Risk Factors and Predictors Of Subsequent ACL Injury After ACL Reconstruction: Prospective Analysis Of 2801 Primary ACL Reconstructions

OBJECTIVES: Retear of an ACL after an ACL reconstruction (ACLR) is devastating for all involved. Understanding risk factors and predictors of subsequent ACL tear after an ACLR is vital for patient education of subsequent risk of injury and if a predictor is modifiable, to make adjustments to minimize the risk of repeat ACL tear. The objectives of this study were 1) to identify the risk factors and predictors for ispilateral and contralateral ACL tears after primary ACLR and 2) to compare retear risk between the 2002/03 and 2007/08 cohorts. This is the largest and most comprehensive prospective analysis of this kind in the literature. METHODS: Data from the 2002-2008 MOON database was used to identify risk factors for ACL retear. Subjects who had a primary ACLR with no history of contralateral knee surgery and had 2 year follow-up data were included. Subjects who had multiligament surgery were excluded. Graft type (auto-BTB, auto-hamstring, allograft), age, Marx score at time of index surgery, sport played post ACLR, sex, smoking status, lateral meniscus tear at the time of ACLR, medial meniscus tear at the time of ACLR, BMI, and MOON site were evaluated to determine their contribution to both ipsilateral retear and contralateral ACL tear. The analysis was repeated using the 2002/3 and 2007/8 cohort and included age, graft, sex, and Marx. An ANOVA with post-hoc analysis was performed to detect significant differences in age and Marx score by graft type over time. RESULTS: A total of 2801 subjects met all inclusion/exclusion criteria. There were 165/2801 (5.89%) ipsilateral and 177/2801 (6.32%) contralateral ACL tears identified in the cohort at the two year follow-up. The odds of ipsilateral retear are 1.68 times greater for hamstring autograft (p=0.04) and 4.67 times greater for an allograft (p<0.001) compared to auto-BTB. The odds of ipsilateral retear decrease by 8% for every yearly increase in age (p < 0.001) and increases by 6% for every increased point on the Marx score (p = 0.017). The odds of contralateral ACL tear increase by 7% for every increased point on the Marx score (p = 0.004) and decreases by 5% for every one point increase in BMI (p = 0.03). In 2002/3, there were 61/815 (7.5%) retears compared to 37/1056 (3.5%) in 2007/8. The odds of retear by for the 2002/03 and 2007/08 cohorts are summarized in table 1. The mean age (figure 1) of subjects receiving BTB and hamstring remained constant over time whereas the mean age of subjects receiving allograft rose by seven years (p < 0.001). Hamstring use was a predictor of retear compared to BTB in the 02/03 group (7.9% vs. 4.2%), but not in the 07/08 group (4.1% vs. 3.4%). CONCLUSION: Age, activity, and graft type were predictors of increased risk of ipsilateral graft failure after ACLR. Higher activity and lower BMI were found to be risk factors in contralateral ACL tears. Allograft use in young active patients was shown to be a risk factor for graft retear in the 02/03 group, subsequent to this, graft choice changed to using allografts in older and less active patients with an associated decrease in graft retear risk in the 07/08 group. The contralateral ACL injury risk did not change from the early group to the later group. The risk of ACL graft retear was lower for all graft types in the 07/08 group compared to the 02/03 group. The relative decrease risk in hamstring autografts compared to BTB in 07/08 compared to 02/03 may be due to improved surgical techniques, rehabilitation, and/or slower return to play guidelines, and bears further investigation.