A725. DELAYED REACTION OF METAL-ON-METAL BEARINGS IN TOTAL HIP REPLACEMENT (THR) AFTER 12 YEARS FOLLOW-UP:

Abstract

Objectives: To evaluate the outcome of a cementless, low carbon MOM (metal on metal) THR with a 28mm ball-head (PPF STRATEC-SYNTHES, since 2002 BIOMET) and the concentration of metal ions within the intra-articular fluid.

Methods: 173 unilateral MOM THR’s performed in 1995 were investigated. Average follow up time was 12 yrs (range 9–14yrs). During the study period there were, 11(6.4%) deaths, 2 (1.2%) lost to F.U. and 5 (2.9%) refused follow up x-rays because of lack of symptoms, and a self perceived perception that these were not necessary. 41 effusions in part of this group could be analysed for levels of Co, Cr and Ni.

Results: 112 THR’s (64.7%) were completely symptom free and did not show any signs of osteolysis. 7 THR’s had revision surgery, unrelated to metallosis (1 cup loosening, 1 early infection and 5 late infections that could be attributed to a large amount of necrotic tissue within the joint space). 36 hips (20.8%) showed over time, progressive signs of a metallosis. Clinically none or moderate complaints in the groin were reported, and massive effusions of up to 90ml were present. The osteolysis began in the majority of these cases in the periosteal region of the acetabulum and the trochanter. No loosening of the implants was seen. A quarter of these implants had late dislocations. The CRP was up to three times above normal levels. Only 26 patients (15.0%) could be convinced to undergo further surgery (synovectomy, exchange of head and liner and bone grafting as required). Typical histology showed massive necrosis within the joint and a peri-vascular infiltrate of CD-3 pos. activated T-lymphocytes and L26 pos. B-lymphocytes. These findings have been recently published as ALVAL.

In the 41 joint effusions, the mean level of Co was 595.6 μg/l (max 4802.2), Cr 481.1 μg/l (max 4602.9) and Ni 3.7 μg/l (max 14.4). The serum ion levels were up to four times the maximal permitted level (Co 3 μg/l, Cr 3 μg/l, Ni 3 μg/l).

Conclusion: High levels of toxic metal ions in the joint space over time can lead to a severe allergic reaction and tissue necrosis.

The current literature reports, that almost all MOM bearings show slightly elevated serum metal ion levels, and therefore a much higher concentration must be calculated within the joint space. In our experience, because of the serious consequences and unpredictable onset of metallosis, we no longer use MOM articulations.