Concussions in sport should be considered a single entity with a range of "modifying factors" instead of being classified as "simple" or "complex", says an international panel of sports concussion experts in a new consensus statement issued after the 3rd International Conference on Concussion in Sport (Zurich statement).1 The Zurich statement abandons the classification terminology proposed by an expert panel just four years earlier.
In classifying all concussions as a single entity, the consensus panel replaced the simple versus complex terminology with a list of potential "'modifying' factors" which, if present at the time of injury, may influence the investigation and management of concussion and, in some cases, predict the potential for prolonged or persistent symptoms:
- Intrinsic factors (age, previous concussion injuries)
- Injury specific factors (for examples, prolonged loss of conciousness, amnesia, concussive convulsions, presence of fatique/fogginess); and
- Extrinsic factors (for example, type of sport, position played)
The consensus statement views gender as a possible risk factor for injury and/or influence injury severity, but is not currently considered a modifying factor based on current research.
Most concussion and return-to-play guidelines issued before 2000 use numeric grading scales and relied on the presence/absence of loss of consciousness (LOC) and post-traumatic amnesia (PTA) to determine the severity of a concussion and return to play (RTP). None gained universal acceptance or were consistently followed by sports medicine professionals, many of whom ended up not using any grading scale for evaluation or RTP purposes.
Concussion management guidelines in the early 2000s moved away from reliance on LOC and PTA as sole predictors of injury severity. They focused instead on the number and duration of all post-concussion signs and symptoms and recognized that severity of injury could only be determined after all signs and symptoms had cleared.
This new approach was best exemplified by the consensus statement issued in 2005 after the 2nd International Conference on Concussion in Sport in Prague. Instead of classifying concussions by grade (Grade 1=mild, Grade 2=moderate, Grade 3=severe), the Prague statement classified concussion as either simple or complex, depending on the type, duration and number of symptoms and how long they took to resolve:
- Simple concussions (the most common form covering 80-90% of all concussions) were those that progressively resolved without complications over seven to ten days,
- A concussion was classified as complex if (a) certain post-concussive symptoms such as convulsions or extended loss of consciousness were present, or (b) symptoms such as cognitive impairment persist beyond 10 days, (c) the athlete has a history of previous concussions, and/or where repeated concussions have occurred with progressively less impact force.
In abandoning the simple versus complex classification and replacing it with a list of potential modifying factors, the Zurich experts recognized that current medical science did not give those evaluating concussions the ability to predict injury severity or outcomes at the time of injury. Writing in the May 2008 issue of the British Journal of Sports Medicine2, Michael Makdissi of the Centre for Health, Exercise and Sports Medicine at the University of Melbourne, recognized that the simple versus complex division had some validity because the vast majority (80-90%) of concussions heal in short (7 to 10 day) time period and thus could be labelled "simple." But, said Makdissi, the simple versus complex classification lacked the "critical feature" of being able to predict concussion severity at the time of injury. Concerns were also raised about the wisdom of using the term "simple concussion" when the long-term effects of repeated head injury remained unclear.
1. Consensus Statement on Concussion in Sport: the 3rd International Conference on Concussion in Sport held in Zurich, November 2008. Br. J. Sports Med. 20090: 43:i76-i84.
Revised June 19, 2009