Osteoarthritis (OA), or degenerative joint disease (DJD), is the most common of the arthritides.

Terminology

Because the osteoarthritis is not primarily an inflammatory process, some authors prefer the term osteoarthrosis instead. 

Pathology

Primary OA is the less common variant and is characterised by the absence of an antecedent insult, it is considered to be hereditary and affects primarily middle-aged women.

Secondary OA is the most common form, caused by abnormal mechanical forces (e.g. occupational stress, obesity) or by a previous joint insult (e.g. trauma, rheumatoid arthritis). 

Radiographic features

The hallmarks of DJD are joint space narrowing, sclerosis, and osteophytosis. If all three of these findings are not present, another diagnosis should be considered.

Joint space narrowing

• characteristically asymmetric in DJD
• least specific findings for DJD, though present in most cases
• joint space narrowing in other arthritides is usually symmetric

Sclerosis

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

Osteophytosis

• are a common DJD finding
• will also be diminished in the setting of osteoporosis
• some osteophytes carry eponymous names, as discussed below

 It affects the distal interphalangeal joints (Heberden nodes), the proximal interphalangeal joints (Bouchard nodes), ( mnemonic H-D, B-P ) and the base of the thumb in a bilaterally symmetric fashion. If it is not bilaterally symmetric, the diagnosis of primary osteoarthritis should be questioned.

Joint erosions

• several joints exhibit erosions as a manifestation of DJD
  • temporomandibular joint
  • acromioclavicular joint
  • sacroiliac joints
  • symphysis pubis

Subchondral cyst 

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