First (thumb) metacarpal fractures

INTRODUCTION — Metacarpal fractures are among the most common hand injuries and frequently present to emergency departments and clinics. Fractures of the first metacarpal (ie, thumb metacarpal) comprise a substantial portion of these fractures.

The presentation, diagnosis, and management of first (thumb) metacarpal fractures is reviewed here. Other injuries of the thumb and surrounding tissues are discussed separately. (See "Evaluation of the patient with thumb pain" and "Scaphoid fractures" and "Ulnar collateral ligament injury (gamekeeper's or skier's thumb)" and "Overview of metacarpal fractures".)

EPIDEMIOLOGY — 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 fifth metacarpal neck (ie, "boxers") fractures in terms of frequency. Of the fractures of the first metacarpal, over 80 percent involve the base.

Thumb fractures overall occur most commonly in children under age 16 and adults over age 65, but thumb metacarpal fractures occur most often among younger males (10 to 29 years old) [2,3]. They are commonly caused by falls and direct trauma secondary to sports, bicycle accidents, and from punching solid objects [4-6]. (See "Evaluation of the patient with thumb pain".)

CLINICAL ANATOMY AND FRACTURE CLASSIFICATION — The thumb is distinct from the other fingers anatomically and biomechanically, and of critical importance to hand function. Accordingly, fractures to the thumb are considered separately from other metacarpal fractures, and must be managed with great care (see 'Management' below). Thumb anatomy is discussed in greater detail separately, but aspects of particular relevance to thumb metacarpal fractures is discussed here (see "Finger and thumb anatomy").

The thumb is highly mobile and lacks an adjacent phalanx on the radial side, both of which make it more susceptible to injury. The first metacarpal is shorter and wider than the four lesser metacarpals, and is not tethered by ligaments to an adjacent metacarpal on either side. Because of these features and the mechanisms commonly involved in injury (eg, axial load on partially flexed digit), the majority of first metacarpal thumb fractures occur at the base. First metacarpal fractures involving the base are prone to displacement due to the opposing forces of the abductor pollicis longus and the volar oblique ligament. These forces cause a common fracture pattern: type I first metacarpal fracture (or Bennett fracture), which is described below.

Metacarpal base fractures — Fractures of the base of the thumb metacarpal are classified into four injury patterns (figure 1) [7]. Types I and II are intra-articular fractures and types III and IV are extra-articular. Discerning whether the articular surface is involved in the fracture is critical as this dictates management.

●Type I injury ("Bennett fracture") is a fracture-dislocation or fracture-subluxation of the base of the metacarpal (figure 2 and figure 3 and image 2C). In this injury, a smaller proximal fragment is held in anatomic position and maintains its attachment to the trapezium via the volar (or anterior) oblique ligament. The remainder of the larger metacarpal is displaced in a dorsal-radial manner, primarily by the abductor pollicis longus [8].

●Type II injuries ("Rolando fracture") can be thought of as a comminuted version of a Bennett fracture, in which the fragments may form a T or Y pattern at the base of the metacarpal (figure 3 and image 1). Severe comminution may occur and the classic Y or T pattern is not present. Type II fractures are quite difficult to treat but fortunately are rare.

●Type III fractures are (image 2A-B) extra-articular and either transverse or less commonly, oblique.

●Type IV fractures are extra-articular pediatric injuries involving the proximal physis. These are generally Salter-Harris (figure 4) type II fractures. Nondisplaced Salter-Harris type II fractures are managed with protective immobilization, typically for four to six weeks.

Metacarpal shaft, neck, and head fractures — Fractures of the mid and distal first metacarpal shaft, neck, and head are relatively uncommon. Metacarpal head fractures are, by definition, intra-articular and are referred for surgical evaluation. (See 'Indications for surgical referral' below.)

Fractures of the mid portion of the first metacarpal shaft and of the metacarpal neck are treated similarly to non-thumb metacarpal fractures. Metacarpal shaft fractures typically are transverse or oblique. Due to the deforming forces of the intrinsic musculature and the absence of stabilizing intermetacarpal ligaments, these fractures can displace and shorten.

MECHANISM OF INJURY — First metacarpal fractures typically occur when a partially flexed thumb sustains a forceful axial load (ie, "jamming" the thumb). Typical mechanisms causing such an axial load include falls (often during sports), bicycle accidents (particularly a fall while gripping the handle bars), and fist fights where the flexed and abducted thumb strikes a hard object (skull, face, wall, etc).

A less common mechanism of first metacarpal fractures involves hyperabduction and/or hyperflexion during a fall. An oblique fracture may be sustained if the mechanism involves torsion (eg, someone grabs and twists the thumb, or the thumb is caught in machinery). Transverse fractures of the first metacarpal shaft are less common but typically result from a direct blow.

SYMPTOMS AND EXAMINATION FINDINGS — Patients with first metacarpal fractures typically present following direct trauma to the thumb complaining of pain, dorsal swelling over the base of the metacarpal, and diminished motion at the metacarpophalangeal (MCP) and carpometacarpal joints. It is important to distinguish tenderness at the base of the first metacarpal from tenderness at the scaphoid, trapezium, or distal radius, suggesting injury at those sites. In addition, if pain, swelling, or ecchymosis occurs more distally at the MCP joint (particularly on the ulnar side), care should be taken to assess the ulnar collateral ligament for signs of injury ("gamekeeper's thumb"). (See "Ulnar collateral ligament injury (gamekeeper's or skier's thumb)".)

DIAGNOSTIC IMAGING

Plain radiographs — Plain radiographs remain the most common imaging technique for diagnosing first metacarpal fractures. Three views of the thumb are indicated to assess potential fractures of the thumb metacarpal. In addition to lateral and oblique views, a true anteroposterior AP (Robert view) should be taken. This view, taken in maximum pronation, provides good visualization of the carpometacarpal (CMC) joint. A true lateral (Bett view) revealing a Bennett fracture-dislocation can be obtained with the palm on the cassette, and the hand then pronated 15 to 20 degrees and the tube angled proximally 15 degrees [8]. Close inspection of an apparent extra-articular fracture is required to ensure that no portion of the fracture line involves the joint surface (image 2A-C). An oblique extra-articular injury can be confused with a Bennett fracture. Computed tomography scanning is helpful at times, particularly with impaction injuries and to define the CMC joint and fracture fragment position in intra-articular injuries.

Musculoskeletal ultrasound — Ultrasound is well suited for investigating fractures in linear areas of bone such as the diaphyseal and metaphyseal regions of the metacarpals.

Musculoskeletal ultrasound (MSK US) examination of the hand is best performed with the patient seated and the hand resting on an examination table or a pillow (picture 1). Examination of the dorsal first (ie, thumb) metacarpal is performed first, followed by the volar/thenar side. A high-frequency transducer of at least 10 mHz is typically used. A small footprint (hockey stick) linear probe makes examination of the hand and metacarpals easier.

Initially, the probe is placed on the dorsum of the hand at the distal metacarpophalangeal (MCP) joint and then moved proximally. Images are obtained in the longitudinal and transverse planes. This allows for evaluation of potential joint involvement of a metacarpal fracture. The cortex of each potentially injured metacarpal is examined carefully for any discontinuity in the hyperechoic surface consistent with a fracture. Cortical discontinuities as small as 1 mm can be identified with high-resolution transducers and may enable visualization of fractures that would be missed with standard radiographs [9]. Occasionally, hematoma, edema, or ligamentous disruption may be seen.

Studies of MSK US for the diagnosis of metacarpal fractures report sensitivities of 90 to 91 percent and specificities of 97 to 98 percent [10-12]. However, while ultrasound can be effective for diagnosing metacarpal fractures, plain radiographs may still be needed to determine angulation and rotation.

DIAGNOSIS — The definitive diagnosis of a first metacarpal fracture is made by diagnostic imaging, typically a plain radiograph. Some clinicians use ultrasound to screen for fracture and make a preliminary diagnosis. A history of direct trauma to the thumb and findings of dorsal swelling over the base of the thumb metacarpal, accompanied by diminished motion at the metacarpophalangeal and carpometacarpal joints, suggest the presence of a fracture.

DIFFERENTIAL DIAGNOSIS — The differential diagnosis for acute thumb pain stemming from trauma is reviewed in detail separately. (See "Evaluation of the patient with thumb pain", section on 'Deformity: dislocation and fracture' and "Evaluation of the patient with thumb pain", section on 'Joint instability'.)

Important alternative diagnoses to consider in the patient with a suspected first metacarpal fracture include the following:

●Fracture of the scaphoid (see "Scaphoid fractures")

●Fracture of the trapezium (see "Trapezium and trapezoid fractures")

●Dislocation or subluxation at the first metacarpophalangeal joint

●Ulnar collateral ligament injury (see "Ulnar collateral ligament injury (gamekeeper's or skier's thumb)")

●Radial collateral ligament injury (see "Evaluation of the patient with thumb pain", section on 'Radial collateral ligament injury')

●Flare of first carpometacarpal (CMC) osteoarthritis

●Isolated dislocation of first CMC joint

INDICATIONS FOR SURGICAL REFERRAL — Immediate surgical consultation is needed for open metacarpal neck fractures (laceration extends to bone) and injuries associated with major neurovascular impairment. Such injuries are uncommon.

All intra-articular first metacarpal fractures warrant referral to an orthopedic or hand surgeon. Because the integrity of the carpometacarpal joint is crucial to hand function, meticulous maintenance of the joint surface is required and most intra-articular fractures require surgical fixation. Less than 1 mm of displacement is desired for optimal outcome [13].

Extra-articular fractures are usually managed without surgical intervention. Nonetheless, due to the functional importance of the thumb, orthopedic referral is reasonable and often warranted if closed reduction is required to establish anatomic alignment. Furthermore, due to the relatively unstable nature of oblique fractures, patients should be informed about the risk of displacement, particularly for fractures requiring reduction.

For fractures of the first metacarpal shaft or neck that may otherwise be suitable for nonsurgical management, indications for surgical referral include the following:

●Adequate reduction either cannot be achieved or maintained using closed techniques.

●There is >20 degrees of angulation.

●There is >2 mm of shortening.

●Any degree of malrotation is present.

MANAGEMENT

Initial treatment — Splinting is used in the initial immobilization of metacarpal fractures [1,14]. 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)".)

Intra-articular fractures — Intra-articular fractures of the first metacarpal (ie, type I - Bennett fracture dislocation and type II - Rolando fracture) should be managed initially using a thumb-spica splint (picture 2) with the interphalangeal (IP) joint free and the wrist in 30 degrees of extension, prior to being referred to orthopedics within two to three days. These patients should aggressively ice and elevate the hand and will need adequate analgesia. Standard over-the-counter medications are generally sufficient for analgesia. Pain management of fractures is reviewed separately. (See "General principles of acute fracture management", section on 'Pain management'.)

Extra-articular fractures — Nondisplaced extra-articular fractures of the first metacarpal should be placed in a short arm thumb-spica splint with the wrist in 30 degrees of extension and the splint extending to the IP joint and followed up in one week (picture 2). (See "Basic techniques for splinting of musculoskeletal injuries".)

If the fracture is oblique or alignment is questionable, the patient should be seen back within three to five days. Up to 20 to 30 degrees of residual angularity is tolerated without functional impairment due to the inherent mobility of the thumb. Extra-articular fractures with >30 degrees of angulation require reduction (see 'Closed reduction' below).

Definitive treatment for extra-articular fractures is thumb spica cast (with IP joint free) for four to six weeks [15,16].

Patients should be made aware that significant swelling or overly aggressive icing to this radial side of the thumb can cause a temporary palsy to the superficial radial nerve resulting in numbness over the dorsum of the thumb.

Pediatric first metacarpal fractures — Pediatric fractures of the first metacarpal fall into one of four fracture patterns (figure 5), three of which involve the physis (ie, Salter-Harris fracture (figure 4)).

●Metacarpal shaft fracture

●Salter-Harris type II fracture with medial (ulnar) "metaphyseal flag" (or fragment) – This pattern is most common

●Salter-Harris type II fracture with lateral (radial) "metaphyseal flag"

●Salter-Harris type III fracture

These fractures should be evaluated for displacement and malrotation. Malrotation is uncommon but must be screened for carefully.

A fully adducted thumb without malrotation should sit perpendicular to the plane of the nails of the lesser four digits, as seen in the following photograph (picture 3).

Minimally displaced or nondisplaced Salter-Harris type II fractures can be managed with immobilization in a thumb spica cast, splint, or custom orthosis, typically for four to six weeks. Displaced, malrotated, or unstable fractures and Salter-Harris type III fractures all warrant referral to an orthopedic surgeon [15,16].

Closed reduction — For angulated extra-articular fractures of the first metacarpal, closed reduction is appropriate prior to splinting. Reduction of thumb metacarpal fractures is typically performed by an orthopedic surgeon. However, if reduction is indicated and the treating clinician is comfortable with the procedure, or if there is no referral option available, reduction of extra-articular first metacarpal fractures can be performed in the following manner:

●Anesthesia is generally readily achieved via hematoma block. Placement of a hematoma block for metacarpal fractures is described separately. (See "Metacarpal shaft fractures", section on 'Anesthesia'.)

●Once adequate anesthesia is confirmed, apply gentle longitudinal traction to the distal fragment while applying pressure over the apex of the fracture and extending the IP joint. Mild pronation of the distal fragment may also help to achieve anatomic alignment (figure 6). The fracture should then be immobilized with a thumb spica cast and post-reduction radiographs should be obtained to confirm alignment.

FOLLOW-UP CARE — Nondisplaced fractures and those fractures with good initial reduction should be seen and reimaged in 7 to 10 days. Patients with oblique fractures or questionable reduction require reimaging within three to five days. If follow-up films reveal angulation greater than 30 degrees, repeat reduction or referral is indicated.

Fractures that retain a stable position at follow up should be placed in a short arm thumb spica cast or a custom orthosis with the wrist in 30 degrees of extension and the interphalangeal joint free. Radiographs should be repeated at two-week intervals and immobilization should be continued for a total of four to six weeks.

Following immobilization, the patient should begin performing active range of motion exercises. Total healing time is six to eight weeks. Occupational therapy can be employed as needed to help patients regain motion and strength [17].

RETURN TO WORK OR SPORT — Patients whose work requires repetitive or forceful gripping can expect to return to regular duty once they are pain-free, the fracture site is nontender, and functional range of motion has been regained. If the patient desires return to contact sport, the thumb should be protected in a club-type pad or a firm thumb-spica orthosis, typically for an additional six to eight weeks.

COMPLICATIONS — With precise reduction of displaced fractures, good fracture care, and early mobilization, the risk of complications from first metacarpal fractures can be minimized. Nevertheless, even with proper care, complications, including those described below, can occur. A more detailed discussion of fracture complications is found separately. (See "General principles of fracture management: Early and late complications".)

●Osteoarthritis – Osteoarthritis (OA), particularly at the first carpometacarpal (CMC) joint, is a relatively common chronic complication of first metacarpal fractures, particularly intra-articular fractures involving the base of the thumb. Achieving precise congruency of any fracture involving the joint is the best way to maintain joint function and decrease the risk for OA. (See "Management of hand osteoarthritis".)

●Stiffness – Stiffness at the CMC joint and the metacarpophalangeal (MCP) joint is a common complication of immobilization, particularly prolonged immobilization. Stiffness is more common in older individuals and can be mitigated by avoiding unnecessarily prolonged immobilization and initiating early mobility exercises (and possibly formal occupational therapy when indicated).

●Weakness – Grip weakness may persist after a first metacarpal fracture, particularly those involving the base. Functional rehabilitation is often helpful for regaining strength.

●Superficial radial nerve palsy – Injury to the superficial radial nerve can develop due to compression from a cast or splint on the nerve where it courses over the dorsoradial aspect of the distal forearm or thumb [18-20]. The palsy manifests as pain, paresthesias, or numbness over the dorsoradial aspect of the wrist and hand; there is no motor component. Ulnar flexion of the wrist with the forearm pronated exacerbates any discomfort. Typically conservative management including activity modification and local glucocorticoid injection is adequate. However, in rare cases, decompression may be necessary and referral to a hand surgeon is prudent in cases with persistent symptoms despite conservative care.

●Malrotation – Malrotation is less common in thumb fractures than in fractures of the lesser four digits. However, attention to rotational alignment is imperative for all metacarpal fractures.

●Recurrent subluxation – Fracture malunion increases the propensity for chronic CMC joint subluxation. These cases present with persistent pain, stiffness, and intermittent episodes of instability at the first CMC joint. Radiographs may show subluxation. Referral to hand surgeon is warranted in suspected cases of recurrent subluxation.

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 acute fracture management".)

●(See "General principles of definitive 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

●Epidemiology – First (thumb) metacarpal fractures are relatively common. Most involve the base of the metacarpal. They occur primarily in younger males (10 to 29 years old). (See 'Epidemiology' above.)

●Mechanism of injury – First metacarpal fractures typically occur when a partially flexed thumb sustains a forceful axial load (ie, "jamming" the thumb). Typical mechanisms causing such an axial load include falls (often during sports), bicycle accidents, and fist fights where the flexed and abducted thumb strikes a hard object. (See 'Mechanism of injury' above.)

●Presentation and physical examination – Patients typically present following direct trauma to the thumb complaining of pain, dorsal swelling over the base of the metacarpal, and diminished motion at the metacarpophalangeal (MCP) and carpometacarpal (CMC) joints. It is important to distinguish tenderness at the base of the first metacarpal from tenderness at the scaphoid, trapezium, or distal radius, which suggest injury at those sites. (See 'Symptoms and examination findings' above.)

●Diagnostic imaging – Plain radiographs remain the most common imaging technique for diagnosing first metacarpal fractures and are used for the surveillance of higher risk injuries. Musculoskeletal ultrasound is a useful screening tool for making an initial diagnosis. (See 'Diagnostic imaging' above.)

●Anatomy and fracture classification – Due to the unique anatomy and biomechanics of the thumb, first metacarpal fractures are classified and managed differently than other metacarpal fractures. The classification scheme for thumb metacarpal base fractures (including Bennett and Rolando fractures) is described above. (See 'Clinical anatomy and fracture classification' above and "Finger and thumb anatomy".)

●Differential diagnosis – The differential diagnosis for first metacarpal fracture includes fracture of the scaphoid, dislocation of the first MCP joint, and thumb ulnar collateral ligament injury, among others. (See 'Differential diagnosis' above.)

●Management of intra- and extra-articular fractures – Thumb metacarpal fractures are divided into two major groups: intra-articular and extra-articular.

•Intra-articular fractures (image 1) require orthopedic referral and generally need surgical fixation. (See 'Diagnostic imaging' above and 'Indications for surgical referral' above.)

•Extra-articular fractures (image 2A) are typically managed in a closed fashion with thumb-spica immobilization (figure 7 and picture 4) and rarely require surgery. Extra-articular fractures do not require perfect anatomic reduction and can tolerate up to 30 degrees of angulation. Nevertheless, some extra-articular fractures warrant surgical referral and the criteria for referral are described in the text. Basic fracture reduction technique is also described in the text. (See 'Initial treatment' above and 'Indications for surgical referral' above and 'Closed reduction' above.)

•Oblique extra-articular fractures, which should be carefully differentiated from Bennett fractures, are prone to displacement, and need to be observed closely (particularly during the initial two weeks). First metacarpal fractures in children may involve the physis and should be carefully assessed for malrotation (which is uncommon). (See 'Initial treatment' above and 'Pediatric first metacarpal fractures' above.)