Fractures of the proximal phalanx can be complex owing to forces exerted on the fracture fragments by a number of muscles and tendons which often result in angular or rotational deformity.
This topic review will discuss fractures of the proximal phalanx. Finger anatomy, other common finger injuries, and thumb injuries are reviewed separately. (See "Finger and thumb anatomy" and "Distal phalanx fractures" and "Extensor tendon injury of the distal interphalangeal joint (mallet finger)".)
Proximal phalanx fractures are often unstable due to the forces exerted on the fracture fragments by both the intrinsic and extrinsic hand muscles via their respective tendons . Anatomy of special importance to proximal phalanx fractures is described below; a more detailed discussion of finger anatomy is found elsewhere. (See "Finger and thumb anatomy".)
Both the lumbrical muscles, which originate on the tendons of the flexor digitorum profundus, and the interosseous muscles, which originate on the metacarpals, insert at or near the proximal phalanx. The lumbricals are involved in flexion of the metacarpal-phalangeal (MCP) joint and extension of the interphalangeal joints of the fingers. The interossei are involved in finger abduction and adduction. The extensor digitorum tendon runs along the dorsum of the proximal phalanx, while the flexor digitorum profundus and superficialis tendons run along the volar aspect.
Proximal phalanx fractures often present with apex volar angulation. Interosseous muscles pull the proximal fragment into a volar position while the distal fragment is pulled dorsally by the extensor hood.