A unicameral bone cyst is a simple bone cyst. It is a benign cystic lesion that is prone to pathologic fracture and recurrence.
A unicameral bone cyst is a type of bone cyst that commonly presents with fracture through the unicameral bone cyst. The treatment is usually to allow the fracture to heal with nonsurgical management. The patient should be followed clinically and with serial radiographs. After the fracture through the cyst heals, aspiration and injection of the cyst may be necessary.
In 50% of patients with unicameral bone cysts, the lesion remains asymptomatic until a fracture occurs, which usually happen due to minor trauma. When the lesion expands the bone, the bone is weakened and this may also cause pain or even a fracture.
The lesion tends to occur in the metaphysis and the diaphysis. It abuts the epiphysis in the proximal humerus and in the proximal femur. The cystic lesion is lined by a fibrous membrane and filled with clear, yellow fluid.
An x-ray is usually used to diagnose a unicameral bone cyst. Some of the cysts have a pathognomonic radiologic finding known as the “fallen leaf sign”. The fallen leaf sign is part of the fracture cortex that settles to the most dependent part of the cyst. There is not really a need for a work-up for patients with unicameral bone cysts.
Typical findings of a unicameral bone cyst on an x-ray include will be thinning of the bone with central lucency and no obvious matrix seen in the x-ray. An incidental finding that is often seen in x-rays of unicameral bone cysts in children is a benign bone tumor.
The most common sites for unicameral bone cysts to occur are the proximal humerus and the proximal femur. Also, approximately 85% of the patients with unicameral bone cysts are under the age of 20.
Aneurysmal bones cysts are different. An aneurysmal bone cyst enlarges the metaphysis more that the width if the epiphyseal plate.
Treatment
Unicameral bone cysts are more likely to present with a pathologic fracture in children. Therefore, the goal of treatment of a unicameral bone cyst is to prevent a pathologic fracture.
Fractures of the humerus are usually minimally displaced and treated by immobilization and allowed to heal this way. However, if the lesions are persistent or progressive, they may need surgical treatment such as curettage and bone graft or injection of the lesion. They may also need percutaneous injection of bone graft or bone graft substitute.
Curettage and bone graft of the proximal femur and in the subtrochanteric area may be needed because these are high stress area and is prone to fracture. In this way, supplemental fixation may be necessary.
