Intra-articular Diagnostic Injection Exhibits Poor Predictive Value for Outcome After Hip Arthroscopy

Purpose To determine whether the amount of pain relief after preoperative intra-articular (IA) anesthetic injection predicts clinical and functional outcomes after hip arthroscopy, especially when controlling for the presence of chondral degeneration. Methods We identified patients who underwent IA injection and subsequent hip arthroscopy for labral pathology between 2007 and 2013 performed by a single surgeon. Inclusion criteria were ultrasound- or fluoroscopic-guided IA anesthetic injection performed at our institution, prospectively documented pre- and postinjection numerical rating scale pain scores, and minimum 1-year follow-up postoperatively. Patients were divided into 2 groups, those who received >50% pain relief from preoperative IA anesthetic injection and those who received ≤50% relief. Preoperative radiographs were reviewed, and degree of osteoarthritis was determined using the Tonnis classification system. Outcomes were assessed with Modified Harris Hip Score and Hip Outcome Score (HOS). Univariate and multivariate models were performed to assess whether percent pain relief correlated with outcome. Results Of the 319 arthroscopic hip surgeries performed between 2007 and 2013, 115 (37%) patients were lost to follow-up, 16 (5%) patients did not receive an IA injection, 16 (5%) patients had an injection containing gadolinium, and 40 (13%) patients completed injections at an outside institution. Five (2%) patients were excluded for a history of ipsilateral hip surgery, and 3 (1%) for a history of contralateral hip surgery, leaving 96 hips in 96 patients. There were 71 females (74%) and 25 males (26%) with a mean age of 37.6 ± 14.0 years. Tonnis was grade 0, 1, and 2 for 26 (27%), 55 (56%), and 16 (17%) patients, respectively. Fifty-one (53%) of the injections contained a corticosteroid. The mean pain relief after IA injection was 73% ± 36% (range, 0% to 100%). Twenty-six hips (26%) had ≤50% pain relief, whereas 70 (73%) had >50% pain relief, and the median time interval from injection to surgery was 3 (range, <1 to 20) months. Outcome scores were obtained at a mean 14.8 (range, 11 to 30) months after arthroscopic surgery. Postoperative mean Modified Harris Hip Score, HOS activities of daily living, and HOS-Sport scores were 79.2 ± 17.3, 82.6 ± 17.3, and 67.4 ± 28.2, respectively. There was no statistical correlation between percent pain relief and outcome. There was no significant difference in outcome scores between those with ≤50% and >50% pain relief. Multivariate regression analysis showed no significant predictors of outcome, including age, gender, Tonnis grade, percent relief with IA injection, or type of surgery. Conclusions In this study of patients undergoing hip arthroscopy for labral pathology, our data indicate that the amount of pain relief from IA injection may be a poor predictor of short-term outcome, even when adjusting for chondral degeneration. Although anesthetic injections can be an important diagnostic tool in select patients, a combination of the clinical history, physical examination, and imaging findings is fundamental. Level of Evidence Level IV, therapeutic case series.