Adjacent Intervertebral Disc Changes in Patients with Isobar Semirigid Dynamic Stabilization System

Abstract

Introduction The reported incidence of adjacent segment degeneration (ASD) after lumbar fusion ranges from 8 to > 100%, average 27%. Another literature review reported that 5.2 to 18.5% of patients required surgery for adjacent segment disease after lumbar fusion surgery. Posterior dynamic stabilization systems may prevent the development and progression of ASD after surgery. Hybrid dynamic stabilization with posterior spinal fusion, or "Topping-off surgery," is applied in patients with preoperative adjacent segment degeneration. The objective of this approach is to protect the degenerative adjacent segment from progressing. Efficacy of this procedure is debated. The objective of this study was to evaluate intervertebral disk changes of the dynamically stabilized spine segment in patients receiving single-level intervertebral fusion and adjacent segment dynamic stabilization using the Isobar (Alphatec Spine, Inc.) semirigid dynamic stabilization system. Materials and Methods Twenty-seven patients with confirmed degenerative disk disease were enrolled in a retrospective study. Patients received single level intervertebral fusion and dynamic stabilization of the adjacent level using the Isobar semi-rigid dynamic stabilization system. Patient outcomes were evaluated by visual analogue scale for pain (VAS) and Chinese version of Oswestry Disability Index (ODI). Intervertebral space ratio (IVS) and range of motion (ROM) were measured on plain radiographs. MRI relative gray-scale values of the central bright area of discs were analyzed by Image J software. Results Of the 27 patients, 16 were male and 11 were female. Ages ranged from 31 to 65 years (average 47 years). Average duration of surgery was 213 (SD = 52) minutes and average blood loss was 225 mL (SD = 105). The average follow-up time was 27 months, ranging from 24 to 40 months. There was no significant change in relative gray-scale value of adjacent disc between preoperative and two year follow-up (23.98 +/- 8.86 and 22.22 +/- 6.25, respectively, p = 0.46). Relative gray-scale values of first cephalic adjacent disc were reduced at 2 years follow-up compared with baseline (28.63 +/- 8.35 and 32.54 +/- 10.75, respectively, p = 0.06). Significant difference was found in relative gray-scale value of second cephalic adjacent disc between baseline and 2-year follow-up (35.51 +/- 8.15 and 29.29 +/- 7.56, respectively, p < 0.01). The inter-vertebral space (IVS) of index level was maintained after the surgery (Table 1). There was no statistical difference between the IVS before the surgery and final follow-up (p = 0.33). The range of motion (ROM) of the adjacent level was reduced from 6.91 +/- 3.14 preoperatively to 2.46 +/- 1.03 degrees at the final follow-up (p < 0.05). There were no significant differences in the index level ROM among any of the follow-up times. VAS and ODI scores significantly improved preoperatively to final follow-up (VAS: 6.12 +/- 0.80 and 1.65 +/- 0.69, respectively, p = < 0.01; ODI: 54.91 +/- 10.96 and 14.61 +/- 3.88, respectively, p = <0.01). One patient received a debridement due to wound infection after operation, but the fixation system and interbody cage were not removed. This patient recovered well after the debridement. At the 2-year follow-up, one patient had two screw fractures at S1 level and another patient had two screws loosen. Conclusion Dynamic stabilization of the level adjacent to the fused level using the Isobar TTL Semi-rigid Spinal System seems to prevent progression of degenerative changes in the stabilized spine segment and is associated with favorable patient outcomes.