Nationwide study highlights a second peak in ACL tears for women in their early forties.

PURPOSE: Anterior cruciate ligament (ACL) rupture continues to be a focus of research on knee injuries. Despite this, data on the total number of ruptures on a national basis including both reconstructed (ACLR) and non-reconstructed injuries are limited. The purpose of this study was to describe the national incidence of MRI diagnosed ACL ruptures in Iceland and its subsequent rate of operation with regard to sex and age.

METHODS: All MRI knee reports taken in Iceland between 2006 and 2011 were gathered to identify ACL ruptures. Software was written to search for phrases relating to ACL rupture. Duplicate records were removed and yearly incidence for sex and age groups was determined. Data from the Icelandic Social Insurance Administration were used identify all those who were operated and to determine the yearly incidence of ACLR. General additive models were used assuming either a Poisson or binomial distribution to model ACL rupture incidence and ACLR rate, respectively.

RESULTS: The average age was 33.9 (95% CI 33.1-34.6; Table 1). The average incidence of ACL tears per year was 75.1 (95% CI 71.3-79.1) per 100,000 person-years. For males the peak incidence was in their early twenties. Females showed two peaks, one in their teens and another in their forties resulting in an older average age at rupture compared to males (35 ± 16 vs 33 ± 13, p = 0.06). The main effects of age and sex and their interaction were significant (p < 0.001). The average incidence of ACLR was 39.4 (95% CI 36.7-42.4) per 100,000 person-years. Those operated were significantly younger than those who were not (27 ± 10 vs 42 ± 15 years, p < 0.001). The main effects of age and the interaction between sex and age were significant (p < 0.001).

CONCLUSION: This nationwide study indicates that ACL rupture incidence may be higher than previously thought, implying an underestimated impact of the burden of this serious knee injury. The incidence of injury peaked twice in the female population, a result not previously reported. Older persons are less likely to undergo ACLR and, therefore, sex-dependent differences in overall mean age at injury are contrary to previous reports. These data suggest that prevention programs focused solely on young girls should be extended to older women who are returning to sports.

LEVEL OF EVIDENCE: II.