Until the 1980s, the most commonly performed procedure for the treatment of simple bone cysts was curettage and grafting. This procedure was first reported by Neer in 1966 [16], who demonstrated that complete healing of SBC occurred in only about 50 % of a large group of 130 patients. Recurrences occurred in 15 % of patients treated with this procedure together with additional chemical resection of cyst walls (phenol or zinc chloride), and in 39 % of patients treated with curettage and grafting alone. Patients with poor response to treatment, 26 % of the group, had to undergo further surgery.
In 1986, Campanacci et al. gained complete healing in 46 %, partial healing in 21 % and recurrences in 33 % of patients after curettage with bone grafting. Most of the recurrences were classified for reoperation. The use of different kinds of grafts (auto or allogenic) had no effect on the outcome. The author emphasizes that as free space enables recurrences, the entire lesion lodge should be filled with grafts. However, the grafts shouldn’t be packed too tightly, to avoid hindering revascularization within the cavity [17].
The percentage of failures in the case of curettage is unacceptable, especially considering that it is simply treatment of benign tumor-like lesion in adolescents. The way to lower the recurrence and complication rates is to use an adjuvant procedure such as chemical or physical resection (phenol, hydrogen peroxide, liquid nitrogen or argon beam) [16, 24], which results in a reduced recurrence rate by broadening the zone of tissue necrosis. In 1997, Schreuder published a retrospective work evaluating the outcomes of SBC treatment with curettage, cryosurgery and filling the cyst cavity with allogenic bone grafts. After mechanical curettage of the cyst, the author filled the cavity with liquid nitrogen, which was washed out with warm saline in the next step. Complete healing was achieved by 50 % of patients, partial healing in 38 % and recurrences requiring reoperation in 12 % [24].
A meta-analysis of 12 studies published by Schreuder was used to compare recurrences after curettage in our study group to outcomes found in literature [24]. The mean number of recurrences is 27.4 % of patients, with the highest percentages of failure being reported by Bovill et al. (46.6 %) [18] and Mylle et al. (47.6 %) [19], and the lowest number of recurrences by Peltier et al. (7.7 %) [25]. The percentage of recurrences in our study is rather high (41.7 %). This may be a result of the fact that mean follow-up time is quite long (6.2 years), with a minimal follow-up time of 3 years. Some of the reports analysed by Schreuder in the meta-analysis note a minimal follow-up time 1–2 years, which is a rather short period of time to observe possible recurrences and rebuilding of synthetic osteoconductive materials [17, 26]. Also, the evaluation of cyst rebuilding on the basis of the Neer scale, the most commonly-used framework, is not clearly defined. Neer fails to clearly define the meaning of “partial healing” and the correct criteria of recurrence and therapy failure. Hence, different values for cyst area or minimal cortical thickness were chosen to determine therapy failure. To make the present study more objective, the Neer scale was used with Chang’s modification, which defines partial cyst healing as taking place if the osteolytic lesion takes less than 50 % the diameter of the bone, with enough cortical thickness to prevent fracture [23]. Our study assumes the minimal cortical thickness qualifying to partial healing is 1 mm. This method of evaluation allows the results qualified in our work as recurrence to be compared with partial healing in other works. This study tightens, or rather systematizes, the criteria for complete healing in response to of patient expectations. Nowadays, even children regularly take part in sport and are very physically active. As complete healing means, for both patient and parents, the ability to return to earlier activity before diagnosis, the mechanical properties of bone need to be fully recovered.
Few studies have attempted to evaluate factors predictive of response to different modes of SBC treatment. After curettage and bone grafting, Neer et al. observed a higher percentage of recurrences in cysts located in the proximal parts of the humerus and distal part of the femur and better results in the tibia and fibula [16]. Campanacci et al. conclude that recurrence rate was higher in case of active cysts after curettage [17]. Schreuder in his work evaluating curettage does not report significant correlations between the risk of recurrence and age, sex, cyst volume, type of previous treatment procedures or pathological fractures [24]. Mik does not note any statistically significant correlation between recurrence ratio and age (p = 0.055), pathological fracture (p > 0.1) or cyst activity (p = 0.41). The mean age varies significantly between the groups: 8.7 versus 11.3 years. Therefore, with the probability slightly lower than usual, it can be assumed that younger children are less likely to experience satisfactory outcomes [27].