Paper 39: A Survival Analysis of ACL Graft and Contralateral ACL Ruptures in Patients Under 18 Years

OBJECTIVES: Although high rates of graft and contralateral anterior cruciate ligament (ACL) ruptures have been reported in younger patients after ACL reconstruction, recent evidence suggests that previously reported crude event rates underestimate the actual event risk. Therefore, the aim of this study was to report rates of graft and contralateral ACL rupture after ACL reconstruction in a large series of younger patients using survival analysis. METHODS: A consecutive series of 400 patients who were under 18 years at the time of primary ACL reconstruction were identified from a single surgeon database over a 12-year period ending January 2018. Patients with a prior contralateral ACL rupture (n=8) or bilateral ACL ruptures (n=2) were excluded as were two patients who died within 6 months of surgery, leaving 388 (203M, 185F) in the final dataset. Bespoke survey data and clinic follow-up data were used to record graft rupture and contralateral ACL rupture events. Rates of graft and contralateral ACL rupture were calculated with Kaplan-Meier survival analysis. Log rank tests were used to compare survival functions between males and females. RESULTS: The cumulative rates of graft rupture via survival analysis were 11% at 2 years, 16% at 4 years and 28% at 8 years. For contralateral ACL injury the cumulative rates were 7% at 2 years, 17% at 4 years and 49% at 8 years. Males had significantly greater rates of graft rupture than females although this was more prominent at 4 years (22% vs 9%) than at 8 years (31% vs 23%) after surgery (figure 1). Contralateral ACL rupture survival functions were not significantly different between male and female patients, although rates were higher in females until 5 years after which males had a notable increase in contralateral ACL ruptures with a cumulate rate of 63% at 8 years compared to 35% for females (figure2). CONCLUSIONS: The current study is one of the largest consecutive series of younger patients with one of the longest follow-up periods that reports a high risk for a second ACL injury. Over time, the cumulative risk for contralateral ACL rupture was higher than for graft rupture. This contradicts previous work that had shorter follow-up times. In males, the risk for contralateral ACL rupture substantially increased after 5 years. Understanding the postoperative time course for second ACL injury in young patients is important so that factors which contribute to this increased risk can be better understood and such injuries prevented.