Pertinent Pointers On Equinus Procedures
Given the various ways people compensate for equinus as well as the many conditions associated with equinus, the author provides an anatomical primer, addresses biomechanical influences and offers pearls on surgical treatment
Equinus is defined as the inability to dorsiflex the ankle sufficiently enough to allow the heel to contact the supporting surface without some form of compensation in the mechanics of the lower limb and foot. During the stance phase of gait, the greatest degree of dorsiflexion required is just before heel lift when the knee is maximally extended and the ankle must dorsiflex past perpendicular for smooth ambulation.
There is a great deal of controversy in the literature as to the amount of dorsiflexion truly necessary for this to occur. It is therefore better to consider a normative range of values necessary for normal gait rather than a definitive number. The accepted range of normal ankle joint dorsiflexion is 3 to 15 degrees past perpendicular with the knee extended. When evaluating the destructive influence of equinus on the limb, the method of compensation that a patient may exhibit is of equal or more importance than the numerical value found on physical examination.
There have been numerous articles and texts published on the methods by which a patient may compensate for an equinus deformity and to what degree he or she may compensate. The method by which patients compensate will often determine what symptoms and pathological conditions may coexist and can affect a multitude of systems. Common methods of compensation include triplanar rearfoot motion resulting in pronation, early heel off, abducted gait, midfoot collapse, hip flexion, lumbar lordosis and genu recurvatum or persistent knee flexion.
Therefore, patients can present with a variety of conditions such as low back pain, chondromalacia of the knee, Achilles tendinopathy, posterior tibial tendinopathy, painful flatfoot condition, plantar fasciitis, calcaneal apophysitis, Lisfranc joint arthrosis, Charcot arthropathy, hallux valgus or rigidus, plantar ulceration, forefoot calluses, metatarsalgia and hammertoe contractures associated with the equinus deformity.
A fully compensated equinus deformity will often result in a severely hypermobile flatfoot with the rearfoot maximally everted and the forefoot inverted to the rearfoot due to the excessive pronation of the subtalar joint resulting in unlocking and instability of the midtarsal joint.
Key Anatomical Considerations With Equinus
To appreciate the causal effect of equinus deformity on the lower limb, a physician must fully comprehend the anatomy of the posterior compartment of the lower leg. The posterior compartment is divided into superficial and deep muscle groups separated by the deep transverse fascia. The superficial compartment of the posterior leg is responsible for the equinus deformity and is made up of the plantaris muscle as well as the gastrocnemius and soleus muscles, which combine to form the tendo-Achilles. The gastrocnemius muscle originates from two heads (medial and lateral) connected to the femoral condyles that then descend into the lower leg as two separate muscles.