What causes compartment syndrome?
Muscles are contained in compartments covered by thick fibrous bands of tissue or fascia. Because of injury, pressure can increase within the compartment to swelling (fluid accumulation) or bleeding. In non-contracting muscle, the compartment pressure is normally about 0-15 mmHg of pressure. If the pressure within the compartment increases (usually greater than about 30 -45mmHg; or are within 30 mm of the diastolic blood pressure) most individuals develop compartment syndrome. When these high compartment pressures are present, blood cannot circulate to the muscles and nerves to supply them with oxygen and nutrients. Symptoms such as pain and swelling will result.
As the muscle cells lose their blood and oxygen supply, they begin to die. If the condition is not recognized and treated, the whole muscle can die, scar down, and contract. Similarly, nerve cells that are damaged may fail causing numbness and weakness in the structures beyond the injury site. If infection or necrosis develops, the individual may need the limb amputated to prevent death.
What are the risk factors for compartment syndrome?
Acute compartment syndrome occurs as a complication of an injury. Often it is due to a fracture of the radius or ulna in the forearm or the tibia and fibula in the lower leg that causes significant bleeding in one or more of the compartments. Bleeding can also be due to a badly bruised muscle. Crush injuries may cause both bleeding and swelling of a muscle.
Some injuries can be more subtle. If a person is incapacitated and immobile for a prolonged period of time, for example, due to alcohol or drug intoxication, swelling or muscle damage may occur because a blood vessel was compressed. The weight of an object (or the weight of the body itself) compressing a muscle group can cause rhabdomyolysis (muscle breakdown).
Compartment swelling may occur after the blood supply is re-established (reperfusion swelling) to an area that has lost it for a period of time. Two examples are: 1) a person is in an auto accident
where their legs are trapped and compressed with heavy debris, which are subsequently freed from the debris after a period of time; 2) when a blood vessel is damaged and subsequently repaired through surgery.
Compartment syndrome may be a complication of bandages or casts that are applied too tightly, or due to swelling that occurs
Other abrupt causes of compartment syndrome include burns, snake bites and other envenomation, and anabolic steroid use. Individuals taking anticoagulants have a higher risk for compartment syndrome after trauma
due to bleeding that cannot clot normally. Because there is some controversy about when fasciotomy is required (especially with snake bites)
immediate consultation with a surgeon is recommended by most experts.
Chronic compartment syndrome occurs because of excessive exercise, where repetitive motion and muscle use cause localized swelling and irritation. Most often, symptoms in the legs are seen with runners and bicyclists and in the arms of swimmers. Symptoms resolve with rest and very rarely progress to an acute limb threatening situation.