Assessing synovitis with conventional static and dynamic contrast-enhanced magnetic resonance imaging in knee osteoarthritis.

Knee osteoarthritis (KOA) is one of the most common causes of physical disability in the elderly population. With an increasing ageing and obese population, the prevalence of KOA is expected to rise substantially. The needs for a better understanding of the disease and tools that can predict the course of the disease, for example following treatment, are therefore imperative. Inflammation has over the last years been recognised as an important factor for both the symptomatology and disease course in KOA. Synovitis, inflammation of the synovium, is the hallmark of intra-articular inflammation and has been associated with pain, symptoms and disease progression. Synovitis can be visualised on conventional static MRI. However, the addition of a dynamic contrast-enhanced (DCE) MRI-sequence enables the assessment of the synovium both in regards of its morphology and perfusion. Studies in both KOA and rheumatoid arthritis have shown that DCE-MRI measures of synovitis are more sensitive than conventional static MRI in regards of microscopic synovitis and patient-reported outcome measures (PROMs). The aims of this PhD project were to characterise synovitis in KOA with conventional static and DCE MRI in regards of histology (study I), its association with PROMs (studies II-III) and changes following a symptoms-improving intervention (study III). We found that DCE-MRI-measures of synovitis seem to be superior to conventional static MRI in their association with histological synovitis (study I) and pain (study II) in a cross-sectional setting. However, the use of DCE-MRI over conventional static CE-MRI cannot be justified when assessing the long-term changes in synovitis following an intervention with intra-articular corticosteroids/placebo and exercise (study III). Evidence is mounting that KOA is constituted of different phenotypes. There is an urgent need to define these in order to improve and individualise treatment and management. It is essential to gain a better understanding of the different pro-cesses taking place in KOA, on an individual level and in the different stages of the disease. DCE-MRI may very well be a useful tool in facing these challenges especially in regards of the role of perfusion and inflammation in KOA and osteoarthri-tis in general.