Although there is no standardized treatment for UBC, the goal of treatment is to prevent pathological fracture and skeletal deformities during growth associated to repeated pathological fractures [3
]. A painful lesion with precarious cortical thinning demands surgical intervention, rendering the bone at risk for pathological fracture. Surgical procedures include injection of corticosteroid [12
] or bone marrow [11
], decompression with cannulated screw(s) [6
], intramedullary nailing [19
] and open curettage followed by bone grafting [21
]. In this study, we evaluated the effectiveness of DBM as a graft material in UBC treatment in terms of overall healing rate, recurrence, time to healing and associated complication. In the present study, the healing rate with a single intervention was 92% (23/25) and it reached 100% after a second procedure.
To explain the etiology of UBC, several theories have been proposed including a true intra-osseous synovial cyst [24
], the degenerative phase of a benign tumor [25
], failure to resorb hematomas [26
], low-grade form of osteomyelitis [27
], and venous obstruction [28
]. Of these theories, venous obstruction has been suggested as being the most probable cause of UBC. Considering that venous obstruction model is preferred, decompression of cyst and injection of steroid or osteogenic materials has replaced aggressive open procedure and bone grafting [3
]. There have been many reports on minimal invasive procedures for the treatment of UBC [12
]. Scaglietti [9
] first described the percutaneous injection of methylprednisolone acetate as a treatment of UBC in 1974. Subsequently, many authors have reported satisfactory result with high success rates ranging from 50% to 90% [21
] Simplicity and low morbidity associated with steroid injection made it popular. However, usually several procedures are necessary to achieve consolidation of the cyst. The classic report by Scaglietti using percutaneous steroid injection showed only 24% healing rate after a single injection [18
]. Many other studies also suggested that close radiological surveillance should be maintained and repeated steroid injections may be needed to achieve adequate consolidation [12
]. Steroid injection might inhibit production of bone resorptive factors by its anti-inflammatory effect. In addition, it reduces internal pressure of cyst through trepanation. However, steroid injection does not provide bone-forming potential in itself.
Since autologous bone marrow grafting for UBC treatment was introduced by Lokiec in 1996 [31
], the injection of bone marrow alone or in combination with DBM has been proposed as an alternative to steroid injection. The injection of bone marrow provides osteoprogenitor cells and DBM could stimulate new bone formation owing to its osteoinductive and osteoconductive properties [5
]. Recently, many authors have evaluated the effectiveness of DBM as a graft substitute and it is applied in many surgical grafting procedures including spinal fusion, joint reconstructive surgery, trauma and oral/maxillofacial surgery. With respect to the use of DBM in UBC treatment, the effectiveness as a graft material after intramedullary decompression has been evaluated by some authors [7
] Kanellopoulos et al [13
] and Rougraff et al [14
] reported about 90% success rate after a single procedure using a mixture of DBM and autologous bone marrow and it took six to nine months to achieve cortical remodeling radiographically. In the present study, we had a cumulative success rate of 100%. In addition, the mean time to healing was 6.6
months. In the current study, two cysts required a repeat procedure. In both cases, the amount of DBM injected was not enough to fill the entire cyst (Figure ). The basic concept of percutaneous procedure is the intramedullary decompression followed by grafting of osteogenic materials. The importance of induction of osteogenesis following intramedullary decompression in UBC treatment has been advocated by several authors. The high recurrence rate of steroid injection was probably caused by absence of osteogenic potential. In this regard, DBM could be a good grafting substitute for UBC treatment after intramedullary decompression owing to its excellent osteogenic property. In addition, it would be desirable to use an adequate amount of DBM to fill the entire cyst. In the case of Figure , it seemed that the insufficient DBM in quantity led to inadequate healing of the cyst and eventually cyst recurrence.
Figure 4 Insufficient DBM in quantity leaded to inadequate healing of the cyst. Plain radiographs A) of the proximal humerus in a 3-year-old boy B) at postoperative 3months showing filling defect of DBM C) at postoperative 14month showing recurrence (more ...)
ExFuse™ (Hansbiomed Inc, Seoul, Korea) used in the current study is a mixture of carboxyl methyl cellulose carrier and DBM extracted from freeze-dried allograft with preserving its osteoinductive and osteoconductive properties.
In the present study, we made a small skin incision and created a cortical window over the thinnest accessible wall of the cyst. This made it possible to allow passage and sweeping movement of curettes and made it easy to decompress the intramedullary pressure, remove the cyst lining and get biopsy material. Even though our procedure may seem to be a more aggressive than other percutaneous procedures, the high success rate in the present study may be attributed to more aggressive removal of cyst lining and intramedullary decompression through a cortical window Killian [8
]. Another advantage of making a cortical window includes obtaining the biopsy material. Some malignant lesions such as Ewing’s sarcoma or osteosarcoma may show cystic features radiologically [34
]. Therefore, obtaining biopsy material is important to confirm the diagnosis of UBC.
Our study has several limitations. First, we could not perform any sound analysis to find associated prognostic factors for persistent cyst or recurrence because the number of patients enrolled was relatively small. However, the recurrence rate of the cyst was low (8%) even though this study included many active cysts in younger patients, which are known to be aggressive and resistant to treatment [19
]. Another limitation of our study is the absence of a comparative group or randomized comparison. In future study, large scale and long-term follow-up clinical studies are required.