Plantar compartment block for hallux valgus surgery: a proof-of-concept anatomic and clinical study

Background Hallux valgus surgery is associated with moderate to severe postoperative pain. We hypothesized that a plantar compartment block may be a good technique for postoperative analgesia. We describe an anatomic approach to ultrasound-guided plantar compartment block and assess the clinical efficacy of the block for outpatient surgery. Methods The anatomic study was aimed to describe the plantar compartment, using both dissection methods and imaging, and to define a volume of local anesthetic. Patients scheduled for hallux valgus surgery with a popliteal sciatic nerve block, and combined plantar compartment and peroneal blocks were included in the clinical study. Data on attaining the criteria for rapid exit from the outpatient center, duration of sensory and analgesic block, visual analog scale (VAS) values for postoperative pain at rest and during movement, and the consumption of morphine as rescue analgesia were recorded. Results Plane-by-plane dissections and cross-sections were done in five cadaveric lower limbs. The medial calcaneal nerve divides into medial plantar and lateral plantar nerves in the upper part of the plantar compartment. These nerves were surrounded by 5 mL of colored gelatin, and 10 mL of injectates dye spread to the medial calcaneal branches. Thirty patients (26 women) were included in the clinical study. There were no failures of surgical block. Ninety per cent of patients successfully passed functional testing for ambulatory exit from the center within 5 hours (25th–75th centiles, 3.8–5.5 hours). The median duration of plantar compartment sensory block was 17.3 hours (10.5–21.5 hours), and the first request for rescue analgesic was 11.75 hours (10.5–23 hours) after surgery. The median VAS score for maximum pain reported within the 48-hour period was 2 (1–6). Twelve patients received 2.5 mg (0–5 mg) of morphine on day 1. Patients were highly satisfied and no adverse events were noted. Conclusions This anatomic description of the ultrasound-guided plantar compartment block reported the injection area to target the medial and lateral plantar nerves with 5 mL of local anesthetic. Normal walking without assistance is attained rapidly with this regional anesthesia technique, and the time to request postoperative analgesia after hallux valgus surgery is long. Trial registration number NCT03815422 .