Concussions are no longer classified as "simple" or "complex" depending on how long it takes for signs and symptoms of concussion [1] to clear. 

Under the consensus statement issued in May 2009 after the 3rd International Conference on Concussion Sport in Zurich (Zurich statement),¹ the evaluation and treatment of sports concussions will be guided by so-called "modifying" factors [2] that, when present at the time of injury, suggest increased likelihood that recovery from concussion will take longer than the 7 to 10 days typical of the majority (80 to 90%) of concussions or increase the risk of a poor long-term outcome.

Coming full circle

"Development of a simple, reliable and universally classification system for concussive injuries has long been a challenge," writes Michael Makdissi of the University of Melbourne in the British Journal of Sports Medicine.  The First International Conference on Concussion in Sport in Vienna in 2001 refused to endorse any of the more than 35 concussion severity scales (most of which classified concussions by "grade" depending on the presence or absence of loss of consciousness (LOC) [3] and post-traumatic amnesia (PTA) [4] which, were once considered important predictors of the severity of injury.

The Second International Conference on Concussion in Sport in Prague in 2004 introduced the concept of "simple" and "complex" concussion, determining severity retrospectively, after all post-concussion signs and symptoms [1] had cleared, the neurological exam was normal, and cognitive function had returned to pre-injury level (e.g. baseline), with simple concussion lasting less than 10 days and complex concussions lasting over 10 days or involving prolonged LOC, concussive convulsions, prolonged cognitive impairment or a history of multiple concussions.

The Zurich consensus statement came full circle.  Acknowledging that the simple versus complex classification lacked the "critical ability to predict injury severity at the time of injury", the Zurich consensus statement replaced it with a list of potential "modifying" factors [2] which, if present at the time of injury, may influence the evaluation and management of concussions, and in some cases may predict the potential for prolonged or persistent symptoms [1].

That list of potential modifying factors has continued to be part of the new 4th consensus statement issued in March 2013 (after another conference in Zurich).² 

1. Consensus Statement on Concussion in Sport: the 3rd International Conference on Concussion in Sport held in Zurich, November 2008.  Br J Sports Med 2009: 43:i76-i84

2. McCrory P, et al. Consensus statement on concussion in sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012. Br J Sports Med 2013;47:250-258.

Updated April 29, 2013