Quantitative assessment of the meniscus using 3 tesla MRI

Radu I. Bolbos, Thomas M. Link, C. Benjamin Ma, Xiaojuan Li, Sharmila Majumdar

Magnetic resonance imaging (MRI) is the most commonly used imaging modality for the diagnosis of a suspected meniscal tear. However, to date little is known about the effect of meniscal injury on the risk of disease progression in osteoarthritis (OA) patients. From a therapeutic viewpoint, an accurate description of a meniscal tear has become increasingly important, with the emphasis on meniscal preservation, repair, and even transplantation. On the other hand, the abnormal meniscal function represents an important consequence for the rate of cartilage loss, since studies of the meniscectomy emphasized the importance of the meniscal function loss as a risk factor for subsequent knee OA. In OA, cartilage and meniscal changes are preceded by damage of the collagen-PG matrix. Using semiquantitative MRI with arthroscopic correlation, a previous study demonstrated a strong association of the meniscal pathology changes with cartilage loss in symptomatic knee OA.

1. T1ρ and T2 longitudinal assessment of the menisci in patients with early OA

The goal of this study was to longitudinally evaluate the meniscus biochemical composition in mild OA patients compared with healthy controls using T1ρ and T2 quantification. In this longitudinal study, significant differences between mild OA patients and healthy controls were found for both T1ρ and T2 matrix parameters in meniscus at baseline as well as at one year (Figure 1). This quantitative assessment reflects significant changes within the biochemical composition of the menisci, demonstrating potential degenerative processes in the knee joint. The differences between patients and controls were more significant for T2 compared with T1ρ. This might suggest that T2 might be better suited for differentiating the patients from the controls, since the main constituent of the meniscus is the collagen, and T2 is more sensitive to collagen content.

2. Longitudinal assessment of the menisci in ACL-injured knees using MR T1ρ quantification

Anterior cruciate ligament (ACL) injuries are frequently associated with the damage of other knee structures such as articular cartilage, subchondral bone and meniscus. Patients with ACL injury tend to develop osteoarthritis (OA) even after ACL reconstruction, so the acute injuries represent a potential risk factor. A previous study using the dGEMRIC technique has shown significant correlations between T1(Gd) of the meniscus and T1(Gd) of the articular cartilage, potentially demonstrating injuryrelated processes in the OA knee. The aim of this study was to evaluate the potential associations between the menisci and adjacent cartilage biochemical structure, as well as to longitudinally assess the menisci biochemical changes in ACL-injured knees using T1ρ mapping technique at 3 Tesla MRI. Significantly increased T1ρ values were found in ACL-injured patients compared with healthy controls. Also, a significant T1ρ elevation was also found in patients’ posterior horn compared with the anterior horn. This T1ρ elevation in posterior horn was significantly correlated with the cartilage T1ρ elevation in the posterior compartment of LT, demonstrating a strong injury-related relationship between meniscus
and cartilage biochemical changes (Figure 2). The two-year longitudinal study has shown a steady decrease of T1ρ values toward control value of both menisci. This preliminary data might suggest that healing of the meniscus can occur despite initial change in biochemical composition. This current finding is in contrast with our previous T1ρ quantification of articular cartilage following ACL reconstructions where no recovery of biochemical composition was observed.