Characterised by a pronounced varus intra-articular deformity and associated insufficiency of the lateral ligamentous structures, high grade varus OA can be treated with a minimally constrained TKR in a procedure requiring an extensive medial release.1 However, “an inadequate release and/or stretching of the lateral complex may result in mediolateral (ML) instability.”1
An alternative solution is to compensate for the lateral laxity with a CCK design, and in so doing avoid the need for medial soft-tissue releases.1 The authors hypothesised that this approach might increase stability, leading to improved patient outcomes.1
Data was extracted from a local arthroplasty database for patients with a pre-op varus alignment of more than 8 degrees, and a minimum follow-up of one year. Patients were grouped according to implant design: CCK (n=21), Posterior Stabilized (PS) (n=20) and Cruciate Retaining (CR) (n=19). The patient reported outcome measures (PROMs) evaluated were Oxford Knee Score (OKS), Forgotten Joint Score (FJS), Knee Society Score (KSS) and UCLA-Activity Score.1
Range of motion, ML laxity and symptoms, and all four PROMs, were significantly better in the CCK group than the CR group.1 The KSS and UCLA were significantly better in the CCK than the PS group.1 There were no other significant differences between these two groups.1
The authors concluded that “leaving the medial soft tissues untouched and compensate the lateral laxity by using a CCK design in high grade varus OA knees results in improved clinical stability and better functional as well as subjective outcome scores compared to less constrained designs.”1
