Os Peroneum Syndrome
The Painful Os Peroneum
An os peroneum is a small bone that is embedded in the peroneus longus tendon as it wraps around the cuboid bone on the outside of the foot. This bone is only present in ~25 percent of people. The purpose of the os peroneum seems to be to create a smooth joint-like gliding surface as the tendon bends almost 90 degrees when it wraps around the foot. Pain associated with this bone is known as os peroneum syndrome. A painful os peroenum is an uncommon cause of chronic lateral foot discomfort. Symptoms tend to occur in patients who are often older, and may have a higher arched foot. Conservative treatment of os peroneum syndrome includes comfort shoes, activity modification, and occasional injections. If symptoms of a painful os peroneum persist surgery to remove the bony ossicle may be beneficial.
What is an Os Peroneum?
So what exactly is an os peroneum? An “os” is an ossicle -a small oval-shaped bone that is actually embedded in a tendon. The os peroneum is embeded in the peroneus longus tendon. An os peroneum is only present in about 25% of the population. This ossicle of bone within the tendon is located right at the point where the tendon wraps around one of the hindfoot bones (the cuboid) and changes direction. The os peroneum thereby serves as a gliding surface to improve the functioning of the peroneus longus tendon. The area where the os peroneum rubs up against the cuboid functions in a similar manner as a gliding joint. It has a smooth cartilage-like surface to allow the ossicle to glide easily past the cuboid bone. There seems to be an increased propensity to have an osperoneum in patients with higher arched feet. These individuals also tend to have more force going through their peroneal tendons due to the shape of their feet.
What Causes a Painful Os Peroneum?
A painful os peroneum is a relatively uncommon source of chronic lateral ankle pain –discomfort in the outside part of the hindfoot. It is sometimes call os peroneum syndrome. The condition creates a localized ache that tends to worsen with activity. Pain is thought to occur when wear and tear affects the gliding surface of the os peroneum. Essentially there is arthritis at the articulation between the os peroneum and the cuboid bone. Pain is believed to result from this degeneration of the gliding surface, combined with the increased force going through the tendon because of its curve path.
Signs and Symptoms
A painful os peroneum appears to be more common in people as they get older, likely because wear and tear to the gliding surface usually occurs gradually over time. Symptoms are quite localized (Figure 1). Direct pressure over the affected area will exacerbate symptoms. The condition can be associated with pain throughout the peroneal tendons from peroneal tendonitis.
Plain x-rays of the hindfoot will demonstrate the presence of an os peroneum (Figure 2). A high arched foot pattern may also be noted. Sometimes the wear and tear degenerative changes can be seen on a regular x-ray. These x-ray changes include narrowing of the joint space and bone spur formation between the os peroneum and the cuboid.
Commonly an MRI or CT scan is required to visualize the changes associated with os peroenum syndrome. An MRI or a CT scan will often show clear evidence of arthritic changes involving the articulation between the os peroneum and the cuboid. These include loss of joint space, and potentially bone spurs associated with the ossicle. An MRI may also show increased edema in the os peroneum and the adjacent cuboid bone.
Treatment of Os Peroneum Syndrome
Non-operative treatment can often improve symptoms associated with os peroneum syndrome. These treatment elements include:
Comfort Shoes: Shoes with a stiff sole and a soft orthotic insert can help improve symptoms.
Activity Modification: Avoiding or limiting activities that create increased impact on the foot (ex. jumping) or require prolonged weight-bearing (ex. hiking or running) can helps improve symptoms.
Ankle Bracing: The use of an ankle brace or ankle taping can limit the motion of the hindfoot and associated the tendons, and thereby decrease the pain through the affected area.
Anti-inflammatory medication (NSAIDs): If a patient can tolerate anti-inflammatory medication these medications can decrease symptoms in the short term.
Corticosteroid injection: An injection often provides effective short and intermediate term improvement in symptoms. These corticosteroid injections are often performed with fluoroscopic or ultrasound guidance to ensure the injection is administered to the area between the os peroneum and the cuboid.
Surgical Treatment of a Painful Os Peroneum
For patients that have persistent symptoms that are localized to the os peroneum surgery may need to be considered. Surgery usually includes removal of the bony ossicle from the associate peroneus longus tendon. In some patients, it may also be advantageous to cut the peroneus longus tendon and transfer it to the nearby peroneus brevis tendon in order to remove the load from cuboid.
Edited January 28th 2024