BACKGROUND: Peripheral regional nerve blocks are commonly used for pain management after lower extremity surgery, but motor blockade can be a significant concern. The lateral femoral cutaneous nerve (LFCN) is a purely sensory nerve from the lumbar plexus. We hypothesised that an LFCN block would reduce movement-related pain after total hip arthroplasty (THA) in patients with moderate-to-severe pain.

METHODS: Sixty patients with visual analogue scale (VAS) score > 40 mm during 30-degree active flexion of the hip on either the first or second postoperative day after THA were included in this prospective, randomised, blinded, placebo-controlled trial. Group A received an LFCN block with 8 ml of 0.75% ropivacaine followed after 45 min by an additional LFCN block with 8 ml of saline. Group B received an LFCN block with 8 ml of saline followed after 45 min by an additional LFCN block with 8 ml of 0.75% ropivacaine.

RESULTS: We found a difference of 17 mm (95% CI, 4-31 mm; P < 0.02) in VAS pain score during 30-degree flexion of the hip 45 min after the first block (primary outcome) in favour of group A. No other significant difference between groups regarding pain during mobilisation and at rest was found. The overall non-responder rate (< 15 mm pain reduction) was 42%.

CONCLUSIONS: LFCN block reduced movement-related pain in patients with moderate-to-severe pain after THA. The substantial non-responder rate limits recommendations of this block as part of a standard analgesic treatment regimen.