What Are Distal Interphalangeal (DIP) Joints?
The distal interphalangeal (DIP) joints are the finger joints located closest to the fingertips, positioned between the middle phalanx (middle finger bone) and the distal phalanx (fingertip bone). 1
Anatomical Location and Structure
DIP joints are present in the index, middle, ring, and small fingers (four joints total in each hand), while the thumb has only an interphalangeal (IP) joint since it lacks a middle phalanx 1
These joints are subjected to the highest joint forces in the hand during gripping and pinching activities 2
The bony anatomy shows asymmetry between the distal phalanx grooves and middle phalanx condyles, suggesting a translational component to DIP joint motion rather than pure hinge movement 3
Clinical Significance in Disease
Osteoarthritis Pattern
DIP joints are the primary target of hand osteoarthritis, with at least 60% of individuals older than age 60 having DIP joint arthritis 2, 1
Heberden's nodes are the characteristic clinical finding - these are posterolateral firm/hard bony swellings at the DIP joints that represent osteophyte formation 1
Radiographic features include joint space narrowing, osteophytes, and subchondral sclerosis without systemic inflammatory features 4
Psoriatic Arthritis Pattern
DIP joint involvement is a distinguishing feature of psoriatic arthritis that differentiates it from rheumatoid arthritis, which typically spares the DIPs 1, 5, 6
The inflammation in psoriatic arthritis affects collateral ligaments, extensor tendons, and entheseal insertions at the DIP joints, with diffuse nailbed involvement and bone edema 7
Rheumatoid Arthritis Pattern
- DIP joints are explicitly excluded from rheumatoid arthritis classification criteria by the American College of Rheumatology and European League Against Rheumatism, as RA predominantly affects MCP and PIP joints while sparing DIPs 5, 6
Examination Approach
Palpate for bony enlargement (Heberden's nodes) suggesting osteoarthritis versus soft tissue swelling suggesting inflammatory arthritis when examining DIP joints 5
DIP involvement, especially if asymmetric, should prompt consideration of psoriatic arthritis or osteoarthritis rather than rheumatoid arthritis 5, 6
Look for associated nail changes (pitting, onycholysis) and psoriatic plaques when DIP arthritis is present, as these strongly suggest psoriatic arthritis 4, 6
Imaging Considerations
Standard three-view radiographic examination of the hand shows most DIP joint fractures and dislocations, though an internally rotated oblique projection increases diagnostic yield 1
For suspected mallet finger injuries, radiographs assess for bony avulsion at the extensor mechanism insertion to the DIP joint, with involvement of more than one-third of the articular surface requiring operative fixation 1