Agreement of Component Sizing Between Contralateral Knees Among Patients Undergoing Bilateral Image-Free Robot-Assisted Total Knee Arthroplasty

The ability to predict component sizes that shall be required during total knee arthroplasty (TKA) helps ensure their availability and increase operating room efficiency. Some literature on bilateral conventional manual TKA indicates the existence of inherent prosthetic size asymmetry, whereas other research correlates component size variations with asymmetric postoperative outcomes. Given the precision offered by robotic technology, we hypothesized that bilateral robot-assisted TKA (ra-TKA) would result in near-perfect component size symmetry and provide for a reliable means of predicting prosthetic sizes that shall be required for surgery of the second knee. Overall, 102 patients who underwent staged bilateral cruciate-retaining image-free ra-TKA for primary osteoarthritis between January 2023 and November 2024 were studied. The proportions of patients with all-component symmetry and asymmetry of one or more components were assessed. The agreement between component sizes of contralateral knees was analyzed. The study cohort comprised 66 women and 36 men with a mean age of 63.1 ± 7.1 years. All modes of isolated and multicomponent size asymmetry were noted. Excellent bilateral agreement for exact femoral (77.5% symmetry, <i>ƙw</i> = 0.83) and tibial (71.6% symmetry, <i>ƙw</i> = 0.80) component sizes, but poor agreement for exact insert sizes (68.6% symmetry, intraclass correlation coefficient = 0.164) was noted. When an error margin of ± 1 size was permitted, however, the predictive potential increased to over 95% for all component sizes. Patients with all-component symmetry and those with asymmetry of isolated components were comparable in terms of age, sex, and preoperative coronal deformity, range of knee flexion, and Knee Society scores. Prosthetic size asymmetry during bilateral TKA seems inherent to an extent and may result from morphological variations or differences in component positioning requirements for attaining optimal gap balance. Ensuring the availability of all insert sizes and exact as well as ± 1 sizes of femoral and tibial components in relation to those used for the first knee surgery seems adequate for the second knee surgery for most patients.