What is osteoarthritis?

What is Osteoarthritis

Osteoarthritis is the most common form of arthritis, characterized by pathology involving the whole joint—including cartilage degradation, bone remodeling, osteophyte formation, and synovial inflammation—leading to pain, stiffness, swelling, and loss of normal joint function. 1

Disease Definition and Prevalence

• OA affects an estimated 302 million people worldwide and is a leading cause of disability among older adults. 1
• It is a highly prevalent, progressive, degenerative joint disorder that leads to pain, stiffness, disability, reduction in quality of life, and limitations in activities of daily living. 1
• The condition is characterized by loss of cartilage, changes in subchondral bone, and abnormalities in other joint tissues such as the synovial membrane and ligaments. 1

Pathophysiology

OA involves not just cartilage but the entire joint structure from early in the disease process. 2

• Progressive cartilage loss leads to bone remodeling, osteophyte formation, and synovial inflammation. 2
• The disease represents pathologic changes in cartilage, bone, synovium, ligament, muscle, and periarticular fat, leading to joint dysfunction. 3
• Mechanical, biochemical, and genetic factors are well-known risk factors for disease development. 1

Most Commonly Affected Joints

• The knees, hips, and hands are the most commonly affected appendicular joints. 1
• In the hand, OA mainly targets the distal interphalangeal (DIP) joints, proximal interphalangeal (PIP) joints, and thumb base joints. 1
• OA can involve almost any joint but typically affects the hands, knees, hips, and feet. 3

Clinical Presentation

Typical symptoms include pain on usage and only mild morning or inactivity stiffness affecting one or a few joints at any one time; symptoms are often intermittent. 1

• Pain is worsened by movement and can lead to disability in activities of daily living. 4
• Limited duration of localized morning or inactivity stiffness (less than 30 minutes) is more specific to OA than inflammatory arthritis. 1, 5
• Clinical hallmarks include Heberden nodes (DIP joints) and Bouchard nodes (PIP joints), and/or bony enlargement with or without deformity. 1
• Physical examination findings useful diagnostically include bony enlargement in knee OA and pain elicited with internal hip rotation in hip OA. 3

Risk Factors

Risk factors include female sex, increasing age over 40, menopausal status, family history, obesity, higher bone density, greater forearm muscle strength, joint laxity, prior hand injury, and occupation or recreation-related usage. 1

• Aging is the single most important constitutional risk factor for OA development, with heritability estimates of 0.39-0.65 from twin studies. 2
• Obesity increases OA risk in both weight-bearing and non-weight-bearing joints, indicating a systemic metabolic mechanism beyond mechanical loading. 2
• Joint trauma accounts for a significant fraction of OA cases, with mechanical damage triggering changes in gene expression and cartilage metabolism. 2
• After age 65, prevalence is about 60% in men and 70% in women. 6

Systemic Nature of Disease

OA should be understood as having systemic implications that extend beyond joint problems. 7

• The metabolic phenotype of OA is linked to obesity and metabolic syndrome, with metabolic inflammation playing a crucial independent role in disease development. 2
• Chronic low-grade inflammation is characteristic of OA, occurring both in the affected joint and systemically, mainly due to adipose tissue inflammation in obese patients. 7
• Persons with OA have more comorbidities and are more sedentary than those without OA, with reduced physical activity leading to 20% higher age-adjusted mortality. 3

Diagnostic Approach

With typical features of pain on usage, mild morning stiffness, and characteristic joint involvement, a confident clinical diagnosis can be made in adults aged over 40. 1

• Plain radiography provides the gold standard for morphological assessment, with classical features including joint space narrowing, osteophyte formation, subchondral bone sclerosis, and subchondral cysts. 1
• A posteroanterior radiograph of both hands on a single film is adequate for diagnosis of hand OA. 1
• Laboratory testing usually does not help in diagnosis. 4

Disease Course and Impact

• OA spans decades of a patient's life, with patients likely to be treated with multiple pharmaceutical and nonpharmaceutical interventions, often in combination. 1
• Functional impairment in hand OA may be as severe as in rheumatoid arthritis. 1
• By 2050, an estimated 40 million individuals will be severely disabled because of OA, with over 130 million suffering from OA worldwide. 8
• The occurrence of OA will increase in the future with demographic development and aging of society, constituting a large and rising economic factor for the health system with high direct and indirect costs. 1