Osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by deterioration of the articular cartilage. OA is a major cause of disability and chronic articular pain all over the world. With advances in modern medicine improving the prevention, diagnosis, and treatment of many diseases that were once life-threatening, the population is now living longer. This increased life expectancy has led to an increased prevalence of degenerative conditions including OA. Worldwide, arthritis is considered to be the fourth leading cause of disability [1]. In both the developed and developing worlds, osteoarthritis is one of the most important factors affecting disability-adjusted life years [2]. It is a progressive and debilitating condition that can affect both young and old people and is a highly prevalent condition, especially in the Western world. It has a radiological prevalence of up to 80% in subjects over the age of 65 years [3–5]. It is estimated that symptomatic osteoarthritis affects 10% of males and 18% of females over the age of 45 years [6]. Prevalence is likely to further increase given the increasing proportion of older people in society [3, 4]. Osteoarthritis affects one or several diarthrodial joints, including small joints (such as those in the hand) and large joints (especially the knee and hip joints). Diarthrodial joints join two adjacent bones that are covered by a layer of hyaline cartilage (specialized articular cartilage) and encased in a synovial capsule [7]. The bone, articular cartilage, and the thin region of calcified cartilage form a biocomposite, which is highly adapted to transfer loads during weight bearing and optimize joint motion. Alteration in the integrity of the individual joint tissues can occur either acutely associated with traumatic injury or can evolve over time through cell-derived or matrix-derived factors that alter the composition, structure, and material properties of this specialized part of the skeletal system. Although pathological processes are usually referred to the hyaline cartilage, all of the joint tissues are affected because of their intimate physical and functional association. OA is thus considered a whole joint disease. OA can be classified as primary (or idiopathic) and secondary (based on the attribution to recognized causative factors (e.g., trauma, surgery on the joint structures, and abnormal joints at birth) [8]. The etiology of primary OA is not fully understood yet. It is clear that it is linked to a combination of risk factors, with increasing age and obesity being the most prominent. Elevated body mass index (BMI) is related mainly to knee OA. Other risk factors for primary OA include articular malalignment, increased biomechanical loading of joints, genetics, and low-grade systemic inflammation. Numerous biochemical mediators such as growth factors, cytokines, metalloproteinases, and enzymes are involved in cartilage homeostasis. Disruption of this homeostasis has been the subject of research in recent years, and further findings in this field are expected to better understand OA disease [9].