Ultrasound-guided flexor sheath block as a valid alternative to blind techniques for finger pain treatment: the horseshoe sign

Background The flexor sheath digital block allows effective analgesia and anesthesia for finger pain control. To date, only blind techniques are described in the literature in patients with finger fractures, supposedly due to the superficial position of the structures used as landmarks. We describe an ultrasound-guided technique with a definite endpoint to achieve this block. To our knowledge, this is the first clinical application of this procedure. Methods We performed a preoperative ultrasound-guided flexor sheath digital block on a young patient with a proximal phalanx fracture, undergoing an osteotomy with plate placement. After performing the block, opioid-free general anesthesia was performed. A “hockey-stick” ultrasound probe and 1.5 mL of 0.5% levobupivacaine were used to infiltrate the flexor sheath. The “horseshoe sign” was our visual endpoint for successful block performance. Results At the time of surgical incision, there was no hemodynamic response. No opioids were administered during the case or in the recovery room, and the patient’s pain scores in recovery and at discharge were 0/10 on the Numerical Rating Scale. No complications were observed or reported. Conclusions The ultrasound-guided flexor digital sheath block is a valid alternative to the blind technique, allowing direct visualization and, thereby, confirming transthecal injection of the local anesthetic. The continuously increasing availability of ultrasound machines in emergency departments and operating theaters may encourage the spread of this technique.