With the snow and ice fast approaching the number of patients heading to the emergency room with suspected ankle fractures is quickly rising! This week I want to talk about a different type of fracture associated with ankle injuries: the 5th metatarsal base fracture!
The 5th metatarsal bone is a long bone in the foot that connects the rearfoot to the 5th toe. It is one of five metatarsal bones in the foot, each corresponding to a digit. Fractures of the 5th metatarsal base (the end of the bone closest to the ankle) are commonly associated with classic ankle injuries where the foot turns inward.
There is a muscle that passes along the outside of the ankle and inserts into the 5th metatarsal bone at its base called the peroneus brevis (PB). With an ankle sprain or injury where the foot turns inward, the PB contracts and pulls on the 5th metatarsal base, sometimes so strong that it avulses, or pulls a piece of bone away from the rest of the metatarsal bone. Therefore, when you twist your ankle and have not suffered an ankle fracture, you may not be completely ‘home-free;’
You should be suspicious of a 5th metatarsal base fracture any time that you are suspicious of an ankle injury. However, residual pain along the outside of the foot along the 5th metatarsal bone is a good indicator of injury to that area. Try sliding your finger along the outside border of your foot from your 5th toe back towards your heel. Along the way you should feel a “bump” which is the landmark of your 5th metatarsal base. Pain in that are can be indicative of a fracture, as that is the most likely place where the PB would have pulled off a piece of bone. Be particularly suspicious if the pain in that area has not improved several days after your ‘ankle twisting incident.’
Fractures of the 5th metatarsal base are particularly tricky to treat because the blood supply to that area of the bone is delicate. In the area of such fractures, two blood supplies are coming together, and disruption of their connection via fracture can permanently hinder the healing process, as blood supply is imperative to bone healing. Keeping that in mind, early detection of a 5th metatarsal base fracture is important so that immobilization can be initiated as soon as possible. The goal of immobilization is to decrease motion at the site of the fracture to encourage healing making the delicate blood supply less of a factor!
There are several ways in which immobilization of the fracture site can be initiated and the choice depends on the severity of the fracture. If the fracture is well aligned and shows no gapping between fragments, conservative treatment with immobilization in a short leg cast is indicated. If the fracture is displaced and there is significant gapping between the fragments, the fracture is unlikely to heel unless the fragments are brought back closer together. In this case, surgery may be indicated to place a pin or screw across the fracture site and immobilize the fragment with the “hardware.” A short leg case is still indicated to ensure that the patient remains non-weightbearing and minimizes the risk on non-healing.
In either scenario, 4-6 weeks in a cast should be expected so that the bone has time to heal. Once healing is noted and pain in the area of the fracture is severely decreased or absent, transition into a walking cast and eventually back into a comfortable supportive sneaker can be allowed.
Next time you twist your ankle, don’t be fooled into thinking is just an ankle injury, unless you’ve been cleared by your Podiatrist and no 5th metatarsal base fracture has been suffered!