Background/Purpose:  Wear, osteolysis, and late aseptic loosening associated with ultrahigh-molecular-weight polyethylene components used in total hip arthroplasties (THA) have led to increased interest in metal-on-metal (MOM) prostheses. The availability of large-diameter metal femoral heads results in increased range of motion, reduced potential for femoral neck impingement on the acetabular rim. Despite the potential advantages, however, a continuing concern with MOM articulation is the release of metal ion debris locally and systemically in patients’ blood and urine. These metal-metal wear-related complications include formation of pseudotumors, metalosis, and soft tissue necrosis. This study reports midterm outcome of THA with a Pinnacle (DePuy, Japan) modular MOM acetabular prosthesis.

Methods: From 2006 to 2008, primary THA, 86 primary THA (80 patients) were performed using a Pinnacle (DePuy, Japan) modular MOM acetabular prosthesis. There were 14 men and 72women with the mean age of 62.4 years. The preoperative diagnosis of most patients was osteoarthritis. Clinical hip function outcomes were evaluated using the Japanese Orthopaedic Association (JOA) hip score at preoperative and final follow-up. A perfect JOA hip score is 100 and the worst score is 0. Radiological analysis was performed at final follow-up. And the potential of MRI was examined for screening of pseudotumors following MOM THA. MRI was conducted in all hips postoperatively.

Results:  Eight patients (9 hips) were lost before their 6-year follow-up. So, 77 THA (72 patients) were evaluated at mean 7.2-year follow-up (range 6-9.1 years). The mean (± SD) preoperative JOA hip score of 45.2 (± 12.2) improved significantly to 86.5 (± 10.7) postoperatively at final follow-up. Four patients (4 hips) experienced problems with dislocation but no recurrent instability. An additional 1 patient (1 hip) was infected at 3.5-year after primary arthroplasty. The infected THA eventually led to removal of the stem and liner, and was performed one stage revision THA. Fifteen patients (17 hips) were observed in pseudotumor attributable to the MOM articulation by MRI from 2-year to 5-year after arthroplasty. Four patient (4 hips) was switched to a metal-on-polyethylene articulation from 5.1-year to 8.1-year postoperatively due to development with pain and swelling. In the 4 patients, 3 patients were observed pseudotumor and 1 patient were not observed, but all patients were diagnosed as ARMD (adverse reactions to metal debris). In 18 patients with pseudotumor and/or revision surgery, we evaluated between 14 patients with not revision surgery and 4 patients with revision surgery. At radiological analysis the mean cup angle of inclination was significant higher in the patients with revision surgery. Kaplan-Meier survivorship for the THA construct in this group was constant at 96.1% at 6 years after arthroplasty.

Conclusion:  Clinical scores such as JOA score revealed excellent outcomes at mean 7.2-year follow-up. However, prevalence of pseudotumors per hip was 22.1%. The current cohort of patients will continue to be followed with special attention being paid to any potential local tissue reaction or other complications resulting from metal wear debris.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/midterm-outcome-of-modular-metal-on-metal-total-hip-arthroplasty/