Can metaphyseal variations in the distal femurs and proximal tibias be distinguished from classic metaphyseal lesions?

Background: Classic metaphyseal lesions (CMLs) are considered specific for child abuse, but the reliability of radiologists in distinguishing CMLs from metaphyseal variations is unclear. Objective: To evaluate whether radiologists can differentiate between CMLs and metaphyseal variations in the knees. Materials and Methods: We performed a retrospective review of distal femur and proximal tibia radiographs in children under two years of age who underwent skeletal surveys for suspected child abuse. The CML group included children diagnosed with abuse and reported CMLs. The metaphyseal variation group included children not diagnosed with abuse, with reported metaphyseal variations and either no fractures or an isolated skull fracture. Radiographs were trimmed to exclude other injuries. Four pediatric and four general radiologists reviewed anonymized studies and categorized each case as CML, metaphyseal variation, normal, or indeterminate, with confidence levels (high, moderate, low). We analyzed diagnoses with moderate or high confidence. Interobserver agreement was assessed using kappa statistics. Results: There were 48 children with CMLs (40 initial, 38 follow-up) and 27 with metaphyseal variations (20 initial, 12 follow-up). Metaphyseal fragmentation was the most common variation, identified in 259 of 356 femurs (72.8%) and 69 of 83 tibias (83.1%). Fragmentations were most frequently located in the posterior or medial metaphysis, or both, in 257 of 259 femurs (99.2%) (257/259) and 68 of 69 tibias (98.6%). In the CML group, 34 of 115 initial CML diagnoses (29.4%) were read on follow-up as either metaphyseal variation (n=17) or normal (n=17). In contrast, in the metaphyseal variation group, only one follow-up case was diagnosed as a CML; the remainder were diagnosed as metaphyseal variation (n=22) or normal (n=2). Diagnostic performance for CML demonstrated high specificity (90.7%) and positive predictive value (94.9%), with moderate accuracy (76.1%), sensitivity (70.2%), and negative predictive value (55.2%). Interobserver agreement was substantial, with a mean kappa of 0.61. Conclusion : Radiologists demonstrated substantial agreement and high specificity in distinguishing CMLs from metaphyseal variations. Metaphyseal fragmentation was the most common variation and was uncommonly diagnosed as CML on follow-up.