Measured resection, gap balancing, and force-sensor-guided total knee arthroplasty result in different femoral and tibial rotational alignment but similar combined knee rotation and clinical outcomes: a randomized controlled trial.

backgroundDifferent alignment philosophies and balancing methods may alter femoral and tibial component rotation in distinct ways within the same knee. This study aimed to (1) determine which of three surgical techniques-measured resection (MR), gap balancing with computer-assisted surgery (GB-CAS), or a force-sensor soft-tissue balancing device (FS-STB)-most closely reproduces native femoral, tibial, and combined rotational alignment in mechanically aligned total knee arthroplasty (TKA), and (2) assess whether differences in rotational alignment affect outcomes at 5 years postoperatively. MATERIAL AND

methodsA total of 60 patients undergoing primary mechanical alignment TKA were randomly assigned to one of three surgical approaches (n = 20 per group): MR, GB-CAS, or FS-STB. Blinded observers assessed the Knee Society Score (KSS), Western Ontario MacMaster Universities Osteoarthritis Index (WOMAC) score, and hip-knee-ankle angle preoperatively and at the 5-year follow-up visit. Pre- and postoperative two-dimensional (2D)-computed tomography scans were used to measure femoral rotation (BFA), tibial rotation, and combined femur-tibia rotation (TE_PTCA and BC_PTCA). Statistical analyses included paired t-tests, one-way analysis of variance, and effect size calculations.

resultsFemoral rotation remained unchanged in the MR and GB-CAS groups, but decreased slightly (1° external rotation) in the FS-STB group (P = 0.010). Tibial rotation increased significantly in internal rotation in the GB-CAS and FS-STB groups (P < 0.001), but not in the MR group (P = 0.061). The combined TE-PTCA rotation decreased slightly across all groups (P < 0.05), with no significant intergroup differences. Combined BCPTCA rotation increased only with GB-CAS (P = 0.006), but again without significant differences between the techniques. At 5 years, functional KSS and WOMAC scores improved in the FS-STB group compared with that in the MR group, although this difference was not statistically significant (P = 0.058 and P = 0.056, respectively).

conclusionsMeasured resection best preserved native knee rotation in mechanically aligned TKA. Although the individual component rotations varied by technique, the overall combined rotational alignment and functional outcomes did not differ significantly. Prosthesis design may govern the kinematics, and soft tissue adaptation may mitigate the impact of minor rotational differences in TKA procedures. More technologically assisted balancing methods may not provide meaningful functional advantages in terms of rotational alignment. LEVEL OF EVIDENCE: Level I, therapeutic study. Trial registration Retrospectively registered on the UK's Clinical Study Registry platform. REGISTRATION NUMBER: ISRCTN66642689). Date of registration: 25/10/2025.