RADIOGRAPHIC EVALUATION OF DEVELOPING INSTABILITY OF THE MECRON CEMENTLESS, THREADED ACETABULAR PROSTHESES

Purpose. To evaluate radiographically the history of the Mecron acetab ular prosthesis. Material and methods: The pelvic radiographs of 350 c onsecutive 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 w as graded fr-om 0 (absent) to 3 (severe). Prostheses with grades 0 and 1 were considered stable and those with grade 3 with or without migra tion were presumed to be unstable. Results: At five years, 62 (62%) of the cups were un stable and only 23 (23%) were stable. The rate of mi gration was unacceptably high, and seen in 43 (43%) patients. Migratio n was only seen in prosthesis with a grade 3 demarcation. Conclusions: Demarcation visible on radiographs is an important sign of instabilit y of the prosthesis. With the grading system it is possible to evaluat e radiographically the history of the prosthesis.