Surgical Fixation of Metacarpal Fractures

William B. Geissler, MD

Christopher A. Keen, MD

Jarrad A. Barber, MD

Dr. Geissler or an immediate family member has received royalties from Acumed, LLC and Arthrex, Inc., Medartis, Integra; is a member of a speakers’ bureau or has made paid presentations on behalf of Acumed, LLC and Arthrex, Inc., Medartis, Integra; and serves as a paid consultant to or is an employee of Acumed, LLC and Medartis, Integra. Neither of the following authors nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter: Dr. Keen and Dr. Barber.

INTRODUCTION

Metacarpal fractures account for as many as one-third of all hand fractures.¹^,² The prevalence of metacarpal fractures increases from the radial to the ulnar side of the hand, with fractures of the fifth metacarpal being the most common.³ Metacarpal neck fractures are the most common; these usually involve the ring and small metacarpals.³ Fifth metacarpal neck fractures are commonly referred to as boxer’s fractures. These fractures are rarely seen in professional boxers, however, occurring most often in amateur boxers who have hit solid objects or in street brawlers.

The metacarpals are long tubular bones with a relatively flat dorsal surface and medial and lateral cortices that converge along the volar aspect, creating a triangular cross section. The metacarpals become quite narrow in the mid diaphyseal region. The metacarpals have an abundant blood supply, being surrounded by the volar and dorsal interosseous muscles. Although the abundant blood supply from the interosseous muscles may be a blessing, when the musculature is severely disrupted, it initially can result in disabling scarring and intrinsic contractures. The deep transverse intermetacarpal ligament lies at the level of the metacarpal neck, which helps limit deformity with low-energy injuries. When intact, the deep transverse intermetacarpal ligament usually limits shortening to approximately 5 mm. The extensor apparatus surrounds the metacarpophalangeal (MCP) joint. The collateral ligaments originate from the tubercle of the metacarpal head and pass obliquely to the volar aspect of the base of the proximal phalanx. Scar from these ligaments may lead to an extensor contracture at the MCP joint.

Metacarpal fractures are generally the result of one of two mechanisms. The most common mechanism is an axial load transmitted from the MCP joint proximally down the shaft of the metacarpal (Figure 1). This results in various common injuries, from fifth metacarpal neck fractures to higher-energy injuries such as metacarpal shaft fractures. A less common mechanism of injury for fractures of the metacarpals is a crush injury. Crush injuries typically involve multiple metacarpal fractures and are also associated with other fractures and significant soft-tissue trauma.

Transverse and short oblique metacarpal fractures tend to angle dorsally because of the deforming forces of the extrinsic flexor tendons and the intrinsic musculature on the distal fragment. Cadaver studies have shown that as much as 7° of extensor lag and 8% loss of grip strength occur for each 2 mm of metacarpal shortening.⁴^,⁵^,⁶ Intrinsic muscle shortening and muscle tension may lead to progressive grip weakness after approximately 30° of dorsal metacarpal angulation.⁵ Most metacarpal fractures heal uneventfully and do not require surgery, but spiral fractures, multiple metacarpal fractures, and comminuted fractures are more likely to shorten and rotate, resulting in overlapping of the fingers and tendon imbalance (Figure 2). The border (index and small) metacarpals have a tendency to greater shortening compared with the long and ring metacarpals because the former lack the support of the deep metacarpal ligaments. Border metacarpals have a greater tolerance for lateral angulation than do the long and ring metacarpals because of the greater divergence and because the border fingers have only one adjacent finger. Rotation of the metacarpals is poorly tolerated. Each degree of metacarpal fracture rotation may produce as much as 5° of rotation at the fingertips. Royle⁷ demonstrated that approximately 10° of metacarpal rotation resulted in 2 cm of fingertip overlap. Clinical deformity from lateral metacarpal angulation is best observed with the fingers straight, whereas rotational deformity is best observed with the fingers in flexion.

PATIENT SELECTION

Most metacarpal fractures are treated nonsurgically. The Jahss maneuver is helpful for reduction of a flexed metacarpal. In this maneuver, a nerve block is performed. The metacarpal shaft is stabilized with the MCP joint flexed to 90°. With the fracture site distracted, upward force is applied to the proximal phalanx metacarpal head to realign the neck and shaft. A splint with three-point molding is applied with dorsal compression at the fracture site and volar support for the metacarpal head and
base. Nondisplaced metacarpal fractures are protected in a splint or cast for 3 to 4 weeks, followed by gradual mobilization. The MCP joints should be immobilized in flexion to stretch the MCP joint ligaments to help prevent contracture and to relax the intrinsic musculature to prevent further deformity at the fracture site.

FIGURE 1 Radiographs show metacarpal fractures. A, Oblique view of the hand demonstrates a metacarpal neck fracture of the small finger (boxer’s fracture). These fractures typically are seen in a patient who has punched a solid object. B, PA view of a different patient demonstrates a fourth metacarpal neck fracture. Concomitant fractures of the ring and small metacarpal neck and/or base are commonly seen as a result of an axial loading mechanism, as seen in A.

FIGURE 2 Photograph of the hand of a patient who sustained a spiral fourth metacarpal shaft fracture. Note the rotational deformity of the ring finger and the digital overlap.

Contraindications

Because of the increased motion of the ring and small metacarpals compared with the index and long metacarpals in the AP plane, greater angulation is accepted in the ulnar digits. For metacarpal shaft fractures, 5° to 10° of angulation is acceptable in the index and long metacarpals, 20° of angulation in the ring metacarpal, and 30° of angulation in the small metacarpal. Similarly, for metacarpal neck fractures, 10° to 15° of angulation in the index and long metacarpals, 30° to 40° in the ring metacarpal, and 50° to 60° in the small metacarpal neck fracture without pseudoclawing are acceptable.

PREOPERATIVE IMAGING

Plain radiographs, including AP and lateral oblique views, usually are adequate to assess a metacarpal fracture. Although it is difficult to evaluate a metacarpal fracture on the lateral view, this view is helpful for evaluating subluxation of the MCP or the carpometacarpal joint. The oblique view is particularly useful for measuring flexion deformity at the fracture site. The AP view is especially
helpful for evaluating coronal plane angular malalignment, which usually is clinically relevant. The Brewerton view can be used to assess metacarpal head fractures (Figure 3). The Brewerton view is obtained by placing the supinated hand on the cassette, with the dorsum of the proximal phalanges flat on the radiograph plate and with the MCP joints flexed to 65° and the radiograph tube positioned 15° ulnar to the midline of the hand.

FIGURE 3 Brewerton view of the metacarpal heads in a normal hand. This view provides excellent visualization of the articular surface.

METACARPAL NECK FRACTURES

The amount of angulation that is acceptable in metacarpal neck fractures involving the ring and small metacarpals is controversial. Ford et al⁸ reviewed 62 fractures of the small metacarpal neck with palmar angulation and concluded that palmar (volar) angulation up to 70° still resulted in good outcomes. In this study, the fracture was not reduced and the hand was immobilized. Eichenholtz and Rizzo⁹ considered palmar angulation greater than 40° to require correction. Other authors have recommended surgical intervention when angulation is greater than 30°. If rotation or claw deformity is noted with digital overlap or MCP joint hyperextension and proximal interphalangeal joint flexion, then reduction and stabilization should be considered. Because of the more rigid index and long carpometacarpal joints, angulations less than 10° for the index finger and less than 15° for the long finger can be tolerated without surgical stabilization. Metacarpal neck fractures with angulation greater than that stated above require reduction and stabilization.

Procedure

Surgical Technique

Several methods of fixation have been recommended for metacarpal neck fractures. These include transverse pinning of the metacarpal head to the adjacent metacarpal, crossed Kirschner wires (K-wires), and intramedullary pinning. These techniques can result in better cosmesis than plate fixation and may be considered, depending on the clinical scenario and patient expectations.

Several techniques of pin fixation are used. The pins may be placed transversely across the metacarpal neck, particularly for a border fracture (Figure 4). Other options are to run the pins from distal to proximal or from proximal to distal. When pinning the metacarpal in a distal to proximal direction, the MCP joint is flexed to gain control of the distal fragment. A smooth 0.045-in K-wire is inserted on the radial and/or ulnar collateral recess, and the ideal placement is confirmed under fluoroscopy. The pin is placed in the deepest cavity of the collateral recess. The wire is then advanced onto the shoulder of the metacarpal and down the intramedullary canal. As the wire approaches the fracture site, the fracture is reduced and the wire is advanced proximally into the base of the metacarpal. Occasionally, it is helpful to advance the wire with a mallet rather than under power so the pin bounces off the far cortex rather than penetrating it.

A bouquet pinning technique can be used for a fracture of the index or small metacarpal. For the index metacarpal, a 2-cm skin incision is made along the radial aspect of the base of the second metacarpal; for the small metacarpal, a similar incision is made on the ulnar side of the metacarpal. The extensor tendon insertion is elevated but not detached. Commercially available pins may be used, or the
tip of a 0.045-in K-wire is cut off and the pin is gently bent along its length. Under fluoroscopic imaging, the proximal aspect of the metaphysis is identified. Penetration is made through the canal with a 2-mm drill and may be enlarged to approximately 5 mm. The precontoured 0.045-in K-ner wire is then placed into the base of the metacarpal and advanced distally across the fracture site. Multiple K-wires may be placed. The goal is to tension the wires off the intact proximal cortex and enter the distal fragment in various locations, creating the so-called bouquet effect.¹⁰

FIGURE 4 Fluoroscopic PA image shows a fifth metacarpal neck fracture that has been closed reduced and stabilized with cross-pinning of the proximal and distal fragments to the fourth metacarpal.

Del Piñal¹¹ reviewed their results in 48 metacarpal fractures treated with intramedullary cannulated headless compression screws. In their series, most metacarpal fractures were treated with a 3.0 mm diameter screw from AutoFix headless cannon screws (Small Bone Innovations, Morrisville, PA). It was noted that the maximum length for the screw is 40 mm and the average length of the metacarpals is approximately 60 mm. The screw was long enough to engage leading threads in the endosteal canal where the screw gains fixation. He noted that the diameter of the medullary canal of the fifth metacarpal is usually larger and he used a 4.0 mm screw, which is available up to 50 mm. A 0.5 to 1 cm transverse incision was made and the extensor tendon was open longitudinally in the midline. Under fluoroscopic guidance, a 1.0 mm guidewire was placed down the longitudinal axis of the metacarpal. At the end of the operation, he ensured the trailing threads were fully buried beneath the articular cartilage line. All 48 metacarpal fractures in their series healed within acceptable radiographic parameters. Two patients required tenolysis.¹¹

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