In the late 1980's Michael Freeman conceived the idea that knee replacement would most closely replicate the natural knee joint, if the medial Tibio-Femoral articulation was configured as a “ball-in-socket”. Over the last three decades, medial rotation and medial pivot designs have proved successful in clinical use. Freeman's final iteration of the medial ball-in-socket concept was the Medial Sphere knee. We report the three-year survivorship, clinical outcomes, patient reported outcome measures (PROMs) and radiographic analysis of this implant in a multi-centre, multi-surgeon, prospective observational study. Patients awaiting total knee replacement were recruited by four centres. They had no medical contraindication to surgery, were able to provide informed consent and were available for follow-up. Primary outcome was implant survival at six months, one, two, three and five years. Secondary outcomes were patient reported outcome measures: Oxford Knee Score (OKS), Euroqol (EQ-5D), International Knee Society Score (IKSS), IKSS Functional score and Health State score, complications and radiographic outcomes. Radiographic analysis was undertaken using the TraumaCad software and data analysis was undertaken using SPSS.Background
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