Certified Hand Therapist (CHT) Practice Exam

What is associated with hyperextension injuries in Eaton classification?

1. Tear of the dorsal capsule

2. Displacement of the distal phalanx

3. Avulsion of the volar plate

4. Complete rupture of flexor tendons

The correct answer is: Avulsion of the volar plate

The Eaton classification is primarily focused on the staging of injuries to the thumb's carpometacarpal (CMC) joint, particularly in the context of osteoarthritis and sprains. Hyperextension injuries, specifically in this setting, often lead to injuries of the volar plate. The volar plate is a fibrous structure located on the palmar side of the CMC joint that helps stabilize the joint. When hyperextension occurs, the volar plate can become avulsed from its attachment, resulting in pain, instability, and difficulty with thumb function. This type of injury is significant as it affects the stability of the CMC joint and can lead to chronic issues without appropriate management. In contrast, the other options, while they describe injuries to different structures in the hand, are not directly associated with hyperextension injuries in the Eaton classification. For example, a tear of the dorsal capsule is relevant in different types of wrist injuries, and displacement of the distal phalanx usually relates to other specific hand traumas. Complete rupture of flexor tendons would typically involve a more severe injury pattern that does not specifically pertain to hyperextension mechanisms. Therefore, the avulsion of the volar plate stands out as the critical injury type associated with hyperextension