Diagnosing Osteoarthritis
Osteoarthritis can be diagnosed clinically without imaging in patients presenting with typical features: usage-related joint pain, short-duration morning stiffness (typically <30 minutes), age over 40 years, and symptoms affecting one or a few joints. 1, 2
Clinical Diagnosis Criteria
The diagnosis of OA is primarily clinical and does not require radiographic confirmation in typical presentations. 1
Key clinical features that establish the diagnosis include: 1, 2
- Usage-related pain that worsens with activity and improves with rest 1
- Brief morning stiffness lasting less than 30 minutes 1, 2
- Age greater than 40 years 1, 2
- Involvement of one or a few joints rather than widespread polyarticular disease 1, 2
For hand OA specifically, the presence of Heberden nodes (DIP joints) and Bouchard nodes (PIP joints) with bony enlargement affecting characteristic target joints (DIPJs, PIPJs, thumb base) is diagnostic. 1, 2
When Imaging Is Required
Imaging is NOT routinely needed for diagnosis but should be obtained in specific circumstances: 1
Indications for imaging include: 1, 2
- Atypical presentation requiring confirmation or exclusion of alternative diagnoses 1
- Unexpected rapid progression of symptoms 1
- Change in clinical characteristics suggesting another diagnosis 1
- Need to differentiate from inflammatory arthritis when clinical features overlap 1
When imaging is indicated, plain radiography should be the first modality used. 1, 2 Classical radiographic features include joint space narrowing, osteophytes, subchondral bone sclerosis, and subchondral cysts. 1, 2, 3 For erosive OA, subchondral erosion is also present. 1, 2
For knee OA, weight-bearing and patellofemoral views are specifically recommended to optimize detection of OA features. 1, 2
Laboratory Testing
Blood tests are NOT required for diagnosing OA. 1 However, laboratory evaluation should be performed when there are marked inflammatory symptoms, atypical joint involvement, or concern for coexistent inflammatory arthritis. 1 In typical OA, inflammatory markers (ESR, CRP) and rheumatoid factor are not elevated. 1
Critical Diagnostic Pitfalls
A single clinical or radiographic feature has limited diagnostic value. 1, 3 The diagnosis depends on a composite of multiple features including age, gender, joint distribution pattern, examination findings showing bony (not soft tissue) swelling, and radiographic changes when obtained. 1, 3
Important differential diagnoses to exclude include: 1, 3
- Rheumatoid arthritis (targets MCPJs, PIPJs, wrists with prolonged morning stiffness >30 minutes) 1, 3
- Psoriatic arthritis (may target DIPJs or affect single rays asymmetrically) 1, 3
- Gout (can superimpose on pre-existing OA with acute flares) 1, 3
- Hemochromatosis (mainly targets MCPJs and wrists) 1, 3
Coexistent conditions are common - OA may coexist with CPPD, gout, or RA, requiring careful evaluation when atypical features are present. 1, 3
Erosive OA Subtype
Erosive OA represents a distinct subgroup with worse outcomes, characterized by abrupt onset, marked pain and functional impairment, inflammatory symptoms, mildly elevated CRP, and radiographic subchondral erosion. 2 This subtype requires differentiation from inflammatory arthritis and may warrant imaging even with typical joint distribution. 2