eMedicine Specialties > Sports Medicine > Neurological

Concussion

Author: David T Bernhardt, MD, Director of Adolescent and Sports Medicine Fellowship, Associate Professor, Department of Pediatrics, University of Wisconsin
Contributor Information and Disclosures

Updated: Aug 6, 2009

Introduction

Background

Concussion has many different meanings to patients, families, and physicians.^1,2,3,4 One definition of concussion is a condition in which there is a traumatically induced alteration in mental status, with or without an associated loss of consciousness (LOC).⁴ A broader definition for concussion is a traumatically induced physiologic disruption in brain function that is manifest by LOC, memory loss, alteration of mental state or personality, or focal neurologic deficits.⁴  Concussions usually result in relatively temporary impairment of neurologic function.^3,5,6

Concussion or mild traumatic brain injury (MTBI) is common among most contact and collision sports participants.^{4,7,8,9,10,11,12} For many physicians, even those who specialize in MTBI, this area is confusing due to the paucity of scientific evidence to support much of the clinical decision making that is faced in the office.^1,2,9,13,14 The inconsiderable amount of good scientific research in the area of MTBI is due to problems with ambiguous definitions of concussion, inconsistent criteria when selecting patients to study, variability of injury mechanisms and locations, and differing means of measuring cognitive function.^15,16 The purpose of this article is to review the epidemiology and diagnosis (but not necessarily the classification) of MTBI, as well as the role of imaging studies, issues regarding return to play, and complications surrounding MTBI.

For excellent patient education resources, visit eMedicine's Back, Ribs, Neck, and Head Center, Brain and Nervous System, and Dementia Center. Also, see eMedicine's patient education articles Concussion, Head Injury, and Dementia in Head Injury.

Related eMedicine topics:
Head Injury [in the Neurology section]
Head Trauma [in the Pediatrics section]
Traumatic Brain Injury: Definition, Epidemiology, Pathophysiology [in the Physical Medicine and Rehabilitation section]

Frequency

United States

The incidence of head injury varies with the sport and the age of the participants; many head injuries are likely unreported due to their supposed mild nature; mild concussions may go unnoticed by teammates, coaches, and even the athletes themselves.⁴ An athlete's fear of medical disqualification may also lead to underreporting. Studies of high school athletes show the rate of concussions per 1000 exposures as follows: 0.59 for football (boys), 0.25 for wrestling (boys), 0.18 for soccer (boys; 0.23 for girls), 0.09 for field hockey (girls), and 0.11 for basketball (boys; 0.16 for girls).

Among National Collegiate Athletic Association (NCAA) soccer players, the rate of injury has been reported as 0.4-0.6 per 1000 athlete exposures¹¹ ; 72% of these injuries were described as mild and were almost always secondary to direct contact with an opponent. None of the injuries in this group of Atlantic Coast Conference (ACC) soccer players was noted to be a direct result of heading the ball. In contrast, boxing is the sport with the highest rate of head injuries and has more deaths than any other organized athletic activity. At the professional level, many of the boxing bouts end with a technical knockout (ie, brain injury).

Sports activities that place the athlete at high risk for a head injury include boxing, football, ice hockey, wrestling, rugby, and soccer. Physicians and other allied health providers who are responsible for the medical care of such contact or collision sports participants should be adept at evaluating, treating, and making playability decisions related to the short- and long-term consequences of an injury to the brain.

Sport-Specific Biomechanics

The mechanisms of brain injury may differ among sports activities. Possible mechanisms of injury include compressive forces, which may directly injure the brain at the point of contact (coup); tensile forces produce injury at the point opposite the injury (contrecoup) because the axons and nerves are stretched; finally, rotational forces may result in a shearing of axons. Therefore, the direct force at the point of contact may not be solely responsible for the severity of an injury if a high rotational component with a significant shear effect occurs.

All of the different mechanisms may result in biochemical changes related to perfusion, energy demand, and utilization at the site of injury that are not well understood. At this time, it is unclear whether any experimental animal model or human studies on more severe brain-injured patients accurately reflect the pathophysiology of the typical mild traumatic alteration in brain function.

Clinical

History

Athletes with an MTBI often appear acutely with a confused or blank expression or blunted affect. Delayed response to simple questioning may be demonstrated, along with emotional lability. The emotional lability may become more evident as the athlete attempts to cope with their confusion. Many athletes report an associated headache and dizziness. Visual complaints may include seeing stars, blurry vision, or double vision.

Both pretraumatic (retrograde) amnesia and posttraumatic (antegrade) amnesia may be present. Usually, the duration of retrograde amnesia is quite brief, with a more variable duration of posttraumatic amnesia (seconds to minutes), depending upon the injury.

A history of persistent vomiting may suggest a significant brain injury with associated elevated intracranial pressure. Other signs of increased intracranial pressure include worsening headache, increasing disorientation, and changing level of consciousness. Possible causes of increasing intracranial pressure include subdural hematomas, epidural hematomas, or some other type of intracranial hemorrhage.

It is important to document a previous history of concussions. Multiple concussions with prolonged neurologic symptoms (eg, headache, hyperacusis, dizziness) suggest postconcussive syndrome and should influence return-to-play decisions.^{7,8,12,17,18,19,20}

• Assessment tools
  • The Glasgow Coma Scale (GCS) is routinely used to assess head injuries in an emergency department.
    • This 15-point scale is used to assess eye (spontaneous opening = 4 to no response = 1), motor (obeys commands = 6 to no response = 1), and verbal responses (oriented = 5 to no response = 1) in an attempt to quantify the patient's level of consciousness.
    • This tool is not sensitive enough to evaluate more mild injuries and should not be used on the playing field to judge playability.
  • McCrea et al developed a sideline evaluation to help the practitioner evaluate the more subtly injured brain.^16,21 A 30-point scale is used to assess an athlete's orientation, concentration, immediate memory, and delayed recall. Preseason testing must be done if a practitioner is hoping to use this tool as a supplement to the neurologic and mental status exam; if the baseline status of an individual is not known, assessment for change after a head injury is useless. McCrea's sideline evaluation uses recitation of the months of the year in reverse order after a study by Young et al showed the lack of reliability of the "serial 7s" test (serial subtraction by 7 from 100) in the baseline evaluation of mental status even in non–head-injured athletes.²²
  • Sport Concussion Assessment Tool (SCAT) is another standardized tool. SCAT combines multiple assessments into a single instrument. This combined tool was produced as a part of the Summary and Agreement Statement of the Second International Symposium on Concussion in Sport.²³
• Classification
  • Many different classification schemes have been proposed over the last 2 decades.
  • No one classification system is necessarily better than another classification system.
  • No scientific basis for any of the classification systems exists.
  • Cantu's guidelines,^12,24 Ommaya and Gennarelli's guidelines,²⁵ the Colorado guidelines,²⁶ and the 1997 American Academy of Neurology (AAN) guidelines²⁷  were proposed to aid in the evaluation of a concussion. The free CDC Tool Kit on Concussion for High School Coaches is available online in English and Spanish and uses the 1997 AAN guidelines to support a classification scheme.²⁸ The authors prefer to characterize concussions as follows²⁸ :
    • A simple concussion injury progressively resolves after 7-10 days without complication. The key to return to play is to hold the athlete from practice or competition until all symptoms have resolved.
    • A complex concussion consists of persistent symptoms that may include those that recur with exertion, specific sequelae such as seizure associated with the injury, prolonged LOC (>1 min), or prolonged impairment of cognitive function.
  • Some studies have suggested that LOC may not be a great predictor of short-term or long-term neurologic functioning, which makes the guidelines more controversial.^29,30
  • Regardless of the classification scheme that is used, all concur with the ultimate recommendation: Do not allow the concussed athlete to return to play until the patient is completely asymptomatic. The athlete must be free of headache, dizziness, amnesia, blunted affect, and delayed verbal or ocular responses, and all cognitive functioning must have returned to normal.

Related eMedicine topics:
Closed Head Trauma [in the Neurosurgery section]
Delirium, Dementia, and Amnesia [in the Emergency Medicine section]
Dementia Due to Head Trauma [in the Psychiatry section]
Intracranial Hemorrhage and Epidural Hematoma [in the Neurology section]
Subdural Hematoma [in the Emergency Medicine section]
Subdural Hematoma [in the Neurosurgery section]

Physical

• Perform a thorough, organized assessment to better define the degree of injury when a player is brought to the sidelines or emergency department for evaluation.
• The initial evaluation should focus on airway, breathing, and circulation for any unconscious patient. Assume all unconscious or mentally impaired patients have sustained an injury to their cervical spine until proven otherwise.
• For conscious patients, the remainder of the examination should be performed in a quiet place, on the sidelines or in the locker room away from teammates and coaches, or in a private room in an emergency department in order to get an accurate assessment of the cognitive status of the injured athlete.
• The initial clinical examination should include a careful inspection of the athlete's general appearance.
• Palpating the head and neck is important when looking for an associated skull or cervical injury.
• Palpate the facial bones and the periorbital, mandibular, and maxillary areas after any head trauma. (See also the eMedicine articles Facial Trauma, Sports-Related Injuries, Facial Trauma, Maxillary and Le Fort Fractures, and Facial Trauma, Management of Panfacial Fractures [in the Plastic Surgery section].)
• Open and close the mouth to help in the evaluation of possible temporomandibular joint (TMJ) pain, malocclusion, or mandible fracture. (See also the eMedicine articles Initial Evaluation and Management of Maxillofacial Injuries [in the Trauma section], Mandible, Fractures [in the Radiology section], and Mandibular Body Fractures [in the Otolaryngology and Facial Plastic Surgery section].)
• Inspect the nose for deformity and tenderness, which may indicate a possible nasal fracture. (See also the eMedicine articles Nasal and Septal Fractures [in the Otolaryngology and Facial Plastic Surgery section], Nasal Fracture [in the Sports Medicine section], and Facial Trauma, Nasal Fractures [in the Plastic Surgery section].)
• Persistent rhinorrhea or otorrhea (clear) indicates a possible associated skull fracture. (See also the eMedicine articles Skull, Fractures [in the Radiology section] and Skull Fracture [in the Neurosurgery section].)
• Perform a careful detailed neurologic examination to include examinations of the visual fields, extraocular movements, pupillary reflexes, and level of the eyes.
• Assess upper-extremity and lower-extremity strength and sensation.
• Assess coordination and balance. Concussed patients often have difficulty with the finger-nose-finger test and will use slow, purposeful movements to complete the task. Catena et al compared the immediate versus long-term effects of concussion on balance control.⁵² Individuals with concussion (n = 30) and matched controls (n = 30) performed a single task of level walking, attention divided walking, and an obstacle-crossing task at 2 heights, with testing occurring 4 times postinjury. The investigators demonstrated no significant difference between the 2 groups in the single-task level walking task. However, although concussed individuals walked slower within 48 hours of the injury and had less motion of their center of mass in the sagittal plane with divided attention during walking, there were no group differences by day 6 for the same task.⁵² In addition, there were no significant group differences in balance control during obstacle crossing during the first 2 testing sessions, but by day 14, concussed individuals had less mediolateral motion of their center of mass. Catena et al concluded that attention divided gait is better at distinguishing gait adaptations immediately postconcussion, but obstacle crossing can be used further along in the recovery process to detect new gait adaptations.⁵²
• Significant sway in Romberg testing may indicate persistent injury.
• When examining an athlete on the sideline, perform repeat examinations every 15 minutes until the symptoms have cleared. Repeat the examinations even if the athlete is allowed to return to play.
• The patient should not be allowed to return to competition if his/her symptoms or physical examination findings do not return to normal after 15 minutes. For a few hours after the initial injury, close observation and monitoring of the athlete for worsening mental status or neurologic status is warranted on the sideline or in the emergency department.

Causes

• A previous concussion is a significant risk factor for sustaining a concussion.^{7,8,12,17,18,19,20}
• One study reported that the risk of sustaining a concussion was 4-5 times higher in patients who had at least 1 concussion in the past. Another study reported that athletes with a history of 3 or more previous concussions were 3-fold more likely to have a concussion than players who had no history of concussion.¹⁹
• Other risk factors for sustaining a concussion that have been suggested but not proven include not wearing mouth guards, poor fitting helmets, and genetic predisposition.^31,32 Research in all of these areas continues.

• Search for CME/CE on This Topic »

• Posttraumatic Vertigo (Otolaryngology and Facial Plastic Surgery)
• Postconcussive Syndrome (Psychiatry)
• Spinal Cord Injuries (Emergency Medicine)
• Commotio Cordis (Pediatrics: Cardiac Disease and Critical Care Medicine)

• Back, Ribs, Neck, and Head Center
• Concussion Treatment
• Dementia Center
• Dementia in Head Injury Overview
• Concussion Overview
• Concussion Symptoms
• Concussion Causes

• New Clinical Instrument Assesses Concussion in Young Athletes
• New VA/DoD Guidelines for Concussion and Mild Traumatic Brain Injury
• NFL Study Finds More Dementia Among Retired Football Players

• Neuropsychiatric Sequelae of Traumatic Brain Injury
• Vomiting in the Pediatric Age Group
• Mild Head Trauma and Chronic Headaches in Returning US Soldiers