Radiographic evaluation of developing instability of the Mecron cementless, threaded acetabular prostheses

Summary PURPOSE: To evaluate radiographically the history of the Mecron acetabular prosthesis. MATERIAL AND METHODS: The pelvic radiographs of 350 consecutive patients with a smooth threaded acetabular prosthesis type Mecron were retrospectively evaluated (follow-up 1 to 6 years, mean 4 years). A demarcation zone seen at the medial side of the prosthesis was graded from 0 (absent) to 3 (severe). Prostheses with grades 0 and 1 were considered stable and those with grade 3 with or without migration were presumed to be unstable. RESULTS: At five years, 62 (62 %) of the cups were unstable and only 23 (23 %) were stable. The rate of migration was unacceptably high, and seen in 43 (43 %) patients. Migration was only seen in prosthesis with a grade 3 demarcation. CONCLUSIONS: Demarcation visible on radiographs is an important sign of instability of the prosthesis. With the grading system it is possible to evaluate radiographically the history of the prosthesis.