Poster 228: Hamstring Muscle Injuries in Major League Soccer: An Analysis of Injury Rate, Associated Factors, and Return to Play

OBJECTIVES: To examine (1) the rate and time to return to play (RTP) after hamstring muscle injury, (2) investigate the rate of reinjury after RTP, and (3) investigate conditions that are associated with increased severity of injury or increased time to RTP. METHODS: MLS Injury Surveillance database was queried for all athletes with hamstring injuries from 2010-2021 were included and categorized by severity. A hamstring injury was defined as an incident that required medical attention and involved the biceps femoris, semimembranosus, or semitendinosus. Demographic characteristics and injury characteristics (setting of injury, activity during onset, severity, management, RTS, and re-injury) were collected and used for descriptive analysis. RESULTS: A total of 2865 injuries were recorded between 2010 and 2021, from 1227 individual players. The average injured player age was 26.2 +/- 4.4 years, with an isolated biceps femoris injury (75.2%), occurring during a match (47.3%). The median time missed per injury was 11.0 days, with 28.2% of injuries resulting in no days missed, 52.7% were classified mild to moderate (4-28 days), and 19.2% severe (29-744 days). Average number of games missed, and practices missed per injury, were 1.3 +/- 2.3 and 4.0 +/- 7.5, respectively. Mean days missed increased significantly from 17.6 days for a hamstring injury occuring during 2010-2015 to 23.9 days for an injury occuring during 2016-2021 (p < 0.001). Overall hamstring re-injury rate was 52.4% (643), following a previously recorded index hamstring injury. Reinjury rate between 2010-2015 and 2016-2021 did not change significantly (50.2% vs. 51.6%, p = 0.4506). Factors associated with prolonged return to sport included acute injury onset (27.8 vs 21.9, p = 0.023), and match injury (24.9 vs 13.2, p <0.001). Position, field type, weather conditions, and in-game time of injury were not statistically significant. CONCLUSIONS: Between 2010 and 2021, hamstring injuries were one of the most common causes of missed time in MLS athletes. Acute onset and match injuries increased time to RTP by 27% (P = 0.023) and 89% (P < 0.0001), respectively. Furthermore, days missed increased for injuries during the 2010- 2015 and 2016-2021 seasons by 35.7% (p<0.001). The current findings emphasize the need for continued prevention and post-injury rehabilitation protocols and expectations. A reinjury rate as high as 50% likely contributes to longer rehabilitation timelines before RTP, however, further study is warranted given that reinjury rates did not decrease.