Biomechanical Study of Patellar Component Fixation with Varying Degrees of Bone Loss.

Background: The decision as to whether or not to resurface the patella in revision total knee arthroplasty (TKA) is affected by the amount of patellar bone stock remaining; however, the impact of the cancellous bone status on patellar component fixation has not been studied. Therefore, we conducted a biomechanical study of patellar component fixation with varying degrees of cancellous bone loss.

Methods: Sixty pairs of cadaveric patellae were randomly assigned between 3 groups and prepared in similar manner to a TKA with the standard 3-hole configuration. A control patella and an experimental patella were designated in each pair. To simulate bone loss in the experimental patellae, 1, 2, and 3 of the standard drill holes were uniformly enlarged to 12 mm in group 1, group 2, and group 3, respectively. Afterward, an all-polyethylene patellar component was cemented to each patella, as done intraoperatively. Patellar components were then sheared off using a materials testing system. The resulting mean offset yield force was analyzed within each group using paired t-tests.

Results: The mean offset yield force for the control patellae was greater than the experimental patellae in group 1. In groups 2 and 3, the experimental patellae produced a greater mean offset yield force than the control patellae. Comparison within each group did not demonstrate a statistically significant difference.

Conclusion: Bone loss with enlargement of the patellar fixation holes, as is frequently seen in revision TKA, with holes up to 12 mm, does not significantly decrease patellar component fixation shear strength in this biomechanical cadaveric study.