Return to play after thigh muscle injury in elite football players: implementation and validation of the Munich muscle injury classification

BACKGROUND: Owing to the complexity and heterogeneity of muscle injuries, a generally accepted classification system is still lacking. AIMS: To prospectively implement and validate a novel muscle injury classification and to evaluate its predictive value for return to professional football. METHODS: The recently described Munich muscle injury classification was prospectively evaluated in 31 European professional male football teams during the 2011/2012 season. Thigh muscle injury types were recorded by team medical staff and correlated to individual player exposure and resultant time-loss. RESULTS: In total, 393 thigh muscle injuries occurred. The muscle classification system was well received with a 100% response rate. Two-thirds of thigh muscle injuries were classified as structural and were associated with longer lay-off times compared to functional muscle disorders (p<0.001). Significant differences were observed between structural injury subgroups (minor partial, moderate partial and complete injuries) with increasing lay-off time associated with more severe structural injury. Median lay-off time of functional disorders was 5-8 days without significant differences between subgroups. There was no significant difference in the absence time between anterior and posterior thigh injuries. CONCLUSIONS: The Munich muscle classification demonstrates a positive prognostic validity for return to play after thigh muscle injury in professional male football players. Structural injuries are associated with longer average lay-off times than functional muscle disorders. Subclassification of structural injuries correlates with return to play, while subgrouping of functional disorders shows less prognostic relevance. Functional disorders are often underestimated clinically and require further systematic study.