CARBON-CARBON COMPOSITE NAIL FOR INTRAMEDULLARY OSTEOSYN- THESIS IN RATS WITH EXPERI- MENTAL OSTEOPOROSIS

Hryhorieva O.A. , Abrosimov Yu.Yu. , Chornyi V.V. Carbon-carbon composite nail for intramedullary osteosynthesis in rats with experimental osteoporosis. Zaporizhzhia State Medical University, Zaporizhzhia, Ukraine ABSTRACT. Background. In Ukraine, there has recently been an increase in the number of limb bone fractures among the population, in particular, due to increase in the number of elderly people, which is associated with the development of agerelated osteoporosis and fragility of bones. Therefore, the use of artificial implants in traumatology is becoming increasingly important. The search for new bioinert and biodegradable materials, that are capable of providing rapid fracture consolidation and do not require repeated surgical intervention, continues. Objective. To elaborate a model for the research of using carbon-carbon composite nail for intramedullary osteosynthesis in laboratory rats with fractures of femur and tibia in norm and with experimental osteoporosis. Methods. The work investigated the lower limbs of 6 groups of Wistar rats. The first part of the study involved 4 groups of rats with modeled tibial fracture with subsequent osteosynthesis in norm and with experimental osteoporosis. The second part of the research included two groups of laboratory rats with modeled femur fracture. In both parts we used metal injection needle, as well as carbon-carbon composite nail for osteosynthesis. Results. All animals underwent surgery well, stepped on the injured limb. X-ray examination after the osteosynthesis demonstrated satisfactory reposition of the fragments. One month after modeled fracture in rats with experimental osteoporosis a violation of the normal consolidation of the fracture was observed, especially in the group where carbon-carbon composite nails were used for osteosynthesis. Further, until the 180 day after the surgery there were no peculiarities, function of the limbs was restored, mainly without expressed angular deformities. Conclusion. The above mentioned model was successfully elaborated for the research of using carbon-carbon composite nail for intramedullary osteosynthesis in laboratory rats with fractures of femur and tibia in norm and with experimental osteoporosis.


Background
In Ukraine, there has recently been an increase in the number of limb bone fractures among the population, in particular, due to increase in the number of elderly people, which is associated with the development of age-related osteoporosis and fragility of bones. Osteoporosis causes 0.3 million femoral fractures per year in the United States and 1.7 million femoral fractures in Europe. In Ukraine, osteoporosis affects more than 2.5 million women and 900 thousand men, with an annual increase in inci-dence by 5% [1,2]. Therefore, the use of artificial implants in traumatology is becoming increasingly important. The search for new bioinert and biodegradable materials, that are capable of providing rapid fracture consolidation and do not require repeated surgical intervention, continues. One of the directions of scientific research in improving the results of osteosynthesis may be the search for new materials that will have more similar mechanical characteristics compared to bone and can be used in osteosynthesis.
It is known that standard surgical alloys, such as stainless steel, cobalt and chromium alloys, are susceptible to corrosion, the products of which cause local inflammation [5; 6]. Issues of connective tissue reactivity in this context remain insufficiently studied and require comprehensive study [7].
Recently, carbon composite porous materials have been studied, in which due to the physicochemical properties of the pores and irregularities of the material are filled with bone tissue, providing implants with biological fixation with the formation of a strong bone-carbon block, which promotes rapid and reliable consolidation. [8] Carbon composite materials and carbon polymers are new materials in medical practice. They are successfully used in reconstructive surgery, dentistry, traumatology and orthopedics. The use of implants made of carbon-carbon composite materials (CCCM) can solve not only the problem of osteosynthesis of any location and length bone diaphysis, but also provide a reliable long-term mechanical connection of bone fragments of metaphyseal parts.
Purpose To elaborate a model for the research of using carbon-carbon composite nail for intramedullary osteosynthesis in laboratory rats with fractures of femur and tibia in norm and with experimental osteoporosis.

Materials and methods
The work investigated the lower limbs of 6 groups of Wistar rats, weighing 170-230 g (10-12 weeks at the beginning of the experiment), which were pre-acclimatized for 14 days. The first part of the study involved 4 groups of Wistar rats with modeled tibial fracture with subsequent osteosynthesis in norm and with experimental osteoporosis. The second part of the research included two groups of laboratory rats with modeled femur fracture. Based on the literature data [9,10], we have chosen the optimal model. The first experimental group consisted of 15 animals. In order to create the experimental osteoporosis, animals of this group were injected intraperitoneally during 14 days with oil solution of retinol acetate (34.4 mg / ml) at a dosage of 70 mg / kg. Subsequently, the rats underwent modeling of a fracture of the left tibia. For this, after anesthesia and treatment of the operating field, approach was performed along the anteromedial surface of the left leg. Using Liston bone cutting forceps, a fracture of the left tibia was performed at the level of the proximal metaphysis, followed by intramedullary osteosynthesis using a metal injection needle (0.7 mm thick). The wound was sutured in layers.
The second group consisted of 15 rats. Animals of the control group underwent a similar operation -modeling a fracture of the left tibia with intramedullary osteosynthesis using a metal injection needle (0.7 mm thick), without preliminary osteoporosis modeling.
The third experimental group consisted of 15 animals. In order to create the experimental osteoporosis, animals of this group were injected intraperitoneally during 14 days with oil solution of retinol acetate (34.4 mg / ml) at a dosage of 70 mg / kg. Subsequently, the rats underwent modeling of a fracture of the left tibia. For this, after anesthesia and treatment of the operating field, approach was performed along the anteromedial surface of the left leg. Using Liston bone cutting forceps, a fracture of the left tibia was performed at the level of the proximal metaphysis, followed by intramedullary osteosynthesis using a carbon-carbon composite nail (1.0 mm thick). The wound was sutured in layers.
The fourth group consisted of 15 rats. Animals of the control group underwent a similar operationmodeling a fracture of the left tibia with intramedullary osteosynthesis using a carbon-carbon composite nail (1.0 mm thick), without preliminary osteoporosis modeling.
The fifth group (18 rats) underwent modeling of a fracture of the left femur. For this, after anesthesia and treatment of the operating field, approach was performed along the anteromedial surface of the left thigh. Using Liston bone cutting forceps, a fracture of the left tibia was performed at the level of the diaphysis, followed by intramedullary osteosynthesis using a carbon-carbon composite nail (1.2 mm thick). The wound was sutured in layers.
The sixth group (18 rats) also underwent modeling of a fracture of the left femur, followed by intramedullary osteosynthesis using a metal injection needle (0.7 mm thick).
Throughout the experiment, the animals were under daily supervision; appetite, weight of animals, condition of fur and mucous membranes, behavior were noted. Every group was divided into three equal parts (5-6 animals), then 30, 180 and 360 days after the operation, laboratory animals were taken out from the experiment for the further study of the fracture site. X-ray examination was performed after surgery and before withdrawal from the experiment When working with animals we were guided by «European Convention for the Protection of Vertebrate Animals used for Experimental and Other Scientific Purposes» (Strasbourg, 18.03.86) and Law of Ukraine «On the protection of animals against cruel treatment» (№ 3447-IV).

Results and discussion
All animals underwent surgery well, stepped on the injured limb. X-ray examination after the osteosynthesis demonstrated satisfactory reposition of the fragments (Fig. 1, Fig.2).
One month after modeled fracture in rats with experimental osteoporosis a violation of the normal consolidation of the fracture was noted, especially in 59 the group where carbon-carbon composite nails were used for osteosynthesis (Fig. 3). We associate this with intraoperative longitudinal bone split, which we observed in some cases in rats with experimental osteoporosis. Fig. 1. X-ray of the tibial fracture after osteosynthesis using metal injection needle, the 1 st day, group without osteoporosis. Further, until the 180 th day after the surgery there were no peculiarities, function of the limbs was restored, mainly without expressed angular deformities (Fig. 4).

Conclusion
The above mentioned model was successfully elaborated for the research of using carbon-carbon composite nail for intramedullary osteosynthesis in laboratory rats with fractures of femur and tibia in norm and with experimental osteoporosis.
Prospects for further research Next step of the research will include histological, histochemical, immunohistochemical study of the fracture site in all groups of laboratory animals. Fig. 3. X-ray of the tibial fracture after osteosynthesis using carbon-carbon composite nail, the 30 th day, group with osteoporosis. Fig. 4. X-ray of the tibial fracture after osteosynthesis using metal injection needle, the 180 th day, group with osteoporosis.

Funding sources
The study is a part of the research project "Morphological features of bone remodeling under conditions of their polysegmental damage and surgical correction" (state registration 0120U103164).

Conflicts of interest
Authors have no conflict of interest to declare.