Fifth-Toe Deformities 

Since the advent of shoes, the fifth toe has been a source of discomfort for many people (see image below). Complaints typically involve poorly fitting shoes that create friction, irritation, and pain with each step. The problem can typically be solved conservatively with shoe modifications or proper foot maintenance; however, structural deformities of the toe often require surgical correction.

Fifth-toe deformities have been present since the evolution of bipedal ambulation. However, correction of these deformities did not become prevalent until the early 20th century, when many authors began describing different aspects of the problem, along with surgical procedures to help correct them.

Fifth-toe deformities comprise several congenital and developmental problems that affect the fifth digit. Most are associated with contractures at the metatarsophalangeal joint (MTPJ) and proximal interphalangeal joint (PIPJ), with or without varus rotation.^[1]

The simplest lesions are hard corns (helomata durum) and soft corns (helomata molle). Both lesions are epidermal hyperkeratoses resulting from frictional or pressure irritation. They develop over bony prominences, such as enlarged phalangeal condyles or exostosis.

Hard corns

Hard corns result from intrinsic pressure from bony prominence combined with extrinsic pressure (typically in the form of footwear irritation) over the exposed fifth toe. The most common site is the dorsal lateral aspect of the PIPJ, but corns can also occur in the same location over the distal interphalangeal joint (DIPJ) (see image below).^[2]

The corn is typically associated with a hammertoe deformity (dorsiflexion contracture at the MTPJ and plantarflexion contracture at the PIPJ) that may have a slight varus rotational deformity. This makes the dorsal lateral aspect of the PIPJ more prominent and susceptible to footwear irritation. The corn that develops can be superficial or deep seeded; the latter is more painful. Additionally, a painful bursa may occur deep in the lesion in response to the constant pressure.

In the neuropathic population, hard corns that go untreated can develop into ulcerations that lead to soft tissue and bone infection.

Soft corns

Soft corns develop between adjacent toes.

Intrinsic pressure develops between adjacent condyles of the lateral fourth PIPJ abutting the medial fifth DIPJ, or the lateral fourth MTPJ abutting the medial fifth PIPJ. The lesions can develop on the skin over the lateral fourth PIPJ, medial fifth DIPJ, medial fifth PIPJ, or deep in the web space (see image below).

Kissing corns

Kissing corns result from 2 calluses rubbing against each other on adjacent toes (see first and second images below). Kissing corns are usually painful when the toes are squeezed together. Maceration is often noted in the web space and may contribute to the development of kissing corns (see third and fourth images below). When they occur, other common problems, such as fungal infections or verruca, need to be ruled out. If left untreated, these lesions may also develop into ulcerations in people with neuropathies.

Hammertoe,^{[3, 4, 5]} claw-toe,^[6] and cock-up deformities are all variations of the same problem.^[7] The presence of a dorsiflexion contracture at the MTPJ and a plantarflexion contracture at the PIPJ is constant between the 3 (see image below). The claw-toe deformity has the addition of a plantarflexion contracture at the DIPJ. The term cock-up deformity is typically used to describe a severe hammertoe, in which the proximal phalanx articulates at a nearly 90° angle to the fifth metatarsal and may be fixed in that position. A cock-up deformity can also be associated with plantar-plate ruptures or adhesions between the plantar MTPJ capsule and the metatarsal head.

Contractures can develop for several reasons; however, they most frequently occur because of mechanical imbalances. The intrinsic foot musculature fails to stabilize the fifth toe at the MTPJ, PIPJ, and DIPJ, allowing the more powerful extrinsic flexors and extensors to act unchecked. This eventually leads to the deformities described above.

Unlike the other conditions mentioned, overlapping and underlapping fifth toes are usually congenital deformities. The overlapping fifth toe is a common familial deformity with equal sex predilection and usually presents bilaterally (see images below). About half of patients become symptomatic because of pressure from footwear against the dorsal aspect of the toe and nail. The toe is dorsally hyperextended at the MTPJ with a varus rotation and medial deviation onto the top of the fourth digit.

Contractures develop dorsomedially at the MTPJ and eventually form in the extensor digitorum longus (EDL) tendon and the dorsomedial skin overlying the MTPJ.

The underlapping fifth toe is another common congenital deformity and is often referred to as a curly toe or congenital varus toe (see images below). This deformity may also occur bilaterally and has a high familial prevalence. The toe is plantarflexed at the MTPJ, rotated into a varus position, and positioned under the fourth digit. A contracture typically occurs at the plantar-medial MTPJ capsule and flexor digitorum longus (FDL) tendon. These are paired with an elongated EDL and attenuated dorsal capsule. Constant pressure at the lateral nail and digital skin creates pain.

Hard and soft corns

Surgical correction is indicated for chronically painful cases in which conservative treatment fails. Patients with neuropathies may also choose surgery or prophylaxis to treat chronic lesions.

Hammer, overlapping, or underlapping toes

Surgical correction is indicated for progressively painful deformities if conservative treatment fails.

Three bones make up the fifth toe. These are the distal, middle, and proximal phalanges. They articulate together to make the DIPJ and PIPJ. The proximal phalanx then articulates with the fifth metatarsal to make the fifth MTPJ.

Medial and lateral condyles are present at the base of each phalanx, and epicondyles are present at the heads of the proximal and middle condyles. A 2-boned fifth toe has been reported in 37-76% of the population and involves a union of the distal and middle phalanges. When this occurs, the fifth toe is less flexible and unable to accommodate pressure from shoes and a normal digit. This toe is therefore more susceptible to irritation and development of a painful deformity.

The MTPJ has an extensor wing-and-sling mechanism that aids in extension of the digit. A slip of the EDL to the fifth toe travels deep to the extensor wing and sling to insert into the dorsal aspect of the distal phalanx. No slip occurs from the extensor digitorum brevis to the fifth toe; however, an occasional anomaly takes place in which an offshoot from the peroneus brevis tendon travels distal to insert into the dorsal lateral aspect of the fifth MTPJ.

The fourth lumbrical muscle inserts into the planter medial fibers of the extensor wing to help abduct and extend the proximal phalanx. The intrinsic third plantar interosseous and flexor digiti quinti brevis muscles insert into the plantar medial and lateral aspects of the proximal phalanx respectively and function to stabilize the MTPJ against the stronger extrinsic FDL and EDL. The abductor digiti minimi muscle originates from the calcaneus and inserts into the plantar lateral aspect of the proximal phalanx to place an abductory force on the toe.

The last 2 muscles to affect the fifth digit are the FDL and flexor digitorum brevis (FDB); both plantarflex the toe. The FDL is deep to the FDB until the PIPJ where the FDB splits, allowing the FDL to become superficial and continue distally to insert into plantar portion of the distal phalanx. The FDB then rejoins to insert into the plantar aspect of the middle phalanx.

Contraindications for surgery include adequate control with conservative treatment, poor circulation, underlying infection, or any systemic condition that would inhibit healing of the surgical site.