Magnetic Resonance Imaging Predictive Model Determines Hamstring Autograft Size for Anterior Cruciate Ligament Reconstruction in Patients Under 18 Years Old

PURPOSE: To evaluate the predictive value of magnetic resonance imaging in determining hamstring autograft size preoperatively for pediatric anterior cruciate ligament reconstruction. METHODS: We conducted an analysis of patients younger than 18 years who underwent quadrupled hamstring autograft anterior cruciate ligament reconstruction. Semitendinosus tendon (ST) and gracilis tendon (GT) cross-sectional areas were measured on preoperative knee magnetic resonance imaging scans. Height, weight, body mass index, and sex were analyzed using ordinal regression analysis. A classification and regression tree (CART) was constructed to identify predictors of the predetermined intraoperative graft size of 8 mm or greater. Sensitivity and specificity were determined based on specified predictors. RESULTS: This study included 102 patients (52 female and 50 male patients). The average age was 15.8 ± 1.4 years. At the time of surgery, 38 patients (37.3%) had open physes, with an average age of 13.4 ± 0.96 years. Of the 102 patients, 55 (53.9%) had 8-mm or larger grafts, 31 (30.4%) had 7.5-mm grafts, and 16 (15.7%) had 7-mm or smaller grafts. In 12 patients (31.6%) with open physes, the graft size was less than 8 mm. Male patients were more likely to have 8-mm or larger grafts (P < .001), as were patients with a greater height (170.1 ± 7.3 cm vs 161.1 ± 12.0 cm, P = .013) and those with a greater weight (79.7 ± 23.4 kg vs 57.1 ± 16.2 kg, P = .005). For all patients, predictive modeling determined that if the cross-sectional areas of the ST and GT were 31.2 mm(2) or greater, then 87.5% of patients would have a graft size of 8 mm or greater with an 80% sensitivity and 74% specificity. Similarly, if the cross-sectional areas of the ST and GT were 31.4 mm(2) or greater in patients with open physes, then 100% of patients would have a graft size of 8 mm or greater with a 46% sensitivity and 99% specificity. CONCLUSIONS: A preoperative summation of the cross-sectional areas of the ST and GT greater than 31 mm(2) in patients younger than 18 years with open or closed physes can help the surgeon preoperatively predict which patients will have an intraoperative graft size of 8 mm or greater. The risk factors for a smaller graft size include female sex, a shorter height, and a lighter weight. LEVEL OF EVIDENCE: Level III, retrospective comparative study.