The Diagnosis of Osteoarthritis

Full thickness cartilage loss is the main pathoanatomic criterion for the multifactorial disease of osteoarthritis. Epidemiology and prognosis The incidence of osteoarthritis rises with age and affects almost 20% of the population over 60 years. The joints of the hands are most often affected, followed by the hip and knee. Progression of the disease is experienced by one third of patients within 10 years. Influencing factors biomechanics, sports and body weight Leg axis deviation as well as the femoroacetabular impingement syndrome of the hip are biomechanic risk factors. The single most important risk factor for osteoarthritis of the knee is increased body weight. International competitive sports or physical work with carrying heavy weights are further risk factors for osteoarthritis. Clinical diagnosis, imaging und quality of life Osteoarthritis patients suffer from pain at rest and activity. Plain radiographs in two planes under body weight are the gold standard for diagnosis. MRI scans are needed for early diagnosis. Quality of life is reduced and mental health may be impaired in osteoarthritis patients. Pathogenesis First and foremost, osteoarthritis originates from the cartilage, subchondral bone, synovium and the muscles surrounding the joint. Biologic processes lead to enzymatic degradation of type II collagen and proteoglycan. Inflammatory cytokines are released into the joint and the organism from the synovia. These cytokines cause hypertrophy and apoptosis of chondrocytes. The weakening of the muscles occurs in the beginning of the osteoarthritic process and not as consequence. The aforementioned risk factors (axis deviation, joint biomechanics, sports and workload) initiate the development of osteoarthritis once the equilibrium state of the joint is disturbed. In addition to increased body weight, the metabolic syndrome causes chronic systemic inflammation accelerating the process. The adipose tissue of patients with metabolic syndrome acts as an endocrine organ releasing proinflammatory cytokines named adipokines. Genetics and epigenetics The association between the individual genetic information and the development of osteoarthritis is being investigated by genome-wide association studies. The different probability for the development of osteoarthritis of the hip and knee has been studied in twins. Epigenetics deals with the interaction between the genetic information, molecular mechanisms and different realisation of clinical phenotypes, influencing factors being the genetic make-up, environmental exposures and stochasticity. The single most important mechanism is DNA methylation. Simple attributes such as the Kellgren-Lawrence Score of the joint, power of quadriceps muscle, body weight and depression have been used in population-based studies to differentiate phenotypes of osteoarthritis. A more individualised treatment based on the phenotype is expected in the future.