Abstract
BACKGROUND: Bone bruises are frequently found on magnetic resonance imaging (MRI) after an anterior cruciate ligament (ACL) tear in pediatric patients. PURPOSE: To establish a classification system for different bone bruise patterns to estimate the severity of a knee injury in pediatric patients with ACL tears. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A medical database was retrospectively reviewed to identify all cases of primary ACL tears in patients who were aged ≤17 years at the time of the injury and underwent MRI at our institution within 4 weeks of the injury between January 2011 and December 2020. A total of 188 patients were identified (67 male, 121 female; mean age, 15.1 ± 1.4 years). Bone bruises were classified according to their depth and location on MRI in the sagittal and coronal planes. RESULTS: The new classification system identified 3 grades of depth: grade I, the bone bruise was located within the epiphysis but did not reach the epiphyseal plate (n = 54 [35.3%]); grade II, the bone bruise was within the epiphysis that reached the epiphyseal plate (n = 55 [35.9%]); and grade III, the bone bruise was in both the epiphysis and metaphysis (n = 44 [28.8%]). The bone bruise location was classified into 4 types: type a, the deepest bone bruise area was in the lateral tibial plateau (n = 66 [43.1%]); type b, the deepest bone bruise area was in the lateral femoral condyle, commonly occurring in the lateral one-third to two-thirds of the lateral femoral condyle (n = 22 [14.4%]); type c, the bone bruise area had a similar depth in both the lateral femoral condyle and lateral tibial plateau (n = 54 [35.3%]); and type d, the bone bruise area was in the lateral tibial plateau and lateral femoral condyle and extended to the fibular head (n = 11 [7.2%]). The prevalence of collateral ligament injuries increased from grade I to III. All patients with grade III type c bone bruises had meniscal lesions. CONCLUSION: This new classification system provides a basis for estimating associated lesions of the knee before surgery.