Comparison of Anterior Cruciate Ligament Injury Rates In High School and Middle School Sports Over a 30-year Period

BACKGROUND: Anterior cruciate ligament (ACL) injuries are a major concern in interscholastic sports. Comparison of ACL injuries between high school (HS) and middle school (MS) athletes over multiple years is limited. PURPOSE: To examine the incidence of ACL injury in HS female [HS-F] and male [HS-M], and MS female [MS-F] and male [MS-M] sports over a 30-year period. METHODS: We studied 55,147 athletes who competed in interscholastic sports at a secondary school from 1988 to 2018. Data included ACL injuries incurred during interscholastic sports, and clinically confirmed by a physician. Injury rates per 100,000 AEs (practice and games where the athlete was at risk of ACL injury) were calculated for gender, sport, and contact status. Incidence rate ratios [RR] and 95% confidence intervals (CIs) were used to compare injury rates. RESULTS: The incidence rate of ACL injury for HS athletes (4.15/100,000 AEs) was almost three times greater (RR=2.63, 95%CI: 1.7-4.2; p<0.0001) than the incidence rate for MS athletes (1.58/100,000 AEs). The risk of sustaining an ACL injury among HS-F athletes (4.26/100,000 AEs) was similar to HS-M athletes (4.06/100,000 AEs) (RR=1.05, 95%CI: 0.7-1.6; p=0.81). The risk of sustaining an ACL injury among MS-F athletes (1.06/100,000 AEs) was less than MS-M athletes (1.96/100,000 AEs) (RR=0.54, 95%CI: 0.2-1.4; p=0.21). While the risk of incurring an ACL injury occurrence was four times greater (RR=4.01, 95%CI: 1.7-9.4; p=0.0002) among HS-F athletes than MS-F athletes, the risk of ACL injury was twice as high (RR=2.08, 95%CI: 1.2-3.7; p=0.009) among HS-M athletes than MS-M athletes. ACL injuries were incurred in 15 HS sports and was greatest for HS-F basketball (25.5/100,000 AEs; p<0.001), HS-M football (20.6/100,000 AEs), and HS-F soccer (20.4/100,000 AEs). ACL injuries were sustained in 7 MS sports and was highest for MS-F softball (9.1/100,000 AEs), MS-M basketball (6.3/100,000 AEs) and MS-M football (5.0/100,000 AEs). The risk of contact-related ACL injury (1.73/100,000 AEs) was almost two times greater than non-contact-related ACL (0.96/100,000 AEs) (RR=1.80, 95%CI: 1.2-2.7; p<0.001). The rate of contact ACL injury was highest among HS-M (3.38/100,000 AEs) while the rate for noncontact ACL injury greatest among HS-F (2.44/100,000 AEs). CONCLUSIONS: The risk for ACL injury is higher in HS than in MS for both sexes. Non-contact ACL injuries were more likely to occur among HS-F athletes while contact injuries were highest for HS-M athletes, suggesting the effects of maturation and competition may play a role with increasing competition level.