Evaluating Factors Affecting Patellar Component Fixation Strength in Total Knee Arthroplasty

Complications related to the patellofemoral joint after total knee arthroplasty (TKA) represent up to 50% of TKA reoperations. Shear forces across the knee produce wear and occasionally result in failure of fixation of all-polyethylene patellar components.

We conducted a study to evaluate the effect of 2 factors on the shear strength of patellar component fixation: time between cement mixing and application of the patellar component, and amount of pressure applied during implantation. Fifty-four patellae were harvested from 27 cadavers and were prepared as for a TKA, allowing 3 different amounts of time for the cement to set or cure before application, and using 3 different pressures. The patellae were mounted and tested for fixation strength with a materials testing machine.

Fixation was significantly stronger (P = .006) at 42 pounds of pressure after curing the cement for 8 minutes (compared with 2 minutes) and was significantly stronger (P = .005) after 2 minutes of curing at 42 pounds of pressure (compared with 62 pounds of pressure).

We concluded that allowing the cement to cure while cementing the femoral and tibial components does not jeopardize fixation of the patellar component and that excessive compression of a patellar clamp may weaken fixation.