What condition results from a rupture or tear of the central portion of the extensor tendon?

The condition resulting from a rupture or tear of the central portion of the extensor tendon is known as Boutonniere Deformity. This injury is characterized by the inability to extend the finger at the proximal interphalangeal joint, often leading to a characteristic "buttonhole" appearance. The central slip of the extensor tendon, which is responsible for the extension at this joint, becomes ruptured or displaced, causing flexion at the proximal interphalangeal joint and hyperextension at the distal interphalangeal joint.

In contrast, De Quervain's Tenosynovitis involves inflammation of the tendons on the side of the wrist and is not primarily related to the extensor tendon. Mallet Finger, while also involving an extensor tendon injury, refers specifically to an injury where the tendon des not rupture, but the distal part of the finger is unable to extend due to either a rupture or fracture of the distal phalanx. Kienbock's Disease is a condition related to the avascular necrosis of the lunate bone in the wrist and does not involve a tear of the extensor tendon. Understanding these distinctions is crucial for accurate diagnosis and treatment.