We observed early loosening of a hydroxyapatite-coated tibial component in a total knee arthroplasty in a randomized study comparing HA-coating with cement fixation. Symptoms of loosening started 8 weeks after surgery. Roentgen stereophotogrammetric analysis revealed stability during the initial 6 weeks followed by a pronounced subsidence up to 6 months after surgery when revision was done. At revision, the HA-coating was found to have separated from the medial part of the tibial component. The synovium was abundant with macrophages and multinucleated giant cells containing HA-crystals. Overloading of the prosthesis and suboptimal quality of the HA-coating was believed to have caused the loosening process.
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Nilsson et al. (1994) studied this question.
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