An exostosis, also called a bony spur or osteoma, occurs when a bony growth extend beyond a bone’s usual smooth surface.
Exostosis can cause chronic pain or irritation, depending on its size and location. Sometimes, cartilage will grow over an area of exostosis, which is called osteochondroma.
These bony outgrowths often occur in the ear when they are called surfer’s ear, on the heel of the foot, or underneath the nail beds. They may also develop around the skull, including inside the mouth and sinuses. Children and young adults are more likely to experience exostosis.
In this article, we look at the different types of exostosis, their causes, symptoms, and treatments. We also look at how this condition is diagnosed and possible complications.
Causes and types of exostosis
Exostosis of the back of the heel bone is known as Haglund’s deformity.Image credit: Lucien Monfils, (2008, 19 July).
The causes of exostosis depend on the type and location of the bone overgrowths. Common causes include injury, chronic irritation of a bone, or a family history of exostosis. In some cases, the cause of exostosis is unknown.
Exostosis that is related to family history is called hereditary multiple exostoses or diaphyseal aclasis. In this case, the condition causes abnormal bone growths on the long bones, including the arms, fingers, legs, and toes.
When someone experiences exostosis, its type will depend on its location. Possible places for exostosis to develop include:
Ear canal or surfer’s ear
Exostosis that occurs in the ear canal is called surfer’s ear. It happens after repeated cold wind and water exposure cause bony growths to develop inside the ear canal.
Medically, surfer’s ear is called exostosis of the external auditory canal.
Exostosis of the nail bed is when a type of bony tumor grows underneath the nailbed. It can be caused by an earlier injury or infection and most commonly affects the big toe. Children and young adolescents are most likely to have this condition.
Exostosis of the nail bed is called subungual exostosis.
Mouth or jaw
This form of exostosis is a rare condition that causes bony growths from the jaw, usually inside the mouth in the back of the teeth. They are often the result of some trauma or injury to the gums and bones underneath.
Exostosis of the mouth or jaw is called buccal exostosis.
Heel of the foot or Haglund’s deformity
Haglund’s deformity is exostosis of the back of the heel bone. It is often made worse by the back of a shoe rubbing against the bone over a long time. For this reason, it is also called ‘pump bump.’
The cause of this is unknown, but genetics, a high arch, and a tight heel cord have been implicated.
Haglund’s deformity or exostosis of the back of the heel bone is also called retrocalcaneal exostosis.
Paranasal sinus osteoma refers to excess bone growth on the walls of the sinuses, which are the nasal cavities inside the skull.
This type of exostosis does not always cause symptoms, though some people may have long-term or chronic pain and sinus pressure because their sinuses cannot drain properly.
Some people who have exostosis may have no symptoms at all. They may not be aware of their exostosis until they have an X-ray for another condition, and a doctor identifies an area of bony growth.
Some people may identify their exostosis because they experience a blockage in a specific area, such as the sinus cavity or ear canal.
A person may start to experience symptoms if the bony growth causes complications, such as pressing on blood vessels or nerves. This can lead to localized pain.
People with hereditary multiple exostoses are usually diagnosed by the age of 5 years old. They may experience no symptoms or extreme symptoms, such as visibly abnormal bone shapes. This is especially true if they have osteochondromas because the areas of cartilage can harden over time and press on nearby blood vessels.
A person with hereditary multiple exostoses may have the following symptoms:
bowed arms or legs
shorter height than average
pain, especially with movement
limbs of different lengths
Exostosis can be either sessile or pedunculated:
Sessile exostoses: This type is broad and fixed to the bone.
Pedunculated exostoses: These are connected to the bone by a narrow stem.
Heel spurs: What you need to know
Heel spurs are bony outgrowths that occur on the heel of the foot. Learn more about the causes, symptoms, and treatment of heel spurs here.
While treatment is often unneccesary, surgery may be required in the case of severe exostosis.
In many cases, no treatment is necessary. If treatment is required, the type of intervention will depend on the location and severity of the exostosis.
A doctor may recommend surgery to remove the exostosis if the condition is severe and causes pain or psychological distress.
In the early stages of surfer’s ear, a doctor may recommend wearing earplugs or special types of head coverings to protect the ears and prevent the condition from getting worse. Otherwise, a surgeon can use a procedure called a canalplasty to remove the exostosis.
For Haglund’s deformity, a doctor may first recommend conservative treatment measures, such as wearing open-backed shoes that place less pressure on the heel bone. Taking anti-inflammatory medications such as Naproxen may help with painful symptoms.
Hereditary multiple exostoses
When caught before the bones are fully developed, the unusual bone growths in a person with hereditary multiple exostoses may be corrected with a surgery called hemiephiphysiodesis, or guided growth. This surgery may help the limbs to grow in alignment.
A doctor will diagnose exostosis by taking a medical history and considering a person’s symptoms. They will take into account the individual’s age, hobbies, and if they have a family history of exostosis.
Imaging tests will aid an exostosis diagnosis as X-ray images can help the doctor identify areas of bone outgrowth that are typical to exostosis.
CT scans and MRI can also be used to take more detailed images of the bone.
Further bone growth related to exostosis can ultimately cause pain, discomfort, and blockages of air, mucus, or earwax, depending upon where the exostosis is located.
Those with surfer’s ear may also develop complications. The bony growths can cause the ear canal to become blocked, trapping water and earwax inside. This can lead to infection and hearing loss.
Bone cancers are very rare in adults. A person with hereditary multiple exostoses is at an increased risk of developing a bone cancer called chondrosarcoma.
Exostosis causes a person to develop bony outgrowths from their bones. In some people, exostosis may not cause symptoms. In others, it can affect someone’s growth and cause significant complications.
Treatment is not always necessary and may depend on the size and location of exostoses, though surgery can be used to remove the bony spurs. Talking to a doctor is advisable to figure out the best treatment for each case.