Ultrasound-guided metatarsal and digital nerve block is useful in the management of the pain subserved by the metatarsal and digital nerves. This technique serves as an excellent adjunct to lumbar plexus block and for general anesthesia when performing surgery on the toes and is seeing increased utilization to provide anesthesia for reduction of fractures and dislocations of the metatarsals and phalanges as well as to provide surgical anesthesia for tendon repairs and plastic surgery repairs of complex toe injuries. Ultrasound-guided metatarsal and digital nerve block can also be used to provide postoperative pain relief following total joint arthroplasties of the joints of the toes.

Ultrasound-guided metatarsal and digital nerve block can also be used as a diagnostic tool when performing differential neural blockade on an anatomic basis in the evaluation of foot and toe pain as well as in a prognostic manner to determine the degree of neurologic impairment the patient will suffer when destruction of a metatarsal or digital nerve is being considered or when there is a possibility that the nerve may be sacrificed during surgeries in this anatomic region. This technique may also be useful in those patients suffering symptoms from compression of the metatarsal and digital nerves from tumor, aneurysms of the digital arteries, sesamoid bones, or osteophytes (Fig. 173.1).

Patients suffering from dysfunction of the metatarsal or digital nerve may suffer from pain with pressure on the nerve making it difficult to wear shoes. Dysesthesias are common as is sleep disturbance. On physical examination, pain can be elicited by compression over the affected nerve. Continued compression of the affected nerve may cause numbness distal to the point of compression. Coexistent arthritis, sesamoiditis, gout, other crystal arthropathies, and synovitis of the metatarsal and interphalangeal joints may predispose the patient to the development of entrapment of the metatarsal and digital nerves.

Plain radiographs of the feet are indicated in all patients suspected of suffering from metatarsal and digital nerve dysfunction to rule out occult bony pathology (Fig. 173.2). Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, uric acid, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging and ultrasound imaging of the foot are indicated to assess the status of the affected nerves as well as to identify other occult pathology including arthritis, sesamoiditis, and synovitis (Fig. 173.3).

In a manner analogous to that of the digital nerves of the hand, the digital nerves of the foot travel through the intermetatarsal space to innervate each toe. The plantar digital nerves, which are derived from the posterior tibial nerve, provide sensory innervation to the major portion of the plantar surface (Figs. 173.4 and 173.5). These nerves are subject to entrapment and resultant development of perineural fibrosis and degeneration resulting in the clinical syndrome known as Morton neuroma (Fig. 173.6). The dorsal aspect of the foot is innervated by terminal branches of the deep and superficial peroneal nerves. The overlap of the innervation of these nerves may be considerable.

The benefits, risks, and alternative treatments are explained to the patient, and informed consent is obtained. The patient is then placed in the supine position with the knee flexed so that the plantar surface of the affected foot rests comfortably on the examination table (Fig. 173.7). With the patient in the above position, the affected metatarsal or toe is identified, and a highfrequency linear ultrasound transducer is placed in a transverse position over the more distal portion of the metatarsal or the proximal portion of the toe to be blocked, and an ultrasound survey scan is taken (Figs. 173.8 and 173.9). The flexor tendon is identified and the metatarsal or digital nerve will be seen flanking the tendon laterally. A longitudinal view can help confirm the location of the nerve as can the use of color Doppler to identify the metatarsal or digital artery, which both lie just dorsal to their corresponding nerves (Figs. 173.10 and 173.11). After the correct metatarsal or digital nerve is identified, the skin overlying the area beneath the ultrasound transducer as
well as the skin on the lateral aspects of the affected toes is then prepped with antiseptic solution. A sterile syringe containing 1.0 mL of 0.25% preservative-free bupivacaine and 40 mg of methylprednisolone is attached to a 1½-inch, 25-gauge needle using strict aseptic technique. The needle is placed through the skin just below the inferior border of the transducer and is then advanced using an out-of-plane approach with the needle trajectory adjusted under real-time ultrasound guidance so that the needle tip ultimately rests in proximity to the digital nerve (Fig. 173.12). When the tip of needle is thought to be in satisfactory position, after careful aspiration, a small amount of local anesthetic and steroid is injected under real-time ultrasound guidance to confirm that the needle tip is in the proper position. After proper needle tip placement is confirmed, the remainder of the contents of the syringe are slowly injected. There should be minimal resistance to injection.