Concussion in Sports and Performance

Epidemiology

Sports-related concussion (SRC) is a type of mild traumatic brain injury (mTBI) that continues to garner increasing concern worldwide ( ). In the United States alone, estimates of sports and recreation-related concussion range from 1.6 to 3.8 million annually ( ). Concussion occurs in 9% of all US high school sports injuries ( ) and, because many of the clinical findings are subjective, it is among the most difficult injuries in sports medicine to diagnose, assess, and manage. Despite the frequency and possible consequences of repeated head trauma, concussions are often underreported.

Definition of Concussion

Agreement on the definition of concussion has come into focus over time ( ). Historically, concussion has been described as a “low velocity” injury leading to a transient disturbance of function rather than structure ( ). In 2001, the first International Conference on Concussion in Sport expanded the definition to include the common clinical presentations of SRC ( ). In the most recent iteration of the international consensus effort, the definition was further specified to be “a traumatic brain injury induced by biomechanical forces” that “may be caused either by a direct blow to the head, face, neck or elsewhere on the body with an impulsive force transmitted to the head” ( ). Additionally, the following common clinical features were described as potentially useful for defining the nature of SRC:

• 1.

  “SRC typically results in the rapid onset of short-lived impairment of neurological function that resolves spontaneously. However, in some cases, signs and symptoms evolve over a number of minutes to hours” ( ).

• 2.

  “SRC may result in neuropathological changes, but the acute clinical signs and symptoms largely reflect a functional disturbance rather than a structural injury and, as such, no abnormality is seen on standard structural neuroimaging studies” ( ).

• 3.

  “SRC results in a range of clinical signs and symptoms that may or may not involve loss of consciousness. Resolution of the clinical and cognitive features typically follows a sequential course. However, it is important to note that in some cases symptoms may be prolonged” ( ).

This definition is well accepted and widely cited in the medical literature. However, the intense focus on concussion in the public eye, particularly in the realm of popular sport, has created an environment in which the term concussion is often used incorrectly to describe either the actual injury mechanism itself, persistent symptoms that outlive the underlying concussion pathophysiology, tissue-level structural changes to the brain, or long-term neurodegenerative processes. Each of these instances is distinct from concussion, and care should be taken to apply the term correctly.

Pathophysiology

A more complete understanding of the pathophysiology of concussion and how it leads to the clinical effects also continues to be elucidated. The primary elements of the pathophysiological process of concussion include the neurometabolic cascade (abrupt neuronal depolarization, subsequent release of excitatory neurotransmitters, ionic shifts, and changes in glucose metabolism), altered cerebral blood flow (CBF), and impaired axonal function.