In patients undergoing ultrasound-guided fascia iliaca compartment blockade before knee replacement surgery, does the addition of hyaluronidase to the local anaesthetic solution improve the success rate and hasten the onset of the nerve blockade?

We aim to investigate the effect of the drug hyaluronidase on the efficacy of ultrasound-guided fascia iliaca compartment block (FICB). Hyauluronidase is a naturally occurring enzyme that it available as a drug. It possesses spreading properties and it is used as a pharmaceutical agent to facilitate the dispersion of drugs and other substances. It has been proven to be effective in enhancing ocular regional anaesthesia but it has not been adequately studied in peripheral regional blockade. FICB is a safe and effective method of lumbar plexus regional anaesthesia. The goal of FICB is to provide femoral nerve, lateral cutaneous nerve of the thigh and obturator nerve block. While the femoral nerve and lateral cutaneous nerve of the thigh are reliably blocked by FICB the overall success rate of the block is limited by obturator nerve anaesthesia which is successful in only ~44% of ultrasound guided FICB - presumably due to the distance the local anaesthetic must traverse from its site of infiltration to reach this nerve. We hypothesise that adding hyaluronidase to a plain 0.5% ropivacine local anaesthetic solution will increase the success of FICB - chiefly the proportion of patients achieving obturator nerve anaesthesia (weakness of thigh adduction). We will also study effects on the speed of onset and blood levels of co-administered local anaesthetic. An improvement in the success of FICB should improve post-operative pain after knee replacement. If proven, there may also be other peripheral nerve block procedures that may benefit from the addition of hyaluronidase.