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Metatarsal fractures

Description

Metatarsal fractures are common injuries to the foot often sustained with direct blows to the foot or twisting forces. If adequately assessed these fractures are easy to treat and have a favorable prognosis. However, if they go on to malunion or nonunion they can lead to disabling metatarsalagia. The metatarsals are also subject to stress fractures and can be seen in conjunction with other injuries of the mid-foot (both discussed elsewhere).

Structure and function

The metatarsals are convex bones of the forefoot consisting of a head, neck, shaft, and base. They are numbered from 1 to 5, medial to lateral or largest to smallest. The base of each metatarsal articulates with one or more of the tarsal bones and the head articulates with the proximal phalanges. The bases of each metatarsal also articulate with each other at the intermetatarsal joints. As a unit, the five metatarsals serve as the major weight-bearing complex of the forefoot. They act as a rigid lever to aid in propulsion and their flexibility aids in balance. The forefoot is mobile in the sagittal plane which enables it to accommodate uneven ground by altering the position of each metatarsal head.

The first metatarsal is larger than the others and most important for weight-bearing and balance; therefore, malunion or malignment at this location is especially poorly tolerated.    There are no interconnecting ligaments between the 1st and 2nd metatarsals, allowing for independent motion.  

The fifth metatarsal is divided into 3 zones (as shown), numbered 1 to 3 from proximal to distal. Zone 1 is the base of the metatarsal  where the peroneus brevis inserts. Avulsion fractures from the pull of this tendon are characteristic of zone 1.  Zone 2 is at the metaphyseal-diaphyseal junction, distal to the cancellous (styloid) tuberosity. Fractures involving Zone 2, called Jones fractures, are particularly susceptible to nonunion and malunion because this region of the bone has a tenuous blood supply. Zone 3 is the diaphysis;  fractures there are commonly stress fractures.  

Figure 1. The zones of 5th metatarsal. This seemingly arbitrary division is clinically important: fractures in each zone have distinct prognoses and treatment needs.

Patient presentation  

Patients with a metatarsal fracture present with acute onset of pain, swelling, ecchymosis, and tenderness to palpation in the forefoot, along with difficulty bearing weight. Gross deformities are rarely seen.

A history of direct impact suggests a transverse or comminuted fracture of the shaft, while a twisting-type injury causes an oblique or spiral fracture pattern.  

Avulsion fractures at the base of the fifth metatarsal, in Zone 1 where the peroneus brevis and plantar fascia insert, may occur during forced inversion of the foot and ankle while plantar flexed. This injury, commonly termed dancer’s fracture (or a pseudo-Jones fracture, a name that should be avoided), can happen after landing awkwardly from a jump or twisting the ankle while running: the ankle passively inverts at the same time the peroneus brevis tendon exerts an eversion force on the metatarsal and a fragment of bone accordingly avulses.

Figure 2. Radiograph of Dancer’s fracture - Zone 1 of 5th metatarsal

True Jones fractures occur in Zone 2 of the fifth metatarsal. The fracture line extends through the proximal articulation with the fourth metatarsal. This fracture is a result of tensile stress along the lateral border of the metatarsal during adduction or inversion of the forefoot. An athlete can sustain this injury with a sudden change in direction while the heel is off the ground. Injuries can range from simple isolated fractures of a single metatarsal to severe crush injuries with several fractures and soft tissue compromise. 

Objective Evidence

Radiographs in the anteroposterior (AP), oblique, and lateral planes should be obtained.  The films should include the entire foot to rule out associated injuries that may require treatment.

The lateral view is important for judging sagittal plane displacement of the metatarsal heads, and the oblique view can help detect minimally displaced fractures.

Fractures of the metatarsal can been with disruption of the tarsometatarsal joint–the so-called Lisfranc injury (discussed in its own section).  To detect Lisfranc injuries, it is important to carefully examine the radiographs for widening between the 1st and 2nd metatarsal space, fleck fractures at the base of the 1st metatarsal, and loss of alignment between the medial edge of the 2nd cuneiform and medial edge of the 2nd metatarsal base. Weight-bearing x-rays can be particularly helpful when trying to rule out of assess Lisfranc injuries.

Figure 3. Radiograph demonstrating a Lisfranc fracture by black circle (Credit: http://en.wikipedia.org/wiki/File:Lisfranc_fracture.jpg)

The most common metatarsal shaft fracture pattern is oblique or transverse with minimal displacement. Additional imaging is rarely necessary. However if there is high suspicion for a Lisfranc fracture, even if the radiographs appear normal, a CT scan or MRI can be helpful in identifying these injuries. 

Stress fractures are rarely visible on plain radiographs until symptoms have been present for 2-6 weeks; before that, an MRI or technetium bone scan may be necessary to make the diagnosis. 

Epidemiology

Excluding toe fractures, metatarsal fractures are the most common foot fracture and represent about 5% of all fractures. In children, the most commonly injured metatarsals are the first and fifth simply due to their anatomical exposure. In adults, high forces are required to fracture the larger and stronger first metatarsal so these are much less common. In industrial injuries, the fifth metatarsal is most commonly injured.

Differential diagnosis

A metatarsal fracture must be suspected in all patients with direct trauma to the forefoot and pain with ambulation. Maintain a high index of suspicion for an associated Lisfranc injury at the tarsometatarsal joint, especially with the involvement of the proximal first through fourth metatarsals and if the patient has plantar ecchymosis on exam. The metatarsophalangeal joint and phalanges should also be assessed for injury.

Red flags

In some sense, a metatarsal fracture is itself a red flag, calling attention to the need to exclude a more serious injury. In particular, fractures of the 2nd, 3rd or 4th metatarsal should raise suspicion of a ligament (Lisfranc) injury; a 5th metatarsal fracture must be scrutinized to make sure a zone 2 (Jones) fracture (which needs more protection) is identified; and a 1st metatarsal fracture must be examined closely to ensure there is no displacement. In short, Lisfranc injuries, zone 2 5th metatarsal fractures and displacement of  1st metatarsal fractures must be detected, and the presence of any fracture near their regions is a red flag alerting the examiner to their possible presence as well.

Pain that persists or even worsens after immobilization may be a sign of a (rare) compartment syndrome of the foot.  Late signs include pallor, paresthesias, and tense swelling–but don't wait for them to appear.

 

Treatment options and Outcomes

The goal of treatment is to restore alignment of the 5 metatarsals to preserve the arches of the foot and allow normal weight distribution over the metatarsal heads. 

Management varies widely depending on the location of the injury. Most isolated central (2nd - 4th) metatarsal fractures, as well as non-displaced fractures of the 1st metatarsal, can be treated with a walking boot and progressive weight bearing as tolerated.   Displacement of a first metatarsal fracture usually represents an unstable pattern that requires surgical fixation.  

Treatment of fifth metatarsal fractures depends on the Zone of injury.  Avulsion fractures (Dancer's Fractures or Zone 1) require only symptomatic therapy with a walking boot for 6 weeks.   Jones fractures in Zone 2 require at the minimum a non-weight bearing cast for at least 6 weeks, with a weight-bearing orthosis 6 or more weeks thereafter.  Immediate surgical fixation may be chosen for athletes. A fracture in Zone 3 is typically a stress fracture caused by overuse and treated "underuse": namely, cessation of the causative activity for 4 or more weeks.  

Most metatarsal fractures will go on to heal uneventfully with appropriate treatment, but complications do occur. Malunion, nonunion, or arthritic degeneration of the TMT and MP joints can lead to metatarsalagia and significant disability, especially in the 1st metatarsal.  In addition, malunion can cause plantar keratoses from significant plantar deviation of the metatarsal heads and dorsal keratoses from uncorrected dorsal angulation. 

Non-surgical treatment is advocated in patients with vascular comprise and neuropathy, as risk of infection and nonunion is elevated. Patients with diabetes are still candidates for fixation providing they have good vascular supply and protective sensation to extremities.

Risk factors and prevention

Not much can be done to prevent an injury to the metatarsal if a large force is applied to the foot in a traumatic incident. However, wearing the appropriate footwear can provide some protection.  

Miscellany

 

An avulsion fracture is fleck of bone pulled off by a ligament or tendon; it is similar to the sliver of paint that may be pulled off a wall when a piece of tape adherent to the wall is removed with sudden force.

The 5th metatarsal’s  growth plates is unusual in that it is at the base of the bone and oriented longitudinally 

Key terms 

Metatarsal fracture, Lisfranc joint, Jones fracture, cancellous (styloid tuberosity), metatarsalagia

Skills  

Be able to pinpoint fracture site by palpation along each metatarsal. 

Differentiate soft tissue injury from fracture by gently applying an axial loading to the metatarsal head.  

Correctly interpret radiographic findings and classify the different types of fractures. 

Be able to apply a cast or splint the foot.

 

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