Author(s): HECKSTEDEN, A., Institution: UNIVERSITÄT INNSBRUCK, Country: AUSTRIA, Abstract-ID: 1677

INTRODUCTION:
After a sport-related concussion, subtle neuromuscular deficits can persist beyond clearing return-to-play (RTP) criteria. While such deficits plausibly increase injury risk in association football (and other team sports), results of epidemiological studies are inconsistent. Differences in outcomes, comparator, duration of follow-up, sample size, and analytical methods arguably contribute to discrepancies between studies. Specifically, it seems imperative to compare concussions to other acute index injuries (as opposed to uninjured controls) when drawing conclusions about their specific consequences, as injury risk is known to be increased in the weeks following RTP from a musculoskeletal injury. More generally, data analysis should reflect transparent causal assumptions. Following these considerations, the present study compared post-RTP risk trajectories (hazard curves) between two index injury categories - concussion vs. acute injuries of the lower limb - using retrospective data from elite European football.
METHODS:
Time-loss injuries as well as match exposures for male players in top European leagues were collected from online sources. Episodes (index injury-RTP-subsequent injury) were constructed and only complete episodes with either a concussion or an acute lower limb index injury were included. Hazard curves were characterized as the local slope of the smoothed cumulative hazard from the respective Kaplan-Meyer-model [1]. Analyses were conducted for chronological time in days as well as for football exposure in weighted hours as time axis. Confidence intervals are based on bootstrapping. The role of differences in time loss between index injury categories was explored by resampling. Results were further scrutinized by comparing the distributions of observed time from RTP to the subsequent injury.
RESULTS:
While the post-RTP risk trajectory after acute lower limb injuries agrees with previous findings [1], two distinct features were salient after concussions: (a) A peak early after RTP and (b) Lower hazard / higher overall survival in the further course (from about 4 weeks onwards). The overall shape of risk trajectories was similar for the two time axes and unchanged by resampling for similar distributions of time loss between index injury categories. In auxiliary analyses, observed time-to-event was numerically higher after concussions for both time axes, although the 95% confidence intervals for the difference included zero (football exposure-to event: -45 to 168 weighted hours, chronological time-to-event: -8 to 25 days).
CONCLUSION:
Compared to musculoskeletal index injuries, injury risk trajectories after returning from a concussion are characterized by an early peak contrasting with lower risk beyond about 4 weeks after RTP. Importantly, these findings likely depend on a complex set of framework conditions (e.g. RTP protocols) and should therefore not be generalized beyond current elite European football.
References: 1. Zhang et al., Sports Med, 2024