UBCs are benign lesions that usually spontaneously regress with skeletal maturity [16
]; however, when pathologic fractures occur with persistent radiographic signs of cyst, these young patients are strictly forbidden to take part in recreational physical activities. Treatment can reinforce the bone cortex. Numerous types of treatments have been proposed such as steroids, natural bone marrow, bone matrix or other injection materials [19
], curettage with bone grafting [34
], subperiosteal resection [10
], and internal or external fixation [17
]; however, until now, there was no consensus regarding the best procedure. Moreover, because the various literature reports all methods of treatment with a wide range of healing rates, it is difficult to derive clearcut criteria (Table ). We therefore determined (1) whether during the first year of followup a single injection of autologous BMC combined with DBM for treating UBC would produce comparable healing rates than multiple steroid injections; (2) the healing rate at last followup; and (3) failure rate correlated with the site and size of the cyst with the location of the cyst in relation to the epiphysis and the age of the patients.
Healing rate (after first treatment and final) in major series reported in the literature according to different methods of treatment
We recognize limitations to our study. First, the Steroid Group has a considerably longer followup compared with the DBM + BMC Group. Thus, we anticipate more failures in the DBM + BMC Group during followup. For this reason, a future study will be necessary to confirm these preliminary results. Second, the BMC used in our protocol is different from that in natural bone marrow, in which progenitor cells are diluted in a liquid media with possible dispersion in the soft tissue outside the cyst [14
], thus explaining poor results reported in some studies [5
]. However, the study was not performed to prove different outcomes between natural BM and BMC. Rather, the rationale in the use of BMC in association with DBM is to provide enough factors such as stem cells and bone morphogenetic proteins, which are able to improve the osteogenic potential in the cystic area, contrasting the catabolic phenomena. Third, there are some differences in the surgical technique between the two methods of cure. In the Steroid Group we used high pressure cyst lavage through a double needle inserted in the cortex, while in the DBM + BMC Group we performed only one needle insertion with internal scraping.
During the first year, the number of cysts healed with a single injection of DBM + BMC (59%) was higher compared with multiple injections of corticosteroids (21%). These data are difficult to compare with data presented in the literature due to differences in the method of evaluation and type and number of bone marrow or steroid injection. However, most reports that specifically refer to the healing rate after the first treatment with bone marrow injection show lower percentages than achieved in our series [5
]. On the other hand, the percentage of healing rate following the first treatment with steroid injection in our series is lower than most of other reports [5
]. Fracture of the cyst is one cause of failure after the first treatment; Neer et al. [27
] reported up to 80% of fractures in patients followed without surgical treatment. In patients surgically treated, fracture has been reported in 2.6% of cases treated with curettage and bone grafting [35
]; from 7.7% [4
] to 28% [41
] and 33% [42
] in patients treated with marrow or steroid injection. We observed no difference in the number of fractures that occurred in our series in the two groups (12% in the DBM + BMC Group versus 17% in the Steroid Group), resulting in the average of fractures reported in series dealing with patients treated with either steroid or bone marrow injection. A good clinical and radiographic initial outcome is important to decrease the number of hospitalizations and surgeries. In some patients treated with steroids, more than eight injections were given, resulting in high costs for families and the healthcare system. On the other hand, in patients with partial or complete healing, daily activities, including sports, could be resumed.
Despite the longer followup in the Steroid Group, the final cyst healing rate was higher in the DBM + BMC Group than the Steroid Group (71% versus 38%). The life table analysis confirmed this difference between the two treatments. This is particularly important considering the smaller number of treatments (multiple injections in the Steroid Group) and injections needed to achieve this result (4.3 average in the Steroid Group versus 1.1 in the DBM + BMC Group). One series comparing steroid to bone marrow injection reported a higher number of steroid injections required to achieve the final healing rate [6
]. However, despite the differences in the evaluation method, most of the failures occurred within the first two years of followup as reported by other series [11
], leaving a number of patients in the Neer III grade evaluation to be followed for a long time until evidence of definitive healing was achieved [3
When considering factors with a negative effect on the treatment outcome, the humeral site did not score more fractures than other sites [5
], although size, younger age and proximity to the growth plate confirmed their negative effect on the final healing rate requiring, despite fracture, a higher number of injections. These observations confirmed previous reports with age less than 10 years old be the major risk factor for failure in the UBC series [3
]. As observed by Sung et al. [35
] there is not likely an age at which risk increases, although younger patients are more likely to need subsequent treatments to achieve final healing. This is also likely true for the size and proximity of the growth plate as these are generally considered signs of active cyst [4
] although these differences would likely be significant only in larger study series. Finally, we believe it important to improve the operative technique by opening of the medullary canal from the diaphyseal side to reduce the pressure inside the lesion. This has been attempted using medullary nails or cannulated screws [2
]; however, in those series, the healing rate of the cyst was not sufficiently consistent because of the lack of osteogenic stimuli. When an adequate cyst opening procedure is associated with the bone formation enhancing agents such as BM and DBM, healing can be more consistent [18
]. A number of cysts can be considered inactive and reasonably heal with no or minimal surgery. Therefore, we need a more accurate cyst index than previously reported [16
] since this did not predict fracture [38
The healing rate of unicameral bone cyst after the first treatment has been more frequently achieved with injection of DBM + BMC than steroid injection. This is also confirmed by the healing rate achieved in the last followup independent from the number of treatments required. We believe the data support the desirability of a more effective osteogenic material for bone regeneration in younger patients with larger cysts or cysts located close to the growth plate.