Answer :
Swan neck deformity: Hyperextension of the PIP joint and flexion of the DIP joint. Boutonniere deformity: Flexion of the PIP joint and hyperextension of the DIP joint.
Swan neck deformity and boutonniere deformity are two hand deformities that can occur due to certain conditions or injuries.
Swan neck deformity is characterized by hyperextension of the proximal interphalangeal joint (PIP) and flexion of the distal interphalangeal joint (DIP) of the finger. This causes the finger to resemble a swan's neck. It can be caused by conditions such as rheumatoid arthritis or trauma to the finger. For example, if the volar plate, which helps stabilize the PIP joint, is damaged, it can lead to swan neck deformity. In this condition, the PIP joint is hyperextended, and the DIP joint is flexed.
Boutonniere deformity, on the other hand, is characterized by flexion of the PIP joint and hyperextension of the DIP joint. This results in a finger that looks like a buttonhole. Boutonniere deformity can occur due to a rupture or tear of the central slip of the extensor tendon, which is responsible for extending the PIP joint. It can be caused by conditions such as rheumatoid arthritis, trauma, or repetitive strain injuries. In this condition, the PIP joint is flexed, and the DIP joint is hyperextended.
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