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Effect of Proteoglycan Depletion on T2 Mapping in Rat Patellar Cartilage¹

¹ From the Department of Pharmacology, Physiopathologie et Pharmacologie Articulaires (UMR 7561), Centre National de la Recherche Scientifique (CNRS)–Université Henri Poincaré Nancy I, Faculté de Médecine, BP 184, Avenue de la Forêt de Haye, F 54505 Vandoeuvre les Nancy, France (A.W.P., P.O., L.G., A.B., P.N., P. Gillet, D.L.); Unité de Recherches en Résonance Magnétique Médicale (UMR 8081), CNRS–Université Paris-Sud, Paris, France (J.P.R., P. Gonord, G.G.); Department of Radiology, Service d’Imagerie Guilloz, Hôpital Central, Centre Hospitalier Universitaire (CHU), Nancy, France (A.B.); and Department of Rheumatology, Hôpitaux de Brabois, CHU, Nancy, France (D.L.). Received March 4, 2003; revision requested May 2; final revision received June 23, 2004; accepted July 12. Supported in part by Projet Hospitalier de Recherche Clinique (1998), Contrat de Projet de Recherche Clinique (2000), Pole Européen de Santé, and Groupement de Recherches CNRS 2237. Address correspondence to P. Gillet (e-mail: pierre.gillet@medecine.uhp-nancy.fr).

PURPOSE: To evaluate experimentally the sensitivity of T2 mapping with magnetic resonance (MR) imaging at 8.5 T in depicting variations in proteoglycan content and concurrent extracellular matrix of rat patellar cartilage.

MATERIALS AND METHODS: The study was performed in 36 immature (age, 5 weeks) and 36 mature (age, 10 weeks) Wistar rats. Maintenance and care of the rats were conducted in accordance with National Institutes of Health guidelines. Fifty-six rats underwent T2 mapping in 28 right patellae degraded with hyaluronidase for 1 and 6 hours and in 28 undegraded age-matched patellae that served as controls. After MR mapping, the rats were sacrificed, and the patellae were studied histologically to evaluate proteoglycan and collagen content and collagen network organization in cartilage. Biochemical analysis was performed in 88 patellae to quantify sulfated glycosaminoglycan and hydroxyproline content. Effects of age and/or degree of degradation were evaluated after rank transformation of continuous data by using rank analysis of variance (ANOVA). Associations between continuous variables were assessed with the Spearman rank correlation coefficient.

RESULTS: Results of histologic analysis showed proteoglycan loss after hyaluronidase degradation without alteration of collagen network. No significant variation in hydroxyproline sulfate content was observed with depletion of proteoglycan. Proteoglycan losses of 19% and 13%, found after 1-hour degradation in immature and mature groups, respectively, were associated with significantly increased global T2 values (ANOVA, P < .001). Six-hour degradation resulted in more severe proteoglycan losses of 45% and 53% in immature and mature groups, respectively, inducing significant increases in global T2 values in immature and mature groups (ANOVA, P < .001). Variations in T2 values between superficial and deep cartilage zones were not affected by proteoglycan depletion.

CONCLUSION: In rat patellar cartilage, T2 mapping permits detection of slight or severe proteoglycan depletion and concurrent changes of extracellular matrix when age-matched samples are compared.

© RSNA, 2004

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