Definition
A fixed equinus deformity of the forefoot in relation to the hindfoot
- resulting in an abnormally high arch that fails to flatten with weight bearing
- deformity may be forefoot, hindfoot or combination
Aetiology
2/3 have neurological disorder
1/3 have CMT
Neuromuscular
Congenital
Traumatic
RA
Idiopathic
Muscle imbalance of intrinsics and extrinsics
1. Neuromuscular
A. Central
- Friedreich's Ataxia (absent ankle jerks & balance)
- Cerebral Palsy
- Hydrocephalus
B. Spinal cord
- Spinal Dysraphism / spina bifida
- Diastematomyelia /Syringomyelia
- Spinal Cord tumours
- CMT Type 2 (degeneration of spinal axons)
C. Anterior horn cell
- Polio (imbalance between anterior and posterior m)
- SMA
D. Peripheral nerves (+roots)
- CMT type 1 (demyelinating peripheral neuropathy)
- Polyneuritis
E. Muscle Disease
- Muscular Dystrophy
2. Congenital
Congenital cavus foot
Residual clubfoot
Arthrogryposis
3. Traumatic
Compartment Syndrome
Malunion of fractured foot
4. Degenerative
OA / RA of hindfoot
5. Idiopathic
CMT / HSMN
Inherited disorder of nerves
- most common inherited neurological disorder
- heterogenous group
- characterised by weak muscles and abnormal sensation
- positive FHx
CMT 1
- most common 80%
- demyelinating disorder
- peripheral nerve roots
Symptoms
- glove and stocking parasthesia
- nil reflexes
- claw toes, cavus feet, stork legs
- loss of intrinsics in hand
- abnormal NCS
CMT 2
- second most common 20%
- primary axonal neuropathy
- degeneration of spinal axons
Symptoms
- normal DTR
CMT 3 / 4 / X
Pathophysiology
Rang Tripod concept
- heel / MTPJ 1st / MTPJ 5th
- all must touch ground
- if 1st MTPJ plantaflexed
- heel must move into varus
Imbalance is the key to understanding
- PL creates cavus and equinus
- TP creates varus
A. PL > T Ant
- equinus forefoot
- plantar flexed first ray
- cavus foot
B. T Post > PB
- varus
C. Weak Intrinsics & EDL < FDL
- clawing
Deformity
A. Cavus foot
PF 1st ray initially
- weak T Ant
- EHL & EDL act to DF ankle
- this increases windlass mechanism
Contracture of plantar fascia
- fixed Cavus
- fixed navicular-cuneiform & 1st CMTJ
- holds MT plantar flexed
B. Varus heel
Causes
1. Overpowering T Post & long toe flexors
- T post may be primary deforming force
2. Supination of forefoot due to PF 1st ray
- then need varus heel to place lateral column on floor with PF ray
- may be primary deformity
C. Clawing of toes
Weak intrinsics
- unopposed flexors and extensors
- hyper-extended MCPJ +/- dorsal subluxation MTPJ's
- claw toes
D. Ankle Instability
Weak P Brevis
- Loss of dynamic restraint
Varus heel increases inversion moment on ankle
DDx
1. Bilateral Cavovarus
Central Pathology
- Spinal Cord Tumour / Dysraphism
- CNS
2. Unilateral Cavovarus
Peripheral or Local Pathology
- Polio
- clubfoot
- Incomplete spinal cord or Cauda equina trauma
- Deep posterior Compartment Syndrome
- Compartment Syndrome of Foot
3. CalcaneoCavus
Hindfoot Cavus 2° DF of calcaneus only
The apex is the differential
- Midfoot Cavus has apex in tarsus
- Forefoot Cavus from PF of 1st Ray (form seen in CMT)
Stages
1. Flexible cavus / Flexible 1st MT
- plantarflexion corrects with pressure on 1st MT
2. Fixed 1st MT equinus / hindfoot mobile varus
- hindfoot corrects with Coleman block test
3. Fixed lesser MT's equinus / fixed hindfoot varus
4. Bony changes
History
Family history
Is it progressing?
Metatarsalgia
Lateral ankle sprain
- secondary to hindfoot varus
Ulcerations due to clawing
Foot numbness
Difficulty shoewear
Examination
Goals
- aetiology
- define deformity / correctability
- motor drive to deformity
Look
Front
- dysmorphism
- stork legs
- shoes
- parents
Side
- cavus foot / plantar flexed first ray
- claw toes
Back
- varus heel
- signs spinal dysraphism
Walk
High stepping gait
- weak T Achilles
- drop foot
Back knee gait
- fixed equinus
Heel walk
Toe walk
Squat
Coleman Block / Lateral Block Test
Technique
- block under lateral foot
- first ray touches the ground
Aim
- eliminate forefoot deformity
- if hindfoot corrects with this test the hindfoot is flexible
- forefoot surgery should be sufficient to correct hind foot
Foot
Toes
- Claw toes - ? correctable
- Plantar keratoses from uncovering MTPJ
- Dorsal toe corns from claw toes
Plantarflexed 1st MTPJ
- ? correctable
Motor examination
- T Post / T Ant / PB & PL
- Ankle DF & STJ Eversion weak
Silverskiold
- is T Achilles tight ?
Neurology
- abdominal reflexes
- LL neurology
- CMT 1 abnormal sensation and absent reflexes
X-ray
Lateral x-ray
- sinus tarsi easily seen
- PF 1st ray
Meary's angle
- talo - 1st metatarsal angle
- normal 0o
- increased in cavus > 30o
Calcaneal Pitch
- normally 20o or less
- > 30o abnormal
- will demonstrate hindfoot DF
- demonstrates calcaneovarus
MRI spine
Exclude spinal dysraphism
NCS
Can help diagnose CMT
Neurology review