Research into the Application of Imaging to the Diagnosis of Hip Disease

Abstract

The early detection of pathologic changes in articular cartilage has emerged as a key component of active research within musculoskeletal imaging of the hip joint. These efforts have focused on the identification of morphologic, physiologic, and molecular markers of cartilage damage. Imaging modalities that utilize these markers must balance the demands of rapid image acquisition, cost, invasiveness, reproducibility, sensitivity and specificity, while also being reliable, and responsive. Two modalities that have proven most promising for clinical application in assessing articular tissue are ultrasound and magnetic resonance imaging (MRI). While ultrasound provides information about the internal derangement of cartilaginous tissue, magnetic resonance imaging (MRI) detects changes in the composition of the tissue as reflected in its content of glycosaminoglycans (GAGs), collagen, and water. Currently, MRI is the best imaging modality for characterizing the articular cartilage of the hip and underlying subchondral bone because of good tissue contrast. Moreover, MRI surpasses surgical visualization in its ability to reveal the underlying femoral and acetabular anatomy. However, conventional MRI techniques are limited in their capacity to quantify defects within cartilaginous tissue, including the presence of fissures, fibrillation, and contained non-displaced delamination. Recent MRI techniques attempt to overcome these issues by better illustrating and characterizing hip hyaline cartilage ultrastructure via type II collagen and glycosaminoglycan content. The next generation of techniques for generating high-resolution MR images of changes in cartilage composition include dGEMRIC, T2 mapping, T2*, T1rho, sodium imaging, gag-CEST, and diffusion imaging. These techniques seek utility in the early detection of osteoarthritis by relating variations in the proteoglycan and water content of articular cartilage to the earliest stages of articular degeneration. As each modality comes with its own advantages and disadvantages, further research is needed into the efficacy of each of these modalities prior to widespread clinical use.