Author: Nicholas S. Tedesco, DO, FAAOS


Chondroblastoma is a benign bone tumor that is made up of rapidly dividing, immature cartilage cells called chondroblasts. Chondroblasts are normal developmental cells that will start to turn on and off certain genes to become mature cartilage cells, or chondrocytes. They help maintain the structure and function of cartilage. However, in chondroblastoma, the cells remain in their immature state, divide, and eat away the bone. Therefore, they can be very destructive where they arise, including damaging bone, joints, and growth plates.


Chondroblastomas most commonly occur in children, adolescents, and young adults. The most common symptom in patients with a chondroblastoma is pain from the damage the tumor is doing to the bone. However, in rare cases, if the tumor is very enlarged and has damaged a growth plate, patients can notice differences in the length of their limbs or a limb growing unevenly.


In many cases there is no obvious lump because the tumors are buried deep in the bone. However, because of the inflammation caused by the tumor, there can be visible swelling, redness, and excessive heat coming from the affected area. The area could be very tender to touch. If it involves a weightbearing bone, there will often be a visible limp when the patient walks, and if it involves an arm or hand, quite often, the patient will not want to use the affected limb because of the increased pain when attempting to lift, push, or pull objects.


X-rays of the affected area are the first step in diagnosis, often showing a region in the bone that has lost calcium as the tumor takes over that space. There may be increased calcium immediately around the tumor where the bone is attempting to wall it off and keep it from causing further damage (Figure 1). The lesions are often near growth plates (in children), where the growth plate was (in adults),  or joints. These regions have the most cartilage, so often are the most affected. An MRI with contrast administered through an IV (Figure 2) should be done to help differentiate the diagnosis from other common mimickers, such as infections, cysts, and other types of bone tumors. Chondroblastoma is not detectable by  blood work, but blood work may be done to help rule out other conditions such as an infection.


Figure 1. Chondroblastoma of the kneecap in a young adult. Note the patchy loss of calcium in the bone where the tumor is as well as the thin wall of increased calcium immediately surrounding the lesion where the bone is trying to contain the tumor.

Figure 2. Chondroblastoma of the kneecap in the same patient as Figure 1. Notice the difference in color of the bone marrow where the tumor has replaced it as well as the thin black line of calcium going all the way around the tumor.


This is an extremely rare tumor in the general population, estimated to affect only a few hundred to a few thousand Americans a year.  Due to its rarity, it is highly recommended that patients are treated by an orthopaedic oncologist who has experience treating these tumors. Although this tumor is classified as benign and not a cancer, in an extremely rare subset of patients, the tumor can spread, or metastasize, to the lungs. Therefore, a screening chest X-ray at the time of diagnosis should be done and yearly for 5 years after treatment to monitor for this rare phenomenon. Usually, if the tumor has not come back by 5 years, it is considered cured. Treatment varies widely depending on size, location, and age of the patient, but the goal is to remove and/or kill the tumor.

To remove the tumor, sometimes this involves scraping it out of the bone, or cutting out the entire region of affected bone. Defects in the bone can be filled with bone graft, bone cement, and/or metal. If the growth plate is damaged, further surgeries to fix the deformity may be considered. To kill the tumor, that can include burning or freezing procedures called ablations. It could also involve chemical or drug delivery to the tumor cavity of compounds or medicines toxic to the abnormal chondroblasts. Recurrence is common. Several studies have reported recurrence rates in anywhere from 5% to 40% of cases.

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