Pre-Operative Femoral Nerve Block for Hip Arthroscopy: A Randomized Controlled Trial

OBJECTIVES: : Arthroscopy has become a standard method of treatment for a variety of intra-articular hip pathologies. While most arthroscopic hip procedures are performed as day-surgeries, patients can still experience significant post-operative pain and opioid-associated side-effects. Our group has shown the potential benefits of preoperative femoral nerve block (FNB) in a previous retrospective review. It was our objective to confirm these findings in a prospective study. METHODS: Fifty patients undergoing hip arthroscopy were included in this prospective, single centre, double-blinded, randomized controlled trial. All patients received a pre-operative ultrasound-guided femoral nerve block with either 20 mL of 0.5% bupivacaine (treatment group, n=27) or normal saline (control group, n=23). Nerve blockade was confirmed via standardized sensory testing prior to the induction of general anaesthesia. Groups were compared with respect to patient sex, age, body mass index (BMI), physical status classification according to the American Society of Anaesthesiologists (ASA); procedure performed; and opioid requirements. The primary endpoint was total oral morphine equivalent consumption in 24 hours. Secondary endpoints included visual analog pain scores; Quality of Recovery (QoR-27) score at 24 hours; incidence of nausea and vomiting; patient satisfaction; and block-related complications. RESULTS: There were no significant differences between groups with respect to sex, age, weight, height, BMI, ASA classification, or type of procedures performed. Total oral morphine consumption at 24 hours was similar between groups. Patient-reported pain scores were lower at all times points in the femoral nerve block group compared to the placebo group with statistical significance reached at 30 minutes, 1 hour, 2 hour, 4 hour, and 6 hours post-operatively. There was no difference in the rates of nausea and vomiting after surgery, Quality of Recovery score at 24 hours, time to discharge, or symptoms of itching, weakness, and injection site bruising and pain. The placebo group had a significantly higher rate of reported constipation at 48 hours. 6 out of 27 patients in the femoral nerve block reported falls (without injury) at 24 hours compared to 0 out of 23 patients in the placebo group. The satisfaction score, however, was similarly high in both groups at all time-points. CONCLUSION: Pre-operatively administered femoral nerve blocks lead to decreased pain scores in the early post-operative phase without affecting opioid consumption or opioid-related side effects. Patient satisfaction with pain control was similarly high between groups. Given the rate of falls observed in this study, we cannot recommend the routine use of femoral nerve blocks for outpatient hip arthroscopy.