Intermetatarsal bursitis refers to a constellation of symptoms including pain and tenderness over the affected intermetatarsal spaces, which radiate distally into the toes especially if the adjacent interdigital nerve is inflamed. The pain of intermetatarsal bursitis is exacerbated by weight bearing and wearing high heels or shoes that are too narrow. Obesity may also predispose to this condition. The patient suffering from intermetatarsal bursitis is often unable to stand on tiptoes or walk upstairs. Walking and standing for long periods make the pain worse. The pain of intermetatarsal bursitis is constant and is characterized as sharp and may interfere with sleep. Coexistent neuritis, neuropathy, Morton neuroma formation, stress fractures, metatarsalgia, and synovitis may confuse the clinical picture. As the bursitis worsens, the affected intermetatarsal bursae tend to expand surrounding the adjacent interdigital nerves making the patient’s clinical presentation indistinguishable from the pain of Morton neuroma. If the inflammation of the intermetatarsal bursae becomes chronic, calcification of the bursae and fibrosis of the surrounding interdigital space may occur.

On physical examination, pain can be reproduced by squeezing the affected web space between the index finger and thumb. If the interdigital nerve is involved or if a Morton neuroma has developed, a positive Mulder sign can be elicited by firmly squeezing the two metatarsal heads together with one hand while placing firm pressure on the interdigital space with the other hand (Fig. 178.1). The patient with intermetatarsal bursitis often exhibits an antalgic gait in an effort to reduce weight bearing during walking.

Plain radiographs are indicated in all patients who present with intermetatarsal bursa. Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging or ultrasound of the intermetatarsal bursa is indicated to help confirm the diagnosis and if fracture, effusion, tendinopathy, crystal arthropathy, joint mice, synovitis, foreign body, bursitis, or ligamentous injury is suspected (Figs. 178.2 and 178.3).

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 (Fig. 178.4). These nerves are subject to entrapment and resultant development of perineural fibrosis and degeneration resulting in the clinical syndrome known as Morton neuroma (Fig. 178.5). 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 intermetatarsal bursa lies between the metatarsal phalangeal joints in a position that is just dorsal to the interdigital nerves (Fig. 178.6). The bursae extend ˜1 cm beyond the distal border of the ligament in the web spaces between the second and third and third and fourth digits.

The benefits, risks, and alternative treatments are explained to the patient, and informed consent is obtained. The patient is then placed in the prone position with the affected foot hanging comfortably over the edge of the examination table (Fig. 178.7). With the patient in the above position, a highfrequency small linear ultrasound transducer is placed in a transverse position over the metatarsophalangeal heads, and an ultrasound survey scan is taken (Fig. 178.8). The intermetatarsal space is identified between the heads of the metatarsals, and the homogeneous-appearing intermetatarsal soft tissue is searched for the appearance of a rounded hypoechoic intermetatarsal bursa (see Fig. 178.3). Dynamic scanning while performing the Mulder maneuver may help identify the inflamed and enlarged bursa as it is forced from between the metatarsal heads (Fig. 178.9). When the intermetatarsal space containing the symptomatic intermetatarsal bursa is identified, the skin on the plantar surface of the foot overlying the area containing the intermetatarsal bursa is then prepped with antiseptic solution. A sterile syringe containing 3.0 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 above the center of the transversely placed 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 within the intermetatarsal bursa (Fig. 178.10). When the tip of needle is thought to be in satisfactory position, after careful gentle 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 within the bursa. 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.