Abstract
Structural magnetic resonance imaging (MRI) has shown great utility in diagnosing soft tissue burden in osteoarthritis (OA), though MRI measures of cartilage integrity have proven more elusive. Sodium MRI can reflect the proteoglycan content of cartilage; however, it requires specialized hardware, acquisition sequences, and long imaging times. This study was designed to assess the potential of a clinically feasible sodium MRI acquisition to detect differences in the knee cartilage of subjects with OA versus healthy controls (HC), and to determine whether longitudinal changes in sodium content are observed at 3 and 6 months. 28 subjects with primary knee OA and 19 HC subjects age and gender matched were enrolled in this ethically-approved study. At baseline, 3 and 6 months subjects underwent structural MRI and a 0.4ms echo time 3D T1-weighted sodium scan as well as the knee injury and osteoarthritis outcome score (KOOS) and knee pain by visual analogue score (VAS). A standing radiograph of the knee was taken for Kellgren-Lawrence (K-L) scoring. A blinded reader outlined the cartilage on the structural images which was used to determine median T1-weighted sodium concentrations in each region of interest on the co-registered sodium scans. VAS, K-L, and KOOS all significantly separated the OA and HC groups. OA subjects had higher T1-weighted sodium concentrations, most strongly observed in the lateral tibial, lateral femoral and medial patella ROIs. There were no significant changes in cartilage volume or sodium concentration over 6 months. This study has shown that a clinically-feasible sodium MRI at a moderate 3T field strength and imaging time with fluid attenuation by T1 weighting significantly separated HCs from OA subjects.
Highlights
Knee osteoarthritis (OA) is a debilitating disease with cartilage degeneration as a major feature of the disease process
A total of 23 healthy subjects were recruited into the healthy controls (HC) cohort, each healthy subject recruited to age (± 5 years) and gender match an OA subjects (OAs) subject
knee injury and osteoarthritis outcome score (KOOS) and pain scoring systems were still more discriminating between groups (p
Summary
Knee osteoarthritis (OA) is a debilitating disease with cartilage degeneration as a major feature of the disease process. The standard assessment of efficacy of OA therapies for regulatory agencies is via radiographs taken over a period of one or more years [1]. There is considerable interest in methodologies which could give a reliable indication of cartilage degradation or preservation over short timescales in order to evaluate new interventions and pharmaceutical therapies. Average cartilage volume change as detected by structural MRI was only 4-6% per year [2], with no consensus on measurement or analysis methodology. Interpretation of T2 changes is complicated by sensitivity to collagen degradation, tissue hydration, and fibril orientation [6], while T1rho is known to be sensitive to several macromolecular components [6]
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