What leads to the hyperextension of the PIP joint in Swan Neck Deformity?

The hyperextension of the PIP joint in Swan Neck Deformity primarily occurs due to a combination of intrinsic hand muscle contracture and the tearing of the volar plate. This condition is characterized by an imbalance in the forces acting on the fingers, particularly affecting the flexor and extensor tendons.

When the intrinsic muscles are contracted, they pull on the proximal phalanx, leading to an extended position at the PIP joint. Concurrently, the volar plate, which is a ligament that stabilizes the PIP joint and prevents hyperextension, becomes torn or disrupted. This loss of stability allows for the extension of the PIP joint beyond its normal range, resulting in the distinctive posture seen in Swan Neck Deformity.

Understanding this mechanism is crucial for recognizing the condition and planning appropriate interventions in therapy or surgery to correct the deformity and restore functional use of the hand.