Eligible patients demonstrated radiographic signs of end-stage osteoarthritis with Ranawat’s type 1 or 2 deformity (pre-op anatomical valgus angulation of up to 20°) on standing radiographs. Integrity of the medial capsular-ligament complex was also confirmed (<10mm of opening on valgus stress test at 10° of knee flexion).1 Historically, this type of limb deformity has represented a technical challenge because of the attenuation of the medial capsular ligament complex and lateral soft-tissue contracture, and has often been treated using more constrained implants.
The surgical technique prioritised establishing a well-balanced extension gap over reproducing a neutral mechanical axis, and so the authors accepted slight post-operative valgus of <5°. Releases of the posterior-lateral soft-tissue envelope were also made as required to balance the extension gap. The most common of which was a posterior-capsular release, which was made in 72% of the TKAs.
All patients were reviewed pre-operatively, and 6 weeks, 3, 12, and 24 months after surgery. The measures taken at these time points were the Knee Society Score (KSS), Forgotten Joint Score (FJS) and Satisfaction and Quality of Life Score. Standard weight-bearing antero-posterior and lateral radiographs, and a standard sunrise view were taken at the same time-points.
At two years minimum follow-up the clinical KSS was 89 ± 6 (range 65-100) and the functional KSS was 82 ± 8 (range 55-100). Overall, 99% of patients had good or excellent KSS scores. The FJS was 72 ± 6 (range 49-88). There were no reports of symptomatic post-operative instability, even in patients with residual valgus alignment of between 6° and 10°, and survivorship free of component revision was 100% at 24 months.
The authors attributed these findings to the high conformity of the MC polyethylene bearing, which differs significantly to both the classical cruciate retaining and posterior stabilized bearing designs.