Predicting Autologous Hamstring Graft Diameter in the Pediatric Population Using Preoperative Magnetic Resonance Imaging and Demographic Data

Abstract

Background: Anterior cruciate ligament (ACL) reconstruction before 18 years of age has been linked with an increased risk for failure when the graft diameter is <8 mm. Purpose/Hypothesis: The purpose of this study was to determine whether autologous hamstring graft size can be reliably predicted with the use of preoperative magnetic resonance imaging (MRI) measurements. We hypothesized that the average of multiple axial cross-sectional area MRI measurements for the semitendinosus tendon and gracilis tendon would alone accurately predict graft diameter. Additionally, factoring in specific demographic data to the MRI cross-sectional areas would provide a synergistic effect to the accuracy of graft diameter predictions. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: We retrospectively reviewed 51 pediatric patients undergoing ACL reconstructions (age <18 years) performed using either a quadruple-strand semitendinosus tendon or combined double-bundle semitendinosus tendon–gracilis tendon autograft. Preoperative axial MRI scans at multiple points along the craniocaudal axis—specifically, at the level of the joint line, 3 cm cephalad to the medial tibial plateau, and 5 cm cephalad to the medial tibial plateau—were used to determine the combined cross-sectional area of the semitendinosus and gracilis tendons. The MRI measurements were analyzed using Pearson correlation as well as regression analysis to evaluate strength of correlation between measurements. Binomial linear regression was used to analyze the same predictive variables assessed by multiple regression. Results: The predicted graft diameter was within 0.5 mm of the intraoperative graft size in 37 of 51 (72.5%) patients and within 1 mm of the intraoperative graft size in 49 of 51 (96.1%). With the addition of demographics, the accuracy of predictions increased to 78.4% within 0.5 mm and 98% within 1 mm of the actual graft size. Additionally, 38 of 42 patients whose true graft diameter was ≥8 mm were correctly classified, giving a sensitivity of 90.4%. For those whose true graft diameter was <8 mm, 8 of 9 patients were correctly classified; therefore, the specificity was 88.9%. Conclusion: The results of our study suggest that taking the average of multiple preoperative MRI measurements can be used to accurately predict autologous hamstring graft size when approaching pediatric patients undergoing ACL reconstruction.