ANALYSIS OF OPTICAL DENSITY OF REGENERATE IN THE AUTOMATIC LOWER LEG LENGTHENING CONDITIONS WITH INCREASED RATE AT DIFFERENT METHODS OF BONE CONTINUITY Gorbach

Aims. The work was aimed at the investigation of the diagnostic value of analysis of the optical density of bone regenerate under conditions of accelerated automatic lengthening of the lower leg. Materials and methods. A comparative analysis of the optical density (on the digitised X-ray images) of different areas of distraction regenerates of the tibia in 14 adult mongrel dogs aged 1 to 3 years at the stages of automatic lengthening of the lower leg with the Ilizarov technique, at a rate of 3 mm per day with preliminary bone damage by flexion osteoclasis (series I) and oblique osteotomy (series II). Results. The study revealed that the method of bone continuity by oblique osteotomy promotes more active osteogenesis in the distraction period and the support ability of the extremity within 14 days after dismantling the apparatus, which reduces the apparatus period by 16% compared with the series for which flexion osteoclasis was used. At the same time, signs of incomplete organotypic rearrangement of the newly formed diaphysis area, especially pronounced in series II, persist after 30 days of the apparatus-free period. Conclusions. When the optical density values of the distraction regenerate in intermediary and endosteal regions with two or more surfaces are more than 0.5 conditional units, and in the rest – not less than 0.33 conditional units, the onset of regenerate support ability was noted in both series. The resulting values can be criteria for dismantling the apparatus.

and control the treatment efficiency [9].
The study was aimed to perform a comparative analysis of optical density in digital X-ray images of distraction regenerates at different stages of the automatic distraction of a lower leg with the rate of distraction of 3 mm/day.

MATERIALS AND METHODS.
The study included 14 adult outbred dogs aged 1-3 years old with bodyweight from 24±3.1 kg, the mean length of the lower leg was 18.6±1.3 cm. The dogs had their lower leg fixed with an Ilizarov apparatus and the bone was damaged. In Series I of tests, the bone was damaged by flexion osteoclasis in the mid-third, in Series II of testsby oblique osteotomy. For the next 10 days, the lengthening of the lower leg was performed by the method of automatic transosseous distraction osteosynthesis with a 3-mm distraction rate and 120-fold division. The limb lengthened by 15.7± 1.3%. (Strasburg, March 18, 1986), ETS N 123 and the Decree of the Ministry of the Russian Federation No. 199N "Good Laboratory Practice" dated April 1, 2016. The study on the evaluation of optical density was performed using digitalized X-ray images taken 10 days after the distraction, after the removal of the external fixation (Series I -30 days, Series II -15 days), and 30 days after the removal of the external fixation.

Experiments on animals were conducted according to the "European Convention for the Protection of Vertebrate Animals Used for Experimental and other Scientific Purposes"
X-ray images of the operated lower legs were taken in the frontal and lateral projections using the X-ray apparatus "VEP X Technology Premium VET" (Spain). The X-ray images were digitalized by their scanning with "HP Scanjet 7400c" (Hewlett Packard, California) and saved on the computer.
The intensity (Ii) of shadows of different parts of the regenerate was evaluated by the Hi-Scene software intended for reading and computed processing of the results of X-ray studies [10].
The evaluation of Ii at the stage of distraction was performed in the periosteal, endosteal, and intermediary areas of the regenerate with the anterior, posterior, and lateral surfaces of the proximal and distal fractured bone fragments, proximal and distal bone sections, and the area of the connective tissue extension (Figure 1). During the next stages of the experiment, the intensity of shadows was evaluated in the analog projections of the regenerate areas. Further, optical density was calculated by the formula ODi = lg((Ii-Im)/I0), where Iithe intensity of the i-th element of the image, Imthe mean intensity of soft tissues shadows, I0the mean intensity of the background.
The statistical processing was performed in the Attestat v.1.0 software [11]. The significance of the difference was evaluated by the methods of variance and non-parametric statistics. Depending on the character of the samplings distributions, Wilcoxon's or Student's t-test was used.

RESULTS.
It was revealed that 10 days after the distraction, the density in the fractured bone fragments in the animals from Series II decreased in comparison with Series I by 12-18%, except for the posterior surface wherein it hardly changed (Table 1). In the proximal bone region, the OD values in the medial surface in the endosteal and intermediary areas in the animals from Series II were lower than in Series I by 8 and 20%, respectively. On the contrary, in the anterior surface, animals after flexion osteoclasis had higher parameters in all the areas by 2.5-3 times and, in the posteriorby 2-3.7 tomes. In the distal bone section, OD values were higher by 1.43 times than the analog parameters in Series I in the lateral intermediary area. In the endosteal and periosteal areas, there were no significant differences revealed.
The analysis of analog areas in the medial surface revealed a decrease in the OD by 8-34% in comparison with the group of animals after flexion osteoclasis.   Table 2). In all the other areas on the anterior and posterior surfaces, the differences in the parameters were either insignificant or higher by 1.2-1.4 times than in Series I.
The highest increase in the parameters was registered in animals from Series II in the periosteal area. *at p˂ 0.01differences are significant in comparison with animals from the other test series; **at p˂ 0.05differences are significant in comparison with animals from the other test series; ***at p≥ 0.05differences are insignificant in comparison with animals from the other test series; +at p ˂ 0.01differences are significant in comparison with the period of distraction; ++at p ˂ 0.05differences are significant in comparison with the period of distraction; +++at p≥ 0.05differences are insignificant in comparison with the period of distraction.
A month after the external fixation removal, the OD parameters in Series II were close to Series I at the level of fractured bone fragments on the lateral and posterior surfaces. On the medial and anterior surfaces, the parameters remained lower by 10-17% than in the fractured bone fragments in Series I (Table 3). Xia Lan et al. [12] suggest that a good outcome after oblique osteotomy for the lengthening of a limb is associated with a major area of the contact between the bone fragments and their better stability. Other authors [13] highlight that oblique osteotomy is rarely used by surgeons. should not be below 0.33 CU.

CONCLUSIONS.
Automatic extraction of the lower leg at the rate of 3 mm/day after the bone damage with oblique osteotomy contributes to more active osteogenesis during the period of distraction, which leads to early substitution of the connective tissue extension with bone tissue and restores the supporting ability already 14 days after the removal of the external fixation, which reduces the period of external fixation by 16% in comparison with flexion osteoclasis. At the same time, 30 days after the removal of the external fixation, the signs of incomplete organ-specific transformation of the newly formed area of the diaphysis remain. When the parameters of the OD were more than 0.5 CU in the distraction regenerate in the intermediary and endosteal areas on two and more surfaces and not less than 0.3 CU in the rest areas, the regenerate acquired the supporting ability. The obtained results can be used as the criteria for the removal of the external fixation.

FINANCIAL SUPPORT AND SPONSORSHIP
Nil.