How do I diagnose osteoarthritis?

Diagnosing Osteoarthritis

Osteoarthritis can be confidently diagnosed clinically in adults over 40 years based on typical symptoms and physical examination findings, with plain radiographs providing the gold standard for morphological assessment when needed. 1

Clinical Diagnosis Algorithm

Key Symptoms to Identify

• Pain on joint usage
• Only mild morning or inactivity stiffness (typically less than 30 minutes)
• Symptoms affecting one or few joints at a time
• Intermittent symptoms
• Pain targeting characteristic sites:
  • Hands: DIP joints, PIP joints, thumb base, index and middle MCP joints
  • Knees: medial compartment, patellofemoral joint
  • Hips: groin, lateral hip

Physical Examination Findings

1. Hand OA:

   • Heberden nodes (bony enlargement of DIP joints)
   • Bouchard nodes (bony enlargement of PIP joints)
   • Bony enlargement with/without deformity
   • Lateral deviation of IP joints
   • Subluxation and adduction of thumb base 1

2. Knee OA:

   • Bony enlargement
   • Crepitus on movement
   • Limited range of motion
   • Joint line tenderness 2

3. Hip OA:

   • Pain elicited with internal hip rotation (highly diagnostic)
   • Limited range of motion
   • Pain with weight-bearing 2

Radiographic Assessment

Plain radiographs remain the gold standard for morphological assessment of OA. A posteroanterior radiograph of both hands on a single film is adequate for diagnosis of hand OA. 1

Classical Radiographic Features:

• Joint space narrowing
• Osteophyte formation
• Subchondral bone sclerosis
• Subchondral cysts
• Subchondral erosion (in erosive hand OA) 1

MRI is not usually indicated in patients for whom radiographs are diagnostic of osteoarthritis unless symptoms are not explained by the radiographic findings. 1

Laboratory Testing

Blood tests are not required for diagnosis of OA but may be needed to exclude coexistent diseases. 1

• ESR, CRP, and RF are usually normal/negative or only mildly elevated in non-erosive OA
• More pronounced abnormalities should prompt investigation for alternative or additional diagnoses 1

Recognized Subtypes of OA

1. Interphalangeal Joint OA:

   • With or without nodes
   • May be symptomatic or asymptomatic

2. Thumb Base OA:

   • Often causes significant functional impairment
   • May occur independently of IP joint involvement

3. Erosive OA:

   • Targets IP joints
   • Shows radiographic subchondral erosion
   • Typically has abrupt onset
   • Marked pain and functional impairment
   • Inflammatory symptoms and signs
   • Mildly elevated CRP levels
   • Worse outcome than non-erosive IP joint OA 1

Differential Diagnosis

The differential diagnosis for OA is wide, with the most common conditions to consider being:

1. Psoriatic Arthritis:

   • May target DIP joints or affect just one ray
   • Shows proliferative marginal erosion on X-ray
   • Retained or increased bone density

2. Rheumatoid Arthritis:

   • Mainly targets MCP joints, PIP joints, wrists
   • Non-proliferative marginal erosion on X-ray
   • Osteopenia
   • More prolonged morning stiffness

3. Gout:

   • May superimpose on pre-existing OA
   • Acute inflammatory episodes
   • Elevated serum uric acid

4. Haemochromatosis:

   • Mainly targets MCP joints, wrists 1

Common Pitfalls in Diagnosis

1. Overreliance on radiographs: Radiographic changes may not correlate with symptoms. Some patients with significant radiographic OA may be asymptomatic, while others with minimal changes may have significant pain. 2

2. Misattribution of symptoms: Not all joint pain in older adults is due to OA, even if radiographs show OA changes. Consider other sources of pain such as enthesopathy or tendinopathy. 3

3. Missing inflammatory arthritis: Failing to recognize inflammatory features that suggest conditions other than OA, particularly when symptoms affect atypical joints or show marked inflammatory signs. 1

4. Overlooking erosive OA: This subtype has more inflammatory features and worse outcomes than typical OA and may be mistaken for inflammatory arthritis. 1

5. Ignoring functional impact: Functional impairment in hand OA may be as severe as in rheumatoid arthritis and should be carefully assessed. 1

By following this diagnostic approach and being aware of the common pitfalls, clinicians can accurately diagnose osteoarthritis and distinguish it from other conditions that may require different management approaches.