An understanding of issues of definition in sports injury surveillance is critical to the accurate interpretation of surveillance data. A number of parameters require strict definition and include injury, severity, and exposure among others.1–3 Regrettably, there is disparity in the levels of discussion in the literature regarding these surveillance definitions; recovery, in particular, has received minimal attention.
We would assert that an examination of published literature reveals that certain surveillance definitions are interdependent, with both “injury” and “recovery” impacting on other surveillance parameters; furthermore, we would argue that the importance of the definition of recovery has been severely overlooked to date.
CURRENT CONCEPTS: SURVEILLANCE DEFINITIONS
Various conditions and restrictions can be incorporated into a sports injury definition.1,4,5 There is debate as to whether to adopt an all-encompassing definition, suggested to be more valid,6 or use a “missed playing time” definition, which is suggested to be more reliable.4 Although a lack of consensus remains regarding the most appropriate definition of injury, the issues are well discussed and a combination of empirical quantification, literature review, and expert opinion has informed the debate.
Defining recovery is central to the determination of a clear and unambiguous end point of an injury episode. Classifications of recovery have included “return-to-play” definitions (where recovery is implied by athlete participation and assumes that an individual is both functionally recovered and “match fit”) and “fully recovered” definitions (with actual medically confirmed recovery).7 When associated with return-to-play, a lack of consensus on the type of activity that constitutes participation exists. Both “match participation”8 and “training participation with match availability”9,10 definitions have been proposed in recent consensus statements on surveillance methods. However, it is not apparent that any studies or articles have directly assessed either criterion.
Recurrence definitions have been based on clinical judgment11,12 or on injuries of the same type occurring to the same body part,8–10 the latter being proposed in methodology consensus statements in various sports. To improve validity, Fuller et al7 suggest that differentiation should be made between a “re-injury” (a repeat episode of a fully recovered index injury) and an “exacerbation” (a worsening in the state of a nonrecovered index injury), as by doing so, the clinical status of the injury at the time of recurrence is incorporated. This overcomes some of the injury reporting issues that arise when players return to full participation before an injury is fully recovered.
Although a number of criteria may be used to assess severity,13 such ratings are based most commonly on duration of absence from sports participation, typically measured in days.8–10 Severity is frequently reported using classifications that generate meaningful groupings of injuries for analysis purposes, for example, “slight” (0-1 days), “minimal” (2-3 days), “mild” (4-7 days), “moderately serious” (8-21 days), and “serious” (more than 21 days).9 Ensuring that these classifications are valid and representative relies on the number of days of absence calculated being the same as the number of days that the athlete was actually suffering from the injury.
Relationship Between Surveillance Definitions
There has been limited discussion of how different injury surveillance definitions are related; these definitions have often been viewed as separate entities that operate independently. Despite this, interdependency exists between definitions of injury and recovery and measures of recurrence and severity. The Table illustrates this relationship and shows how, for the purposes of injury surveillance, both recurrence and severity are directly influenced by a definition of recovery. Therefore, consideration of the potential effects on injury surveillance findings of the different recovery criteria (return-to-match, return-to-training, and medical opinion) is warranted.
EFFECTS OF DIFFERENT RECOVERY DEFINITIONS
Using a “match participation” criterion for defining recovery has limitations. It may result in inaccuracies in severity calculations, as the recovery date is determined by match scheduling or team selection rather than by the date the player is deemed recovered. Although published research assessing playing whilst injured is limited, anecdotally, its occurrence is well known.14 With a “match participation” recovery definition, players who are injured and only partaking in limited team training, but play in a match due to extraneous factors, may be declared recovered. In professional sports, for example, factors including fear of losing one's place in the team, eligibility for contract bonuses, and wanting to play due to the number of forthcoming important games have been shown to be common incentives to play in matches when injured.15,16 Such practices may result in an exacerbation of the existing injury, causing an increase in reported recurrence rates; arguably, the true effect is of a single, more severe, injury. Therefore, an overall inflation in recurrence and reduction in severity rate would be observed. The adoption of a framework for recording recurrences, reinjuries, and exacerbations7 is of particular importance in such circumstances to negate some of these effects.
A “training participation with match availability” definition may more truly reflect the number of days of absence from injury than a “match participation” definition, as it is independent of most match-related factors. However, the issues surrounding the definition are complex; “full, unrestricted training” implies complete recovery from an injury, yet “availability for match selection” (for the same reasons outlined relating to “match participation” definitions) may occur prior to the commencement of unrestricted participation in training. This raises potential reliability issues. When defining injury, it is suggested that reliability levels decrease when using “missing training,” compared to “match time loss only,”4 as it is a less objective criterion. Similar issues may arise when using this criterion for defining recovery, although no evaluation of this issue has taken place to date.
Medical Opinion Definition
The use of medical opinion and clinical judgment may be valuable in improving the validity of recovery definitions, as has been shown when defining recurrence.7,17 Nevertheless, there may be a large subjective element in relying on clinical judgment for a definition, as different individuals may judge cases in different ways, compromising the reliability of study findings. Furthermore, medical staff are unlikely to declare an injury “not recovered” while at the same time advocating a return-to-match play, as this places staff in a difficult situation. Given the potential litigious consequences that such practices could create, the accuracy of subsequent injury reporting may be altered to reflect the return-to-play decision rather than the true situation. This would impact negatively on the reliability and validity of any data generated. Such reporting issues may not be considered or be apparent when using nonclinical recovery criteria.
Important interdependent relationships exist between various definitions in injury surveillance. Although injury definition is well discussed in the literature, we suggest that the importance of a robust “recovery” definition has been underestimated, particularly given its direct influence on both recurrence and severity. Consequently, the nature and effects of this definition have not been addressed or appreciated within the sports medicine literature.
Conflicts between reliability and validity can occur when selecting an appropriate injury definition4,6 and may similarly affect definitions of recovery. It is of paramount importance that the effects of recovery definitions are evaluated, to facilitate interpretation of surveillance data and improve intra- and interstudy consistency. To address this weakness of the current literature, research is required that evaluates the effects of using “return-to-training” and “return-to-match” criteria, determines the reliability of a “return to training” definition, and assesses the utility of clinical judgment as an appropriate criterion in any operational definition of recovery.
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