Thick layers of tissue called fascia separate groups of muscles in the arms and legs from each other. The contents of each layer of fascia, which include not only muscle but also nerves and blood vessels, are defined as a compartment. For example, if a telephone wire was thought of as an arm or leg, the insulation on the four wires inside the telephone line (red, green, yellow and black) can be thought of as fascia defining a compartment, and the wires inside the insulation as the contents of the compartment.

Unlike a balloon, fascia does not expand, so any swelling in a compartment will lead to increasing pressure in that compartment, which will compress the muscles, blood vessels and nerves. If this pressure is high enough, blood flow to the compartment will be blocked which can lead to permanent injury to the muscle and nerves. If the pressure lasts long enough, the limb may even need to be amputated.

Swelling leading to compartment syndrome is associated with high-energy trauma, such as from a car accident or crush injury, or surgery. A cast also cannot expand, and if there is significant swelling under a cast, pressure will build up and can cause the same syndrome. Chronic compartment syndrome can be caused by repetitive activities like running that cause an increase in pressure in a compartment only during the activity.

Compartment syndrome is most common in the lower leg and forearm, although it can also occur in the hand, foot, thigh and upper arm.

The hallmark symptom of compartment syndrome is pain out of proportion to injury. The pain does not respond to elevation or to pain medication. In more advanced cases, there may be decreased sensation, weakness, and paleness of the skin.

Typical physical exam findings include severe pain when a muscle running through a compartment is passively moved. For example, when the doctor moves the toes up and down when there is compartment syndrome in the foot or lower leg, the patient will experience severe pain. The skin overlying the compartment will be tensely swollen and shiny. There will also be pain when the compartment is squeezed.

The test that will absolutely diagnose this condition involves directly measuring the pressure in the compartment by inserting a needle attached to a pressure meter into the compartment. When the compartment pressure is greater than 45 mmHg or when the pressure is within 30 mmHg of the diastolic blood pressure (the lower number of the blood pressure), then the diagnosis is made. When chronic compartment syndrome is suspected, this test must be performed immediately after the activity that causes pain.

Treatment is surgical release of the compartment for both acute and chronic compartment syndrome. Long incisions are made in the fascia to release the pressure building inside. If a cast is causing the problem, then the cast should be removed to relieve the pressure.

If the diagnosis of compartment syndrome is made promptly and surgical release performed, the prognosis is excellent for recovery of the muscles and nerves inside the compartment. However, the overall prognosis will be determined by the injury leading to the syndrome.

If there is a delay in diagnosis, there can be permanent nerve injury and loss of muscle function. This is more common when injured person is unconscious or heavily sedated and incapable of complaining. Permanent nerve injury can occur after 12-24 hours of compression.

Complications include permanent injury to nerves and muscles that can dramatically impair function.

In more severe cases, limbs may need to be amputated because all the muscles in the compartment have died from lack of oxygen.

If you have suffered an injury and have severe swelling and/or pain that does not improve with pain medications, contact your health care provider to be evaluated for compartment syndrome.

While there is probably no way to prevent compartment syndrome, being very aware of this condition and early diagnosis and treatment will help to prevent many of the complications. People placed in casts need to be made aware of the risk of swelling and need to see their health care provider or go to the emergency room if they have increasing pain under the cast despite elevation and pain medicine.