Surgical Treatment of Solitary Bone Cyst in Children Using Alloimplants

Methods: The results of examination and treatment of 11 patients (8 boys, 3 girls, age from 5 to 16 years) were analyzed. The diagnosis was made on the basis of a combination of clinical manifestations of the disease, laboratory test data, X-ray and pathomorphological studies. Distribution by localization of the pathological focus: proximal femur 6 (54.5%), humeral 2 (18.2%), calcaneal 2 (18.2%), pubic 1 (9.1%). Indications for surgical treatment: the presence of a massive focus of bone tissue destruction in the loaded area, a high risk of a pathological fracture, pronounced long-term pain syndrome. All patients underwent marginal resection and chemical treatment of SBC, the defects were filled with osteoplastic material.


Introduction
A solitary bone cyst (SBC) is a single-chamber cavity filled with clear or bloody fluid and lined with a shell of varying thickness, formed by weakly vascularized connective tissue with giant cells similar to osteoclasts, and sometimes with areas of fresh blood crystals [1].

Surgical Treatment of Solitary Bone Cyst in Children Using Alloimplants
G. Dupuytren first pointed to the existence of the SBC in 1833 [9]. The clinical and histological picture was described in 1876 by Rudolf Virchow, who considered the SBC as a "decaying enchondroma" [2,5,8,10]. According to the International Histological Classification (2013), "a bone cyst belongs to tumor-like processes and is defined as a cavity filled with serous or serous-hemorrhagic fluid and bounded by a layer of connective tissue of various thicknesses containing single giant cells" [11].
Today there is no generally accepted theory of etiology and pathogenesis of bone cysts, the main reason for their occurrence is considered to be a dystrophic process, the development of which is associated with hemodynamic disorders and impaired outflow of interstitial fluid into the metaphyseal region. Local disorders of hemodynamics lead to increased intraosseous pressure in limited areas of bone with the involvement of adjacent blood vessels and the formation of a cavity filled with fluid (serous, hemorrhagic), with high fibrinolytic activity [6,9].
SBC are mostly asymptomatic until the appearance of a pathological fracture, which can occur after a minor injury and in 50 -75% of cases is the cause of the first clinical manifestations [2]. Sometimes SBC is diagnosed after an X-ray examination performed for other reasons [6,10]. Clinical signs in the form of pain, contractures in the adjacent joint more often noted in the case of cysts in the proximal femur, they are associated with pathological microfractures [2].
Radiologically, the SBC looks like a lytic center of destruction located in the center of the metaphysis with clear boundaries and a zone of sclerosis on the periphery, often spread concentrically. During growth, the child can migrate to the diaphysis [4,10].
Among the methods of treatment of SBC, puncture and surgery predominate. Puncture of SBC with subsequent injections of steroids is used to reduce intraosseous pressure and suppress proteolytic activity of bone content [8,9]. However, the consolidation of the pathological focus occurs in only 24% of patients after the first injection of steroids [7,10], so usually perform from 2 to 5 manipulations [9].
The disadvantages of the method include the frequency of punctures, a high recurrence rate, the negative impact of steroids on the child's body, the systemic response to them (Cushing's syndrome) [9].
At the Institute named after prof. M. Sytenko in the 30s and 40s of the last century used excochleation of the cyst cavity with the subsequent filling of the defect with bone chips. Since 1951, under the conditions of all SBC of long bones in children, the method of M.
Novachenko was used -radical resection of the affected area of bone with leaving or removal of periosteum and replacement of the defect with an autograft. In case of large defects, two autografts were placed in them in order to ensure uniform loading of the epiphyseal cartilage. Subsequently, plastics were performed with an alloy implant with Korzh -Talyshynsky fixation (1968), and combined plastics with an autoimplant were also used [12]. Surgery is considered the most appropriate, because often SBC causes pathological fractures, deformities, shortening of bones and, consequently, limb dysfunction [6]. It must include the following elements: decompression, mechanical (curettage of cyst contents) and chemical (phenol, ethyl alcohol, etc.) treatment with bone defect plastic. The most common among the materials for defect replacement are: autobone, allocyst material and various ceramic implants [8]. Currently, the problem of choosing bone and plastic material for reconstructive surgery on skeletal bones, especially in pediatric patients, remains relevant due to high requirements for it. Such material should perform not only replacement function, but also to gradually integrate into the bone, to maintain the physiological level of osteoblastic and osteoclastic activity, promoting the formation and remodeling of bone tissue. The relationship of biomaterial with adjacent tissues, its stability and the nature of osteogenesis in the bone bed depends on the physicochemical properties, histogenetic origin and structure [13].

Materials and Methods
The study was performed in accordance with modern requirements of bioethics, its materials were approved by the Committee on According to the localization of the pathological focus, patients were distributed as follows: proximal femur -6 (54.5%), humerus -2 (18.2%), heel -2 (18.2%), pubic -1 (9.1%).
Diagnosis of patients was performed based on a set of clinical manifestations of the disease, laboratory tests, X-ray and pathomorphological examination.
In our observations, the indications for surgical treatment of patients were massive destruction of bone tissue, which can cause pathological fractures.
Surgical interventions were performed under conditions of general or combined (regional in combination with sedation) anesthesia.
After the affected part of the bone was skeletonized, fenestration was performed. This usually resulted in a straw-yellow liquid with blood in it. Then, edge resection and chemical treatment of SBC with ethyl alcohol were performed. The resulting defect was tightly filled with deproteinized alloimplant in the form of bone powder. During and after the intervention, they were additionally visually monitored using an electron-optical transducer in several projections. A characteristic feature of the use of the described plastic material is the ability to tightly fill the defect of any size and shape. In cases where the defect is very large (relative to the total size of the bone), additional osteosynthesis was performed. In each clinical case, the metal structure was selected individually. This was most often a plate, and sometimes an intramedullary rod. External fixation of the limb was performed for 1 -1.5 months. Plaster bandages or orthoses of various stiffnesses were used for this purpose.
The outcome of treatment was evaluated according to the data.

Results and Discussion
The results of surgical treatment using osteoplastic material to replace post-resection defects were evaluated for 2.5 years in 4 (36.4%) patients, 18 months in 3 (27.2%), 12 months in 4 (36.4%).
According to the X-ray examination, the reconstruction of bone tissue in the area of the operation was determined after 6 -12 months.
Later (after 12 -18 months), the bone structure of children mostly corresponded normal with no or slight remnants of plastic material.
No signs of infection or other postoperative complications, such as recurrence of the pathological process or re-fracture, were observed. The pain syndrome was absent, the volume of movements in the adjacent joint was restored. In general, the results are classified as good and excellent.
Here are clinical examples of the use of de-proteinized alloimplant "OMS-A" in patients with SBC.

Clinical example № 1
Patient V., 6 years old, went to the clinic in May 2016 with complaints of minor pain in the right hip joint during exercise. From the anamnesis it is known that more than a year ago she received treatment in another institution for a pathological fracture of the proximal right femur.
Clinically, at the time of hospitalization, a slight restriction in range of motion (not more than 5° in all planes) in the right hip joint was detected. Radiologically, the focus of lytic destruction with a clear sclerosis rim and a slight "swelling" of the cortical layer in the proximal part of the right femur was diagnosed as SBC (Figure 1a and 1b). Surgical intervention was performed: marginal resection of the cyst with bone defect plastics with implants of allogenic origin (Figure 1c). After surgery for 1.5 months carried out cast fixation, then 3 months the patient moved with crutches (2 months -without weight baring, 1 month -with weight baring as tolerated). Full weight baring is allowed after 5 months after surgery (Figure 1d).   The approach to the treatment of SBC should be individual in each case and depends on the localization, aggressiveness and prevalence of the process. Although there is no standardized surgical treatment of SBC, its purpose is to eliminate the bone defect, restore its integrity and functionality and prevent the occurrence of pathological fractures [7]. It includes the following stages: decompression, mechanical (curettage) and chemical (phenol, ethyl alcohol, etc.) treatment with plastic bone defect. Bone autograft, allograft material and vari ous ceramics are most often used for this purpose [8]. They all have both positive and negative qualities. In particular, taking an autograft prolongs the operation time, worsens the patient's condition due to additional injury [14]. Ceramic implants differ from natural bone in architecture and mechanical properties. The use of allogenic bone implants (allograft) to replace defects after SBC removal is considered to be the most effective in childhood. They perform not only a replacement function, but also gradually integrate into the adjacent bone tissue, maintain the physiological level of activity of osteoblasts and osteoclasts, promote the formation and remodeling of bone tissue [6,13]. In our study used for bone cavities after removal of SBC certified material of allogenic origin "OMS-A" (certificate of conformity № UA.TR.101-21-2016). According to the results of the study, radiological signs of its reconstruction were established, which lasted from 1.5 to 18 months. After 15 months in 5 patients (45%) complete restructuring of implants with restoration of bone structure was recorded.

Conclusion
In the study, bone allogenic implants are a promising material for defect plastics after removal of benign tumors and tumor-like bone lesions.
The obtained results make it possible to recommend bone-plastic material of allogenic origin for use in the scheme of surgical treatment of solitary bone cysts in children.