The risk of anterior cruciate ligament (ACL) injury after an ACL reconstruction has been reported to be as high as one third. This study was designed to better understand the incidence of second ACL injuries in a population-based cohort, and to determined risk factors associated with these injuries.

Data were obtained through the Rochester Epidemiology Project, a medical record linkage system with access to complete medical records for all residents of Olmsted County, Minnesota. This database was reviewed for all occurrences of ACL tears between January, 1990, and December, 2000. Second ACL tears were defined as any that occurred after the primary injury, and until December 2015.

Between 1990 and 2000, of the 1，107 acute tears, six percent were second tears. Of these, 33.3% involved the ipsilateral graft and 66.7% involved the contralateral ACL. Among individuals less than 20 years of age, the graft failure rate was 5.9%, while the failure rate for those under 16 years of age was 1.8%. Of the failures, the allograft had the highest rate of second tears, accounting for 26.9%, followed by hamstring autografts at 11.4%, and patella autografts at 6.3%. Multivariate regression analysis revealed that use of an allograft was the single significant independent variable predicting second ACL injuries (P<0.001). The probability of a second ACL injury was highest among those 17 to 25 years of age, followed by those 26 to 35 years of age.

This observational cohort study of citizens of Olmsted County, Minnesota, found that six percent of ACL repairs were second repairs, with 66.7% of these occurring on the side contralateral to the initial surgery.