Diaphyseal Fractures of the Metacarpals

22 Diaphyseal Fractures of the Metacarpals

Pierluigi Tos, Simona Odella, Ugo Dacatra, Jane Messina, Emilio Pedrini

Abstract

The purpose of this chapter is to understand when surgical treatment is necessary in case of diaphyseal metacarpal fractures and which is the best surgical technique when it’s necessary. Metacarpal fractures account for 30% of hand fractures, and non-thumb fractures for 88%. Most patients (70%) are in the second and third decade of life. The bone shaft is affected in injuries involving axial loading, torsion, direct falls, or crushing. The initial evaluation focuses on fracture stability to establish whether surgical or conservative treatment is required; the deformity that is less tolerated is malrotation because it causes overlapping finger. Our favorite technique is pinning and intramedullary fixation to obtain a good stability avoiding soft tissue damage during dissection. In case of long spiral fracture, an open reduction and an internal fixation by screws can be performed, only in case of transverse or oblique or multiple metacarpal fracture, we perform an open reduction and internal fixation using plate and screws.

Metacarpal fractures have a good prognosis if treated conservatively or surgically, complications are generally related to nonunion, shortening, and malrotation in case of incorrect indication to the nonsurgical treatment; when surgery is performed, stiffness, tendon adhesion, loss of range of motion, and superficial infections are the most common complications.

None of the available operative methods have proved superior in treating of metacarpal fractures. Also in this context, a number of studies have documented the value and reported good long-term outcomes of various operative approaches.

Keywords: metacarpal fractures, metacarpal fractures treatment, plate or screw fixation metacarpals, external fixation metacarpals

22.1 Trauma Mechanism

Metacarpal fractures account for 30% of hand fractures, and non-thumb fractures for 88%. Most patients (70%) are in the second and third decade of life. The bone shaft is affected in injuries involving axial loading, torsion, direct falls, or crushing. Metacarpal fractures can be classified as transverse, oblique, spiral, and comminuted. If the trauma involves directly the hand, the fracture pattern is usually transverse or comminuted, whereas a fall on an outstretched arm mostly causes spiral or oblique fractures. The majority of metacarpal fractures are isolated, simple, and stable and can be managed without surgery. The most common event affecting the thumb shaft is a spiral or oblique fracture.

22.2 Classification

Metacarpal fractures can be classified in relation to anatomical region. This chapter examines diaphyseal fractures. There are four major types of metacarpal fractures: transverse, oblique, spiral, and comminuted. The AO classification identifies six major patterns: head subcapital, head intra-articular, shaft oblique, shaft transverse, shaft multifragmentary, and base fracture.

22.3 Clinical Signs

The initial evaluation focuses on fracture stability to establish whether surgical or conservative treatment is required.

Fractured metacarpal bones, from the first to the fifth, are characterized by edema and deformity; in oblique or spiral fractures, the finger may be malrotated and shortened. In the case of the thumb, the misalignment is more difficult to detect because it cannot be directly compared to a finger.

On examination, the hand presents swelling and dorsal deformity; when the patient is asked to close the hand into a fist, the interosseous muscles depress the metacarpal head and the knuckle disappears (dropped knuckle). A rotation problem is easily identified by having the patient flex the fingers into a fist, which demonstrates overlapping fingers or malrotation of the nail apparatus. If the patient cannot flex the fingers, local anesthesia at the fracture site is required to assess them for malrotation.

Shortening is detected by X-rays, it is more common in the little and index finger and in case of multiple fractures. The intermetacarpal ligaments prevent shortening by more than 3 to 4 mm in the central digits; shortening exceeding 5 mm reduces the efficiency of intrinsic muscle contraction and extension is impaired.1,2

22.4 Investigatory Examination

Three radiographical views, posteroanterior, lateral, and oblique, are required for diagnosis. Semipronated oblique views allow evaluating the index and middle finger; semisupinated oblique views enable evaluation of the ring and little finger. Computed tomography (CT) is rarely indicated and should be used in complex fractures.

22.5 Possible Concurrent Lesions of Bone and Soft Tissue

If soft tissue is involved and the fracture is open, the standard approach includes debridement, irrigation, and antibiotic administration. Extensive soft tissue loss requires coverage with local tissue if possible or else with a free flap. A wound requires surgical exploration and examination (and repair as needed) of the extensor tendon. Kirschner (K)-wire or intramedullary fixation is preferred in open fractures where soft tissue healing is a cause for concern. In open fractures with bone loss and inpatients with multiple metacarpal fractures, we feel that locking plate fixation is more effective in preserving length and alignment, if the soft tissue envelope permits. In patients with bone loss and/or soft tissue damage, external fixation is to be preferred. Dorsal fasciotomy is required in crush injury if compartment syndrome is to be prevented. In severely comminuted fractures with bone loss, cement application to replace the bone loss followed by use of secondary bone chips (induced membrane technique) or by a bone graft has been reported.3

22.6 Evidence and Anatomical Considerations

A lack of randomized control trials and nonrandomized comparative studies is reported by Daniel Winston in the FESSH Instructional Courses 2017 chapter “Metacarpal shaft fractures” (Evidence-based data in hand surgery and therapy—FESSH IC book).4 There is robust evidence for conservative treatment options in two randomized control trials. According to the literature, the application of a functional cast to manage transverse metacarpal fractures significantly improves outcomes. Selection of the treatment option for metacarpal fractures requiring fixation is less straightforward, and there is no significant advantage in using any one fixation technique.

The goals of treatment are to restore length, correct rotational deformity, and enable early mobilization to prevent stiffness.

A detailed anatomical knowledge is essential to understand local biomechanics and select the correct treatment; the index and the middle finger are fixed to the carpus whereas the ring and the small finger are mobile, with a flexion arc of 15 to 20 degrees at the carpometacarpal (CMC) joint.

Collateral ligaments of the metacarpophalangeal (MCP) joint are lax in extension and the joints may deviate in ulnar and radial direction; in flexion, the ligaments are taut and only minimal lateral motion is allowed; increased stability provides greater grip strength and key stability. The inter-metacarpal ligaments connect the volar plate between adjacent digits and stabilize the fingers, minimizing shortening and rotation in case of fracture; the volar plate stabilizes the MCP joint in extension. The interosseous muscles arise from the metacarpal bones and insert into the extensor expansion and proximal phalanx; proximally, the extensor carpi radialis longus and brevis insert into the base of the middle and index finger; the extensor carpi ulnaris attaches to the base of the metacarpal of the little finger. The ring finger is the only finger lacking tendon attachment and is therefore less prone to deformation forces in case of fracture. The metacarpal bones form a volar concave arc and provide a stable platform for the phalanges and neurovascular structures. The sagittal bands stabilize the extensor tendon over the head of the metacarpal and unite the collateral ligaments and the intermetacarpal ligaments of the volar plate.

When using a dorsal surgical approach, the complexity of hand anatomy should always be kept in mind to prevent impairment/loss of extension or stiffness.

The majority of metacarpal fractures can be managed without surgery. The fibrocartilage volar plate and the intermetacarpal ligaments form a strong structure between the bones and prevent shortening in case of fracture of a single metacarpal bone. Transverse fractures show a dorsal angulation, due to the unequal traction of the interosseous muscles and the force exerted by the extrinsic extensor tendons on the distal fracture segment.

22.7 Indications for Surgery

The tolerance to dorsal angulation is different in each metacarpal bone: 10 degrees are the maximum in the index finger and 20 degrees in the middle finger, owing to the poor mobility of these metacarpal bones; 30 and 40 degrees are the maximum in the ring and little finger, respectively, due to the greater mobility of the CMC joints. Each 2 mm of shortening results in 7 degrees of extensor lag. Since the MCP joints are endowed with 20 degrees of natural hyperextension, a shortening up to 6 mm is tolerable with a neutral MCP joint, although it results in inadequate force to the proximal interphalangeal (PIP) joint, leading to extensor lag (pseudoclawing). In spiral or oblique fractures, the rotational deformity is the most obvious problem and the one tolerated least: 1 mm causes 5 degrees of malrotation, which results in 1.5 finger overlap in flexion.5 Considering that most metacarpal fractures are stable, they can be managed conservatively with a variety of splint and cast techniques. Often, thumb shaft fractures can also be managed conservatively; malrotation and angular deformity are rarely a functional problem, because the CMC joint that can compensate for the lack of motion. Up to 30 degrees of angulation can be tolerated. Patients with 75% bony apposition of the thumb shaft may have aesthetic concerns. After 30 degrees of dorsal angulation, the MCP joint compensates for the volar plate stretch, allowing hyperextension.

Several approaches are available to restore normal anatomy and provide stability. The use of intramedullary fixation, external fixation, screws, and plates is determined by fracture type, the number of metacarpals involved, and the finger affected.

Different shaft fractures are managed with different hardware.

Transverse fractures are managed with intramedullary techniques, either anterograde or retrograde (nails, K-wires, headless screws), which involve minimal dissection. These techniques can also be used to treat multiple transverse shaft fractures. Sometimes these fractures require open reduction and internal fixation because of the disruption of surrounding support structures, especially the intermetacarpal ligaments.

In patients with shaft fracture of the fourth and fifth metacarpal, and sometimes also those with fracture of other metacarpal shafts, external fixation with K-wires, and/or external fixation (Joshi or others) is an optimal solution that avoids soft tissue damage and bone devascularization and provides stable reduction and early mobilization.

In case of a long oblique fracture line, the use of interfragmentary compression screws is indicated if the fracture length is double in length of the bone diameter; this permits the positioning of at least two screws. Soft tissue dissection is required for anatomical reduction, and achieving compression is technically demanding.

In short, oblique fractures or transverse fractures, plate and screws can provide stable fixation and ensure early mobilization. A variety of plates and screws are available; titanium and locking plates have been the most widely used in the past few years. This technique also involves soft tissue dissection. Complication rates up to 35% have been reported in some series due to hardware failure, infection, and poor fracture healing.1

The use of cast for immobilization does not induce stiffness; immobilization for the first few weeks to support soft tissue and bone healing after K-wire fixation has been reported to induce no functional impairment, whereas reoperation due to functional impairment was required when the cast was not applied following open reduction and internal fixation.

First metacarpal extra-articular fractures can generally be managed conservatively,⁶ although screw and plate fixation also enable early mobilization.⁷ An angulation exceeding 30 degrees usually requires closed reduction and K-wire fixation, which provides stabilization through the trapezoid bone or external fixation. The main concern with shaft fractures of the first metacarpal is the possible loss of the first web space due to adduction deformity determined by the flexor and extensor pollicis muscles, which reduces both pinch and grip strength of the hand.

22.8 Authors’ Favored Treatment Option

We always try to reduce and treat conservatively all metacarpal fractures, also in patients where two metacarpals are involved. In stable fractures, we suggest a cast where the involved ray is splinted, with the MCP flexed to 30 to 40 degrees; in unstable fractures, or when shortening is possible, continuous finger traction is applied in addition to the cast (see below).

If misalignment or rotational deformity cannot be managed conservatively, we favor intermetacarpal pinning and intramedullary techniques to provide fracture stability without affecting the extensor tendons or other soft tissues during dissection. Long spiral fractures can be managed by open reduction and screw fixation; plate fixation is reserved for transverse/short oblique, comminuted fractures, or for multiple metacarpal fractures where other methods are not practicable. In patients with severe trauma and multiple fractures where fasciotomy is indicated, external or internal fixation is performed depending on tissue condition.

These methods are described briefly below.

22.8.1 Nonsurgical Treatment

Whenever possible, we treat metacarpal shaft fractures conservatively to preserve the complex anatomy of the extensor mechanism and prevent stiffness or lack of extension; immobilization does not induce stiffness.7

Closed reduction of metacarpal shaft fractures involves local anesthesia (5 mL of 1% lidocaine injected into the fracture line and in subcutaneous tissue), with longitudinal finger trap traction, dorsal pressure at the fracture site, and correction of rotation with MCP joint flexion as needed. Three-point molding—dorsal pressure at the fracture site and palmar pressure proximally and distally—is important in transverse fractures.

Several different splint and cast techniques have been devised. We describe five major approaches⁸:

1. MCP joint flexion with full range of motion of IP joints ( Fig. 22.1a).

2. MCP joint extension with full range of motion of IP joints ( Fig. 22.1b).

3. Intrinsic-plus position with MCP joint flexion and IP joint immobilization in extension ( Fig. 22.1c).

4. Same as above, but with “continuous traction” applied with a tubular finger bandage and glue ( Fig. 22.1e) that is our favored treatment.

5. Functional treatment with a small “metacarpal cast” and syndactyly⁹ ( Fig. 22.1d).

The immobilization period is 5 weeks.

The potential for secondary displacement is so high that X-rays should be taken weekly for at least 3 weeks. Any displacement should be treated with repeat reduction and cast or surgery if necessary.

Tavassoli et al⁸ reported that MCP joint position and the absence/presence of IP joint motion during immobilization had little effect on motion, grip strength, and fracture alignment. These findings contradict the common notion that the MCP joint must be immobilized in flexion to prevent long-term loss of extension. Such outcomes are probably due to the young age of the patient population typically affected by these fractures, where tissues are smooth and less prone to develop stiffness.