Metacarpal neck fractures

INTRODUCTION

Metacarpal fractures are common injuries that account for 30 to 40 percent of all hand fractures [1]. Metacarpal neck fractures are the most common and are usually due to direct trauma. They most often involve the 5th and, to a lesser degree, the 4th metacarpal neck. Fractures of the 5th metacarpal neck ("boxer's fractures") account for approximately 10 percent of all hand fractures.

This topic will review issues related to metacarpal neck fractures. A general overview of metacarpal fractures is presented separately. (See "Overview of metacarpal fractures".)

PERTINENT ANATOMY

The heads of the metacarpals are bulbous and "cam" shaped, thereby permitting adduction, abduction, flexion, extension and passive rotation of the fingers. The collateral ligaments join the metacarpal to the proximal phalanx and are taut in flexion, while having some laxity in extension (figure 1). These characteristics have important implications for therapy. During splinting or casting, the metacarpophalangeal (MCP) joints should be immobilized in flexion to prevent shortening of the collateral ligaments and subsequent loss of motion.

MECHANISM OF INJURY

The usual mechanism of injury with metacarpal neck fractures involves direct trauma to a clenched fist, such as punching a wall or solid object. A "roundhouse" type of motion common in street fights (but rare in formal boxing) generally transmits significant force to the 5th metacarpal, resulting in fracture. Experienced boxers rarely sustain this type of fracture and the term "boxer's fracture" is a bit of a misnomer.

SYMPTOMS AND EXAMINATION FINDINGS

In metacarpal neck fractures, the dorsum of the hand is swollen and bony tenderness is found over the fractured metacarpal. Significant tenderness or ecchymosis on the palmar (volar) bony surfaces is highly suggestive of fracture.