Joints Affected by Rheumatoid Arthritis
Rheumatoid arthritis primarily affects small joints of the hands and feet, along with the wrists, and characteristically involves these joints in a symmetric pattern. 1
Small Joints Most Commonly Affected
The classification criteria for RA specifically define small joints as: 1
- Metacarpophalangeal (MCP) joints of the hands
- Proximal interphalangeal (PIP) joints of the fingers
- 2nd through 5th metatarsophalangeal (MTP) joints of the feet
- Thumb interphalangeal joints
- Wrists
Small joint involvement scores higher in diagnostic algorithms because it is the hallmark presentation of RA. 1, 2 The American College of Rheumatology criteria require at least one small joint to be involved to achieve higher diagnostic scores, reflecting the disease's predilection for these joints. 2
Large Joints Frequently Involved
Large joints are also commonly affected and include: 1, 3
Large joint destruction occurs frequently in RA and can progress significantly, though it is less emphasized in diagnostic criteria. 3 Studies show that 33 out of 264 large joints demonstrated radiographic progression over 2 years in RA patients, indicating substantial involvement. 3
Joints Characteristically Spared
The distal interphalangeal (DIP) joints, first carpometacarpal joints, and first metatarsophalangeal joints are specifically excluded from RA assessment criteria because they are rarely involved. 1 Additionally: 5
- Sacroiliac joints are rarely affected
- Lumbar spine joints are rarely involved
- DIP joints are characteristically spared (this helps distinguish RA from osteoarthritis and psoriatic arthritis)
Clinical Pattern Recognition
Morning stiffness lasting ≥1 hour in and around affected joints is a typical early manifestation, reflecting the inflammatory burden during inactivity. 2, 5 The clinical presentation typically includes: 5
- Symmetric joint involvement (bilateral and mirror-image distribution) 5, 4
- Tender swelling on palpation with early severe motion impairment 5
- Hand involvement as the typical early manifestation, with MCP, PIP, and wrist synovitis causing characteristic swelling even before radiologic bone damage appears 5
Urgent Referral Indicators
Urgent specialist referral is warranted when small joints of hands or feet are affected, even with normal acute-phase reactants or negative rheumatoid factor. 1, 2 This emphasizes the critical importance of recognizing small joint involvement for early diagnosis and treatment initiation. 1
Radiographic Features by Joint Location
The most frequently involved joints radiographically are the small joints of hands and feet, wrists, knees, elbows, and glenohumeral/acromioclavicular joints. 4 The radiographic hallmarks include soft tissue swelling, osteoporosis, joint space narrowing, and marginal erosions with relatively minimal reactive bone formation. 4
The combination of symmetric small joint involvement (especially MCPs, PIPs, and MTPs) with wrist involvement is the signature pattern of rheumatoid arthritis. 1, 5, 4