Articular cartilage of knee: normal patterns at MR imaging that mimic disease in healthy subjects and patients with osteoarthritis.

PURPOSE: To evaluate normal magnetic resonance (MR) imaging findings that may mimic articular cartilage diseases in healthy subjects and patients with osteoarthritis of the knee.
MATERIALS AND METHODS: Sagittal fat-suppressed intermediate-weighted fast spin-echo (FSE) (repetition time msec/echo time [TE] msec, 4,000/13), sagittal T2-weighted FSE (4,000/39), and sagittal fat-suppressed three-dimensional (3D) spoiled gradient-echo (SPGR) (60/5, 40 degrees flip angle) MR images were acquired in 28 patients and four volunteers. FSE images with a TE of 13 msec were considered "short-TE images"; those with a TE of 39 msec were considered "long-TE images." Presence of normal MR imaging appearance of articular cartilage was determined by one author. Contrast between cartilage and adjacent structures (meniscus, joint capsule, synovial fluid, muscle) was calculated in posterior regions of the femoral condyle on images obtained with each sequence; Wilcoxon signed rank testing was performed.
RESULTS: The following appearances were observed in patients with knee osteoarthritis (on short-TE FSE, long-TE FSE, and SPGR MR images, respectively): (a) ambiguity of surface contour in posterior region of the femoral condylar cartilage (in zero, zero, and 20 patients), (b) linear area of high signal intensity in deep zone adjacent to subchondral bone of femoral condyle (in zero, zero, and 26 patients), (c) pseudolaminar appearance in posterior region of femoral condylar cartilage (in seven, nine, and 24 patients), (d) truncation artifact in patellofemoral compartment (in seven, six, and 27 patients), (e) susceptibility artifact on cartilage surface caused by air or metal (in three, three, and 11 patients), (f) decreased signal intensity in distal part of trochlear cartilage (in 28, 28, and 28 patients), (g) cartilage thinning adjacent to the anterior horn of the lateral meniscus (in 19, 19, and 21 patients), and (h) focal cartilage flattening in posterior region of femoral condyle (in 16, 16, and nine patients). Cartilage-meniscus and cartilage-synovial fluid contrast was significantly higher on fat-suppressed FSE than on fat-suppressed 3D SPGR MR images (P <.001).
CONCLUSION: Fat-suppressed FSE and 3D SPGR MR images showed nonuniform signal intensity arising from articular cartilage and cartilage thinning, both of which could mimic disease. Copyright RSNA, 2004