Definition

Hammer toe refers to an abnormal flexion posture at the proximal interphalangeal (PIP) joint of one or more of the lesser four toes [1]. If the flexion contracture is severe and of long duration, concomitant hyperextension of the metatarsophalangeal (MTP) joint and extension of the distal interphalangeal (DIP) joint may occur (Fig. 88.1). In contrast to clawing, which tends to involve all toes, hammer toe deformity usually affects only one or two toes [2]. Hammer toes are classified as either flexible (passively correctable) or rigid (not passively correctable to the neutral position). The most commonly affected toe is the second, although multiple digits can be involved [3].

Hammer toe is the most common of the lesser toe deformities and occurs primarily in the sagittal plane. It is arguably the most common toe disorder that presents to the foot and ankle surgeon’s office. Women are more commonly affected, and the incidence of hammer toe increases with age [4–6].

Contributing factors include long-term wear of poorly fitting shoes, especially those with tight, narrow toe boxes. Crowding and overlapping from hallux valgus are other causes. A long second ray with subsequent buckling of the toe may also lead to the deformity. Other predisposing factors are diabetes, connective tissue disease, and trauma [5].

Symptoms

Patients commonly complain of pain or tenderness in the area of the PIP joint, especially when wearing shoes or during weight-bearing activities. Patients also commonly present with cosmetic complaints. Pain may be the result of corn or callus formation over the dorsal aspect of the PIP joint from shoe compression. In cases in which hyperextension of the MTP joint has occurred, there is also increased pressure under the metatarsal heads. Metatarsalgia with subsequent callus formation underneath the metatarsal heads may occur secondary to their plantar displacement [2], with distal displacement of the plantar fat pad.

Physical Examination

The diagnosis is confirmed by the presence of MTP joint hyperextension, PIP joint flexion, and DIP joint extension in the affected toe. Palpation of the PIP joint usually causes tenderness, with the plantar aspect more commonly affected.

On inspection, determine the degree of PIP flexion. Also note accompanying foot deformities, such as ulcerations and callus formation over the PIP joint and tip of the toe. Hammer toe deformities become more prominent in stance phase. Examination of the joint range of motion of the affected toe will differentiate a fixed deformity from the one that is flexible. The presence or absence of crepitus should be noted. Flexor digitorum longus contracture is assessed with the ankle in dorsiflexion and plantar flexion. Correction of the deformity on plantar flexion signifies a flexible hammer toe. Dorsiflexion, in turn, accentuates the deformity [7].

The Kelikian push-up test is used to assess the degree of flexibility. Press upward on the plantar aspect of the metatarsal head; in flexible deformities, the MTP joint will align and the proximal phalanx will assume a more normal position.

A mild deformity hammer toe implies no fixed contracture at the MTP or PIP joint, but the deformity increases with weight bearing. A moderate deformity hammer toe has a fixed or partially fixed contracture at the PIP joint and zero to mild extension contracture at the MTP joint. A severe deformity hammer toe involves fixed flexion contracture at the PIP joint with a fixed extension contracture of the MTP joint. Subluxation or dislocation of the proximal phalanx on the metatarsal head may also be present [7].

Also assess for signs of swelling, temperature change, or erythema that might indicate the presence of an infectious or rheumatic process responsible for the deformity.

Inspection of the patient’s footwear is necessary to determine the ability of the toe box to accommodate the forefoot. The presence of corns or callus over the PIP joint, which may ulcerate, is often indicative of poorly fitting footwear.