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MR Imaging of Normal and Matrix-depleted Cartilage: Correlation with Biomechanical Function and Biochemical Composition¹

¹ From the Orthopaedic Research Laboratory, Departments of Biomedical Engineering and Orthopaedic Surgery (J.S.W., K.J.S., C.Y., J.R.O.) and Department of Radiology (K.A.K., D.G.D.), Virginia Commonwealth University, 1112 E Clay St, 325 McGuire Annex, PO Box 980694, Richmond, VA 23298; and Commonwealth Radiology, Richmond, Va (D.G.D.). Received December 7, 2001; revision requested January 19, 2002; final revision received December 12; accepted January 14, 2003. Supported in part by a grant from Virginia’s Commonwealth Health Research Board. Address correspondence to J.S.W. (e-mail: jswayne@vcu.edu).

View larger version (27K): [in a new window]   Figure 1. Bar graph illustrates effects of enzymatic treatment on biochemical components of cartilage. Proteoglycan content and collagen content are expressed on a per-wet-weight basis. Chondroitinase (white bars) and collagenase (gray bars) treatments resulted in significant reductions in proteoglycan content (P < .001) and collagen content (P < .001), respectively. Black bars represent no treatment (ie, normal cartilage).

View larger version (25K): [in a new window]   Figure 2. Bar graph illustrates effects of enzymatic treatment on biomechanical properties of cartilage, as determined from indentation experiments. With chondroitinase treatment (white bars), the modulus decreased significantly (P < .001) while permeability increased (P < .05). The modulus and permeability were less affected by collagenase treatment (gray bars). Black bars represent no treatment (ie, normal cartilage).

View larger version (26K): [in a new window]   Figure 3. Bar graph illustrates effects of enzymatic treatment on T1, T2, and apparent diffusion coefficient (ADC) (thickness direction). Although both chondroitinase treatment (white bars) and collagenase treatment (gray bars) caused increases in these imaging parameters from the normal levels, a difference between the two treatments in terms of resulting T2 was evident. Black bars represent no treatment (ie, normal cartilage).

View larger version (93K): [in a new window]   Figure 4. Effects of enzymatic treatment seen on T2-weighted MR imaging maps (calculated from eight T2-weighted MR images [4,000/24-192]) of patellar quadrants. Two quadrants were imaged at a time. A, B, MR images of two quadrants of cartilage before (A) and after (B) matrix depletion with chondroitinase. C, D, MR images of two other quadrants of cartilage before (C) and after (D) matrix depletion with collagenase. The images have qualitatively different gray scale levels in the region of interest (ovals) throughout the cartilage layer. These differences were quantitatively reflected in the calculated T2 values in the regions of interest and are depicted in Figure 3. The decreased gray level in B, compared with the gray level of the normal cartilage image in A, resulted from chondroitinase treatment. The signal intensity of the collagenase-treated cartilage (D) differed from that of the chondroitinase-treated cartilage (B).

View larger version (23K): [in a new window]   Figure 5. Bar graph illustrates effects of enzymatic treatment on T1 when quadrants of cartilage are bathed in an anionic contrast material solution (gadopentetate dimeglumine2- [Gd] with Hanks normal saline) for 60 minutes. T1 ratio was calculated by dividing the T1 of the quadrant after being bathed in solution by the T1 of the cartilage quadrant before being bathed in solution. The T1 ratio for the enzymatically treated cartilage was significantly different from the T1 ratio for the normal (ie, untreated) cartilage (P < .001). The time constant was calculated by means of exponential fitting of T1 at numerous gadolinium-based contrast agent exposure times of up to 60 minutes. Faster contrast agent uptake occurred with chondroitinase treatment (white bars). Gray bars represent collagenase treatment, black bars represent no treatment (ie, normal cartilage).

View larger version (20K): [in a new window]   Figure 6a. Linear correlations (a) between the modulus and proteoglycan content (in wet-weight micrograms per milligram), (b) between the modulus and T2, and (c) between proteoglycan content and T2. Each linear fit was significant (P < .001 for correlations depicted in a, b, and c). Goodness-of-fit values (R2) are given.

View larger version (20K): [in a new window]   Figure 6b. Linear correlations (a) between the modulus and proteoglycan content (in wet-weight micrograms per milligram), (b) between the modulus and T2, and (c) between proteoglycan content and T2. Each linear fit was significant (P < .001 for correlations depicted in a, b, and c). Goodness-of-fit values (R2) are given.

View larger version (19K): [in a new window]   Figure 6c. Linear correlations (a) between the modulus and proteoglycan content (in wet-weight micrograms per milligram), (b) between the modulus and T2, and (c) between proteoglycan content and T2. Each linear fit was significant (P < .001 for correlations depicted in a, b, and c). Goodness-of-fit values (R2) are given.