Osteoarthritis (OA) is the most common form of arthritis, being widely prevalent with high morbidity and social cost. 

Terminology

Some authors prefer the term osteoarthrosis instead of osteoarthritis as some authors do not believe in an inflammatory cause as might be suggested by the suffix "itis". To differentiate OA from its erosive osteoarthritis, which is a different clinical and radiological entity, theThe condition is sometimes called non-erosive osteoarthritis, to differentiate it from erosive osteoarthritis, although this is considered a form of osteoarthritis ⁶.

Epidemiology

Osteoarthritis is common, affecting ~25% of adults ⁷.

Clinical presentation

Patients present with decreased function from joint pain, instability and stiffness ^7,10. Many cases of radiological OA are asymptomatic and conversely clinically apparent OA may not manifest radiographic change ^9,10. 

Pathology

The pathogenesis and pathophysiology of OA are yet to be fully understood ⁷. Despite emphasis being placed on articular cartilage degeneration, the remainder of the joint is involved including bone remodelling, osteophyte formation, ligamentous laxity, periarticular muscle weakness and synovitis ^8,10.

LocationDistribution

OA can affect both the axial and appendicular skeleton. The most common peripheral joints affected include ^ref:

• hands
• knee
• hip

Risk factors

Strong risk factors for developing OA include ^7,10:

• obesity
• increasing age
• female sex (particularly between ages 50-80)
• family history

Classification

Osteoarthritis can be:

• primary/idiopathic/typical
  • absence of an antecedent insult
  • strong genetic component with the disease primarily affecting middle-aged women ⁵
• secondary/atypical
  • abnormal mechanical forces (e.g. occupational stress, obesity)
  • previous joint injury
    • post-traumatic osteoarthritis
      • accounts for ~12% of all OA ¹¹
      • major cause in young adults ⁹
    • prior surgery
    • crystal deposition (e.g. gout, CPPD)
    • haemochromatosis

Radiographic features

Key radiographic features are joint space narrowing (JSN), sclerosis, and osteophytosis. If all three of these findings are not present, another diagnosis should be considered.

Joint space narrowing

• characteristically asymmetric
• least specific: present in many other pathological processes

Sclerosis

• sclerotic changes occur at joint margins
• frequently seen unless severe osteoporosis is present

Osteophytosis

• i.e. development of osteophytes
• common DJD finding
• will also be diminished in the setting of osteoporosis
• some osteophytes carry eponymous names, e.g. Heberden nodes, Bouchard nodes

Joint erosions

• several joints may exhibit degenerative erosions ¹
  • temporomandibular joint
  • acromioclavicular joint
  • sacroiliac joints
  • symphysis pubis

Subchondral cyst 

• also known as a geode
• cystic formations that occur around joints in a variety of disorders, including, rheumatoid arthritis, calcium pyrophosphate dihydrate crystal deposition disease (CPPD) and avascular necrosis.

Treatment and prognosis

There is no effective treatment to slow or reverse the changes of osteoarthritis ⁷. The mainstays of treatment include exercise, walking aids, bracing, and analgesia (including intra-articular steroid injections) ⁸. Arthroplasty can result in improved function and reduced pain ¹⁰.