Analysis of Femoral Flexion Angle Distribution and Range of Motion in Total Knee Arthroplasty.

Background: Optimal coronal and rotational alignment in total knee arthroplasty is essential for satisfactory outcomes. There has been limited focus on sagittal alignment in assessing outcomes. This study investigated the impact of femoral implant flexion (FF) angle on knee kinematics and postoperative outcomes.

Methods: In this multicenter, prospective case series, we analyzed demographics, preoperative and postoperative range of motion (ROM), and implant alignment in patients undergoing total knee arthroplasty with a computed tomography-based robotic system. The study included 976 patients (age 66 years [range, 38 to 90]; body mass index 32.6 [range, 14.3 to 50.2]; 56.6% women). The ROM was assessed at four intervals: preoperative, early postoperative, middle postoperative, and late postoperative. Patients were divided into "high FF" and "low FF" groups based on mean FF. Comparisons were made using t-tests and Pearson's Chi-square tests.

Results: The average FF was 4.05° ± 2.10 (range, 0 to 9). The low FF group (n = 528) had a mean FF of 2.45° ± 1.28. The high FF group (n = 448) had a mean of 5.93° ± 1.06. No differences were found in patient height, weight, or body mass index. No differences were noted in preoperative knee alignment or ROM between groups. The high FF patients were more frequently women (62.5 versus 53.0%; P = 0.006), had more cemented implants (20.4 versus 14.4%; P = 0.020), and had smaller implants (P < 0.001). At the latest follow-up, a nonclinically significant difference in extension ROM was noted (low FF 0°, high FF 0.1°; P = 0.050). No differences in flexion ROM were observed at any visit.

Conclusions: The FF angles showed a normal distribution, with higher angles associated with cemented implants, smaller implants, and women. No clinically meaningful differences in ROM were found between the high and the low FF groups across all visits.