Predictors of Contralateral Anterior Cruciate Ligament Reconstruction A Cohort Study of 9061 Patients With 5-Year Follow-up

Background: Identifying predictors of contralateral anterior cruciate ligament (ACL) reconstruction is important to focus preventive strategies and related research on high-risk groups. Purpose: To investigate predictors of contralateral ACL reconstruction in patients who have already undergone a primary ipsilateral reconstruction. Study Design: Cohort study; Level of evidence, 2. Methods: This study was based on data from the Swedish National Knee Ligament Register from January 1, 2005, to December 31, 2013. Patients aged 13 to 59 years who underwent primary ipsilateral (index) ACL reconstruction with hamstring tendon or bone-patellar tendon-bone autografts were included. Follow-up started on date of index ACL reconstruction and ended either with primary contralateral ACL reconstruction, after 5 years of follow-up, or on December 31, 2013, whichever occurred first. The investigated variables were patient sex, age at index reconstruction, activity at the time of index injury, timing of surgery, graft selection, graft harvest site, and meniscal and chondral injury. The study end point was primary contralateral ACL reconstruction. Relative risks (RRs) and 95% CIs were calculated and adjusted for confounding factors using multivariate statistics. Results: A total of 9061 participants were included (n = 5196 males [57.3%] and 3865 females [42.7%]), of which 270 participants (3.0%) underwent primary contralateral ACL reconstruction during the 5-year follow-up. There was no difference in contralateral reconstruction rates between males and females (3.0% vs 2.9%, P = .695). Age <20 years significantly increased the risk of contralateral reconstruction (males: RR = 2.4 [95% CI, 1.7-3.4] and females: RR = 2.9 [95% CI, 1.9-4.5]; P < .001). Among female patients undergoing reconstruction using autograft hamstring, harvest of a contralateral hamstring tendon significantly increased this risk (RR = 3.4 [95% CI, 1.4-7.9]; P = .006). Conclusion: In both male and female participants, age <20 years predicted an almost 3 times higher 5-year risk of contralateral ACL reconstruction. Among female participants undergoing reconstruction with autograft hamstring, a contralateral harvest predicted a more than 3 times higher 5-year risk of contralateral ACL reconstruction. Patient sex, activity at the time of index injury, graft selection, meniscal injury, and chondral injury were not predictors of contralateral ACL reconstruction.