Which joint does not help distinguish between osteoarthritis and rheumatoid arthritis?

• A. PIP joints
• B. MCP joints
• C. Wrists
• D. DIP joints

Answer: (A)

Understanding how osteoarthritis and rheumatoid arthritis typically affect the small joints of the hand helps you separate the two. Rheumatoid arthritis classically involves the MCP and PIP joints and often the wrists, reflecting a synovitis pattern that targets these joints. Osteoarthritis, on the other hand, commonly involves the DIP joints (and to some extent the PIP joints) but usually spares the MCP joints.

Because the PIP joints can be involved in both conditions, their involvement does not point you toward one diagnosis over the other. In contrast, involvement of the DIP joints leans toward osteoarthritis, and involvement of the MCP joints or wrists leans toward rheumatoid arthritis. So the joint pattern that does not help distinguish between OA and RA is the PIP joints, since they can be affected by both diseases.