Exostosis is a benign tumor that results in a bone growth. It can occur at different levels of the body. Exostosis of the foot and exostosis of the knee are two common cases. Surgical treatment is only considered if discomfort or a risk of complications is observed.

Definition of exostosis

Exostosis is also called osteochondroma or osteogenic exostosis. It is the most common benign bone tumor. It results in the development of an outgrowth in the bone. It develops from cartilage, the tough, flexible tissue that covers the joints.

We distinguish:

• single, solitary or sporadic exostosis that appears in isolation;
• multiple exostoses which are the consequence of an exostosing disease or disease of multiple exostoses.

Causes de l’exostose

In the majority of cases, the exostosis is solitary. Its cause is still poorly understood. It could be a growth defect or be related to trauma.

Regarding multiple exostoses, they are due to an inherited genetic disease. This is called multiple exostosis disease or Bessel-Hagen disease. It is a rare disease with a prevalence of one in 20 cases.

Locations of exostoses

Exostoses can develop on any bone but often tend to develop at the ends of long bones. They are particularly frequent in the leg with exostosis of the knee and exostosis of the foot. The shoulders and wrists are also areas that are quite frequently affected. In rarer cases, exostoses have been observed in the ribs, spine, shoulder blades and pelvis.

Diagnosis of exostosis

The discovery of exostoses can happen accidentally during medical imaging examinations. 

These benign tumors can also be suspected in front of certain symptoms, in particular in the event of small bumps on the level of a member associated or not with pain. Several examinations can then be considered:

• a magnetic resonance imaging (MRI) exam which not only confirms the diagnosis but also looks for all possible complications;
• a computed tomography, or scanner, which allows a precise analysis of the exostosis;
• a genetic test in case of multiple exostoses.

People affected by exostosis

The exostoses appear mainly between 10 and 20 years, and are generally diagnosed before 30 years. They can develop in both men and women, but men seem to be more often affected.

Possible swelling

The exostosis is asymptomatic in a majority of cases. No symptoms appear, which explains the often fortuitous discovery of exostoses.

In some cases, swelling can be seen in the exostoses. It can result in the presence of small bumps that are not necessarily painful and / or bothersome.

Risk of discomfort and / or complications

Discomfort and pain may be noted in some cases. Depending on the size and location of the exostosis, it can also be the cause of:

• growth disorders;
• axial deformations;
• compressions at the vascular, nervous or spinal cord level (related to the spinal cord);
• bursites ;
• muscle tears;
• fractures (rare);
• degeneration into chondrosarcoma, a type of bone cancer (rare in case of a single exostosis but more common in cases of exostosing disease).

Treatment is considered in case of discomfort or complications. This is a surgical operation to remove the tumor (s).

To date, there is no prevention for exostosis.