| Objective: To reveal the relationship between the MRI signal intensities changes and pathology appearance, and to evaluate the effect of MRI in diagnosis of early stage erosion and its clinical significance.Methods: Twenty six patients (27 knees) with knee pain scheduled for arthroscopy were imaged on a 1.5-T superconducting magnet (Signa GE Co., America) with FSE T1WI and FSE PDWI. Ten knees of them were imaged with additional 3D FS-FSPGR sequence. One cadaveric knee and ten OA knees to undergo subsequent total knee replacement (TKA) were also imaged with additional 3D FS-FSPGR sequence. Then MRI of cartilage lesions was staged by the scheme proposed by Rent. Within two weeks after examined, The 27 knees underwent subsequent arthroscopy, and rated the cartilage according to the Outerbridge criteria and recorded the results, which compared with that of MR imaging. Sixty specimens, which best demonstrated one cartilage lesion were obtained corresponding precisely to that of MR images in the ten OA human knees and one one fresh human knee within six hours after the death of the donor, and stained by HE, Toluidine blue and collagenâ…¡immunohistochemistry. The results were analyzed and compared with MR images appearances.Results: Using arthroscopic results as the standard of reference, the 3D FS-FSPGR images had the higher sensitivity(96.5%) and accuracy(95.0%) than the standard MR imaging, there was significance between them (P<0.00227). The 3D FS-FSPGR sequence is well consistent with the result of arthroscopy, Kappa value was higher (0.776) than the other sequences. Sixteen normal cartilage samples, thirteen gradeâ… lesions, fifteen gradeâ…¡lesions, and sixteen gradeâ…¢lesions were confirmed by pathology. Compared with pathology, the diagnosis value of 3D FS-FSPGR sequence was that the sensitivity, specificity, accuracy and Kappa were 93.2%, 75%, 88.3% and 0.71 respectively.With the increase of the erosion stages, PG content decreased gradually, and typeâ…¡collagen content increase gradually in the grade 0 to 2 lesion, especially in the superficial layer, decreased in the grade 3 lesions. And chondrocytes proliferated, formed clusters or clones. Pathohistologically, damage to the cartilage matrix could result in the change of MR imaging signal intensity.Conclusion 3D FS-FSPGR is an optimal sequence for assessment the articular cartilage lesions. These changes of both signal intensity and morphology of articular cartilage can reflect histopathologic and biochemical abnormality. At the early stage, PG decrease and Collagenâ…¡increase made the loss of the trilaminar appearance and low signal intensity within cartilage that had a normal surface in MR images. With increase of the erosion stage, the rupture of collagen meshwork, the formation of fissures, PG content decrease and superficial cartilage defects led to the irregular outline of cartilage surface in addition to the trilaminar disappearance.Compared with arthroscopy and pathology, 3D FS-FSPGR sequence was accurate for the detection and grading of artilcular cartilage abnormalities including to the early stage. So it has a wide application prospects.
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