Sesamoiditis is one of the most common pain syndromes that affects the forefoot. Caused by inflammation of the sesamoid bones, sesamoiditis is characterized by tenderness and pain over the metatarsal heads. The first sesamoid bone of the first metatarsal head is most commonly affected, although the sesamoid bones of the second and fifth metatarsal heads also are subject to the development of sesamoiditis (Fig. 179.1). The patient suffering from sesamoiditis frequently complains that it feels like he or she is walking with a stone in his or her shoe. The pain of sesamoiditis worsens with prolonged standing or walking for long distances and is exacerbated by improperly fitting or padded shoes. Sesamoiditis is most often associated with pushing-off injuries during football or repetitive microtrauma from running or dancing.

On physical examination, the pain of sesamoiditis can be reproduced by pressure on the affected sesamoid bone. Metatarsalgia is frequently confused with sesamoiditis. In contradistinction to metatarsalgia where the tender area of palpation remains over the metatarsal heads, with sesamoiditis, the tender area moves with the flexor tendon when the patient is asked to actively flexes his or her toe. The patient with sesamoiditis often exhibits an antalgic gait in an effort to reduce weight bearing during walking. With acute trauma to the sesamoid, ecchymosis over the plantar surface of the foot may be present, and on occasion fracture of the sesamoid bone may occur (Fig. 179.2).

Plain radiographs are indicated in all patients who present with sesamoiditis. 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 sesamoid bone 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. 179.3 and 179.4).

The sesamoid bones are small, rounded structures that are embedded in the flexor tendons of the foot and usually are in close proximity to the joints. Sesamoid bones of the first metatarsal occur in almost all patients, with sesamoid bones being present in the flexor tendons of the second and fifth metatarsals in a significant number of patients (see Fig. 179.1). These sesamoid bones serve to decrease friction and pressure of the flexor tendon as it passes in proximity to a joint.

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 patient’s arms folded comfortably across his chest (Fig. 179.5). With the patient in the above position, a high-frequency small linear ultrasound transducer is placed in a longitudinal plane over the painful metatarsophalangeal (MTP) head, and an ultrasound survey scan is taken (Fig. 179.6).

The hypoechoic joint space is identified between the head of the metatarsal, and the base of the proximal phalanges and the curvilinear sesamoid bone with its acoustic shadow are identified (Figs. 179.7 and 179.8). When the sesamoid bone is identified, the skin overlying the area above and beneath the ultrasound transducer 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 above the center of the longitudinally 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 proximity to the sesamoid bone (Fig. 179.9). 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 realtime 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.