Analysis of the Primary Outcome for the Study: Ultrasound Guided Fascia Iliaca Block Versus Spinal Opioid for Analgesia After Primary Hip Arthroplasty

Introduction : The optimal anaesthetic technique for total hip arthroplasty (THA) is yet to be established. Fascia iliaca blocks and spinal opioids are analgesic strategies that provide intra- and post-operative analgesia. Fascia iliaca block provides blockade of the main nerves supplying pain to the hip. Ultrasound guidance has increased success rates (1). We proposed a randomised, controlled, double blind, non-inferiority study to compare ultrasound guided fascia iliaca block with spinal morphine for analgesia provision after THA. Methods: IRB approval was granted and informed consent obtained from all participants. Study methodology including a priori statistical analysis was published prior to commencement. The trial was registered with clinicaltrials.gov (NCT01217294)(2). Patients were assigned to either Group Fascia Iliaca (FI) or Group Spinal Morphine (SM). Patients in Group FI received spinal anaesthesia with hyperbaric bupivacaine and no spinal morphine plus ultrasound guided fascia iliaca block with 2 mg/kg levobupivacaine diluted to 40 ml with sterile saline. Patients in Group SM received spinal anaesthesia as above with spinal morphine 100 mcg and “sham” ultrasound guided fascia iliaca block with 40 ml sterile saline. Post-operative analgesia included paracetamol 1 g qds and morphine patient controlled analgesia (1 mg bolus, 5 minute lockout). Pre-operative analgesics were continued. Primary outcome was 24 hour post-operative morphine consumption. Statistical analysis was performed using R studio Version 0.98.953 © 2009-2013. Both intention to treat and ‘as treated’ analyses were performed. Results: From May 2011 to April 2014, 108 patients were recruited and randomised. Five patients were withdrawn (Figure 1). Patient demographics were similar between groups (Table 1). Median 24 hour morphine consumption was calculated for each study group. The difference between medians was calculated employing a bias correcting bootstrapping technique with 10,000 replications. The difference was 25mg (95% CI 9.0 - 30.5mg) in the 'as treated' analysis and 24mg (95% CI 14 - 29mg) in the ITT analysis. This is greater than the pre-specified non-inferiority margin (δ = 10mg) and is displayed in Figure 2. Conclusions: Ultrasound guided fascia ilaca block is significantly worse than spinal morphine in the provision of analgesia after THA. From these data, we would not recommend to replace spinal morphine with ultrasound guided fascia iliaca block.