Simple bone cysts: Steroid injections may be the best first-line treatment

James G. Wright, MD, MPH, FRCSC, answers 4 Questions on classifying and treating these lesions usually seen in pediatric populations.

This month I have asked James G Wright, MD, MPH, FRCSC, to update us on his clinical approach to treating simple bone cysts in children. His experience is based not only on treating these bone lesions but also on his recently published randomized clinical trial comparing the use of steroid and bone marrow injections.

Most of us see these bone cysts infrequently and I found his responses to 4 Questions to be very reassuring.

Douglas W. Jackson, MD
Chief Medical Editor

Douglas W. Jackson, MD: What constitutes a “simple” bone cyst and how are they graded or classified?

James G. Wright, MD, MPH, FRCSC: Simple bone cysts are benign lesions of growing children located primarily in the proximal humerus or femur. Most children present due to pain from pathologic fracture and the cysts seldom heal spontaneously. Although bone cysts generally resolve with skeletal maturity, without treatment children are at risk for pain or recurrent fracture leading to restricted physical activity for many years. Recurrent fractures can also lead to limb length discrepancy and deformity.

The etiology is unknown, but two main theories include vascular obstruction and the presence of bone resorptive factors in the cyst fluid. Current treatments address disruption of the cyst lining either chemically with injections, or mechanically by scraping it with needles or direct curettage.

Vascular obstruction can be relieved by cyst decompression using Kirschner wires, cannulated screws or flexible intramedullary nails. Both treatments can be further enhanced using various osteoinductive products such as demineralized bone matrix or calcium sulphate pellets.

Simple bone cysts are graded based on radiographic assessment. The most commonly used assessment method is a four-grade scale. Satisfactory healing is defined as cysts with significant sclerosis or complete obliteration of the cyst.

Jackson: Are there circumstances when you would not treat a simple bone cyst and what are the risks and benefits of nontreatment?

Wright: In cases where the cyst is not expansive, has thick cortical walls, there is no history of low energy fracture(s), and the child does not have high physical demands for sport, observation may be a reasonable treatment. The weight-bearing status of the involved bone should also be considered; humeral cysts may be better candidates for observation due to reduced mechanical forces on bone and the reduced consequence of fracture in a nonweight-bearing bone.

Risks of nontreatment include fracture, pain, anxiety, restriction from activity and repeated radiographs until the cyst consolidates. Pathologic fracture(s) can lead to limb length discrepancy and deformity. Growth arrest, an uncommon complication, may occur due to the assault of cyst fluid on the physis itself, multiple fractures through the cyst that damage the physis, or as a direct extension of the cyst through the physis. Regardless of the cause, growth arrest can lead to limb length discrepancy and deformity.

Benefits of nontreatment include no exposure to general anesthesia, no scar or general morbidity associated with surgical intervention, and no risk of growth arrest following some forms of surgical treatment adjacent to the physis. Also, there is no risk of additional surgeries due to primary treatment with hardware that may need to be removed or revised. Patients will also not be at risk of adverse reaction to any products that are injected into the cyst.

Jackson: What are the indications for injecting a bone cyst in children and adolescents — is there an age where you would not consider an injection? What are the risks and benefits of injections?

Wright: Indications for injecting a bone cyst in children or adolescents are pain that limits daily function, history of low-energy fracture(s), and radiographic signs of impending fracture such as large cysts. Cysts in the neck of the femur are also at higher risk of fracture due to weight-bearing status and indicate a greater need for treatment. Patients who are involved in high demand physical activity may be appropriate for injection treatment as the recovery from treatment is minimal. Simple bone cysts are rarely diagnosed in infancy. There is no age limit to injection treatment.

Risks of injection treatment are exposure to general anesthesia, infection, adverse reaction to injected substance or product, and multiple injections may be needed to achieve healing.

Benefits of injection treatment are it is minimally invasive surgery, a same day procedure, and it has the potential to combine mechanical disruption of cyst and biologic treatment.

Jackson: What are your recommendations based on your recent published work and other available literature?

Wright: The only level I randomized clinical trial indicates that steroid injections are superior to bone marrow injections in healing simple bone cysts. There is only one level II prospective comparative study and it indicates that cannulated screws are superior to curettage and bone grafting and steroid injections. There are 13 level III retrospective comparative studies, only four had statistically different results. Two of these four studies indicated that steroid injection was superior to curettage and bone grafting.

At this point in time, my recommendation to surgeons is to use steroid injections as the first line of treatment. In terms of the next step for research, a randomized clinical trial comparing steroid injection to some form of mechanical disruption and cyst decompression is necessary. Not only would this provide surgeons with a definitive clinical answer, it may offer further insight into the two main theories of bone cyst etiology, vascular obstruction and the presence of bone resorptive factors in the cyst fluid.

For more information:

• James G. Wright, MD, MPH, FRCSC, can be reached at the Division of Orthopaedics, The Hospital for Sick Children, 555 University Ave., Suite 1254, Toronto, ON M5G 1X8, Canada; 416-813-6433; e-mail: james.wright@sickkids.ca.

Reference:

• Wright JG, Yandow S, Donalson S, et al. A randomized clinical trial comparing intralesional bone marrow and steroid injections for simple bone cysts. J Bone Joint Surg (Am). 2008;90(4); 722-730.