The choices facing the physician when presented with a child with a UBC are deciding whether to observe or treat and, if the decision is made to treat, how to treat. The main indication for treatment is prevention of pathologic fracture. Reliable methods to determine fracture risk only recently have been published [37
]. That issue is not the goal of this article; our question is, once the decision is made to treat, how to treat. Although the eventual success of UBC treatment almost always is assured, multiple attempts often are required. We sought to identify which of the three treatment methods we were using during the time of this study has the lowest failure rate per attempt and a minimum of complications based on retrospective analysis. We also sought to identify other predictors of failure.
Our study has certain limitations, including inherent selection bias like all retrospective studies. Indications and treatment selection were based on clinical criteria and physician discretion rather than objective criteria. Multiple surgeons were involved, and although this may not be ideal, it is reflective of how patients are treated in practice. Most of the procedures were performed by the senior author (MCG) who was consistent in the use of the techniques throughout the study period. Another concern is, although multiple logistic regression showed treatment with steroids was an independent predictor of a higher rate of initial treatment failure, we were only able to take into account the potential confounders of age, femoral versus humeral location, gender, hospital, and history of pathologic fracture; data on size, activity, and proximal versus distal location of the cyst were unavailable. Although we did not see a significant difference between lesions in the femur versus humerus or lesions that were curetted and internally fixed versus those that were just curetted, our study was not designed and powered to detect such differences. We did see a significant difference in the length of followup: SDB is a newer treatment and patients were followed an average of 4.03 years versus 7.77 and 8.92 years for steroids and curettage, respectively; shorter followup may cause late adverse events to be missed. Another consideration is, when evaluating outcomes of a second treatment, our results may have been biased by the first treatment received, because there were not enough patients to stratify by first and second treatments. Similarly, our findings concerning rates of refracture, pain, and other complications may have been influenced by subsequent treatments that patients may have received or the effects of pathologic fractures. Finally, although the unique radiographic and clinical appearances of UBCs are considered diagnostic and often were confirmed by aspiration/cytology or biopsy, pathologic specimens were not available for every case.
Nonetheless, our study of 167 patients is one of the largest in the literature, with patients having an average followup of 7.3 years, and we directly compared different treatments. Our finding that steroids were associated with an 84% failure rate after one treatment is comparable to the 76% failure rate after one procedure in a series of 163 patients [34
]; other smaller series have reported failure rates of 41% [10
], 47% [13
], 50% [29
], and 78% [42
] after one injection. Although others have reported using doses as much as 240 mg [34
], we are not aware of any dose-response curve that suggests higher doses are more effective. Our finding that curettage was associated with a 64% failure rate after one treatment is higher than the 47% reported by one large study [13
], and others have reported lower failure rates of 38% [29
], 36% [38
], 25% [39
], and even 22% [28
]. One possible explanation for the differences in failure rates in our study versus published rates is the longer followup in our study, which may have resulted in detection of more late failures.
Our other findings with regard to complications and factors influencing outcome are supported by the literature. Curettage and other invasive procedures have long been associated with high complication rates [29
], although we could not find any studies that reported on pain or discomfort. The relationship between younger age and higher failure rates has been noted in other studies [14
]. Although most consider age 10 as the cutoff between patients who do well and those who fare poorly, we believe there is a more linear relationship between younger age and higher failure rates. We also examined whether outcomes differed between males and females because some studies reported higher rates of failure in males [27
] and others reported higher rates of failure in females [27
]. These results may have been confounded by factors such as age and treatment. According to our multivariate regression analysis, taking into account age, treatment, location, and hospital, gender had no effect on outcome.
In addition to SDB, other new methods have been proposed for treating UBCs, many with excellent results. Trephination and drilling with or without Kirschner wire placement have resulted in failure rates after one treatment of 27% [22
], 30% [6
], and 52% [36
]. Even greater successes have been reported with intramedullary nailing, with failure rates after one treatment of 0% [11
] and 6% [31
]. However, intramedullary nailing remains controversial because local relapse of UBC is usually tolerable and rarely limb-threatening, and one has to balance the invasiveness and complications of a procedure with disease control. Furthermore, one study noted 28% of patients needed another operation because the nail became too short for the growing bone [31
]. For other injection techniques, an 18% failure rate has been reported after one DBM injection [21
], and failure rates of 11% [19
] and 22% [32
] have been reported after one injection of DBM plus bone marrow. However, early promising results may later be shown as false; although a 0% failure rate initially was reported after one injection of bone marrow [23
], a later study reported a 50% failure rate [42
], and a study comparing bone marrow injection with steroids reported failure rates of 57% versus 49%, showing no advantage with bone marrow [5
]. This same observation applies to our finding of a failure rate of 50% after one SDB injection.
Because many factors may impact outcome, it is difficult to compare results across studies; study populations may differ with regard to age, location of cyst, and size. In addition, the uncertainty surrounding the pathogenesis of UBCs makes it difficult to anticipate effects of treatments. The action of SDB may be mediated by the osteoinductive properties of DBM and bone marrow coupled with the inhibitory effect of steroids on phospholipase and prostaglandin formation (and subsequent decrease in osteoclastic activity).
Until the pathogenesis of UBC is elucidated, the primary focus of patient care is empiric treatment. These findings show SDB is more effective as an initial treatment than steroids and is associated with less morbidity than curettage. We contend SDB could be considered a first-line therapy for UBCs in the humerus or femur in patients younger than 20 years requiring treatment for symptomatic UBCs. Patients with femoral cysts may require internal fixation to prevent fracture, and in those patients, curettage may be preferable, although we did not observe a benefit compared with SDB. Although our study was retrospective and contained selection bias, our subgroup analysis showed a trend in which, in both locations and across age groups, patients treated with steroids had higher failure rates than those treated by curettage or SDB. We observed curettage had a better chance of success than either injection as a second treatment; however, this difference was not significant and should be interpreted cautiously, especially given the potential morbidity of a more invasive procedure. Large, randomized clinical trials are needed to objectively compare SDB and other treatments for UBCs.