Table 3 Clinical studies using Isobar semi-rigid system

Qian et al. (2016) [20]

Retrospective cohort study

22

Single-level non-fusion

18 (12–27)

1.L4/5 or L5/S1 disc herniation or significant prolapse

2.Lumbar degenerative spondylolisthesis Meyerding grade I or II

VAS, JOA, ODI, ROM (FS)

VAS: 6.42 pre-op; 1.71, 1.38, and 1.37 at 1, 3, and 12 months post-op, respectively JOA: 9.54 pre-op; 21.21, 22.50, and 23.46 at 1, 3, and 12 months post-op, respectively ODI: 42.04% pre-op; 22.79, 18.63, and 15.08% at 1, 3, and 12 months post-op, respectively ROM: 3.46° at pre-op; 2.25° at last follow-up

IV

Deng et al. (2015) [21]

RCT

120

Single-level non-fusion

24

L4/5 or L5/S1 disc herniation or significant prolapse

VAS, ODI, ROM (FS)

VAS and ODI improved after surgery in both groups, but the above parameters of Isobar group higher than Dynesys group ROM: Dynesys > Isobar (4.4° vs. 2.8°)

II

Huang et al. (2016) [22]

Retrospective cohort study

36

Single-level non-fusion

48

L4/5 or L5/S1 disc herniation or significant prolapse

DH (FS), NPV of AS

The DH of FS were not significantly different between final follow-up and before surgery The NPV of AS increased post-op, showing no significant difference at 6, 12, and 18 months, but significant difference was found at 24, 36, and 48 months when compared with pre-op

IV

Tian et al. (2018) [23]

Retrospective cohort study

20

Single-level non-fusion

14.4 (12–27)

L4/5 or L5/S1 disc herniation or significant prolapse

VAS, ODI, JOA, DH (FS and AS), ROM (FS and AS), UCLA (AS)

VAS: 7.75 pre-op; 3.40, 1.60 and 0.85 at 1-, 3-, and final post-op, respectively ODI: 43.05 pre-op; 15.75, 17.19, and 12.27 at 1-, 3-, and final last follow-up JOA: 8.80 pre-op; 25.25, 27.55 and 27.65 at 1-, 3-, and last follow-up DH: FS: 13.51 mm at pre-op 12.77 mm at last follow-up AS: 15.29 mm at pre-op; 15.06 mm at last follow-up ROM: FS: 4.50° at pre-op; 2.50°at last follow-up AS: 4.80° at pre-op; 4.10° at last follow-up UCLA of AS were not significantly different pre-op and post-op

IV

Yang et al. (2012) [24]

Retrospective cohort study

98

Single-level non-fusion or Hybrid

36

1. Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2 Spondylolisthesis (Meyerding grade I or II)

JOA, LL, SS, ASD, Complication

JOA improved in both groups, TTL group > Ti rods LL: TTL vs. Ti rods → 22.8° vs. 13.9° SS: TTL vs. Ti rods → 15.9° vs. 12.2° TTL Hybrid group: 2 ASD and 1 unfused in TTL Hybrid group Ti group: 2 screws breakage and 3 unfused and 8 ASD

III

Wen et al. (2011) [25]

Retrospective cohort study

72

Hybrid

24

1. Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2 Lumbar degenerative spondylolisthesis Meyerding grade I or II

VAS, JOA, Complication

VAS and JOA improved after surgery in both groups, but no significant difference was detected between the 2 groups TTL Hybrid group: 1 patient had cauda equina nerve root encroachment, 1 ASD Ti group: 1 patient had screw breakage at the head–screw interface but remained pain free, 3 ASD

III

Zhang et al. (2012) [26]

Retrospective cohort study

38

Single-level non-fusion or Hybrid

27.8 (8–53)

1.Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2.Lumbar degenerative spondylolisthesis Meyerding grade I or II

VAS, JOA, ROM (FS)

VAS: 8.20 pre-op; 1.93 final post-op JOA: 4.87 pre-op; 23.06 final post-op ROM: 3.17° at last follow-up

IV

Lu et al. (2019) [27]

Retrospective cohort study

49

Single-level fusion with isthmus bone grafting

32.12 (26–42)

Lumbar spondylolysis or with Meyerding I spondylolisthesis

VAS, ODI, Fusion rate

VAS: 6.17 pre-op; 1.76 final post-op ODI: 65.87 pre-op; 18.31 final post-op Fusion rate: 85.71% and 97.96% fusion at 6-month and 12-month post-operation

IV

Feng et al. (2017) [28]

RCT

60

Hybrid

with Cage

12

1.Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2.Lumbar degenerative Meyerding I spondylolisthesis

VAS, JOA, Complication, UCLA (AS)

VAS and JOA improved after surgery in both groups, but no significant difference was detected between the 2 groups Screws loosening: 5 (TTL 2.5%) vs. 17 (Ti rod 8.7%) UCLA of AS in Ti rod group was inferior to TTL group at 12 months postoperatively

II

Zeng et al. (2017) [29]

Retrospective cohort study

26

Single-level fusion with isthmus bone grafting

36.5 (24–60)

Lumbar spondylolysis or with Meyerding I spondylolisthesis

VAS, ODI, Fusion rate, UCLA (AS)

VAS: 5.84 pre-op; 1.46 final post-op ODI: 61.46 pre-op; 19.08 final post-op 23/26 (88.5%) fusion rate at final follow-up UCLA of AS was not significantly different between pre-op and post-op

IV

Cao et al. (2019) [30]

Retrospective cohort study

97

Hybrid with intertransverse fusion

9.2

Double-segment disc herniation combined with lumbar instability

VAS, Modified Pfirrmann grading

VAS scores improved after surgery in both groups, TTL superior to Ti rods The modified Pfirrmann grading was significantly improved postoperatively in both groups, TTL superior to Ti rods

III

Huang et al. (2012) [31]

Retrospective cohort study

74

Single-level non-fusion or Hybrid

24

1.Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2.Lumbar degenerative spondylolisthesis Meyerding grade I or II

JOA, LA, SS ASD, Complication

JOA improved in both groups after surgery, and scores of TTL were significantly higher than that of Ti group at 6 months, 12 months, and 24 months postoperatively The LL and SS significantly different between the TTL and Ti groups, and the TTL group with a larger angle than the Ti group. (20.5° vs. 14.1°, 15.8° vs. 12.3°) TTL Hybrid group: 1ASD. Ti group: 4 ASD, 2 screws breakage and 3 segmental unfused

III

Xu et al. (2013) [32]

Retrospective cohort study

40

Single-level non-fusion or Hybrid

36 (12–46)

1.Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2.Lumbar degenerative spondylolisthesis Meyerding grade I or II

VAS, ODI, ROM (lumbar)

VAS and ODI improved after surgery in both groups, but no significant difference was detected between the 2 groups ROM: there was not significantly difference in the TTL group between pre-op and final follow-up TTL group: 14.72° at pre-op, 13.92° at final follow-up Ti group: 13.55° at pre-op, 7.34° at final follow-up

III

Ma et al. (2019) [33]

Retrospective cohort study

40

Unilateral single-level non-fusion

53.6

L4/5 or L5/S1 disc herniation or significant prolapse

VAS, ODI, JOA, ROM, DH, UCLA, Modified Pfirrmann grading

VAS: 6.5 pre-op; 2.1 and 1.6 at 6 and 12 months post-op, respectively ODI: 71.3% pre-op; 24.8% and 20.9% at 6 and 12 months post-op, respectively JOA: 6.7 pre-op; 23.3 and 23.8 at 6 and 12 months post-op, respectively The DH was no significant difference between preoperative and postoperative (0.8 mm vs. 0.76 mm) The ROM in the AS increased significantly (2.93° vs. 5.18°), while ROM in FS decreased after surgery (2.85° vs 2.33°) The UCLA grading scale and modified Pfirrmann grading were not statistically significant between preoperative and postoperative

III

Liu et al. (2011) [34]

Retrospective cohort study

35

Single-level non-fusion or Hybrid

18 (12–36)

1.Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2.Lumbar degenerative spondylolisthesis Meyerding grade I or II

VAS, ODI, ROM (lumbar and FS)

VAS: pre-op:6.45 last follow-up:2.12 ODI: pre-op:76.5% last follow-up:21.13% ROM (Lumbar): pre-op 14.72° vs. post-op 13.92° (p > 0.05) ROM (FS): pre-op 5.17° vs. post-op 4.04° (p > 0.05)

III

Rao et al. (2013) [35]

Retrospective cohort study

18

Single-level non-fusion or Hybrid

35 (15–52)

1.Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2.Lumbar degenerative spondylolisthesis Meyerding grade I or II

VAS, ODI, JOA, DH (FS), ROM (FS), UCLA

VAS: pre-op:7.89 last follow-up:1.11 ODI: pre-op:24% last follow-up:6.94% JOA: pre-op:7.33 last follow-up:23.17 DH: pre-op (11.48 ± 1.70) mm vs. post-op (10.85 ± 1.32) mm (p > 0.05) ROM: pre-op 3.71° vs. post-op 2.72° (p > 0.05)

IV

Yao et al. (2017) [36]

Retrospective cohort study

20

Single-level non-fusion or Hybrid

24

1.Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2.Lumbar degenerative spondylolisthesis Meyerding grade I or II

VAS, ODI UCLA, ROM (AS and FS), DH (AS and FS), LL, Modified Pfirrmann grading (AS and FS), Complication

VAS: pre-op:5.3 last follow-up:0.6 ODI: pre-op:54.4% last follow-up:12.9% At the latest follow-up, a significant decrease of FS: DH and ROM (from 5.26° to 2.23°) was noted; however, no significant difference in UCLA was observed compared with those before surgery AS: No significant difference was found in the DH, ROM, UCLA LL: pre-op 31.05° post-op 31.85° (p > 0.05) 16 patients who accepted repeat MRI at the final follow-up had no significant difference in modified Pfirrmann grading compared to that preoperatively 4/124 (3.2%) loosening screws

IV

Li et al. (2011) [37]

Retrospective cohort study

28

Single-level non-fusion

14.6 (6–24)

1.Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

2.Spondylolisthesis Meyerding grade I or II

VAS, ODI, ROM (lumbar, AS and FS)

VAS and ODI improved after surgery in both groups, but no significant difference was detected between the 2 groups In the TTL group, no significant changes of lumbar spine ROM (L2-S1) and segmental ROM (L4–5 and L3–4/L5–S1) were measured

III

Cedric Barrey et al. (2013) [38]

Retrospective cohort study

18

Single-level fusion with cage

10.2 years (7–14)

Lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability

Fusion rate, ASD

Fusion rate: 16/18 cases (89%) 8 ASD

IV

Zhang et al. (2019) [39]

Retrospective cohort study

37

Hybrid

N/A (6–36)

1.Lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability

2.Spondylolisthesis (Meyerding grade I or II)

VAS, ODI, DH (anterior edge and posterior edge)

VAS: pre-op:7.81 last follow-up:3.51(p < 0.05) ODI: pre-op:64.84% last follow-up:25.16% (p < 0.05) DH (anterior edge): pre-op:13.45 mm last follow-up:11.86 mm (p < 0.05) DH (posterior edge): pre-op:10.26 mm last follow-up:9.97 mm (p > 0.05)

IV

Liu et al. (2019) [40]

Retrospective cohort study

62

Single-level non-fusion

6

L4/5 or L5/S1 disc herniation or significant prolapse

ODI, JOA, ROM (lumbar and AS), Pfirrmann grading (AS)

ODI and JOA improved after surgery in both groups, and the ODI scores of the TTL group were significantly lower than control group and the JOA scores were significantly higher than control group The total ROM of lumbar vertebrae in the TTL group was significantly higher than that in the control group post-operation. (7.64° and 7.59° vs. 6.22° and 3.68°) And the ROM of AS in TTL group was significantly lower than that of the control group (7.30° and 7.27° vs. 7.14° and 8.26°) The Pfirrmann grading of AS in TTL group was significantly lower than that in the LD group

III

Liu et al. (2020) [41]

RCT

55

Single-level non-fusion

16.73

Singe-level disc herniation or significant prolapse

VAS, ODI, DH, ROM (FS and AS)

VAS and ODI improved after surgery in both groups, and the scores of the TTL group were significantly lower than PLED group. At final follow-up, the TTL group had significantly higher DH and ROM of FS than the PLED group (0.75 mm vs. 0.58 mm and 5.26° vs. 2.37°), and the ROM of AS was significantly lower than that of the PELD group. (7.38° vs. 9.46°)

II

Ji et al. (2020) [42]

Retrospective cohort study

41

Hybrid

22 (15–37)

Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability) in two consecutive segments (L3/4 and L4/5)

VAS, ODI, fusion rate, UCLA, DH(AS)

VAS and ODI improved after surgery in both groups, and difference between the two groups was not significant fusion rate: 95% (TTL) vs. 95.2% (Ti) According to the UCLA system, the incidence of ASD was 5.0% in the Isobar TTL group and 19.0% in the rigid group DH (AS): Ti group < TTL group

III

Song et al. (2021) [43]

Retrospective cohort study

15

Single-level non-fusion

45.27 ± 9.13

ASD after single-level rigid fusion

VAS, ODI, ROM (FS and AS), LL (FS and AS)

VAS: back pain: pre-op 8.07; post-op 1.07 Leg pain: pre-op 7.93; post-op 0.87 ODI: pre-op 78.65%; post-op 20.18%

ROM: FS: pre-op 6.32°; post-op 3.16° (p < 0.05)

AS: pre-op 4.84°; post-op 5.51° (p > 0.05)

LL: FS: pre-op 27.12°; post-op 30.95° (p > 0.05) AS: pre-op 10.14°; post-op 11.32° (p > 0.05)

IV

Zhang et al. (2019) [44]

Retrospective cohort study

80

Single-level non-fusion or Hybrid

31.9 (17–45)

1.Lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability

2.Spondylolisthesis (Meyerding grade I or II)

VAS, ODI, ROM (FS and AS)

VAS: pre-op: 9.15 last follow-up:0.24 (p < 0.05) ODI: pre-op:38.65% last follow-up:0.16% (p < 0.05) ROM: FS: pre-op 6.87°; post-op 3.14° (p < 0.05) AS: pre-op 4.84°; post-op 5.51° (p > 0.05)

IV

Gao et al. (2014) [45]

RCT

54

Hybrid

24

Lumbar degenerative spondylolisthesis Meyerding grade I or II

ODI, JOA, Pfirrmann grading (US)

ODI and JOA improved after surgery in both groups, and difference between the two groups was not significant At 24 months postoperatively, intervertebral disc degeneration in the TTL group slowed, and 14 dynamic fixation intervertebral discs showed improvement in Pfirrmann grade. However, in the Ti group, there were 23 discs which showed higher grade degeneration

II

Li et al. (2013) [46]

Retrospective cohort study

37

Hybrid

24 (12–36)

Lumbar degenerative disease (including lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability)

ODI, VAS, ROM (FS), Pfirrmann grading (US)

VAS: back pain: pre-op 6.3; post-op 1.1 Leg pain: pre-op 7.9; post-op 1.8 ODI: pre-op 46.9%; post-op 25.4% ROM (FS): pre-op 11.2°; post-op 2.9° (p = 0.013)

IV

Rong et al. (2016) [47]

Retrospective cohort study

13

Single-level non-fusion

36 (24–53)

1. Spondylolysis with or without spondylolisthesis Meyerding grade I

2. Age < 25 years

3. No obvious disc degeneration at the spondylolysis level or at the adjacent level

VAS, ODI, UCLA

The mean improvement in VAS and ODI scores was 82% and 83%, respectively The AS degeneration including UCLA I grade (13 levels) and UCLA II grade (2 levels) at the final follow-up was same to pre-operation and no adjacent degenerative disease was observed

IV

Guan et al. (2022) [48]

Retrospective cohort study

80

Single-level non-fusion

52.23 ± 2.97

1.Lumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability 2.Lumbar degenerative spondylolisthesis (Meyerding I and II)

VAS, ODI, ROM (FS and AS), DH (FS and AS), UCLA (US)

No significant differences in the ODI VAS improved after surgery in both groups, the EVO group was lower compared with the TTL group ROM (FS) and DH (FS) were significantly higher in the EVO group as compared to the TTL group. (FS: 4.23° vs. 2.16°; 11.33 mm vs. 10.98) TTL group: 5 cases of UCLA grade I changes and 1 case of UCLA grade II changes occurred EVO group: 1 case of UCLA grade I change in the EVO group

III

Guan et al. (2023) [49]

Retrospective cohort study

45

Hybrid

56.09 ± 5.47

1.Mechanical low back pain, focal radiculopathy, or neurogenic claudication. 2.MRI showing nerve root compression or spinal stenosis in two segments (L3/L5 or L4/S1) with herniated or prolapsed discs (more than half of the spinal canal)

3.lumbar spondylolisthesis (Meyerding I and II)

ODI, VAS, ROM (FS and AS), DH (FS and AS), Modified Pfirrmann grading (AS and FS), LL, ASD (UCLA)

VAS improved after surgery in both groups, and difference between the two groups was not significant ODI scores, the TTL group was better than the Rigid group at 1 year after surgery and at the final follow-up ROM (FS): TTL vs. Ti rods → 3.61° vs. 1.44° ROM (US) increased in both groups, but the TTL group was lower than the Rigid group. (8.51° vs. 9.32°) The modified Pfirrmann classification of AS was significantly increased in both groups at the last follow-up LL: TTL vs. Ti rods → 38.04° vs. 37.57° The UCLA classification, the incidence of ASD was 4.2% in the TTL group and 23.8% in the Rigid group

III

Zhao et al. (2023) [50]

Retrospective cohort study

68

Single-level non-fusion

37.0 ± 19.97

1.Llumbar disc herniation, lumbar spondylotic stenosis, spondylolisthesis, and instability

2.Lumbar degenerative spondylolisthesis Meyerding grade I or II

ROM (FS and AS)

ROM: pre → post FS: TTL 9.76° → 2.60° EVO 9.90° → 5.30°

PITF 9.68° → 0.77°

AS: TTL 10.34° → 12.44° EVO 10.44° → 11.19° PITF 10.35° → 13.94°

III