Spastic Equinovarus Foot (Cerebral Palsy)

Spastic equinovarus is the most common foot deformity in cerebral palsy and a high-yield paediatric orthopaedic topic. It exemplifies muscle imbalance: spastic overactivity of the invertors and plantarflexors overwhelms weak evertors and dorsiflexors. Management rests on distinguishing dynamic from fixed deformity, identifying which muscles are overactive and when in the gait cycle, and planning single-event multilevel surgery.

Who. Cerebral palsy is the most common motor disability in childhood, with an incidence of approximately 2 to 3 per 1000 live births globally. Equinovarus affects roughly 15 to 30 percent of children with spastic CP, making it the most prevalent foot deformity. Spastic diplegia (bilateral CP) carries the highest prevalence, followed by hemiplegia, though unilateral involvement often shows more severe varus due to unopposed tibialis posterior spasticity.

What it costs the child. Gait is disturbed by toe-walking, lateral border weight-bearing, tripping and poor push-off. The overloaded peroneal tubercle and fifth metatarsal base cause lateral foot pain, and callus forms over the lateral border, with a risk of ulceration in severe cases.

Why it gets worse. AFOs cannot adequately control dynamic varus, which leads to poor compliance. Untreated, dynamic deformity progresses to fixed contracture with secondary bony changes.

The imbalance. The deformity results from spastic overactivity of the plantarflexors and invertors combined with relative weakness of the dorsiflexors and evertors. Tibialis posterior inverts and plantarflexes the hindfoot; tibialis anterior dorsiflexes and inverts (supinates) the forefoot. Overactivity of either or both creates the equinovarus pattern.

The antagonists. Peroneus longus, peroneus brevis and extensor digitorum longus are typically weak or underactive and fail to counterbalance the invertors. The table sets out what each muscle does and when in the gait cycle it misbehaves.

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Dynamic becomes fixed. Over time dynamic spasticity leads to muscle contracture, ligamentous shortening and eventually bony deformation of the growing foot. Where a foot sits on that path decides the operation, and the test is examination under general anaesthesia, which shows whether soft tissue surgery alone will suffice.

Dynamic deformity is present during activity but corrects passively and fully under anaesthesia: spasticity alone, without contracture. It may respond to BTX-A, AFO bracing, physical therapy or tendon transfer.

Fixed deformity persists under general anaesthesia, with passive correction incomplete or absent, because of muscle contracture, joint capsule shortening and bony deformation. It requires surgical lengthening, release, osteotomy or arthrodesis.

History. The history places the child on the CP map and sets the goals:

• Birth history - prematurity, birth asphyxia, neonatal complications
• Motor milestones - delayed sitting, crawling, walking
• CP classification - topography (hemiplegia, diplegia, quadriplegia) and GMFCS level
• Gait pattern - onset of toe-walking, how often the child trips, the pattern of falls
• Previous treatment - BTX-A injections, AFO use, prior surgery
• Functional level - community ambulation distance and assistive devices used
• Patient and family goals, where a discussion of realistic expectations is essential

Examination. Work through it in order:

• Inspect standing posture, foot progression angle, the toe-walking pattern and lateral border callus
• Look from behind (too many toes signals hindfoot valgus, no toes visible signals varus) and from the side at the heel contact pattern
• Feel the tibialis posterior tendon during inversion for overactivity or palpable spasm, and the bulk of the peroneal tendons
• Move the ankle (equinus), the subtalar joint (whether the varus corrects) and the forefoot (supination) passively
• Grade spasticity in tibialis anterior, tibialis posterior and gastrocnemius-soleus on the Modified Ashworth Scale, by passive stretch of the target muscle (grade 0 to 4, with grade 3 or above considerable spasticity), which guides BTX-A dosing and surgical planning

The Silfverskiold test. Measure passive ankle dorsiflexion with the knee extended and then flexed to 90 degrees. Flexing the knee relaxes gastrocnemius, which crosses the knee, and not soleus, which does not. Dorsiflexion that improves by more than 10 degrees with the knee flexed is a positive test and means isolated gastrocnemius tightness; no significant improvement means soleus is tight as well.

What the result decides. Isolated gastrocnemius tightness is treated with gastrocnemius recession, a proximal release. Combined gastrocnemius-soleus tightness may require TAL (Achilles tendon lengthening), open or percutaneous, although percutaneous TAL is avoided in the ambulatory child because over-lengthening the Achilles causes calcaneus gait (see Complications).

3-D instrumented gait analysis is the gold standard for surgical planning. It quantifies joint angles, moments, powers and the EMG timing of individual muscles through the gait cycle, identifying which muscles are overactive and when, and so guides the choice between SPLATT, TP lengthening or both. It has been shown to change the surgical plan in approximately 40 to 60 percent of cases compared with clinical examination alone.

Who needs it. Ambulatory children (GMFCS I-III). It is not required at GMFCS IV-V, where the goals are positioning and comfort. Video gait analysis is useful where 3-D analysis is unavailable, which is common in limited-resource settings.

What it shows in equinovarus. In swing, tibialis anterior overactivity inverts the foot and supinates the forefoot during clearance. Equinus then gives a toe-first contact: heel strike is absent, the normal first rocker is lost and the child lands on the lateral border. The ground reaction vector is deviated, producing a knee hyperextension moment.

Weight-bearing radiographs are most useful in fixed deformity, to assess bony changes and plan osteotomies. Take standing AP and lateral views of the foot and ankle, adding a saltarelli view (dorsiflexion lateral) if the equinus is severe.

What to look for. Talar flattening, navicular-medial malleolar overlap (subtalar subluxation), the calcaneal pitch, the Meary angle (talar-first metatarsal angle) and hindfoot alignment.

MRI of the spine is indicated for progressive deformity, bowel or bladder changes, asymmetric signs, or an absent CP diagnosis. It may show a tethered cord, syrinx, diastematomyelia or lipoma, and neurosurgical intervention may halt progression and change orthopaedic management.

Putting it together. The decision guide below maps each common presentation to its operation.

The incidence ranges in this table are conventional estimates from the cerebral palsy foot-surgery literature and clinical experience rather than single-study measurements; the GMFCS-stratified success and failure rates quoted in the Classification section are the sourced anchors (Aleksic 2020, Limpaphayom 2015 - Evidence Base).

SEMLS produces durable results in GMFCS I-III, with approximately 80 to 90 percent maintaining improved gait at 5-year follow-up. Recurrence is the main concern in younger children and at higher GMFCS levels.

Best prognosis. The ambulatory child at GMFCS I-II with dynamic deformity, good selective motor control and good balance, operated on at age 7 to 10 and compliant with post-operative therapy.

Poor prognosis. GMFCS IV-V, fixed bony deformity, poor selective motor control and absent balance reactions, surgery under age 5 (with its high recurrence), and poor compliance with rehabilitation.