Background

Interphalangeal (IP) joint dislocations of the fingers and toes are common.^{[1, 2]} Typically associated with forced hyperextension or hyperflexion of the digit, they require immediate reduction. The IP joint is a hinge joint that allows only flexion and extension and consists of several ligamentous complexes. The volar plate provides stability against hyperextension injury and dorsal dislocation of the phalanx. It often ruptures during a dorsal dislocation and may be associated with an avulsion fracture at the base of the phalanx. The strong collateral ligament complex resists hyperextension and lateral dislocation injury. The extensor hood complex stabilizes against hyperflexion injury and volar displacement of the phalanx.

Dislocations of the distal IP (DIP) joint of the fingers are often associated with fracture, tendon rupture, and/or proximal interphalangeal (PIP) joint involvement. Upon axial loading and hyperextension of the fingertip, the volar plate of the DIP joint tears and the joint may be displaced.^[3]

Pathophysiology

Forced hyperextension with axial compression causes a dorsal dislocation of the proximal IP (PIP) or distal IP (DIP) joint, in which the middle (or distal) phalanx is dislocated dorsal to the proximal (middle) phalanx.^{[4, 5]} Forced hyperflexion results in a volar IP joint dislocation (eg, where the distal phalanx is dislocated volar to the middle phalanx).^[6]

Patients whose digits have neurovascular compromise, an open joint dislocation, ligamentous or volar plate rupture, joint instability, or an associated fracture should have immediate orthopedic consultation. All finger dislocations should be reevaluated subsequently by an orthopedic or hand specialist to manage potential subtle ligamentous, cartilaginous, or bony injury.^{[7, 8]} A lateral or volar PIP joint dislocation, although rare, requires an orthopedist for possible open reduction with internal fixation. A dislocation of the metacarpophalangeal (MCP) joint, although rare in adults, may be more common in children.^{[9, 10]} MCP dislocation usually requires open reduction by a pediatric orthopedist.

Epidemiology

Frequency

United States

Dorsal PIP dislocation is the most common IP dislocation.^[11] Volar IP joint dislocations are relatively uncommon.^[6] PIP joint dislocations occur more frequently than DIP joint dislocations.