Fascia iliaca block for primary hip arthroplasty – a reply

We commend Kearns et al. for their excellent randomised controlled trial that found ultrasound-guided fascia iliaca block (FIB) provided significantly worse analgesia than spinal morphine in the first 12 h (numeric rating scale) and 24 h (cumulative postoperative 24-h morphine consumption) after total hip arthroplasty [1]. The authors explain this finding by noting correctly that sacral nerve innervation of the postero-inferior hip joint is not affected by FIB. We would like to invite the authors to comment on other reasons that we think might have resulted in inferior analgesia after FIB. Firstly, the methods describe an ultrasound-guided FIB with 40 ml levobupivacaine administered cranially out-of-plane below the inguinal crease and laterally to the femoral nerve. The efficacy of the block was not assessed, and the authors acknowledge that this was a weakness of their study. We suggest that more reliable block of the lateral cutaneous nerve of the thigh is achieved by positioning a linear ultrasound probe 2 cm inferomedially to the anterior superior iliac spine angled towards the umbilicus and injecting 40 ml levobupivacaine in-plane just inferior to the ‘bow-tie’ knot at the confluence of internal oblique and sartorius muscles [2]. Assuming a block failure rate of 5% by a trained anaesthetist, insufficient postoperative analgesia might be expected in ~2–3 of the 54 FIB group participants. Could we invite the authors to re-analyse their comparison, omitting data suggestive of failed blocks (e.g. a mean numeric rating score 7 or more at 3 h and 6 h), to compare functioning FIB and spinal morphine? Secondly, not all surgeons use an anterolateral incision for total hip arthroplasty. Nationally, approximately 70% of incisions are posterior (2015 data, [3]) and may not be anaesthetised by blocking the lateral cutaneous nerve of the thigh as part of a FIB. Can the authors provide data about the type of incision used, and re-analyse their data to compare FIB vs. spinal morphine in patients who only received non-posterior incisions, provided any new sample size is sufficiently powered to do so? Thirdly, can we invite the authors to comment on why patients over the age of 85 were excluded from the study, given that ~13,000/85,000 (15%) of patients undergoing primary total hip arthroplasty are over 80 years of age (~5% > 85 years) (2015 data, [4]). Do the authors think that their results/conclusions would have been affected by the inclusion of data from this age group? Given the variety of approaches used in primary total hip arthroplasty and the disparate innervation of the hip, it is perhaps not surprising that FIB is not as effective a postoperative analgesic technique as spinal morphine. However, we would like to encourage the authors to use their research framework experience to conduct further similar trials involving comparison between local anaesthesia infiltration and spinal morphine in primary hip arthroplasty, between FIB and spinal morphine, and between spinal morphine and diamorphine, in both dynamic hip screw insertion and hemi-arthroplasty operations for hip fracture. S. White P. Stott Royal Sussex County Hospital, Brighton, UK Email: stuart.white@bsuh.nhs.uk