ION-IMPLANTED TITANIUM HEADS AND METALLOSIS

Abstract

Purpose: Although hip prosthesis heads made of titanium are no longer implanted to our knowledge, it is important to officially record the failures related to their use. Device monitoring experts can only prove the hazard resulting from these implants if results of human clinical series have clearly described the inconveniences. We found a rich body of literature dating from the end of the eighties that concluded that the rate of wear with the polyethylene lined titanium implants was very low but have found no paper describing the problems related to its use. We report this work to fill the gap.

Material and methods: This prospective study included a consecutive series of the first 100 total hip prostheses using the ion-implanted titanium 22.2 mm head (NITRU-VID) implanted between January 30, 1990 and June 19, 1991. There were 45 men and 55 women, 55 right hips and 45 left hips implanted for primary degenerative disease in 92, dysplasia in two and congenital dislocation in six. Mean age at implantation was 60 years (28–82). The same operative technique was used for all patients using the same Atlas-PSM implant. Eleven patients died and six were lost to follow-up. Thus 83 ere retained for analysis with the Postel-Merle-d’Aubigné (PMA) score on the AP and lateral views of the hip. Kaplan-Meier survival curves were established.

Results: Eleven patients underwent revision surgery for different causes, metallosis in seven. The delay to revision for metallosis was eight years in two, nine years in one and ten years in four. These cases of metallosis were expressed clinically by moderate pain and minimal radiographic signs: bone defect in the greater trochanter in seven, acetabular lines in three. Four cups loosened, none of the femur components. The diagnosis of metallosis was made at revision in five cases, and on the basis of hip biopsy in two. Metallosis was intense with black coloration of all the tissues. Pathology confirmed the diagnosis; the head were depolished with wear of the upper pole and loss of spherical shape as verified in the laboratory. The 10-year survival was 91.33%. For the 72 patients who did not have revision surgery, only nine still had moderate pain and four limped. There were eleven cases with trochanteric defects in zone 3 requiring close follow-up as this can be an early sign of metallosis.

Discussion: This study proves that despite the ion-implantation, the heads wear and lead to metallosis. No metallosis was observed when using the same implants with different heads at a maximal follow-up of 14 years. In an earlier study on the first 100 implants of this type, the 10-year survival was 98.7%. The drop in the 10-year survival from 98.7 to 91.33% can only be explained by the ion-implanted titanium heads.

Conclusions: Ion-implanted titanium heads wear and lead to metallosis. Their use is formally contraindicated. Hip biopsy can provide early diagnosis of metallosis.