Key Differences Between Osteoarthritis (OA) and Rheumatoid Arthritis (RA) in the TMJ

Feature	Osteoarthritis (OA)	Rheumatoid Arthritis (RA)
Etiology	Mechanical wear and tear (degenerative)	Autoimmune inflammation
Onset	Typically later in life (40+), often unilateral	Can occur at any age, often bilateral
Joint Involvement	Usually unilateral; localized to overused joints	Typically bilateral and symmetric
Pain	Deep, dull ache worsened by function	Achy or sharp pain with morning stiffness lasting >1 hour
Joint Sounds	Crepitus, grating, or clicking common	May be silent or with mild crepitus
Inflammation	Mild or absent	Prominent inflammation, swelling, warmth
Deformity	Flattening and osteophyte formation of condyle	Condylar erosion, flattening, possible ankylosis
Radiographic Findings	Condylar flattening, osteophytes, subchondral sclerosis, joint space narrowing	Erosions of condyle, loss of cortical outline, decreased joint space, pannus formation
Synovial Fluid	Non-inflammatory	Inflammatory with elevated WBCs
Lab Tests	Normal labs	Elevated ESR, CRP, positive RF or anti-CCP antibodies
Systemic Features	None	Yes – fatigue, malaise, joint involvement elsewhere
Progression	Slowly progressive	Can be rapid and destructive