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Approach to Arthritis

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1. Definition and Epidemiology

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2. Pathophysiology

• Two subchondral bone ends covered with articular cartilage
• A fibrous joint capsule lined by the synovial membrane
• Synovial fluid - a viscous lubricant allowing near-frictionless motion

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3. Broad Classification

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4. Step 1 - History

Key Clinical Factors to Assess (Rosen's Emergency Medicine, Box 102.1)

• Age of the patient
• Number of joints involved (mono- vs oligo- vs polyarticular)
• Time course: Acute (<7 days) | Subacute (7 days - 3 weeks) | Chronic (>3 weeks)
• Trauma history
• Systemic symptoms (fever, fatigue, rash, eye changes, GI symptoms)
• Aggravating/alleviating factors
• Medication history (many drugs cause arthralgia)

Mono vs. Polyarthritis - Clinical Significance

• Monoarthritis - must urgently exclude septic arthritis; a delay causes irreversible joint destruction and death
• Polyarthritis - widens the differential toward systemic rheumatologic disease; rarely infectious

Characteristic Historical Clues

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5. Step 2 - Physical Examination

General Examination

• Vital signs - fever/tachycardia (note: most septic arthritis patients are afebrile on presentation)
• Gait and posture
• Skin: psoriasis/nail pitting (PsA), butterfly rash (SLE), tophi (gout), skin breaks (septic)
• Eyes: uveitis (SpA, reactive arthritis)
• Mucous membranes: oral ulcers (SLE, Behçet's, reactive arthritis)
• Lymph nodes, salivary glands, thyroid
• Spine: axial involvement (SpA, OA)

Joint Examination (systematic approach)

1. Inspection - swelling, deformity, erythema, muscle wasting
2. Palpation - warmth, tenderness, effusion
3. Range of motion (active and passive)
4. Neurovascular assessment
5. Special tests per joint

Joint Findings Differentiating Conditions

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6. RA vs. OA Comparison

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7. Joint Distribution Patterns

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8. Step 3 - Laboratory Investigation

Targeted (not "routine") - guided by differential:

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9. Step 4 - Synovial Fluid Analysis (Arthrocentesis)

Synovial Fluid Classification

• Monosodium urate (MSU) crystals in gout: needle-shaped, negatively birefringent
• Calcium pyrophosphate (CPPD) in pseudogout: rhomboid, positively birefringent
• Hemarthrosis (bloody fluid): suggests trauma, pigmented villonodular synovitis, or coagulopathy

Arthrocentesis Sites (Rosen's Emergency Medicine)

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10. Step 5 - Imaging

Plain Radiographs - Diagnostic Clues

• CT scan: better for fractures, osteomyelitis, bone disease
• MRI: superior for early synovitis, cartilage, tendon/ligament pathology, sacroiliitis
• Ultrasound: bedside effusion detection, guides arthrocentesis, detects early synovitis and erosions

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11. Approach Summary Algorithm

Acute Joint Pain
        │
        ▼
  Number of Joints?
  ┌─────┴─────────────┐
Mono/Oligo          Polyarticular
  │                     │
  ▼                     ▼
Arthrocentesis      Symmetric?
MANDATORY          ┌────┴────┐
  │               Yes       No
  ▼                │         │
Fluid analysis    RA,       PsA, ReA,
- WBC count     Viral      Gout, AS
- Crystals
- Culture
  │
  ▼
WBC >50,000 or
positive culture?
  │
 Yes → Septic Arthritis (IV antibiotics + urgent washout)
  No → Crystal? (gout/pseudogout) or Inflammatory (RA, etc.)

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12. Key Points / Pitfalls

1. Septic arthritis is the #1 must-not-miss diagnosis in acute monoarthritis - do not delay aspiration based on clinical grounds alone
2. Serum uric acid is unreliable during acute gout - levels may be normal; diagnosis requires synovial fluid crystal analysis
3. Most patients with septic arthritis are afebrile on presentation - do not use absence of fever to rule out infection
4. Morning stiffness >1 hour is a hallmark of inflammatory arthritis (especially RA); stiffness lasting <30 minutes (gel phenomenon) suggests OA
5. Acute monoarthritis can be the first presentation of systemic rheumatologic disease (e.g., RA, PsA, reactive arthritis) - always consider
6. Drug-induced arthropathy is common - always take a thorough medication history
7. Anti-CCP antibodies are more specific for RA than RF and may be positive years before clinical disease

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