Unicameral Bone Cyst

  • What is an unicameral bone cyst?

    A unicameral bone cyst is a benign fluid-filled cavity in the bone, which does not spread. It usually affects children between ages 5-15, but can affect older children and adults.

    Typically unicameral bone cysts appear in the long bones of the upper arms and legs, but other bones can be affected. For example, in older children and adults the cyst can form on flat bones such as the pelvis, jaw, rib cage, skull or heel bone.

    There are two classifications of unicameral bone cysts:

    • Active cysts, which tend to grow larger and are located next to growth plates — the soft parts of the ends of bones which determine how tall a person will grow — and can have long-term effects on bone length.
    • Latent cysts, which are located further away from growth plates and generally heal completely after treatment.

    Unicameral bone cysts can cause fractures or prevent a limb from growing properly. In some children, unicameral bone cysts can cause limb length discrepancies, meaning, for example, one leg would be shorter than the other. While leg function would not be impaired, the difference in length can cause gait issues and make some children and teens self-conscious.

  • Causes

    It is not known what causes unicameral bone cysts.

  • Signs and symptoms

    Most children with a unicameral bone cyst will experience no symptoms. In many cases, unicameral bone cysts are only discovered when the child breaks a bone that has been weakened by the bone cyst.

  • Testing and diagnosis

    At The Children’s Hospital of Philadelphia (CHOP), your child's diagnostic evaluation begins with a thorough medical history and physical examination of your child.

    Clinical experts use a variety of diagnostic tests to diagnose unicameral bone cysts, including:

    • X-rays, which produce images of bones on film.
    • Magnetic resonance imaging (MRI), which uses a combination of large magnets, radiofrequencies and a computer to produce detailed images of organs and structures within the body.
    • Computed tomography (CT) scan, which uses a combination of X-rays and computer technology to produce cross-sectional images ("slices") of the body.
    • Radioisotope bone scan, which helps locate an area of abnormal bone growth. 
    • Biopsy, which is a short surgical procedure to take a large sample of the growth, may be necessary to confirm any findings.
    • EOS imaging, an imaging technology which creates 3-dimensional models from two planar images. Unlike a CT scan, EOS images are taken while the child is in an upright or standing position, enabling improved diagnosis due to weight-bearing positioning.
  • Treatments

    Treatment for unicameral bone cysts depends on a number of factors including where the cyst is located, how strong the bone is where the cyst is located and what are the chances of a bone fracture.

    In some cases, your child’s physician may recommend “watchful waiting” — regular monitoring. Some cases of unicameral bone cysts resolve on their own.

    In more severe cases of unicameral bone cysts, active treatment may be recommended.


    If the bone is weakened in the area where your child's cyst is located, a surgery called curettage is generally recommended. Curettage involves scraping out the bone to completely remove the tumor and filling the hole with a bone graft or calcium phosphate pellets, which stimulate bone regrowth.

    Though surgery for unicameral bone cysts is highly effective, we understand that any procedure can be a stressful experience for your child and family. At CHOP, we offer a wealth of resources about how to prepare your child for surgery and what to expect during surgery.

    Additionally, we employ numerous best practices before, during and after surgery to decrease the risk of infection and increase positive outcomes. For more information about safety protocols at The Children's Hospital of Philadelphia, see safety in surgery.

  • Follow-up care

    At The Children's Hospital of Philadelphia, we offer ongoing support and services for patients and families at our Main Campus and throughout our CHOP Care Network. Our team is committed to partnering with parents and referring physicians to provide the most current, comprehensive and specialized care possible for your child.

    Unicameral bone cyst tumors recur in 15 percent of cases — even after treatment — so it is important for your child to continue to see a doctor after treatment.

    Your child will see the orthopedic surgeon about one to two weeks after surgery, then again at three and six months post-surgery. Annual monitoring by trained clinicians is strongly encouraged to monitor for possible recurrence of the growth and other complications.

    One such complication is limb-length discrepancy. If your child's unicameral bone cyst is located on a growth plate of a leg or arm, it can stunt the growth of that bone.

    If the limb affected is an arm, surgery is not recommended. If the limb affected is a leg, an additional procedure called epiphysiodesis may be recommended to remove the epiphysis (the end of a bone) to slow the growth of the limb without the cyst so the difference between the length of the two legs is minimized.

  • Outlook

    The health outlook for children with unicameral bone cysts is good. Most of these benign bone cysts will be treated successfully or will heal on their own by the time your child stops growing.

Reviewed by Jason L. Katz, PA-C, MHS, ATC-R on May 19, 2014