The peroneus brevis, sometimes called the fibularis brevis muscle, is the shorter and smaller of two lateral leg muscles running down the outer sides of each lower leg. This muscle is important for walking, running, and standing on your toes, among other activities.
It emerges approximately one-third of the way from the top of the fibula, from the lateral or outer side. After rounding the lateral malleolus of the ankle, it terminates at the fifth metatarsal bone of the upper and outer side of the foot.1
Along with the other lateral leg muscle, the peroneus longus, the peroneus brevis plays an instrumental role in foot motion. It helps with flexion, the ability to point your foot away from the body, as well as eversion, which is tilting the sole of the foot away from the body.2
Injury to the peroneus brevis is not uncommon and is most often associated with ankle fracture, sprain, or dislocation of its tendon. Painful chronic inflammatory conditions, like tendinitis, can also impact the peroneus brevis, prompting a wide range of treatment options.
Structure and Location
The peroneus brevis is composed of striated skeletal muscle fibers, which are the type that you can voluntarily control. These fibers arise from the distal side (farthest from the middle of the body) of the fibula, next to the anterior intermuscular septum (a band of tissue dividing the lateral and anterior or “front-facing” compartments of the leg).
Running downward and towards the middle just next to the peroneus longus, the fibers form a muscular border or “belly” along the outside of the leg.1
At approximately two-thirds of the way down the fibula, the peroneus brevis coalesces into a broad flat tendon. This tendon continues downward and towards the middle just in front of the tendon of the peroneus longus, curling behind the lateral malleolus (the outer part of the ankle), crossing the ankle, to the outer foot.
It terminates at the base of a protuberance (or “tuberosity”) of the fifth metatarsal bone of the upper and outer side of the foot.1
Some are born with anatomical variations involving the peroneal muscles, which may or may not cause symptoms or issues. Here’s a quick breakdown:
Peroneus quartus is common variation in anatomy seen in up to 20% of people, in which an additional peroneus muscle emerges in the foot and ankle.4 Though it’s usually asymptomatic, it can contribute to tendonitis of the peroneus brevis tendon.
Fused peroneus brevis and longus is a much rarer abnormality, in which there is no separation between the two lateral leg muscles.5
Low-lying peroneus muscle is another congenital variation, in which the belly of the peroneus brevis extends further down than usual. Though it can be asymptomatic, this condition increases the chance of tendonitis or other tendon issues in the foot.4
In coordination of the peroneus longus, as well as a number of other muscles of the calf and lower leg, the peroneus brevis is intimately involved in ankle and foot motion. Since it wraps around and crosses the ankle joint, it can use this as a kind of fulcrum.
Specifically, this muscle is associated with two different activities:
Plantarflexion: This is when you point your toes away from the body. In a coordinated fashion with surrounding muscles, the peroneus brevis tenses and helps to push the foot down.
Eversion: Since this muscle accesses the side of the foot, when it tenses it can also help curl the sole outward, away from the middle of the body.2
The location of the peroneus brevis makes it particularly prone to injury problems. Ankle and foot injuries can definitely impact this muscle and are especially damaging to its tendon. These conditions may arise:
Tendon sprain: The most common injury of the peroneus brevis tendon is due to ankle sprain or fracture. An unnatural motion of the ankle can stretch and tear this tendon, leading to swelling and pain. This can be caused by severe ankle sprains or fractures, such as those caused by supination-adduction (SAD) injury (rolling your ankle).
Tendon dislocation: In more severe cases of ankle sprain or fracture, the peroneus brevis to be ripped completely or partially out of place. This leads to a great deal of pain and inflammation. Fracture of the fifth metatarsal bone of the foot, sometimes called Jones fracture, can partially or complete dislocate the tendon.
Tendon splitting: Severe injury can also cause this tendon to split along a vertical axis, which can severely impact function.
Microtears: Tiny tears in the peroneus brevis form due to wear, tear, and repeated injury. These little rips can advance to peroneal tendonitis, a chronic condition characterized by swelling and pain.3
Treatments for sprains, dislocations, or other conditions of the peroneus brevis range from physical therapy to pharmaceutical treatments and surgeries. Generally speaking, doctors try to explore less-invasive options before opting for surgery.
Rehabilitation from peroneus brevis injury very much depends on the specific case, but here are the most common approaches taken:
Immobilization: In many cases, the tendon can be allowed to heal on its own; however, this does require a period of wearing a cast, brace, or medical boot to stabilize the area. Recovery time depends on the scope of the injury, and you may need assistance walking.
Pharmaceutical treatments: Medications that manage pain and inflammation, such as non-steroidal anti-inflammatory drugs (NSAIDs), can also help. In minor cases, over-the-counter varieties, such as Advil (ibuprofen), Tylenol (acetaminophen), and others can help, though you may need prescription medication.
Surgical repair: Severe cases of dislocation or splitting may require surgery to repair and/or reposition the damaged tendon. This may involve grafting together torn pieces of the tendon to repair it or using surgical wires or meshes to prompt healing. Nowadays, minimally-invasive techniques are available, reducing operative time and recovery.4
Rest, ice, compression, and elevation (R.I.C.E.): If you’ve injured yourself and need immediate relief from symptoms, regular sessions of R.I.C.E. can help. Ensure no weight is placed on the foot, ice the area regularly, compressing it, and keeping it elevated are a standard approach to reduce pain and swelling associated with injury or tendonitis.
Physical therapy: Throughout rehabilitation, working with a physical therapist—as well as performing prescribed exercises at home—can greatly boost outcomes. These experts will show you specialized exercises you can do to help promote proper healing of the affected area6