Abstract
Introduction
This study reports outcomes of primary and revision total hip arthroplasties of a recalled metal-on-metal (MOM) monoblock prosthesis performed by a single surgeon.
Methods
We performed a retrospective review of all patients who underwent both primary and revision total hip arthroplasties at our institution between 2006 and 2014. Only those patients who underwent primary recalled MOM monoblock prosthesis placement and/or revision of the recalled prosthesis were included. We evaluated revision group versus non-revision group for age, BMI, gender, existence of medical comorbidities, primary cup abduction and anteversion, primary combined angle, post-operative complications, cobalt and chromium ion levels, and Harris Hip Scores. Student t-test was used to compare groups.
Results
During the study period, 105 patients underwent 115 primary total hip arthroplasties with the recalled system. Thirty-six patients underwent 40 revisions surgeries for pain, high metal ions, infection, aseptic loosening, failure of ingrowth, and/or pseudotumor. The revision rate was 34.8%. Except for a higher percentage of women undergoing revision (17.4% vs 50%, p=0.0002), there were no significant differences in patient demographics, medical comorbidities, or pre-operative Harris Hip Scores (Table 1). Revision group showed higher cup abduction angles (47.8 vs 42.4, p = 0.005), smaller average cup size (53.3 vs. 55.2, p = 0.003), smaller average femoral component size (4.7 vs 5.6, p = 0.02, respectively), and lower post-operative Harris Hip Scores (87.9 vs 93.8, p = 0.0007). The revision group had higher cobalt levels (34.5 vs 5.8, p = 0.00003) and higher chromium levels (14.0 vs 1.3, p = 0.00003). There were five post-operative complications in the revision group (2 infections, 2 dislocations, and one DVT) versus one DVT in the non-revision group (p=0.01). Harris Hip Scores for revision surgeries increased from a mean of 44.2 pre-operatively to 74.9 post-operatively (p=1.45×10−5).
Conclusion
This study presents 115 primary total hip arthroplasties and 40 revisions performed by a single surgeon at our institution. To our knowledge, this is the largest single-surgeon study reported in the literature. Hips requiring revision had significantly higher cup abduction angles, smaller cup and femoral component sizes, lower post-operative Harris Hip scores, and higher metal ion levels. Age, BMI and comorbidities did not contribute to revision in our study; however, there was a higher chance of undergoing revision if you are a woman (p=0.0002). There was a 30.7 mean improvement in Harris Hip Score after revision.
