Freiberg infraction is an osteochondrosis of a lesser metatarsal head. The second metatarsal is affected in 68% of patients, and the third metatarsal is affected in 27%.¹ The disease most commonly affects girls and women and is most prevalent during adolescence. Repetitive minor trauma is commonly but not universally associated with the condition. Recurrent microtrauma or overloading of the metatarsal can lead to interruption of the blood supply to the metatarsal head, with resulting ischemia, bone resorption, and collapse. The entire foot must be examined to determine the factors contributing to lesser metatarsal overload in a patient with Freiberg disease. These factors can include a gastrocnemius contracture, an unstable first ray, and relatively long lesser metatarsals.

An IPK is a painful callus on the plantar aspect of the foot secondary to excess pressure from the metatarsal head or sesamoid (Figure 1). There are two forms, which are treated differently. The discrete form of IPK affects a single metatarsal, has a keratotic core, and may occur secondary to the prominence of a fibular condyle or the tibial sesamoid (Figure 2). The diffuse form of IPK appears as a thickening of the skin under an entire metatarsal head or multiple metatarsal heads, and it does not have a discrete keratotic core. In IPK primarily involving the second metatarsal, the overloading is caused by an incompetent first metatarsal and may involve first tarsometatarsal instability, hallux valgus, or an iatrogenically short first metatarsal.² An equinus contracture may be the sole underlying etiology if the callus is present over multiple metatarsals including the first ray. An equinus contracture can occur with both the discrete and diffuse forms and must be assessed in every patient. Alternate diagnoses include plantar warts, a foreign body reaction, and epidermal inclusion cysts.

A Morton (interdigital) neuroma is believed to develop as an entrapment neuropathy of the digital nerve. Chronic pressure on the digital nerve as it courses beneath the
transverse intermetatarsal ligament leads to perineural and endoneural fibrosis. Degeneration of the myelinated fibers is common and must be histologically verified. The anatomy of the digital nerves formerly was believed to create a predisposition to a Morton neuroma in the third web space. Branches from the lateral and medial plantar nerves enter the web spaces as common digital nerves; it was believed that both the lateral and medial plantar nerves have branches extending to the third web space, thus creating a relatively thick nerve predisposed to microtrauma. The medial communicating branch to the third web space is present in only 27% of the population, however, and if present, the common interdigital nerve is no thicker than other interdigital nerves.³

Wearing narrow-toed shoes may contribute to neuroma formation. Dorsiflexion of the MTP joints causes plantar flexion of the metatarsal heads, making the nerve subject to repetitive trauma through increased compression of the metatarsal heads and stretching over the intermetatarsal ligament. Extrinsic factors also can influence neuroma formation. Ganglions or synovial cysts arising from the MTP joint may cause direct pressure on the digital nerve. Degeneration of the MTP joint capsule in a patient with an inflammatory condition such as rheumatoid arthritis often causes subluxation of the joint and stretches the nerve. Distortion of the MTP joint also can compress the bursae surrounding the ligament, increasing pressure on the surrounding tissues.

The sesamoids are primary load-bearing structures of the forefoot, in addition to their function in decreasing friction and increasing the mechanical advantage of the flexor hallucis brevis. The importance of these structures is underscored by their absorption of as much as 32% of the energy generated during the stance phase of sprinting. Sesamoiditis is inflammation and pain affecting the sesamoids resulting from arthrosis, osteonecrosis, acute fracture, stress fracture, or mechanical overloading. The medial (tibial) sesamoid is most commonly involved because of the increased load on the medial aspect of the foot during gait. Bipartite sesamoids occur in 10% to 30% of the population and should not be confused with acute fracture. Only 85% of these individuals have bipartite sesamoids in both feet; therefore, a normal contralateral radiograph is not sufficient to determine the presence of an acute fracture. These injuries commonly occur in athletes and must be aggressively treated to prevent long-term disability. Unlike lesser metatarsal pain, which can be secondary to an unstable first ray, sesamoid pain may be associated with a plantarflexed rigid first ray (as in a cavus foot).

Incompetence of the medial column during the load-bearing phases of gait increases stress on the lesser metatarsals.⁴ This phenomenon may be a factor in Freiberg disease, IPK, and Morton neuroma as well as
stress fracture, synovitis, and joint subluxation, and it must be considered in all patients with lesser metatarsalgia. Hallux valgus with associated first tarsometatarsal instability is a common cause of stress transfer. Iatrogenic shortening or elevation of the first ray also must be considered. The weight-bearing function of the medial column must be restored during an isolated lesser metatarsal correction to avoid increasing the risk of recurrent pain and deformity.

The inciting factors and the location of a patient’s forefoot pain are critical for determining the underlying cause.

Weight-bearing activities, in particular those associated with running, are a common inciting factor in all forefoot pathologies. Taking a careful history of a patient’s symptoms with different types of shoes can aid in diagnosing metatarsalgia. Symptoms that worsen with constrictive shoe wear are associated with Freiberg disease or a Morton neuroma. Wearing shoes with very high heels (4 inches or higher) universally exacerbates forefoot pain; patients having an underlying gastrocnemius contracture will have relief from pain in shoes with a 1- to 2-inch heel. Ambulation without shoes typically reduces pain in patients with neuroma but worsens the discomfort in patients with another etiology. The use of a cushioned insole is common but offers little relief to patients with Freiberg disease or a Morton neuroma.

The location of a patient’s symptoms is the most helpful component of the history in diagnosing metatarsalgia. In Freiberg disease, the pain is limited to one lesser MTP joint but never is associated with the first or fifth metatarsal. The primary location is the dorsal aspect of the affected joint. Plantar pain directly over a callus is associated with an IPK. A callus over both the first and fifth metatarsal heads suggests a cavus foot deformity. Pain in multiple lesser metatarsals may be secondary to a Morton neuroma, transfer metatarsalgia, or gastrocnemius contracture. A history of a burning sensation, tingling, or numbness ideally should be elicited before a Morton neuroma is diagnosed. Isolated pain over the plantar aspect of the first metatarsal without an associated callus probably is secondary to sesamoid pathology. Lesser metatarsal symptoms that arise after hallux valgus correction suggest transfer metatarsalgia rather than an isolated lesser metatarsal condition.

The physical examination should begin with a standing examination of the alignment of the foot, with a focus on the medial column. A forefoot-driven cavovarus deformity (a plantarflexed first ray) will contribute to sesamoid pain and possibly to isolated discrete IPK, whereas a midfoot cavus deformity leads to a diffuse IPK. Medial column instability, as may occur in hallux valgus deformity, contributes to lesser metatarsal symptoms. Iatrogenic dorsal elevation of the medial column may be noted clinically if the condition is severe but is more easily identified radiographically. Compression during shoe wear can exacerbate neuroma symptoms in a splay foot with hallux valgus or a bunionette deformity (Figure 3). These associated deformities must be treated if nonsurgical or surgical treatment is to be successful.

Inspection of the soft tissues will reveal gastrocnemius contracture, transfer metatarsalgia, calluses in IPK, or swelling in Freiberg disease. The Silfverskiöld test should be used to assess for isolated contracture of the gastrocnemius in all patients. In this test, ankle dorsiflexion is assessed with the knee in full extension and in 90° of flexion (Figure 4). The foot must be locked in subtalar neutral position. Lack of dorsiflexion past neutral is consistent with an equinus contracture. An increase in dorsiflexion with the knee in flexion is indicative of an isolated gastrocnemius contracture.

Palpation for tenderness is useful for determining the source of the pain and narrowing the differential diagnosis. In Freiberg disease, there is tenderness to palpation at the affected joint when a plantar-directed force is applied from the dorsal surface. Isolated dorsal-directed pressure from the plantar surface typically is painless unless the patient has an IPK. Compression of the joint elicits pain in patients with MTP synovitis or Freiberg disease. To mitigate confounding pain from an IPK, care must be taken to avoid placing pressure on any callus during this test while compressing the joint. The presence of a palpable dorsal osteophyte allows Freiberg disease to be easily differentiated from MTP synovitis. Provocative testing for a neuroma is done by compressing the forefoot while alternating plantar and dorsal pressure at the affected web space. This test may elicit a palpable click (the Mulder click) when the nerve and bursal tissue snap between the metatarsal heads. The Mulder click without pain also may be present in patients without foot pathology, however. A positive Mulder sign requires the click to be accompanied by pain radiating into the affected toes, and it is diagnostic for interdigital neuritis. The compression should be applied proximal to the metatarsal head to avoid irritating the joint, possibly leading to a false-positive test in the setting of MTP synovitis or Freiberg infraction. The range of motion of the toe typically is normal unless the patient has Freiberg infraction, in which the range of motion gradually becomes limited, with progressive articular collapse and osteophyte formation. Absolute dorsiflexion varies, and a comparison with the contralateral foot or the unaffected lesser toes provides a reliable reference. Deformity of the phalanx, as seen with hammer toes, claw toes, or a crossover toe, requires a different treatment algorithm. The vertical drawer test is 99.8% specific and should be performed to rule out the presence of a plantar plate injury.⁵ Dorsally directed pressure placed directly along the sesamoids will reproduce pain in patients with sesamoid pathology. Identification of the affected sesamoid is critical because resection of only a single sesamoid can be done without creating a cock-up toe deformity. Metatarsosesamoid pain may be relieved with plantar flexion of the first MTP joint but is exacerbated with dorsiflexion of the joint, which engages the sesamoids onto the plantar aspect of the metatarsal head.

Three weight-bearing radiographic views of the foot are necessary to identify a pathologic process of the MTP joint, depression or elevation of the first metatarsal, or an abnormal relative length of the lesser metatarsals.

Common radiographic findings in Freiberg disease include resorption of the central metatarsal bone adjacent to the articular surface, flattening of the metatarsal head, and osteochondral loose bodies (Figure 5). In late-stage disease, joint space narrowing with osteophyte formation and collapse of the articular surface can be seen (Figure 6). An axial view of the forefoot with dorsiflexion of the MTP joints may reveal relative prominence of the fibular condyle in patients with a discrete IPK. A non-weight-bearing medial oblique view and an axial sesamoid view are recommended for patients with suspected sesamoid pathology (Figure 7). According to a recent imaging review study, the radiographic interval separating the two halves of a bipartite sesamoid on routine foot anterior-posterior (AP) radiographs averaged 0.79 mm in asymptomatic patients. Hyperextension injury to the plantar hallux MTP joint should be suspected if this interval is greater than 2 mm.⁶ Radiographs typically are normal in patients with Morton neuroma, but a malunited metatarsal fracture with narrowing of the intermetatarsal space is seen in rare instances. The possibility of a
shortened or elevated first metatarsal should be evaluated in all patients and specifically in patients who have had surgery. This deformity may result in transfer metatarsalgia or may be associated with Freiberg disease, and it may require correction in addition to treatment of osteonecrosis of the lesser metatarsal (Figure 8).

Additional imaging is not routinely required for diagnosing a patient with metatarsalgia. An MRI of a patient with Freiberg disease will show low fat saturation with T1 weighting in the subchondral bone of the metatarsal head and variable fat saturation with T2 weighting, and flattening of the metatarsal head is seen. With eventual fragmentation of the bone, intra-articular loose bodies are formed. Arthritis in late-stage disease is indicated by subchondral bone marrow edema involving both the metatarsal and the phalanx (seen as high signal on T2-weighted MRI). The use of MRI in Morton neuroma is controversial. Before the development of high-resolution scanners, the predictive value of MRI was low. Currently, MRI can detect aberrant pathology such as a cyst or ganglion, but its usefulness for detecting and diagnosing an interdigital neuroma remains open to debate.

Ultrasonography has high sensitivity and variable specificity in the diagnosis of a neuroma. One study found that ultrasonography accurately predicted the size and location of the neuroma in 98% of 55 neuromas,
with no false-positive readings, but other studies found 95% sensitivity and only 65% specificity.⁷ Routine use of ultrasonography is not required because neuroma is a clinical diagnosis.