Curly Toes

Curly toe is a flexion-and-rotation deformity of a lesser toe that makes it curl under its neighbour. It is a common paediatric condition, most often affects the 3rd, 4th or 5th toes, and is caused by tightness of the flexor digitorum brevis (FDB) and flexor digitorum longus (FDL) tendons.

Who. It usually presents in early childhood, is bilateral in many cases and often runs in families. It is more common than the other lesser toe deformities in children, and it is developmental rather than acquired, which sets it apart from the lesser toe deformities of adults.

Why it matters. Some of these toes are painless and only a cosmetic concern; others hurt, catch on socks and make shoes difficult. For the flexible symptomatic toe in a child aged 4-12 years a simple flexor tenotomy succeeds in over 90%, so the examiner's interest is in whether you can pick the right toe, the right age and the right operation.

Cause. The FDB and FDL are relatively tight, so the flexors overpower the extensors. A familial tendency (a genetic component) is recognised, and the deformity is present from early childhood. Tight shoes may worsen it but do not cause it, it may become more apparent with growth, flexible deformities respond better to tenotomy, and older children may develop fixed contractures.

Natural history. Under 4 years some toes improve spontaneously with growth, but published rates run from about 25% to over 90%, so do not commit to a figure; the toes that persist are usually asymptomatic. Between 4 and 12 years the deformity is usually stable or slowly progressive if untreated, and beyond 12 it may become rigid and less responsive to simple tenotomy. Functional impact is variable: some children have no symptoms and others have significant problems.

Curly toe is one of the lesser toe deformities, and its defining feature is that the deformity is driven by a tight flexor tendon in a toe with otherwise normal joints. That separates it from hammer toe (PIPJ flexion with MTPJ extension) and claw toe (MTPJ extension with both interphalangeal joints flexed), and it is why a flexor procedure alone corrects it.

What the tight flexor does. The toe flexes at the PIPJ and DIPJ, rotates medially or laterally, and curls under the adjacent toe. The result is pain, difficulty with shoes and catching.

Flexor Tendon Anatomy

Flexor digitorum brevis. FDB arises from the calcaneal tuberosity and inserts on the middle phalanges, splitting into two slips before it does so; it flexes the PIPJ and MTPJ. It lies superficial to FDL, so it is the first tendon met and the first divided at tenotomy.

Flexor digitorum longus. FDL arises from the posterior tibia and inserts on the distal phalanges as a single tendon; it flexes the DIPJ, PIPJ and MTPJ. It lies deep to FDB and is divided second.

Digital neurovascular anatomy. The digital nerves run along the medial and lateral sides of each toe, with the digital arteries beside them, and the midline holds only the flexor sheath and its tendons. That is why the tenotomy incision is a 2-3mm transverse cut placed exactly in the midline at the PIPJ flexion crease: the sheath is safe to open there, both tendons are reached, and neither neurovascular bundle is met.

Curly toes are grouped by flexibility, which decides whether a soft-tissue operation can work, and by severity, which decides whether anything needs doing at all. The age-based grouping is the treatment decision itself and sits under Management.

History. Age comes first, because it frames everything that follows. Then ask what the toe actually does to the child: pain, difficulty with shoes or with particular shoes, catching on socks, any limit on activities, and whether the deformity is getting worse or has stayed the same. Ask whether other family members have curly toes.

Examination. The examination has one question at its centre, which is whether the toe can be straightened by hand.

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Differential Diagnosis of the Deformed Lesser Toe

The single most common examiner trap is to label every malpositioned lesser toe a "curly toe". Each deformity has a distinct plane, mechanism and operation. Curly toe is a flexion-and-rotation deformity driven by tight long flexors; it must be separated from the coronal-plane overlapping toe, the hyperextension-based hammer/claw/mallet toes, the crossover toe of the adult second ray, and the dorsally subluxed congenital overriding fifth toe.

A clinical diagnosis. A flexed and rotated toe curling under its neighbours is diagnostic, and a simple case may not need imaging at all. AP and lateral radiographs of the foot are usually normal; when they are taken their job is to rule out a skeletal abnormality and to assess joint alignment, and they confirm that there is no bony deformity rather than make the diagnosis.

When to image. Reserve radiographs for:

• An atypical presentation with an unusual deformity pattern
• A rigid deformity, to look for joint contracture or a bony abnormality
• Multiple deformities, to rule out an underlying condition
• Pre-operative planning in a complex case

Algorithm

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The decision. Age is the primary factor in choosing treatment, and flexibility is assessed alongside it: a rigid deformity needs a bony procedure regardless of age.

Under 4 years: observe, for the right reason. The spontaneous-resolution figures cannot be reduced to one number (see the pearl under Controversies), so observation is justified because the deformity is usually painless and surgery can wait, not because correction is predictable. Tell parents honestly that some toes straighten, many do not, and that the literature does not allow a confident percentage, but that persistence is usually painless; promising resolution sets a family up to feel misled at age 5. Avoid surgery in very young children and reassess at age 4 if the toe is still there.

4-12 years: flexor tenotomy. This is the optimal age. For the symptomatic flexible toe, division of FDB and FDL succeeds in over 90% with appropriate technique, and it can be done at any point in this age range.

Over 12 years: assess flexibility before choosing. If the toe is still flexible, tenotomy may still work. If it is rigid, it needs a tendon transfer, FDL to the extensor hood (Girdlestone-Taylor), or an osteotomy if there is bony deformity.

Why the transfer is reserved for the rigid toe. A double-blind randomised trial (Hamer, PMID 8331129) is conventionally cited as showing that simple tenotomy matches flexor-to-extensor transfer in the childhood curly toe. In a flexible deformity, then, the transfer's extra dissection, scar and stiffness risk buy nothing. The transfer earns its place only where a tenotomy cannot work because the deformity is no longer flexor-driven.

Conservative measures. For mild cases or children under 4, the options are observation and reassurance. Explain the natural history accurately: persistence is the commoner outcome, and it is persistence without symptoms that makes observation reasonable. A wider toe box may help and padding between the toes may provide some relief.

Strapping and taping. In the older child strapping is ineffective: Turner found 68% of toes improved while the strapping was on, but the correction was lost once it stopped. The exception is the neonate. Taping begun within about 10 days of birth improved or cured 94% of 84 toes in Smith's prospective series. So the honest statement is not "taping does not work" but "taping works only in a window that closes in the first weeks of life", which is also why it is worth recognising these toes on the newborn check.

Indications for surgery. Most symptomatic cases in the 4-12 year age group benefit from surgical release. Operate for:

• Pain, from nail weight-bearing or dorsal rubbing
• Corns or calluses from shoe pressure
• Functional problems: catching on socks, difficulty with shoes
• Under-riding that puts pressure on the adjacent toe
• Significant cosmetic concern causing distress
• Failed observation (if under 4, reassess at 4)
• Age 4-12 years, the optimal window for tenotomy

Recurrence is the complication to know, and it is usually from incomplete division of FDB or FDL. The others are listed for completeness; the nerve injury is the one the midline incision is designed to avoid.

The aftercare is simple. The gauze between the toes is what holds the correction and prevents recurrence.

Results. Ross and Menelaus reported success in roughly 95% of 188 toes, and results above 90% are the expectation when the operation is done correctly; the keys are complete division of the offending flexor tendon(s) and an incision that does not cross a flexor crease. Recurrence runs at 5-10%, usually from incomplete division. It is a day-case procedure with a quick recovery, most children are back to normal activities within 2-4 weeks, and the cosmetic and functional improvements are usually excellent. It is one of the most successful and lowest-morbidity paediatric foot procedures.

What predicts a good result.

• Age 4-12 years
• A flexible rather than rigid deformity
• Complete division of both FDB and FDL
• Gauze between the toes afterwards, to prevent recurrence

Global epidemiology

• Congenital curly/varus/underlapping and overlapping toes were found in 2.8% of newborns screened in a prospective study (Smith et al).
• The deformity is frequently bilateral and often familial (autosomal dominant tendency reported in some families), affecting the 3rd, 4th and 5th toes most often.
• Spontaneous improvement is quoted from about 25% (Smith et al, citing world literature) to over 90% in other series - the spread reflects different ages at review, different definitions of "resolved", and screened versus clinic-presenting cohorts. Quote the range, not a point estimate; toes that persist are commonly asymptomatic.
• There is no implant or arthroplasty registry relevant to curly toe - it is a soft-tissue paediatric procedure - so the evidence base is case-series driven rather than registry driven, unlike adult forefoot reconstruction.

Side-by-side guidance from major bodies

The points of genuine divergence are timing (earlier in severe overlapping per the Tokioka school versus a symptom-led approach elsewhere) and division versus lengthening of the flexor. All converge on observation for the asymptomatic flexible toe and on a flexor-based soft-tissue operation as the workhorse.

High- versus limited-resource practice variation

The "facts" most candidates recite about curly toes are softer than they sound. Being able to articulate the genuine areas of debate marks out a strong answer.

Timing of surgery. There is no consensus age. A symptom- and flexibility-led pathway is widely taught, but Tokioka and colleagues argue that severe overlapping toes should be corrected by 2-3 years because spontaneous correction is unlikely and later surgery risks skeletal deformity. Others defer until school age to avoid operating on toes that may settle. The honest answer is that timing is individualised, not fixed.

Tenotomy versus lengthening. Simple division sacrifices active toe flexion, which is usually clinically irrelevant, whereas Z-lengthening (Jacobs and Vandeputte) aims to preserve flexion power and strength. Whether retaining active flexion of a lesser toe matters functionally is unproven, and lengthening is technically more demanding.

Which tendon to divide. Teaching ranges from FDB slip only (Tokioka) to both FDB and FDL, the common exam answer. Ross and Menelaus emphasised dividing whatever short flexor is the sole cause of deformity. The pragmatic rule is to divide enough that the toe straightens fully on the table, then confirm.

The role of conservative treatment. Strapping fails to hold correction once stopped in older children (Turner), yet neonatal taping cured or improved 94% of toes (Smith). The window in which non-operative treatment works may be confined to the first weeks of life, a genuine and underappreciated nuance.