Pain Character — Mechanical Wear vs Inflammatory Flare
OA pain worsens with use; RA pain flares with rest and inflammation.
- Mechanical: OA Pain Pattern (worse with activity)
- Inflammatory: RA Pain Pattern (worse after rest)
- >50: OA Typical Onset Age (gradual over years)
- 30–60: RA Typical Onset Age (weeks to months)
How OA pain behaves
Pain increases through the day, eases with rest.
How RA pain behaves
Pain and swelling dominate mornings and after inactivity.
Systemic clues
RA often brings fatigue, low fever, and malaise; OA rarely does.
Stiffness Duration — the Classic 30-Minute Cutoff
Stiffness under 30 minutes points to OA; over an hour points to RA.
- <30 min: OA Stiffness Duration (brief, localized)
- >60 min: RA Stiffness Duration (prolonged, diffuse)
- OA trait: Gel Phenomenon (brief stiffness after rest)
- High: ACR/EULAR Weight (stiffness in RA criteria)
Why RA stiffness lasts longer
Ongoing synovial inflammation keeps joints stiff for hours.
Why OA stiffness resolves fast
Cartilage wear causes brief gelling, not sustained inflammation.
Using the slider
Drag stiffness duration and watch RA likelihood climb past 60 minutes.
Symmetry Pattern — Which Joints, and How Many Sides
RA strikes symmetric small joints; OA favors asymmetric load-bearing ones.
- Bilateral: RA Symmetry (same joints, both sides)
- Asymmetric: OA Symmetry (load-dependent side)
- MCP, PIP, wrist: RA Hallmark Joints (spares DIP joints)
- Knee, hip, DIP: OA Hallmark Joints (spares MCP joints)
RA joint map
Small hand joints, wrists, and MCPs light up on both hands.
OA joint map
Knees, hips, and DIP joints bear the wear pattern.
Symmetry score logic
Score rises as marker and stiffness inputs shift toward RA.
Lab Panel — CRP, ESR, RF, and Anti-CCP
Elevated CRP/ESR and positive RF or anti-CCP favor RA over OA.
- Elevated: CRP in RA (active synovitis)
- Normal: CRP in OA (non-inflammatory)
- ~95%: Anti-CCP Specificity (for RA diagnosis)
- ~70%: RF Sensitivity (positive in RA)
Reading the marker slider
Higher marker level simulates rising CRP, ESR, RF, and anti-CCP.
Why OA labs stay quiet
OA is degenerative, not autoimmune, so inflammatory labs stay normal.
Why RA labs spike
Autoantibodies and cytokines drive measurable systemic inflammation.
Final Call — Weighing the Combined Evidence
Stiffness, symmetry, and markers combine into one confidence score.
- 4: Inputs Combined (stiffness, symmetry, markers, joints)
- OA % vs RA %: Output (relative likelihood)
- Weighted sum: Confidence Basis (slider-driven)
- Screening aid: Clinical Use (not a replacement for exam)
How the verdict is computed
Stiffness and marker sliders drive a weighted RA-vs-OA score.
Reading the confidence bar
A wider red bar means stronger evidence for RA.
Next steps in real care
Imaging and rheumatology referral confirm what labs suggest.