Biomechanical study of intensity of pressure of intervertebral disc after short segment unilateral pedicle screw fixation in Chinese mini-pigs / 中华骨科杂志

ABSTRACT

Objective@#To explore the mechanical changes and distributions of pressure in each characteristic intervertebral disc after short segment unilateral pedicle screw fixation in Chinese mini-pigs.@*Methods@#Six characteristic spine segments of 6-week-old Chinese mini-pigs (T3-4、T11-12、T15-L1、L3-4、L4-5 segments with adjacent upper and lower vertebrae) were chosen as experimental models. A biomechanical machine and pressure sensitive film were used to measure the pressure on the vertebral columns when they were subjected to pressures of 200 N as unfixed group. Compression was carried out under vertical, 5 °flexion, 5 °extension and 5 °lateral bending, respectively. Then the PCF (posterior cervical fixation) system were fixed on all segments (left side) as fixed group, and biomechanical tests were repeated to obtain data. A Fujitsu densitometer (Japan) was used to measure the pressure on each direction of the pressure sensitive film.@*Results@#In vertical pressures, 5° flexion and 5°extension conditions, the posterior pressure of T3-4、T11-12、T15-L1、L3-4 and L4-5 intervertebral discs were decreased after fixation, the differences were statistically significant; The fixed side pressures of T3-4、T11-12、T15-L1、L3-4 and L4-5 in the fixed group were significantly lower than those in the unfixed group in the corresponding segments and load conditions, and the differences were statistically significant. The concave disc pressures of T3-4、T11-12、T15-L1、L3-4 and L4-5 in the fixed group were 0.83±0.12, 0.93±0.12, 0.50±0.05, 0.60±0.10 and 0.55±0.08 MPa respectively, which were lower than those of the unfixed group 1.70±0.18, 1.79±0.14, 1.84±0.22, 1.74±0.28, 1.60±0.23 MPa, and the differences were statistically significant. The total disc pressure of the fixed group was significantly lower than that of the non-fixed group in vertical compression, 5 degree flexion and 5 degree extension, and the differences were statistically significant.@*Conclusion@#Unilateral pedicle screw fixation can decrease the pressure on fixed side of fixed group in all conditions and change the distribution of pressure. The posterior pressure decreased particularly. Short- segment unilateral pedicle screw fixation can decrease the average pressure of intervertebral disc, which is an excellent surgery in curing scoliosis in young children.