The Incidence of Second Anterior Cruciate Ligament Injury in Young Athletes is Not Influenced by Time to Return to Sport

BACKGROUND: Incidence of second anterior cruciate ligament (ACL) injury among the population of young athletes is reported to be as high as 30%. Time between ACL reconstruction (ACLR) and return to sport (RTS) has been considered as a factor in second injury risk. HYPOTHESIS/PURPOSE: The purpose of this study was to investigate the effect of time between ACLR and RTS on incidence of 2nd ACL injury. The tested hypothesis was that incidence of 2nd ACL injury among young athletes would not be influenced by time to RTS or patient-reported function following primary ACLR. METHODS: 188 participants (mean age=16.8±3.0 years; 124 females) underwent ACLR, completed rehabilitation, and were medically cleared to RTS. Subjects were enrolled in the study within 4 weeks of their medical clearance to RTS. At this time, each subject completed the International Knee Documentation Committee (IKDC) Survey, the Knee injury and Osteoarthritis Outcome Score (KOOS) and was grouped into an early RTS group (<6 months post-operative (PO)) (n=19), an average RTS group (6-9 months PO)(n=106), and a late RTS group (≥9 months PO)(n=63). Subjects were then tracked for 24 months to record the incidence of a second ACL injury to either the involved limb or contralateral limb. One-way ANOVA was used to identify differences in demographics and patient-reported outcomes among the groups. Crude incidence of 2nd ACL injury was identified within each group and chi-squared analyses were used to determine the difference in proportion of 2nd ACL injuries between groups. RESULTS: No significant differences in age (p=0.40), height (p=0.65) or weight (p=0.92) existed among the groups. At time of RTS, no differences between the early RTS, average RTS and late RTS groups were seen in patient-reported function on the IKDC (84.9±10.8, 90.5±9.5, 88.7±10.9; p= 0.08) and all KOOS subscales (p=0.05-0.41). With respect to 2nd ACL injury, there were no group differences (p=0.716) in the proportion of patients within each group who suffered a 2nd ACL injury within 24 months of RTS date (26.3% (5/19) of patients in the early RTS group, 18.9% (20/106) in the average RTS group and 22.2% (14/63) in the late RTS group). CONCLUSION: In accordance with our hypothesis, length of time between ACLR and RTS had no influence on incidence of second ACL injury among a population of young athletes after ACLR. Furthermore, patient-reported function at time of RTS was similar among groups, regardless of time between ACLR and RTS.