Historical perspectives on evolving operational definitions of concussive brain injury: From railway spine to sport-related concussion.

Objective: Concussion is a clinical syndrome of biomechanically induced alteration in brain function. The historical derivation of current operational definitions of uncomplicated concussive brain injury based on acute injury variables especially posttraumatic amnesia (PTA) vs. symptom presence (no PTA) are reviewed. Methods: Major milestones from 150 plus years of concussion research include (a) railway spine; (b) traumatic neurosis; (c) duration of loss of consciousness predicting severity of brain injury; (d) early neuropsychological studies; (e) sport related concussion; and (f) chronic traumatic encephalopathy. Results: After initial organic explanations proved untenable, 19th century conceptions of concussion were operationally defined from symptom presence, attributed primarily to psychogenic (emotional, motivational, and/or predispositional) causes. In the 1930s, duration of PTA was linked to brain injury severity via outcome studies. Concussion (as defined by PTA < 1 h) was later found to cause a transient lowering of neuropsychological test scores in memory and executive function. In the 1990s, organizational definitions of sport-related concussion began to include biomechanical events without PTA that produced symptoms. Such events have not been linked to neuropsychological impairment. Conclusions: Two differing operational definitions of concussion are in the current use, involving the presence vs. absence of PTA. These two groupings are not clinically similar, although they are currently being widely treated as such. Operational definitions of concussion should address both minimum and maximums for duration of PTA, initial Glasgow Coma Scale score, complications, and symptom presence.