Gastrocnemius (Equinus) Contracture & the Silfverskiöld Test

Isolated gastrocnemius contracture is increasingly recognised as an under-appreciated, correctable root cause of common foot and ankle complaints rather than an incidental finding. Some degree of gastrocnemius tightness is highly prevalent in the general adult population, and it is frequently present in patients presenting with metatarsalgia, plantar fasciitis, Achilles tendinopathy, adult-acquired flatfoot and the diabetic forefoot ulcer.

The habit the topic tests. Examine for equinus in any forefoot or hindfoot complaint, because correcting the contracture can resolve a problem that repeatedly fails local treatment.

Two muscles, one tendon. The gastrocnemius arises from the femoral condyles, above the knee, and joins the soleus to form the Achilles tendon, so it spans both the knee and the ankle. The soleus arises from the tibia and fibula below the knee and crosses only the ankle.

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Why the knee position matters. A contracted gastrocnemius restricts ankle dorsiflexion most when the knee is straight and is "let out" when the knee bends, because bending the knee slackens a muscle that crosses it. That is the basis of the Silfverskiöld test.

Equinus. Limited ankle dorsiflexion, commonly defined as less than about 10 degrees with the knee extended and the hindfoot held neutral.

Forefoot overload. A tight gastrocnemius forces the foot into relative plantarflexion, transferring load to the forefoot and altering gait, with early heel rise and increased toe-extensor recruitment. That forefoot overload underlies mechanical metatarsalgia, with plantar keratoses under the lesser metatarsal heads, and contributes to:

• Plantar fasciitis
• Achilles tendinopathy and insertional heel pain
• Posterior tibial tendon dysfunction and adult-acquired flatfoot
• Midfoot and forefoot deformity
• Diabetic forefoot ulceration, where equinus is a key, correctable risk factor

Treating the equinus can off-load and help these conditions.

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Aetiology of equinus contracture

Equinus is the end-point of several distinct processes, and identifying the cause changes management: a spastic equinus is treated very differently from a constitutional one.

Constitutional or idiopathic. The commonest pattern in adult foot and ankle practice is a constitutionally tight gastrocnemius that increases with age, sedentary lifestyle and, in women, sustained high-heel wear, presenting as a Silfverskiöld-positive isolated contracture. This is the group that responds to stretching and, if refractory, gastrocnemius recession.

Neuromuscular or spastic. Upper-motor-neuron spasticity, from cerebral palsy (the classic paediatric cause of equinus), stroke or traumatic brain injury, produces a dynamic and then a fixed equinus. Treatment integrates tone management, with botulinum toxin and serial casting, with lengthening, and the contracture tends to involve the whole gastroc-soleus complex.

Post-traumatic or iatrogenic. Prolonged immobilisation in a cast or splint in plantarflexion, compartment syndrome or calf fibrosis, deep posterior compartment scarring, or healing in equinus after tibial, pilon or calcaneal trauma can fix the ankle in plantarflexion.

Metabolic and other. Diabetes stiffens the Achilles–gastrocnemius complex through non-enzymatic glycosylation of collagen, raising forefoot pressure and ulcer risk. Congenital causes, such as residual or relapsed clubfoot and a congenitally short gastrocnemius, also present with fixed equinus.

Measuring dorsiflexion. Hold the hindfoot in neutral, in inversion, to lock the midfoot and the transverse tarsal joint. Otherwise the foot can dorsiflex through the midfoot and the reading is false dorsiflexion.

The Silfverskiöld test. Measure dorsiflexion with the knee extended, then with the knee flexed to about 90 degrees. Dorsiflexion limited with the knee extended but improving with the knee flexed is a positive test: flexing the knee has slackened the biarticular gastrocnemius, so the restriction that eases is gastrocnemius-driven, an isolated gastrocnemius contracture. Dorsiflexion limited regardless of knee position is a negative test: the soleus and Achilles, which do not cross the knee, are also tight, a combined gastroc-soleus contracture. The result localises the contracture and so chooses the level of any lengthening.

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The rest of the examination. Examine the forefoot for metatarsalgia and callosities, watch the gait for early heel rise, and look deliberately for the associated conditions listed under forefoot overload.

A clinical diagnosis. Gastrocnemius equinus is fundamentally a clinical diagnosis: the goniometric dorsiflexion measurement (hindfoot neutral, knee extended then flexed) and the Silfverskiöld test are the core "investigations", and equinus itself is not seen radiographically. Adjuncts have a supporting role:

• Weight-bearing radiographs of the foot and ankle identify associated or alternative pathology (forefoot deformity, midfoot arthritis, flatfoot)
• Pedobarography, plantar pressure mapping, can objectively demonstrate the elevated forefoot pressures the contracture produces, useful in research and in the diabetic foot
• Gait analysis may show early heel rise and increased toe-extensor recruitment
• MRI and ultrasound have no routine role for the contracture itself, though they may be used to assess an associated tendinopathy or the plantar fascia

Soft-tissue or bony equinus. A muscle lengthening only helps soft-tissue equinus. Before attributing limited dorsiflexion to a tight gastroc-soleus, exclude a structural, bony block and a pseudoequinus.

The bony block. Anterior tibiotalar osteophytes (anterior ankle impingement) or tibiotalar osteoarthritis limit dorsiflexion with a hard, abrupt end-feel that does not change with knee position, so a bony block can masquerade as a Silfverskiöld-negative combined contracture. It will not respond to a gastrocnemius recession or a tendo-Achilles lengthening; it needs a cheilectomy or osteophyte excision instead. Look for the spur on a weight-bearing lateral radiograph, and feel for the abrupt, rather than springy or soft, end-point.

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Pseudoequinus. Apparent equinus generated through the forefoot or midfoot: a plantarflexed first ray or forefoot equinus in a cavus foot, or simply dorsiflexion measured through an unlocked midfoot. The second is the reason for the hindfoot-neutral measurement described under Clinical Assessment.

The sequence before operating. Confirm the limit is real (hindfoot neutral), confirm it is soft-tissue (soft end-feel, no blocking spur), then localise it with the Silfverskiöld test.

Conservative first. Knee-extended gastrocnemius stretches, eccentric loading and night splints or dorsiflexion orthoses come first; heel lifts, orthoses and footwear modification off-load the forefoot symptomatically. Most patients improve, and these are the mainstay before any surgery.

Gastrocnemius recession. For an isolated, Silfverskiöld-positive contracture refractory to conservative care. An Achilles-sparing recession reliably increases dorsiflexion while preserving push-off power, which is the advantage over Achilles lengthening. The recessions, proximal to distal:

• Baumann, a proximal intramuscular recession of the gastrocnemius (with or without soleus) fascia, with the muscle in continuity
• Strayer, release of the gastrocnemius aponeurosis at the musculotendinous junction, just distal to the muscle bellies, with the soleus left intact; the commonest, and the one in which the sural nerve must be protected
• Vulpius, an inverted-V release of the more distal conjoined gastroc-soleus aponeurosis

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Tendo-Achilles lengthening. Reserved for a combined, Silfverskiöld-negative contracture, accepting some plantarflexion and push-off weakness. In the diabetic neuropathic forefoot ulcer, Achilles lengthening reduces ulcer recurrence (the Mueller randomised trial, in the Evidence Base).

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Cerebral palsy and the crouch-gait trap. Equinus correction in cerebral palsy carries a specific hazard absent in the adult constitutional contracture: over-lengthening the triceps surae causes an iatrogenic calcaneus or crouch gait that is very hard to reverse, "the calf muscle is a one-way street". The gastroc-soleus provides the plantarflexion–knee-extension couple that holds the knee straight in stance, so an excessive isolated tendo-Achilles lengthening, especially in a spastic diplegic child already prone to crouch, collapses the child into excessive ankle dorsiflexion and knee flexion. The principles:

• Prefer the most muscle-selective, proximal lengthening (a gastrocnemius recession, Strayer or Baumann, over a tendo-Achilles lengthening), guided by the Silfverskiöld test and ideally instrumented gait analysis; reserve a true TAL for a genuine fixed combined contracture
• Address dynamic equinus first with tone management, botulinum toxin and serial casting, before it becomes fixed, integrated with the child's GMFCS level and the Winters-Gage hemiplegic gait pattern
• Isolated TAL is more dangerous in diplegia than hemiplegia, because the diplegic child has a bilateral crouch tendency; never lengthen the Achilles aggressively in a child who already over-dorsiflexes

The contracture's main "complication" is the forefoot and hindfoot pathology it drives, set out above; the surgical complications are level-specific.

Global Practice Picture

Isolated gastrocnemius contracture is increasingly recognised worldwide as an under-appreciated, correctable driver of forefoot and hindfoot pathology. The internationally consistent approach: measure dorsiflexion in hindfoot neutral, apply the Silfverskiöld test to localise the contracture, treat conservatively first, and use an Achilles-sparing gastrocnemius recession (rather than Achilles lengthening) for refractory isolated gastrocnemius equinus.

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