From wikipedia:
Compartment syndrome is a condition in which increased pressure within one of the body's anatomical compartments results in insufficient blood supply to tissue within that space.[6][7] There are two main types: acute and chronic.[6] Compartments of the leg or arm are most commonly involved.[3]
Symptoms of acute compartment syndrome (ACS) can include severe pain, poor pulses, decreased ability to move, numbness, or a pale color of the affected limb.[5] It is most commonly due to physical trauma such as a bone fracture (up to 75% of cases) or crush injury, but it can also be caused by acute exertion during sport.[3][8] It can also occur after blood flow returns following a period of poor blood flow.[4] Diagnosis is generally based upon a person's symptoms[5] and may be supported by measurement of intracompartmental pressure before, during, and after activity. Normal compartment pressure should be within 12-18 mmHg; anything greater than that is considered abnormal and would need treatment.[9] Treatment is by surgery to open the compartment, completed in a timely manner.[5] If not treated within six hours, permanent muscle or nerve damage can result.[5][10]