Osteochondroma

What is Osteochondroma?

Osteochondromas, the most common type of benign bone tumor, make up 20% to 50% of all non-malignant bone growths. They develop on the surface of bones and are made up of both cortical (the outer layer of the bone) and medullary (the innermost part of the bone) bones with a cap made of hyaline cartilage (a type of connective tissue). A clear sign that distinguishes osteochondromas is the direct connection between the tumor and the underlying bone.

You can have just one osteochondroma, or you might have many, which is a genetically inherited condition known as hereditary multiple exostosis (HME) or familial osteochondromatosis. They can be found by accident, or they can become noticeable due to a mass you can feel, or symptoms caused by the tumor pressing on nearby structures. The symptoms can vary depending on what part of your body is affected. Complications include bone deformities, fractures, formation of a fluid-filled sac with or without inflammation (bursa formation with or without bursitis), restricted blood flow, neurological symptoms, and the possibility of the tumor turning into a malignant one.

X-rays are often used to diagnose osteochondromas. However, further imaging might be required to check for complications, assess the cartilage cap, or confirm that the tumor is connected to the medulla (innermost part) of the bone. In patients who are still growing, the tumor might increase in size. However, if the size or shape changes after the patient has stopped growing, this could be a cause for concern as it might indicate that the tumor has become malignant. Tumors can either be sessile, meaning they sit directly on the bone, or pedunculated, meaning they extend away from the nearest joint.

There are various types of growths that resemble osteochondromas, including subungual exostosis, dysplasia epiphysealis hemimelica (Trevor disease), turret exostosis, traction exostosis, bizarre parosteal osteochondromatous proliferation (BPOP or Nora lesion), and florid reactive periostitis. Other growths that need to be ruled out include subperiosteal hematomas, parosteal osteosarcomas, or juxtacortical chondromas – none of these have a direct connection to the medulla of the bone as osteochondromas do.

In most cases of single osteochondromas, no treatment is required. However, treatment using retinoid acid receptor gamma (RARy) agonists is being explored. If a surgical procedure is needed, it usually involves removing the outer edge of the tumor, but extensive surgery is reserved for cases where the tumor has become malignant.

What Causes Osteochondroma?

Osteochondroma, a bone growth, can come alone or as multiple growths in those with a condition called Hereditary Multiple Exostoses (HME). What causes a lone osteochondroma isn’t always clear and it may develop spontaneously (primary osteochondroma) from no known trigger. In other cases, however, osteochondromas can result from a specific type of bone fracture known as Salter-Harris, from surgery, or from radiation therapy (secondary osteochondroma).

Indeed, osteochondromas are the most frequent type of benign (non-cancerous) bone tumor linked to radiation therapy. They can show up in anywhere from 6% to 24% of cases after someone has had radiation therapy. These bone growths can take anywhere from 3 to 17 years to develop after the radiation therapy is completed.

In some cases, a secondary osteochondroma can develop as cancerous transformation of an existing solitary osteochondroma or from Hereditary Multiple Exostoses. Secondary osteochondromas are low-grade tumors meaning they grow slowly and are less likely to spread. These tumors are pretty rare in children, but they tend to be more common in people who are 50 years old and upwards. The most common spot for an osteochondroma to develop is in the pelvic area.

Risk Factors and Frequency for Osteochondroma

Osteochondroma is the most common type of benign bone tumor. It accounts for 30% of all benign bone tumors and 10% to 15% of all bone tumors, benign and malignant combined. Up to 2% of patients getting X-rays might have an osteochondroma that they didn’t know about.

This type of tumor usually shows up in the first four decades of life, with about 75% of cases found before the age of 20. Males are more likely to have osteochondromas. The actual number of osteochondroma cases is unknown, as many people have no symptoms and never get diagnosed. The type of osteochondroma also affects its incidence rate. Solitary osteochondromas are very common and make up 85% of all osteochondromas. The other 15% are a type called Hereditary Multiple Exostoses (HME).

HME is a genetic type of osteochondroma. It shows up on a dominant gene, but it doesn’t always affect women who carry the gene. About 65% of people with HME have a family history of it. In the West, new cases of HME occur at a rate of around 1.5% per year. It is usually found in the first ten years of a person’s life, and affects 3 times as many males as females. It is more common in Caucasians.

• The most commonly affected bone by an osteochondroma is the femur, accounting for 30% of cases.
• The next most common bones to be affected are the tibia and humerus, each comprising 10% to 20% of cases.
• Osteochondromas are very common around the knee.
• Osteochondromas originating from flat bones such as the pelvis, scapula, and spine, are rare.
• Osteochondromas originating from the vertebrae and ribs are even more rare.
• Bones that grow from cartilage cells displaced from growth plates can develop an osteochondroma.
• 50% of osteochondroma cases affect the long bones, with a ratio of 2:1 for lower to upper extremities.

Signs and Symptoms of Osteochondroma

Osteochondromas are growths on bones that usually get discovered by chance during X-ray tests. Another typical way they show up is as a harmless, touchable bump on the bone. These bumps can be unsightly, especially if they show up on visible areas like the upper shin bone or ribs. They can also cause a range of symptoms due to their effect on nearby tissues, such as swelling, fracture, or even malignant transformation.

• Harmless, touchable bump on the bone
• Can appear unsightly if visible
• Can cause swelling, fracture, or malignancy

These bone growths can also pinch nerves, causing symptoms like tingling and numbness. Vascular compression symptoms may include changes in skin color, loss of pulses, or changes in blood flow. There could also be complications such as blood clots, aneurysms, or false aneurysms. These symptoms are common when the growths occur around the knee, affecting the behind-knee artery, or nerves in the lower leg.

In some cases, osteochondromas can grow near tendons, causing discomfort and irritation when moving. They can also stress the soft tissues, causing a fluid-filled sac to develop along with inflammation.

If an osteochondroma occurs near the discs between the vertebrae, it could cause a hunched back or slipped vertebrae. Though these growths usually form outside the spinal cord, they seldom cause spinal cord pressure.

Hereditary multiple exostoses (HME), a condition associated with multiple osteochondromas, typically doesn’t show symptoms in newborns. Almost half of HME patients present visible tumors by the age of 5, and it increases to 80% by age 10. They can also show a range of deformities, including misalignment of the ankle, knee, or hip, differences in limb length, bending of the wrist or forearm, shortening of the fingers or toes. HME patients may also develop irregularities of the hip joint, hip impingement, or early-onset arthritis. Unusual dislocation or partial dislocation of the hip, kneecap, or ankle bone is also common.

Testing for Osteochondroma

Osteochondromas are changes that occur on the surface of your bones, often found at the end of the bone closer to the joint. They are connected with the main bone and are covered with a cartilage cap. These osteochondromas can be either sessile, which means they have a broad base, or pedunculated, meaning they have a narrow stalk and grow away from the nearby joint. Sessile osteochondromas are prone to a higher risk of becoming malignant or cancerous.

X-ray images may show changes like an increase in size, change in shape, inflammation of the bone tissue, or blurry edges of the bone. Sometimes, these changes may suggest a risk of the lesion becoming malignant or cancerous. Notably, lesions on flat bones like the shoulder blade, pelvis, and spine are often vague on X-ray and need more thorough imaging to better understand their nature.

A CT scan or MRI can give a clearer image of the lesion. Doctors may request these imaging tests if the X-ray suggests possible malignant transformation. These imaging techniques can also help determine the thickness of the cartilage cap covering the osteochondroma. Thickness varies among patients. Younger patients tend to have thicker caps, ranging from 1 to 3 cm, while in adults, the cap is often just a few millimeters. Caps that are thicker than 2 cm, particularly in adults, might suggest the possibility of malignant transformation, requiring further testing through tissue sampling.

MRI is also practical in assessing additional complications linked to osteochondromas, such as inflammation of the bursae – small fluid-filled sacs that cushion the bones, tendons, and muscles near your joints. Furthermore, MRI can also help identify if the osteochondroma is pressing against or alienating any nearby nerves or blood vessels. In such a case, the affected nerve might appear displaced, enlarged, or show certain signals under imaging. Muscles that the nerve controls may also show signs of injury or damage.

Bone Scintigraphy, a type of bone scan, is typically not very helpful in these cases. That’s because both benign (not harmful) and malignant (harmful) lesions may display increased activity, which may not definitively suggest whether the osteochondroma is harmful or not.

Treatment Options for Osteochondroma

If you have a small, single, symptom-free bone growth, you often won’t need any immediate medical treatment. In most cases, these bone growths, known as osteochondromas, can be safely managed without surgery until the patient has finished growing.

As of now, we don’t have medicines specifically for treating osteochondromas. However, there’s ongoing research into biological therapies, aimed directly at the body’s cells. One promising future treatment is something called RARy agonists. The RARy receptor plays a fundamental role in cartilage development and growth. By increasing the action of this receptor (this is what an agonist does), we might be able to stop abnormal bone growth.
Different studies on mice and rats have shown promising results, with indications that the number of osteochondromas can be reduced.

However, when needed, surgery can be done to remove the osteochondroma. This involves carefully excising the lesion from its base, which includes removing its stem and the cap made of cartilage. When it comes to children, we recommended delaying surgery until the child has finished growing, as osteochondromas are more prone to recur on growing bones. Extra care should be taken when the osteochondromas are near areas of the skeleton that are still growing.

There are situations where surgical removal is usually required. These include symptomatic osteochondromas, those causing cosmetic issues, or those with questionable features on imaging scans, such as irregular or unclear borders, isolated radiolucent (showing up as dark areas on an X-ray) areas, bone erosions, or destruction of the bone.

Furthermore, in spinal osteochondromas, surgery is needed when it causes nerve symptoms, if it presses on the spinal cord or blood vessels. Surgery is also crucial when osteochondromas restrict joint movement, cause dislocation, or happen to be around the joints.

The surgical removal of these growths becomes even more crucial in cases of multiple hereditary exostoses (HME), a condition characterized by the development of multiple osteochondromas, because of the higher chance of these growths becoming malignant and causing severe bone deformities.

When a patient develops secondary chondrosarcoma, a type of bone cancer that can develop from an osteochondroma, complete removal of the tumor is planned following the same approach used in typical chondrosarcoma treatment.

There may be scenarios when removing an osteochondroma may create a gap in the affected bone (like in the pelvis). In this instance, it may require additional reconstructive procedures, such as bone grafting, and internal fixation methods to restore the integrity of the skeletal structure after complete tumor removal.

What else can Osteochondroma be?

When a person is suspected to have osteochondroma, a type of bone growth, the doctor needs to rule out other possible conditions that might resemble it. These conditions can either be harmless (benign) or cancerous (malignant).

• Subungual Exostosis (Dupuytren exostosis): These are common skin lesions around the nail bed, often resulting from previous injuries or infections without continuity in the bone marrow. They can cause discomfort and could lead to skin ulcers.
• Dysplasia Epiphysealis Hemimelica (Trevor disease): This rare condition affects commonly the lower extremities. It causes multiple osteochondromas to develop on the ends of long bones and is three times more likely to occur in males. The patients often present with altered walking pattern, bone deformations, or noticeable lumps.
• Turret Exostosis: This refers to an unusual growth on the backside of either the middle or proximal phalanx (bones of the fingers or toes) with non-continuity in the bone marrow.
• BPOP (Nora lesion): This surface lesion, the cause of which is yet unknown but speculated to be injury-related, is seen primarily in the hands and feet bones. It doesn’t link with the bone marrow and shows no tendency to become malignant.
• Parosteal Osteosarcoma: This cancerous tumor originates on the surface of the long bones. It appears as a large, bumpy, dense bone mass without bone marrow continuity but could extend into the bone marrow as the disease progresses. It typically occurs at the end of long bones, often behind the knee.
• Juxtacortical Chondroma: This tumor forms on the bone surface and is mainly seen in individuals aged 20 to 40. It usually results in damage and inflammation to the adjacent bone tissue (cortex).
• Subperiosteal Hematoma: This surface lesion appears as a smooth and oval-shaped growth in people with prior injury history. It doesn’t show bone marrow continuity. Characteristically, the lesion could show distinctive features, such as cystic areas, calcium deposits or fat.

Accurate diagnosis is essential to determine the correct line of treatment for these varied conditions, which may appear similar to osteochondroma.

What to expect with Osteochondroma

The condition known as osteosarcoma usually has a positive prognosis, meaning the outcomes are generally good. This is because malignant transformation, or cancerous changes, occur in fewer than 1% of patients with this condition. Most of the time, these are small, solitary lesions that don’t cause any symptoms. If these lesions are near a joint (what we call ‘juxta-articular’), simply removing them can improve joint movement.

In a related condition called Hereditary Multiple Exostoses (HME), about 5% to 10% of patients can develop a specific type of bone cancer called secondary chondrosarcoma. However, in around 30% of HME cases, the exostoses (which are bony projections) have been known to shrink on their own. It’s been reported that in HME, malignant transformation can occur in as many as 25% of cases, though more recent studies put this figure closer to 3% to 5%. It’s worth mentioning that patients with HME can experience significant bone deformities that may affect their daily life.

For cases where the bone growths were completely removed, leaving no remnants of the cartilage cap and surrounding connective tissue (perichondrium), the risk of the growths returning is extremely low.

Possible Complications When Diagnosed with Osteochondroma

The complications linked to osteochondroma, a bone growth, can vary from concern about physical appearance to serious problems affecting the nerves or blood vessels, and even cancerous changes. The issues can be grouped into three main categories: physical deformity, mechanical impact, and malignant transformation.

Common Complications:

• Physical Deformity: The main symptom that leads patients to consult a doctor is usually a painless swelling. This deformity can be more severe in cases of multiple hereditary exostoses (HME) than with a single osteochondroma.
• Mechanical Impact: This impact can cause pinching and continuous mechanical pressure on nearby structures like nerves and blood vessels – with the knee being a typical location for an osteochondroma, risks to blood vessels can occur.
• Vascular Complications: Conditions such as pseudoaneurysm of the popliteal artery, vascular compression, and blood clots can hinder blood circulation to nearby structures.
• Neurological Complications: Depending on where the lesion is located, it can cause peripheral nerve damage (like common peroneal nerve palsy leading to muscle wasting in the front and side of the leg) and spinal cord issues.
• Malignant Transformation: This refers to the conversion of the lesion into a cancerous growth. It is estimated to occur in 1% of single lesions and up to 3% – 5% in HME. Increased size or changes in the radiographic appearance can hint towards malignancy. Chondrosarcoma is the most common form of malignant transformation.
• Surgical Complications: The risk of complications due to elective surgery for removal is higher than the tumor itself. Some of these complications may include nerve damage (neuropraxia), artery injury, compression of muscle tissue (compartment syndrome), and fracture of the fibula bone.

Preventing Osteochondroma

Osteochondroma is a type of non-cancerous bone tumor. It has a very small chance of turning into cancer–around 1% for singular tumors and a slightly higher chance of 3% to 5% for circumstances where multiple osteochondromas are present, a condition known as HME. These tumors typically do not cause any symptoms and are usually monitored rather than actively treated. Your doctor primarily uses traditional X-ray images to study them. An MRI, a more detailed imaging test, is saved for cases where the patient is experiencing symptoms from the tumor, or when the tumor is found in flatter bones.

If the osteochondroma is causing problems, your doctor will remove it surgically. If imaging tests reveal features that suggest the tumor might turn into cancer, it’s also a reason to remove it or take a sample of the tissue for testing. If you have the hereditary variety of the bone tumor, known as HME, you will need regular check-ups because of the slightly higher chance of the tumor developing into cancer.