Metatarsalgia
Brett R. Fink, MD, and Mark S. Mizel, MD

Background
Metatarsalgia describes an assortment of conditions that cause plantar pain in the forefoot around the MTP joints.

Metatarsalgia is not, in itself, a diagnosis, but rather an anatomic description of where the patient is experiencing discomfort. Successful treatment of this condition hinges on identifying the underlying cause. A clear understanding of its etiologies and a systematic approach to examination are necessary to accomplish this. Metatarsalgia is best characterized by pain under the metatarsal heads exacerbated by weight-bearing.

The fatty cushion of the forefoot is a highly specialized tissue. Fibrous septae beneath the dermis compartmentalize the subcutaneous fat. When weight is applied, hydrostatic pressure builds within the compartments, dampening and dispersing forces on the plantar skin. This mechanism acts as a cushion, protecting the area from potentially damaging focal concentrations in pressure.

Inflammatory arthritis, trauma, or neuromuscular disorders can cause imbalances of flexion and extension forces around the small joints of the toes. Toe deformity is a consequence of this imbalance. Hyperextension at the MTP joint is a common component of these deformities and draws the fatty cushion of the forefoot distally and dorsally with the proximal phalanx (Fig. 5–53). When this occurs, the weight transferred through the metatarsal heads is applied to the thinner proximal skin without the intervening fatty cushion. Increases in local pressure result in a hyperkeratotic reaction of the plantar skin. This causes further increases in pressure, and eventually, a painful intractable plantar keratosis (IPK) forms (Fig. 5–54).

IPKs are often confused with plantar warts. Both cause hyperkerotic lesions of the plantar surface of the skin, which can be painful. However, plantar warts occur as a result of infection of the epidermis with papillomavirus. Whereas the treatment of IPKs is mechanical (shaving, cushioning, relief pads), the treatment of symptomatic plantar warts is directed toward eradicating the infected tissue. Care should be used to ensure that the sometimes-caustic plantar wart preparations do not cause scarring of the plantar skin, which can be more painful than the initial wart. IPKs, unlike plantar warts, are almost always found directly below a weight-bearing area of the foot (e.g., metatarsal head). Plantar warts bleed with a characteristic “punctate” fashion when shaved, with multiple punctate areas of bleeding.

Synovitis and instability (Fig. 5–55) of the MTP joints can also cause pain along the metatarsal heads. Although inflammatory arthritides can incite this, the etiology of the instability is commonly mechanical. Chronic hyperextension of the MTP joints (claw toes) and flexion at the interphalangeal (IP) joints can occur in an attempt to accommodate a shoe toe box that is too small (Fig. 5–56). Eventually, this attenuates the plantar plate and collateral ligaments, leading to instability and subluxation (Fig. 5–57). The toes can develop varus or valgus malalignment in relation because of this. Dorsal MTP joint dislocation is sometimes seen in severe cases.

Extra-articular cause of pain in the metatarsal region should also be considered. Morton’s neuroma is a hypertrophy and subsequent irritation of the common interdigital nerve as it passes between the metatarsal heads. Inflammation of the intermetatarsal bursa and impingement by the intermetatarsal ligament are thought to contribute to the development of this condition. It most commonly affects the nerve of the third web space. It is often mistaken for synovitis (see Morton’s neuroma section) and can coexist with it. It rarely involves more than one common digital nerve. The tenderness from a stress fracture of the metatarsal is typically in the metatarsal neck or shaft. These can be invisible on radiographs for several weeks after onset. Finally, pain from a herniated lumbar disc, tarsal tunnel, or other neurologic problem can be appreciated in the forefoot and is often mistaken for pain from a disorder originating in the foot.

History and Physical Examination
A careful history and physical examination are the most important tools for differentiating the etiologies of metatarsalgia. This should begin with an evaluation of suitability of footwear in relation to the size of the foot. Measure the patient’s true shoe size and width, and then see what size shoe he or she wears into the office. A complete evaluation of the foot and ankle can disclose problems in other areas of the foot that may make the forefoot painful. For instance, medial foot disorders can cause lateral forefoot pain because of lateral weight shifting. Weakness in the anterior tibial tendon can cause toe deformity through adaptive overuse of the extrinsic toe extensors, resulting in forefoot pain.

The plantar skin should be inspected for plantar keratoses. Paring these lesions is important, not only to decrease pressure but also to differentiate them from plantar warts. Plantar warts, unlike plantar keratoses, contain vessels within the keratinized tissue that are easily seen open and bleeding after paring. The interdigital spaces should also be inspected for soft corns. Sensation should be tested and pulses palpated. Careful palpation of the metatarsal heads and intermetatarsal spaces, localizing the exact area of tenderness, narrows the differential diagnosis.

Manual compression of the interspace (Mulder’s click) can elicit crepitus, tenderness, and radiating pain from a Morton’s neuroma (see Morton’s neuroma section). A drawer maneuver of the MTP joint (Fig. 5–58) can detect articular stability problems. It is done by applying dorsally directed pressure to the plantar base of the proximal phalanx while stabilizing the metatarsal with the opposite hand.

The contralateral toes as well as the other toes on the ipsilateral foot should be evaluated to establish a baseline degree of normal translation on MTP joint drawer testing for each patient. MTP joint tenderness, swelling, and bogginess usually signify synovitis of the MTP joint, whereas pain with a relative increase in translation during MTP drawer testing usually signifies joint instability.

Radiographic Evaluation
Radiographs are important to define forefoot deformities and identify neoplasms, fractures, dislocations, and arthritic joints that may contribute to pain in the metatarsal area. The relative lengths of adjacent metatarsals should be compared, because discrepancies in metatarsal length can cause concentration of stress. Patients with significant shortening of the first metatarsal after a bunion operation sometimes develop pain under the second metatarsal (transfer metatarsalgia). When combined with lead markers placed on the IPK skin, the radiographs help to identify prominent condyles or sesamoids under the metatarsal head that cause plantar keratoses. Isolated second metatarsal pain may be caused by Freiberg’s infraction (Fig. 5–59).

Other imaging techniques, such as MRI and CT, are helpful only when specifically indicated and are not a routine part of the evaluation of metatarsalgia.

Although exercise and stretching offer little relief for most patients with metatarsalgia, pedorthic management can figure prominently in the initial treatment. For most patients who present with inappropriate (high heels) or tight shoewear, a discussion of the fit of the shoes should focus on the shape and room in the toe box for the toes. In addition, shoes with laces, stiff soles, and low heels help disperse and reduce the pressure on the forefoot. Occasionally, patients have severe fixed forefoot deformities that require prescription extradepth shoewear.

Full-length PPT and Plastizote or silicone insoles are very helpful in dispersing the pressure on tender areas in the forefoot. If this is unsuccessful, more sophisticated orthotic devices may be necessary. Soft metatarsal pads made of felt or silicone (Fig. 5–60A) by themselves or added to a Spenco insert can be used to relieve pressure. Correct placement of the pad is crucial. The crest of the pad should be approximately 1 cm proximal to the tender area (see Fig. 5–60B). To help position the insert, lipstick or magic marker can be applied to the tender area on the foot and the patient asked to step on the insole, making apparent where to place the pad (1 cm proximal). A custom-molded accomodative insert can also be fabricated with a well-excavated well beneath the tender metatarsal to unload it (relief well).

Metatarsal bars can be built onto the shoe to unload the forefoot, but these tend to wear out quickly and encounter resistance from patients for cosmetic reasons. A rocker-bottom sole, along with a stiffener placed into the sole, helps reduce toe motion and disperse pressure away from the metatarsal heads.

Steroid injections combined with 1% lidocaine have a definite, but limited, role in diagnosing and treating pain due to synovitis or irritation of a Morton’s neuroma from intermetatarsal bursitis.

Surgery is offered to patients in whom nonoperative treatment fails to relieve pain.