Background The incidence of anterior cruciate ligament (ACL) injuries is commonly reported as an annual rate. There is relatively little information about their seasonal aspects.

Objective The aim was to analyze the distribution of ACL injuries during the season in amateur football, handball and basketball. It was hypothesized that ACL injuries they were more common after the summer break in comparison to the rest of the season.

Design Retrospective case series

Setting Hospital-based registry

Patients Three hundred and seventy-one (282 males, 89 females) injuries were included according to the following criteria: ACL injury occurring in football (n=258), handball (n=56) or basketball (n=57) and confirmed through clinical examination, MRI and arthroscopy where applicable, under 35 years of age and pre-injury participation in competitive sport.

Interventions (or Assessment of Risk Factors) Gender; age; sport at injury; injury mechanism; previous or contralateral ACL injury.

Main Outcome Measurements The injury occurrence during the calendar year was divided into six periods of two months. Segment 1 (S1) represented the first two months after summer break (Football: September/October, handball/basketball: October/November).

Results The occurrence of ACL injuries differed significantly between segments (p<0.01) and according to sports (p<0.01). Almost one third occurred in S1 (n=104; 28%). The distribution was similar in other segments (S2: 13%, S3: 16%, S4: 16%; S5: 12%, S6: 15%). Fewer ACL injuries occurred in S2 in football (9%) compared to basketball (23%) (p<0.05). More ACL injuries occurred in S5 in football (17%) compared to handball (2%) and basketball (2%) (p<0.05).

Conclusions The majority of ACL injuries in amateur football, handball and basketball sports occurred immediately after the summer break in the first two months of the season. This indicates that amateur athletes should start ACL injury prevention programs before the start of the season to allow for gradual increases of load.