Compartment syndrome is a painful, potentially dangerous condition where pressure builds up inside a closed group of muscles to the point that blood can no longer flow through the tissue. Your muscles are organized into compartments, each wrapped in a tough layer of tissue called fascia that doesn’t stretch. When swelling or bleeding occurs inside one of these compartments, the pressure rises, cuts off circulation, and starves the muscles and nerves of oxygen. Without treatment, muscle tissue can begin to die within 6 to 8 hours.
The condition most often affects the lower leg and forearm, though it can develop in the hand, foot, thigh, or abdomen. There are two distinct types, acute and chronic, and they differ dramatically in severity and urgency.
How Pressure Causes Damage
Every muscle compartment has a network of tiny blood vessels (capillaries) that deliver oxygen and remove waste. These capillaries operate at low pressure. When internal swelling pushes the pressure inside a compartment above the pressure in those capillaries, blood flow slows and eventually stops. The muscles and nerves trapped inside the compartment begin to suffer from a lack of oxygen, a process called ischemia.
Because fascia does not expand like skin, even a relatively small increase in fluid volume can spike the pressure quickly. During exercise, for example, muscles can swell by up to 20%. In a healthy person that swelling resolves naturally, but in compartment syndrome the pressure keeps climbing or doesn’t drop fast enough, and the cycle of swelling, reduced blood flow, and tissue damage feeds on itself.
Acute Compartment Syndrome
Acute compartment syndrome is a medical emergency. It develops rapidly, usually after a traumatic injury, and requires surgery within hours to prevent permanent damage. Crushing injuries are the most common trigger, but fractures (especially of the shinbone and forearm), severe sprains, and even tight casts or bandages can set it off. Notably, patients who develop acute compartment syndrome without a fracture tend to have higher rates of muscle death compared to those whose syndrome follows a broken bone, likely because the diagnosis gets delayed when no fracture is visible on imaging.
Less common causes include burns, blood-thinning medications that lead to internal bleeding, and prolonged limb compression during surgery or while unconscious.
Warning Signs
The hallmark symptom is pain that feels far worse than the injury should cause. Early on, this pain may appear only when someone else gently stretches the affected muscles. The earliest physical sign a clinician can detect is a compartment that feels abnormally tense and firm, sometimes described as “wood-like.” As pressure continues to rise, additional symptoms follow: numbness or tingling, weakness or inability to move the limb, pale skin, and eventually a loss of pulse below the affected area. Clinicians sometimes refer to these warning signs collectively as “the five Ps”: pain, paresthesia (tingling), paralysis, pallor, and pulselessness.
Pain that suddenly worsens after a fracture or injury, or that doesn’t respond to normal pain relief, should be treated as an urgent red flag.
Diagnosis and Pressure Thresholds
When a clinical exam alone isn’t conclusive, doctors can measure the pressure inside the compartment directly using a needle connected to a pressure monitor. The key number isn’t the compartment pressure in isolation. Instead, doctors compare it to your diastolic blood pressure (the lower number in a blood pressure reading). A 2025 guideline from the American Academy of Orthopaedic Surgeons confirms that if the gap between diastolic pressure and compartment pressure narrows to 30 mmHg or less, the diagnosis is essentially confirmed and surgery is indicated. In a study of 116 patients with shinbone fractures, using this threshold led to zero missed cases and zero unnecessary surgeries.
For patients who can’t report their own symptoms, such as those who are sedated or unconscious, the AAOS recommends continuous or repeated pressure monitoring until compartment syndrome is either confirmed or ruled out. If regional anesthesia has been given (which can mask pain), frequent physical exams and pressure checks are also recommended.
Chronic Exertional Compartment Syndrome
Chronic exertional compartment syndrome is a very different condition. It develops gradually during repetitive exercise, typically in runners, endurance athletes, soccer and lacrosse players, and military trainees. The key distinction: symptoms reliably go away with rest. There is no traumatic event. Instead, the muscles swell during activity, pressure builds inside the compartment, blood flow drops, and the athlete experiences a deep aching or tightness that forces them to stop. Once they rest, the pressure normalizes and the pain fades.
This form peaks in adults between 20 and 25 years old, is more common in men, and affects both legs in the majority of cases. While it is not life-threatening, it can be stubborn enough to sideline athletes for months or years. Overuse injuries and microtrauma that lead to scar tissue formation inside the compartment can make the condition worse over time.
A rarer and more dangerous variant, acute exertional compartment syndrome, blurs the line between the two types. It strikes during or after intense physical activity, typically in adolescents and young men, but unlike the chronic form, the symptoms do not resolve with rest. It carries the same risk of permanent muscle and nerve injury as traumatic acute compartment syndrome and requires emergency surgery. Because there’s no obvious injury like a fracture, this variant is frequently diagnosed late.
Surgical Treatment: Fasciotomy
The definitive treatment for acute compartment syndrome is a fasciotomy, a procedure where a surgeon cuts open the fascia to relieve the trapped pressure. Research based on tourniquet models shows that muscles can tolerate up to 6 to 8 hours of oxygen deprivation before irreversible death of the tissue begins. Fasciotomies performed more than 8 hours after diagnosis carry a significantly higher risk of infection and complications.
In the lower leg, surgeons may use one long incision along the outer side of the calf or two incisions (one on the outer side, one on the inner side) to access all four muscle compartments. For the forearm, the incision typically runs along the inner surface from near the elbow down to the wrist, sometimes extending into the palm to release pressure in the carpal tunnel as well. In every case, the skin incision is left open after surgery. The wound cannot be closed immediately because the swollen tissue needs room to expand. Dressings are changed every one to two days to prevent infection, and the wound is typically closed days later once swelling subsides, sometimes requiring a skin graft.
For chronic exertional compartment syndrome, fasciotomy is considered only after conservative measures like activity modification and physical therapy have failed. A substantial portion of athletes with refractory symptoms eventually choose surgery.
What Happens if Treatment Is Delayed
When compartment syndrome goes untreated or is caught too late, the consequences can be severe and permanent. Prolonged oxygen deprivation kills muscle fibers, which are gradually replaced by scar tissue. This scarring contracts over time, pulling joints into fixed, bent positions. In the forearm, this is known as Volkmann contracture, where the wrist and fingers curl inward and cannot be straightened. Severe cases involve both the flexor and extensor muscles, causing pronounced deformity and significant loss of hand function.
Nerve damage accompanies the muscle loss. Numbness and loss of sensation in the areas served by the affected nerves are common. In the forearm, this typically means permanent sensory loss in the hand along the distribution of the median and ulnar nerves, affecting grip, fine motor control, and the ability to feel objects. Reconstructive surgery, including free muscle transfer, can partially restore function in severe cases, but carries its own risks of flap failure, infection, and tendon scarring.
The stakes are even higher in certain body regions. In orbital compartment syndrome (around the eye), vision loss can begin after just 60 to 100 minutes of elevated pressure. Patients treated within 2 hours of symptom onset generally retain good vision, while delays beyond that window dramatically worsen outcomes.
Location Matters
While the lower leg is the most commonly affected site, compartment syndrome can develop wherever muscles are enclosed in fascia. The forearm is the second most common location, particularly after fractures near the elbow. The thigh, hand, foot, and buttocks are all possible but rarer sites. Abdominal compartment syndrome, which develops when pressure inside the abdomen rises dangerously high (often in critically ill patients), follows similar principles but is managed differently. In abdominal cases, decompression within 6 hours of diagnosis is associated with better outcomes.
Regardless of where it occurs, the underlying problem is the same: too much pressure in a space that can’t expand, choking off blood flow to the tissues trapped inside. Speed of recognition and treatment is the single biggest factor in determining whether the outcome is full recovery or permanent disability.