Does Relief from Intra-articular Anesthetic Injection Predict Outcome after Hip Arthroscopy?

OBJECTIVES: Arthroscopy is being used more frequently as a treatment for intra-articular hip pathology due to femoroacetabular impingement (FAI). Prior to surgery, intra-articular anesthetic injection is commonly performed as a diagnostic test to localize the source of pain. Currently, there is a paucity of data correlating post-injection pain relief and functional outcomes after hip arthroscopy for FAI. The purpose of this study is to determine whether the amount of pain relief after preoperative intra-articular anesthetic injection predicts clinical and functional outcomes following hip arthroscopy with minimum one year follow-up. We hypothesize that increased pain relief (>50%) will correlate with better outcomes after surgery. METHODS: The records of patients undergoing hip arthroscopy for FAI at our institution between April 2007 and April 2012 were reviewed. We identified patients who underwent pre-operative intra-articular anesthetic injection and subsequent hip arthroscopy. Inclusion criteria were: ultrasound or fluoroscopic guided intra-articular anesthetic injection performed at our institution, documented pre- and post-injection Numerical Rating Scale (NRS) pain scores, no prior ipsilateral hip surgery, and minimum 1 year follow-up. Pre-operative radiographs were reviewed and degree of osteoarthritis was determined using the Tonnis classification system. Outcomes were assessed with Modified Harris Hip Score (MHHS) and Hip Outcome Score (HOS). Univariate and multivariate models were performed to assess whether percent pain relief correlated with outcome scores. RESULTS: 57 hips in 55 patients met our inclusion criteria and included 37 females (67%) and 18 males (33%) with a mean age of 42.6 ± 14.7 (range 15-68) years. 8 patients had Tonnis grade 0, 35 had Tonnis grade 1, and 14 had Tonnis grade 2. Mean pain relief after intra-articular injection was 74.4 ± 31.9 (range 0-100) percent. 13 patients (23%) had ≤50% pain relief while 44 (77%) had >50% pain relief. Outcome scores were obtained at a mean 25.5 (range 12- 60) months. Mean MHHS, HOS-ADL, and HOS-Sport scores were 82.1 ± 17.4 (range 42.9-100), 85.0 ± 16.6 (range 39.7-100), and 71.8 ± 28.1 (range 11.1-100) respectively. There was no correlation between percent pain relief and MHHS, HOS-ADL, or HOS-Sport scores. There was no significant difference in outcome scores between those with ≤50% and >50% pain relief. When adjusting for Tonnis grade there was no correlation between percent relief and any of the outcome scores measured. CONCLUSION: In patients undergoing hip arthroscopy for FAI, our data indicates that the amount of pain relief from intra-articular anesthetic injection does not correlate with minimum 1 year clinical and functional outcomes even when adjusting for Tonnis grade. Although pain relief did not predict outcomes in our study, we still believe it is a useful diagnostic tool to localize the source of pain in patients considering hip arthroscopy.