Improving the accuracy of sports medicine surveillance: when is a subsequent event a new injury?

The recent increased use of injury and illness surveillance programmes has the potential to greatly advance our knowledge about risk factors and treatment effectiveness. Maximising this potential requires that data be entered in a format that can be interpreted and analysed. One remaining challenge concerns whether and when an increase in symptoms should be documented within an existing injury record (eg, exacerbation) versus a new injury record. In this review, we address this challenge using the principles of the multistate framework for the analysis of subsequent injury in sport (M-FASIS). In brief, we argue that a new injury record should be documented whenever there is an increase in symptoms due to activity-related exposures that is beyond the normal day-to-day symptom fluctuations, regardless of whether the athlete was in a 'healthy state' immediately before the event. We illustrate the concepts with concrete examples of shoulder osteoarthritis, ankle sprains and ACL tears.