Background: Previous literature has suggested an important association between a history of anterior cruciate ligament (ACL) reconstruction (ACLR) and future thigh muscle injuries, but more and larger studies are needed, particularly for quadriceps muscle injuries. Purpose: To determine the incidence of hamstring and quadriceps muscle injuries after return to play (RTP) from ACLR using patellar tendon (PT) and hamstring tendon (HT) autografts in professional male soccer players. Study Design: Cohort study; Level of evidence, 3. Methods: A total of 5447 players from 74 clubs were followed prospectively from July 2001 to May 2022. The injury incidence (number of injuries per 1000 hours) was compared between players with ACLR and those without ACL injuries as well as for players with ACLR between a 2-year period before the ACL injury and a 2-year period after RTP. The rate ratio (RR) was calculated with the 95% confidence interval (CI) and examined for significance with Z statistics. Results: There were 110 ACLR cases (76 PT and 34 HT grafts) in 107 players included. Players with ACLR had a 60% higher thigh muscle injury incidence (RR, 1.6 [95% CI, 1.3-2.0]) within 2 years after RTP compared with players without ACL injuries. Players with ACLR had a doubled thigh muscle injury incidence (RR, 2.0 [95% CI, 1.4-2.9]) in the 2 years after RTP compared with 2 years before their ACL injury. Players with a PT autograft had a higher quadriceps muscle injury incidence (RR, 3.5 [95% CI, 1.4-8.8]) in the 2 years after RTP compared with 2 years before their ACL injury, whereas there was no difference in the hamstring muscle injury incidence in players with an HT autograft (RR, 1.7 [95% CI, 0.5-5.8]). Conclusion: ACLR in professional male soccer players was associated with an increased thigh muscle injury incidence, particularly quadriceps muscle injuries in players with a PT autograft.
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