Surgical indications for hip arthroscopy continue to evolve in an effort to optimize long term survivorship and durability. Radiographic joint space narrowing less than 2mm is a well-established risk factor for conversion to total hip arthroplasty (THA) after hip arthroscopy; however, it is unclear why some patients convert early to THA compared to others. The purpose of this study was to determine which factors differentiate those patients who convert to THA within 2 years of hip arthroscopy compared to those who convert later than 2 years.
Included in this study were patients who underwent conversion to THA within two years of primary hip arthroscopy from a prospectively-collected patient registry from 2007 to 2017. Patients who underwent early conversions to arthroplasty were matched 1:1 with patients who converted after two years, based upon age and gender. Preoperatively outcome scores were collected including Short Form-12, modified Harris Hip Score, and Hip Outcome Score. Additionally, variables from the preoperative radiographic evaluation, surgical findings, and procedures performed were also compared.
Forty-nine patients were included in the early conversion group and were matched with forty-nine patients in the later conversion group. Patients with lateral center edge angle of less than 25° were more likely to be in the early failure group [OR: 3.9;95%CI: 1.01 to 15]. Patients with unipolar chondral defects on either the femoral (p = 0.128) or acetabular side (p = 0.656) were not at increased odds for early conversion compared to later conversion; however, those with bipolar chondral lesions at the time of surgery had increased odds of early conversions [OR:3.3; 95%CI:1.4 to 8] (p=0.01). Neither microfracture treatment (p = 0.666), labral reconstruction (p = 0.07), labral debridement (p = 0.298), preoperative intraarticular injection (p = 0.598), nor preoperative patient reported outcome measures were associated with early conversion.
Patients with low lateral center edge angles or bipolar chondral lesions seen at the time of hip arthroscopy are at increased risk for conversion to total hip arthroplasty within two years. Imaging modalities to more reliably and accurately predict these intraoperative findings are necessary to prevent unsuccessful surgeries.