Introduction
Background
Hammertoe deformity is the most common deformity of the lesser toes.Diagram comparing the clinical appearance of lesser-toe deformities.
It primarily comprises flexion deformity of the proximal interphalangeal (PIP) joint of the toe, with hyperextension of the metatarsophalangeal (MTP) and distal interphalangeal (DIP) joints (see Image 1).
History of the Procedure
Surgical treatment of hammertoe deformity has historically been based on altering the relative lengths of the toe and its tendons. Options have included PIP joint resection arthroplasty, PIP joint fusion, tendon transfers, tendon lengthening, and metatarsal shortening. Metatarsal shortening has gained renewed interest, but PIP joint resection arthroplasty and tendon transfers are the main procedures for hammertoe correction.
Problem
With progressive PIP joint flexion deformity, compensatory hyperextension of the MTP and DIP joints typically occur. The hyperextension of the MTP joint and flexion of the PIP joint make the PIP joint prominent dorsally. This prominence rubs against the patient's shoe, causing pain. The deformity is flexible and passively correctable early in its natural history but typically becomes fixed with time. Progressive deformity can lead to MTP joint dislocation.
Frequency
The incidence of hammertoe deformity is undefined, but the condition is strongly associated with the presence of a second ray that is longer than the first. Indeed, this length disparity is found in most patients presenting with foot complaints, although the actual prevalence of this foot shape also is undefined.
Etiology
Morton foot, wherein the second ray (metatarsal and corresponding toe) is longer than the first ray.
Etiologies of hammertoe deformity include a foot in which the second ray is longer than the first (see Image 2), MTP synovitis and instability, inflammatory arthropathies, neuromuscular conditions, and ill-fitting shoe wear.
MTP synovitis and instability are associated with a second ray that is longer than the first. Inflammatory arthropathies typically involve more than 1 of the lesser MTP joints. Ill-fitting shoe wear compounds the effects of any of the etiologies.
Pathophysiology
Pathomechanics of hammertoe deformity. An elongated plantar plate, caused by either metatarsophalangeal (MTP) synovitis and instability or chronic MTP hyperextension due to toe crowding, results in MTP subluxation or dislocation with compensatory proximal interphalangeal (PIP) flexion.
When a foot's second ray is longer than the first and shoe wear does not fit correctly, flexion of the PIP joint occurs to accommodate the shoe. This length difference also causes MTP synovitis to develop from overuse of the second MTP joint. Attenuation of the collateral ligaments and plantar plate result, and the MTP joint hyperextends and may even progress to dorsal subluxation or dislocation (see Image 3). Rheumatoid arthritis causes hammertoe deformity by progressive MTP joint destruction, leading to MTP joint subluxation and dislocation.1,2 3
With all 3 of these etiologies, the extensor digitorum longus (EDL) tendon gradually loses mechanical advantage at the PIP joint, as does the flexor digitorum longus (FDL) tendon at the MTP joint. The intrinsic muscles sublux dorsally as the MTP hyperextends. They now extend the MTP joint and flex the PIP joint, as opposed to their usual functions of flexing the MTP joint and extending the PIP joint.
Presentation
Painful dorsal callus over proximal interphalangeal (PIP) joint of second toe, caused by long-standing, fixed hammertoe deformity.
Physical examination maneuver to diagnose metatarsophalangeal (MTP) instability, wherein the examiner attempts to dorsally translate the proximal phalanx relative to the metatarsal head. In most patients, subluxation is possible; therefore, this test is positive only when it causes pain.
The patient with symptomatic hammertoe typically complains of pain over the dorsal aspect of the PIP joint. Occasionally, the patient also complains of pain over the plantar area of the metatarsal head, especially if the MTP joint is hyperextended, subluxed, or dislocated. A callus may be present over the dorsal surface of the PIP joint, over the plantar surface of the metatarsal head, or at the tip of the toe (see Image 4). In addition, patients with MTP instability often complain of pain over the dorsal part of the MTP joint, and they may describe the sensation of a lump in the plantar area of the MTP joint.
The physical examination of hammertoe deformity must include a neurovascular evaluation, including palpation of pulses, a sensory examination, and an evaluation of intrinsic muscle bulk. The deformity should be assessed while the patient is standing, to appreciate its functional significance. Accompanying deformities, such as hallux valgus, combined hammertoe and rotational deformity, and cavus foot deformity, must be catalogued. Passive correction of the deformity should be attempted, because this will help determine which treatment options are appropriate for the patient.
Palpate both the plantar and articular portions of the metatarsal head, because patients with MTP instability have greater tenderness of the articular portion and may require treatment different from that of patients with isolated hammertoe. Pain with dorsal subluxation of the MTP joint implicates MTP instability (see Image 5). Palpate the webspace and compress the forefoot by squeezing the metatarsals together from medial to lateral. These 2 maneuvers help to exclude an interdigital neuroma, which often is confused with MTP instability.
Indications
The indication for surgical treatment of hammertoe deformity is disabling pain that does not improve with adequate nonoperative treatment, including taping (for flexible deformity) and the use of accommodative footwear featuring a toe box of adequate depth (for fixed deformity). Surgical correction of an asymptomatic hammertoe is indicated at the time of hallux valgus correction, to minimize the likelihood of recurrent hammertoe.
Flexibility of the deformity determines which technique is appropriate for correction. Passively correctable deformity is amenable to Girdlestone-Taylor flexor-to-extensor tendon transfer. Fixed deformity requires either PIP resection arthroplasty or partial proximal phalangectomy. Both flexible and fixed deformities also may require MTP arthroplasty and/or extensor tenotomy to achieve adequate correction. A rotational deformity may require the addition of derotational phalangeal osteotomy,
A metatarsal shortening osteotomy may need to be added for a dislocated MTP joint or MTP instability with synovitis. Plantar condylectomy of the metatarsal head may need to be added for plantar metatarsal head pain without instability or synovitis.
Relevant Anatomy
The lesser toe comprises 3 phalanges that articulate at the proximal and DIP joints. The proximal phalanx articulates with the metatarsal at the MTP joint. Medial and lateral collateral ligaments, a fibrocartilaginous plantar plate, and a thin dorsal capsule stabilize each of the 3 joints.
The EDL tendon originates in the leg and crosses the ankle anteriorly. Although it extends all 3 joints of the lesser toe, it primarily acts at the MTP joint. The extensor digitorum brevis originates in the sinus tarsi and blends with the EDL tendon over the proximal phalanx to form the extensor expansion. The EDL continues distally from the extensor expansion and trifurcates to form the central slip, which inserts onto the middle phalanx, and the lateral bands, which insert onto the distal phalanx. The central slip and lateral bands extend the PIP and DIP joints, respectively, when the MTP joint is in neutral position or in plantarflexion.
The FDL tendon originates in the leg, crosses the ankle medially, and flexes all 3 joints, although it acts primarily at the DIP joint. The flexor digitorum brevis tendon originates from the plantar surface of the calcaneus and primarily flexes the PIP joint. The lumbricals originate from the medial and lateral surfaces of the metatarsals, pass plantarly to the MTP, and then extend dorsally to coalesce with the lateral bands. Thus, the lumbricals flex the MTP joint and extend the PIP and DIP joints.
The neurovascular bundles of each toe arise from a common interdigital artery and interdigital nerve. Each bifurcates at approximately the level of the MTP joint. Each branch then extends along the medial and lateral aspects of the toe deep to the subcutaneous tissue. Both the interdigital artery and nerve are plantar to the intermetatarsal ligament at the level of the MTP joint. Both can become contracted in a chronic hammertoe and are subject to traction injury with hammertoe correction.
Contraindications
Contraindications for surgery include active infection, inadequate vascular supply, and the desire for cosmesis alone. The patient must understand that the goal of surgery is pain relief, not cosmesis.
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References
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Bouché RT, Heit EJ. Combined plantar plate and hammertoe repair with flexor digitorum longus tendon transfer for chronic, severe sagittal plane instability of the lesser metatarsophalangeal joints: preliminary observations. J Foot Ankle Surg. Mar-Apr 2008;47(2):125-37. [Medline].
Trnka HJ, Gebhard C, Muhlbauer M, et al. The Weil osteotomy for treatment of dislocated lesser metatarsophalangeal joints: good outcome in 21 patients with 42 osteotomies. Acta Orthop Scand. Apr 2002;73(2):190-4. [Medline].
Keywords
hammertoe deformity, claw toe, toe deformity, foot deformity, deformed toe, deformed foot lesser-toe deformity, deformity of the lesser toes, fifth-toe deformities, Morton foot, Morton's foot, diabetic foot, arthrodesis
