Metacarpal base fractures

INTRODUCTION — 

Metacarpal fractures are common [1]. They account for 30 to 40 percent of all hand fractures. Fractures of the base of the metacarpal bones may be the result of direct or indirect trauma.

This topic will review the presentation, diagnosis, and nonoperative management of fractures of the base of the metacarpal bones (not including the thumb). A general overview of metacarpal fractures is presented separately, as are discussions of each specific type of metacarpal fracture. (See "Overview of metacarpal fractures" and "Metacarpal shaft fractures" and "Metacarpal neck fractures" and "Metacarpal head fractures".)

Although first (thumb) metacarpal fractures typically occur at the base, the anatomy and biomechanics of the thumb are unique, and fractures of the metacarpal of the thumb are presented separately. (See "First (thumb) metacarpal fractures".)

CLINICAL ANATOMY — 

Fractures of the metacarpal base (figure 1) are provided a degree of stability due to the dorsal and palmar carpometacarpal (CMC) ligaments as well as the interosseous ligaments (figure 2). This is particularly true for second (index finger) and third (middle finger) metacarpal base fractures. Fractures of the fourth (ring finger) and fifth (little finger) metacarpal base are somewhat less stable due to increased mobility at the CMC joint. In addition, the motor branch of the ulnar nerve (figure 3 and figure 4) runs in close proximity with the fourth and fifth metacarpal bases; accordingly, fractures of these areas warrant a thorough evaluation of ulnar-distributed motor function.

The fifth metacarpal CMC joint surface slopes in ulnar fashion and is only buttressed on the radial side (by the fourth metacarpal and the hamate bone). The tendon of the powerful extensor carpi ulnaris muscle attaches on the ulnar aspect of the fifth metacarpal base (figure 5), making it common for fractures at this site, particularly intra-articular fractures, to have a large fragment displaced in an ulnar and proximal direction.

MECHANISM OF INJURY — 

Fractures of the metacarpal base are generally caused by a torsional force exerted on the distal portion of the affected metacarpal. This can happen when the distal aspect of the hand is grabbed and twisted or, less commonly, when the hand is caught in another individual's athletic padding or equipment, as might occur during an American football match. Metacarpal base fractures can also be caused by a direct blow to the hand. They may also be the result of a fall onto an outstretched hand or punching a solid object.

SYMPTOMS AND EXAMINATION FINDINGS — 

Fingers with fractures involving the metacarpal base are usually swollen and tender at the fracture site. Movement at the wrist exacerbates pain. Assessment for rotational malalignment and function of muscles innervated by the ulnar nerve proximal and distal to the wrist are both imperative. Even a subtle rotational deformity at the base of the metacarpal can leave a pronounced malalignment at the fingertip.

Rotational alignment — Rotational alignment should be assessed with the metacarpophalangeal (MCP) joint in flexion. The rotational alignment of the metacarpals can be assessed in two ways:

●With a semi-clenched fist (flexion to 90 degrees at the MCP and proximal interphalangeal [PIP] joints), normal alignment will enable each finger to point toward the scaphoid pole and show convergence of the digits, but not necessarily to a single point (picture 1A-B).

●With the MCP joint flexed 90 degrees and the PIP and distal interphalangeal (DIP) joints in full extension, the plane of the fingernails should be aligned and can be compared with the contralateral side (picture 2).

Ulnar nerve motor branch integrity — Assessment of intrinsic hand muscle function should be performed by having the patient abduct (picture 3 and picture 4) and adduct (figure 6) the fingers to ensure ulnar nerve motor integrity. Impaired intrinsic muscle strength in the absence of weakness of the flexors of the ring and little fingers (supplied by the ulnar nerve proximal to the wrist) is suggestive of damage to the motor branch. (See "Overview of upper extremity peripheral nerve syndromes", section on 'Ulnar nerve syndromes'.)

DIAGNOSTIC IMAGING — 

Standard hand series (anteroposterior, lateral, and oblique) are the initial images used for evaluating metacarpal base fractures (image 1 and image 2). However, if the metacarpal base cannot be seen clearly using standard views, 30-degree oblique pronated and supinated views may be needed. Lateral views are particularly important in detection of dorsal displacement, subluxation, or dislocation of the metacarpal from the distal carpal row.

Clinicians adept at musculoskeletal ultrasound (MSK US) can use this tool to screen for metacarpal fractures (image 3), while keeping in mind that MSK US is less accurate for detecting fractures of the metacarpal base compared with the shaft [2]. In an observational study of 66 patients presenting to the emergency department with suspected metacarpal fracture, MSK US was reported to have sensitivity of 92 percent and specificity of 87 percent when using plain radiographs as the gold standard [3].

Ultrasound screening for a metacarpal fracture is performed primarily in the long axis and in sagittal planes using B-mode (ideally 12 to 18 MHz) linear transducers. The sonographer looks for a step-off or cortical disruption of the normally smooth, hyperechoic metacarpal bone surface. The involved metacarpal should be evaluated in its entirety from proximal to distal, as well as the integrity of the adjacent distal carpal bones. While ultrasound can be helpful for initial diagnosis, it may not provide adequate fracture detail [4]. This is particularly true with suspected intra-articular metacarpal base fractures. In addition, plain radiographs are indicated in cases where ultrasound is negative but clinical suspicion of fracture remains moderate or high.

As metacarpal base fractures can sometimes be difficult to detect, specialized views (Brewerton views) or computed tomography (CT) is sometimes necessary. The Brewerton view involves flexing the metacarpophalangeal joint approximately 65 degrees. If the index of suspicion for a fracture is high but plain radiographs are unrevealing, CT is a good choice because it is widely available and can detect subtle bony abnormalities.

DIAGNOSIS — 

Fractures of the metacarpal base are diagnosed by diagnostic imaging, typically plain radiographs. Clinicians should suspect such injuries in patients who have sustained a twisting injury or direct trauma to the proximal hand. Pain, swelling, and focal tenderness are present at the dorsum of the hand.

DIFFERENTIAL DIAGNOSIS — 

The differential diagnosis for acute wrist pain is discussed in detail separately; the diagnoses most commonly confused with a metacarpal base fracture are described briefly below. (See "Evaluation of the adult with acute wrist pain", section on 'Differential diagnosis by regions of the wrist'.)

Wrist sprain — A carpal-metacarpal ligament (CMC) sprain can present with swelling and tenderness and may, at times, mimic a metacarpal base fracture. These are generally distinguished clinically by the focality of examination findings (eg, location of tenderness, presence or absence of a visible deformity over the metacarpal base) and by plain radiographs. (See "Evaluation of the adult with acute wrist pain", section on 'Wrist sprain'.)

Bone contusion — Plain radiographs are needed to distinguish a focal metacarpal base contusion from a fracture, particularly in cases with significant focal tenderness.

Metacarpal-carpal boss — A carpometacarpal boss is a bony protuberance, typically over the base of the second or third metacarpal or at the CMC joint (image 4). Unlike a fracture, a carpometacarpal boss is not caused by acute trauma, develops insidiously over time (often occurs after the third or fourth decade of life), and is often asymptomatic. Further, no fracture is seen on the radiograph. (See "Evaluation of the adult with subacute or chronic wrist pain", section on 'Carpal boss'.)

Carpal-metacarpal (CMC) dislocation — Patients with a dislocation of the CMC joint present with a painful and swollen CMC joint that can mimic a metacarpal base fracture following trauma. CMC dislocations are relatively rare (except at the thumb, where fracture-dislocations are more common) and often manifest more prominent deformity than metacarpal base fractures. Plain radiographs (particularly lateral and oblique views) are needed to distinguish between these injuries.

INDICATIONS FOR SURGICAL REFERRAL — 

Immediate surgical consultation is required for all open fractures and for all fractures with associated vascular compromise or nerve injury, although such complications are uncommon in the setting of isolated metacarpal base fractures.

Evaluation by an orthopedic or hand surgeon within three to five days is needed for the following injuries:

●Intra-articular fractures

●Extra-articular fractures with malrotation, subluxation, or dislocation of the carpometacarpal (CMC) joint (see 'Rotational alignment' above)

In addition, fractures of the base of the fifth metacarpal typically require operative fixation and should be referred.

INITIAL TREATMENT

Splinting and basic care — Splinting is used for initial immobilization, and in some cases may serve as the definitive treatment, of metacarpal fractures [1,5]. A detailed description of the techniques for applying splints is presented separately. (See "Basic techniques for splinting of musculoskeletal injuries" and "Patient education: Cast and splint care (Beyond the Basics)".)

Patients with displaced metacarpal base fractures warranting orthopedic referral should be splinted using dorsal and volar splints with the wrist in 30 degrees of extension and metacarpophalangeal (MCP) joints flexed to approximately 70 to 90 degrees (picture 5). These patients should be seen within three to five days. Nondisplaced fractures should be immobilized with dorsal and volar splints (or a short arm cast if swelling is not too great) with the MCP joints free and the wrist extended to 30 degrees.

All fractures should be kept elevated above the level of the heart as much as possible during the first 48 to 72 hours to minimize swelling. Regular icing is also helpful for reducing pain and swelling. We typically recommend icing for 20 minutes at a time, three to four times per day (although longer contact times may be needed when ice is applied to a cast or splint).

Closed reduction of displaced fractures — Displaced fractures tend to lack stability following closed reduction and ultimately require surgical referral (although fractures in adolescents with thicker periosteum may be more stable). However, when prompt surgical consultation cannot be obtained, it is reasonable to attempt closed reduction.

After appropriate anesthesia (typically with a hematoma block), reduction can usually be accomplished by applying axial traction to disimpact the fracture, while simultaneously applying downward pressure on the dorsum of the hand at the fracture site (most fractures displace dorsally). After verifying adequate reduction by plain radiograph, the hand is splinted with the wrist in extension and MCP joints flexed to approximately 70 to 90 degrees. The performance of a hematoma block for distal radius fractures is discussed separately, and the basic principles and approach described can be applied to metacarpal fractures. (See "Distal radius fractures in adults", section on 'Performance of hematoma block'.)

FOLLOW-UP CARE — 

Patients with nondisplaced or anatomically reduced fractures of the base of the metacarpal with no rotational deformity should be seen within a week for repeat radiographs. If the fracture position is adequate, these patients are placed in a short arm cast for four weeks (picture 6). Prior to application of the cast, ulnar nerve motor function should be reassessed, particularly in fractures involving the base of the fourth or fifth metacarpals. If there is a neurologic deficit or displacement has occurred, referral for possible surgical intervention should be made.

Radiographs should be performed weekly for three weeks in patients managed with a short arm cast to assure maintenance of fracture position. Loss of anatomic position warrants orthopedic referral, as displacement can lead to early carpometacarpal (CMC) arthrosis and chronic pain. (See "General principles of definitive fracture management", section on 'Casting'.)

It is reasonable, and common clinical practice, to transition from a cast to a removable splint at three to four weeks. At that point, the fracture is typically stable and transition to a removable splint allows the patient to begin mobility exercises. The wrist can become stiff with immobilization. Once the short arm cast is removed, many patients with a fracture of the metacarpal base benefit from a rehabilitation program focused on regaining full wrist flexion, extension, and grip strength. If a trial of home mobility and strength exercises does not yield adequate results, referral to occupational therapy is appropriate.

RETURN TO SPORT OR WORK — 

Athletes desiring to return to contact sport may wish to wear a removable orthotic for protection during contact activity for several weeks once continuous immobilization (eg, cast) is discontinued. Return to work requiring regular use of the affected hand is acceptable when patients are pain-free, non-tender, and have radiographic evidence of healing and functional range of motion. This usually takes four to six weeks. In certain cases, surgical treatment may facilitate a more rapid return to sport and can be considered appropriate [6].

PEDIATRIC CONSIDERATIONS — 

Metacarpal base fractures in children are managed in much the same way as they are in adults. One notable difference is the shorter interval for obtaining an initial follow-up radiograph due to the accelerated healing times in children. These fractures tend to be more stable and less likely to displace compared with adults. If there is any concern about fracture alignment or position, follow-up radiographs should be obtained within one week of the initial evaluation.

Of note, these fractures are unusual in nonambulatory children. Abuse should be considered in cases involving young children, particularly if the mechanism is questionable or additional fractures or other injuries are identified. A thorough examination should be performed in such cases. (See "Physical child abuse: Diagnostic evaluation and management".)

ADDITIONAL INFORMATION — 

Several UpToDate topics provide additional information about fractures, including the physiology of fracture healing, how to describe radiographs of fractures to consultants, acute and definitive fracture care (including how to make a cast), and the complications associated with fractures. These topics can be accessed using the links below:

●(See "General principles of fracture management: Bone healing and fracture description".)

●(See "General principles of fracture management: Fracture patterns and description in children".)

●(See "General principles of definitive fracture management".)

●(See "General principles of acute fracture management".)

●(See "General principles of fracture management: Early and late complications".)

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Fractures of the skull, face, and upper extremity in adults" and "Society guideline links: Acute pain management".)

SUMMARY AND RECOMMENDATIONS

●Anatomy – Fractures of the base of the second, third, and fourth metacarpals (associated with index, middle, and ring fingers, respectively) are relatively stable due to their fixed position at the carpometacarpal (CMC) joints and to adjacent metacarpals. (See 'Clinical anatomy' above.)

●Mechanism of injury – Fractures of the metacarpal base are generally caused by a torsional force exerted on the distal portion of the affected metacarpal, for example when the hand or finger is grabbed and twisted. Less often, direct trauma (eg, blow, fall) is the cause. (See 'Mechanism of injury' above.)

●Indications for surgical referral – Immediate surgical consultation is required for open fractures and fractures with associated vascular compromise or nerve injury. Such complications are uncommon with isolated metacarpal base fractures. (See 'Indications for surgical referral' above.)

Evaluation by an orthopedic or hand surgeon within three to five days is needed for the following injuries:

•Intra-articular fractures

•Extra-articular fractures with malrotation, subluxation, or dislocation of the CMC joint

Fractures of the base of the fifth metacarpal (associated with the little finger) are unstable and warrant early orthopedic referral for surgical fixation.

●Clinical presentation and examination – Assessment of rotational malalignment is imperative and is best done with the patient in a clenched fist position (picture 1A-B). Any malrotation warrants referral. (See 'Rotational alignment' above.)

Fractures of the base of the fourth and fifth metacarpals can result in damage to the motor branch of the ulnar nerve (figure 3), which supplies intrinsic musculature of the hand (enabling finger abduction and adduction). Special care must be taken to assess the integrity of this motor function (picture 4 and figure 6). (See 'Ulnar nerve motor branch integrity' above.)

●Diagnostic imaging – Standard hand plain radiographs are used to evaluate metacarpal base fractures (image 1 and image 2). If the metacarpal base cannot be seen clearly, 30-degree oblique pronated and supinated views may be needed. Lateral views are important for detecting dorsal displacement, subluxation, or dislocation of the metacarpal from the distal carpal row. Ultrasound is an effective screening tool.

●Management – Fractures of the metacarpal bases require near anatomic correction to avoid the development of early CMC arthrosis and chronic pain. Definitive treatment of nondisplaced fractures involves dorsal and volar splinting followed by short arm casting. (See 'Initial treatment' above and 'Follow-up care' above.)

●Follow-up and return to activity – Patients with nondisplaced or anatomically reduced fractures with no rotational deformity are seen within a week for repeat radiographs. If the fracture position is adequate, these patients are placed in a short arm cast for four weeks (picture 6).

●Pediatric considerations – Management in children is generally the same as adults. As children heal more quickly, the first follow-up radiograph should be obtained within one week of the initial evaluation.

Metacarpal base fractures are unusual in nonambulatory children and physical abuse should be considered in young children, particularly if the mechanism is questionable or additional fractures or other injuries are identified.