Osteoarthritis (OA) is a disabling joint disease characterized by a noninflammatory degeneration of the joint complex (articular cartilage, subchondral bone, and synovium) that occurs with old age or from overuse. It mainly affects the weight-bearing and high-use joints, such as the hip, knee, hands, and vertebrae. Despite the widespread view that OA is a condition caused exclusively by degenerative “wear and tear” of the joints, newer research indicates a significant heterogeneity of causation, including pre-existing peculiarities of joint anatomy, genetics, local inflammation, mechanical forces, and biochemical processes that are affected by proinflammatory mediators and proteases. Major risk factors include advanced age, obesity, previous injuries, and asymmetrically stressed joints. In early-stage osteoarthritis, patients may complain of reduced range of motion, joint stiffness, and pain that is aggravated with heavy use. As the disease advances, nagging pain may also occur during the night or at rest. Diagnosis is predominantly based on clinical and radiological findings. Classic radiographic features of OA do not necessarily correlate with clinical symptoms and appearance. If lifestyle changes (moderate exercise, weight loss) and physical therapy fail to improve symptoms, analgesics are used for the management of active osteoarthritis. If medical interventions fail to improve the patient's quality of life, surgical procedures such as joint replacement may become necessary.
- Prevalence: most common joint disorder in the USA, affecting more than 20 million adults 
- Incidence: increases with age
- Sex: ♀ > ♂, especially in patients older than 50 years
- Incidence rates in specific joints: knee > hip > hand 
Epidemiological data refers to the US, unless otherwise specified.
- Modifiable risk factors 
- Nonmodifiable risk factors 
Osteoarthritis can be classified according to the underlying cause: 
- No identifiable underlying cause
- Can be localized or generalized
- Genetic factors of causation have been implicated, but not definitively proven.
- Secondary OA
Chronic mechanical stress on the joints and age-related decrease in proteoglycans → cartilage loses elasticity and becomes friable → degeneration and inflammation of cartilage ; → joint space narrowing and thickening and sclerosis of the subchondral bone 
Early clinical findings
- Pain during or after exertion (e.g., at the end of the day) that is relieved with rest
- Pain in both complete flexion and extension
- Crepitus on joint movement
- Joint stiffness and restricted range of motion
- Radiating or referred pain; (e.g., coxarthrosis may lead to knee pain)
- Possible varus formation if the knee is affected (loss of cartilage usually begins medially)
- Joints are usually asymmetrically involved (opposed to rheumatoid arthritis).
- Late clinical findings
Subtypes and variants
- Heberden's nodes: pain and nodular thickening on the dorsal sides of the distal interphalangeal joints (DIP), ♀ > ♂
- Bouchard's nodes: pain and nodular thickening on the dorsal sides of the proximal interphalangeal joints (PIP), ♀ > ♂
- Rhizarthrosis: osteoarthritis of the first carpometacarpal joint (between the trapezoid and the first metacarpal bone)
- Hallux rigidus: arthrosis of the first metatarsophalangeal joint (between the first metatarsal and the first proximal phalanx), characterized by hypertrophy of the sesamoid bones.
Osteoarthritis is usually diagnosed on the basis of clinical features. Radiographic evidence of joint degeneration supports the diagnosis of OA. 
Radiological signs of osteoarthritis 
- Irregular joint space narrowing
- Subchondral sclerosis: dense area of bone (visible on x-ray) just below the cartilage zone of a joint, formed due to a compressive load on the joint
- Osteophytes (bone spurs); : bony projections that develop on joint surfaces as spurs or densifications; Osteophytes develop on the edges of the joint and thereby increase the joint surface
- Subchondral cyst: fluid-filled cyst that develops at the surface of a joint due to local bone necrosis induced by the joint stress of osteoarthritis
The patient's history and clinical diagnosis are essential for the assessment and treatment of osteoarthritis. Radiographic signs often do not correlate with the patient's perception and clinical findings.
The differential diagnoses listed here are not exhaustive.
- General measurements 
- Pharmacotherapy 
- Interventional therapy: intraarticular glucocorticoid injections (not a long-term treatment) 
- Surgical therapy: if conservative and interventional measures fail
Pharmacotherapy should be used as acute and symptomatic therapy only; long-term NSAID therapy should be avoided due to its many side effects.