Towards an operational definition of sports concussion: identifying a limitation in the 2012 Zurich consensus statement and suggesting solutions

A fundamental precept in managing injury risks1 and preventing injuries2 ,3 is that the size of the injury issue needs to be well established. The size, or importance, of the particular injury issue depends on factors such as the injury incidence (how many injuries occur per participant per unit of exposure) and severity (eg, typical degree and duration of impairment; costs associated with the injury).3 The most common means of measuring the size of an injury issue is via an injury surveillance system, by which all injuries meeting some predetermined criteria are counted. To understand the size of an injury issue, the injury being counted needs to be well defined. Theoretical definitions of injury specify what injuries ‘are’4; operational definitions of injury specify which injuries become cases, that is, how injuries can, or will, be counted in a given context.5–7 Although controversies remain about exactly what does and does not fall within a good theoretical definition of an injury,4 most definitions include some reference to an abnormal transfer of energy, and the resulting outcome(s). Theoretical definitions of injury are helpful in providing a conceptual framework by which to consider injuries, however, they leave open the question of operationalising the definition for the purposes of injury surveillance, and subsequent risk management and injury prevention initiatives. It is for this reason that various sports medicine groups have produced ‘injury definitions’ guidelines specifying which events meet the criteria for inclusion in injury counts.6 ,8 The Zurich Consensus Statement on Concussion (hereafter referred to as the Zurich Guidelines) provides a relatively clear theoretical definition of concussion.9 The concept of a transfer of injury resulting in some physical change is reflected in the Zurich Guidelines. To paraphrase, the Zurich Guidelines specify that concussion is …