Swan neck deformity is largely due to what anatomical change?

Swan neck deformity is characterized by hyperextension at the proximal interphalangeal (PIP) joint and flexion at the distal interphalangeal (DIP) joint. The primary anatomical change that leads to this deformity is the stretching or laxity of the volar plate at the PIP joint.

The volar plate is a fibrous structure that functions to stabilize the PIP joint and prevent hyperextension. When the volar plate is stretched or compromised, it loses its ability to maintain proper joint alignment, resulting in the characteristic hyperextension of the PIP joint seen in Swan neck deformity. This weakening of the volar plate often occurs in conditions such as rheumatoid arthritis, contributing to the overall instability and deformity of the finger.

Understanding this anatomical change helps clarify the mechanism behind Swan neck deformity, highlighting the role of the volar plate in maintaining joint integrity.