Skewfoot

Skewfoot is a complex, often misunderstood deformity encompassing elements of both flatfoot and metatarsus adductus. The foot assumes a "Z" or serpentine shape.

• Forefoot: Adducted (similar to Metatarsus Adductus).
• Midfoot: Abducted (Lateral translation of navicular).
• Hindfoot: Valgus (Everted).

It is distinct from simple Metatarsus Adductus because the hindfoot valgus is pathologic and rigid, often accompanied by Achilles contracture.

Aetiology:

• Primary (Idiopathic): A true congenital germ plasm defect similar to CVT or Clubfoot. It may represent a form of "Undercorrected Clubfoot variant" or a distinct entity.
• Secondary (Iatrogenic): Classic Exam Scenario. A well-meaning clinician casts a rigid Metatarsus Adductus foot. They apply pressure to the medial forefoot to abduct it, but fail to stabilize the hindfoot. The force is transmitted to the hindfoot, pushing it into severe valgus. The forefoot remains adducted relative to the midfoot, but the midfoot breaks laterally. "The foot buckles in the middle." This highlights the importance of the three-point mold technique in casting.

Historical Perspective: The condition was first clearly described by Peabody and Muro (1933) as "Congenital Metatarsus Varus". Later, McCormick and Blount coined the term "Skewfoot" to describe the offset between the forefoot and hindfoot. The understanding of the iatrogenic cause has significantly influenced modern casting techniques for metatarsus adductus.

Pathophysiology / Pathoanatomy:

• Hindfoot: The calcaneus is in valgus and eversion. The talus is plantarflexed (though not as severe as CVT). The sustentaculum tali may be hypoplastic.
• Talonavicular Joint: The navicular is laterally subluxated on the talus head. This is the crucial difference from Metatarsus Adductus (where navicular is medial/neutral).
• Tarsometatarsal Joint (Lisfranc): The metatarsals are adducted relative to the cuneiforms/cuboid.
• Result: The talus points medial, the midfoot shifts lateral, and the forefoot points medial again. A "Zig-Zag".

Achilles Tendon: Usually shortened (contracted), contributing to the hindfoot valgus (as the calcaneus everts to dorsiflex). This acts as a deforming force.

Biomechanics: The foot is mechanically unstable. The ground reaction force passes medial to the subtalar axis, perpetuating the valgus. During the stance phase of gait, the midfoot collapses further into abduction, while the forefoot adduction forces the foot to roll over the lateral border. This causes:

1. Medial Talar Head Prominence: Pressure area.
2. Lateral Border Callosity: Due to weight bearing on the base of the 5th metatarsal.
3. Inefficient Lever Arm: The triceps surae loses its mechanical advantage.

Why differentiation matters:

• Treating Skewfoot like MA (casting) causes iatrogenic worsening.
• Treating Skewfoot like Clubfoot (Ponseti) is ineffective because the hindfoot is already valgus (Ponseti corrects varus).
• Treating Skewfoot like CVT (Dobbs) is closer to the mark but the forefoot deformity is opposite.

History:

• Often a child treated for "Metatarsus Adductus" that "didn't get better" or "looks worse".
• Parents report the foot looks "flat" but the toes point "in".
• Pain in older children (sinus tarsi pain from valgus, or lateral border pain/bunionette).
• Difficulty with shoe fitting due to the C-shape/Z-shape.

Physical Examination:

• Inspection:
  • Weight-bearing: Serpentine Shape.
  • Heel in Valgus (Check from behind).
  • Midfoot prominent medially (Talar head).
  • Forefoot Adducted.
• Range of Motion:
  • Subtalar joint: Often stiff/restricted.
  • Ankle: Check for equinus (Silfverskiold test).
  • Midfoot: Assessment of rigidity of adduction.
• Callosities: Under the talar head (medial) or base of 5th MT (lateral).
• Shoe Inspection: Look for medial wear on the heel counter and lateral wear on the sole.

Plain Radiographs (Weight Bearing AP/Lateral):

• AP View:
  • Talocalcaneal Angle (Kite's): Increased (greater than 35-40 degrees) indicates Hindfoot Valgus.
  • Talus-1st Metatarsal Angle: Broken. The line through the talus passes medial to the 1st MT.
  • Metatarsus Adductus Angle: Increased.
• Lateral View:
  • Talar Declination: Increased (Talus points down).
  • Calcaneal Pitch: Decreased (Flatfoot).
  • Meary's Angle: Broken (in extension/dorsiflexion at TN joint).

CT Scan:

• Useful for surgical planning in adolescents (tarsal coalition exclusion).
• Can characterize the specific deformity of the medial cuneiform.

Protocol for Double Osteotomy (Evans + Cotton):

• 0-2 Weeks:
  • Splint/Backslab in neutral position.
  • Strict Elevation.
  • Non-weight bearing.
• 2-6 Weeks:
  • Wound check.
  • Short leg fiberglass cast.
  • Molded to hold hindfoot neutral and forefoot abducted.
  • Non-weight bearing.
• 6-8 Weeks:
  • Radiographic check for graft union.
  • Transition to partial weight bearing if union evident.
• 8-12 Weeks:
  • Walking cast or CAM boot.
  • Full weight bearing.
• 3-6 Months:
  • Transition to shoes with arch support.
  • Physiotherapy for ankle and subtalar motion.

• Non-operative: Generally poor for rigid skewfoot. Pain and footwear difficulties persist. The deformity tends to progress with growth.
• Operative: Good functional results with "double osteotomy" techniques (Evans + Medial Column). Mosca (1995) reported excellent results using the Evans procedure for valgus deformities including skewfoot.
  • Satisfaction: High patient and parent satisfaction regarding foot shape and shoe fit.
  • Function: Most children return to full sports activities.
• Long Term: Risk of early triple arthrodesis if deformity remains uncorrected due to joint incongruity and degenerative changes. Adult skewfoot is notoriously difficult to reconstruct and often requires fusion.
• Recurrence: Can occur if the Evans graft resorbs or if the medial column was under-corrected. Monitoring until skeletal maturity is advised.

Skewfoot has one of the weakest evidence bases in paediatric foot surgery — almost all literature is Level IV/V case series. Examiners reward candidates who can articulate the genuine uncertainty rather than overstate dogma.

• Does the iatrogenic mechanism truly exist? The "failed metatarsus adductus casting" story is widely taught and biomechanically plausible (forefoot abduction levering an unstabilised hindfoot into valgus), but it rests on small series and is hard to separate from a primary congenital deformity that was simply misdiagnosed as metatarsus adductus. Many authors regard most cases as primary.
• Is skewfoot a distinct entity or the severe end of a spectrum? Some authors (including the Tönnis tradition) view "skewfoot" and "serpentine foot" as simply the severe end of complex metatarsus adductus rather than a separate disease, which has implications for how aggressively to treat.
• Single- versus double-osteotomy. Whether every operative skewfoot needs both a lateral-column lengthening and a medial-column procedure, or whether selected feet can be corrected with one, is unresolved; the principle of "address both ends of the Z" is consensus-based, not trial-proven.
• Subtalar arthroereisis. Promoted by some as a less invasive option for the valgus component, but evidence in skewfoot specifically is minimal and complication/implant-removal rates are a concern; most paediatric foot surgeons regard it as adjunctive at best.
• Allograft versus autograft and the role of fixation. Both wedge graft choices have advocates; rigid internal fixation versus reliance on a tightly impacted graft is surgeon-dependent.
• Asymptomatic skewfoot. Because long-term natural history is poorly defined and many feet remain pain-free, the threshold for operating on an asymptomatic deformity is genuinely contested.

Global epidemiology

• Skewfoot is rare; fewer than ~50 cases were reported in the English literature at the time of Peterson's 1986 series, and most modern data remain single-centre case series.
• No dedicated registry exists for paediatric foot deformities; unlike arthroplasty, there is no NJR/AJRR/AOANJRR equivalent capturing skewfoot outcomes, which is itself a recognised evidence gap.
• Where the deformity follows treatment of metatarsus adductus, true incidence is unknown and almost certainly under-reported.

Society guidance and practice positions (no single-country framing)

High- versus limited-resource practice variation

• High-resource settings: weight-bearing radiographs (or simulated weight-bearing/standing CT in adolescents), allograft availability, image intensifier for the calcaneal osteotomy, and access to specialist paediatric orthopaedic foot services.
• Limited-resource settings: reliance on clinical examination and a single plain film; autograft (iliac crest) preferred over allograft for cost and availability; greater use of soft-tissue and simpler single-osteotomy strategies; later presentation of neglected/rigid deformity is more common.
• Universal principles: differentiate the deformity correctly before treating, never cast/brace a foot in a way that drives the hindfoot into valgus, and address both the forefoot adduction and the hindfoot valgus when operating.