Abstract
Background
Large head metal on metal total hip arthroplasty MOM THA have been consistently shown substantial improvement in wear performance compared with metal on polyethylene articulations. Large diameter femoral heads theoretically can reduce dislocation risk by increasing range of motion before impingement, increasing prosthetic jump distance. However, early failure associated with adverse local tissue reactions (ALTRs) to metal debris is an emerging problem after MOM THA. The purpose of this study was to evaluate mid-term results of MOM THA.
Materials and Methods
Twenty-five patients, 28 hips were included in this study. The average age of the patients at the time of surgery was 66.9 years. Three patients were men and 22 were women. MOM THAs were performed using 28 PINNACLE Cup system (DepPuy) (C-STEM: 23, S-ROM: 5) with posterior approach and head size of 36mm. Twenty-five primary THAs due to osteoarthritis in 22 cases and rheumatoid arthritis (RA) in one, and two revisions due to recurrent dislocation THA patients, were performed. The average follow up was 56.7 months. Evaluation items are JOA score, cup anteversion /lateral opening angle, and complications. Indication of the system were applied for patients with high risk of dislocation such as recurrent dislocation in primary and/or THAs, posterior pelvic tilt, elderly, RA and mental disorders.
Results
The average JOA score improved from 48.3 (range: 26–77) preoperatively to 88.3 (range: 55–100) postoperatively. The average cup anteversion was 21.7 degrees (range: 2–38) and average lateral opening was 45.5 degrees (range: 37–60). Three patients (12%) developed dislocation. Two patients (8%) required reoperations from the deep infection. One female patient (4%) remained hip pain and was suspected pseudotumor / ALTR, which was confirmed by computed tomography and magnetic resonance imaging.
Conclusion
Large femoral head MOM THA was useful for patients with recurrent dislocation in revision THA. However, three patients developed dislocation in primary THAs (12% of primary cases), which suggested that the more accurate placement of the acetabular cup is important even in the large diameter cup. Although only one case (4%) revealed ALTR, however, continuous careful follow-up would be necessary in the MOM system.
