Etiology
Neurological (Most Common ~66%):
Charcot-Marie-Tooth (CMT) disease: Most frequent cause; results from muscle imbalance between the extrinsic and intrinsic foot muscles.
Spinal Cord Pathology: Tethered cord, syringomyelia, diastematomyelia, or spinal cord tumors.
Others: Cerebral palsy, Friedreich ataxia, and myelomeningocele.
Traumatic: Residuals of compartment syndrome (Volkmann contracture), sciatic nerve palsy, or malunion of talar neck/calcaneus fractures.
Congenital: Residual deformity from clubfoot (CAVE residuals: Cavus, Adductus, Varus, Equinus).
Idiopathic: Symmetric cases where a subtle neurologic lesion remains below clinical detection.
Pathophysiology
Fundamental Cause: Muscle imbalance leads to bony structural changes if it occurs before skeletal maturity.
CMT Pattern:
Strong Peroneus Longus (PL) overpowers a weak Tibialis Anterior (TA), causing plantar flexion of the first ray (forefoot equinus).
Strong Tibialis Posterior (TP) overpowers a weak Peroneus Brevis (PB), leading to hindfoot varus.
Weak intrinsic muscles versus stronger extrinsic extensors lead to claw toe deformities (recruitment of EHL for dorsiflexion).
Forefoot-Driven Varus: In many cases, the hindfoot varus is initially a flexible compensation for the plantar-flexed first ray to maintain a plantigrade "tripod".
Clinical Presentation
Symptoms: Frequent ankle sprains (instability), lateral column pain, metatarsalgia under the metatarsal heads, and painful callosities.
Physical Exam:
Gait: Observe for foot drop or "cock-up" hallux deformity.
Spine: Look for midline defects (hairy patches, dimples) indicating dysraphism.
Leg Atrophy: Hemiatrophy of the calf suggests a unilateral neurological cause.
Coleman Block Test:
Places the heel and lateral border on a block while the first ray hangs off.
Flexible Hindfoot: Heel varus corrects to neutral/valgus (driven by the first ray).
Fixed Hindfoot: Heel varus persists (requires bony hindfoot surgery).
Imaging
Meary’s Angle: Axis of the talus vs. the axis of the 1st metatarsal on standing lateral view (Normal = 0°; Cavus > 0°).
Hibbs Angle: Axis of the calcaneus vs. the axis of the 1st metatarsal (Normal > 150°; Cavus < 150°).
Calcaneal Pitch: Often > 30° in hindfoot-driven cavus (common in post-polio).
Subtalar Joint: Appears "en face" (can see through the joint) on lateral radiographs due to malrotation.
Treatment
Nonoperative
Stretching: Focus on eversion and dorsiflexion.
Orthotics: Custom foot orthoses with a recess for the 1st metatarsal head, a lateral forefoot wedge, and an elevated heel for gastrocnemius tightness.
Shoes: Accommodative footwear with an extra-depth toe box.
Operative
Soft Tissue (Supple Deformity):
Plantar Release: Steindler stripping or aggressive open release of the plantar fascia.
PL to PB Transfer: Removes the deforming force on the 1st ray and strengthens the weak evertor.
Jones Procedure: Transfer of EHL to the 1st metatarsal neck with IP joint fusion for claw hallux.
Bony Procedures (Fixed Deformity):
Dorsiflexion Osteotomy of the 1st Ray: For a fixed plantar-flexed first metatarsal.
Calcaneal Osteotomy (Dwyer/Lateralizing): For fixed hindfoot varus.
Midfoot Osteotomy (Cole/Japas): For rigid cavus with an apex in the midtarsal joints.
Triple Arthrodesis: Salvage procedure for patients >10 years old with severe, rigid, or failed previous corrections.