Cartilaginous defects of the femorotibial joint: Accuracy of coronal short inversion time inversion-recovery MR sequence

Purpose: To retrospectively assess the diagnostic performance of the short inversion time inversion-recovery ( STIR) magnetic resonance (MR) sequence for depiction and classification of articular cartilaginous lesions in femorotibial joint, with arthroscopy as reference standard. Materials and Methods: Institutional review board did not require approval and informed consent for review of patients' records or images. All patients ( and parents of underage patients) agreed to use of their data. Two musculoskeletal radiologists independently analyzed femorotibial cartilage on coronal STIR images from 84 knee MR examinations in 83 patients ( 48 male patients [ 49 knees], 35 female patients; mean age, 39.5 years). Slightly modified Outerbridge classification was used: grade 0, normal cartilage; grade 1, softening or swelling; grade 2, partial-thickness defect; grade 3, fissuring to the level of the subchondral bone; and grade 4, exposed subchondral bone. Arthroscopy performed within 15 weeks was the standard of reference. Classification for arthroscopy differed only in definition of grade 1 ( softening or swelling of cartilage). Sensitivity, specificity, accuracy, positive and negative predictive values, and weighted k values were calculated to assess interobserver reliability. Results: At arthroscopy, 212 (63%) of 336 surfaces were classified as grade 0 ( normal); 37 (11%), as grade 1 abnormalities; 30 (9%), as grade 2 lesions; 25 (7%), as grade 3 lesions; and 32 (10%), as grade 4 lesions. Grades 0 and 1 were considered normal; grades 2 - 4, as abnormal. For detection of contour defects of the cartilaginous surface, coronal STIR MR imaging had sensitivity values of 77% and 76%, specificity values of 96% and 89%, accuracy values of 91% and 85%, positive predictive values of 86% and 70%, and negative predictive values of 92% and 91% for readers 1 and 2, respectively. Weighted k value was 0.63. Conclusion: Contour defects of femorotibial cartilage can be detected with reasonable accuracy with routine STIR sequence.