Unicameral Bone Cysts

Unicameral bone cysts (UBCs), or simple bone cysts, are benign lesions that are more commonly found in children and adolescents. They are fluid filled and cause destruction of the bone they are located within.  While UBCs can occur in any bone, they are usually found in the upper arm bone near the shoulder joint or in the thigh bone near the hip. UBCs are considered active if they are located within 5 cm of the growth plate and latent if located more than 5 cm from the growth plate.  Active unicameral bone cysts can continue to grow and affect the entire bone shaft (length of the bone) if left untreated. Latent cysts do not continue to grow or expand into the bone.  

Cause of Unicameral Bone Cysts

The cause of unicameral bone cysts is not known.

Diagnosing Unicameral Bone Cysts

Unless there is a fracture in the area of the cyst, unicameral bone cysts don’t usually cause symptoms so they are often found incidentally (as a result of looking into some other problem). On an x-ray they have a transparent appearance with a shell around the lesion.

CT scan or MRI scans may be useful in determining the extent of the lesion and whether it has invaded the growth plate.

Treatment of Unicameral Bone Cysts

Unicameral bone cysts don’t always require treatment, instead a process of “watchful waiting” is often recommended. This involves regular x-rays of the area as long as there are no symptoms. Latent UBCs will typically heal without intervention provided there is no fracture in the area.

Because active UBCs are more likely to progress and cause destruction of the bone, the treatment recommendation may be surgical curettage (scooping out) followed by filling the area with bone cement or bone graft material. If there is a fracture, then the lesion is curetted, filled, and the bone stabilized so the fracture will heal.

Long-term Outlook

Unicameral bone cysts will often resolve without treatment. If they do require treatment it is unlikely that they will recur. A process of regular monitoring of a cyst during childhood and adolescence will help to assure the lesion has healed without consequence.

Kadhim M, Thacker M, Kadhim A, Holmes L; Treatment of unicameral bone cyst: systematic review and meta analysis; .J Child Orthop. 2014 Mar; 8(2): 171–191