Biochemical-based MRI in diagnosis of early osteoarthritis

Abstract

Cartilage anatomy Each biochemical MRI technique targets a specific part of the cartilage anatomy; thus, understanding its structure becomes paramount. A majority of the articular cartilage comprises water, type II collagen and proteoglycans, particularly glucosaminoglycan (GAG) chains [3]. Each GAG chain has considerable negative charge, which attracts water at times of unloading. Here, swelling is prevented by a strict organization of collagen fibers [2]. As described by Ulrich-Vinther et al., normal cartilage can be divided into three zones [3]. A superficial zone contains the highest water content, but the lowest proteoglycan concentration. Collagen fibers present here are in parallel orientation to the articular surface. An intermediate zone consists of fibers in a more oblique fashion. Finally, the deep zone has a dense array of collagen fibers oriented perpendicular to the articular surface. It contains the highest proteoglycan concentration and the lowest water content, an inverse relationship to its superficial counterpart. Underneath these zones is a small layer of calcified cartilage, consisting of radially oriented collagen fibers embedded in a calcified matrix. This separates overlying deep zone from underlying subchondral bone [3].