Evaluating Differences in Baseline Knee Hyperextension and Postoperative Stiffness Between Patients With Tibial Spine Fracture Versus ACL Tear.

Background: While generalized ligamentous laxity is a risk factor for anterior cruciate ligament (ACL) reconstruction failure, there is a paucity of literature evaluating underlying dynamic risk factors predisposing pediatric and adolescent patients to ACL tears or tibial spine fractures.

Purpose: To (1) evaluate differences in baseline knee hyperextension and postoperative knee stiffness between patients who sustained tibial spine fractures versus ACL tears and (2) determine whether there were other demographic and dynamic injury differences between these patients.

Study Design: Cross-sectional study; Level of evidence, 3.

Methods: We evaluated patients aged between 9 and 17 years old who were treated at a tertiary pediatric hospital between 2012 and 2020 for a tibial spine fracture or an ACL tear. Patients in each injury group were matched based on age and physeal closure status. The demographic characteristics and pre- and postoperative clinical variables were recorded, and bivariate analysis and binomial logistic regression were performed to compare the proportion of patients with knee hyperextension- denoted as uninjured knee hyperextension >3°-between injury types and evaluate additional risk factors for injury, respectively.

Results: Overall, 405 patients were included, 81 with tibial spine fractures and 324 with ACL tears. Patients with ACL tears were more likely to have increased knee hyperextension compared with those with tibial spine fractures (36% [115/324] vs 24% [19/81]; = .047). This was also observed when controlling for age and physeal closure status. In patients aged ≤14 years with open physes, 39% with ACL tears had hyperextension versus 18% with tibial spine fractures ( = .003). No difference was observed in the proportion of patients who developed postoperative stiffness (2.5% for ACL tears vs 6% for tibial spine fractures; = .091). Patients with ACL tears were more likely to have sustained a noncontact mechanism of injury compared with patients with tibial spine fractures (62% [202/324] vs 39% [32/81]; = .0002).

Conclusion: Patients with ACL tears were more likely to have increased knee hyperextension and to have sustained a noncontact injury compared with those with tibial spine fractures. Postoperative knee stiffness after tibial spine fixation may be related to this baseline reduced knee extension rather than the injury itself.