Answer :
Final answer:
Boutonniere deformity is caused by a flexion contracture at the proximal interphalangeal (PIP) joint, not by ulnar deviation, hyperextension, or radial deviation.
Explanation:
A boutonniere deformity is caused by a flexion contracture at the proximal interphalangeal (PIP) joint. This condition is characterized by flexion of the PIP joint and sometimes hyperextension of the distal interphalangeal (DIP) joint. It is not caused by ulnar deviation, hyperextension of PIP joint, or radial deviation.
Instead, this deformity typically occurs when the central slip of the extensor tendon that goes over the PIP joint is damaged, leading to the inability to fully extend the PIP joint while the lateral bands slip out of place, resulting in the flexion at this joint.
