Metacarpal Neck Fractures

Hebe Désirée Kvernmo

Abstract

Fractures of the metacarpal neck are common injuries. The small finger metacarpals are most frequently involved, and account for around one-fourth to one-third of all metacarpal fractures. Controversy exists regarding choice of treatment, but majority of metacarpal neck fractures respond well to conservative management. The degree of acceptable deformity depends on which metacarpal is involved. The literature suggests that fractures of small finger metacarpal neck of less than 50 to 70 degrees of volar angulation may be best treated conservatively with early mobilization, although there is weakness in existing literature due to heterogeneity of the data. Using functional treatment, no reduction should be performed, as the mobilization depends on the stability of an impacted fracture. The initial treatment may, however, be in a cast for a few days until pain settles, and then followed by mobilization with a buddy strap to the ring finger. Fractures with angulation of more than 50 to 70 degrees are few. Operative treatment should be considered for fractures with rotational malalignment or pseudo-clawing of the small finger. Antegrade intramedullary (bouquet) pinning is a good method of choice, and allows for immediate mobilization. Less angulation is accepted for the other metacarpal necks, with as less as 15 to 20 degrees for the second and third metacarpal to as much as 30 to 40 degrees for the forth metacarpal.

Keywords: metacarpal neck fracture, boxer’s fracture, definition of metacarpal neck, measurement of angulation and shortening, conservative treatment, operative treatment, evidence

23.1 Trauma Mechanism

Metacarpal neck fractures are common fractures. They occur most often in the small finger metacarpals, which account for 10% of all hand fractures 1 and 25 to 36% of all metacarpal fractures.^1–3 The index, middle, and ring finger metacarpal neck fractures account for 6, 2, and 5% of all metacarpal fractures, respectively.¹ The small finger metacarpal neck fracture is often called boxer’s fracture. This is a misnomer, as fractures in professional boxers usually occur in the metacarpal neck of the index finger. The small finger metacarpal neck fractures occur most often in brawlers, who impulsively hit a solid object or another person with a closed fist. The direct blow is causing a longitudinal compression through the knuckle, resulting in a fracture of the neck of the metacarpal ( Fig. 23.1). The injury usually occurs in association with alcohol intake and violence.³

23.2 Classification

There are no definitions commonly used in the literature for metacarpal neck fractures. Although angulation of the metacarpal neck results in less shortening than angulation of the metacarpal shaft ( Fig. 23.2), the transition zone between the shaft and the distal segment has not been uniformly defined and used. This may have contributed to difficulties in comparing results of different studies. The Orthopaedic Trauma Association (OTA) divides the metacarpals into distal, shaft, and proximal segments.⁴ The implementation of this definition in metacarpal neck fractures is, however, difficult. In a study of Sletten et al,⁵ the validity and reliability of nine different neck fracture definitions were tested against expert opinion, using a logistic regression and inter- and intraobserver coefficient. Based on this study, the authors showed that the metacarpal neck area is best defined as the squared distance between the insertions of the collateral ligaments in the metacarpal head ( Fig. 23.3) and that 75% or more of the fracture line should be distal to the proximal border of the neck area. This definition is used in the authors’ later randomized controlled trial (RCT) where a functional treatment is compared with bouquet pinning.⁶

23.3 Clinical Signs and Tests

The typical symptoms of a metacarpal neck fracture are pain and tenderness localized around the knuckle. There may be pain with movement of the fingers. The hand may swell, and a discoloration and/or bruising of the affected area may be seen. The metacarpals are concave in the sagittal plane and relatively flat on the dorsal side. The neck of the metacarpals has a normal volar angulation of 14 degrees.7 The direct blow causing the fracture results in an additionally volarly flexed position of the metacarpal neck. The knuckle disappears ( Fig. 23.4), and a hard lump may be felt in the palm. Because of shortening of the metacarpal bone ( Fig. 23.2), a weakness of flexion force may result as the flexors become relatively too long for the finger.⁸ The extension may also be affected, with development of a compensatory metacarpophalangeal (MCP) joint hyperextension and proximal interphalangeal (PIP) joint flexion, called a pseudo-clawing of the finger ( Fig. 23.5). However, pseudo-clawing is seldom seen. The fracture may also result in a malrotation of the fracture, leading to scissoring or overlap of the fingers on flexion. This may lead to discomfort, decreased grip, and cosmetic complaints. Also, a laceration of the skin may be seen. This indicates a more serious type of a metacarpal neck fracture.

Fig. 23.1 The metacarpal neck fracture typically results from striking an object or another person with a closed fist, causing longitudinal compression through the knuckle. (Copyright Hebe Désirée Kvernmo and Massimiliano Crespi.)

Fig. 23.2 The figure illustrates shortening of the metacarpal bone, which is more pronounced when the shaft fracture is angulated rather than the neck. (Copyright Hebe Désirée Kvernmo and Massimiliano Crespi.)

Fig. 23.3 The metacarpal neck is defined as the squared distance of the C-line, which represents the line between the tuberosities of the metacarpal head at the broadest part. (Sletten et al 2011)

Fig. 23.4 Typical clinical appearance of a boxer’s fracture with loss of the knuckle. (Copyright Hebe Désirée Kvernmo and Massimiliano Crespi.)

Fig. 23.5 Pseudo-clawing of the small finger, which is a compensatory metacarpophalangeal (MCP) joint hyperextension and proximal interphalangeal (PIP) joint flexion.

23.3.1 Investigatory Examination

Imaging helps in assessment of angulation, shortening, possible metacarpal head involvement, and possible associated fractures.

23.4 Radiographs

Standard radiographs for evaluation of metacarpal fractures include anteroposterior (AP) ( Fig. 23.6), lateral ( Fig. 23.7), and oblique views. The AP view is better than the posteroanterior (PA) view as it gives better and more symmetrical frontal projection of the small finger metacarpal.⁹ Volar angulation and shortening of the neck fracture are two important determinates in assessment of indication for operative treatment. The measurements of these determinates differ extensively in the existing literature.

Fig. 23.6 Metacarpal shortening for small finger metacarpal fracture is best measured as the distance between the line going through the neighboring middle finger and ring finger metacarpal head and the small finger metacarpal head, both lines going at the most distal point of the heads.

23.4.1 Measurement of Angulation

It is difficult to measure the degree of angulation in the metacarpal neck fractures consistently.10 The measurements have been performed on either the lateral view or oblique views, by measuring lines that pass through the center of the metacarpal head and the shaft on the dorsal aspect of the bone, in the mid-medullary canal or on the volar aspect. In a cadaveric study, the mid-medullary canal measurement in the lateral view was proven to be most valid.¹¹ This result is supported by a recent clinical RCT,⁶ in which study, inter- and intraobserver reliability of four different methods for evaluation of angulation were performed. The measurement of the mid-medullary canal on the lateral view ( Fig. 23.7) was shown to be both most reliable and valid.

23.4.2 Measurement of Shortening

The angulation of the metacarpal neck fracture causes a shortening of the metacarpal neck ( Fig. 23.2). This shortening may be evaluated by two different methods.¹² First, the length may be evaluated by measurements on the contralateral hand radiograph. Another method, which only requires a radiograph of the injured hand, is to make a stipulation of shortening by drawing a line through the most distal point of the heads of two neighboring fingers ( Fig. 23.6).

Fig. 23.7 Volar angulation is measured on the lateral view by measuring the angle between the line that passes through the center of the metacarpal head and a line in the mid-medullary canal.

Computed Tomography Scan

A computed tomography (CT) scan may be necessary for inconclusive radiographs involving a complex metacarpal head fracture.

23.5 Possible Concurrent Lesions of Bone and Soft Tissue

High-energy injuries may result in a comminuted fracture or involvement of a metacarpal head fracture. There may also be a wound, indicating an open fracture and associated injuries. In these cases, this may result from a fight bite over the MCP joint ( Fig. 23.8), where the injured person is hit by the opponent’s teeth. This is a human bite. The cartilage of the metacarpal head may be injured and a remnant of the teeth may be seen. Human bites may result in septic arthritis due to the virulent microorganisms in the mouth, unless it is treated immediately. Also, the extensor tendon(s) may be injured and retracted, with loss of finger extension.

23.6 Evidence

A review of the evidence for treatment of metacarpal neck fractures was published in the FESSH Instructional Course book in 2017.13 Thirteen existing RCT or pseudo-RCT concerning either conservative or operative treatment of metacarpal neck fractures were included. The outcome measures were not reported consistently, and a further meta-analysis was therefore not performed. Seven of the 13 RCT evaluated conservative treatment only, two compared operative to conservative techniques, and four compared the use of different operative techniques. Only four studies reported patient reported outcome measures.^6,14–16

23.6.1 Conservative Treatment

The study of Yum Man and Trickett 13 concluded that most metacarpal neck fractures may be treated conservatively. Research effort has been focusing on identifying the optimal method of conservative treatment. A previous Cochrane review² on conservative treatment of small finger metacarpal neck fractures demonstrated that no conservative treatment strategy is statistically superior over others and that no definitive recommendations could be given due to the heterogeneity of the data. However, all seven studies comparing functional treatment with cast immobilization^16–22 favored functional treatment with neighbor strapping and early mobilization, with beneficial effects demonstrated for both range of motion (ROM) and grip strength. The study of van Aaken et al,¹⁶ which included fractures of up to 70 degrees of volar flexion deformity, showed 11 days less of work for functional treatment compared to casting. The functional treatment consisted of no reduction and early mobilization, which depends on the stability of an impacted fracture as it gives less pain. Usually, a soft wrap is used to remind the patient of his/her fracture and a neighbor strapping prevents painful abduction of the finger. A reduced fracture will most likely redislocate, due to the flexion forces of the intrinsic muscles that are crossing the MCP joint since they lie volar to the axis of rotation.

23.6.2 Conservative versus Operative Treatment

The issue of conservative versus operative treatments is evaluated in two RCT, both comparing bouquet pinning to conservative treatment.6,23 No statistical difference in ROM or grip strength was demonstrated. The first study also measured Quick-DASH, but found no significant difference between the groups. The study recommended conservative treatment with early mobilization for fractures up to 50 degrees of volar angulation. There was a trend toward better satisfaction with hand appearance in the operative group, but longer sick leave and more complications were seen. The latter study found that satisfaction and appearance were superior in the operative group, and concluded that operative treatment offers an aesthetic, but not functional advantage.