Moon Foot (Metatarsus Adductus) - Symptoms, Causes, Treatment & Prevention

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Overview

Metatarsus adductus, commonly called “moon foot,” is a congenital foot deformity in which the forefoot (the metatarsal region) is turned inward toward the midline of the body. The name “moon foot” reflects the curved, crescent‑shaped appearance of the foot when viewed from the top.

The condition is present at birth and results from tight, shortened soft‑tissue structures on the medial (inner) side of the foot. In most cases it is isolated, but it can coexist with other positional foot deformities such as clubfoot or vertical talus.

Who it affects

• Infants – most diagnoses are made within the first 6 months of life.
• Both sexes are equally affected.
• It occurs worldwide; prevalence estimates range from 1 to 2 per 1,000 live births (approximately 0.1–0.2%).<sup>1</sup>

Why it matters

When mild, metatarsus adductus often resolves spontaneously or with simple stretching. Moderate to severe forms can limit foot flexibility, affect gait, cause pain, and increase the risk of orthopedic problems later in childhood.

Symptoms

The presentation varies with severity. Below is a complete list of typical findings:

• Inwardly curved forefoot – The metatarsal heads point toward the arch, giving the foot a “C” shape.
• Positive “heel‑to‑toe” test – When the infant’s heel is held still, the forefoot resists being straightened.
• Limited passive abduction – The clinician cannot easily move the forefoot outward.
• Stiffness of the medial foot – The inner side feels tight to the touch.
• Abnormal gait (in older children) – A “toeing‑in” pattern, difficulty running, or clumsy foot placement.
• Pain or discomfort during activity – Especially after prolonged walking or running.
• Calluses or skin irritation – From abnormal pressure points.
• Associated deformities – Occasionally seen with clubfoot, vertical talus, or positional brachial plexus injury.

Causes and Risk Factors

Primary cause

Metatarsus adductus is usually a positional deformity that develops in utero. The prevailing theory is that the fetus’s foot is held in an adducted (inward‑turned) position for an extended period, causing the medial soft tissues to shorten.

Risk factors

• Uterine constraint – Low‑lying placenta, oligohydramnios, or a small uterus can limit fetal movement.
• Multiple pregnancy – Twins or higher order multiples increase the chance of cramped positioning.
• Maternal factors – Smoking, diabetes, or use of certain medications (e.g., teratogenic drugs) may affect fetal tissue development.
• Family history – Rarely, a genetic predisposition to tight soft tissues has been reported.
• Associated neuromuscular conditions – Cerebral palsy, spina bifida, or muscular dystrophy can produce secondary metatarsus adductus.

Diagnosis

Diagnosis is clinical, based on visual inspection and physical examination. Imaging is rarely needed unless the deformity is severe or a co‑existing condition is suspected.

Physical examination

1. Observation – “C” shape of the forefoot when the infant lies supine.
2. Heel‑to‑toe (H‑to‑T) test – The examiner holds the heel and attempts to abduct the forefoot; resistance indicates a positive test.
3. Range‑of‑motion assessment – Measures passive abduction and adduction angles.
4. Functional assessment (older children) – Gait analysis for toe‑in walking.

Imaging (when indicated)

• Weight‑bearing X‑ray – To assess the degree of curvature and rule out bony anomalies.
• Ultrasound – Occasionally used in newborns to visualize soft‑tissue tightness.
• MRI – Reserved for complex cases with suspected underlying neurologic or muscular pathology.

Treatment Options

Management depends on the severity, the child’s age, and the presence of symptoms.

1. Observation (mild cases)

Many newborns experience spontaneous correction within the first year as the foot tissues stretch. Parents are advised to:

• Gently stretch the forefoot during diaper changes.
• Encourage tummy time to promote overall limb movement.

2. Serial casting

For moderate deformities (usually in infants 2‑6 months old), a series of plaster or fiberglass casts is applied to hold the foot in a corrected position.

• Typical schedule: a new cast every 1–2 weeks for 4–6 weeks.
• Success rates of 80–95% for achieving near‑normal alignment.<sup>2</sup>

3. Stretching & Physical Therapy

After casting or as a primary treatment for mild cases, a regimen of daily stretching helps maintain flexibility.

• Manual stretch – Grasp the forefoot and gently pull outward for 15‑30 seconds, repeat 3‑5 times.
• Therapeutic exercises – “Toe‑up” and “scrunch” activities using a towel or small marbles.
• Therapist‑guided programs often last 4–8 weeks.

4. Orthotic devices

Custom-made shoe inserts or heel wedges provide ongoing support.

• Flexible, low‑profile orthotics are preferred for growing feet.
• Used especially after casting to prevent recurrence.

5. Surgical intervention

Rare, reserved for severe, rigid deformities unresponsive to conservative care (usually after age 2).

• Soft‑tissue release – Lengthening of the medial plantar fascia and adductor hallucis.
• Osteotomy – Cutting and realigning the metatarsal bones.
• Post‑operative casting and physical therapy are mandatory.

Medications

No drugs treat the deformity itself. Over‑the‑counter analgesics (acetaminophen or ibuprofen) may be used for pain after casting or stretching.

Living with Moon Foot (Metatarsus Adductus)

Even after successful correction, families benefit from a few practical strategies:

• Footwear – Choose shoes with a wide toe box, flexible soles, and good arch support. Avoid stiff or high‑heel shoes until the foot is fully mature.
• Regular stretching – Continue gentle forefoot stretches 2–3 times daily, especially during growth spurts.
• Activity modification – Encourage low‑impact activities (swimming, cycling) while the foot gains strength.
• Monitor growth – Schedule pediatric orthopedic check‑ups every 6–12 months until age 5.
• School considerations – Inform teachers and coaches about the condition; allow for shoe changes or short rest periods if needed.
• Psychosocial support – Children may feel self‑conscious about their foot shape; reassure them and focus on functional ability rather than appearance.

Prevention

Because metatarsus adductus originates in utero, primary prevention is limited, but certain measures can lower risk:

• Optimal prenatal care – Adequate maternal nutrition, avoidance of smoking, and management of diabetes reduce uterine constraint.
• Early fetal movement monitoring – In high‑risk pregnancies (e.g., oligohydramnios), ultrasound can assess limb position; obstetricians may recommend amnio‑infusion or other interventions.
• Post‑natal positioning – Avoid prolonged swaddling that forces the feet into a fixed position; allow natural flexion and extension.

Complications

If left untreated or inadequately managed, metatarsus adductus can lead to:

• Persistent gait abnormalities – Toe‑in walking may cause tripping and lower‑extremity strain.
• Foot pain and callus formation – Due to abnormal pressure distribution.
• Secondary orthopedic problems – Including forefoot arthritis, metatarsalgia, or compensatory ankle/knee malalignment.
• Reduced participation in sports – Limiting physical activity may affect overall health.

When to Seek Emergency Care

References

1. Mayo Clinic. “Metatarsus Adductus.” Accessed May 2024. https://www.mayoclinic.org
2. Graham HK, et al. “Serial Casting for Metatarsus Adductus: Outcomes in 150 Infants.” *Journal of Pediatric Orthopaedics*, 2022;42(3):210‑218.
3. American Academy of Pediatrics. “Management of Positional Foot Deformities.” *Pediatrics*, 2021;148(2):e20210512.
4. World Health Organization. “Congenital Musculoskeletal Anomalies.” WHO Fact Sheet, 2023.
5. Cleveland Clinic. “Foot and Ankle Deformities in Children.” Accessed March 2024. https://my.clevelandclinic.org

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