Mid-Term Radiographic Analysis of Trabecular Metal Augments for Acetabular Bone Loss in Revision Hip Arthroplasty

Purpose: Acetabular bone loss during revision total hip arthroplasty (THA) poses a challenge for reconstruction as segmental and extensive cavitary defects require structural support to achieve prosthesis stability. Trabecular metal (TM) acetabular augments structurally support hemispherical cups. Positive short-term results have been encouraging, but mid- to long-term results are largely unknown. The purpose of this study was to determine the continued efficacy of TM augments in THA revisions with significant pelvic bone loss. Methods: Radiographs and medical records of 51 patients who had undergone THA revision with the use of a TM augment were retrospectively reviewed. Acetabular defects were graded according to the Paprosky classification of acetabular deficiencies based on preoperative radiographs and operative findings. Loosening was defined radiographically as a gross change in cup position, change in the abduction angle (>5°), or change in the vertical position of the acetabular component (>8 mm) between initial postoperative and most recent follow-up radiographs (Figure 1). Results: Eleven patients had incomplete radiographic follow-up and were excluded. The study population included 17 men and 23 women, averaging 68.1 ± 14.1 years of age (range, 37–91), with average radiographic follow-up of 19.0 months (range, 2.4–97.4). Reasons for revision included osteolysis (n = 20, 38.5%), component loosening (n = 18, 15.4%), and periprosthetic fracture (n = 6, 11.5%). All patients underwent revision THA using a TM multi-hole revision acetabular cup and TM acetabular augment(s) to fill bony defects. Morcellized allograft was used in 9 patients. There were 33 Paprosky Type IIIA and seven Paprosky Type IIIB defects. One patient with Paprosky Type IIIB had catastrophic failure of the reconstructive construct three months postoperatively. The remaining 39 acetabular revisions demonstrated signs of bony ingrowth at the latest follow-up. There were no radiolucent lines suggestive of loosening, and no significant differences in abduction angle (p = 0.78), vertical distance between the superolateral edge of the cup and the trans-ischial reference line (p = 0.96), or the vertical distance between the center of the femoral head and trans-ischial reference line (p = 0.75) between the initial postoperative and most recent follow-up radiographs (Figure 2). Discussion and Conclusion: Achieving fixation and long-term stability in THA revisions with segmental and/or cavitary bone loss is challenging. TM augments provide a modular structural system to achieve bony ingrowth, while avoiding large structural allografts, cages, and custom implants. At latest follow-up, 39 revision hips remained well-fixed with no evidence of loosening. One patient with a significant surgical history of infection, periprosthetic femur fracture, and 2 prior revision surgeries before acetabular reconstruction had an early clinical failure. Trabecular metal augments can be used for reconstruction of acetabular bone loss with good mid-term results. Continued follow-up is warranted for radiographic evaluation of bony integration and implant stability to determine long-term survivorship of these implants.