Flashcards in Rheumatology - OA Deck (12)
What is OA?
OA is the most common arthropathy of adults, and its aetiology is multifactorial. It is characterised by progressive joint degeneration. Inflammation is not a marked feature.
What age group is most affected by OA?
The incidence of radiographic features of OA increases with age. More than 80% of >75s may be affected.
Females are slightly more affected than males, particularly in the interphalangeal joint disease.
What is the aetiology of OA?
The cause of OA is unknown. Family history may play an important role. Siblings of patients undergoing major lower limb joint replacement for OA are 3 times more likely than the general population to require surgery themselves.
Most cases are secondary to other causes such as trauma or inflammatory joint disease.
What are the pathological features of OA on plain film x ray?
Use the mnemonic "LOSS":
- loss of joint space due to cartilage damage
- osteophytes caused by reactive bone hypertrophy
- subchondral sclerosis
- subchondral cysts
How is OA classified?
OA can either be primary or secondary.
Secondary OA arises from:
- trauma, including repetitive injury in some occupations and fracture
- obesity increases risk of OA
- congenital conditions - e.g. hip dysplasia or dislocation
- inflammatory arthritis (e.g. RA, gout)
- late complication of bacterial joint infection
What are the important clinical features of OA?
- joint pain tends to be insidious in onset; typically there is slow stepwise deterioration in symptoms
- pain; aggravated by activity, relieved by rest, is worse at the end of the day; may occur at night
- stiffness is minor in the morning but recurs throughout the day with periods of rest
- bony swelling may be noted particularly in the hands as Heberdens' nodes (DIPJ) and Bouchard's nodes (PIPJ)
What is the distribution of joints affected in OA?
CMC (esp 1st)
PIPJs (less frequently)
What are the physical findings in OA?
Bony prominence due to a combination of marginal osteophytes and joint deformities (occasionally OA can cause an effusion, particularly if it is associated with intra-articular calcium crystal deposition).
There is a reduction in range of movement in affected joints with "end of range" pain and limitation, and palpable crepitus.
Instability in later stages particularly where there is substantial muscle wasting.
What are the subsets of OA?
1) Primary generalized OA: predominantly in middle aged women, affecting the 1st CMC joint, PIPJ, DIPJ and knee, hips and spine
2) Chondromalacia patellae: limited patellofemoral joint OA causing pain on climbing stairs, running or squatting
3) Inflammatory OA: this affects predominantly postmenopausal women in the DIP/PIPJs of the hand. Episodes of pain and inflammation may mimic RA or psoriatic arthritis. X rays often show erosions as well as the classic hallmarks of OA. It is probably associated with crystal deposition
What are the key investigations in OA?
- inflammatory markers (e.g. ESR, CRP) are normal
- serology for ANA and RA are unnecessary except in cases with symptoms suggestive of inflammation
- synovial fluid from joint aspiration is clear with normal viscosity and is non - inflammatory (low WCC); the fluid should be examined for calcium pyrophosphate crystals (pseudogout)
- plain film x-rays show classic features
What are the differential diagnoses to consider in OA?
- psoriatic arthropathy
- Reiter's syndrome
- crystal deposition disease (e.g. gout, pseudogout)
NB - consider iron and calcium studies in those with an atypical distribution or age of onset (to exclude haemachromatosis or hyperparathyroidism)