Mechanical Versus Restrictive Kinematic Alignment in Robotic-Assisted Total Knee Arthroplasty: A Randomized Controlled Trial

Background: Lower limb malalignment is a hallmark of knee osteoarthritis, with surgical correction techniques evolving from traditional mechanical alignment (MA) to kinematic alignment (KA) approaches. Restrictive kinematic alignment (rKA) represents a hybrid strategy combining principles from both techniques. This study evaluated short-term functional outcomes following robotic-assisted total knee arthroplasty (RoTKA), comparing MA versus rKA alignment strategies. Methods: This prospective, randomized, single-center study enrolled 96 patients with grade 3–4 idiopathic knee osteoarthritis (Kellgren–Lawrence classification). Patients were randomized to MA (n = 49, mean age 67 ± 9 years) or rKA (n = 47, mean age 66 ± 7 years) groups. Preoperative hip–knee–ankle (HKA) angles were 172.6° ± 1.1° and 172.9° ± 0.9° for MA and rKA groups, respectively. Outcomes were assessed using Visual Analog Scale (VAS) pain scores, range of motion (ROM), Knee Society Score (KSS), Oxford Knee Score (OKS) (primary outcome), SF-36, and Forgotten Joint Score (FJS-12). Results: Postoperative HKA angles were 179.5° ± 1.2° (MA) and 176.0° ± 1.5° (rKA). At 14 days postoperatively, knee ROM increased by 20.5% in the MA group and 25.7% in the rKA group, with a statistically significant 5.2% intergroup difference, indicating faster postoperative recovery (p = 0.008). VAS pain scores decreased by 7% in the rKA group while increasing by 13% in the MA group (p < 0.001). At one-year follow-up, FJS-12 scores were significantly higher in the rKA group (94.8 ± 3.2 vs. 91.9 ± 2.2, p < 0.001). No significant differences were observed in KSS, OKS, or SF-36 score between groups. Conclusions: Restrictive kinematic alignment demonstrated superior early postoperative outcomes compared to mechanical alignment in RoTKA, with significantly reduced pain and improved ROM. While one-year functional outcomes were comparable between techniques, rKA may offer advantages in the immediate postoperative period, supporting its consideration as a viable alignment strategy in robotic-assisted knee arthroplasty.