The Stability of the Porous Tantalum Components Used in Revision THA to Treat Severe Acetabular Defects

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Abstract
Background: The acetabular components used in revision total hip arthroplasty (THA) to treat severe acetabular bone defects have high rates of re-revision at mid to long-term follow-up. Early translation of acetabular components used in revision THA is a good predictor of later loosening, and radiostereometric analysis (RSA) is the most sensitive method to measure migration. The objectives of the present study were to use RSA to compare the migration of the porous tantalum acetabular components used to treat severe bone defects with the previously established acceptable proximal translation threshold of ≤1 mm within 2 years, and to determine the effect on migration of the addition of inferior screws through the component into the ischium or pubis. Methods: RSA was utilized to measure the migration of 55 porous tantalum components used to treat severe acetabular defects (28 Paprosky IIIA, 27 Paprosky IIIB; 21 hips with pelvic discontinuity) at a mean follow-up of 4 years (range, 2 to 12 years). Results: Forty-eight of the 55 components migrated less than the threshold that predicts later loosening (>1 mm) and 50 had not been re-revised at the time of the latest follow-up. Seven components, none of which had inferior screw fixation, exceeded the translation threshold. Of these, 6 were implanted to treat pelvic discontinuity. Of those 6 components, 5 were re-revised for loosening related to patient symptoms. At 2 years, the absolute median proximal translation of components with inferior screw fixation was |0.3| mm (range, |0.1| to |0.9| mm), compared with |0.4| mm (range, |0.03| to |16.4| mm) for those without inferior screws (p = 0.04). Conclusions: As measured with use of RSA, the majority of porous tantalum acetabular components used in a revision THA to treat severe acetabular defects had acceptable early migration. This predicts good long-term survivorship of these components. The use of inferior screws further improved acetabular component fixation. Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

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