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 are provided a degree of stability due to the dorsal and palmar carpometacarpal (CMC) ligaments as well as the interosseous ligaments. 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 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, 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, more rarely, 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. Rarely, a fall onto an outstretched hand or punching a solid object can cause these fractures.

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 and adduct the fingers to ensure ulnar nerve motor integrity. Impaired intrinsic muscle strength in the absence of weakness of the finger flexors (the latter 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 — A standard hand series (anteroposterior, lateral, and oblique) is 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, 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.

As metacarpal base fractures can sometimes be difficult to detect, specialized views (Brewerton views) or computed tomography (CT) is sometimes necessary. 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 radiograph. 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 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 — Metacarpal-carpal boss is a bony protuberance, typically over the base of the second or third metacarpal or at the carpometacarpal (CMC) joint. Unlike a fracture, metacarpal-carpal 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 radiograph. (See "Evaluation of the adult with subacute or chronic wrist pain", section on 'Carpal boss'.)

Carpometacarpal 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 is used in the initial immobilization of and sometimes is the definitive treatment for 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 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 free. 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 MCPs free and wrist extended at 30 degrees. All fractures should be iced aggressively and elevated above the level of the heart during the first 48 to 72 hours to minimize swelling.

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 position is adequate, these patients are placed in a short arm cast for four weeks (picture 3). 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'.)

Once the short arm cast is removed, fractures of the metacarpal bases require rehabilitation 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 may be needed.

RETURN TO SPORT OR WORK — Athletes desiring return to contact sport should use an orthotic for protection during activity for four to six weeks after continuous immobilization 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. 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/other injuries are identified. (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

●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.)

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

●Fractures of the metacarpal bases require near anatomic correction to avoid development of early CMC arthrosis and chronic pain.

●Assessment of rotational malalignment is imperative and is best done with patient in a clenched fist position. Any malrotation warrants referral. (See 'Rotational alignment' above.)

●Definitive treatment of nondisplaced fractures involves dorsal and volar splinting followed by short arm casting. (See 'Initial treatment' above and 'Follow-up care' above.)

●Fractures of the base of the fourth and fifth metacarpals can result in damage to the motor branch of the ulnar nerve, 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. (See 'Ulnar nerve motor branch integrity' above.)