Peripheral nerve blocks are essential in ensuring effective regional anesthesia and postoperative analgesia in forefoot surgery for hallux valgus repair, with or without minor concomitant toe procedures. Many factors influence the onset and duration of peripheral nerve blocks. In the advent of ultrasound-guided nerve blocks, the accuracy in administering LA has significantly improved, potentially reducing the required dosage, which is also associated with less risk for toxicity. However, the effect of the concentration of LA on the onset time and duration of ultrasound-guided ankle blocks for forefoot surgery has not yet been studied. This poses a clinically relevant dilemma regarding the necessity of administering lower or higher concentrations of ropivacaine to achieve a clinically relevant faster onset time and longer duration of an ankle block.

This study aims to evaluate the differential effects of 0.25%, 0.5%, and 1% ropivacaine on the onset time and duration of ultrasound-guided ankle blocks in patients having forefoot surgery for anesthesia and postoperative analgesia. We hypothesize that the use of 1% ropivacaine for ultrasound guided ankle blocks will result in a significantly faster onset time and a longer sensory block duration, and thus analgesia, compared to the use of 0.25% and 0.5% ropivacaine in patients having forefoot surgery. The primary outcome is the difference in the duration of the sensory blocks. The secondary outcomes are the difference in onset time of the sensory block, motor function, the postoperative pain scores, opioid consumption, and proportion of failed blocks.

Inclusion Criteria:

• Provide signed and dated informed consent
• Age 18 up to and including 75 years, scheduled for elective forefoot surgery for hallux valgus repair, with or without one or more of the following: minor toe procedures, osteotomies, arthrodesis or toe extensor/flexor procedures, under unilateral ankle block at ZOL Genk
• ASA physical I-II-III
• Able to ambulate (ability to walk independently, with or without assistive devices)
• Able to learn and perform study sensory and motor assessment by exhibiting sensitivity to pinprick, cold, and light touch (tested beforehand with pinprick/cold/ light touch sensation test) as the patient will have to perform these sensory and motor assessments by him/herself at home at postoperative day 0 to 2

Exclusion Criteria:

• Language barrier
• Preexisting lower extremity neuropathy
• Contraindications to ankle block (local infection, edema, burn, soft tissue trauma, or distorted anatomy with scarring in the area of block placement)
• Contraindications for use of NSAIDs
• Allergy to local anesthetics
• Uncontrolled anxiety, psychiatric or neurological disorder that might interfere with study assessment
• Weight below 50 kg based on a maximum dose of 3 mg/kg ropivacaine and a maximum dose of 150 mg ropivacaine.
• Preoperative use of opioids or gabapentin less than 3 days before surgery
• Contraindications for use of paracetamol
• Contraindications for use of tramadol

Staff performing perineural blocks will not be blinded to the concentration of ropivacaine that will be administered. However, patients, and research personnel collecting postoperative data will be blinded to group allocation. The clinical anesthesiologist in the operating theatre is blinded to the concentration of ropivacaine administered as this is not the same practitioner as the one performing the ankle block.