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 are typically subdivided into the pathology of the hallux, or great toe, and pathology of the lesser toes. The fifth toe is the most distal and lateral structure in the forefoot is comprised of 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, 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 one and is comprised of the flexor digitorum longus (FDL) tendons, which insert on the base of the distal phalanx of toes 2to 5 and serve to flex the proximal and distal interphalangeal joints. The flexor hallucis longus (FHL) tendon, which inserts on the base of the distal phalanx of the great toe and serves to flex the interphalangeal joint of the great toe. The quadratus plantae muscle, which inserts on the tendon of the flexor digitorum longus, assists with flexion of toes 2 to 5. Finally, the lumbrical muscles which originate from the tendon of FDL and insert on EDL serve to flex the metatarsophalangeal joints and extend the interphalangeal joints of toes 2 to 5
Layer 3 is comprised of the flexor hallucis brevis muscle, which inserts on the base of the proximal phalanx of the hallux and flexes the great toe. Within the two heads of the flexor hallucis, brevis lie the sesamoid bones of the great toe. The adductor hallucis muscle, which is comprised of an oblique and transverse head serves to adduct 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 is comprised of the dorsal interosseous muscles which serve to abduct the toes at the metatarsophalangeal joints while 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 invertor, and is crucial to the maintenance of the arch of the foot
The dorsum of the foot contains the muscle bellies of 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 extends the interphalangeal (IP) joint of the hallux.
Understanding the anatomy of the foot is critical to understanding its various deformities. Deformities of the fifth toe are often congenital and include deformities such as an overlapping fifth toe or a congenital curly toe.
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.
Congenital Curly Toe
A curly toe, underlapping toe, or underriding toe is a congenital deformity of the fifth toe that is 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 (FDL) subluxation, which alters the mechanical axis of the flexor tendons and results in the flexion and varus deformity seen in some children. Another theory states that the cause of a curly toe is due to an over-pull of the flexor digitorum longus (FDL) tendon and eventual shortening of the tendon, which can result in a flexion deformity.
Overlapping fifth toes and congenital curly toes do not appear to have an increased prevalence based upon gender and the condition is commonly a bilateral finding.
Patient's with a congenital deformity of the fifth toe are frequently brought to orthopedists as small children by their parents with cosmetic concerns, or as later when the child has difficulty in obtaining comfortable shoewear.
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 resulting in an exacerbation of the deformity. The condition is often passively correctable, and observing the foot during weight-bearing may result in a reduction of the deformity.
Curly Toe Deformity
A curly toe will present as a flexion deformity of the interphalangeal joints of the fifth toe, and result 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.
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 the evaluation of such deformities.
Overlapping Fifth Toe
Generally, an overlapping fifth toe will correct as children begin to walk. Strapping and bracing may be used in some cases, but the deformity will often return after the bracing is stopped. Thus custom shoewear may be a better option for cases of symptomatic overlapping fifth toe deformities that do not correct themselves.
Operative intervention is reserved for refractory cases of an overlapping fifth toe resulting in irritation of the toe and difficulty with shoewear. The goal of any operative intervention is to abduct, plantarflex, and internally rotate the deformed toe. This has been achieved historically by transfer of the extensor digitorum longus (EDL) tendon to the conjoining tendons of the abductor digiti minimi and the flexor digitorum brevis. 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. 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 MTP, and the capsule and extensor tendon are incised, allowing the toe to rest in the anatomically correct position.
Congenital Curly Toe
Congenital curly toe most frequently corrects during early ambulation, and therefore observation is appropriate 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.
Historically, flexor tenotomies and flexor to extensor transfers were the mainstays of surgical treatment for refractory curly toe deformities; however, flexor to extensor transfers was shown to be less effective and more invasive than simple flexor tenotomies.
Lesser toe deformities are generally caused by an imbalance of the intrinsic and extrinsic musculature in the foot.
Mallet toes are flexion deformities of the distal interphalangeal joints and 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.
Hammertoes are flexion deformities of the proximal interphalangeal joints and extension of the distal interphalangeal joints, caused by an overpull of the extensor digitorum longus. Occasionally, metatarsophalangeal joint hyperextension is 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.
The vast majority of congenital fifth toe deformities resolve once childhood ambulation begins. Those that do not can generally be managed with nonoperative measures such as toe strapping and shoe modifications as previously discussed. In the rare case where operative intervention is indicated, the Butler procedure and flexor tenotomies generally provide favorable outcomes and correction of overlapping toes and congenital curly toes respectively.
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 most common.
Children with congenital deformities of the fifth toe and their parents should be reassured that these deformities are generally asymptomatic and will likely resolve with ambulation. If patents have discomfort with shoewear, there are many options to manage these deformities without surgery conservatively.
Congenital deformities of the fifth toe typically resolve on their own. When intervention is necessary, it is important to have a dedicated clinical team consisting of physicians and nurses to educate patients and their parents about the deformity and treatment strategy. [Level 5]
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