Acceptable migration of a fully cemented rotating hinge-type knee revision system measured in 20 patients with model-based RSA with a 2-year follow-up

BACKGROUND AND PURPOSE: Rotating hinged knee implants are highly constrained prostheses used in cases in which adequate stability is mandatory. Due to their constraint nature, multidirectional stresses are directed through the bone–cement–implant interface, which might affect fixation and survival. The goal of this study was to assess micromotion of a fully cemented rotating hinged implant using radiostereometric analysis (RSA). PATIENTS AND METHODS: 20 patients requiring a fully cemented rotating hinge-type implant were included. RSA images were taken at baseline, 6 weeks, and 3, 6, 12, and 24 months postoperatively. Micromotion of femoral and tibial components referenced to markers in the bone was assessed with model-based RSA software, using implant CAD models. Total translation (TT), total rotation (TR), and maximal total point motion (MTPM) were calculated (median and range). RESULTS: At 2 years, TT(femur) was 0.38 mm (0.15–1.5), TR(femur) was 0.71° (0.37–2.2), TT(tibia) was 0.40 mm (0.08–0.66), TR(tibia) was 0.53° (0.30–2.4), MTPM(femur) was 0.87 mm (0.54–2.8), and MTPM(tibia) was 0.66 mm (0.29–1.6). Femoral components showed more outliers (> 1 mm, > 1°) compared with tibial components. CONCLUSION: Fixation of this fully cemented rotating hinge-type revision implant seems adequate in the first 2 years after surgery. Femoral components showed more outliers, in contrast to previous RSA studies on condylar revision total knee implants.