Local infiltration analgesia or femoral nerve block for postoperative pain management in patients undergoing total hip arthroplasty. A randomized, double-blind study.

BACKGROUND AND AIMS: Several methods for pain management following total hip arthroplasty (THA) have been described but the best postoperative pain management technique remains uncertain. We compared surgeon applied local infiltration analgesia (LIA) with anaesthesiologist performed femoral nerve block (FNB) using ultrasound. The primary aim was to assess pain intensity 24h after THA.

METHODS: In this randomized, double-blind study, 56 patients (ASA I-III) undergoing THA consented to participate. In Group FNB, patients received an ultrasound-guided femoral nerve block using 30ml of ropivacaine 7.5mg/ml (225mg) while Group LIA received a similar volume of saline. Spinal anaesthesia was then performed and bupivacaine heavy, 3-3.5ml injected depending on patient characteristics. During surgery, patients in Group LIA received a mixture of 300mg (150ml) ropivacaine, ketorolac 30mg (1ml) and adrenaline 0.5mg (0.5ml) (total volume 151.5ml) peri-articularly and subcutaneously while Group FNB received 151.5ml of saline peri-articularly in a systematic way by the surgeon. A multi-hole catheter was placed with the tip placed intra-articularly at the end of surgery in both groups. After 23h, the LIA mixture consisting of 20ml ropivacaine (7.5mg/ml), ketorolac 30mg (1ml), adrenaline 0.1mg (1ml) (total volume 22ml) was injected in Group LIA and the same volume of saline in Group FNB. Postoperative pain, analgesic consumption (postoperative and post-discharge), side effects, home discharge, quality of life and hip function were recorded, the latter up to 6 months after surgery.

RESULTS: Postoperative pain intensity was significantly lower in Group LIA compared to Group FNB during mobilization at 24h (primary endpoint), mean difference 1.8 NRS units (95% CI 0.7-2.9) (P=0.006), at rest after 4h (P=0.029) and on standing after 24 (P=0.0003) and 48h (P=0.043). Rescue morphine consumption was also significantly lower in Group LIA during 0-24, mean difference 13.5mg (95% CI, 6.1-20.9) (P=0.002) postoperatively. Motor block was greater at 6h (P=0.029) postoperatively in Group FNB. Two patients (one in each group) had persistent post-surgical pain (NRS>3) at 3 months (3.6%) but none at 6 month. No other differences were found between the groups.

CONCLUSION: Local infiltration analgesia significantly reduces pain intensity on standing and mobilization, and rescue analgesic consumption compared to femoral nerve block without causing significant side effects. The superior analgesia in the LIA group may result from the secondary injection at 23h postoperatively and needs to be further evaluated in future studies. No differences were found in home discharge, quality of life and hip dysfunction between the groups.

IMPLICATION: Local infiltration analgesia is the preferred method for postoperative pain management following THA compared to single-shot femoral nerve block.