Fifth-Toe Deformities

Three bones make up the fifth toe: the distal, middle, and proximal phalanges. They articulate together to make the distal interphalangeal (DIP) joint (DIPJ) and the 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 two-boned (biphalangeal) 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 often unable to accommodate pressure from standard shoes. This variant is more susceptible to irritation and may develop into a painful deformity.[3]

In a descriptive prospective study of 2494 feet in 1247 people, Gallart et al reported that a biphalangeal fifth toe was present in 46.3% of the feet and was bilateral in 97.4% of these cases.[4] The percentage of pathologic toes was significantly higher in patients with triphalangeal fifth toes (29.91%) than in those with biphalangeal toes (15.60%). The authors suggested that there may be an association between pathologic deviations and the greater mobility of triphalangeal fifth toes and that the greater rigidity of biphalangeal fifth toes may lead to lesser accommodation inside the shoe, which might result in less painful feet and decreased need for surgery.

In a cross-sectional obervational study, Ucpunar et al compared the incidence of biphalangeal fifth toe in 672 patients with foot deformities with that in 332 control subjects.[5]  They found no significant difference in incidence between the two groups (33% in the foot deformity group vs 31.9% in the control group). 

The MTPJ has an extensor wing-and-sling mechanism that aids in extension of the digit. A slip of the extensor digitorum longus (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 (EDB) 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 plantar-medial fibers of the extensor wing to help adduct and plantarflex 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 flexor digitorum longus (FDL) and EDL. The abductor digiti minimi originates from the calcaneus and inserts into the plantar-lateral aspect of the proximal phalanx to place an abductory force on the toe.

The final two muscles to affect the fifth digit are the FDL and the flexor digitorum brevis (FDB), both of which 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 the plantar portion of the distal phalanx. The FDB then rejoins to insert into the plantar aspect of the middle phalanx.

Corns

The simplest of the fifth-toe deformities are corns—namely, the hard corn (heloma durum) and the soft corn (heloma 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 a 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 proximal interphalangeal (PIP) joint (PIPJ), but corns can also occur in the same location over the distal interphalangeal (DIP) joint (DIPJ) (see the image below).[6]

The corn is typically associated with a hammertoe deformity (dorsiflexion contracture at the metatarsophalangeal [MTP] joint [MTPJ] and plantarflexion contracture at the PIPJ) that may have a varus rotational contracture. This makes the dorsal lateral aspect of the PIPJ more prominent and susceptible to footwear irritation. The corn can be superficial or deeply seeded; the latter is more painful. Additionally, constant pressure may cause a painful bursa to develop deep in the lesion, leading to nerve entrapment and increased pain.

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

Kissing corns

Kissing corns are two calluses rubbing against each other on adjacent toes (see the 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 the third and fourth images below). When they occur, other common problems, such as fungal infections or verruca, must be ruled out. If left untreated, these lesions may also develop into ulcerations in patients with neuropathy.

Hammertoe, claw-toe, and cock-up deformities

Hammertoe,[7, 8, 3]  claw-toe,[9] and cockup deformities are all variations of the same problem.[10] The presence of a dorsiflexion contracture at the MTPJ and a plantarflexion contracture at the PIPJ is constant among the three (see the image below). The claw-toe deformity has the addition of a plantarflexion contracture at the DIPJ. The term cockup 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 cockup 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, the PIPJ, and the DIPJ, allowing the more powerful extrinsic flexors and extensors to act unchecked. This eventually leads to the deformities described above.

Overlapping and underlapping fifth toes

Unlike the other conditions mentioned, overlapping and underlapping fifth toes are usually congenital deformities.[11] The overlapping fifth toe is a common familial deformity with equal sex predilection and usually presents bilaterally (see the 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, often referred to as curly toe or congenital varus toe (see the 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 an attenuated dorsal capsule. Constant pressure at the lateral nail and digital skin creates pain.

The only laboratory studies needed are standard preoperative tests.

Standard anteroposterior (AP), lateral, and oblique weightbearing radiographs are obtained as part of the initial workup. (See the images below.) Lesion markers can be applied over the hard and soft corns to help identify the correct underlying condyle. AP and oblique views readily show exostosis, enlarged condyles, and varus deformity of the toe. The lateral view is helpful in identifying the severity of the dorsal and plantar contractures at the metatarsophalangeal (MTP) joint (MTPJ) and the proximal interphalangeal (PIP) joint (PIPJ).

Surgical correction is indicated for chronically painful hard and soft corns in cases where conservative treatment fails. Patients with neuropathy may also choose surgery for prophylaxis against chronic lesions that may lead to ulceration and other morbidity. This has also proved beneficial for treating patients with chronic ulcerations to prevent amputations.[12]  Surgical correction is also indicated for progressively painful hammertoes or over- or underlapping toes if conservative treatment fails.

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.

Medical therapy is commonly considered conservative care. Conservative treatment for hard corns and soft corns involves periodic shaving by a healthcare professional using a scalpel or paring device. This is reinforced by regular use of a pumice stone or callus file during or after bathing.

Protective padding can be used over hard corns to decrease shoe irritation, and toe spacers are available to ease pressure on soft corns. To decrease pressure, multiple devices such as gel pads, foam, felt, devices with cutouts to accommodate lesions, and moleskin are available over the counter. Wearing wider shoes is a simple way to decrease pressure placed on hammertoes or other rotational deformities. Modifying and stretching the shoes can accomplish the same goals.

Surgical therapy depends on the type and level of the deformity. One must determine the underlying pathology and the degree of bone and soft-tissue involvement.

Angular deformities can be corrected with a combination of bone cuts and derotational skin incisions. Areas with contracted skin or tendons may require lengthening procedures, tenotomy, or both.[13, 14]

Hard corns

Hard corns are probably the most common fifth-toe deformities and yield the most options for treatment. These lesions occur most frequently on the dorsum of the proximal interphalangeal (PIP) joint (PIPJ) as a result of a hammertoe deformity or on the dorsolateral aspect of the PIPJ as the result of a hammertoe with varus rotation. Corrective procedures include the following:

• Partial condylectomy
• Exostectomy
• Hemiphalangectomy
• PIPJ arthroplasty with resection of the proximal phalangeal head
• Some combination of the above

A derotational skin plasty is often included for the varus-rotated toe, and a flexor tenotomy or extensor lengthening can be included for a straight hammertoe deformity.

Soft corns

Surgical correction for soft corns involves resection of the appropriate bony prominence. This usually involves a combination of condyles from the fourth and fifth digits. A rotational deformity may also be present in the fifth toe, which should be addressed. Typical surgical options are as follows:

• Resection of the lateral condyle on the base of the fourth toe proximal phalanx and the medial condyle on the head of the fifth toe proximal phalanx
• Resection of the prominent condyles at the lateral aspect of the fourth PIPJ and the medial aspect of the fifth distal interphalangeal (DIP) joint (DIPJ)

Web-space incisions should be avoided to prevent infections and painful scarring.[15]

Hammertoe, claw-toe, cockup fifth-toe deformities

Surgical approaches vary, depending on the severity of the deformity. The simplest hammertoe is one that is completely reducible with no bony obstruction to straightening. This is clinically determined by manually straightening the toe. If a very mild deformity is completely reducible, a soft-tissue procedure with proper splinting of the digit may be all that is needed for correction. Examples of these are extensor tendon lengthening, dorsal metatarsophalangeal (MTP) joint (MTPJ) capsulotomy, and flexor-tendon release.[16, 17]

PIPJ arthroplasty is added to the soft-tissue releases in more advanced cases that are semireducible or nonreducible. Most surgeons favor PIPJ arthroplasty as a primary procedure because it resolves a contracted PIPJ and functionally lengthens the extensor and flexor tendons, decompressing the MTPJ and the DIPJ. After this is performed, the foot is put into a simulated weightbearing position by pushing up on the fifth metatarsal head.

The dorsal contracture at the MTPJ should resolve, and the toe should straighten. If residual contracture at the MTPJ is present, dorsal capsulotomy is performed and lengthening of the extensor tendon should be considered. Arthrodesis is described for correction of hammertoes but should not be performed in the fifth digit; it leaves the toe too straight, and this causes irritation when shoes are worn.

The Ruiz-Mora and syndactylization procedures are commonly described salvage options for severe or recurrent cockup fifth-toe deformities.[18] The original Ruiz-Mora procedure involved removing the entire proximal phalanx, which left the toe somewhat shortened and unstable. Janecki described the modification more commonly used today, which calls for a subtotal proximal phalangectomy.[19] Patients should be advised that a good deal of shortening occurs, which may not be cosmetically appealing. (See the images below.)

The initial step of the Ruiz-Mora procedure is the removal of an ellipse of skin plantar to the proximal phalanx curving slightly medial at the proximal margin of the incision. The flexor tendons are dissected and retracted to expose the PIPJ. A transverse capsulotomy is performed, the collateral ligaments are released, and a subtotal phalangectomy is performed at the head of the proximal phalanx. If a large portion of the bone is removed, the flexor and extensor tendons are held together with purse-string sutures of 2-0 nonabsorbable material. The skin is closed in such a way as to allow correction of the toe in a plantar-medial direction.

Complications of the Ruiz-Mora procedure include the following:

• Instability of the toe
• Fourth digit hammertoe formation
• Callus formation
• Bunionette deformity

Postoperatively, the patient is allowed to ambulate in a stiff-soled shoe, and the toe is splinted or taped in the corrected position for 6 weeks.

Syndactylization of the fifth toe to the fourth is generally reserved as a salvage procedure or to resolve a painfully fibrosed web-space lesion secondary to long-standing soft corns. Syndactylization provides excellent stability for an unstable or flail fifth toe.[20] With this procedure, the skin incisions on the fourth and fifth toes should be mirror images of each other. A good technique is to scribe the initial incision on the fifth digit with a surgical pen and then press the two digits together where they are to be joined. The ink is transferred to the fourth digit in the precise area where the incision should be placed.

The island of tissue created with the incision is carefully dissected to remove only the skin and to leave the subcutaneous tissue intact. Meticulous hemostasis is practiced, and a needle-tipped electrocautery device should be used for precision. Bone work and isolated tendon balancing can be performed through the open sulcus if needed. The skin is closed by placing all of the sutures throughout the site prior to tying the knots. This allows easier and more accurate passage of the needle through the skin margins of the toes. Sutures are left in for 1 extra week (total, 3 weeks), and the digits are splinted for an additional 2-3 weeks.

Underlapping and overlapping fifth-toe deformities

Many procedures have been described for the correction of an overlapping fifth toe. The deformities range from moderate to more severe, and the procedure chosen should address the existing contractures. The surgical treatment often includes the following:

• Lengthening of the contracted skin and tendon and release of the tight capsular structures
• Resection of redundant skin and soft tissue

Osseous contractures, if present, also must be addressed by means of ostectomy, arthroplasty, or both.

The images below illustrate one technique for correcting a painful overlapping fifth-toe deformity. Schuh et al described their experiences with the Butler technique.[21]  Simoes et al also found the Butler arthroplasty to be effective for an overriding fifth toe.[22]

The DuVries procedure is indicated for correcting a mildly overlapping fifth toe. The area over the fourth interspace is longitudinally incised from the base of the toe to just proximal to the fifth metatarsal head. The MTPJ contractures are released via medial capsulotomy and release of the medial collateral ligament. The extensor digitorum longus (EDL) tendon is then released or lengthened to achieve the final release. The toe is placed into an overcorrected plantar and lateral position, and the skin is closed in this orientation. Dog-ears are removed when they occur.

Wilson described a modification to the procedure incorporating a V-Y skin advancement to lengthen the contracted skin dorsomedially.[23] Similar releases of the capsule and tendon are performed through the V-Y incision to complete the procedure. The authors use a Z-plasty advancement technique to lengthen the contracted skin dorsomedially. This affords greater lengthening potential, and the results are more cosmetically appealing than would be the case without the modification. PIPJ arthroplasty with appropriate capsule balancing completes the procedure, resulting in an excellent correction.

Lapidus described using a tendon transfer to correct severely overlapping fifth toes.[24] He transferred the EDL under the MTPJ and into the abductor digiti quinti. Other modifications have been described, including transfer of the EDL into the metatarsal neck, Z-plasty, dorsal capsulotomy with plantar capsulorrhaphy, and PIPJ arthroplasty. When possible, extensive dissection should be avoided because the toes tend to become postoperatively edematous, leading to pain and difficulty fitting shoes.

Underlapping fifth toes typically have a contracted plantar MTPJ capsule and flexor digitorum longus (FDL) with an attenuated EDL and a redundant dorsal MTPJ capsule. Underlapping fifth toes are usually flexible deformities in the pediatric population; tenotomy at the FDL and the flexor digitorum brevis (FDB) with appropriate splinting typically offers good results. However, as with the other conditions mentioned, the degree of deformity must be accounted for, and the appropriate adjunct procedures should be performed.

The Thompson technique is widely used and offers good results.[25, 26] Thompson described a Z-type incision over the proximal phalanx with the distal limb laterally oriented and the proximal limb medially oriented. Dissection extends to the PIPJ, where the head of the proximal phalanx is freed of soft-tissue attachments and resected using a microsagittal saw. The amount of head resection depends on the severity of the deformity, but care should be taken not to remove too much because this makes the toe unstable.

The soft tissue is appropriately augmented, the toe is derotated, and the flexor and extensor tendons are held together with purse-string sutures by using 2-0 nonabsorbable material. In less severe deformities, the purse-string suture can be left out and the capsule simply closed in a standard fashion. Adding a Kirschner wire (K-wire) across the PIPJ for 3-4 weeks or splinting with dressings for the same period can provide stability.

Finally, the Z-incision is reversed and closed with 4-0 nylon. A variation of the Thompson procedure involves a derotational skin plasty by creating a tissue island with a converging semielliptical incision over the PIPJ oriented from distal-dorsal-medial to proximal-plantar-lateral. As with the other procedures, the patient is allowed to ambulate in a postoperative shoe and is gradually transitioned to a roomy athletic-style shoe. The toe should be splinted in the corrected position for 6 weeks.

The most common complication involving fifth-toe procedures is the development of a flail toe. Other potential problems include vascular embarrassment, undercorrection, recurrence, and prolonged edema. Meticulous dissection and tissue handling are the best defenses against vascular problems or prolonged edema. Proper planning should decrease the chance of recurrence or undercorrection.