Phalanx Fractures of the Hand

Phalanx fractures are some of the most common fractures occurring in humans. They are often noted to be in the more common of all upper extremity fractures and present with a long list of post-injury complications regardless of treatment, most commonly in relation to finger and hand function. Nonetheless, they generally heal well with either conservative or surgical treatment.

Phalanx fractures are most often classified using a descriptive pattern noting location, angulation, and displacement. They are often divided in location to the base, shaft, or condyle of their respective phalanx. Therefore, understanding of proper diagnosis and treatment of phalanx fractures starts with a knowledge base of the intricate anatomy.

Each thumb (first digit) contains a proximal and distal phalanx, while the index (second digit), long (third digit), ring (fourth digit), and small (fifth digit) fingers all contain a proximal, middle, and distal phalanx. The proximal and middle phalanges can be subdivided into a base, shaft, and head from proximal to distal. The heads of the middle and proximal phalanges are formed by two condyles separated by an intercondylar notch. The proximal and middle phalanges tend to have a slight palmar concavity, while the distal phalanx is relatively straight. The distal phalanx is divided into a base, shaft, and tuft and is protected dorsally by the nail plate with dense fibrous connections to the surrounding soft tissue.

The base of each proximal phalanx articulates with its respective metacarpal forming the metacarpophalangeal (MCP) joints. The base of the middle phalanx in digits 2 to 5 articulates with the head of the respective proximal phalanx to form the proximal interphalangeal (PIP) joint. The base of the distal phalanx in digits 2 to 5 articulates with the head of the respective middle phalanx to form the distal interphalangeal (DIP) joint. The articulation between the head of the proximal phalanx and the base of its respective distal phalanx forms the interphalangeal (IP) joint of the thumb. Collateral ligaments lie on radial and ulnar borders of each of these joints and are most taut at about 90 degrees of flexion. The volar plate is a strong ligamentous structure overlying the volar aspect of the joints that resists hyperextension.

The soft tissue anatomy surrounding the phalanges is intricate with distinct flexor and extensor mechanisms that contribute to motion and overall stabilization of fracture fragments. The flexor digitorum superficialis (FDS) tendon passes over the volar surface of the MCP joint, proximal phalanx, PIP joint, where it splits into two slips, and inserts on the junction of the proximal and middle one-third of the middle phalanx. The flexor digitorum profundus (FDP) tendon passes dorsal to the FDS tendon over the volar aspect of the MCP joint, proximal phalanx, PIP joint passing between the two slips of the FDS tendon, middle phalanx, DIP joint, and inserts on the base of the proximal phalanx. A complex network of vincula acts as a tether between the flexor tendons and the proximal and middle phalanges. The extensor hood is the complex expansion of the extensor tendons on the dorsal aspect of the finger. The central slip of the extensor mechanism attaches to the base of the middle phalanx dorsally while lateral bands proceed to a terminal slip, which attaches to the base of the distal phalanx. Intrinsic muscles of the hand (lumbricals and interossei) attach to the lateral bands of the extensor mechanism. Sagittal bands on each side of the finger attach the extensor hood to the volar plate and flexor tendon sheath near the PIP joint.

A single digital nerve and artery lie on both the radial and ulnar aspects of the finger slightly volar to midline with small branches and capillaries supplying the surrounding soft tissue and superficial structures.