Unrestricted kinematic alignment in varus total knee arthroplasty outperforms mechanical alignment in CPAK I phenotype, but yields comparable outcomes in CPAK IV: A retrospective analysis from the FP‐UCBM Knee Study Group

Abstract Purpose To compare clinical outcomes in varus‐aligned patients undergoing cruciate‐retaining total knee arthroplasty (TKA) with mechanical alignment (MA) versus unrestricted kinematic alignment (KA). The hypothesis was that KA would yield superior outcomes, and that preserving joint line obliquity—regardless of alignment technique—would be associated with better results. Methods A retrospective analysis of prospectively collected data from 140 KA and 209 MA TKA cases was performed. Inclusion criteria were: end‐stage varus osteoarthritis (aHKA < 178°), MA or unrestricted KA TKA and ≥ 1‐year follow‐up. Exclusion criteria included prior major surgery (osteotomies, fractures) on the affected limb, inadequate preoperative full‐length radiographs, or post‐operative complications unrelated to alignment strategy. Patients were categorised by CPAK phenotype (I, IV and VII) based on the joint line obliquity. Clinical outcomes at 1‐year follow‐up were assessed using the Knee Society Score (KSS) pt.1 and 2, Oxford Knee Score (OKS), SF‐12, and Forgotten Joint Score (FJS). ANOVA was used to compare results of MA and KA in the overall varus population, and in CPAK subgroups. Statistical significance was set at p < 0.05. Results KA led to significantly higher KSS pt.1 (84.6 ± 15.3 vs. 73.9 ± 18.9; p < 0.001) and FJS (90.5 ± 15.3 vs. 80.4 ± 15.8; p < 0.001) than MA. In CPAK I patients, KA outperformed MA in KSS pt.1 (83.5 ± 16.2 vs. 74.9 ± 19.1; p < 0.001) and FJS (89.8 ± 15.5 vs. 80.7 ± 17.8; p < 0.001). No differences were found between KA and MA in CPAK IV patients ( p > 0.05). KSS pt.1 (80.1 ± 13.8) and FJS (86.5 ± 18.1) achieved with MA in CPAK IV were significantly higher than in both the overall varus aHKA group and CPAK I patients treated with MA ( p < 0.05). Conclusions Cruciate‐retaining unrestricted KA yields better clinical outcomes compared to MA in varus aHKA patients, and in the CPAK I subgroup. In CPAK IV, preserving joint line obliquity leads to similar outcomes with both MA and KA. Level of Evidence Level IV.