Continuing Education Activity

Deformities of the fifth toe are often congenital and include deformities such as an overlapping fifth toe or a congenital curly toe. Many of these deformities are asymptomatic, while some can result in discomfort and limitations on shoewear. Overlapping fifth toes and congenital curly toes do not appear to have an increased prevalence based on gender, and the condition is commonly a bilateral finding; for example, 13.8% was estimated to be the prevalence of bunionette deformity, and 61.2% of people had a positive family history. This activity reviews the deformities involving the fifth toe and the anatomy relevant to diagnosis and treatment. It highlights the role of the interprofessional team in the care of patients with this condition.

Objectives:

• Assess the anatomy relevant to deformities of the fifth toe.

• Evaluate the common deformities encountered in the fifth toe.

• Differentiate the appropriate treatment options for common deformities of the fifth toe.

• Communicate the importance of interprofessional collaboration in diagnosing and treating fifth toe deformities.

Introduction

Anatomically, the forefoot is considered the portion of the foot that extends from the tarsal-metatarsal joint to the tips of the toes, and pathology of the toes is typically subdivided into the pathology of the hallux, or great toe, and pathology of the lesser toes. The fifth toe is the forefoot's most distal and lateral structure and comprises the proximal, middle, and distal phalanges. The proximal phalanx articulates with the metatarsal at the metatarsophalangeal joint, and in turn, the proximal phalanx articulates with the middle phalanx at the proximal interphalangeal joint, and the middle phalanx articulates with the distal phalanx at the distal interphalangeal joint.

Layer 1, or the most superficial layer, is comprised of the following structures: The abductor hallucis muscle serves to abduct the great toe, whereas the flexor digitorum brevis muscle which inserts on the base of the middle phalanx of toes 2 to 5 and flexes the proximal interphalangeal joints and the abductor digiti minimi muscle which serves to abduct the fifth toe.

Layer 2 is immediately deep to layer 1 and comprises the flexor digitorum longus tendons, which insert on the base of the distal phalanx of toes 2 to 5 and serve to flex the proximal and distal interphalangeal joints. The flexor hallucis longus tendon inserts on the base of the great toe's distal phalanx and flexes the great toe's interphalangeal joint. The quadratus plantae muscle, which inserts on the tendon of the flexor digitorum longus, assists with the flexion of toes 2 to 5. Finally, the lumbrical muscles, which originate from the tendon of the flexor digitorum longus and insert on the extensor digitorum longus, serve to flex the metatarsophalangeal joints and extend the interphalangeal joints of toes 2 to 5

Layer 3 comprises the flexor hallucis brevis muscle, which inserts on the base of the proximal phalanx of the hallux and flexes the great toe. Within the 2 heads of the flexor hallucis brevis lie the sesamoid bones of the great toe. The adductor hallucis muscle, comprised of an oblique and transverse head, adducts the great toe. Finally, the flexor digiti minimi brevis muscle, which inserts on the base of the fifth toe proximal phalanx, flexes the fifth toe at the metatarsophalangeal joint.

Layer 4 is the deepest and comprises the dorsal interosseous muscles, which abduct the toes at the metatarsophalangeal joints. In contrast, the plantar interosseous muscles serve to adduct the toes at the metatarsophalangeal joints. The peroneus longus tendon travels from lateral to medial within the foot and inserts on the medial cuneiform, providing eversion and flexion to the ankle joint. Finally, the tibialis posterior tendon inserts on the navicular and acts as a foot supinator and inverter, crucial to maintaining the foot arch.

The dorsum of the foot contains the muscle bellies of the extensor digitorum brevis and extensor hallucis brevis. The extensor digitorum longus originates in the anterior compartment of the lower leg and inserts on the dorsum of the middle and distal phalanges of toes 2 to 5, serving to extend the toes and assist in ankle dorsiflexion while the extensor hallucis longus inserts on the dorsal base of the distal phalanx of the great toe and thus extend the interphalangeal joint of the hallux. Understanding the anatomy of the foot is critical to understanding its various deformities. Fifth-toe deformities are often congenital and include an overlapping fifth toe, a congenital curly toe, and a bunionette deformity.

Etiology

Overlapping Fifth Toe

Most commonly referred to as overlapping or overriding fifth toe, crossover toe, or digiti quinti varus is a congenital deformity that results from soft tissue contractions involving the dorsal skin, metatarsophalangeal joint capsule, or extensor tendon complex of the fifth toe resulting in dorsiflexion, adduction, and an external rotation type deformity of the toe. Medial displacement of the extensor digitorum longus tendon line of pull or axis, over time, leads to worsening contraction and exacerbation of the deformity.[1][2][3][4]

Congenital Curly Toe

A curly toe, underlapping toe, or underriding toe is a congenital deformity of the fifth toe characterized by a plantarflexion, varus, and external rotational deformity of the fifth or sometimes fourth toe interphalangeal joints. There has been debate about the underlying cause of a curly toe. One theory states that excessive pronation in the late midstance phase of gait results in flexor digitorum longus subluxation, which alters the mechanical axis of the flexor tendons and results in flexion and varus deformity seen in some children.[5] Another theory states that the cause of a curly toe is due to an over-pull of the flexor digitorum longus tendon and eventual shortening of the tendon, which can result in a flexion deformity.[4][6]

Bunionette Deformity

The bunionette deformity, or the tailor's bunion, includes lateral bony protrusion along the fifth metatarsal head. A large metatarsal head, lateral metatarsal bending, increased intermetatarsal angle (IMA), and keratosis development are known factors for symptomatic bunions.[7]

Epidemiology

Overlapping fifth toes and congenital curly toes do not appear more prevalent based on gender; the condition is commonly a bilateral finding.[4] For example, 13.8% was estimated to be the prevalence of bunionette deformity, and 61.2% of people had a positive family history.[8]

History and Physical

Patients with a congenital deformity of the fifth toe are frequently brought to orthopedists as small children by their parents with cosmetic concerns or later when the child has difficulty obtaining comfortable footwear.[3][4][9]

Overlapping Fifth Toe

The pathology of the overlapping fifth toe is observed at the metatarsophalangeal joint with adduction, dorsiflexion, and external rotation deformity of the fifth toe, resulting in an overlapping of the dorsum of the fourth toe. One may observe skin contractions or be able to palpate a tense extensor mechanism over the dorsum of the fifth toe. Sometimes, the deformity may extend to the interphalangeal joints of the toe, exacerbating the deformity. The condition is often passively correctable, and observing the foot during weight-bearing may show a reduction of the deformity.[3][4][10]

Curly Toe Deformity

A curly toe presents as a flexion deformity of the interphalangeal joints of the fifth toe and results in a toe that scissors underneath the adjacent toe towards the center of the foot. This deformity is typically passively correctable but may develop into a rigid deformity when there is a contracture of the flexor skin and soft tissue of the foot. Hyperkeratotic areas of skin may be noted at the tip of the toe or other points due to increased contact pressures within a shoe.[4][6][11][12]

Bunionette Deformity

The patients usually present with painful callosities over the head of the 5th metatarsal bone and increased forefoot width. This deformity is associated with flat feet and hallux valgus deformities. 

Evaluation

Congenital deformities of the fifth toe do not require routine laboratory or radiographic evaluation. X-rays may demonstrate an observed deformity, but physical examination is the most important tool in assessing such deformities. The weight-bearing radiograph reveals an increased intermetatarsal angle (>12 degrees) and metatarsophalangeal angle (>14 degrees) in Bunionette Deformity.[13]

Treatment / Management

Overlapping Fifth Toe

Nonoperative

Generally, an overlapping fifth toe corrects as children begin to walk.[14] Strapping and bracing may sometimes be used, but the deformity often returns after the bracing is stopped. Thus, custom shoewear may be a better option for symptomatic overlapping fifth toe deformities that do not correct themselves.[4][15][16]

Operative

Operative intervention is reserved for refractory cases of an overlapping fifth toe resulting in toe irritation and difficulty with shoewear. Any operative intervention aims to abduct, plantarflex, and internally rotate the deformed toe. This has been achieved historically by transferring the extensor digitorum longus tendon to the conjoining tendons of the abductor digiti minimi and the flexor digitorum brevis.[16][14][16] Some have attempted to correct the deformity by syndactylization of the fourth and fifth toes, which functions by using the fourth toe as a permanent splint for the fifth toe.[17] However, the Butler procedure is the gold standard of operative treatment for the overlapping fifth toe. In the Butler procedure, a racquet-shaped incision is made over the dorsum of the metatarsophalangeal joint, and the capsule and extensor tendon are incised, allowing the toe to rest in the anatomically correct position.[4][9]

Congenital Curly Toe

Nonoperative

Congenital curly toe most frequently corrects during early ambulation; therefore, observation is appropriate for initial management. Strapping has shown to be largely ineffective and has almost no role in management. Therefore, shoe modifications are appropriate for curly toes that cause discomfort after early childhood.

Operative

Historically, flexor tenotomies and flexor-to-extensor transfers were the mainstays of surgical treatment for refractory curly toe deformities; however, flexor-to-extensor transfers were shown to be less effective and more invasive than simple flexor tenotomies.[4][6] Painful lesions and deformities of the proximal interphalangeal joint (PIP) can be effectively treated by resecting the head of the proximal phalanx. The degree of flexion contracture at the proximal interphalangeal joint determines the extent of bone excision. The medial and lateral collateral ligaments are kept intact to eliminate the potential of a flail toe. After correcting the sagittal plane and rotational deformity, a K-wire is passed to hold the toe in the corrected position. Applying a Silastic lesser toe implant is a remedy for unsuccessful fifth toe resection arthroplasty.[18] Resection arthroplasty produces better results than the Ruiz-Mora procedure (phalangectomy).[19] The callus that forms over a bony protrusion in 1 of the little toes is known as a "corn." A thickened keratotic skin develops around the interphalangeal joint due to external shoe pressure. The treatment options range from using an enlarged toebox, doughnut-shaped pads, and foam pads to shaving the callus and excision of the bony prominences (condylectomy).[20]

Bunionette Deformity

Nonoperative

Conservative treatment options include wearing wide shoes, specialized accommodating orthotics, nonsteroidal anti-inflammatory drugs, and forefoot barrier pads. 

Operative

When conservative management fails, operative intervention is required according to the severity and grade of bunionette deformity. Resection of the lateral condyle and capsule plication is required for grade 1 deformity, preserving joint mobility and metatarsal length. The distal metatarsal osteotomy is used for type 2 deformity, which includes chevron-medializing osteotomy, step-cut osteotomy, transverse osteotomy, or oblique distal osteotomy. An oblique diaphyseal rotational osteotomy (Ludloff, scarf) is recommended for bunionette deformity with increased intermetatarsal angle (IMA). A lateral incision along the 5th metatarsal bone is made in all surgical approaches.[21][14]

Differential Diagnosis

An imbalance of the intrinsic and extrinsic musculature in the foot generally causes lesser toe deformities. Mallet toes are flexion deformities of the distal interphalangeal joints. They are most commonly caused by tightness or contracture of the flexor digitorum longus that inserts at the base of the distal phalanx of the lesser toes. Hammer toes are flexion deformities of the proximal interphalangeal joints and extension of the distal interphalangeal joints caused by an overpull of the extensor digitorum longus. Metatarsophalangeal joint hyperextension is occasionally present, and the deformity may be flexible or rigid. Claw toes are characterized by an extension deformity of the metatarsophalangeal joint, which results in unopposed flexion of the proximal and distal interphalangeal joints. This deformity is more commonly associated with neuromuscular diseases and inflammatory arthropathies.[22][23]

Staging

Bunionette Deformity Classification

1. Enlarged 5th metatarsal head
2. Lateral bowing of fifth metatarsal shaft but normal IMA
3. Increased IMA
4. Combination of enlarged head size and IMA[7]

Prognosis

The vast majority of congenital fifth toe deformities resolve once childhood ambulation begins. As previously discussed, those that do not can generally be managed with nonoperative measures such as toe strapping and shoe modifications. In rare cases where operative intervention is indicated, the Butler procedure and flexor tenotomies generally provide favorable outcomes and correct overlapping and congenital curly toes, respectively.[4] Minimally invasive techniques have produced promising results following bunionette correction.[24]

Complications

The most likely complaint associated with refractory cases of congenital fifth toe deformities is discomfort with shoewear. In cases that do not resolve in early childhood, nonoperative management is still often effective, but recurrence of the deformity may be more likely long-term. If surgery is attempted, complications are minimal, with infection and scarring being the most common.[25] Delay in wound healing, malunion, nonunion, metatarsalgia, recurrence, overcorrection, under-correction, and subluxation of the metatarsophalangeal joint are among the complications that might result after bunionette correction.[26]

Postoperative and Rehabilitation Care

K-wire fixation has proven to be more effective than serial strapping. Sutures are routinely taken out 2 to 3 weeks following imaging, and K-wires are retrieved in the clinic 6 weeks afterward. For an extra 6 weeks, bonnet tapping in the form of strapping is suggested.[4] Following metatarsal osteotomies, foot splints are advised for 2 weeks, and a short leg cast is applied for another 4 weeks. Patients can put weight on their feet at 6 weeks, although they are encouraged to return to normal activities in 8 to 10 weeks while wearing supportive shoes. By 12 weeks, most people can withstand contact activity.[7]

Deterrence and Patient Education

Children with congenital deformities of the fifth toe and their parents should be reassured that these deformities are generally asymptomatic and likely resolve with ambulation. If patients have discomfort with shoewear, many options exist to manage these deformities without surgery conservatively.

Enhancing Healthcare Team Outcomes

Congenital deformities of the fifth toe typically resolve on their own. When intervention is necessary, a dedicated interprofessional team consisting of clinicians (MDs, DOs, NPs, PAs, and podiatrists), physical therapists, surgical assistants, and nurses must educate patients and their parents about the deformity and treatment strategy. Nurses often liaise between the various disciplines working on the case. All interprofessional team members must document their findings and interventions with the patient. If they note any concerns, open communication is necessary to alert the appropriate team members regarding the need for a change in strategy or other changes to the patient's management. This interprofessional paradigm yields the best patient results.