Catastrophic stem taper wear in ceramic on polyethylene bearing couple: a case report.

A severe abrasion occurred at the stem taper 13 years after total hip arthroplasty. The bearing couple was 28 mm ceramic on polyethylene. The ceramic head had almost no damage, whereas the stem taper had severe damage. An ectopic bone probably contributed to the abrasion. The ectopic bone had grown to restrict the normal motion in the bearing couple and all stress and torque seemed to concentrate in the junction until the junction obtained mobility instead of the original bearing couple.