Are metacarpophalangeal (MCP) joints typically involved in osteoarthritis (OA)?

MCP Joint Involvement in Osteoarthritis

You are correct that MCP joints are typically spared in classic hand osteoarthritis, but this is not absolute—MCP involvement occurs in approximately 32.5% of hand OA patients, though it is generally mild and predominantly affects the first and second MCP joints. 1

Classic Hand OA Joint Distribution

The traditional teaching that MCP joints are spared in osteoarthritis is largely accurate for typical hand OA patterns:

• Primary targets of hand OA are the DIP joints (Heberden's nodes), PIP joints (Bouchard's nodes), and thumb base (CMC joint), not the MCP joints 2, 3, 4
• The EULAR guidelines specifically identify IPJ OA (interphalangeal joints) and thumb base OA as the recognized subsets of hand OA 2
• MCP joint sparing is a key distinguishing feature from rheumatoid arthritis, which predominantly affects MCP and PIP joints while sparing DIPs 5

When MCP Joints ARE Involved in OA

Recent evidence challenges the absolute sparing of MCP joints:

• Radiographic MCP joint OA (defined as ≥2 MCP joints with Kellgren/Lawrence score ≥2) was present in 32.5% of symptomatic hand OA patients in a 2022 French cohort study 1
• When present, MCP OA is typically not severe and predominates at the first and second MCP joints 1
• MCP involvement is more frequent in the dominant hand, suggesting mechanical factors 1

Mechanical vs. Systemic Factors

MCP joint involvement in hand OA appears predominantly related to mechanical rather than systemic factors:

• Manual occupation increases the odds of MCP OA by 3.74-fold (95% CI 1.21-11.54) 1
• Occupational factors involving repetitive joint use increase OA risk, with differential joint distribution depending on specific repetitive tasks 2, 3
• MCP OA was associated with older age (OR 1.05 per year), scaphotrapezial OA (OR 2.18), and high number of PIP joints with OA, but not with metabolic syndrome or symptom severity 1
• Certain occupations like cotton picking increase HOA risk, mainly targeting DIP and MCP joints 2

Clinical Implications for Diagnosis

When evaluating hand arthritis, MCP involvement should prompt consideration of:

• Rheumatoid arthritis (MCP + PIP involvement with DIP sparing is the classic RA pattern) 5
• Psoriatic arthritis (can affect any joint including MCPs, often asymmetric with dactylitis) 5
• Erosive OA (targets IPJs specifically; one study showed erosive OA had significantly higher scores at DIP, PIP, and thumb IP joints, but not at MCP joints) 2
• Hemochromatosis (MCP + wrist involvement pattern) 5

Key Distinguishing Features

Look for these clinical clues to differentiate OA from inflammatory arthritis:

• Bony enlargement (Heberden's/Bouchard's nodes) = osteoarthritis 3, 5
• Soft tissue swelling = inflammatory arthritis 5
• Morning stiffness <30 minutes = OA; >30 minutes = inflammatory arthritis 3, 5
• Pain on usage that worsens with movement and improves with rest = OA 3

Bottom Line

Your understanding is fundamentally correct for classic hand OA patterns, but recognize that MCP involvement can occur in approximately one-third of hand OA patients, particularly with mechanical stress, manual occupations, and in the dominant hand. 1 The key is that when MCP joints are involved in OA, the involvement is typically mild and associated with mechanical factors rather than the systemic inflammatory processes seen in rheumatoid arthritis. 1