Poster 150: Defining the True Incidence of Glenohumeral Instability Among American Football Players: an Epidemiological Study of Non-missed-time Shoulder Instability Injuries in the National Football League
Authors: Anderson Matthew , Mack Christina , Herzog Mackenzie , Levine William , Confino Jamie 
Published: July 2022

Objectives: Shoulder instability is a common injury among contact- and collision-sport athletes that encompasses a spectrum of glenohumeral pathology ranging from subluxation to dislocation. While glenohumeral dislocation frequently leads to removal from play, athletes are often able to play through glenohumeral subluxation. Previous research on glenohumeral instability among athletes has largely focused on missed-time injuries only, which has likely disproportionately excluded subluxation injuries and underestimated the overall incidence of shoulder instability. The objective of this study is to describe the epidemiology of shoulder instability injuries not resulting in missed time among professional athletes in the National Football League (NFL) during the 2015 through 2019 seasons. Methods: The NFL’s Electronic Medical Record was retrospectively reviewed to identify shoulder instability injuries that did not result in missed time during the 2015 through 2019 seasons. For each injury, player age, player position, shoulder laterality, instability type, instability direction, injury timing, injury setting, and injury mechanism were recorded. For injuries that occurred during games, incidence rates were calculated based on timing during the season as well as player position. The influence of player position on instability direction was also investigated. Results: During the 2015 through 2019 seasons, 546 shoulder instability injuries were documented in the NFL’s Electronic Medical Record. Of these, 162 (29.7%) did not result in missed time beyond the date of injury. The majority of non-missed-time injuries were subluxations (97.4%), occurred during games (70.7%), and resulted from a contact mechanism (91.2%). The overall incidence rate of game-related instability was 1.6 injuries per 100,000 player-plays and was highest during the postseason (3.5 per 100,000 player-plays). With respect to player position, the greatest number of non-missed-time instability injuries occurred in defensive secondary (28.4%) and offensive linemen (19.8%), while kickers/punters and defensive secondary had the highest game incidence rates (5.5 and 2.1 per 100,000 player-plays, respectively). In terms of direction, 54.3% of instability events were posterior, 31.9% anterior, 8.5% multidirectional, and 5.3% inferior. Instability events were most often anterior among linebackers and wide receivers (50% and 100%, respectively), while posterior instability was most common for defensive linemen (66.7%), defensive secondary (58.6%), quarterbacks (100.0%), running backs (55.6%), and tight ends (75.0%). Conclusions: Shoulder instability injuries that do not result in missed time beyond the date of injury are much more common among collision-sport athletes than previously thought, accounting for approximately 30% of all instability events in the NFL. The majority of these injuries are posterior subluxations, though instability direction appears to vary by player position. This study highlights the diverse nature of shoulder instability injuries and underscores the need for increased surveillance among collision-sport athletes, as even subluxations can result in significant damage to the capsulolabral complex. [Table: see text][Table: see text][Table: see text][Figure: see text]