Residual varus alignment can reduce joint awareness, restore joint parallelism, and preserve the soft tissue envelope during total knee arthroplasty for varus osteoarthritis

Abstract

Purpose The objectives were to compare the coronal joint configuration of the knee joints, coronal gap imbalances requiring substantial medial release, and patient-reported outcomes, including the forgotten joint score, between knees in which residual varus alignment was intentionally allowed according to an individualised lower limb analysis and those with mechanical alignment in total knee arthroplasty for varus osteoarthritis. Methods Consecutive primary navigated total knee arthroplasty procedures for varus osteoarthritis were retrospectively reviewed. The study cohort was stratified based on whether residual varus alignment was intentionally allowed. Propensity-score matching was performed based on the baseline characteristics, including demographic characteristics, preoperative radiological measurements, and the Western Ontario and McMaster University Osteoarthritis Index (mechanical alignment group vs residual varus group). The patient-reported outcomes and coronal joint line orientation of the knee (relative to the ground) and ankle were evaluated. Coronal gap differences and coronal gap imbalances were analysed using intraoperative gap measurements. Results Relative to the ground and ankle, the postoperative knee joint line orientation slanted down laterally in the mechanical alignment group (- 3.05 degrees +/- 1.62, relative to the ground; - 2.65 degrees +/- 1.56, relative to the ankle joint), but was parallel in the residual varus group (- 0.75 degrees +/- 1.59, relative to the ground; - 0.95 degrees +/- 1.71, relative to the ankle joint). Coronal gap differences at extension and the proportion of coronal gap imbalances requiring substantial medial release were 1.27 +/- 1.53 and 6% in the residual varus group and 2.32 +/- 1.24 and 15% in the mechanical alignment group. Postoperatively, the residual varus group showed higher Western Ontario and McMaster University Osteoarthritis Index scores and total forgotten joint scores than the mechanical alignment group (6.97 +/- 4.75 vs. 10.31 +/- 5.74 and 56.42 +/- 12.85 vs. 45.69 +/- 14.49, respectively). Conclusion Intentionally allowed residual varus alignment with individualised analysis of lower limb alignment restored the parallel joint line of the knees, preserved the soft tissue envelope, and reduced joint awareness after total knee arthroplasty for varus osteoarthritis.