The value of fixed segment mobility in posterior dynamic stabilization: a single-center retrospective study

Abstract

Purpose: This study aims to compare the effects of two generations of the Isobar dynamic fixation system-Isobar TTL (first-generation, less mobile) and Isobar EVO (second-generation, more mobile)-on the surgical and adjacent intervertebral disc segments, based on MRI findings.

Methods: A retrospective analysis was conducted on 29 patients treated with fenestrated decompression and Isobar EVO stabilization and 34 patients treated with fenestrated decompression and Isobar TTL stabilization. Clinical outcomes and radiographic parameters, including the disc height index (DHI) and range of motion (ROM) of the surgical and upper adjacent segments, lateral neural foraminal protrusion value (LNPV) of the upper adjacent segment, and Pfirrmann grading of disc degeneration, were evaluated and compared between the two groups.

Results: At the 48-month follow-up, no significant differences in Visual Analog Scale (VAS) scores or Oswestry Disability Index (ODI) were observed between the two groups (P > 0.01). The EVO group demonstrated significantly higher surgical segment DHI and ROM compared to the TTL group (P < 0.01). Meanwhile, the upper adjacent segment ROM was significantly lower in the EVO group compared to the TTL group at the final follow-up (P < 0.01). Additionally, the upper adjacent segment LNPV was larger in the EVO group than in the TTL group (P < 0.01). Pfirrmann grading revealed greater degeneration in surgical segments treated with TTL compared to EVO (P = 0.008).

Conclusion: Compared to the first-generation, less mobile Isobar TTL, the second-generation, more mobile Isobar EVO offers superior preservation of the surgical segment and slows the progression of degeneration in the upper adjacent segments. These findings highlight the benefits of greater mobility in posterior dynamic stabilization devices.

Keywords: Adjacent segment degeneration; Dynamic stabilization; Isobar system; Lumbar degenerative diseases; Non-fusion.

Fig. 1

The TTL system is on the left, and the EVO system is on the right [10]

Fig. 2

A and B show LNPV measurements, and Both A and C are median sagittal plane of the MRI image. A. The h represents 1/2 of the height of the highest point in the middle of the nucleus pulposus in the median sagittal position of MRI. B. The a and b represent 1/2 of the anterior posterior diameter and width of the MRI cross-sectional ellipse, respectively. C. DHI was calculated using the MRI sagittal parameter de / cd

Fig. 3

Rom of surgical segment between the TTL and EVO groups

Fig. 4

Rom of upper segment between the TTL and EVO groups

Fig. 5

A-Eanda-e. A 47-year-old male patient underwent Isobar TTL stabilization due to spinal stenosis in L4/5. He underwent fenestration decompression at L4-5, and instrumentation at L4–5 using the Isobar TTL. A-E The preoperative radiographs. A-B. Preoperative frontal and lateral x-ray of lumbar spine. C. The preoperative lumbar sagittal T2WI with fat suppression. The Pfirrman grading of L4/5 was grade III, and that of L3/4 was grade II. D. The preoperative lumbar axial T2WI of L3/4 nucleus pulpous, and the LNPV of L3/4 nucleus pulpous was 4.86 mm³. F-G. The pre-operative ROM of the surgical segment was 8.3° based on X-ray. a-e. The radiographs obtained 48 months after the operation. a-b. Postoperative frontal and lateral x-ray of lumbar spine. c. The lumbar sagittal T2WI. The Pfirrman grading of L4/5 was grade IV, and that of L3/4 was grade III. d--e. The lumbar axial T2WI of L3/4 nucleus pulpous, and the LNPV of L3/4 nucleus pulpous was 4.32 mm³. f-g. The post-operative ROM of the surgical segment was 2.4° based on X-ray

Fig. 6

A-E and a-e. A 43-year-old male patient underwent Isobar EVO stabilization due to spinal stenosis in L4/5. He underwent fenestration decompression at L4-5, and instrumentation at L4–5 using the Isobar EVO. A-B. Preoperative frontal and lateral x-ray of lumbar spine. C-E The preoperative MRI scans. C. The preoperative lumbar sagittal T2WI with fat suppression. The Pfirrman grading of L4/5 was grade IV, and that of L3/4 was grade II. D. The preoperative lumbar axial T2WI of L3/4 nucleus pulpous, and the LNPV of L3/4 nucleus pulpous was 4.93 mm³. F-G. The pre-operative ROM of the surgical segment was 8.7° based on X-ray. a-e. The radiographs obtained 50 months after the operation. a-b. Postoperative frontal and lateral x-ray of lumbar spine. c. The lumbar sagittal T2WI. The Pfirrman grading of L4/5 was grade III, and that of L3/4 was grade II. d-e. The lumbar axial T2WI of L3/4 nucleus pulpous, and the LNPV of L3/4 nucleus pulpous was 4.71 mm³. f-g. The post-operative ROM of the surgical segment was 4.6° based on X-ray

Fig. 7

Preoperative and postoperative LNPV between the TTL and EVO groups

Fig. 8

The correlation between ROM and LNP

Fig. 9

The correlation between ROM of surgical segment and Pfrrimann of upper segment disc