Posterior Tibial Slope is Associated With Adolescent Anterior Cruciate Ligament Tears, Contralateral Tears, and Graft Failures

Background: Increased posterior tibial slope angle (PTSA) is a well-recognized risk factor for ACL injury and graft failure in adults; however, its relevance in adolescents remains unclear. PTSA is potentially a modifiable risk factor, with emerging growth modulation techniques like anterior hemiepiphysiodesis showing promise. This study aimed to compare PTSA in adolescent patients with primary ACL reconstruction, revision ACL reconstruction, and bilateral ACL injury to a control group. A secondary aim was to identify candidates for slope reduction through growth modulation. It was hypothesized that adolescent patients who sustained ACL injury would have increased PTSA compared with controls. Methods: A total of 250 knees were included: 50 each in the primary ACL reconstruction, revision ACL reconstruction, and bilateral (sequential) ACL injury groups, and 100 knees in a 2:1 bone age–matched control group with diagnoses not associated with PTSA changes. Demographics, including bone age (from knee MRI), sex, and concomitant injury, were collected. PTSA was measured using the perfect circle method on lateral radiographs. Growth remaining was determined by years to skeletal maturity from bone age. Results: Mean bone ages were similar across the groups ( P =.10). The bilateral ACL group had a significantly higher proportion of females (74%) than other groups ( P= .001). Remaining growth was higher in the primary ACL group (76%) compared with the control (55%) and bilateral groups (40%) ( P =.007, P =.002). Ten percent of knees in the ACL groups had both growth remaining and PTSA >12 degrees. PTSA was significantly increased in primary, 9.4±2.5 degrees ( P =.001), revision, 10.0±2.9 degrees ( P <.001), and bilateral ACL groups, 10.1±2.5 degrees, ( P <.001) compared with controls, 7.3±3.6 degrees. Conclusion: Adolescents undergoing ACL reconstruction, revision, or with bilateral ACL injury have an increased PTSA compared with controls. Approximately 10% of these patients may be candidates for slope correction through growth modulation. Level of Evidence: Level III—retrospective cohort study.