26th January 2024

Investigations 

OA is a clinical diagnosis; therefore, investigations should be ordered if there is a suspicion of alternative diagnoses, such as inflammatory arthritis, based on initial history and clinical examination.

OA is a clinical diagnosis; therefore, investigations should be ordered if there is a suspicion of alternative diagnoses, such as inflammatory arthritis, based on initial history and clinical examination.

Blood tests

• Serum CRP and ESR: levels would be normal in OA
• Rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP): can be requested if there is diagnostic uncertainty, or suspicion of co-existing rheumatoid arthritis with OA
• FBC, U&Es and LFTs: may be checked prior to commencing non-steroidal anti-inflammatory drugs (NSAIDS)

Imaging

Routine radiography of the affected joints is not usually required for confirmation of diagnosis of OA. Plain X-rays can be considered if the diagnosis is uncertain to exclude alternative causes for pain and when there are unexpected changes in symptoms or rapid progression in a patient with known OA. However, radiological findings are thought to correlate poorly with symptoms and functional impairment. Typical x-ray findings in OA are:

• Loss or narrowing of joint space (indicates severity of cartilage damage)
• Osteophyte formation (formation of new bone at joint margins)
• Subarticular sclerosis
• Subchondral cysts

Image Source: Wikimedia Commons (2017). Severe (Tönnis grade 3) osteoarthritis of the hip, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Severe_(Tönnis_grade_3)_osteoarthritis_of_the_hip.jpg  (Accessed: 24 June 2021).

Kellgren-Lawrence radiographic classification of osteoarthritis

The Kellgren-Lawrence system is frequently used in epidemiological studies to demonstrate the grading of radiological findings in OA:

• Grade 0 (none): no radiological findings of osteoarthritis
• Grade 1 (doubtful): doubtful joint space narrowing and possible osteophytic lipping
• Grade 2 (minimal): definite osteophytes and possible joint space narrowing
• Grade 3 (moderate): moderate multiple osteophytes, definite narrowing of joint space and some sclerosis, and possible deformity of bone ends
• Grade 4 (severe): large osteophytes, marked narrowing of joint space, severe sclerosis, and definite deformity of bone ends.

Although MRI is more sensitive in investigating changes associated with OA, it is not indicated for the diagnosis of simple OA. Therefore, the use of MRI is limited to excluding other causes for hip or knee pain, such as bone tumours or avascular necrosis. It should also be considered in cases of spinal OA with the presence of neurological deficits to rule out nerve involvement. Ultrasound (US) and computed tomography (CT) scans can be used to investigate alternative diagnoses – US is more useful for imaging soft tissues, whereas bone is best visualised on MRI or CT. In cases where diagnoses such as septic arthritis or crystal arthropathies are suspected, patients may need to undergo a joint aspiration.