Effect of chondral defect size, shape, and location on MRI diagnostic performance in the porcine knee

The purpose of this study was to determine the sensitivity and positive predictive value of magnetic resonance imaging (MRI) in the identification of full-thickness articular cartilage defects in the porcine knee. Seventy-two full-thickness chondral defects (small or large; circular, oval, or triangular) were created in 12 porcine knees. The authors used 3.0-T MRI with 3-dimensional gradient echo water-selective/fluid (WATSf) sequences acquired in axial, coronal, and sagittal planes. Sensitivity and positive predictive value parameters were calculated for 2 readers. Magnetic resonance imaging was highly sensitive for detection of full-thickness defects in the knee (85%). The highest sensitivity was observed at the medial femoral condyle (93%), while the lowest was observed at the medial patella (71%). The sensitivities for detecting different shapes were unique to each shape, with oval lesions identified with greatest sensitivity (93%). Small lesions (86%) were detected at a similar sensitivity as large lesions (83%). The positive predictive values for accurate true-positive reads were low for all lesion shapes (18%-57%) and moderate for small (69%) and large (59%) sizes, with significant differences observed between the 2 readers. Magnetic resonance imaging has a high sensitivity in the detection of full-thickness articular cartilage defects in the porcine knee. Variability in defect shape and intra-articular location affects MRI sensitivity, while size does not. Magnetic resonance imaging was not effective in describing lesion shape or size. Further, there was subjectivity in reading defect shape and size between 2 radiologists.