyethylene-metal interface by making it modular leads to more wear on the backside, not the articular surface.

Modularity with metal tibial base plates has the advantage of being able to customize implants intraoperatively. However, a disadvantage of modularity is increased rates of osteolysis and backside polyethylene wear due to micromotion between tibial baseplate and undersurface of polyethylene that occurs during loading. A monoblock tibial component creates intraoperative challenges as determination of tibial component size is done prior to cementing.

Weber et al. reviewed 1000 TKAs performed with 5- to 11-year follow-up. Of tibial components, 698 were monoblock and 353 were modular assembly design. Higher rates of osteolysis, radiolucent lines, and revision were found with the modular design. The TKAs done with a monoblock design gave better clinical and radiologic results.

Collier et al. reviewed 365 TKA cases followed for 5-10 years. They concluded that polishing the tibial baseplate counterface and avoiding polyethylene gamma radiation in air led to decreased rates of osteolysis.

Figure A shows an example of a modular polyethylene-metal interface design. Figure B shows an example of an all-polyethylene tibial component.

Incorrect Answers:
Answer 1: Tibial component modularity does not affect the ductility of the polymer.
Answers 2 and 3: Polyethylene wear does not change with modularity on the articular side.
Answer 5: Polyethylene wear increases on the backside of modular polyethylene tray.