Equinus

http://runningreform.com/clinicians-guide-to-ankle-dorsiflexion/
http://www.podiatrytoday.com/understanding-biomechanics-equinus

Definition:
Traditionally defined as a structural or functional deformity in which there is less than 10 degrees of dorsiflexion at the ankle joint from a 90-degree angle with the leg when the subtalar joint is maintained in its defined neutral position and the midtarsal joint is in its defined locked position and the knee is fully extended

However there is confusion in the literature as to the needed range of motion at this joint:
• 20 degrees of passive motion is widely considered normal
• for normal walking, Murray et al (1966) considered 8-10 degrees is needed during the stance phase; Stauffer et al (1977) found 10.2 degrees; Jordan et al (1979) found only 4 degrees during barefoot walking.
Not clear from all studies if they were measured with the subtalar joint in its neutral position or the amount of force used to passively dorsiflex the foot or the consistency of the position of the reference lines used for the measurement.

Prevalence:
Unknown. Assumed to be common.

Aetiology:
Four types:
1) Osseous block due to congenital or traumatic morphology of the ankle joint; or flattened trochlear surface; or osteoarthritic changes in the joint.
2) Muscular - congenital shortage (triceps surae; hamstrings; hip flexors)
- acquired shortage (eg repetitive use of high heel shoes)
- spasm (eg cerebral palsy)
3) Dysfunction of fibula – this can mimic a calf muscle shortage – this is a ‘fixation’ of the fibula in which it prevents the ankle mortise from widening to accept the wider anterior aspect of the trochlea surface of the talus.
4) Pseudoequnius – plantarflexed forefoot on rearfoot  need more than 10º of dorsiflexion at ankle for normal gait

Diagnosis:
Test ankle joint with knee extended and flexed (Silfverskiold test). If limited when knee extended but not limited when knee flexed  gastrocnemius and/or soleus tightness. If limited when knee flexed and extended  soleus tightness or osseous block. Differentiate between osseous block and soleus tightness by feel – osseous block will have abrupt end to ROM and soleal tightness will have soft feel.
For fibula dysfunction  palpate head of fibula to check for movement as the foot is repeatably plantarflexed and dorsiflexed.

Pathomechanics:
One of two types of compensations will occur for an ankle equinus – either the heel will come off the ground early (that’s if it reached the ground) or the dorsiflexion needed will be found at other joints  compensations that increase the risk for tissue damage.

The dorsiflexion can be obtained from subtalar joint pronation (dorsiflexion, eversion and abduction) which ‘unlocks’ distal joints  pronation at midtarsal joint to allow more dorsiflexion  pronation related pathologies. This is considered a very ‘destructive’ type of pathological pronation.

This type of foot is very flexible and is considered very destructive  very susceptible to increased risk of tissue damage from pronatory pathologies.
It is very flat in stance with a relatively normal arch during non-weightbearing.
Forefoot supinatus is common.

The partially compensated variety has a limited ROM at STJ, so tends to have an early toe off.

The uncompensated type has no heel contact.

These theoretical bases for the compensation of a restriction at the ankle joint have not been investigated empirically, except for the work of Cornwall and McPoil (1999). Three dimensional motion analysis was conducted on two groups (one group <10 degrees and one group >15 degrees). Mild to moderate reductions in ankle joint dorsiflexion were found not to affect rearfoot kinematics. However, an earlier re-inversion of the rearfoot was found and earlier heel off was found in the restricted motion group compared to the full range of motion group. The study did not investigate any compensatory motions that may have occurred in the midfoot.

Treatment:
Heel lifts; stretching

Orthoses:

Surgical lengthening
Surgical anterior advancement of attachment of achilles tendon is indicated for spastic equinus (decreases lever arm at ankle joint)

Related Topics:
IQ Medical | UltraFlexx

Sub Topics:

 
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