Effects of Dynesys dynamic fixation versus fusion fixation on sagittal alignment of lumbar degenerative diseases involving 2 to 4 segments / 中华骨科杂志

ABSTRACT

Objective:To compare the effects of Dynesys dynamic fixation and fusion fixation on the sagittal parameters of lumbar degenerative diseases of 2-4 segments.Methods:A total of 45 patients with 2-4 segments lumbar degenerative diseases, who underwent decompression and internal fixation in our hospital from March 2014 to July 2019, were retrospectively analyzed. There were 23 males and 22 females with an average age of 55±18 years (range 15-86 years). Dynesys dynamic fixation was performed in 22 cases and fusion fixation in 23 cases. Lumbar anteroposterior, flexion and extension lateral and standing full-length spine radiographs were taken before surgery, 2 weeks postoperatively, 3 months postoperatively and at the last follow-up. Sagittal alignment parameters were measured on those radiographs and compared between two groups. Lumbar parameters included lumbar lordosis (LL), lordosis of the fixed segments (LFx), lordosis of the adjacent level to fixed segment (LAdj) and lumbar range of motion (ROM). Pelvic parameters included pelvic incidence (PI), pelvic tilt (PT) and sacral slope (SS).Results:All cases were followed up for 12-50 months with an average of 18.5 months. There was no significant intra- and inter-group difference of LL value between Dynesys dynamic fixation and fusion fixation group before and after surgery ( P>0.05). The overall difference of LFx between groups was not statistically significant ( F=0.700, P=0.406). There was statistically significant variance between time points ( F=7.960, P<0.001) and an interaction effect between group and time ( F=3.940, P=0.006). The LFx of the fusion fixation group was more than that of the dynamic fixation group at 3 months postoperatively and at the last follow-up ( P<0.05). The difference of LAdj value between the two groups was not statistically significant ( F=0.520, P=0.476), while the difference between time points was significant ( F=4.810, P=0.002) with interaction effect between group and time ( F=3.560, P=0.010). Postoperative ROM values of the two groups showed statistically significant differences in group effect, time effect and interaction effect, respectively ( F=4.770, P=0.034; F=18.510, P<0.001; F=5.940, P=0.002). Dynamic fixation group's ROM was more than that of the fusion fixation group at 3 months postoperatively and at the last follow-up ( P<0.05). There was no significant difference of PI between groups and between different time points ( F=0.580, P=0.451; F=0.750; P=0.477). There was no interaction effect in PI between group and time ( F=0.120, P=0.886). There was no significant difference of PT and SS between two groups ( F=0.320, P=0.576; F=0.020, P=0.901). Both time effect and interaction effect were statistically significant ( P<0.05). One complication of unilateral S 1 screw loosening happened in one patient with dynamic fixed at 2 years after surgery. There was no complication in the fusion fixation group during the follow-up. Conclusion:Both Dynesys dynamic fixation and fusion fixation can effectively reconstruct the lumbar lordosis. The fixed segments' lordosis of Dynesys was less than that of fusion fixation from 3 months after operation. Theoretically, the similar increasing trends of LAdj after fixation implied that the degeneration of adjacent segments may occur in both fixation systems. The dynamic fixation can retain more ROM than the fusion fixation. Both two fixation systems have similar influence on the pelvic parameters.