Changes in MR relaxation times of the meniscal body with loading: an in vivo pilot study in knee osteoarthritis

Abstract

Purpose: The meniscus, a fibrocartilaginous tissue found within the knee joint, is responsible for joint congruity, shock dissipation, load transmission, lubrication, and stability of the joint. The meniscus is increasingly being recognized as an important tissue in knee osteoarthritis (OA). Recent studies have shown the potential of magnetic resonance (MR) relaxation times (T1r and T2) in studying biochemical composition of meniscus and therefore they may play a role in quantifying early meniscal degeneration and injury. One central function of themenisci is load transmission and studying the effect of acute loading on the meniscal T1r and T2 values may provide insight into the development of joint degeneration. Thus the purpose of this study is to prospectively compare changes in T1r and T2 in the meniscal body with acute loading in knees with OA and with those of age-matched healthy control menisci. Methods: Female subjects (age: 40-70 years, BMI: 20-35 kg/m2) with (KL score of 2 or 3, n 1⁄420) and without (KL score of 0, n1⁄410) radiographic evidence of knee OA, were imaged on a 3T GEMR scanner using a custommade loading device. MR images (Coronal SPGR and T1r and T2 mapping sequences) were acquired with the knee flexed at 20 with and without a compressive load of 50% of the subject's bodyweight (Figure 1) using established pulse sequences. The regions of interest (ROIs) for quantifying T1r and T2 values in the meniscus body were defined on the coronal SPGR images and superimposed over relaxation time maps. Anterior and posterior horns were not evaluated due to substantial partial volume effects in coronal images. Three different zones (outer, middle, and inner) of meniscus were defined by dividing the meniscus ROIs into three different parts with each part occupying one-third the width of the meniscus (Figure 2). After adjusting for age and BMI in the general linear regression model, repeated measures ANOVAwas used to detect significant differences in T1r and T2 with and without loading. Results: The average T1r and T2 values in all zones were significantly higher in OA patients compared with controls in unloaded condition, but not in loaded condition (Figure 3 and Figure 4). ΔT1r and ΔT2 in the outer zone of the medial meniscus in controls was significantly higher than the OA subjects (14.8% vs. 6.6%, P1⁄40.046 for ΔT1r, and 15.7% vs. 5.8%, P1⁄40.027 for ΔT2). In other zones (middle and inner), the same trend was observed but did not reach significance. Pooled data showed, significant increase in T1r of the outer zone of both medial (9.1%, P<0.0001) and lateral (6.8%, P1⁄40.014) meniscus body was observed with loading. Whereas, significant increase in T2 was observed in the outer zone of the medial meniscus (8.4%, P1⁄4 0.0003) only with minimal changes in the lateral meniscus (2.6%, P1⁄40.221). Conclusions: Elevated T1r and T2 in subjects with OA in the unloaded condition agree with literature and suggest that relaxation times of the menisci may have value in monitoring early disease. Significant relaxation time elevations in the outer portion of the meniscus with acute loading in both groupsmay reflect tissue hydration changes as the inner and middle portions of the meniscus bear load. The observation that Abstracts / Osteoarthritis an