Compartment syndrome

Compartment syndrome is an abnormal increase in pressure inside a muscle compartment, an anatomical space bounded by structures with little capacity to stretch — mainly fasciae. The lower leg contains several muscle compartments: the anterior compartment, the lateral compartment, the superficial posterior compartment and the deep posterior compartment.

Two situations must be clearly distinguished, as they differ in mechanism, urgency and management.

Acute compartment syndrome

It occurs suddenly, usually after trauma or a fracture, a crush injury, a haemorrhage, vascular reperfusion or, more rarely, exceptional or prolonged exertion. It is a medical and surgical emergency, because the rapid rise in pressure can compromise muscle and nerve perfusion in the limb.

Chronic exertional compartment syndrome

It develops gradually during exercise: pressure rises in one or more compartments during exertion, causing pain, a feeling of tightness or swelling, sometimes with neurological symptoms. The clinical picture is very characteristic: pain comes on during exercise after a fairly reproducible duration or distance, then gradually disappears after stopping. This is the form that mainly affects runners, endurance athletes and some military personnel — and it is the one covered in the rest of this guide.

A muscle compartment is a relatively closed space. It contains muscles, blood vessels, nerves and connective tissue, all enclosed by a fascia with relatively little capacity to stretch. During exercise, muscle blood flow increases and muscle volume also increases; normally, the compartment adapts to this increase in volume. In chronic exertional compartment syndrome, this adaptation becomes insufficient and intracompartmental pressure then gradually rises.

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The four compartments of the lower leg

Anterior compartment — this is the classic location. It contains the tibialis anterior, the extensor digitorum longus, the extensor hallucis longus and the deep fibular nerve. Involvement can cause anterolateral leg pain, marked tightness, sometimes paraesthesia on the top of the foot and weakness of dorsiflexion or toe extension.

Lateral compartment — it mainly contains the fibularis longus, the fibularis brevis and the superficial fibular nerve. Symptoms may include lateral leg pain, a feeling of pressure and paraesthesia on the top of the foot.

Superficial posterior compartment — it contains the gastrocnemius, the soleus and the plantaris. Pain tends to be posterior and can be confused with a triceps surae condition.

Deep posterior compartment — it contains the tibialis posterior, the flexor digitorum longus, the flexor hallucis longus and the tibial nerve. This compartment is harder to diagnose and must be distinguished in particular from shin splints, a stress fracture or tibialis posterior tendinopathy.

Pathophysiology

The exact mechanism is still not fully understood. Put simply, during exercise: increased blood flow leads to increased muscle volume, which leads to increased pressure in the compartment, which leads to a reduced perfusion gradient, resulting in pain and, possibly, neurological symptoms. Several factors may contribute: muscle hypertrophy, low fascial compliance, a marked increase in blood flow, changes in running mechanics, high training volume, sudden changes in terrain or intensity. However, compartment syndrome should not be reduced simply to the idea of a “muscle that is too big”: the relationship between measured pressure, symptoms and the true pathophysiology is still debated. The phenomenon is therefore more a problem of mechanical tolerance and pressure in a closed space than a simple muscle inflammation.

Chronic exertional compartment syndrome mainly affects physically active people. It is particularly well described in runners, trail runners, endurance athletes, military personnel and athletes who perform repetitive activities placing heavy demands on the lower limbs. The anterior compartment is the most typical location.

It is a well-described cause of exercise-related leg pain in runners, but it remains less common than some other causes such as tibial stress syndromes or muscle injuries. Diagnosis should therefore remain cautious, as exercise-related leg pain has many other causes.

No single factor can predict with certainty the onset of chronic exertional compartment syndrome. Nevertheless, the following factors are frequently found; they are not necessarily direct causes but can alter the load applied to the different compartments.

Training-related factors

Sudden increase in mileage, increased intensity, returning too quickly after a break, more hill sessions, abrupt change of terrain, increased interval training volume.

Biomechanical factors

Recent change in running technique, marked increase in cadence or stride length, change of shoe type, change of drop, major change in running surface.

The classic presentation is extremely reproducible. Athletes often describe it like this: “After 15 minutes, my leg becomes hard and painful. If I stop, it goes away.” Symptoms may include pain, a feeling of tightness, a feeling of swelling, cramp, burning, numbness, pins and needles or muscle weakness.

Reproducibility is particularly important: pain often comes on after a similar duration, a similar distance or at a similar intensity — for example, it consistently appears after 20 minutes of running and then disappears 10 to 20 minutes after stopping. This reproducibility is highly suggestive.

If exercise is continued despite the pain, the pain increases, the feeling of pressure becomes stronger, paraesthesia may develop, muscle weakness may occur and performance declines. In advanced forms, the athlete may be forced to stop completely.

Clinical examination

The clinical examination should ideally be carried out at rest, then immediately after the exercise that usually triggers the symptoms — this is a key point.

At rest, the examination may be completely normal. In particular, the clinician looks for provoked pain, a neurological deficit, muscle asymmetry, a muscle hernia, vascular abnormalities, a tendon abnormality or bone pain.

After exercise, the clinician looks for increased compartment tension, tenderness on palpation, pain on muscle stretching, motor deficit and sensory disturbances. A normal examination at rest in no way rules out chronic exertional compartment syndrome.

Functional tests

The aim is to reproduce the symptoms, for example by running on a treadmill or outdoors, climbing stairs, jumping or doing exercises specific to the athlete’s sport. The test should ideally reproduce the athlete’s usual speed, duration, gradient and symptoms. A negative test performed at low intensity does not necessarily rule out the diagnosis.

When should surgery be considered?

Surgery is generally discussed when the diagnosis is sufficiently robust, the symptoms are typical and disabling, the athlete wishes to continue their sport, conservative treatment has failed or is insufficient, and when compartment involvement has been objectively confirmed where indicated.

Fasciotomy: the reference treatment

Surgical treatment consists of performing a fasciotomy, that is, opening the fascia of the compartment to reduce the stress caused by the increased pressure. Surgery can be open, minimally invasive or endoscopic, depending on the surgical team and the compartments involved. Recent literature confirms that fasciotomy remains the reference surgical treatment for chronic exertional compartment syndrome that does not respond to conservative treatment.

Results of surgery

Results are generally favourable in well-selected patients, but studies report very variable rates of satisfaction and return to sport: in a recent systematic review, satisfaction after fasciotomy was reported at roughly 42 to 94%, and return to sport at 26 to 100%. This wide variability reflects, among other things, the different compartments involved, surgical techniques, study populations, the success criteria used, whether the athletes were civilian or military, and recurrences or residual symptoms. Surgery is therefore no absolute guarantee of a return to the previous level.

Why does surgery sometimes fail?

Several mechanisms are possible: incorrect initial diagnosis, wrong compartment identified, incomplete decompression, unrecognised involvement of several compartments, recurrence, adhesions, associated nerve involvement, or another coexisting cause of pain. It is therefore particularly important to reassess the diagnosis before considering revision surgery.

Two or four compartments?

How many compartments to release depends on the clinical picture and the pressures measured. Some studies show comparable results between two-compartment and four-compartment fasciotomy, but the data remain of limited quality and heterogeneous: the decision should therefore be individualised rather than based on a fixed rule.

Rehabilitation after surgery

Recovery after fasciotomy is gradual, in four phases. Phase 1 — protection: wound healing, reduction of oedema, recovery of range of motion, gradual return to walking. Phase 2 — muscle recovery: progressive mobility, strengthening, balance and neuromuscular control work. Phase 3 — return to impact: gradual introduction of brisk walking, small hops, single-leg hops and then light running. Phase 4 — return to running: progression from slow running to duration, volume, intensity, intervals and then sport-specific terrain. However, postoperative protocols remain heterogeneous in the literature and no universal timeline can be considered validated.

Criteria for returning to running

The return should not be based solely on time since surgery. The criteria sought are, clinically: a healed scar, no significant oedema, minimal or no pain, no paraesthesia; in terms of mobility: satisfactory ankle mobility and range of motion close to the opposite side; in terms of strength: satisfactory recovery of the triceps surae, good strength in the lower limb muscles and no significant functional deficit; and functionally: the ability to perform brisk walking, stair climbing, jumps and single-leg or sport-specific exercises without significant pain.

Return to sport

The return to sport should be gradual, increasing only one variable at a time: slow running on flat ground, then gradually increasing running time, then weekly volume, then introducing changes of pace, then hill work, then intervals, then returning to the specific demands of the sport. Avoid resuming volume, speed, elevation gain and specific sessions all at the same time.

No single factor can predict with certainty the onset of compartment syndrome, but careful management of the identified contributing factors remains the best preventive approach: avoid sudden increases in mileage or intensity, favour a gradual return after a break, and limit the number of hill sessions and overly rapid increases in interval training volume.

From a biomechanical point of view, any major change in running technique, cadence, stride length, shoe type, drop or running surface should be introduced gradually rather than abruptly, so as not to change the load applied to the different muscle compartments too quickly.