Impact of soft-tissue management technique on functional alignment in total knee arthroplasty among Japanese population with severe varus deformity.

Abstract

Simultaneously optimizing alignment and soft-tissue balance in total knee arthroplasty (TKA) still remains challenging. Functional alignment (FA), particularly with navigation or robotic systems, enables real-time intraoperative assessment of implant positioning, joint gaps, and limb alignment. This study compared one-year outcomes of TKAs performed with FA principles by a single surgeon. Two soft-tissue management techniques were compared, a conventional method (manual FA) and an instrumented gap-balancing method (instrumented FA). A retrospective review was conducted on 50 consecutive TKA cases, with 25 manual FA-TKAs followed by 25 instrumented FA-TKAs. Both cohorts were performed using an image-free navigation system with a tibia-first workflow. In manual FA-TKAs, the femoral cuts were determined by assessing flexion and extension gaps using spacer blocks. In instrumented FA-TKAs, femoral cuts and component positioning were guided by gap balancing using a force-controlled tensioning device maintaining constant distraction force. The primary laxity goal was a stable medial compartment throughout the range of motion. Baseline demographics (age, height, weight, body mass index) did not differ between groups. Femoral component rotational alignment was significantly different between groups (5.2° ± 2.6°, instrumented FA-TKA vs. 1.5° ± 1.0°, manual FA-TKA, p < 0.0001). The hip-knee-ankle angle was not significantly different between groups, preoperatively (169.8° ± 4.0° vs. 169.7° ± 3.5°) or postoperatively (176.1° ± 2.1° vs. 176.0° ± 3.1°). The average total KOOS and Forgotten Joint Score-12 scores were not significantly different between groups (79.5 vs. 72.1, and 65.8 vs. 52.3, respectively). The KOOS Sports sub-score was significantly higher in instrumented FA-TKAs than manual FA-TKAs (68.3 vs. 45.8, p = 0.029). Instrumented FA-TKA using tibia-first, force-controlled balancing achieved superior outcomes in demanding activities measured by KOOS Sports subscale compared to manual FA-TKA. Objective gap balancing data may enhance postoperative outcomes in TKA by more accurately addressing the individual soft-tissue balance.