Sports-related concussion represents a unique type of brain injury because the goal of medical care is to return the athlete safely and expeditiously to the same activity that led to the concussion. The Sport Concussion Assessment Tool has standardized assessment of concussed athletes and their return to play. Advances in brain imaging, assessment of molecular biomarkers in blood and other body fluids, and accurate wearable sensors of force and acceleration are being applied to the study of concussion in athletes. In conjunction with long-term outcome data, such technologies will continue to make athletic competition as safe as possible.
Key points
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The vast majority of concussions are not accompanied by loss of consciousness.
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Players must be fully recovered and free of symptoms before they can return to competition.
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Most baseball players who suffer a concussion can return to play after roughly a week, but some require significantly more time.
Introduction
Ray Chapman is the only player ever to die after being struck by a baseball in a major league game. He was a shortstop for the Cleveland Indians. While he was batting in an afternoon game on August 16, 1920, a pitched ball struck him in the head. Batters did not wear helmets in that era. He died in a hospital approximately 12 hours after injury.
Thankfully, sports-related traumatic brain injury (TBI) is almost never fatal, especially in baseball. However, it has become a widely discussed topic in popular culture. Most attention focuses on reported potential long-term effects of concussion and repetitive head impacts (RHIs). Worries about possible risk cause many parents to limit their children’s activity in contact sports. Lack of understanding of what concussion is and is not may hinder appropriate care, overlook the real source of persistent symptoms, and contribute to underreporting. Of special concern is that failure to recognize the signs and symptoms of concussion can lead to devastating consequences, particularly in children and adolescents. To combat these important gaps in knowledge, accurate information about concussion must be widely disseminated and often repeated.
Definition
The definition of concussion has long been a subject of debate in the medical and scientific communities. Much of the confusion arises because concussion can present with a wide range of symptoms, and individual responses to TBI can vary significantly.
Concussion was recognized as a transient physiologic abnormality without gross brain lesions by the Islamic physician Rhazes in the tenth century. In 1280, Lanfrancus articulated the concept of commotio cerebri , or shaking of the brain, as the cause of concussions, and this type of injury differed from contusio cerebri , which is associated with structural damage. Current definitions of concussion rely on this centuries-old concept of a complex pathophysiological process caused by external biomechanical forces that affect the brain. A review published 2 decades ago identified more than 40 different sets of guidelines for concussion. That number has likely increased during the intervening years.
By definition, computed tomography (CT) scans of the brain—in those uncommon cases in which imaging studies are obtained in patients with concussion—show no acute traumatic findings. If acute trauma-related abnormalities are identified on CT scan in someone who has sustained a blow to the head, the patient is diagnosed with a more severe form of TBI, and the term “concussion” should not be used.
Among patients with mild TBI who seek medical attention, MRI may reveal acute trauma-related abnormalities in roughly a quarter of patients in whom CT scanning is unremarkable. Such patients have a longer course of recovery from their brain injury. As discussed in a later section, the question arises as to whether the definition of concussion should be modified to include the results of MRI scanning. However, because the majority of athletes with sports-related concussion neither require nor receive imaging studies of the brain, there is no need to add CT or MRI results as required elements for making this diagnosis.
American Association of Neurological Surgeons
The American Association of Neurological Surgeons defines concussion as “a clinical syndrome characterized by immediate and transient alteration in brain function, including alteration of mental status or level of consciousness, that results from mechanical force or trauma.” Several components of this definition deserve emphasis: (1) Symptoms of concussion occur immediately after trauma (even though recognition may be delayed). (2) The symptoms are transient in the vast majority of cases. (3) An external mechanical force is the cause of the symptoms. (4) Concussion is a disturbance of function but not structure.
Concussion in Sport Group
The definition adopted by the expert panel at the 6th International Conference on Concussion in Sport in 2023 adds that sports-related concussion is “caused by a direct blow to the head, neck or body resulting in an impulsive force being transmitted to the brain” and that “clinical symptoms and signs of concussion cannot be explained solely by (but may occur concomitantly with) drug, alcohol or medication use, other injuries (such as cervical injuries, peripheral vestibular dysfunction) or other comorbidities (such as psychological factors or coexisting medical conditions).” The definition goes on to state, “No abnormality is seen on standard structural neuroimaging studies (CT or MRI T1-weighted and T2-weighted images), but in the research setting, abnormalities may be present on functional, blood flow or metabolic imaging studies.”
Ultimately, any definition should incorporate the facts that concussion is caused by a direct blow that results in the rapid onset of a range of disparate symptoms that are typically short-lived but can last longer and, by definition, does not result in abnormalities on CT or standard structural MRI.
Additional Considerations
Importantly, loss of consciousness is not required to make a diagnosis of concussion. This misconception persists despite extensive educational efforts in the sports world as well as in society at large. In fact, only a small minority of concussions are accompanied by loss of consciousness.
Another concept that has become obsolete is assigning a grade to the severity of concussions. In years past, duration of loss of consciousness and other symptoms were used to classify the severity of a patient’s concussion. However, it is now recognized that such grades did not correlate with the severity or duration of an athlete’s symptoms or to their prognosis and recovery. Such grading schemes have been abandoned, at least until an accurate and useful classification system can be developed.
Various authors have described predominance of different symptom clusters in many patients with concussion ( Table 1 ). Focusing treatment on a patient’s specific symptoms may expedite recovery. Ultimately, concussions may one day be broken down into specific subtypes, with each subtype perhaps being linked to a specific pathophysiologic process. Such knowledge would, in turn, create the possibility of highly targeted treatments.
| Subtype | Some Common Symptoms |
|---|---|
| Cognitive/fatigue |
|
| Vestibular |
|
| Oculomotor |
|
| Anxiety/mood |
|
| Posttraumatic migraine |
|
| Cervical |
|
Epidemiology
Several authors have examined rates of concussion in baseball. Gessel and colleagues studied concussion rates across 9 different sports in a data set created from a nationally representative sample of high schools and colleges. They found that high school baseball players had 0.05 concussions per 1000 athletic exposures (AEs; defined as any practice or competition event). The rate in college players was 0.09. This is lower than the average of 0.23 concussions per 1000 AEs across all sports for high schoolers and 0.43 at the college level. Zuckerman and colleagues found a rate of 0.9 concussions per 1000 AEs in National Collegiate Athletic Association baseball players. The rate of concussion was higher in competition than in practice.
Another investigation examined emergency room visits for concussions in pediatric baseball and softball players and found that these decreased slightly in frequency from 2012 to 2021. Head-to-ball injuries were the most common mechanism.
Data from a 2015 study of major and minor league baseball revealed that approximately 40% of concussions occurred in catchers. When the catchers were fielding (not batting), 40% of their concussions were caused by impacts between players.
Evaluation
In the past, diagnosing concussions in athletes was often challenging because of poor understanding of associated symptoms and lack of standardized protocols. In addition, concussions were not often thought of as being a significant problem in athletes and were therefore likely underdiagnosed. Players and coaches often subscribed to the antiquated notion that an athlete showed weakness if he or she complained of problems after a concussion.
Fortunately, more widespread recognition of the significance of concussion, and of the risks of continuing to compete despite the presence of ongoing concussion symptoms, has gone a long way to eliminate the stigma that once accompanied an athlete’s decision to refrain from practice and competition after a concussion. Although stigma has declined as a barrier to effective management of concussion, it still rears its head far too frequently. Additional diagnostic and therapeutic challenges continue to arise because of the complexities of this injury.
Sport Concussion Assessment Tool
Addressing these problems was one motivation behind the creation of the Concussion in Sport Group (CISG), which works to “analyze, aggregate, and interpret the world’s scientific literature for the evaluation, management, and prevention of sports-related concussion.” One important work product of the CISG is the Sport Concussion Assessment Tool (SCAT), which was initially published in 2005 to guide clinicians in assessment and management of athletes with concussion. The SCAT pulled together several different validated concussion diagnostic tools into a single instrument. Although the overall SCAT may not have the same degree of validation as some of its component parts, it is still quite valuable as a way to encourage medical personnel to follow the same standardized approach to the evaluation of athletes for possible concussion. The SCAT has been updated every 4 years, but the coronavirus disease pandemic and lockdown in 2020 interrupted that cadence. The most recent iteration is the SCAT6, published in June 2023.
Sport Concussion Assessment Tool 6: Immediate Assessment
The SCAT6 functions as a detailed assessment algorithm. The first section focuses on an immediate assessment and neuro screen, with an emphasis on “red flags” or signs or symptoms that may indicate the presence of an injury that is more urgent than concussion. These indicators include deteriorating level of consciousness, visible skull deformity, worsening headache, and similar findings. If the clinician sees any of these warnings or red flags, the athlete should be removed from play for immediate medical assessment or transport to a hospital or medical center.
The SCAT6 then takes the health care provider through the remaining parts of the immediate assessment and neuro screen. Step 1 is an assessment for observable signs of concussion, such as confusion or a blank or vacant look. Step 2 is a determination of the Glasgow Coma Scale score. This scale is widely used to assess severity of TBI, with scores spanning the spectrum from normal level of consciousness to deep coma. For major league baseball (MLB), this section has been omitted from on-field assessment because confusion or an abnormal level of alertness in an athlete will have been detected earlier, during the screen for red flags.
Step 3 of the immediate assessment and neuro screen focuses on cervical spine assessment, and step 4 addresses coordination and oculomotor function. Step 5 uses Maddocks questions to assess memory.
Sport Concussion Assessment Tool 6: Off-field Assessment
The SCAT6 then addresses off-field assessment. Step 1 is a brief questionnaire about the athlete’s background. Step 2 includes the symptom evaluation, in which the athlete is asked about the presence of 22 specific symptoms ( Box 1 ). The severity of each symptom is graded on a scale from 0 to 6. The cognitive screen is performed in step 3 and includes orientation questions, immediate recall of a 10-word list, reverse-order repetition of progressively longer lists of numbers, and timed recitation of the months of the year in reverse order. In step 4, coordination and balance are tested by the Modified Balance Error Scoring System and timed tandem gait. Finally, step 5 assesses delayed recall by asking for the same 10-word list that was used in step 3.
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Headaches
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Pressure in head
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Neck pain
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Nausea or vomiting
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Dizziness
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Blurred vision
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Balance problems
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Sensitivity to light
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Sensitivity to noise
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Feeling slowed down
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Feeling like “in a fog”
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“Don’t feel right”
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Difficulty concentrating
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Difficulty remembering
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Fatigue or low energy
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Confusion
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Drowsiness
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More emotional
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Irritability
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Sadness
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Nervous or anxious
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Trouble falling asleep
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