Metatarsus Adductus

Metatarsus Adductus is a benign, self-limiting congenital foot deformity caused by intrauterine packaging. It is characterized by adduction of the forefoot at the tarso-metatarsal joints while the hindfoot remains normally aligned (or in slight valgus). This condition is distinct from Clubfoot (Talipes Equinovarus) where the hindfoot is in varus and equinus.

Aetiology: The exact aetiology is multifactorial but strongly linked to mechanical factors in utero.

• Intrauterine Packaging: The most widely accepted theory. Increased pressure in a growing fetus, particularly in firstborns or in oligohydramnios, forces the feet into an adducted position against the uterine wall. This mechanical compression explains the strong association with other "packaging disorders" like muscular torticollis (sternocleidomastoid contracture) and Developmental Dysplasia of the Hip (DDH).
• Genetics: Familial tendency (polygenic inheritance). There is a higher incidence in siblings of affected patients (approx 1 in 20).
• Muscular Imbalance Theory: Some theories propose an imbalance between the abductor hallucis (which is found to be hypertrophied and tight) and the peroneal muscles (which are weak/lengthened). However, it is debated whether this is a primary cause or secondary to the deformity. The tibialis posterior tendon is also typically shortened.

Epidemiology:

• Incidence: Approximately 1 in 1000 live births. However, mild cases are often underdiagnosed or resolve so quickly they are not recorded in birth registries.
• Gender: Generally reported as equal Male = Female, though some series show a slight female predominance (similar to DDH).
• Laterality: Bilateral in approximately 50-60% of cases. In unilateral cases, the left foot is slightly more commonly affected, ostensibly due to the common position of the fetus (Left Occiput Anterior).
• Birth Order: Significantly more common in firstborn children due to the "tight" nulliparous uterus (known as the "primigravida effect").

History of Treatment:

Historically, treatment involved forceful manipulation and strapping, or aggressive soft tissue releases (Heyman-Herndon). Long-term follow-up studies (Rushforth, Farsetti) demonstrated the benign natural history, leading to a shift towards observation for flexible cases and serial casting for rigid ones. Surgical intervention is now strictly reserved for older children with persistent rigid deformity causing symptoms.

Pathoanatomy: The deformity is primarily located at the Lisfranc Joint (Tarsometatarsal joint).

• Metatarsals: All metatarsals are adducted (deviated medially) relative to the cuneiforms and cuboid. The 1st metatarsal is often the most severely affected.
• Cuneiforms: The medial cuneiform is often misshapen (trapezoidal or wedge-shaped with the base lateral). This bony deformity helps maintain the adduction of the 1st ray.
• Navicular: Usually laterally subluxated on the talus head in Clubfoot, but in Metatarsus Adductus, the navicular position is relatively normal or slightly lateral.
• Hindfoot (Subtalar Joint): CRITICAL FEATURE. The calcaneus and talus are in a normal divergent relationship or in slight valgus. The talocalcaneal angle is normal. This is the key differentiator from Clubfoot (where the hindfoot is in varus and equinus) and Skewfoot (where the hindfoot is in distinct valgus).
• Soft Tissue Contractures:
  • Medial: Tightness of the abductor hallucis muscle, tibialis posterior tendon, and the medial tarsometatarsal joint capsules.
  • Lateral: Attenuation (lengthening) of the peroneal muscles (peroneus brevis and longus) and the lateral soft tissues.

Associated Anatomy:

• Acetabulum: Due to the association with DDH, the hip anatomy may be abnormal (dysplastic). Careful screening is mandatory.
• Sternocleidomastoid: May be contracted (Torticollis), leading to head tilt and rotation.

Biomechanics of Gait: If untreated, the adducted forefoot leads to an intoeing gait (pigeon-toed). Children often compensate by externally rotating the tibia or hip to bring the foot progression angle to neutral. This can lead to complex rotational profiles later in life ("squinting patellae" if femoral anteversion is also present). However, functional limitation is rare, and the condition is largely cosmetic in adulthood unless severe.

History:

• Onset: Note when the deformity was first noticed (birth vs later). Late onset suggests localized pathology or mimicking conditions.
• Family History: Ask about foot deformities, hip dysplasia, or "packaging" issues in siblings/parents.
• Pregnancy History: Breech presentation, oligohydramnios, first obstetric event.
• Gait: If walking, describe the foot progression angle (Intoeing). Parents often report the child "trips over their own feet".

Physical Examination:

• Inspection:

  • Forefoot Adduction: "Kidney Bean" shape.
  • Lateral Border: Convex.
  • Medial Crease: Deep crease in midfoot suggests rigidity.
  • Hindfoot: Neutral or slight valgus (NOT varus - that suggests Clubfoot).
  • Base of 5th: Prominent styloid.
  • Toe Splaying: Often a widened gap between the 1st and 2nd toes (resembling a thumb separation).

• Heel Bisector Test: Perform with child prone. Determine the Bleck grade (Normal, Mild, Mod, Severe).

• Flexibility Assessment: Stabilize the hindfoot with one hand. Use the other hand to apply valgus pressure to the forefoot. Can you get it to neutral? Past neutral? This dictates management.

• Lateral Border Stimulation (Tickle Test): Stroke the lateral border of the foot. A flexible foot will actively abduct due to peroneal muscle contraction. A rigid foot will not.

• Hindfoot Exam: CRITICAL STEP. Verify the hindfoot is neutral or valgus. If it is in varus, suspect Clubfoot. If it is in severe valgus with a rigid adducted forefoot, suspect Skewfoot.

• Hip Examination: MANDATORY. Perform Ortolani and Barlow maneuvers to rule out DDH. Document hip range of motion.

• Spine Exam: Rule out spinal dysraphism (hairy patch, dimple) which can cause foot deformities (e.g., cavovarus, but always good to check).

Plain Radiographs (Weight Bearing AP/Lateral):

• Infants: Generally NOT indicated. The tarsal bones are largely cartilaginous and not visible. Diagnosis is clinical.
• • Heel Bisector Line (Bleck): Normal passes through 2nd/3rd toe webspace. In MA, it passes lateral to the 3rd toe (through 4th or 5th toe).

• Metatarsus Adductus Angle: Angle between axis of tarsus and metatarsals (greater than 20 degrees is abnormal).

• Engel's Angle: Angle between the 2nd metatarsal and the intermediate cuneiform. Normal is less than 24 degrees.
• Talocalcaneal Angle (Kite's Angle):
  • Normal/MA: 20-40 degrees (divergent).
  • Clubfoot: Parallel (less than 15 degrees).
  • Skewfoot: Increased (greater than 40 degrees) due to hindfoot valgus.

Ultrasound:

• Hip Ultrasound: Indicated for any infant with Metatarsus Adductus if there are clinical risk factors or uncertain hip exam findings, due to the high association with DDH.

CT/MRI:

• Rarely indicated. May be used for complex tarsal coalition workup if rigidity is unexplained.

Immediate Post-operative Phase (0-2 Weeks):

• Immobilization: Non-weight bearing (NWB) short leg cast or backslab is applied in the operating room.
• Elevation: Strict elevation for the first 48 hours to minimize oedema and pain.
• Neurovascular Monitoring: Routine checks for toe perfusion, sensation, and movement (prevent compartment syndrome, though rare in foot).

Intermediate Phase (2-6 Weeks):

• Wound Check: At 2 weeks, the initial cast/splint is removed to inspect the incisions. Sutures are removed if non-absorbable.
• Re-casting: A definitive fiberglass short leg cast is applied. The foot is held in the corrected position.
• Weight Bearing: Continues to be Non-Weight Bearing to allow osteotomy union without displacement.

Union Phase (6 Weeks):

• Pin Removal: If percutaneous K-wires were used, they are removed in the clinic (or under sedation if buried).
• Radiographs: Check for callus formation and osteotomy union.
• Mobilization: Transition to a weight-bearing walking cast or a stiff-soled shoe (e.g., Darco shoe) for a further 2-4 weeks depending on radiographic consolidation.

Rehabilitation Phase (3 Months onwards):

• Shoe Wear: Return to normal footwear. Broad-toe box shoes recommended.
• Activity: Gradual return to running and sports.
• Follow-up: Annual reviews to monitor for recurrence or growth disturbance until skeletal maturity.

• Natural History: Excellent. Rushforth (JBJS 1978) showed 86% spontaneous resolution. Even mild residual deformity is compatible with normal function and shoe wear.
• Non-Operative: Serial casting has a greater than 90% success rate for rigid deformities if started in the first year of life.
• Operative: Good cosmetic correction. Functional outcomes are generally good, but there is a risk of midfoot stiffness and metatarsalgia in the long term.
• Adult Sequelae: Untreated metatarsus adductus is a risk factor for Hallux Valgus (Bunions) and lateral foot pain (Jones fracture risk due to load on lateral column) in adulthood, but this is debated.

Epidemiology:

• Common referral to Paediatric Orthopaedic clinics in Australia.
• Often managed by physiotherapists initially.

Management:

• State-based guidelines: Most children's hospitals (RCH, SCH) advocate observation for flexible cases.
• Casting clinics: Run by physiotherapists/plaster technicians in major centers.