Total hip arthroplasty complicated by mismatched implant sizes. Report of two cases.

Numerous alternative types and sizes of implants for total hip arthroplasties are currently available. Two cases are reported in which the head size of the femoral component inserted was larger than the corresponding inner diameter of the acetabular cup. These are the first reported cases of this technical complication. The error can be avoided with careful preoperative planning and proper selection of implants. At 12- and 30-month follow-up evaluation, however, neither of these hips had dislocated or required revision. Immediate revision is not recommended, unless the hip dislocates or has symptomatic subluxations.