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Abstract

Introduction Reduction of the period of limb lengthening with the Ilizarov method and preservation of limb functions in large elongations are the tasks to be solved by modern traumatology and orthopedics. The aim was to study the functional state of the limb, dynamics of the tibial regenerate formation, histostructural changes in the articular cartilage and the tibial nerve under the conditions of automatic high-frequency elongation of the tibia with the method of transosseous distraction osteosynthesis at a rate of 3 mm using a preliminary Z-shaped achillotomy. Material and methods The 24-hour high-fractional mode provided with automatic distractor was used to lengthen tibiae of 12 adult mongrel dogs with the method of transosseous distraction osteosynthesis. Distraction rate was 3.0 mm per day in 120 steps. To prevent formation of foot equinus, a Z-shaped achillotomy was performed. Methods of light microscopy, morphometry and X-ray electron probe microanalysis were used to study the distraction regeneration in the tibia, the articular cartilage of the medial condyle of the femur and the tibial nerve. Results During the periods of distraction and fixation, the regenerate was characterized by a normotrophic structure with a large proportion of bone component which provided the limb support function after 45 days of the experiment. Thirty days after the removal of the apparatus, a newly formed bone of a typical structure was seen in the distraction gap. Achillotomy helped prevent equinus deformity of the foot and flexion contractures of the knee joint and the metatarsal joint. However, histostructural changes in the articular cartilage were detected at the stages of osteosynthesis. Despite the restoration of the thickness of the cartilage, there was a decrease in the number of isogenic groups and the presence of cells with chondoptosis by the end of the experiment. Not a single case of neuropathy of the tibial nerve was revealed histologically due to prevention of overstretching of the anterior surface of the tibia by an increase in the length of the calcaneal tendon with tenotomy. The proportion of destructively altered nerve fibers in all animals did not exceed 5 %. Necrobiotic changes in the epineural vessels were compensated by hypervascularization of the epineurium and endonevria, as a result of which the majority of nerve conductors retained their normal structure, numeric density, and restored dimensional characteristics at the end of the experiment. Conclusions The conditions of the experiment provide for functional restoration of the limb, promote active reparative osteogenesis and structural adaptation of the tibial nerve, do not cause any gross destructive changes in the articular cartilage and reduce the period with the Ilizarov frame on by 30 % as compared with the classical variant.