Swan Neck Deformity
The pattern you describe—flexion deformity of the second DIP joint and dorsiflexion (hyperextension) of the second PIP joint—is called a swan neck deformity 1.
Definition and Mechanism
Swan neck deformity is characterized by:
- Hyperextension at the PIP joint
- Flexion at the DIP joint
This deformity results from an imbalance of the tendons and ligaments in the finger 1. The pathology is divided into three categories:
- Intrinsic (related to intrinsic hand muscles)
- Extrinsic (related to extrinsic tendons)
- Articular (related to joint structures themselves)
Clinical Significance
This deformity represents a disruption of the normal biomechanical balance of the finger's extensor apparatus. The hyperextension at the PIP joint allows the extensor mechanism to shift dorsally, while compensatory flexion occurs at the DIP joint to maintain some functional finger position.
Contrast with Boutonnière Deformity
It's important to distinguish this from the opposite pattern—boutonnière deformity—which presents with:
- Flexion at the PIP joint
- Hyperextension at the DIP joint
- Results from disruption of the central slip of the extensor tendon 1, 2
Management Considerations
Treatment depends on the underlying cause and includes both surgical and non-operative options 1. The functional gain and risks must be realistically assessed before pursuing any intervention. In cases where degenerative changes develop in the PIP joint from chronic deformity, more advanced interventions may be required 2.