Joint Space Predicts THA After Hip Arthroscopy in Patients 50 Years and Older

All patients considering joint-preserving hip arthroscopy should be educated on the risk of THA after arthroscopy. The degree of radiographic osteoarthritis predicts subsequent THA. To provide patients with the best information, the best radiographic measure that predicts THA after hip arthroscopy should be identified. We therefore determined if Tonnis grade, Kellgren-Lawrence grade, or joint space narrowing was superior in predicting THA after hip arthroscopy. We retrospectively reviewed 203 patients 50 years of age or older treated with hip arthroscopy between March 2007 and October 2010. Of these, 96 patients met the study inclusion criteria. Sixty-five did not undergo THAs during the followup time (non-THA group) and 31 patients did (THA group). We determined Tonnis grade, Kellgren-Lawrence grade, and/or joint space narrowing before arthroscopy. The median followup for the non-THA group was 54 months (95% confidence interval, 49.9-58.9 months). In 81% of the patients, joint space accurately predicted THA or non-THA, whereas Kellgren-Lawrence was accurate in 73% and Tonnis grade was accurate in 65%. On binary logistic regression, the only predictor (r(2) = 0.45) of THA was joint space of 2 mm or less. Measuring joint space by determining if any measurement is 2 mm or less predicts patients progressing to THA after hip arthroscopy approximately 80% of the time. At this early time point, joint space measurements were the most accurate predictor of THA and should be used in patient education to define the risk of early failure from hip arthroscopy. Level III, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.