The palmar plate (volar plate) of the thumb interphalangeal joint is a fibrocartilaginous structure on the palmar surface of the thumb IP joint, attached proximally to the proximal phalanx neck (via check-rein extensions) and distally to the base of the distal phalanx. It resists hyperextension of the thumb IP joint. Two sesamoid bones may be embedded within it at the distal attachment. It works with the collateral ligaments to provide IP joint stability.
Prevents hyperextension of the thumb IP joint; provides the palmar articular surface during full IP joint extension; the proximal check-rein attachments limit the rate of IP joint extension; distally it anchors the FPL insertion zone.
Thumb IP joint dorsal dislocation from hyperextension tears the palmar plate from its distal insertion (distal avulsion) or occasionally ruptures it in the mid-substance. Reduction is usually straightforward with traction and flexion. A ruptured palmar plate with interposition into the joint may prevent closed reduction (irreducible dislocation requiring open reduction). Post-reduction, extension block splinting at 15-20 degrees of flexion allows palmar plate healing while preventing re-dislocation. The sesamoid bones at the IP joint help identify the palmar plate on radiograph and may avulse with the plate in hyperextension injuries.
Forced hyperextension of the thumb IP joint tears the palmar plate producing IP joint dislocation; closed reduction by traction and flexion restores joint congruity confirmed on radiograph; extension block splinting at 20 degrees for 4-6 weeks allows palmar plate healing; inability to close-reduce suggests palmar plate interposition requiring open reduction.
