Risk Factors for Concussion and Prolonged Recovery

History of prior concussion, collision sports, female sex, and women's soccer are the strongest known risk factors for concussion, while symptoms such as persistent headaches, migraines, amnesia, and multiple symptoms appear to be associated with prolonged recovery, says a new study.¹

Reviewing relevant studies for the period 1996 to 2011, researchers at Maine Medical Center Sports Medicine in Portland, ME found, despite an explosion in concussion research over the past 15 years, that reliable evidence for risk factors for concussion and prolonged recovery "remains sparse" :

Risk of concussion

• History of concussion:
  • For high school athletes, a history of concussion more than doubled the risk that an athlete would suffer another concussion, with the association greatest in football and amateur rugby; and
  • College football players with a history of 3 or more concussions are at 3-times-higher risk of repeat concussion.
•   Sports
  • collision sports (football, ice hockey, rugby) have the highest rates of concussion in men at all levels of competition;
  • for women, soccer was the sport which consistently had the highest risk;
  • wrestling, men's soccer, basketball and lacrosse also put student-athletes at risk for concussion;
  • In most sports, the rates of concussion is significantly higher in games than practices.
• Positions: More concussions are sustained by:
  • football linebackers, defensive backs, and offensive linemen;
  • soccer goalkeepers, defensive field players, and 
  • rugby midfield backs.
• Age: The relationship of age to overall risk of concussion is unclear:
  • younger age was associated with increased risk in one study of 12- to 24-year-olds;
  • high school football players had a higher concussion rate than college players in one study, but another study - this one of athletes in various sports - found a higher overall rate of concussion for collegiate than high school sports, although concussions accounted for a greater proportion of total injuries in most high school sports (13.2% of high school athletic injuries in the most recent study² versus 5.8% in college); 
• Sex: Female athletes are at increased risk of concussion:
  • Overall rates of concussion are higher for high school and collegiate male athletes, but when sports are examined where the men's and women's games are similar (including soccer and basketball), female athletes are at higher concussion risk;
  • 9 out of 10 such studies found higher injury rates for women, with 4 finding the difference statistically significant.
• Migraines. The overlap of symptoms between migraines and concussion suggests a relationship, but there is little quality data to support the connection, and multiple unanswered questions remain regarding the association.
• Genetics. 
  • There is little evidence on the role of family history and genetics as concussion risk factors 
  • The Apolipoprotein E (APOE) gene has been implicated in Alzheimer's disease, chronic traumatic encephalopathy, and worse outcome after traumatic brain injury. 
• Equipment
  • Football helmets reduce the acceleration of the head from collision and decrease severe head injuries but concussion rate and severity are not affected by different helmets; the same is true for ice hockey helmets.
  • Studies of rugby headgear have yielded mixed results, without conclusive evidence for a protective effect.
  • One small study suggests that soccer headgear may decrease concussion risk but has significant weaknesses
  • Mouth guards³ in multiple sports and face shields in ice hockey decrease the risk of dental and orofacial injuries but have not been shown to reduce concussion risk.

Risk of prolonged recovery

While a majority of athletes suffering concussion are asymptomatic within a week, some suffer prolonged symptoms lasting weeks to months.

A meta-analysis of studies suggest that the following are linked to prolonged recovery:

• Signs and symptoms: 
  • Loss of consciousness was believed to be a marker for concussion severity, but the data overall suggest the relationship is weak, and, because LOC is rarely present (less than 5% of concussions in high school sports, according to a 2010 study⁴ ), it is no longer considered a major marker of severity
  • Posttraumatic amnesia, both retrograde and anterograde, has been associated with more and longer duration of concussion symptoms.
  • Risk factors in professional football for return to play longer than 7 days include retrograde amnesia, general cognitive problems, fatigue, and a greater number of symptoms at initial presentation.
  • A study of Australian football players found that longer time to return to play was linked to prolonged headache (more than 60 hours), fatigue, "fogginess," or greater than 3 symptoms at initial presentation.
  • Another study found several factors significantly related to prolonged return to play (greater than 7 days): headache lasting longer than 3 hours, trouble concentrating longer than 3 hours, retrograde amnesia, loss of consciousness, and a trend for retrograde amnesia.
  • Confusion, memory problems, and a greater number of symptoms are also associated with slower resolution of symptoms
  • Greater deficits in visual memory and processing speed on computerized neurocognitive testing are associated with recovery longer than 10 days.
• History of prior concussion: a statistically significant association between multiple prior concussion and recovery lasting more than 7 days was found in a study of college football players, but two other studies found no difference in recovery (more than 14 days) when comparing those with and without prior concussion.
• Attention deficit/hyperactivity disorder and learning disability: Most concussion studies exclude those with ADD/ADHD and learning disability. Studies that have included them have not found an association between either and time to return to play.
• Mood disorders: Anxiety and depression have been shown to occur after traumatic brain injury but have not been specifically studied as, with ADD/ADHD and learning disabilities, such so-called "pre-morbid" (e.g. pre-existing) conditions may affect baseline cognitive function and cofound (e.g. influence) postconcussion symptoms.
• Migraine and Migraine-like symptoms: One small study did not show that pre-morbid headaches or migraines predict protracted recovery after concussion, although posttraumatic migraine symptoms in concussed athletes have been associated with greater deficits on neurocognitive testing and higher overall symptoms scores compared with those with nonmigraine symptoms. A study of high school football players showed a statistically significant association betwee migraine symptoms and longer time to recovery. 
• Age: Several studies suggest a relationship between younger age and slower concussion recovery.  The developing brain has prolonged and widespread cerebral swelling and increased sensitivity to glutamate in response to head injury. Concussed high school athletes take longer to recover neurocognitive function compared to collegiate and professional athletes, but another study failed to show an association between age less than 18 years and prolonged return to play (greater than 7 days).
• Sex: Women show more cognitive function deficits and more symptoms than men after concussion.  Because multiple early symptoms are associated with a longer return to play, female sex may represent an underlying risk factor. 

1. Scopaz KA, Hatzenbuehler JR. Risk Modifiers for Concussion and Prolonged Recovery.  Sports Health: A Multidisciplinary Approach 2013;20(10). DOI:10.1177/1941738112473059 (published online ahead of print January 17, 2013). 

2. Marar M, McIllvain NM, Fields SK, Comstock RD. Epidemiology of Concussions Among United States High School Athletes in 20 Sports.  Am J Sports Med 2012;40(4):747-755

3. Daneshvar DH, Baugh CM, Nowinski CJ, McKee AC, Stern RA, Cantu RC.  Helmets and Mouth Guards: The Role of Personal Equipment in Preventing Sport-Related Concussions.  Clin Sports Med 2011; 30: 145-163.  

4. Meehan W, d'Hemecourt P, Comstock D, "High School Concussions in the 2008-2009 Academic Year: Mechanism, Symptoms, and Management" Am. J. Sports. Med. 2010; 38(12): 2405-2409.

Posted January 31, 2013 

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