Saphenous Nerve Block: Single Shot Versus Continuous Infusion to Supplement a Continuous Sciatic Nerve Block After Major Ankle Surgery

A Randomized Comparison of Single Injection vs. Continuous Saphenous Nerve Block to Supplement a Continuous Sciatic Nerve Block in Postoperative Pain Treatment After Major Ankle Surgery: Clinical Outcome and Cost Analysis

The most useful method to manage pain after major ankle surgery is infusion of local analgesics with a catheter close to the sciatic nerve.

Sensation from the ankle are carried by three nerves: The tibial and peroneal nerve (unified in the sciatic nerve) and the saphenous nerve.

Study purpose is to test whether continuous infusion of local analgesics by saphenous nerve catheter provide a better treatment of pain in comparison with a single injection nerve block. In addition cost-effectiveness of the two methods are compared.

The 50 patients of the trial are randomized in clusters of ten. We intend to do a preliminary analysis of the data from the first 40 patients. However, it is not an interim analysis. Fifty patients will be included independent of the result of the preliminary analysis. The random allocation of the last 10 patients will also be double-blinded.

Major ankle surgery are known to be very painful the first 48 hours after the operation due to surgical oedema. This pain is difficult to control with systemic analgesics. Pain relief with systemic analgesics requires high doses of intravenous opioids and is associated with breakthrough pain and adverse effects of opioids (sedation, nausea, vomiting, obstipation, urinary retention, respiratory depression).

Continuous, peripheral nerve block with catheter technique for two days minimizes the need for systemic analgesics. Today such a continuous sciatic nerve block is part of the standard pain treatment after major ankle surgery on Aarhus University Hospital. Despite accurate placement of the catheter many patients are in great pain because the saphenous nerve remain unaffected. A single injection block relieve the pain but a block with Ropivacaine only last 8-15 hours.

Severe postoperative pain leads to high opioid dosages, cognitive blurring, nausea, vomiting, reduced ambulation, increased surgical stress response and increased morbidity. Pain problems and adverse effects prolongs postoperative observation time and maybe also time to discharge.

The aim of the study establish whether continuous saphenous nerve block is efficient (pain relief or reduced opioid consumption) and justified (cost-effectiveness analysis) compared with single injection block.

Inclusion Criteria: Elective major ankle surgery

• total ankle arthroplasty
• subtalar fusion
• ankle fusion (non arthroscopic)

Exclusion Criteria:

• coagulation abnormalities
• infection in the region of needle insertion
• systemic infection
• preoperative consumption of high dose opioid
• preoperative sciatic or femoral nerve neuropathy
• preoperative sensory deficit in either of the lower extremities
• Charcot-Marie-Tooth disorder
• diabetic neuropathy
• severe peripheral vascular disease
• allergy to local anesthetics
• lack of understanding of Numeric Rank Scale (NRS)
• communication problems
• dementia
• body mass index above 35
• bilateral continuous sciatic nerve block
• lack of consent