Ankle: Functional and Structural Ankle Equinus

An Ankle Equinus means that there is insufficient dorsiflexion of the foot at the talocrural (ankle) joint when the subtalar joint (STJ) is in its neutral position. In simple terms, someone has an Ankle Equinus when they cannot flex their toward the front of the shin bone far enough. Ideally a person needs a minimum of 10 degrees of dorsiflexion at the ankle joint in order to walk normally.

An Ankle Equinus can be both congenital or acquired, i.e. something you are born with or something that happens later on. Another way of classifying this condition is either as “functional” or “structural”, i.e. due to soft-tissue adaptation or fixed anatomical abnormalities.

Tightness or contraction in the posterior group muscles of the lower leg, specifically gastrocnemius and soleus, can restrict the movement of the ankle joint. Anomalies in the structure of the bones of the ankle joint can also limit the range of available movement. Wearing high-heeled shoes for prolonged periods of time can also lead to an Ankle Equinus through shortening of the Achilles tendon complex in accordance with the principles of Davis’ Law.

Compensations for this condition that allow people to walk “normally” usually involve excessive pronation of the STJ. In other words, your instep reduces and you have “flat feet” so that your ankle can flex far enough to carry your centre of gravity over the tips of your toes and allow you to move forward. Other compensations include an early heel lift, which is observable as a “bouncing gait”, a short stride length, toe-walking, genu recurvatum, excessive flexion (bending) of the knee during gait, and an abductory twist after midstance. An Ankle Equinus may the underlying cause or at least a significant factor in the development of many other conditions related to excessive STJ pronation, such as Plantarfasciopathy, hallux adductovalgus (bunions), functional/structural hallux limitis leading to osteoarthritic changes to 1st metatarsal-phalangeal joint (big toe joint), Morton’s Neuroma, and many others.

A structural Ankle Equinus is due either to a congenital restriction of the Achilles tendon or to abnormalities of the shapes of the bones within the ankle mortice, namely the talus and the articulating surface of the tibia. The bony abnormalities in particular can lead to chronic tissue stress, discomfort, swelling, pain and possibly osteoarthritic changes to the joints themselves. Pain is usually experienced at the anterior aspect (front) of the ankle.

In a fully compensated case, where the STJ has enough movement to allow for 10 degrees of more of ankle dorsiflexion. In some cases, even the midtarsal joints (MTJ) may need to pronate excessively in order to make up the shortfall. A fully compensated Ankle Equinus is one of the most destructive foot pathologies, for reasons already mentioned.

In an uncompensated case there will be little or no STJ or MTJ pronation. This case will often present with forefoot pathologies, such a metatarsal lesions or lesions associated with the clawing of the toes. High forefoot plantar pressures can also increase the risk of metatarsal fractures and capsulitis of the metatarsal-phalangeal joints.

Partially compensated cases will present with a mix of the two symptom pictures depending on the degree and type of available compensation.

Treatment for Ankle Equinus involves the use of heel raises and orthotics, stretching exercises to address soft-tissue adaptions, and changes in footwear, following a thorough biomechanical assessment. Acupuncture can be used to manage any local pain or inflammation.

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