Impact of Implant Size Variation on Surgical and Clinical Outcomes in Staged, Bilateral Total Knee Arthroplasty.

Abstract

This study evaluated differences in surgical and clinical outcomes among patients who have identical versus different implant sizes in sequential total knee arthroplasty (TKA) surgeries. We retrospectively reviewed patients who underwent primary, elective, staged, bilateral, same-surgeon, same-prosthesis TKA between 2011 and 2024 at a large academic health system. Patients were grouped by femoral and tibial implant size consistency: same femoral and tibial (SS), different femoral, same tibial, different tibial, same femoral, and different femoral and tibial (DD). A total of 4,536 TKAs were performed in 2,268 patients. The SS had the shortest length of stay compared to DD (51.8 versus 58.2 hours, P < 0.001). The majority had the same femoral (75.6%) and tibial (76.6%) sizes in both knees, whereas polyethylene thickness varied. Undergoing contralateral surgery within one year was associated with receiving the same implant sizes (P < 0.001). The DD were more common in manual surgery, and the SS were more common using navigation assistance (P < 0.001). Different assistance modalities between surgeries increased different femoral, same tibial and DD, whereas the same navigation assistance increased SS (P < 0.001). Complication and revision rates were not significantly different between the groups. All groups showed improvement in their Knee injury and Osteoarthritis Outcome Score for Joint Replacement and Patient-Reported Outcomes Measurement Information System Pain Intensity and Interference scores with no significant intergroup differences (P > 0.05). Over one-third of patients (37.3%) undergoing staged, bilateral TKA received different implant sizes for at least one component, and over half had different polyethylene thicknesses. Although implant size consistency was influenced by factors such as time between surgeries and assistance modality, these variations did not significantly affect length of stay, complications, or patient-reported outcomes. Surgeons should be aware that minor implant size differences between knees are common, even when using the same prosthesis.