Metacarpal Fractures

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Clinically Relevant Anatomy

The five metacarpal bones form the skeleton of the palm of the hand between the carpal bones and the phalanges. Each are comprised of a base, shaft, and head. The proximal bases of the metacarpals articulate with the carpal bones, and the distal heads of the metacarpals articulate with the proximal phalanges and form the knuckles. The 1st metacarpal (of the thumb) is the thickest and shortest of these bones. The 3rd metacarpal is distinguished by a styloid process on the lateral side of its base. Soft tissues generally involved with fractures include cartilage, joint capsule, ligaments, fascia, and the dorsal hood fibers. With severe polytrauma cases, the tendons and nerves adjacent to the fracture can also be injured¹.

Mechanism of Injury / Pathological Process

Metacarpal Base Fractures: These fractures are intra-articular and result from high forces (violent accidents), direct blows, or crushing injuries that disrupt the rigid carpal ligaments, or overwhelm the normal flexibility of the ulnar metacarpals. They also occur with an avulsion of the wrist flexors or extensors, that insert on the metacarpal base, resulting from a direct blow or torsional injury. The most common occurrence is at the 5th metacarpal-hamate articulation. The healing rate varies from three to six weeks¹.

Metacarpal Shaft Fractures: These fractures are extra-articular and are caused by longitudinal compression, torsion, or direct impact that may result from a fall, blow, or crushing force that usually angulates dorsally. They are described by the fracture configuration as transverse, oblique, spiral, or comminuted. Metacarpal shaft fractures are slower to heal than the more distal or proximal locations because of the predominantly cortical bone found there. The healing rate varies from three to seven weeks¹.

Metacarpal Neck Fractures: Most common metacarpal fracture. The weakest point of the metacarpal bone is the extra-articular neck. These fractures result from a compression force such as a direct blow with a closed fist. The 4th and 5th metacarpals are most often involved and are referred to as a “fighter’s” or “boxer’s” fracture. Trauma causes the fractured metacarpal head to displace with volar angulation. The healing rate is three to five weeks¹.

Metacarpal Head Fractures: These fractures are intra-articular and are caused by direct impact and high axial loads that can involve avulsion of the collateral ligaments, including a fracture fragment, fracture of one or both condyles, or shattering of the joint surface into many small, comminuted pieces¹.

Clinical Presentation

Metacarpal fractures represent 35% of all hand fractures and up to 85% occur in men2,3. Sports account for 12.8% of all fractures, with simple falls among elderly people (45.3%) and direct blows/assault (14.1%) being the two major causes⁵. Due to their good blood supply, metacarpal fractures heal rapidly with osseous restoration in six weeks1. Fractures of these bones are described at four distinct locations: the base, shaft, neck and head. Of all hand fractures, fractures of the 5th metacarpal bone at the level of the neck are the most common, accounting for 16-34%^2,4. Patients with metacarpal fractures generally present with pain, swelling, ecchymosis or discoloration, limitation of movement, and often deformity. Knuckle asymmetry may be observed, and the knuckle may appear to be missing. Finger misalignment may also be noted. In patients with a metacarpal head fracture, axial compression of the extended digit causes severe discomfort. In patients with a metacarpal base fracture, movement of the wrist or longitudinal compression exacerbates the pain. Any metacarpal fracture angulation can produce a pseudo-claw deformity.

Diagnostic Procedures

Physical examination and radiographs can be considered the definitive standard for diagnosis of metacarpal fractures. Physical examination of a suspected metacarpal fracture should concentrate on hand deformity, tenderness, digit malrotation, and presence of open wounds. Painful range of motion, point specific bone tenderness and ecchymosis should be considered red flags for fractures during a clinical physical examination. Routine radiographs include three views: anteroposterior, lateral, and oblique. These views assist in properly assessing angulation of fracture fragments as well as involved joint surfaces. Computed Tomography scans, or CT scans, may be ordered to evaluate complicated fractures^2,6.

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