Certified Hand Therapist (CHT) Practice Exam

What is the "critical corner" in relation to joint stability?

1. Where the flexor tendons converge at the wrist

2. At the PIP joint where three ligaments converge

3. The point of maximum joint mobility

4. Where the extensor tendons meet the phalanges

The correct answer is: At the PIP joint where three ligaments converge

The "critical corner" refers specifically to the anatomical junction at the proximal interphalangeal (PIP) joint, where three key ligaments converge: the central slip, the lateral bands, and the volar plate. This intersection is crucial for joint stability. The integrity of these ligaments is vital for maintaining the alignment and functionality of the PIP joint during motion, particularly in grasp and pinch activities. When the ligaments at this critical corner are compromised, the stability of the joint can be severely affected, leading to conditions such as swan neck deformity or other joint-related dysfunctions. Understanding this anatomical feature is essential for clinicians in assessing joint stability and developing appropriate rehabilitation protocols for patients with hand and finger injuries. The other contexts provided do not apply to the concept of the "critical corner" in the same way. The convergence of flexor tendons at the wrist is important for overall hand function but is not specifically related to joint stability as defined by the interaction of the PIP joint ligaments. Similarly, maximum joint mobility and the meeting of extensor tendons with the phalanges pertain to different functional aspects of finger mechanics rather than the specific stability provided by the ligaments at the PIP joint.