Figure 1.

(a) Dorsal and (b) lateral view of the basic anatomic structures that comprise the finger. The proximal interphalangeal (PIP) joint is composed of the proximal and middle phalanges, the radial and ulnar collateral ligaments to provide lateral and medial joint stability to prevent dislocation, and the volar plate to provide stability in the anterior and posterior directions to prevent hyperextension. Each collateral ligament comprises a proper and accessory ligament that opposes each other’s actions. The proper collateral ligament (PCL) is the most important stabilizing structure of the PIP joint in flexion, and the volar portion of the PCL and the proximal portion of the accessory collateral ligament (ACL) stabilize the PIP joint in extension. The central slip reinforces the joint dorsally and helps to resist volar subluxation and dislocation. The DIP joint is made up of the middle and distal phalanges but functions in a manner similar to the PIP joint. The radial and ulnar collateral ligaments and volar plate remain present, but dorsal support is provided by the lateral bands and terminal insertion of the extensor mechanism.