title: Effects of a symptom-free waiting period on clinical outcome and risk of reinjury after sport-related concussion.
abstract: OBJECTIVE
  This study is the first to investigate the influence of a symptom-free waiting period (SFWP) on clinical outcome and risk of repeat injury after sport-related concussion.
  
  
  METHODS
  This was a prospective, nonrandomized study of 16 624 player seasons from 1999 to 2004, including a cohort of 635 concussed high school and college athletes grouped on the basis of an SFWP or no SFWP observed after their concussion. Clinical outcome in symptoms, cognitive functioning, and postural stability 45 and 90 days postinjury was compared with preinjury baseline. Data on SFWP and same-season repeat concussion were recorded.
  
  
  RESULTS
  An SFWP was observed in 60.3% of cases. There were no significant differences between the SFWP and no SFWP groups in acute injury characteristics or clinical outcome with respect to symptom recovery or postinjury performance on formal neuropsychological and balance testing. Most repeat concussions (79.2%) occurred within 10 days of the initial injury. The rate of repeat concussion was actually higher in the SFWP group (6.49%) than the no SFWP group (0.90%) (P < 0.005), but the repeat concussion subgroup's SFWP was 2.82 days shorter (95% confidence interval, 0.61-5.03; P < 0.01) and these athletes resumed participation 3.55 days sooner (95% confidence interval, 0.06-7.04; P < 0.05) than those in the SFWP group in which there was no repeat concussion.
  
  
  CONCLUSIONS
  Our findings suggest that an SFWP did not intrinsically influence clinical recovery or reduce risk of a repeat concussion. The overall risk of same-season repeat concussion seems to be relatively low, but there may be a period of vulnerability that increases risk of repeat concussion during the first 7 to 10 days postinjury. Further study is required to investigate this preliminary finding and help determine whether this risk can be reduced further with specific injury-management strategies.
authors.affiliation: Neuroscience Center, Waukesha Memorial Hospital, Waukesha, Wisconsin 53188, USA. michael.mccrea@phci.org
authors.forename: Michael
authors.initials: M
authors.lastname: McCrea
authors.forename: Kevin
authors.initials: K
authors.lastname: Guskiewicz
authors.forename: Christopher
authors.initials: C
authors.lastname: Randolph
authors.forename: William B
authors.initials: WB
authors.lastname: Barr
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Hammeke
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Marshall
authors.forename: James P
authors.initials: JP
authors.lastname: Kelly
mesh_terms: D000293:Adolescent; D000328:Adult; D056352:Athletes; D001265:Athletic Injuries / Q000150:complications* / Q000503:physiopathology*; D001924:Brain Concussion / Q000209:etiology* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D020127:Recovery of Function; D012306:Risk; D013995:Time; D055815:Young Adult