foot and ankle manifestations of neuromuscular disease

Charcot-Marie-Tooth disease

diagnosis

· leg weakness

· pes cavus

· positive family history

· slow nerve conduction velocity

clinical features

History

· weakness of foot and ankle

· painful corns

· difficulty with shoewear

· lateral ankle instability

· progressively high arched foot

· numbness of foot (uncommon)

Examination

· cavovarus foot

· hindfoot varus

· marked cavus

· forefoot supination from plantarflexion of 1st ray

· gait

· marionette gait

· foot drop

· compensatory pelvic elevation and hip and knee flexion

· MTP hyperextension and 2^o dorsiflexors (EDL and EHL) recruited to dorsflex ankle

· flat-foot or toe-heel floor contact

· hindfoot remains in varus

· assessment of hindfoot

· Coleman block test

· if hindfoot varus flexible, heel corrects

· elimination of forefoot deformity will correct hindfoot deformity if hindfoot flexible

· cavus

· hindfoot cavus from dorsiflexion of calcaneus

· midfoot cavus has apex in tarsus

· forefoot cavus from plantarflexion of 1st ray (form seen in CMT)

· toes

· claw toes

· plantar keratoses

· dorsal toe corns

· muscle bulk

· atrophy distal to knees

· gives stork legs

· neurological examination

· decreased or absent tendon reflexes

· sensory impairment in 25% only

· motor examination

· ankle plantarflexion and subtalar inversion strong

· ankle dorsiflexion and subtalar eversion weak

Radiography

· forefoot adduction

· plantarflexion of first ray

· decreased talocalcaneal angle

· hindfoot varus

aetiology of foot and ankle posture

Overview

· tibialis posterior overpowers peroneus brevis

· peroneus longus overpowers tibialis anterior

Claw toes

· weak intrinsics and EDL

· normal toe flexors

Cavus

· strong peroneus longus (and weak tibialis anterior) causes plantarflexion of 1st ray

· strong tibialis posterior (and weak peroneus brevis) supinates forefoot

· contracture of short plantar muscles and plantar fascia contribute

Hindfoot varus

· primarily from overpowering tibialis posterior and long toe flexors

· secondarily from supination of forefoot as plantarflexed 1st ray and less plantarflexion of lesser rays causes forefoot to supinate and leads to hindfoot varus to accommodate it

Ankle instability

· dynamic lateral restraint of peroneus brevis compromised

· varus heel places ankle at increased risk for inversion injuries

differential diagnosis

Bilateral cavus

· spinal cord tumour

· spinal dysraphism

· CNS trauma

Unilateral

· polio

· incomplete spinal cord or cauda equina trauma

· deep posterior compartment syndrome

· crush syndrome of foot

treatment

Nonoperative

· night splint to prevent deformity

· AFO to prevent footdrop

· extra-depth shoes to accommodate claw toes

· moulded insoles to redistribute weight across plantar forefoot

Operative

Soft tissue

· plantar fascia release

· releases cavus deformity

· transfer of tibialis posterior to dorsum of foot

· removes cavus-producer to dorsiflexor

· peroneus longus to brevis transfer

· removes 1st ray plantarflexor and strengthens eversion

· Jones procedure (EHL transfer to 1st MT neck)

· improves EHL as ankle dorsiflexor

· Girdlestone-Taylor procedure (flexor to extensor transfer)

· for flexible claw toes

Bony

· dorsiflexing closing wedge osteotomy of 1st MT

· to correct plantarflexion of 1st ray

· calcaneal osteotomy (lateral wedge or sliding)

· to correct fixed hindfoot varus

· triple arthrodesis

· for salvage of rigid deformity

Cerebral palsy

equinus

Aetiology

Equinus

· weak tibialis anterior overpowered by spastic triceps surae

Varus

· weak peronei overpowered by spastic tibialis posterior

Clinical

· differentiation between gastrocnemius and soleus tightness traditionally used Silfverskiold test

· based on fact that gastrocnemius crosses knee joint and soleus does not

· if equinus present with knee extended and reduced when knee flexed, tightness in soleus rather than gastrocnemius

· found to be inaccurate by EMG

· thought that flexion of hip required for knee flexion causes reflex spasticity in triceps surae and test negated

Treatment

Equinus

· bracing of little preventitive use

· heel cord lengthening usually required

· if hamstrings tight, crouch gait occurs

· with equinus, knee forced back into extension

· when equinus corrected, knee remains flexed because of tight hamstrings

· results in crouched position

· avoided by lengthening hamstrings at same time if required

Varus

· transfer of tibialis posterior through interosseous membrane

equinovalgus

Aetiology

Equinus

· spastic triceps surae

Valgus

· ligamentous laxity allows midfoot to break (dorsiflex)

· allows foot to become plantigrade

· forefoot abducts and medial arch lost

Treatment

Equinus

· heel cord lengthening

Valgus

· if deformity flexible, Grice subtalar arthrodesis

· if deformity rigid, triple arthrodesis

Meningomyelocoele

· rigid and flail deformities in anaesthetic feet

varus +/- equinus (clubfoot)

· due to lesion at L3 or L4 with absence of tibialis anterior function

· rigid severe deformity from birth

· foot numb

Treatment

Nonoperative

· serial casting not indicated because of insensate skin

· stretching often corrects varus

· may require percutaneous lengthening of tendo Achilles

Operative

· extensive posterior and medial release

· if fails, talectomy

Talipes calcaneus

· due to lesion at L4 or L5 with absence of calf function and unopposed tibialis anterior

· causes difficulty with gait and heel ulceration

Treatment

Nonoperative

· calipers if poor ambulators

Operative

· release of tibialis anterior and brace