Sports related concussion (SRC) in the broadest terms is defined as the immediate and transient symptoms of traumatic brain injury (TBI) induced by biomechanical forces that may or may not result in loss of consciousness (LOC).1 It is more specifically defined as a subset of mild traumatic TBI that involves complex pathophysiological processes that cannot be explained by drugs, alcohol or other underlying comorbidities. 2
SRC may result from either a direct impact to the head, or an impact elsewhere in the body, that results in an impulsive force transmitted to the head and brain.1 Of note, symptoms of suspected SRC must not be explained by drug, alcohol, or other underlying conditions such as vestibular dysfunction.1
Epidemiology including risk factors and primary prevention
There are an estimated 1.7-3.8 million sport-related concussions in the U.S. each year, although the true incidence remains largely unknown, given the likelihood of underreported cases.3 To reinforce the large discrepancy amongst SRC, Bryan et al reports 1.1 to 1.9 million SRC occur annually in US children aged ≤18 years. 4 Some data suggest a trend of increased annual concussion rates over the past decade, which is speculated to be a result of the emphasis on concussion education and awareness leading to increased identification and reporting.5,6,7 Actual incidence may be higher, with studies showing up to 50% of concussions going unreported.8.9.10 Sports with the highest risk appear to be football and girls’ soccer. Other high-risk sports include ice hockey and lacrosse.11,12,13 History of a previous concussion is a clear risk factor. Soccer and basketball demonstrated a significantly higher incidence of concussions in females compared with males.14
Although not completely understood, the pathophysiology of concussion is theorized to be secondary to disruptive stretching of neuronal cell membranes after a direct or indirect hit, resulting in neuronal damage.1 This neuronal damage leads to intracellular ionic shifts and mitochondrial dysfunction that results in subsequent reactive oxygen species and an increase in glucose metabolism, to restore the homeostasis of sodium and potassium within the cell. 15
Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)
The onset of symptoms following a concussion is typically immediate or within minutes after the initial impact. The most common reported symptoms are headache and dizziness. Acutely, the athlete may also describe a feeling of fogginess, complain of tinnitus, confusion, flashing lights, nausea, or amnesia. Other commonly reported symptoms are sensitivity to bright lights, altered sleep patterns, poor concentration, and irritability. In addition, an athlete may notice increasing fatigue and delayed reaction time with physical and mental tasks. Long-term effects might include neurobehavioral or cognitive impairments.1,2
Following a SRC, there is typically a step-wise gradual reduction in symptoms. The majority of concussive symptoms resolve within 7 to 10 days, but some cases may evolve to post-concussive syndrome (PCS) through a process that is poorly understood. PCS should be suspected if there is failure of clinical recovery, defined by symptoms lasting >10–14 days in adults and >4 weeks in children.1
Specific secondary or associated conditions and complications
Complications of a concussion in the absence of other significant medical diagnoses or injuries are usually related to cognitive impairments. The athlete may experience insomnia, emotional lability, memory impairments, depression, anxiety, fatigue, headache, and/or dizziness.1
Essentials of Assessment
It is essential to understand that direct head trauma is not necessary for a concussion to occur. After a suspected concussion, the athlete should be quickly assessed and examined for any concussive like symptoms. Ideally, the injury is witnessed by the covering physician or other medical professional on the field who can describe the mechanism, and any immediate signs of injury, trauma, or LOC. A graded symptoms checklist provides an early tool for the initial assessment and tracking of symptoms over subsequent evaluations. The Center for Disease Control’s Heads Up Concussion Signs and Symptoms Checklist provides four domains:
1) observed signs (eg: LOC, posttraumatic amnesia),
2) physical symptoms (eg: headaches, nausea committing),
3) cognitive symptoms (eg: feeling foggy, “does not feel right”), and
4) emotional symptoms (eg: irritable, sad, more emotional).16
The athlete may not be able to recall the incident, thus spectators may need to be questioned or game tapes reviewed.
Initially, the on-field examination should focus on evaluating for emergent injuries and symptoms. Red flag symptoms that at the minimum require removal from play include neck pain or tenderness, paresthesias, worsening headache, LOC, convulsion, vomiting, worsening confusion, or deteriorating consciousness. 2,17 The cervical spine, skull, and facial bones need to be palpated for any evidence of fracture. If the athlete is stable, the remainder of the examination may be performed on the sideline. A thorough neurological evaluation needs to be performed that includes cranial nerves, sensation, strength, coordination, balance, and cognition..
Functional assessment of the concussed athlete includes a thorough neuromuscular and cognitive evaluation. Standardized assessment tools are available, and they are designed to reduce the degree of subjectivity encountered by medical providers responsible for making a rapid and precise injury assessment and concussion diagnosis decision. When possible, sideline tests can be compared to a reliable pre-injury baseline.2 The primary endpoint for sideline assessment in suspected athletes with SRC is to determine the probability that an athlete has sustained a concussion. If there is definite or probable evidence of concussion, then the athlete should be removed from competition and serially assessed. The Sports Concussion Assessment Tool 5th edition (SCAT5) incorporates a neurological assessment that includes tandem gait, concentration, modified Balance Error Scoring System (mBESS) testing,and delayed recall after using either a 5 or 10-word list assessed after 5 minutes. 17 The mBESS, which is used to assess postural stability to test for objective neurologic functioning.18
The Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) is another assessment tool. This 20-25 minute computer based assessment uses a baseline assessment and in the event of a SRC, a post-injury test is used to help aide in the diagnosis of a SRC. Athletes are generally not allowed to return to play until the post-injury scores are closer to baseline, but that is up to the discretion of the healthcare professional.19
The Vestibular Ocular Motor Screening (VOMS) tool is another tool used by practitioners that allows for a standardized method of assessing vestibular-ocular function. It uses 5 domains: 1) smooth pursuit, 2) horizontal and vertical saccades, 3) near point of convergence distance, 4) horizontal vestibular ocular reflex, and 5) visual motion sensitivity.20
Another unique assessment in SRC is reaction time using a dropped weighted and metered stick. The examiner drops the stick between the athlete’s open hand, who must catch it. Eckner et al. found that reaction time appears to decipher between concussed and non-concussed athletes similarly when compared to other concussion tools.21
The athlete will often have cognitive deficits after sustaining a SRC. The length of the deficits can be highly variable. Concentration, attention, mood, and sleep can be affected, which can further impact school, work, and daily activities. The athlete’s school performance should be closely followed after a SRC. A comprehensive neuropsychological evaluation can be used to identify subtle cognitive deficits as cognitive recovery may either come before or after clinical symptom resolution .1,2
Further description of standardized assessment tools will be discussed below under “Supplemental Assessments Tools”. Of note, repeat annual baseline testing after an initial baseline evaluation is no longer recommended for collegiate athletes.22
There are currently no recommendations for laboratory studies directly related to a SRC.
Neuroimaging is typically normal after a player has sustained a SRC, and is therefore not recommended. Computed tomography (CT) scan and magnetic resonance imaging (MRI) should be reserved for those athletes suspected of intracranial pathology. Findings that would warrant neuroimaging include worsening mental status, declining level of consciousness, focal neurological deficits, seizures, intractable vomiting, anisocoria, rhinorrhea, or otorrhea.
Supplemental assessment tools
While there is no standard, the SCAT5 is the most widely utilized tool for evaluating concussions on the field and if done prior to play, as a measure to compare pre and post injury baseline. The SCAT5 consists of 2 locations of interview 1) on the field and 2) in the clinician’s office after the injury. The on-field assessment includes 5 general steps: 1) red flag symptoms, 2) observable signs, 3) memory assessment using Maddocks’ questions, 4) Glasgow Coma Scale, and 5) cervical spine assessment. The clinical evaluation is a more thorough 6 step assessment that includes a cognitive assessment and extensive symptom evaluation. The symptom evaluation component may be particularly helpful in tracking recovery.1,2
Another tool used is the King–Devick (KD) test. The KD test is a 2-minute sideline assessment of rapid number naming, where the athlete reads numbers on three cards. This requires eye movements, language function, and attention – all of which are usually affected in SRC. 23
Early predictions of outcomes
Early predictions of outcomes continue to be an area of evolving research that may help in identifying more vulnerable populations after SRC. A recent 2017 study described 5 relationships that are commonly asked, and are of significant clinical relevance:
- The relationship between age and clinical recovery. They report that professional athletes may have a faster recovery when compared to amateur athletes. Moreover, they report that the rate of those affected by SRC that continue to have symptoms past 4 weeks are 5–7=17.9%, 8–12=26.3% and 13–17=39.9% indicating that older children may have longer recovery times. Interestingly, the discrepancy may arise from the ability of older children to communicate more succinctly than younger children who cannot, because of normal intellectual differences between a 17-year-old and a 7-year-old.24
- The relationship between sex and clinical recovery. After a SRC, females tend to take longer to recover and have more persistent symptoms >4weeks. The discrepancy is multifactorial and continues to necessitate further research.24
- The relationship between history of concussion and clinical recovery. After an athlete has sustained a SRC, they are more likely to have another SRC. Those who have sustained a first SRC will have higher pre-injury symptoms prior to their second SRC. More research is needed in this area, but there is research to suggest that history of concussions may result in symptoms lasting greater than 4 weeks. 24
- Relationship between neurodevelopmental disorders, mental health, migraine and clinical recovery. This is a unique population as children with neurodevelopmental disorders, such as ADHD and learning disabilities report more concussion symptoms without ever having a SRC, thus their pre-injury scores may become unreliable. Pre-morbid depression and migraine may also prolong recovery with symptoms lasting greater than 4 weeks.24
- Relationship between surrogate measures of injury severity and clinical recovery. LOC was found to be a weak predictor of persistent symptoms after SRC. Post-traumatic amnesia was found not to be related to clinical recovery, but retrograde amnesia, although in a limited amount of studies, was found to have slower recovery time when compared to LOC and anterograde amnesia. The strongest predictor of longer recovery time is the acute and sub-acute symptom burden after the SRC. 24
Social role and social support system
Individuals may notice that attempting tasks in the home and at work/school often increase their concussive symptoms. For student athletes, teachers need to have the understanding that they may need additional time with homework or testing due to problems with attention and concentration. Cognitive rest is very important in the acute recovery from a concussion, and includes restrictions on cell phone use, texting, video games, physical activity and school work until symptoms abate.
Some athletes experience mood-related consequences including anxiety and depression. Contributing factors may include frustration over uncertain recovery time, isolation from teammates and sport, and lack of social support. Prior to pharmacologic or psychotherapy, treatment involves behavioral management interventions, such as regulated sleep schedule, proper nutrition and stress reduction. 1.2
If athletes are returned to play prior to full cognitive and physical recovery they are at risk for worsening symptoms, a prolonged recovery, and an increased risk of suffering additional concussions.2
Second impact syndrome is a potentially life-threatening and catastrophic injury, resulting from a second concussion in which the athlete never fully recovered from the first concussion.2
Concussion legislation has been emerging in this country since the state of Washington passed the first concussion bill in 2009, the Lystedt Law, which required athletes to be removed immediately from athletic activities if it is suspected they have sustained a concussion. Within 5 years, all 50 states have passed a similar law.25 In order to return to play, athletes must be evaluated and receive written clearance from a health care provider trained in concussion assessment.
Rehabilitation Management and Treatments
Available or current treatment guidelines
The rehabilitation of concussion is also an evolving and emerging field, as rehabilitation was not previously included in the 4th consensus statement in Berlin. Rehabilitation research is difficult , and limited data is available, since most concussion resolve after 10-14 days. As previously stated, rehabilitation is now being considered as part of the mainstay in treatment which includes sub-symptoms threshold cognitive and physical activity.
Activity and exercise intolerance may be a result of impaired autonomic dysregulation, leading to symptom manifestation, thus the importance of increasing activity at a sub symptom threshold.2 The Buffalo Concussion Exercise Treatment Protocol, which is a progressive sub-symptom threshold aerobic exercise program, monitors heart and symptoms using the Buffalo Concussion Treadmill Test. 26
Return to learn is the transition back to school and the classroom. It is important to keep an open line of communication with professors, teachers, and school administrators as to the student-athlete’s recent injury. Although most recover relatively quick, some student-athletes with persistent symptoms may require more time to complete school tasks and will require accommodations. Interestingly, return to sport should come after a successful return to the classroom.2
In general, return to sport should progress in an individualized manner that is based on the injury, athlete’s age, history and level of play. There is a 6 stage approach which includes: 1) symptom limited activity, 2) light aerobic exercise, 3) sports specific exercise, 4) non-contact drills, 5) full-contact drills, and 6) return to sport. In general, each stage should allow for 24 hours of symptom free activity. Interestingly, the return to sport is more of an empiric approach rather than evidence based as there is limited data to support how long an athlete should remain in each stage. 2,27
Unfortunately, there is significantly limited data on return to drive and no guidelines exist.2
At different disease stages
As previously described, most concussions and sequalae resolve within 2 weeks for adults, and 4 weeks for adolescents and children.20 It is important to keep in mind that clinical recovery may not correlate with physiologic recovery.20 Treatment of SRC has remained controversial, but clearer clinical guidelines are emerging. Previously thought to be a mainstay of treatment, prolonged total physical and cognitive rest is no longer advocated. Consensus guidelines now endorse 24-48 hours of symptom-limited cognitive and physical rest, followed by gradual increase in activity as long as the athlete remains symptom free throughout the progression. 1,2 As per the consensus statement in Berlin, treatment should be individualized, including a symptom-limited aerobic exercise program, targeted physical therapy program, and a multidisciplinary approach including neuropsychology and cognitive behavioral therapy.1
Coordination of care
The approach to an athlete with a SRC should integrate multiple disciplines. A physician familiar with SRC should be directing care and decisions, often involving collaboration with physical/occupational therapists and neuropsychologists. Additionally, athletic trainers, family, coaching staff, teachers, and friends are integral in the well-being of the athlete.
Patient & family education
The athlete, family, friends, teachers, and coaches need to be educated on the effects of SRC. There needs to be an understanding of the injury in order to protect the athlete and support him/her through the recovery process.28
Neuropsychological testing is used to evaluate cognitive impairment. New forms of testing utilize computer-based programs that are simple and sensitive, but are not substitutes for formal neuropsychologic testing1. These computerized tests evaluate an athlete’s visual memory, verbal memory, processing speed, and reaction time and can follow the resolution of cognitive deficits with serial testing.2,20 Although there is insufficient evidence to recommend the widespread routine use of baseline neuropsychological testing, this may be more important in high-risk athletes with a prior history of concussion, confounding conditions (learning disability, mood and attention disorders, migraine headaches), or those in high-risk sports.1,2
Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills
One of the most important aspects of SRC is the removal of athletes from sports activities as they are recovering, and when to allow return to play. There are many useful tools for monitoring symptoms and cognition to help aid in the decision on when the athlete is ready to return to full participation that were previously described above. Return to sport should progress in an individualized manner that is based on the injury, athlete’s age, history and level of play. Most athletes recover within 10-14 days if the athlete is >18 years old, while athletes <18 years old are expected to return back to baseline cognitive and athletic function in <4 weeks. Concussion is a clinical diagnosis, so a fully negative examination, even when utilizing a comprehensive tool such as the SCAT5, does not rule out concussion.
Cutting Edge/ Emerging and Unique Concepts and Practice
Cutting edge concepts and practice
There is increasing concern that head impact exposure and recurrent concussions contribute to long-term neurologic sequelae such as chronic neurological impairment. Some studies have suggested an association between previous concussions and chronic cognitive dysfunction.2 Chronic Traumatic Encephalopathy (CTE) represents an interesting and unique entity in concussion research. CTE is thought to be a result of multiple repetitive head impact exposures and history of concussions with Tau protein found in postmortem athletes. Currently, the incidence in athletes and non-athletes are unknown, and cause and effect of SRC and repetitive head impacts are unknown.1 Confounders in CTE may be duration of career, genetic factors, previous use of anabolic steroids, and previous use of drugs in the past.2
New, emerging treatments for concussion include high dose omega-3 fatty acids, Vitamin D, progesterone, N-methyl-D-aspartate, and ketogenic diets. Currently, all studies are inconclusive, but research is continuing in those areas. 2
Another interesting, but not yet validated tool are helmet monitors. These monitors allow for sensors to monitor linear and angular acceleration forces to the brain. A limitation of the monitors is that some athletes experience high forces with no resultant concussion, while others have lower impact forces with concussion. 2
Imaging such as CT and MRI, are usually not necessary in concussion workup unless there is concern for intracranial bleeding or there is prolonged recovery. Newer, advanced MRI technologies, including diffusion tensor imaging, resting state functional MRI, arterial spin labelling, are being actively researched. 2
Fluid biomarkers, including those found in blood, saliva, and cerebrospinal fluid, are also being investigated. More recently in 2018, the Federal Drug Administration approved biomarkers for the diagnosis of TBI. The biomarkers approved were ubiquitin carboxy-terminal hydrolase L1 and glial fibrillar acidic protein in patients with Glasgow scores from 9-15.27 There are currently no SRC-specific tests to recommend.2
As previously mentioned, activity and exercise are currently being evaluated to establish a more definitive protocol for athletes to return to play, but clear protocols and guidelines still require more research.
Gaps in the Evidence- Based Knowledge
Gaps in the evidence-based knowledge
One of the major questions in SRCs is a determination on when an athlete should retire from playing a respective sport due to multiple concussions. Limited data is available, and more research is needed to assess for sub-concussive impacts and on neurological health. There are currently no evidenced-based guidelines for recommendation on retiring an athlete from their sport based on the number of concussions sustained.1,2
Additional research in objective neuroimaging modalities as well as fluid biomarkers are needed in SRCs as well as factors that may prolong recovery. Nutraceuticals is another domain of SRCs that is evolving but is also lacking in clear evidence-based foundation. 2
Additional research is needed to validate current assessment tools, further delineate the role of neuropsychologic and balance testing, validate return-to-play guidelines, and improve identification of those at risk for prolonged concussive symptoms. Large-scale, epidemiological studies are needed to more clearly define risk factors and causation of any long-term neurological impairment as well as establishing prevalence and incidence of amateur and professional SRCs.2
- McCrory P, Meeuwisse W, Dvorak J, et al Consensus statement on concussion in sport—the 5th international conference on concussion in sport held in Berlin, October 2016 British Journal of Sports Medicine 2017;51:838-847.
- Harmon, Kimberly G, et al. “American Medical Society for Sports Medicine Position Statement on Concussion in Sport.” British Journal of Sports Medicine, vol. 53, no. 4, 2019, pp. 213–225., doi:10.1136/bjsports-2018-100338.
- Cheng, J, Ammerman, B, Santiago, K, et al. Sex-based differences in the incidence of sports-related concussion: systematic review and meta-analysis. Sports Health. 2019;11:486-491.
- Bryan MA , Rowhani-Rahbar A , Comstock RD , et al. Sports- and recreation-related concussions in US youth. Pediatrics2016;138:e20154635.doi:10.1542/peds.2015-4635
- Gessel, Luke M., et al. “Concussions among United States high school and collegiate athletes.” Journal of athletic training 42.4 (2007): 495.
- Langlois JA, Rutland-Brown W, Wald MM. The epidemiology and impact of traumatic brain injury: a brief overview. J Head Trauma Rehabil. 2006;21(5):375-378.
- Lincoln AE, Hinton RY, Almquist JL, et al. Head, face, and eye injuries in scholastic and collegiate lacrosse: a 4-year prospective study. Am J Sports Med. 2007;35:207–215.
- Hootman JM, Dick R, Agel J. Epidemiology of collegiate injuries for sports: summary and recommendations for injury prevention initiatives. J Athl Train. 2007;42:311–319.
- Meehan III, William P., et al. “The prevalence of undiagnosed concussions in athletes.” Clinical journal of sport medicine: official journal of the Canadian Academy of Sport Medicine 23.5 (2013): 339.
- McCrea, Michael, et al. “Unreported concussion in high school football players: implications for prevention.” Clinical Journal of Sport Medicine 14.1 (2004): 13-
- Lincoln, Andrew E., et al. “Trends in concussion incidence in high school sports a prospective 11-year study.” The American journal of sports medicine 39.5 (2011): 958-963.
- Gessel, Luke M., et al. “Concussions among United States high school and collegiate athletes.” Journal of athletic training 42.4 (2007): 495.
- Marar, Mallika, et al. “Epidemiology of concussions among United States high school athletes in 20 sports.” The American journal of sports medicine 40.4 (2012): 747-755.
- Cheng, Jennifer, et al. “Sex-Based Differences in the Incidence of Sports-Related Concussion: Systematic Review and Meta-Analysis.” Sports Health: A Multidisciplinary Approach, vol. 11, no. 6, 2019, pp. 486–491., doi:10.1177/1941738119877186.
- Barkhoudarian G ,Hovda DA ,Giza CC. The Molecular Pathophysiology of Concussive Brain Injury – an Update. Phys Med Rehabil Clin N Am 2016;27:373–93.doi:10.1016/j.pmr.2016.01.003
- “Concussion Signs and Symptoms Checklist.” CDC Heads Up , Aug. 2019, www.cdc.gov/headsup/pdfs/schools/tbi_schools_checklist_508-a.pdf.
- THE CONCUSSION IN SPORT GROUP. “SPORT CONCUSSION ASSESSMENT TOOL — 5TH EDITION.” SCAT 5: SPORT CONCUSSION ASSESSMENT TOOL, 2017, bjsm.bmj.com/content/bjsports/early/2017/04/26/bjsports-2017-097506SCAT5.full.pdf.
- Guskiewicz KM. Assessment of postural stability following sport-related concussion. Current Sports Medicine Reports. 2003; 2: 24-30
- Dessy, Alexa M, et al. “Review of Assessment Scales for Diagnosing and Monitoring Sports-Related Concussion.” Cureus, 2017, doi:10.7759/cureus.1922.
- Mucha, Anne, et al. “A brief vestibular/ocular motor screening (VOMS) assessment to evaluate concussions: preliminary findings.” The American journal of sports medicine 42.10 (2014): 2479-2486.
- Eckner, James T., et al. “Effect of sport-related concussion on clinically measured simple reaction time.” British journal of sports medicine 48.2 (2014): 112-118.
- National Collegiate Athletic Association (NCAA). Interassociation consensus: diagnosis and management of sport-related concussion best practices. Indianapolis, IN, 2016.
- Leong DF, Balcer LJ ,Galetta SL , et al. The King-Devick test for sideline concussion screening in collegiate football. J Optom2015;8:131–9.doi:10.1016/j.optom.2014.12.005
- Iverson, Grant L, et al. “Predictors of Clinical Recovery from Concussion: a Systematic Review.” British Journal of Sports Medicine, vol. 51, no. 12, 2017, pp. 941–948., doi:10.1136/bjsports-2017-097729.
- Lowrey, Kerri McGowan. “State Laws Addressing Youth Sports-Related Traumatic Brain Injury and the Future of Concussion Law and Policy.” J. Bus. & Tech. L. 10 (2015): 61.
- Leddy JJ, Haider MN, Ellis M, et al. Exercise is medicine for concussion. Curr Sports Med Rep 2018;17:262–70.
- Bazarian, Jeffrey J, et al. “Serum GFAP and UCH-L1 for Prediction of Absence of Intracranial Injuries on Head CT (ALERT-TBI): a Multicentre Observational Study.” The Lancet Neurology, vol. 17, no. 9, 2018, pp. 782–789., doi:10.1016/s1474-4422(18)30231-x.
- Kontos, Anthony P., Jamie McAllister Deitrick, and Erin Reynolds. “Mental health implications and consequences following sport-related concussion.” British journal of sports medicine (2015): bjsports-2015.
Original Version of the Topic:
Ken Mautner, MD, Matthew Axtman, DO. Sports Concussion. 11/15/2011.
Previous Revision(s) of the Topic
Timothy Tiu, MD , Rakhi Sutaria MD, Se Won Lee, MD. Sports Concussion. 5/5/2016.
Timothy Tiu, MD, FAAPMR, CAQSM
Nothing to Disclose
Armando Alvarez MD/MPH
Nothing to Disclose