November 2015

Equinus: Its surprising role in foot pathologies

11Equinus-iStock74787919-copyAlthough milder than the spasticity-induced cases of equinus, limited ankle dorsiflexion in the non-neurological pop­ulation is increasingly recognized as a source of excessive strain throughout the foot and a factor in the pathogenesis of many foot conditions.

By Nicholas V. DiMassa and Jeffrey M. Whitaker DPM, FACFAS   

Equinus has been investigated extensively throughout the literature, and can be described as an inability to dorsiflex the ankle joint enough to allow for normal pain-free ambulation. Equinus of the foot is the most common deformity in children with spastic cerebral palsy and, as early as the 1920s, Swedish orthopedic surgeon Nils Silfverskiöld advocated the use of a gastrocnemius recession as a way to treat cerebral palsy patients who suffered from a contracture of the posterior calf muscles.1,2 Practitioners, however, are beginning to emphasize a form of soft tissue equinus that occurs as a result of an isolated contracture of the gastrocnemius muscle in the healthy adult population.3-5

Although milder than the spastic neuro-induced cases of equinus, the gastrocnemius contracture in the non-neurologically impaired population is being highlighted as a source of deformity that will lead to excessive strain throughout the foot. It is thought to be a primary factor in the pathogenesis of many common pedal ailments, including plantar fasciitis, hallux valgus, metatarsalgia, Achilles tendinopathy, fatigue of the anterior extensor muscles, ulcers, and a variety of other pathologies that are seen in clinics daily.3,5-7

Although definitions of equinus vary, the literature generally recognizes equinus as being present when the patient is unable to achieve 10° of ankle joint dorsiflexion.

The reported prevalence is astounding. In a 1995 article in the Journal of the American Podiatric Medical Association (JAPMA), Hill stated that 96.5% of examined patients in his clinic had reduced ankle joint dorsiflexion requiring compensation during gait.8 Patel and DiGiovanni corroborated that finding by evaluating every patient that presented with either acute or chronic plantar fasciitis. They revealed that 83% of patients suffered from equinus, with 57% being diagnosed as an isolated gastrocnemius contracture.9

Identification

Figure 1. If the patient is able to achieve more ankle dorsiflexion with the knee flexed (top) than with the knee extended (bottom), an isolated gastrocnemius contracture is likely. If knee flexion does not significantly affect the degree of ankle dorsiflexion, then a gastroc-soleus complex equinus is likely.

Figure 1. If the patient is able to achieve more ankle dorsiflexion with the knee flexed (top) than with the knee extended (bottom), an isolated gastrocnemius contracture is likely. If knee flexion does not significantly affect the degree of ankle dorsiflexion, then a gastroc-soleus complex equinus is likely.

The superficial posterior crural compartment is separated from the deep posterior compartment by the deep transverse fascial septum of the leg. The muscles of the superficial posterior compartment are powerful plantar flexors of the ankle joint and include the gastrocnemius muscle and the soleus muscle. Together, the gastrocnemius and soleus are referred to as the triceps surae. The triceps surae originates from three separate heads and converges into the Achilles tendon, which serves as the combined attachment of the gastrocnemius and soleus muscles onto the posterior portion of the calcaneus.

Calf muscle tightness is generally an inherited trait that manifests later in life, but can also be caused by nerve injuries, diabetes, and stroke.10,11 According to Hill, the high incidence of equinus points to “acquired deformity” related to lifestyle factors that leave the calf muscles at a physiologic disadvantage.8 In 2002, DiGiovanni and colleagues authored a study that showed 88% of healthy patients with forefoot or midfoot pathologies or both presented with posterior muscle group tightness.5 More specifically, they, like others, found the majority of the patients suffered from an isolated gastrocnemius equinus, as opposed to a gastroc-soleus complex equinus.3-6,9

Although equinus is defined as the inability to dorsiflex the ankle joint enough to allow for normal motion, there is not an absolute consensus on the degree of dorsiflexion necessary for normal pain-free ambulation.5,10,13 The literature generally recognizes equinus as present when less than 10° of ankle joint dorsiflexion is attainable.10,13 Using the Silfverskiöld test makes it possible to determine whether the tightness originates from the gastroc-soleus complex or strictly due to an isolated contracture of the gastroc­nemius muscle.2,10

To perform the exam, clinicians should position the foot and ankle in a position mimicking the point in the gait cycle when the most ankle dorsiflexion is required. This can be done with the patient in a supine position and the knee fully extended. The examiner places the foot in a subtalar joint neutral position, eliminating any supination or pronation. Congruity should be felt on both the medial and lateral sides when the navicular is centered on the talus. A dorsiflexory force should be applied to the foot, concentrated on the medial aspect to avoid pronation, until maximum dorsiflexion is achieved. To measure the degree of dorsiflexion, a goniometer or tractograph can be used. The reference lines for the measurement should be the bisection of the lower third of the lateral aspect of the leg and the plantar surface of a line correlating with the fifth ray.6 The test is then repeated with the knee in a flexed position using the same reference lines and technique.

If the patient is able to attain sufficient dorsiflexion (typically about 10°) when the knee is flexed, but not when it is extended, the equinus is determined to be an isolated gastrocnemius contracture, likely due to a contracture in the muscle belly or aponeurosis.2,5,14 If, however, the patient is not able to achieve more dorsiflexion with the knee flexed then with it extended, then the equinus is said to be a gastroc-soleus complex equinus and is most likely due to an osseous deformity or contracture within the Achilles tendon itself.10

Compensation and gait changes

IQ-med--equinus-braceMany pathogenic manifestations of equinus occur due to the center of pressure displacement that is seen in diseased states. Typically, the center of pressure on the foot can be measured 6 cm anterior to the ankle during gait, but with equinus, it is shifted distally and laterally.15,16 The pull of the Achilles tendon cannot adequately compensate for the new distal and lateral center of pressure and, as a result, an overall pronatory force remains.

Generally, three stages of compensation due to equinus are recognized clinically. In an uncompensated equinus, the patient will appear to walk on the toes or ball of the foot, with the heel appearing to float off the ground.15,17 This is the most drastic manifestation, and accounts for a very small percentage of cases. While it can be seen in someone suffering from an isolated gastrocnemius equinus, it is more often indicative of a spastic cerebral palsy induced equinus. Pathologies expected in the true toe-walker include submetatarsal tylomas and digital contractures due to the need for extensor substitution.13 By and large, gastrocnemius-related equinus is seen in its partially compensated or fully compensated forms, which can make it more difficult to identify.

Compensations for the tightness in the calf can occur proximally and include genu recurvatum, flexion of the hip, and lumbar lordosis.15,19,20 Early heel-off will be noted in a partially compensated equinus and appear as a “bouncing gait.” In fully compensated equinus, the foot will likely appear severely pronated with abnormal abduction and dorsiflexion needed to allow the heel to rest on the ground. Often, midfoot and first ray hypermobility can be noted due to unnatural dorsiflexion at the naviculocuneiform and tarso­metatarsal joints. A weakening of the pull of the peroneus longus muscle leads to an inability to lock the midtarsal joint and has been attributed to such causes of medial column hypermobility.13,21 These compensations have been shown to be associated with a variety of foot pathologies, including neuropathic ulcers, metatarsalgia, hallux abducto valgus, and even Charcot neuroarthropathy in patients with diabetes.22

Treatment

Treatment for equinus should be aimed at increasing ankle joint dorsiflexion to facilitate normal gait mechanics. In most cases, nonspastic forms of equinus tend to be more treatable and easily corrected than the spastic neuro-induced forms of equinus.13 A variety of conservative measures can be employed, including stretching, bracing, and orthotic devices.

The merits of manual stretching for the gastrocnemius muscle have been a topic of debate, but studies have demonstrated that favorable results are possible when stretching is done correctly even for short time periods. Grady and Saxena found that manual stretching for five minutes per day over six months increased dorsiflexion by an average of 2.7°.23,33 Similarly, Macklin and colleagues were able to elicit excellent results in a group of runners with equinus contractures. Their results produced an average increase in ankle joint dorsiflexion from 5° to 16° following an eight-week stretching program.24

Clinical approaches that include treatment for secondary equinus will be inherently more successful than treatment limited to the presenting foot pathology alone.

For stretching to be effective, it has been recommended that it be done with the foot adducted to allow for locking of the subtalar and midtarsal joints.25,26 With the subtalar and midtarsal joints locked, distal compensatory mechanisms arising from hypermobility along the first ray and an abnormally dorsiflexed naviculocuneiform joint are minimized so the stretching is primarily focused on the posterior calf musculature. Recent studies, however, have shown that an increase in dorsiflexion can be achieved regardless of whether the foot is stretched in a pronated or supinated position.27-29 In addition to stretching, night splinting can be employed. A 2001 study in JAPMA demonstrated favorable outcomes in a series of cases that involved an element of equinus, when night splinting and stretching were used as a combination therapy.30

Distal compensations such as pronation at the subtalar joint and inappropriate unlocking of the midtarsal joint lead to pes planus deformities, which in some cases can be effectively managed with foot orthoses.31,32 An effective orthosis aimed at correcting pes planus secondary to equinus should provide medial longitudinal arch support and correct the flexible nature of the deformity. A typical orthosis will include a medial wedge and, most importantly, a heel lift when equinus is present.32 Patients will feel significantly more comfortable in shoes with an elevated heel, and will have the most difficulty ambulating barefoot or in sandals, flip-flops, or flat shoes that offer no additional elevation. Care should be taken to avoid conditions in which the rearfoot could sink below the forefoot, such as walking on the beach or in sand. An ankle foot orthosis (AFO) provides an option for the patient suffering from an equinus with an element of drop foot. AFOs improve walking and reduce the risk of falling in individuals with paretic dorsiflexory muscles, providing clearance through the swing phase of gait by limiting the speed of plantar flexion.33

When conservative measures fail to correct the deformity, there are a number of surgical options for management of equinus. It is important that the selected surgical procedure is tailored to the specific deformity. Again, using the Silfverskiöld test remains the most accurate way of distinguishing a global gastroc-soleus equinus from an isolated gastrocnemius equinus.2

Armstrong and colleagues, as well as Sgarlato et al, were proponents of a tendo-Achilles lengthening procedure.17,35 The procedure is best for addressing a shortened tendon or osseous deformity that may be seen more often with a gastroc-soleus equinus than an isolated gastrocnemius equinus, but care must be taken to avoid complications including overlengthening, rupture, and loss of strength.

A gastrocnemius recession is typically reserved for patients with an isolated gastrocnemius contracture. Studies suggest the procedure is simple and effective, and addresses almost all complications associated with the tendo-Achilles lengthening procedure.36,37 The biggest risk associated with gastrocnemius recession was injury to the sural nerve, which can be avoided with careful dissection and incision planning. Maskill and his partners reported in a 2010 study that 27 of 29 patients were satisfied with the results from the procedure.38 Sammarco et al also reported on the outcomes of a
gastroc-soleus recession, noting a statistically significant increase of ankle joint dorsiflexion averaging 18.3° in a group of 40 patients. In Sammarco’s population, 38 of the 40 patients reported no pain at the incision site, while two patients had reports of paresthesia associated with the area of sural nerve distribution.36

Conclusions

As the medical literature continues to show equinus is present in a majority of patient populations afflicted by common foot pathologies, it is crucial for practitioners to identify the influence of equinus in biomechanical evaluations. Therapeutic approaches that include treatment for secondary equinus will be inherently more successful than treatment limited to the presenting pathology alone. An accurate clinical assessment should be based on the amount of dorsiflexion present on exam. Conservative care should always be the staple of early treatment plans and should include stretching, splinting, and orthotic devices. If conservative care fails, gastrocnemius recession or tendo-Achilles lengthening procedures should be
considered.

Nicholas V. DiMassa is a podiatric medical student and Jeffrey Whitaker, DPM, FACFAS, is the head of the Division of Podiatric Surgery and an associate professor in the Department of Foot and Ankle Surgery at Kent State University College of Podiatric Medicine in Independence, OH.

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