Preoperative Evaluation of the Grade and Stability of Osteochondritis Dissecans of the Knee by Magnetic Resonance Imaging.

Objective To assess the diagnostic performance of magnetic resonance imaging (MRI) in the grading of osteochondritis dissecans (OCD) of the knee.Methods Totally 47 patients with OCD of the knee confirmed by arthroscopy were retrospectively enrolled in this study.The OCD lesions were classified into four stages according to classification system of the International Cartilage Repair Society.Two radiologists analyzed all MRI findings independently,and the results were compared with those of arthroscopy.Sensitivity,specificity,and accuracy were calculated.Kappa value were calculated to quantify inter-observer agreement of the diagnostic OCD grade between two doctors by MRI.Specificity,sensitivity,and accuracy of MRI criteria indicating instability for detection of OCD instability were calculated.Results Of these 47 patients with 48 OCD lesions,stages Ⅰ,Ⅱ,Ⅲ,and Ⅲ lesions were detected in 4,8,16,and 20 patients,respectively.The specificity,sensitivity,and accuracy for the diagnosis of OCD stability were 75.0% (83.3%),88.9% (86.1%),and 85.4% (85.4%) for observer l (2),and the agreement of OCD grade between these two readers was substantial with a Kappa value of 0.82.The specificity,sensitivity,and accuracy of MRI criteria for the detection of OCD instability including high T2 signal intensity at the interface between the OCD and the underlying bone,multiple cysts or a single cyst of>5 mm in diameter surrounding OCD lesions,high T2 signal intensity cartilage fracture line traversing the articular cartilage,and osteochondral defect were 83.3%,80.6%,and 81.3%;75.0%,72.2%,and 72.9%;66.7%,69.4%,and 68.8%;100%,86.1%,and 89.6%,respectively. Conclusions Osteochondral defect is the most specific MRI sign for diagnosing instable OCD of the knee,whereas osteochondral fracture line has the lowest accuracy.MRI is a useful method to evaluate the grade and stability of OCD of the knee.