eMedicine Specialties > Orthopedic Surgery > Hand & Upper Extremity

Metacarpal Fractures

Author: T Michael Dye, MD, Orthopedic Surgeon, Surgical Critical Care Element Chief, Department of Orthopaedic Surgery, Eglin Air Force Base, Hurlburt Field, Florida
Contributor Information and Disclosures

Updated: Feb 13, 2008

Introduction

This article reviews metacarpal fractures and dislocations in the hand.

Injury to the thumb metacarpals is discussed in the chapters Bennett Fracture, Rolando Fracture, and Thumb Reconstruction.

For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education articles Broken Hand, Broken Finger, and Finger Dislocation.

History of the Procedure

Trauma to the hand is exceedingly common, not infrequently resulting in metacarpal and phalangeal fractures and dislocations. Most of these injuries can be managed nonoperatively, utilizing immobilization or controlled mobilization. For certain intra-articular fractures, displaced and angulated fractures, unstable fracture patterns, combined or open injuries, as well as irreducible and unstable dislocations, surgical intervention may be required for restoration of function and appearance.

Problem

Most metacarpal fractures occur in the active and working population, particularly adolescents and young adults. In the United States, upper extremity injuries result in over 16 million days off of work and a further 90 million days of restricted activity. Lost revenue and costs exceed 10 billion dollars.^1,2,3

Frequency

• Fractures of the metacarpals and phalanges constitute approximately 10% of all fractures.
• Metacarpal fractures account for 30-40% of all hand fractures.
• Fractures of the 5th metacarpal neck alone account for 10% of all fractures in the hand.
• Lifetime incidence of metacarpal fractures is approximately 2.5%.

Related eMedicine topics:
Malunion of Hand Fracture
Hand, Fracture and Dislocations: Thumb
Hand, Anatomy

Related Medscape topic:
Conservative treatment for closed fifth (small finger) metacarpal neck fractures

Etiology

Injury to the metacarpals is the result of either direct or indirect trauma. The nature and direction of the applied force determines the exact type of fracture or dislocation.^1,2 Specific injury patterns that occur from commonly seen trauma are as follows:

• Carpometacarpal (CMC) injuries: Metacarpal base fractures and dislocations of the CMC joint commonly result from an axial load or other stress on the hand with the wrist flexed.
• Metacarpal shaft and neck injuries: Typically, metacarpal shaft fractures are produced by either axial loading or direct trauma. Torsional forces on the digits may also produce these injuries. Metacarpal neck fractures, the most common metacarpal fractures, usually result from striking a solid object with a clenched fist.
• Metacarpal head injuries: Metacarpal head fractures are intra-articular injuries and result from axial loading or direct trauma. Avulsion fractures at the origin of the collateral ligaments are caused by forced deviation of the flexed metacarpophalangeal joint.
• Metacarpophalangeal (MCP) dislocations: Dorsal MCP dislocations are the most frequent dislocations, resulting from forced hyperextension of the digits.

Pathophysiology

Metacarpal base injuries

CMC joints, especially the central joints, are quite stable. The metacarpal bases are held in position by dorsal and palmar carpometacarpal ligaments, as well as by interosseous ligaments.¹

CMC dislocations may occur with or without fracture. Avulsion (chip) fractures of the metacarpal base, or fractures involving the dorsal carpus, frequently accompany CMC dislocations. A CMC dislocation should signal the examiner to look for either a fracture or dislocation of the adjacent joints. Disruption of the strong ligaments stabilizing the central CMC joints signifies high-force transmission; in these cases, the examiner must maintain an even higher level of suspicion for other injuries.

Fracture-dislocation of the 5th metacarpal base is a common intra-articular injury and has been dubbed the reverse Bennett fracture. A direct blow to the ulnar border of the hand tends to cause an extra-articular 5th metacarpal base fracture. Axial load more often results in an intra-articular or reverse Bennett fracture. Generally, the volar radial ¹/ ₃ -¹/ ₄ of the 5th articular base remains reduced. The remainder of the metacarpal displaces in a dorsal and ulnar direction. Displacement is caused by dynamic forces, similar to that seen with Bennett fracture of the thumb. The 5th metacarpal is the most mobile of the 4 ulnar CMC joints; therefore, it is prone to arthrosis from articular incongruity.⁴

Metacarpal shaft/neck fractures

Axial loading, direct blow, or torsional loading can cause metacarpal shaft fractures. Usually, the fractures are classified anatomically as transverse, oblique, or spiral. The fracture pattern often denotes the mechanism of injury, with direct or axial injury leading to transverse or oblique fractures and torsion leading to spiral fracture.

Fractures of the 5th metacarpal neck are among the most common fractures in the hand. Usually, these fractures are caused by striking a solid object with a closed fist and thus are dubbed boxer fractures, although this injury almost never occurs during boxing. Typically, a skilled fighter fractures the index metacarpal because instead of using a "roundhouse" motion, the blow comes straight from the body along the line of greatest force transmission.

Metacarpal head injuries

Fractures of the metacarpal head are rare injuries. These fractures are intra-articular and periarticular. If displaced, metacarpal head fractures usually require open reduction and internal fixation (ORIF). Direct trauma to the joint or an avulsion injury of the collateral ligaments are the typical causes. Injuries caused by direct trauma often are comminuted.

Metacarpophalangeal dislocations

Almost all MCP dislocations occur with the proximal phalanx displaced dorsally on the metacarpal head, as there is no specific dorsal restraint to the MCP joint other than the joint capsule and extensor mechanism. The collateral ligaments remain intact, and the weak proximal insertion of the volar plate avulses from the metacarpal neck.

Presentation

Injuries to the metacarpal base

Many fractures and fracture dislocations of the metacarpal base are caused by substantial axial loads and frequently are associated with other injuries. Diagnosis usually is directed by the history and clinical examination. Tenderness, swelling, and loss of motion are common, as with any fracture or dislocation. Additionally, dorsal CMC joint dislocations may be associated with marked swelling and sometimes a palpable step-off. Stress of the 5th metacarpal reveals instability in cases of intra-articular fractures of that metacarpal base.

Fractures of the metacarpal shaft and neck

Problems associated with metacarpal shaft fractures relate to shortening, rotation, and dorsal apex angulation. Of these, malrotation is the most critical. Minor rotational deformities can cause the fingers to overlap when the hand is made into a fist. Rotational abnormalities are best judged clinically by comparing the injured and uninjured digits through a full range of motion (ROM). With flexion, each digit should point toward the scaphoid tuberosity. The plane of the nail should be similar between the injured digit and the contralateral corresponding finger when evaluated in an intrinsic plus position.

Like shaft fractures, metacarpal neck fractures usually are easily diagnosed by localized tenderness and swelling with loss of dorsal knuckle contour. The ring and small metacarpals are most commonly fractured.

Injuries to the metacarpal head

Pain, swelling, and loss of motion are the key clinical signs of injury to the MCP joint. Crepitus may be present with motion in intra-articular injuries.

Metacarpophalangeal dislocations

Dorsal dislocations are readily identified by a hyperextension posture of the digit with loss of joint flexion. Dimpling of the skin dorsally may also be observed.

Indications

Most metacarpal injuries are managed by closed reduction and immobilization or sometimes controlled mobilization utilizing a dorsal block splint. Indications for operative treatment include the following:

• Failure to achieve or maintain acceptable reduction using closed techniques
• Open fractures
• Multiple hand fractures
• Complex injuries
• Displaced intra-articular fractures
• Fractures with severe soft-tissue loss requiring a stable skeleton

Specific indications are further described below.

Fractures and dislocations of the metacarpal base

Impaction fractures of the metacarpal bases that are not significantly displaced can be treated with splinting, followed by early mobilization.

CMC dislocations and fracture-dislocations, especially when multiple, are unstable injuries. In the past, these fractures were managed by closed reduction and external immobilization, which frequently lead to grip weakness and residual pain. The current literature supports closed reduction, if joint congruity can be obtained, but with the addition of internal fixation.

Displaced fracture-dislocations of the 4th and 5th metacarpals, which are accompanied by fracture of the dorsal hamate, require ORIF. Reverse Bennett fractures frequently need K-wire stabilization to counteract the deforming forces. If little articular incongruity is present, this may be a closed procedure.

Fractures of the metacarpal shaft

Metacarpal shaft fractures tend to angulate apex dorsal with the head displaced palmarly due to the deforming pull of the interossei muscles. Only small amounts of angulation (£10°) are acceptable in the 2nd and 3rd metacarpals. The 4th and 5th finger metacarpals are much more mobile, and angulation of 20° and 30°, respectively, can be accepted. The more proximal the fracture, the more pronounced the deformity and the less angulation that can be accepted. Any malrotation is an indication for surgical intervention. Shortening from 3-4 mm is well tolerated.

In addition to fractures that cannot be reduced and stabilized closed, fractures such as open fractures, multiple fractures, and malreduced subacute fractures are best addressed surgically.

Fractures of the metacarpal neck

Metacarpal neck fractures rarely require surgery. Although the acceptable degree of angulation is controversial, as much as 50-60° of angulation can be tolerated with little or no functional deficit. This level of angulation is especially true for boxer's fractures of the 5th metacarpal neck. Despite overall good functional results, this degree of angulation alters dorsal knuckle contour and may result in a tender palmar mass with heavy gripping. Though quite unusual, fracture rotation is an indication for surgical intervention.

Fractures and dislocations of the metacarpal head

Except for some collateral ligament avulsion fractures, metacarpal head fractures are intra-articular and, if displaced, should be treated by ORIF, with the goal being anatomic reduction and early mobilization.

Relevant Anatomy

Patterns of injuries result from the unique anatomy of the hand. Metacarpals are long tubular bones with an intrinsic longitudinal arch and a collective transverse arch. Bones are concave on the palmar surface and are joined proximally and distally by ligamentous attachments. The 2nd and 3rd metacarpals are fixed rigidly at their bases, while the 4th and 5th CMC joints are capable of at least 15° and 25° of motion, respectively. The thumb CMC saddle joint is highly mobile, and its unique motion and injury patterns are addressed in other eMedicine chapters (see Bennett Fracture and Rolando Fracture).

The CMC joints of the 2nd and 3rd metacarpals are very stable, and there is very little relative motion at these joints. The sawtooth articular arrangement combined and the strong dorsal and palmar CMC ligaments and metacarpal ligaments form very strong and relatively immobile joint capsules.

These joints are further stabilized by extensor carpi radialis longus and brevis tendon insertions on the bases of the 2nd and 3rd metacarpals, respectively. The insertion of the flexor carpi radialis at the base of the 2nd metacarpal contributes as well. The articulation with the hamate and the 4th and 5th metatarsal bases allows for much freer movement, but the CMC and metacarpal ligaments are still very strong. The insertion of the extensor carpi ulnaris (ECU) on the dorsal aspect of the ulnar 5th metacarpal base often provides a deforming force in fractures of the 5th metacarpal. Articular fractures of the base of the 5th metacarpal often occur between the metacarpal ligament insertions and the insertion of the ECU, resulting in proximal and dorsal migration of the fractured metacarpal due to the unopposed tendon action (often called "reverse Bennett fracture" due to its similarity to the injury in the thumb).

The MCP joints are multiaxial condyloid joints capable of flexion, extension, and some lateral motion and circumduction. The cam-shape of the metacarpal heads leads to relaxation of the collateral ligaments in extension, permitting adduction and abduction of the finger. With about 70° of MCP joint flexion, the collateral ligaments become taut, stabilizing the finger for power pinch and grip. Increased tension in the collateral ligaments with MCP flexion can be helpful in stabilizing the metacarpal head while reducing a metacarpal neck fracture. MCP joints are routinely immobilized in at least 70° of flexion to maintain maximum stretch of these ligaments, thus lessening postimmobilization stiffness.

The volar plate is a cartilaginous structure on the palmar aspect of each MCP joint, which limits extension of the joint. The volar plate is thicker at its insertions on the proximal phalanges and weaker at the proximal metacarpal origin. Volar plates are interconnected through deep transverse intermetacarpal ligaments, which provide additional volar stability.

Contraindications

No absolute contraindications exist for treatment of metacarpal injuries. Almost all injuries are amenable to either immobilization or closed or open reduction, with or without fixation.

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