Metal-Backed Patella Implants in Knee Arthroplasty: Can the Past Predict the Future?

Background: There is a renewed interest in uncemented total knee arthroplasty to potentially provide longer durability, including the use of newer design metal-backed patellae (MBPs). The purpose of this study was to review survivorship with failure mode and time to failure of an earlier version MBP at up to 10-30 years of follow-up that may influence the desirability of using these components today.

Methods: A retrospective review was performed of patients that had uncemented total knee arthroplasty with an uncemented MBP. All-cause revision rates were obtained from chart reviews and telephone discussions with patients and family members of deceased patients. Kaplan-Meier plots were used to determine the implant survivorship. Outcome scores were compared between revised and nonrevised patients.

Results: The 97 knees that had an end point of an aseptic revision or last known contact with implant survivorship averaged 15 years (range, 0-32 years). There were 40 knees that underwent revision that included 37 patella component failures (38.1%). All patellar failures had polyethylene wear or fracture. None were revised due to loosening. Survivorship was 97.9% at 5 years, 88.7% at 10 years, and 53.0% at 20 years. Median time to failure was 11 years.

Conclusion: Loosening is not a failure mode with this MBP. There were 75% of the failures occurring after 10 years. Use of contemporary MBP with improved but still thin polyethylene warrants guarded optimism when used in younger patients where longer survivorship than with a cemented all-polyethylene patellar component is the goal.