Abstract
New magnetic resonance imaging (MRI) techniques for imaging cartilage have an ever-increasing role in the evaluation, diagnosis and monitoring of joint disorders. Relatively few studies have been undertaken to determine the long-term response of the cartilage to different treatments such as microfractures, osteochondral autograft, osteocondral mosaicplasty and autologous chondrocyte transplantation.
Intravenous administration of gadolinium diethylene-triamine-pentacetic acid (GdDTPA) on MR represents an exciting possility to explore and validate strategies for repairing cartilage. GdDTPA is an ionic contrast agent that is administered and is given time to penetrate cartilage where it is distributed according to the concentration of the charged molecules in cartilage matrix. The main macromolecular constituents of cartilage are glycosaminoglycans (GAG) and collagen. GAG have abundant negatively charged carboxyl and sulphate groups that by osmotic effect give the cartilage stiffness. GdDTPA enhances the cartilage that is depleted of GAG, then is distributed in an inverse relation to the concentration of the negatively charged GAG. In the normal articular cartilage tissue GAG has a lower concentration at the articular surface and a higher concentration in the deeper zone as histological and GdDTPA on MR studies have confirmed. Many problems we can consider to be the choice between i.v. contrast administration and intra-articular injection, which is an invasive route. Furthermore, the time course of penetration of Gd-DTPA into cartilage depends on the cartilage thickness. The time for maximum signal enhancement may vary from 45 min. for the thin ventral femoral condyle to about 4 h in patellar cartilage. Progress has also been made in evaluating the distribution of GAG in patients with osteoarthrits.
Our goal is to gain information regarding the state of the cartilage in follow-up of autologous condrocyte transplantation correlated with the clinical implications. The severity of the focal defect of cartilage in one negative result is estimated from the morphologic appearance of the hyperintense lesions on contrast-enhanced MR images. In agreement with Gillis et al. we could observe clear time-associated differences of GAG density in the patients who received autologous chondrocyte implants.
