Imaging Modalities in Osteoarthritis

Osteoarthritis (OA) is a degenerative and progressive joint disease that causes physical inactivity and impaired quality of life and whose frequency is increasing. OA most commonly affects the elderly population: 70% of those over 65 years of age are affected. OA is considered a multifactorial disease in which numerous risk factors are involved: advanced age, female gender, mechanical factors (trauma, overuse, articular malposition or malformation, joint instability, occupational and sport activities), genetic predisposition, inflammation, obesity and endocrine disorders (diabetes, hyperuricaemia); in particular, the increased prevalence of obesity is associated with the rise of OA, especially knee OA in women. The typically affected joints are the knees, hips, lumbar–sacral spine, neck, feet and hands. Clinically, OA is characterised by pain, morning stiffness (lasting less than 30 minutes), functional limitation and crackles. The joint structures involved are articular cartilage, bone and synovium; most commonly, abnormalities are represented by articular cartilage breakdown, osteophytes at the joint margins, subchondral sclerosis and subchondral cysts, ligamentous contractures and relaxation, muscle atrophy and spasm and morphological alterations of the synovium.^1–5 However, OA remains a poorly understood disease. Imaging techniques have been demonstrated to have a relevant role in the diagnosis and monitoring of joint disease. Imaging presents numerous advantages as a marker of disease activity in OA. Indeed, an appropriate image provides data in a compact and succinct way, aiding documentation through easy storage of the image, a high level of reproducibility and communication of source data to other observers. Moreover, imaging is useful in the demonstration of structural damage (a marker of disease) and in the detection of current activity in soft tissue and the bony parts of the musculoskeletal system. Over the last few years, imaging techniques have became more sophisticated, especially with advances in magnetic resonance imaging (MRI) and ultrasound technologies. Although the use of MRI and other imaging techniques allows the detection of early cartilage fibrillation and defects not seen on conventional radiography (X-ray), several studies have demonstrated that X-ray remains the mainstay of imaging in OA owing to its accessibility, low cost and reproducibility.^6–9 Ultrasound examination may be considered useful in OA assessment owing to its low cost, short duration of examination and the possibility of performing a multiregional joint evaluation in the same scanning session. This technique allows various anatomical structures to be depicted in fine detail and changes in minute particulars to be detected, but is not able to measure cartilage thickness with any accuracy. Ultrasound can thus be considered a promising imaging technique for OA evaluation. However, X-ray remains the most commonly used tool in daily clinical practice for the evaluation of most OA abnormalities.¹⁰ The aim of this article is to review the role of different imaging modalities in the assessment of OA.