Review of Complex Foot Fractures Affecting the Fifth Metatarsal Bone

You might not realize it, but a fracture of the long bone in the foot to the little toe can be a very serious injury. It's called a fifth metatarsal fracture and it's most often seen in athletes. What makes this such a problematic injury?

Disruption to any part of the anatomy such as the bones, ligaments, joint capsule, blood supply to the area, and nerves controlling sensation can lead to poor recovery. In fact, the risk of nonunion and even refracture after successful union is a reality for many patients.

To help us better understand fifth metatarsal fractures, surgeons from the Foot and Ankle Center of South Texas in San Antonio offer this review article on the problem. They provide information on the anatomy and classification of fifth metatarsal fractures. The three main parts of the fifth metatarsal bone include the base, diaphysis, and head.

The base is the part of the long foot bone (metatarsal) toe that sits next to the midfoot. The diaphysis is the middle portion or shaft of the long bone. Because the diaphysis is in the middle, one end attaches to the base. The other end (closest to the toes) connects with the third part called the head of the metatarsal. Each end of the diaphysis has a growth plate called the metaphysis, which allows the bone to grow longer at either end in a growing child or teenager. In the adult, the metaphysis and the diaphysis fuse together. A fracture of any of these components usually affects one of the other three.

The breaks are divided into base fractures, metaphyseal fractures, diaphyseal fractures, and head fractures. This classification scheme follows the bone anatomy of the three parts described. If the break involves the joint or joint capsule, it is considered an intraarticular fracture. If the bone is fractured more in the middle and away from any of the other bones or joints, then it is extraarticular.

Wherever the fracture occurs, the patient usually has pain, swelling, and can't put weight on that foot. Treatment depends on the location and severity of the fracture. The more displaced or separated the broken parts are, the greater likelihood that surgery will be needed to repair the damage.

If the broken ends of the base fracture are less than two millimeters apart, then the patient can use a cast boot, walking cast, or even a hard-sole shoe to protect the bone while it heals. Patients should expect about a six weeks period of time before healing is complete. This can take longer if there has been any damage to the ligaments, blood vessels, or nerves.

More severe base fractures and fractures that don't heal with conservative (nonoperative) care require surgery. An incision is made directly over the bone. The surgeon is careful to avoid the nerves in that area while aligning the bone and holding it together with screws. This procedure is called an open reduction and fixation.

Postoperative recovery can take quite awhile. The patient is treated in a series of steps. First is a weight bearing cast boot. The patient wears it for the first two to three weeks. Once pain has been controlled, then a motion-controlled athletic shoe is worn for another three to six weeks. A physical therapist sees the patient early on to begin rehab. The goal is to return the patient to sports participation as soon as possible.

With metaphyseal-diaphyseal fractures, an acute injury can become a chronic problem if the symptoms are mild at first. Even a mild ankle or foot malalignment can increase the likelihood of refracture. Sometimes a corrective shoe or shoe insert called a foot orthosis can realign the ankle and foot and prevent this from happening.

As with base fractures, metaphyseal-diaphyseal fractures can be compromised by disruption of the blood vessels or tears in the ligamentous attachments that hold the bones together. Loss of blood supply can result in slow healing or failure to heal. When MRIs are used, the fracture lines can be seen and the injury addressed quickly. The patient is placed in a non weight-bearing cast or goes right to surgery for internal fixation (plate and/or screws).

Sometimes, a bone graft is needed to help fuse the pieces of the broken bone together. There is a slight curve along the bottom of the fifth metatarsal that is preserved with wires and screws. To avoid a stress fracture of this bone, alignment of the foot and ankle is once again preserved as much as possible. The surgeon must leave enough bend in the bone without too much stiffness in order to have a successful fracture repair.

Head fractures are treated with conservative care (walking cast or cast boot) when the two ends of the fracture have not been displaced (moved apart). Too much displacement requires surgical repair. The authors describe the technique they use to expose the area and correct the problem. Head fractures are more likely to affect the joint so problems can occur after surgery with stiffness, hardware that sticks out or causes pain, and the formation of a painful neuroma (nerve tumor).

The authors comment that even with these treatment guidelines, there are still many unknowns about treating fifth metatarsal fractures. Future studies are needed to identify which patients need surgery and when (how soon). Results may vary with different types of fixation devices. Research to show which ones to use with each fracture type would be helpful. And finally, studies are needed to develop evidence-based guidelines on when it's safe for the athlete to return to sports (and at what level of activity).

Reference: 

Mark M. Casillas, MD, and Nicholas F. Ortiz. Fifth Metatarsal Fractures. In Current Orthopedic Practice. March/April 2009. Vol. 20. No. 2. Pp. 140-145.

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