Certified Hand Therapist (CHT) Practice Exam

Which condition presents with passively flexible DIP joint in Pseudo-boutonniere deformity?

1. Fracture of the PIP

2. Avulsion of the collateral ligament

3. Hyperextension injury at the PIP joint

4. Distal phalanx fracture

The correct answer is: Hyperextension injury at the PIP joint

The condition characterized by a passively flexible distal interphalangeal (DIP) joint in a pseudo-boutonniere deformity is associated with a hyperextension injury at the proximal interphalangeal (PIP) joint. In this scenario, the hyperextension trauma causes the central slip of the extensor tendon to be compromised or disrupted. As a result, the PIP joint becomes unstable, leading to a tendency for the DIP joint to flex while still allowing passive flexion. In a pseudo-boutonniere deformity, the intrinsic muscles remain intact, which permits the passively flexible DIP joint. This phenomenon occurs because the flexion of the DIP is not due to a direct influence of the flexor tendons but rather a result of the altered mechanics caused by the primary injury at the PIP. In contrast, other options involving fracture or ligament avulsion do not typically present with the same passive flexibility at the DIP joint since these injuries tend to impact the overall integrity and coordination of the hand's movement. For instance, an avulsion of the collateral ligament would compromise joint stability, disrupting the normal range of motion, while a fracture of the PIP would lead to more significant restrictions in joint movement due to pain and mechanical instability