Metacarpal Fractures Causes, Presentation and Treatment

Metacarpal fractures are fractures of long tubular bones of hand that connect carpal bones to proximal phalanges.

Metacarpal fractures account for 30-40% of all hand fractures. The metacarpal neck is the most commonly fractured region which constitutes around 10% of all hand fractures.

They mostly occur between age group 10-30 years. Men are affected more.

Metacarpal fractures are divided into fractures of metacarpal head, neck, shaft. The treatment is based on the metacarpal involved and location of the fracture.

A degree of angulation which varies with the location of fracture is acceptable but malrotation is not.

Anatomy and Mechanism of Injury

[Read detailed Hand Anatomy}

Metacarpals are the long tubular bones between carpal bones and phalanges. They are five in number and numbered as first, second, third, fourth and fifth from thumbside to little finger side.

Each metacarpal has a longitudinal arch with convexity on the dorsal side and concavity on dorsal side. Together, the arrangement of metacarpals in hand also has a collective arch transversely.

Metacarpals held together to one another are joined proximally and distally by ligaments.

Out of all metacarpals, the second and third metacarpals are fixed rigidly at the base whereas the fourth and fifth carpometacarpal joints are capable of at least 15° and 25° of motion, respectively.

The carpometacarpal joint of the thumb is highly mobile.

Extensor carpi radialis longus and brevis tendon insert on the bases of the second and third metacarpals, respectively. The flexor carpi radialis inserts at the base of the second metacarpal bone.

These insertions also contribute to the rigid stability of the second and third metacarpals.

Extensor carpi ulnaris inserts on the dorsoulnar aspect of the fifth metacarpal base. This often causes a displacement of the fifth metacarpal fractures.

The metacarpophalangeal joints are multiaxial condyloid joints. The main movements that occur on this joint are flexion and extension. Limited lateral motion and circumduction can also occur.

The peculiar shape and alignment of the head relative to shaft causes of the collateral ligaments to become relax in extension and become taut in flexion at 70 degrees and beyond.

Thus we can have lateral motion in the extended metacarpophalangeal joint position because ligaments are relaxed.

When the metacarpophalangeal joints are taut inflexion, it functions to stabilize the finger.

The volar plate is a cartilaginous structure on the palmar aspect of each metacarpophalangeal joint. It , which limits extension of the joint. The volar plate is thicker at its insertions on the proximal phalanges and weaker at the proximal metacarpal origin. Volar plates are interconnected through deep transverse intermetacarpal ligaments, which provide additional volar stability.

A direct blow to hand or rotational injury with axial load are the most common causes of metacarpal fractures.

High energy injury as in motor vehicle accident results in  multiple fractures.

Apart from fractures and dislocations, soft tissue injuries like tendon injuries orneurovascular compromise due to soft tissue injury may be present.

Most of the injuries are closed by but open fractures may occur especially in crush injuries.

Base of metacarpal is quite stable as dorsal and palmar carpometacarpal ligaments and interosseous ligaments act as stabilizers. Carpometacarpal joint injuries may result in dislocations with or without fractures, often avulsion or chip fractures on the dorsal side.

Carpometacarpal dislocations are often caused by high energy trauma and could cause multiple metacarpal joint injuries.

 

Injury to the fifth metacarpal base is often caused by a direct blow to the ulnar border and is an extrarticular fracture.

In contrast axial loading of the results in intra-articular fracture.

Metacarpal shaft/neck fractures are caused by axial loading, direct blow, or torsional loading.

These fractures could be transverse, oblique, or spiral.

Metacarpal neck fractures are the most common metacarpal fractures and usually result from striking with a clenched fist.

Fractures of the metacarpal head are caused by direct trauma to the joint or an avulsion injury of the collateral ligaments. These injuries could be intra-articular as well.

In addition, metacarpophalangeal dislocations can occur. These are almost always dorsal as the only dorsal restraint present is joint capsule and extensor mechanism. These dislocations result from forced hyperextension of the digits.

Clinical Presentation of Metacarpal Fractures

The patient complains of pain and swelling after the injury. The swelling can be substantial in high energy injuries.

Open wounds and associated injuries could be present. Dorsal wounds over metacarpal fractures almost always indicate open fractures.

The location of swelling or deformity could guide towards the location of the injury. For example deformity at the metacarpal base may indicate carpometacarpal dislocation.

Malrotation can be assessed by noting the finger alignment in flexion. With flexion, each digit should point toward the scaphoid tuberosity.

A comparison to the opposite side can highlight the difference if present.

Fingers should be examined by flexion and extension to rule out tendon injuries in the presence of open wounds.

A detailed neurovascular examination should be conducted to check the status.

A hyperextension posture of the digit with loss of joint flexion and dimpling of the skin indicates dorsal dislocation.

ray of hand showing a united fracture of the second and third metacarpal.

Imaging

Metacarpal fractures are sufficiently evaluated by plain x-rays.

AP, lateral and oblique views are often done views for evaluation of these fractures.

To accommodate a specific region, the views can be customized.

For example, lateral view in 30° pronated position is done for the second and third metacarpal fractures.

Similarly, fourth and fifth metacarpals are better visualized with and a 30° supinated lateral view.

Brewerton view is done to look for fractures in metacarpal heads and is done by flexing metacarpophalangeal joint 65° with the dorsum of the proximal phalanx flat against the radiograph cassette and the beam angled 15° ulnar to radial.

It may be needed in multiple carpometacarpal dislocations and complex metacarpal head fractures.

Roberts view is the best view to see the thumb carpometacarpal joint fracture or dislocation.

It is a true anteroposterior view of thumb and is done with the forearm in maximal pronation & dorsum of the thumb resting on the x-ray cassette.

Treatment of Metacarpal Fractures

Principles of Treatment

• Most metacarpal injuries are managed by closed reduction and immobilization by the splint.
• If the reduction cannot be maintained closed pinning under c-arm should be done.
• Following are generally treated by surgery
  • Presence of malrotation
  • Shortening more than 3-4 mm
  • Open fractures
  • Multiple fractures or dislocations
  • Irreducible or malreduced fractures
  • Articular step more than 2mm
  • Associated injuries to carpal bones
  • Unacceptable angulation in shaft fractures which does not reduce or hold
    • More than 10 degrees in second and third metacarpals
    • More than 20 degrees in the fourth metacarpal
    • More than 30 degrees in fifth metacarpal
  • Metacarpal neck fractures with angulation which does not hold or reduce
    • More than 15 degrees in the second and third metacarpal
    • more than 50 degrees in third and fourth
  • Almost all metacarpal head fractures

Splinting

The splint is often required after nonoperative as well as operative treatment.

The splint is applied with the wrist in 20-30 degrees of extension and metacarpophalangeal joints in 70-80 degrees of flexion.

Especially after closed reduction, the splint should be applied both on the dorsal and palmar aspect of metacarpals. As phalanges need to be mobile, the palmar splint should not go beyond proximal interphalangeal joint whereas dorsal splint covers phalanges.

Immobilization should continue for 3-4 weeks or earlier if fixation is rigid. Active finger movement is encouraged throughout the immobilization period.

Surgical Options and Implant

• External fixation – severely comminuted fractures
• MCP fusion- Arthritis late disease
• Closed reduction and percutaneous pinning – Fracture can be reduced but not stable
• MCP arthroplasty- Severely comminuted fractures
• Open reduction and internal fixation
  • Dorsal Approach
  • Irreducible fractures or other indications as above
  • Plates used for transverse fractures, screws for oblique and spiral fractures

Treatment of Specific Injuries

Metacarpal Base Injuries

Undisplaced fractures require splinting only.

Displaced fractures with more than 2 mm of displacement or dislocation or angulation require reduction with splinting or percutaneous pinning.

 

Displaced and irreducible fractures would require open reduction and internal fixation.

Metacarpal shaft fractures

These fractures are best treated nonoperatively by closed reduction and splinting.

Percutaneous pinning can be considered in some selected cases.

Open reduction and internal fixation is rarely indicated.

The amount of acceptable angulation varies depending on the location of the fracture and the specific metacarpal involved

Metacarpal neck fractures

Minimally angulated or displaced fractures can be managed with simple immobilization for 3-4 weeks. The degree of acceptable angulation is controversial and

Reduction followed by immobilization or reduction and fixation is considered for cases where angulation is not acceptable.

Metacarpal head fractures

Nondisplaced fractures can be managed with splinting for 3 weeks, followed by gentle motion. Fractures in which the articular surface is displaced greater than 1-2 mm should be managed operatively.

Metacarpophalangeal dislocations

Reduction of simple MCP dislocations is carried out easily with local or regional anesthesia

MCP dislocations that are not readily reducible are characterized as complex. The reduction is prevented by either interposed soft tissue These dislocations require operative reduction.

Complications of Metacarpal Fractures

• Carpometacarpal injuries
  • Recurrent dislocations
  • Arthritis of the involved joint.
• Metacarpal shaft and neck fractures
  • Malunion
    • Angulation – Loss of dorsal contour, prominence of the metacarpal head in the palm
    • Rotation – Overlapping fingers on flexion
  • Metacarpal Head
    • Metacarpophalangeal joint stiffness

Prognosis

Proper treatment leads to good results. Nonunion is rare but malunion is common.

References

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• Kollitz KM, Hammert WC, Vedder NB, Huang JI. Metacarpal fractures: treatment and complications. Hand (N Y). 2014 Mar. 9(1):16-23.
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