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". The 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. The prevalence increases with age. In the age group below 50 years men are more often affected, while in the older population the disease is more common in women. It is estimated that over 300 mln people in the world suffered from OA in 2017 ¹³.

Clinical presentation

Patients present with decreased function from joint pain, instability and stiffness ^7,10. The pain is typically worsened by activity and decreases at rest; in later disease stages it may become continuous ¹². 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.

Distribution

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 agesthe age 50-80 and 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. Recently, with increasing use of MRI in the assessment of OA, other findings have been studied, such as bone marrow lesions and synovitis. 

Joint

• joint space narrowing

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

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

• 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

joint

erosions

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

Subchondral cyst

subchondral cysts

 

• also known as a geodegeodes
• 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.