Comparative analysis of changes in the desmal and chondral structures of spinal motion segment at various methods for posterior spine fixation in experiment

Purpose: to elaborate the criteria for the assessment of the degree of spinal motion segment degradation at various methods for posterior spine fixation in experiment. Material and methods. The study included mongrel dogs with body mass of 12±1.5 kg aged 21±3 months. Transpedicular lumbar spine fixation was performed with either rigid titanium alloy rods (1st group, n=5) or dynamic nitinol rods (2nd group, n=5). X-ray examination and morphologic study of the structural elements of spinal motion segment (SME) were performed to all animals in 3, 6, 12, 18 and 24 months after surgery. Results. Functional examination showed that in both groups the range of motion made up 18±1.2° preoperatively. In the 1st group of animals the range of motion in the operated SME made up 0±0.03°. In the second group the range of motion was preserved throughout the experiment and averaged 15±1.3° that made up 78.9% of the preoperative range. In both groups the disc height at the fixation level was constant throughout the experiment and made up 0,3±0.003 cm pre- and postoperatively. Obtained roentgenologic and morphologic data indicated that posterior dynamic spine fixation with nitinol rods ensured more balanced distribution of loads on the supportive elements of the construction and enabled prevent the development of the adjacent segments degeneration. Based on the study results the criteria for the assessment of the degree of the facet joints and discs degradation were formulated.

spinal motion segment, nitinol, dynamic fixation, rigid fixation