Ultrasound-guided Ulnar Nerve Block in the Management of Digital Abscess and Hand Cellulitis

A 38-year-old man with no medical history presented to the emergency department with pain and swelling to the fifth digit on his dominant right hand. Physical examination revealed induration, erythema, and fluctuance to the dorsal aspect of the proximal phalanx of his fifth digit. There was erythema tracking proximally over the metacarpal–phalangeal joint onto the dorsum of the hand, but there were no neurovascular deficits, and the patient had full range of motion at the metacarpal–phalangeal joint.

A focused bedside ultrasound of the right fifth digit was performed by the treating emergency physician using a high-frequency linear transducer (Model XD11XE, Philips, Andover, MA) and a water bath technique. This was performed by having the patient submerge his hand into a basin filled with water, allowing examination of the digit using the water as a conducting medium. This decreases patient discomfort by eliminating the need to apply direct pressure to the skin surface and also improves resolution of superficial structures. The ultrasound demonstrated a hypoechoic collection along the dorsum of the proximal phalanx consistent with abscess (Figure 1 and Video Clip S1). Given the erythema over the metacarpal–phalangeal joint, a traditional digital block was avoided. Instead, a midforearm ulnar nerve block was performed using real-time ultrasound guidance, and local anesthetic was observed spreading around the ulnar nerve (Figure 2 and Video Clip S2). To perform this block, a high-frequency linear transducer is applied in a transverse plane to the midforearm. The ulnar artery is identified as a round, pulsatile structure and the nerve can be visualized as a hyperechoic structure located medial (ulnar) to the ulnar artery. The author’s preference is to insert the needle in an in-plane orientation, entering the skin at the ulnar aspect of the transducer and oriented in a parallel plane to the transducer to allow continuous visualization of the needle along its entire length. Within 5 minutes, the patient experienced complete anesthesia of the fifth digit, and an incision and drainage was performed without complications. The patient was discharged with oral antibiotics, and follow-up at 2 days demonstrated marked improvement of his symptoms, and his physical examination revealed decreased erythema and overall improvement of his acute digital abscess and cellulitis.

Figure 1.  Ultrasound image of the proximal phalanx of the patient’s right fifth digit. The water bath (w) allows for detailed imaging of the dorsal finger abscess (asterisk) and the cortex (c) of the proximal phalanx.

Figure 2.  Real-time ultrasound-guided ulnar nerve block. The needle tip (n) is seen approaching the ulnar nerve (asterisk), adjacent to the ulnar artery (a).