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.

The development of metalosis is a not commonly reported complication after THR. The exact reasons are still unknown, but hypersensitivity reaction is favored ahead of toxic effects, immune defects and exogen causes. The phenomenon of metalosis occurred at an unpredictable time in situ and is often misinterpreted as a low grade infection.

In a retrospective study, we analysed all 173 (102 women and 71 men) primary and single cement less PPF THR (STRATEC®) with metal-on-metal (low carbide 0.08%) articulation of 1995. One patient was lost to follow-up, 18 patients were deceased. The average age at the time of surgery was 63.3 years and the follow-up time was 115 months.

40 (23.1%) metalosis cases were observed. Revision was done in 29 (16.8%) patients: three femur fractures, five cases of infection and 21 cases of metalosis. The median HHS at follow-up was 95. 18 cases (10.4%) had metalosis signs: six patients (3.2%) had periprosthetic osteolysis and pain, 16 patients (9.2%) had osteolysis without pain and nine patients (5.2%) had pain without osteolysis in the radiographs. Pain caused by metalosis typically occurred inguinal and at an average time of thirty months postoperatively. Dislocation was observed in 13 cases at an average time of 44 months with an average cup inclination of 48°. Extensive necrosis and diffuse lymphoplasmacytic infiltrates were noted. In most cases the bursa ileopectinea was highly filled and in this synovial fluid extremely elevated levels of chrome (32 – 46095 μg/l) and cobalt (30 – 67410 μg/l) were detected.

Since 2003, we do not implant or recommend metal-on-metal for THR anymore. Close radiographic and computertomographic monitoring with high mark on typical osteolysis and exact clinical evaluation is recommended for metal-on-metal THR. Patients without symptoms with severe osteolysis must be detected, and head and inlay changes must be performed.