Limited ankle dorsiflexion or equinus during normal gait is responsible for a number of pathologies of the ankle and foot such as hallux valgus, plantar fasciitis and ankle instability; this makes understanding the pathomechanics of equinus necessary for the treatment of the aforementioned conditions.
A two-stage definition of equinus proposed by Charles et al. accurately describes the gradual progression of the condition – the first stage entails an ankle dorsiflexion of less than 10 degrees with minimal gait compensation and a slight increase in forefoot pressure whereas the second stage involves ankle dorsiflexion of less than 5 degrees with considerable gait compensation and maximal amount of forefoot pressure.
Considered to be the most common form of soft tissue equinus, isolated gastrocnemius contracture in non-neurologically impaired individuals implies tightness in the superficial posterior compartment in addition to chronic forefoot and mid-foot symptoms.
Perhaps one of the most note-worthy studies to be conducted in this regard was by Christopher W. DiGiovanni for The Journal of Bone and Joint Surgery in 2002.
Thirty-four patients with isolated forefoot or mid-foot pain were clinically examined to identify the presence of gastrocnemius contracture. This was followed by an assessment of maximal ankle dorsiflexion with the use of an equinometer.
The purpose of accruing data from both these evaluations was to observe whether the subjective determinations (by the clinician) matched with the objective determinations (with the equinometer) indicating the presence or absence of equinus.
The study concluded that isolated gastrocnemius contracture is responsible for less than maximum ankle dorsiflexion with the knee extended in patients with forefoot and/or mid-foot pathologies; this difference was found to disappear when the knee was flexed to 90 degrees.
Ankle joint equinus facilitates significant alterations to gait such as limitation in the forward pivotal motion as the lower limbs realign the posterior displacement of the body’s centre of gravity.
There is an increase in the range of motion at the knee or hip in the form of genu recurvatum from hyperextension of the knee and lumbar lordosis occurring from flexion at the hip and knee, in an attempt to restore pivotal motion over the ankle.
Treatment options for nonspastic forms of equinus need to include stretching exercises in conjunction with the use of customised orthotics such as MASS4D® to increase ankle joint dorsiflexion and to treat the secondary effects of the condition by stabilising the medial longitudinal arch.
With an improvement in ankle range of motion, there is a reduction in the load placed on the soft tissue supportive structures around the ankle, helping diminish compensatory movements of the lower limbs and providing a stable base of support for resistance of body sway.
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Repetitive plantarflexion can lead to pain and mechanical limitation in the posterior ankle joint which is known as posterior ankle impingement syndrome. This pathology commonly occurs in ballet dancers and football players.