Impact of femoral mediolateral diameter on femoral component selection during total knee arthroplasty and its effect on postoperative knee function and pain: a retrospective cohort study.

OBJECTIVE: To investigate the influence of different intraoperative reference dimensions on femoral component selection during total knee arthroplasty (TKA) and to compare the postoperative knee function, pain, and radiographic outcomes between two sizing strategies when the femoral mediolateral (ML) and anteroposterior (AP) diameters are discrepant. METHODS: This retrospective cohort study included 86 patients (86 knees) with primary knee osteoarthritis who underwent TKA. Patients were allocated to two groups based on the intraoperative femoral sizing reference: Group A (n = 52), in which the component was selected strictly according to the femoral AP diameter; and Group B (n = 34), in which, on the basis of AP evaluation, a component one to two sizes larger was chosen to improve mediolateral coverage when the ML/AP ratio exceeded 1.13. Operative time, intraoperative and postoperative blood loss, Hospital for Special Surgery (HSS) knee score, Visual Analogue Scale (VAS) for pain, and knee range of motion (ROM) were recorded preoperatively and at 1 week, 3 months, and 1 year postoperatively. RESULTS: Both groups achieved significant improvement in HSS score, VAS score, and knee ROM at each follow-up time point compared with preoperative values (all P < 0.001). Group B showed a smaller knee ROM (96.74° ± 4.19° vs. 100.83° ± 5.50°, P < 0.001) and higher VAS score (3.35 ± 0.60 vs. 2.90 ± 0.66, P = 0.002) at 1 week, and similar trends persisted at 3 months. Operative time, intraoperative blood loss, and postoperative drainage were comparable between groups (all P > 0.05). Radiographic shadowing of the uncovered distal femoral condyle region was significantly more frequent in Group A than in Group B (65.38% vs. 20.59%, χ 2 = 16.54, P < 0.001). No deep infection, aseptic loosening, or periprosthetic fracture occurred in either group during follow-up. CONCLUSION: TKA remains an effective treatment for end-stage knee osteoarthritis. In Asian patients with an ML/AP ratio greater than 1.13, choosing a femoral component one to two sizes larger than that predicted by the AP reference appropriately increases distal mediolateral coverage without adversely affecting one-year functional outcomes or anterior knee pain, and significantly reduces radiographic shadowing in the uncovered distal femoral area. This strategy deserves consideration in routine clinical practice.