Abstract
Introduction
This study reports outcomes of 35 revisions of a recalled metal-on-metal (MOM) monoblock prosthesis performed by a single surgeon.
Methods
We prospectively collected data on all patients who underwent revision of a recalled metal-on-metal monoblock prosthesis between 2010 and 2015. Average follow-up was 2.5 years post-revision and 6.9 years post-primary procedure. We evaluated the cohort for age, BMI, gender, existence of medical comorbidities, and post-op complications. We compared pre and post-revision cup abduction angles, anteversion angles, combined angles, cup sizes, and Harris Hip Scores. Cobalt and chromium levels were followed throughout the study period for each patient.
Results
Thirty-one patients underwent 35 revisions surgeries for pain, high metal ions, infection, aseptic loosening, failure of ingrowth, leg length discrepancy and/or pseudotumor. Two of these revisions were subsequently re-revised – one for continued pain and one for failure involving multiple dislocations, breakage of screws, and acetabular fracture. The survival rate for our revisions to date is 94.3%. Female patients comprised a majority of revisions (54%) despite comprising a minority (28%) of primary hip replacements using the studied prosthesis. Revised patients were an average of 51.8 years of age with a BMI of 31.07. Demographics are included on Table 1. There were five post-operative complications, including 2 infections, 2 dislocations, and one DVT. Cups were revised from a mean abduction angle of 47.5° in primary hips to 42.3° in revisions. Cups were revised from a mean of 53.4 to 57.8. Cobalt and chromium levels were followed in all patients and showed significant decrease after revision (Graph 1). Cobalt levels decreased from an average of 33.7 to 13.1 ng/mL while Chromium levels decreased from an average of 12.4 to 9.2 ng/mL. Harris Hip Scores increased significantly after revision (45.8 to 72.1).
Conclusion
This study presents 35 revisions of a recalled monoblock hip prosthesis performed by a single surgeon at our institution from 2010 to 2015. To our knowledge, this is the largest single-surgeon study reported in the literature. Acetabular cups were revised to a lower average abduction angle. Patients have had significant improvements in Harris Hip Scores and significant decreases in Cobalt and Chromium levels after revisions. Our revision survival rate to date is 94.3% at an average of 2.5 years (range 2 weeks – 4.3 years).
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