Major orthopaedic surgery is painful and requires safe and effective postoperative analgesic therapy. The successful use of continuous peripheral nerve blocks provides sustained analgesia while minimizing the need for opioid analgesics throughout the postoperative period and avoiding the side effects associated with central neuraxial techniques. Excellent analgesia can be maintained and opioid-related side effects avoided allowing improved rehabilitation. However using existing methods a failure rate of >20% significantly limits the analgesic benefits in a substantial proportion leading to uncontrolled pain and side effects of opioid analgesics.

A major concern with the use of continuous peripheral nerve blocks is difficulty in placement of the catheters close enough to the nerve to allow for effective local anaesthetic spread and therefore analgesia. The benefit of ultrasound to precisely place needles adjacent to nerves and increase efficacy of block success is undisputed. However ultrasound is of less help in accurately placing catheters. Indeed the final position of the catheter tip is not predictable and can be inadequate in 10%-50% of cases. The explanation for that is the material in currently used catheters is stiff and designed to avoid kinking. Unfortunately this same stiffness often leads to inadequate placement of the catheter tip. We have developed a catheter which coils up as soon as it is advanced beyond the needle tip, thus allowing the catheter tip to remain close to the initial needle tip position and therefore the nerve. The aim of this prospective randomized double blind controlled study is to determine the effectiveness of this new catheter in comparison with standard of care methods for continuous femoral nerve block commonly used after total knee arthroplasty. The primary outcome measure will be the incidence of catheter related block failure 24 hours after surgery. Our hypothesis is that the coiled catheter will significantly improve the efficacy of continuous femoral nerve block as compared to existing techniques.

Aims of the study The aim is to determine the effectiveness of a the coiled catheter for continuous peripheral nerve block after total knee arthroplasty based on secondary block failures compared to the secondary block failures of the conventional, currently used stimulating catheters.

Study design The trial is a prospective single-centre randomized double-blinded controlled trial. Patients will be randomized to (1) use of conventional stimulating catheters or (2) to use of a coiled catheter.

Patient population Adult patients of at least 18 years of age undergoing unilateral knee arthroplasty, under spinal anaesthesia will be recruited in this randomized double blind controlled trial.

Inclusion criteria: Ability to provide informed consent, understanding of the possible local anaesthetic-related complications, and understanding of the study protocol.

Exclusion criteria: Any contraindication to peripheral nerve block, allergy to local anaesthetics, infection near the insertion site, ASA classification IV or V, pregnancy, chronic opioid analgesic therapy (>30mg morphine equivalent per day), coagulopathy, known hepatic or renal insufficiency, peripheral neuropathy and patient refusal.

Inclusion Criteria:

Ability to provide informed consent, understanding of the possible local anaesthetic-related complications, and understanding of the study protocol.

Exclusion Criteria:

Any contraindication to peripheral nerve block, allergy to local anaesthetics, infection near the insertion site, ASA classification IV or V, pregnancy, chronic opioid analgesic therapy (>30mg morphine equivalent per day), coagulopathy, known hepatic or renal insufficiency, peripheral neuropathy and patient refusal.