Cases of a fracture of the hydroxyapatite (HA)-coated stem in patients who underwent total hip arthroplasty have occasionally been reported. This article describes a case of stem fracture seen in a 61-year-old female patient more than 11 years after cementless bipolar head prostheses performed at this hospital. The patient had idiopathic avascular necrosis of the right femoral head, and at the age of 48, she underwent cementless bipolar head prosthesis using a titanium, HA-coated MCF stem (Kyocera Corporation, Kyoto, Japan). The stem was successfully implanted, and the postoperative clinical progress was uneventful. Eleven years and 10 months after operation, the patient had acute weakness of the right hip when she stood up, resulting in gait disturbance. Hip radiography revealed a fracture of the basal portion of the stem neck, and a revision hip arthroplasty was performed. Analysis showed that the fracture developed from the site of a rectangular notch serving as a gripper made at the stem neck. Therefore, the fracture might be caused by stress concentration at the rectangular part and the resultant metal fatigue. Implants with such design may be associated with breakage even a long time after bipolar head prostheseis.
