Commentary & Perspective on
"Treatment of Active Unicameral Bone Cysts with Percutaneous Injection of Demineralized Bone Matrix and Autogenous Bone Marrow"
By Bruce T. Rougraff, MD, and Thomas J. Kling, MD

Commentary & Perspective by
Jay R. Lieberman, MD*,
Department of Orthopaedic Surgery, UCLA Medical Center, Los Angeles, CA

In this issue of The Journal, Rougraff and Kling report the successful treatment of simple bone cysts by percutaneous injection of a mixture of demineralized bone matrix and autologous bone marrow. Twenty-three patients with active unicameral bone cysts were treated with trephination and injection of allogeneic demineralized bone matrix and autogenous bone marrow. Five of the twenty-three patients required a second injection because of recurrence of the cyst. All of the patients eventually had complete pain relief and there were no pathologic fractures.

For the past two to three decades percutaneous injection of corticosteroids has been the most popular treatment for active unicameral bone cysts. Although this technique has been successful, the biological mechanisms of the healing of cysts after steroid injections have never been identified. In addition, multiple percutaneous injections of corticosteroids are usually required to heal a cyst.¹ The techniques that have been reported by other investigators include the drilling of multiple holes into the cyst² and injecting the cyst with autogenous bone marrow³ or injecting demineralized bone matrix alone.⁴ All of these techniques have been successful.

Autologous bone marrow contains osteoprogenitor cells and proteins (such as bone morphogenetic protein) which can provide an osteogenic signal. Demineralized bone matrix provides a scaffold on which new bone forms and it also has some osteoinductive potential. The degree of osteoinductive potential varies among the different demineralized bone matrices that are commercially available. The availability of osteoprogenitor cells is critical when demineralized bone matrix is used. Demineralized bone matrix placed in a milieu with a limited vascular supply or few osteoprogenitor cells will probably not induce substantial bone formation.

Generally, after removing the contents of the cyst, the bone lining of a unicameral cyst can support new bone formation, so long as an osteogenic signal is present. Muschler et al. have demonstrated that most of the bone marrow cells from an iliac-crest aspirate are harvested in the first 5 mL. Therefore, if one is going to harvest more than 5 mL of autologous marrow, multiple aspirations will have to be performed from different sites in the iliac crest.^4,5 Lokiec et al. demonstrated healing of bone cysts in a small group of patients (ten children) with injections of 15 to 50 mL of marrow into the cysts.³ n the present study by Rougraff and Kling, 6 to 8 mL was aspirated from each site but multiple punctures were used 1 to 2 cm apart. Killian et al. demonstrated that demineralized bone matrix alone could be used successfully to heal unicameral cysts.⁴

Rougraff and Kling described a number of technical points that are critical to the success of this procedure. They recommended placing the needles as far from each other as possible. In this study all the recurrent cysts developed at either end of the original site. In addition, they suggested that completely filling the cyst may decrease the recurrence rate and therefore limit the number of injections required for each patient.

Since this study was not a randomized trial, it is impossible to determine which ingredient of the injection is more important, the demineralized bone matrix or the autologous bone marrow. Although the autologous marrow contains osteoprogenitor cells that may provide an osteogenic signal, one potential problem is the need for a substantial amount of marrow that would have to be aspirated from a patient with large cysts. One advantage of combining demineralized bone matrix with autologous marrow is that the larger volume would completely fill the defect and thus reduce the likelihood of recurrence. The demineralized bone matrix used in this study is in gel form and can be easily injected into the cyst.

A note of caution is in order in the interpretation of these results. This technique may not be readily applicable to other demineralized bone matrices, and the success of the procedure may be influenced by the vehicle of the demineralized bone matrix (e.g., glycerol versus hyaluronic acid). Since there is a low morbidity associated with bone marrow aspirate, it seems that combining the autologous marrow with the demineralized bone matrix is a reasonable option and should be continued until a randomized trial is performed that provides data for improvement of this technique.

*The author did not receive grants or outside funding in support of his research or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. A commercial entity (the Musculoskeletal Transplant Foundation) paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

1. Capanna R, Dal Monte A, Gitelis S, Campanacci M. The natural history of unicameral bone cyst after steroid injection. Clin Orthop. 1982;166;204-11.
2. Komiya S, Minamitani K, Sasaguri Y, Hashimoto S, Morimatsu M, Inoue A. Simple bone cyst. Treatment by trepanation and studies on bone resorptive factors in cyst fluid with a theory of its pathogenesis. Clin Orthop. 1993;287:204-11.
3. Lokiec F, Ezra E, Khermosh O, Weintroub S. Simple bone cysts treated by percutaneous autologous marrow grafting. A preliminary report. J Bone Joint Surg Br. 1996;78:934-7.
4. Killian JT, Wilkinson L, White S, Brassard M. Treatment of unicameral bone cyst with demineralized bone matrix. J Pediatr Orthop. 1998;18:621-4.
5. Muschler GF, Midura RJ. Connective tissue progenitors: practical concepts for clinical applications. Clin Orthop. 2002;395:66-80.
6. Muschler GF, Boehm C, Easley K. Aspiration to obtain osteoblast progenitor cells from human bone marrow: the influence of aspiration volume. J Bone Joint Surg Am. 1997;79:1699-709.