First (thumb) metacarpal fractures

INTRODUCTION

Metacarpal fractures are common [1]. They account for 30 to 40 percent of all hand fractures. First metacarpal (thumb) fractures make up almost 25 percent of all metacarpal fractures, placing them second only to 5th metacarpal fractures in terms of frequency. Of these fractures, over 80 percent involve the base of the metacarpal

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

PERTINENT ANATOMY AND CLASSIFICATION

The thumb is distinct from the other fingers anatomically and biomechanically. Accordingly, fractures to the thumb are considered separately from other metacarpal fractures. The majority of thumb metacarpal fractures occur at the base. Fractures of the thumb metacarpal are classified into four patterns (figure 1). Types I and II are intraarticular fractures and Types III and IV are extraarticular. Discerning whether the articular surface is involved in the fracture is critical as this dictates management.

• Type I injury ("Bennett's fracture") is a fracture-dislocation of the base of the metacarpal (picture 1A). In this injury, a proximal metacarpal fragment maintains its ulnar aspect attachment to the trapezium via the volar ligament. The distal aspect of the metacarpal is supinated and dislocated radially by the adductor pollicis. The proximal aspect of this fragment is pulled proximally by the abductor pollicis longus.
• Type II injuries ("Rolando's fracture") can be thought of as a comminuted version of a Bennett's fracture, in which the fragments may form a T or Y pattern at the base of the MC (picture 2). Severe comminution may occur and, in these cases, the classic Y or T pattern is not present. Type II fractures are quite difficult to treat, but fortunately, are a rare type of first metacarpal fracture.
• Type III fractures are the most common thumb fractures and are extraarticular (picture 1B-C), either transverse or, less commonly, oblique.
• Type IV fractures are extraarticular pediatric injuries involving the proximal physis and are not addressed in this section.

MECHANISM OF INJURY

First metacarpal fractures typically occur with an axial load to a partially flexed thumb. Fistfights are a frequent culprit in these fractures. First metacarpal fractures can also be seen with hyperabduction and/or hyperflexion occurring with a fall. If a torsional force is included in the mechanism, the fracture will often be oblique. Intraarticular and extraarticular fractures occur from similar mechanisms.