Unrestricted kinematic alignment for total knee arthroplasty

Aims: Kinematic alignment (KA) offers a personalized approach by restoring each patient's pre-arthritic joint lines. Unrestricted KA (urKA) removes alignment boundaries defined by restricted KA concept, but concerns regarding reproducibility and clinical success persist. This study evaluates mid- to long-term survivorship and functional outcomes of urKA total knee arthroplasty (urKA-TKA) performed using a manual surgical technique by a single surgeon, with a minimum follow-up of three years. Methods: We prospectively reviewed 229 consecutive urKA-TKAs performed between March 2014 and October 2019 using a medial pivot design TKA and calipered measured resection (mean follow-up 87 months (36 to 136)). Patella was not routinely resurfaced. No restrictions were applied regarding preoperative limb alignment. Outcomes included survivorship (revision and reoperation), radiological alignment, and patient-reported outcomes: Knee Injury and Osteoarthritis Outcome Score (KOOS), Forgotten Joint Score (FJS), and Numerical Rating Scale (NRS) for pain. Survivorship was calculated using Kaplan-Meier analysis. Results: Preoperative and postoperative hip-knee-ankle (HKA) axis ranged respectively from -20.4° to 25.2° and -9.4° to 10.6°. The mean KOOS improved from 28.8 (SD 10.3) preoperatively to 75.8 (SD 16.6) postoperatively (p < 0.001). FJS was 87.6 (SD 17.7) at final follow-up, while NRS pain scores averaged 1.6 (SD 2.4), with 60% reporting no pain. At nine years (n = 32 at risk), implant survivorship was 97% free from revision for any reason and 96% free from reoperation, with no cases of aseptic loosening. Patients with preoperative alignment outliers (>± 5° HKA) demonstrated greater improvements in KOOS and FJS than neutral knees. Outcomes and implant survival were similar between knees within or outside restricted alignment boundaries. A trend towards higher rates of secondary patellar resurfacing was observed in valgus phenotypes, although this finding was not statistically significant. Conclusion: UrKA TKA provides excellent mid- to long-term survivorship and significant functional improvement without compromising safety in all knee phenotypes including patients with extreme preoperative alignment.