Unicameral Bone Cyst: Understanding Solitary Bone Cysts in Children
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
TL;DR
A unicameral bone cyst (UBC), also called a simple or solitary bone cyst, is a benign (noncancerous), fluid-filled space inside a bone that is most often found in children and adolescents under 20. Most children have no symptoms and the cyst is discovered by chance on an X-ray, but a cyst can weaken the bone enough to cause a fracture. Most cysts go away on their own once a child is fully grown. Large or symptomatic cysts, or bones at risk of fracturing, may need treatment with steroid injections or surgery, and cysts return after treatment in up to 50% of children.
Quick Answer: Key Facts About Unicameral Bone Cysts
Feature | Details |
What is it? | A noncancerous, fluid-filled single chamber inside a bone |
Who gets it? | Mostly children and adolescents under age 20; more likely in males |
Common locations | Long bones of the arms and legs — most often the upper arm near the shoulder and the leg near the hip |
Main risk | A fracture, because the bone around the cyst can weaken |
Recurrence | Up to 50% (1 in 2) after treatment, more likely in very young children |
Long-term outlook | Most cysts go away on their own when a child is fully grown |
What the research says
Cysts cluster in predictable places and tend to resolve with growth. A 2018 review reports that about 85% of unicameral bone cysts occur in children and adolescents, that the proximal humerus and femur account for almost 90% of cases, and that cysts are more aggressive in the first decade of life, with a recurrence rate four times that of adolescents. By skeletal maturity most cysts tend to resolve, and nonoperative treatment may be a viable option for many patients with small or symptomatic lesions. (Noordin et al., Ann Med Surg, 2018)
There is no consensus on the single best treatment. A Cochrane review found only one eligible randomized trial (90 children) comparing steroid with bone marrow injection. Healing on X-ray at two years was seen in 16 of 38 children after steroid injection and 9 of 39 after bone marrow injection (risk ratio 0.55, 95% CI 0.28 to 1.09; very low-quality evidence), and healing was well under 50% for both. The reviewers concluded that the evidence is insufficient to determine the best method. (Zhao et al., Cochrane Database Syst Rev, 2017)
What is a unicameral bone cyst?
A unicameral bone cyst, also known as a simple or solitary bone cyst, is a benign (noncancerous) bone tumor that appears as a fluid-filled space inside a bone. The word "unicameral" means "one chamber" and describes the single fluid-filled chamber in each cyst. These cysts occur most often in children and adolescents under 20 and are more likely to occur in males.
Unicameral bone cysts can grow in any bone. Most form in the long bones of the upper arms near the shoulders and in the legs near the hips. Usually, a unicameral bone cyst is painless and is found by chance on an X-ray taken for another reason. Pain and swelling can occur if the bone around the cyst fractures. Their actual occurrence is unknown because many people with these cysts have no symptoms and are never diagnosed.
What are the types of unicameral bone cysts?
Unicameral bone cysts develop near growth plates, which are the areas of active growth near the ends of bones. As a child's bone grows, the cysts tend to move away from their growth plate. Healthcare providers describe two types:
Active cysts are next to the growth plate and may expand over time. As the cyst expands, the bone around it can weaken and fracture.
Latent cysts are located away from the growth plate and are no longer growing. As a child reaches maturity and bone growth stops, most cysts will fill in with bone and disappear.
What causes it, and what are the symptoms?
Healthcare providers aren't sure what causes unicameral bone cysts. A defect in the bone or a blockage in a vein may cause fluid to build up and cysts to form.
Most children with unicameral bone cysts have no symptoms or only mild symptoms close to where the cyst is located, such as:
Slight pain.
Swelling.
Tenderness.
If the cyst causes the bone to fracture (a pathologic fracture), symptoms include:
Bruising.
Difficulty moving the limb.
Pain.
Swelling.
A visible change in the shape or alignment of the bone.
Some cysts (1 in 4) will heal on their own after a fracture.
How is a unicameral bone cyst diagnosed?
An X-ray is the main tool healthcare providers use to diagnose a unicameral bone cyst, because X-rays typically show good contrast between the bone and the cyst.
Your child's provider may recommend additional testing to distinguish a unicameral bone cyst from other conditions, such as an aneurysmal bone cyst or fibrous dysplasia:
MRI: Used to evaluate the inner cavity of the cyst.
CT scan: Especially useful for cysts in areas that are difficult to assess with X-rays, such as the spine or pelvis.
Biopsy: A small tissue sample is removed, and a pathologist examines it under a microscope for abnormalities.
How is a unicameral bone cyst treated?
Your child's treatment depends on many factors, including the size of the cyst, the strength of the bone, their symptoms, and their age and activity level.
For small cysts that don't cause symptoms, your child's provider may monitor the cyst with routine X-rays. Your child may also need to limit certain types of physical activity to reduce the risk of fracture. If the cyst is large, causes symptoms, or the bone is at risk of fracturing, your child's provider may recommend treatment.
Steroid injections
Minimally invasive treatment with injections can be effective in helping cysts heal. Your child's provider numbs the area and uses a needle to remove fluid from the cyst. The provider then injects methylprednisolone, a steroid, into the cavity. This may require a series of injections.
Curettage and bone grafting
Sometimes a surgical procedure called curettage is the best treatment option. A surgeon opens the cyst and scrapes out its contents and lining. The surgeon may apply a substance, such as ethanol, to the inside of the cavity to destroy any remaining cyst cells. Afterward, the surgeon may fill the cavity with a bone graft (a piece of bone taken from another part of the body or from donated bone) or with cement.
What is recovery like?
After surgery, your child's provider will immobilize the affected bone with a cast or sling while it heals. Most children resume their normal activities within three to six months after surgery. Follow-up care may include physical or occupational therapy to help your child gradually return to full activity.
What if the bone fractures?
Treatment for a fracture usually involves a cast to immobilize the bone and allow it to heal. If the fracture involves the growth plate, your child may need additional treatment depending on the severity, such as casting, setting the bone, or surgery, possibly with metal screws, pins, or plates. Some cysts (1 in 4) will heal on their own after a fracture. If the cyst does not heal, your child's provider may recommend surgery to remove the cyst and prevent another fracture.
Can the cyst come back?
Unicameral bone cysts return (recur) after treatment in up to 50% of children (1 in 2). Recurrence is more likely in very young children. Your child's provider will schedule routine follow-up visits and X-rays to monitor for a returning cyst. Rarely, a fracture or surgical procedure may cause the bone to stop growing; if this happens, your child's provider will offer care and resources.
The Bottom Line
A unicameral bone cyst sounds alarming, but it is a benign, fluid-filled space in a growing child's bone, and most cysts cause no symptoms and go away on their own once growth is finished. The real concern is a fracture through a weakened bone, which is why large cysts, symptomatic cysts, and cysts that put the bone at risk are treated with steroid injections or surgery, and why follow-up X-rays matter — cysts come back in up to half of children, especially very young ones.
Take the Next Step
Call your child's provider if your child complains of pain near a bone or if you notice any swelling. Early detection of a unicameral bone cyst can prevent possible fractures and bone abnormalities. If your child has already been diagnosed, keep up with routine follow-up visits and X-rays until growth is complete.
Frequently Asked Questions
Is a unicameral bone cyst a type of cancer?
No. It is a benign, noncancerous tumor.
Will my child's cyst go away on its own?
Most unicameral bone cysts don't cause symptoms and resolve on their own when a child is fully grown. Latent cysts are the ones that most often fill in with bone once bone growth stops.
Can a bone cyst affect my child's growth?
Rarely, a fracture or a surgical procedure may cause the bone to stop growing. If this happens, your child's healthcare provider will offer care and resources. Close monitoring by a specialist is important.
How common is recurrence after treatment?
Unicameral bone cysts return after treatment in up to 50% of children (1 in 2). Recurrence is more likely in very young children, so routine follow-up visits and X-rays are scheduled.
What activities should my child avoid?
For small cysts that don't cause symptoms, your child's provider may suggest limiting certain types of physical activity to reduce the risk of fracture. Ask your provider which activities are safe for your child.
Does a fracture mean the cyst is getting worse?
Not necessarily. A fracture happens when the bone around the cyst weakens. Some cysts (1 in 4) heal on their own after a fracture, and if a cyst does not heal, surgery may be recommended to remove it and prevent another fracture.
What is the difference between an active and a latent cyst?
Active cysts are next to the growth plate and may expand over time. Latent cysts are located away from the growth plate and are no longer growing.
What is a bone graft?
A bone graft is a piece of bone taken from another part of the body or from donated bone. After a cyst is scraped out, the surgeon may fill the cavity with a bone graft or with cement.
Will my child need a cast?
After surgery, the affected bone is immobilized with a cast or sling while it heals. A fracture is also usually treated with a cast to hold the bone in place while it heals.
Can these cysts occur in adults?
Unicameral bone cysts occur most often in children and adolescents under 20, and they can grow in any bone.
Is there any way to prevent these cysts?
No. There is no known way to prevent unicameral bone cysts because providers aren't sure why they occur.
What is methylprednisolone?
It is a steroid. In the injection treatment, the provider numbs the area, removes fluid from the cyst with a needle, and injects methylprednisolone into the cavity. This may require a series of injections.
How often will my child need X-rays?
For small cysts without symptoms, the provider may monitor the cyst with routine X-rays. After treatment, routine follow-up visits and X-rays are scheduled to look for a returning cyst. Your provider will tell you how often.
When should we call the doctor?
Call your provider if your child complains of pain near a bone or if you notice any swelling. Early detection can prevent possible fractures and bone abnormalities. Seek care promptly for sudden pain, bruising, swelling, or difficulty moving a limb, which can be signs of a fracture.
Related Reading
References
Cleveland Clinic. Unicameral bone cyst. Cleveland Clinic. Last updated February 8, 2022. Accessed October 14, 2026. https://my.clevelandclinic.org/health/diseases/22412-unicameral-bone-cyst
Noordin S, Allana S, Umer M, et al. Unicameral bone cysts: current concepts. Ann Med Surg (Lond). 2018;34:43-49. PMID: 30224948. https://doi.org/10.1016/j.amsu.2018.06.005
Zhao JG, Wang J, Huang WJ, et al. Interventions for treating simple bone cysts in the long bones of children. Cochrane Database Syst Rev. 2017;(2):CD010847. PMID: 28158933. https://doi.org/10.1002/14651858.CD010847.pub3
Disclaimer: This guide is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a physician or other qualified health provider with any questions about a medical condition. Never disregard professional medical advice or delay seeking it because of something you have read here.
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