Investigations
1st investigations to order
clinical diagnosis
Test
Imaging studies are not usually required, as the diagnosis can be made on clinical grounds.
Result
localised pain and tenderness over a bursa, and swelling if superficially sited
Investigations to consider
Gram stain and culture of fluid aspirate
Test
Analysis of fluid aspirate is indicated in suspected septic bursitis. White blood cell counts from infected bursa tend to be lower than those from infected joints, and counts of <20,000/mm^3 may be consistent with septic bursitis.[17]
Result
raised white cell count or grossly purulent fluid in septic bursitis; usually normal if a non-septic aetiology
crystal analysis
Test
Analysis of the aspirated fluid is recommended to look for the presence of crystals and, if present, to classify them on the basis of their shape and birefringence. Urate crystals and calcium pyrophosphate crystals are easily seen with polarised light.
Result
monosodium urate crystals in gout; calcium pyrophosphate crystals in calcium pyrophosphate deposition disease
x-ray of affected region
Test
Useful to exclude other differentials such as bone tumours, osteonecrosis of the hip, or calcific tendinopathy.
The American College of Radiography (ACR) recommends plain x-rays for investigating chronic hip, knee, or shoulder pain, where bursitis is suspected, and for excluding less common causes of chronic pain.[14][15][16]
Result
usually normal; may show features of underlying osteoarthritis
MRI
Test
Not required to confirm a diagnosis of bursitis but useful if associated pathology is suspected (e.g., rotator cuff tear with subacromial bursitis). Non-contrast MRI is recommended by the ACR to investigate chronic hip or shoulder pain when x-ray has been non-diagnostic.[14][16]
The ACR states that MRI of the knee is not usually useful if knee x-ray in non-diagnostic, although it may help in the diagnosis of deep infrapatellar bursitis.[15]
Result
soft-tissue swelling and fluid-filled bursa may be evident
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