Increased constraint of rotating hinge knee prosthesis is associated with poorer clinical outcomes as compared to constrained condylar knee prosthesis in total knee arthroplasty

The aim of this study was to evaluate whether there are any differences in patient-reported outcome measures between semi-constrained condylar constrained knee (CCK) and fully constrained rotating hinge knee (RHK) prostheses in midterm follow-up. We reviewed prospectively collected data of our hospital arthroplasty registry between 2007 and 2014. Thirty-nine patients were identified to have RHK prosthesis TKA and matched for a number of primary/revision TKA, gender, age, body mass index and pre-operative clinical scores to a control group of 78 patients with CCK TKA. Patient demographics, range of movement, varus/valgus deformity, Short Form 36 (SF-36) scores, Oxford Knee Score (OKS), Knee Society Score (KSS) and patient satisfaction were evaluated. Pre-operatively, the RHK and the control group of CCK had similar demographics, proportion of primary/revision TKA and baseline clinical scores ( p > 0.05). At 2-year follow-up, patients with CCK prostheses had significantly better clinical outcomes as compared to patients with RHK prosthesis in terms of KSS functional scores, OKS, SF-36 sub-domains of physical functioning, physical role functioning and physical component score. We conclude that at midterm follow-up of 2 years, the CCK patients as compared to RHK patients reported better clinical and functional outcomes in terms of OKS, KSS functional score and SF-36 with a greater proportion of patients who were satisfied and had their expectations met by surgery. Further biomechanical studies are needed to investigate the association between component constraint and clinical outcomes for these prostheses.