Predictors of Anterior Cruciate Ligament Re-tear and Return to Sport in Adolescent Athletes

Objectives: The purpose of this study was to characterize recent epidemiologic trends of ACL injuries and re-tear rates in high school adolescents and determine variables associated with sustaining secondary ACL injury. We hypothesized protective rehabilitation factors (i.e., greater time to return to sport, formal sport clearance, and physical therapy compliance) would decrease the risk of secondary ACL injury. Methods: A prospectively maintained database from a single institution with standardized data collection focused on ACL injuries was retrospectively reviewed for all patients 18 or younger who underwent primary ACL reconstruction between 2015 to 2020. Patients were eligible for inclusion in this study if they were between the ages of 13-18 years old, participated in sporting activity in high school, and underwent evaluation and primary ACLR at a single institution. Electronic medical records (EMR) were reviewed for patient demographic information and documentation review from prior injury/surgery. This information included the following: age, sex, body mass index (BMI), school grade (if documented), race, sport played, mechanism of injury (contact versus non-contact), time to return to sport (RTS), and number of post-operative physical therapy (PT) visits. Injury in contact and non-contact sport were defined based on the level of impact on the mechanism of injury sustained. Contact injury was defined as impacted collision with another person or object directly prior to injury onset. Non-contact injuries include isolated twisting movements of the knee without a sustained direct impact injury due to another player or object. Time to RTS was defined as the number of months following ACL reconstruction surgery until the patient was documented clear to return to sporting activity by the operating surgeon. Number of PT visits was calculated by EMR review of documented PT visits. Results: A total of 387 pediatric patients were included in statistical analysis. Of these patients, 72 (19%) sustained a secondary ACL injury and 315 (81%) did not. The overall mean age at primary ACLR and standard deviation was 16.0 ± 1.4 years (range 12-18 years). By univariable analysis, age at primary ACLR, time to RTS, and follow-up duration were all associated with secondary ACL injury (p < 0.05). Patients with a secondary ACL injury were significantly younger than those who did not sustain a subsequent ACL tear (16.2 ± 1.3 versus 15.5 ± 1.6 years, respectively, p = 0.0026). Time to RTS following primary ACL injury was shorter in patients who sustained a secondary ACL injury (7.9 ± 2.0 months versus 8.9 ± 2.5 months, p = 0.0361). Cox regression analysis performed demonstrated as age at primary ACLR increases by 1 year, the rate of secondary ACL injury decreases by 29%. Similarly, a 1-month delay in return to sport decreases the rate of secondary ACL injury by 17%. Conclusions: Younger age and longer time to return to sport following ACL injury are significant variables associated with sustaining secondary ACL injury in the pediatric patient population. Counseling of young adolescent athletes should include adequate physical therapy compliance and allowing for adequate healing and time to return to sport.