Ultrasound Improves the Success Rate of a Tibial Nerve Block at the Ankle

Background: The tibial nerve provides the majority of sensation to the foot. Although multiple techniques have been described, there exists little evidence-based medicine evaluating different techniques for blocking the tibial nerve at the ankle. We hypothesized that an ultrasound (US)-guided tibial nerve block at the ankle would prove more successful than a conventional approach based on surface landmarks. Methods: Eighteen healthy volunteers were prospectively randomized into this controlled and blinded study. Each subject was placed prone, and one ankle was randomly assigned to receive either an US-guided tibial nerve block (group US) or a traditional landmark-based tibial nerve block (group LM). The subject's other ankle then received the alternate approach. All blocks were performed with 5 mL of 3% chloroprocaine. We evaluated sensory and motor blocks. A successful block was defined as complete loss of sensation to both ice and pinprick at 5 cutaneous sites. Secondary outcome variables included performance times, number of needle passes, participant satisfaction, and presence of any complications. Results: At 30 mins, the block was complete in 72% of participants in group US as compared with 22% in group LM. At all times, the proportion of complete blocks was higher in group US. Ultrasound-guided blocks took longer on average to perform than traditional blocks (159 vs 79 sees; P < 0.001). There were more needle redirects in group US, with 8 subjects requiring 3 or more redirects versus none in group LM. Subjects preferred the US block 78% of the time (95% confidence interval, 52%-95%). Conclusions: in healthy volunteers, US guidance results in a more successful tibial nerve block at the ankle than does a traditional approach using surface landmarks.