Background Magnetic resonance imaging (MRI) has become a critical imaging tool for use in osteoarthritis (OA) research. Recently, the T1ρ relaxation time was developed to quantify the composition of the cartilage matrix with respect to the proteoglycan concentration. However, the limited availability of this parameter due to the longer testing time compared to that required for the usual clinical sequences prevents its routine use in the clinical management of OA patients. Characterizing the relationship between T1ρ values and MRI findings according to prevalent sequences should be of clinical benefit.
Objectives The purpose of this study was to identify factors on routine clinical sequenced MRI associated with cartilage degeneration observed on T1ρ relaxation mapping.
Methods This study included 137 subjects with knee pain (mean: 50.6 years). Standard anteroposterior radiographs of the knee were obtained in all subjects. The Kellgren-Lawrence (KL) grade was determined by three experienced orthopaedic surgeons. MRI was performed using a 3-T scanner (Achieva 3T, Philips Medical Systems). Coronal images were acquired based on 3D T1ρ-weighted fast field echo imaging. We placed 12 regions of interest (ROIs) on the surface layer of the cartilage on mid-coronal images of the femorotibial (FT) joint. The assessment of cartilage, subchondral bone, meniscus and ligaments was performed using sagittal and coronal fat-suppressed T2-weighted images (T2-FFE). Meniscal scoring was carried out using a modified WORMS score for the knee. Extrusion, posterior root tears and posterior horn/root junction tears in the medial meniscus were recorded in addition to the presence of bone marrow edema and anterior cruciate ligament (ACL) tearing. A multiple regression analysis was performed to determine the factors affecting the T1ρ values of the cartilage.
Results The KL grades were as follows: 0=33 joints, 1=58 joints, 2=34 joints, 3=12 joints. The T1ρ values were significantly higher among the patients with a KL grade of 3, and no significant differences were observed between the patients with a KL grade of 0 and 1. The WORMS scores of the posterior horn of the medial meniscus were associated with the T1ρ values of the medial FT cartilage. In particular, posterior root/horn radial tears in the medial meniscus were strong factors increasing the T1ρ values (P<0.01, for ROIs on the medial FT). Even when the analysis was limited to the KL 0 and 1 subjects, the existence of radial tears in posterior segments significantly affected the T1ρ values of the cartilage. The multiple regression analysis revealed posterior root/horn tears to be independent factors increasing the T1ρ values of the cartilage. In contrast, bone marrow edema, ACL injury and the WORMS scores of the middle and anterior segments of the medial meniscus did not affect the T1ρ values.
Conclusions Meniscal tears have been reported to be related to the progression of cartilage loss in the knee, which can lead to osteoarthritis. This study showed that posterior root/horn radial tears in the medial meniscus depicted on MRI are particularly important findings associated with cartilage degeneration observed on T1ρ relaxation mapping even in patients with pre-radiological knee OA.
Disclosure of Interest None declared