Study design: A retrospective study.
Objective: To analyze and compare the sagittal spinopelvic alignment variation after implantation of purely dynamic and hybrid pedicle screw-based stabilization systems, seeking for its clinical implication.
Summary of background data: Numerous studies have investigated the kinematic features of pedicle screw-based dynamic stabilization systems since their clinical application. However, there is a lack of literature concerning their influence on the sagittal spinopelvic alignment, which has been proved to be important in the development of future adjacent segment degeneration (ASD).
Methods: Lateral standing lumbar radiographs of 29 patients (17 males, 12 females, 27 to 64 y) who were implanted with purely dynamic (Dynesys: group A, n=15) or hybrid (FlexPLUS: group B, n=14) stabilization systems, and with a minimum follow-up of 1 year, have been reviewed. These parameters were measured using Spineview software and were compared within and between groups: L1 to S1 lordosis, lordosis of instrumented segments (ISL), cranial adjacent segment lordosis (CASL) next to the instrumentation, highest instrumented segment lordosis (HISL), pelvic incidence, sacral slope, and pelvic tilt.
Results: Preoperative lordosis parameters were not significantly different between group A and B. The average L1 to S1 lordosis decreased from 55.3 degrees preoperatively to 52.6 degrees postoperatively in group A (P=0.007) and from 60.2 degrees to 59.3 degrees in group B (P=0.054). There was no significant difference between both groups (P=0.083). The average ISL decreased from 25.9 degrees preoperatively to 21.7 degrees postoperatively (P=0.00002) in group A and from 30.0 degrees to 28.6 degrees in group B (P=0.153). The prepostoperative ISL variation was significantly different between group A and B (P=0.015). The average HISL decreased from 9.5 degrees to 6.2 degrees in group A (P=0.0007) and from 13.1 degrees to 12.4 degrees in group B (P=0.295). The loss of HISL was significantly greater (P=0.010) in group A than in group B. The average CASL increased from 6.9 degrees to 9.2 degrees (P=0.013) in group A. The CASL variation from 10.6 degrees to 10.4 degrees was not significant (P=0.763) in group B. When comparing both groups, the difference of CASL variation was statistically significant (P=0.043). The pelvic incidence, sacral slope, and pelvic tilt did not change significantly before and after instrumentation in both groups.
Conclusions: On the basis of the result of this study, the hybrid stabilization system could better preserve the lordosis of instrumented segments and subsequently reduce the extent of compensatory lordosis increase at the cranial adjacent segment. This could theoretically prevent the development of an ASD. The long-term outcome and the correlation between lordosis-preserving capacity and ASD need to be further prospectively analyzed.