Concussion grading systems

Concussion grading systems are sets of criteria used in sports medicine to determine the severity, or grade, of a concussion, the mildest form of traumatic brain injury. At least 16 such systems exist, and there is little agreement among professionals about which is the best to use. Several of the systems use loss of consciousness and amnesia as the primary determinants of the severity of the concussion.

The systems are widely used to determine when it is safe to allow an athlete to return to competition. Concern exists that multiple concussions received in a short time may present an added danger, since an initial concussion may leave the brain in a vulnerable state for a time. Injured athletes are prohibited from returning to play before they are symptom-free during rest and exertion and their neuropsychological tests are normal again, in order to avoid a risk of cumulative effects such as decline in mental function and second-impact syndrome, which may occur on very rare occasions after a concussion that occurs before the symptoms from another concussion have resolved.

Three grading systems are followed most widely: one was developed by Robert Cantu, one by the Colorado Medical Society, and a third by the American Academy of Neurology.

Cantu guidelines
The Cantu guidelines, published in 1986, classify an injury associated with no loss of consciousness and less than 30 minutes of post-traumatic amnesia as grade I. In grade II, the patient loses consciousness for less than 5 minutes or experiences amnesia for between 30 minutes and 24 hours. In grade III, loss of consciousness lasts longer than 5 minutes or amnesia lasts longer than 24 hours. The most commonly seen type of concussion is a grade I by this guideline.

In a 2001 update, Cantu changed the guidelines to include other concussion signs and symptoms in addition to amnesia in the grading criteria. He also changed the grade II criteria to include only concussions with loss of consciousness for less than 1 minute, and included those with loss of consciousness for greater than 1 minute, or with signs or symptoms lasting over a week, under grade III. More than one grade III concussion during a professional or collegiate athlete's career may lead health professionals to recommend that the player cease playing the sport.

Colorado Medical Society guidelines
The Colorado Medical Society guidelines were published in 1991 in response to the death of a high school athlete due to what was thought to be second-impact syndrome. According to the guidelines, a grade I concussion consists of confusion only, grade II includes confusion and post-traumatic amnesia, and grade III involves a loss of consciousness.

By these guidelines, an athlete who has suffered a concussion may return to sports after having been free of symptoms, both at rest and during exercise, as shown in the following table:

American Academy of Neurology guidelines
The guidelines devised in 1997 by the American Academy of Neurology (AAN) are based on those by the Colorado Medical Society. According to these guidelines, a grade I concussion is associated with no loss of consciousness and symptoms of confusion last less than 15 minutes. Grade II is the same, except symptoms last longer than 15 minutes. In grade III, loss of consciousness does occur. Grade III can be further divided into grades IIIa and IIIb, with brief loss of consciousness (measured in seconds) and prolonged loss of consciousness (measured in minutes) respectively. According to the AAN, permanent brain injury can occur with either Grade II or Grade III concussion.

By these guidelines, an athlete suffering a single, grade I concussion is given a neurological evaluation every five minutes starting immediately after the injury and may return to the competition if signs and symptoms resolve within a quarter of an hour. Otherwise, the return to play rules are the same for the AAN and Colorado Medical Society guidelines.