26th January 2024

Diagnosis

Background

NICE guidelines recommend suspecting a diagnosis of OA if the following features are present and alternative diagnoses have been excluded:

• Age 45 years or over
• Activity-related joint pain
• Absence of morning joint-related stiffness or morning stiffness lasting no longer than 30 minutes
• Functional impairment

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.

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.

Classification

American College of Rheumatology criteria for the classification and reporting of osteoarthritis of the knee

Clinical and laboratory diagnostic criteria:

• Knee pain plus at least 5 of the following 9 criteria: age >50 years; stiffness <30 minutes; crepitus; bony tenderness; bony enlargement; no palpable warmth; erythrocyte sedimentation rate (ESR) <40 mm/hour; rheumatoid factor <1.40; synovial fluid signs of OA.

Clinical and radiographic diagnostic criteria:

• Knee pain plus osteophytes, plus at least 1 of the following 3 criteria: age >50 years; stiffness <30 minutes; crepitus.

American College of Rheumatology criteria for the classification and reporting of osteoarthritis of the hand

Clinical criteria:

• Hard tissue enlargement involving at least 2 of 10 selected joints, swelling in <3 metacarpophalangeal (MCP) joints, and hard tissue enlargement of at least 2 distal interphalangeal (DIP) joints.
• If the patient has <2 enlarged DIP joints, then deformity of at least 1 of the 10 selected joints is necessary to classify the symptoms as being due to OA.

American College of Rheumatology criteria for the classification and reporting of osteoarthritis of the hip

Clinical and laboratory diagnostic criteria:

• Hip pain is present plus either 1) hip internal rotation ≥15°; pain present on internal rotation of the hip; morning stiffness of the hip for ≤60 minutes; age >50 years, or 2) hip internal rotation <15°; ESR ≤45 mm/hour. If no ESR was obtained, hip flexion ≤115° is substituted (sensitivity 86%, specificity 75%)

Clinical and radiographic diagnostic criteria:

• Hip pain plus 2 of the following 3 radiographic criteria: osteophytes (femoral or acetabular); joint space narrowing (superior, axial, and/or medial); ESR <20 mm/hour (sensitivity 89%, specificity 91%).

References 

• Wesseling J, Bierma-Zeinstra SM, Kloppenburg M, Meijer R, Bijlsma JW. Worsening of pain and function over 5 years in individuals with ‘early’ OA is related to structural damage: data from the Osteoarthritis Initiative and CHECK (Cohort Hip & Cohort Knee) study. Annals of the Rheumatic Diseases. 2015 Feb 1;74(2):347-53
• Kellgren JH, Lawrence JS. Radiological assessment of osteo-arthrosis. Ann Rheum Dis. 1957 Dec;16(4):494-502.
• Altman R, Asch E, Bloch D, Bole G, Borenstein D, Brandt K, Christy W, Cooke TD, Greenwald R, Hochberg M, Howell D. Development of criteria for the classification and reporting of osteoarthritis: classification of osteoarthritis of the knee. Arthritis & Rheumatism: Official Journal of the American College of Rheumatology. 1986 Aug;29(8):1039-49.
• Hayashi D, Roemer FW, Jarraya M, Guermazi A. Imaging of osteoarthritis. Geriatric imaging. 2013:93-121.
• Conaghan PG, Dickson J, Grant RL. Care and management of osteoarthritis in adults: summary of NICE guidance. Bmj. 2008 Feb 28;336(7642):502-3.
• National Institute for Health and Care Excellence (Great Britain).Osteoarthritis: care and management. National Institute for Health and Care Excellence (NICE); 2014