Base Of The Middle Phalanx, Posterior View

Description

Middle phalanx base anatomy is centered on the proximal articular surface that accepts the head of the proximal phalanx to form the proximal interphalangeal (PIP) joint. From a posterior (dorsal) perspective, the concave, shallowly indented base faces proximally, while the shaft extends distally in the midline toward the head of the middle phalanx. Along the dorsum at the base, the bony contour transitions from the articular margin to the nonarticular dorsal surface where the extensor mechanism anchors, with the radial and ulnar margins flanking the joint line laterally. Dorsal base detail matters because the central slip of the extensor digitorum (with contributions from extensor indicis or extensor digiti minimi depending on digit) inserts onto the dorsal base of the middle phalanx, a relationship that underlies boutonniere deformity after central slip rupture and explains the clinical focus on dorsal PIP lacerations. Small avulsion fragments at this location can be subtle but clinically meaningful, and fractures involving the articular rim of the base affect PIP stability and congruence even when the shaft is intact. Joint alignment is everything. The fixed posterior view helps separate the dorsal nonarticular surface from the proximal articular concavity and clarifies the dorsal lip where extensor-related avulsions and posttraumatic irregularity are assessed. Use this illustration for hand and upper limb anatomy teaching, orthopedic and plastic surgery lectures on PIP fracture-dislocations, and figure support in manuscripts discussing extensor tendon injuries, boutonniere patterns, and dorsal avulsion fractures at the middle phalanx base. Anatomical accuracy verified by SciePro's Medical Advisory Board.