Table 4 Biomechanical studies

A.E. Castellvi et al. (2005) [51]

Finite element

Finite element

N/A

Ti rods, TTL (L5–S1 was fused, and L4–5 segment was fixed with instrumentation)

Adjacent disc stresses

A 1% to 2% reduction in peak compressive stresses in the L3–4 (at 45° flexion), and the increased axial motion component of TTL reduced peak disc stress by 8% to 9%. Areas of disc tissue exposed to 80% of peak stresses of 6.17 MPa were 47% less for adjacent discs to TTL than for those adjacent to Ti rods

Cedric Barrey et al. (2010) [52]

Cadaveric lumbar spines

Displacement controlled loading

6

Intact, L4–L5 laminectomy, and L4–L5 instrumented with TTL

ROM

Flexion/extension, axial rotation and lateral bending retain 20%, 40% and 15% of intact ROM, respectively

S.N. Sangiorgio et al. (2011) [53]

Cadaveric lumbar spines

Displacement controlled loading

9

Intact, injured, X-Stop, PercuDyn

DH, ROM

With load, under maximum flexion, the Isobar increased anterior DH by 40%, compared to intact. In the neutral position with a follower load, the Isobar increased posterior DH by 40% ± 19% Comparing injured to treated specimens, the Isobar reduced flexion by a mean of 56% ± 46%. And the Isobar was the only device to reduce axial rotation

Cedric Barrey et al. (2013) [38]

Cadaveric lumbar spines

Displacement controlled loading

13

Ti rods, intact, injured (laminectomy at L4–5, L4–5 laminectomy, and partial facetectomy)

ROM, IDP

ROM decreased significantly following TTL and Ti rods compared to intact spine, with no significant difference between 2 groups, except in extension IDP significantly decreased in extension after TTL versus both intact and injured configurations

Liu et al. (2013) [54]

Finite Element

Finite Element

1

Intact, Ti rods (L4–5, L5–S1 was fused), TTL (L5–S1 was fused, and L4–5 segment was fixed with instrumentation)

ROM, stability, AS IDP, Stress distribution

The ROM of the Isobar TTL was not significantly different from that of intact model in flexion, extension, lateral bending and rotation Adjacent disc stresses increased (L3–4): TTL: flexion, extension, lateral bending, and axial rotation were 6.2%, 9.7%, 3.6%, and 3.8%, respectively. Ti rod: 8.5%, 13.5%, 4.3%, and 4.8%, respectively The stress of TTL distributed at the screw was lower than Ti rods, and the stress concentration of the fusion segment screw is more obvious

Tang et al. (2015) [55]

Cadaveric lumbar spines

Displacement controlled loading

6

Disc normal, Disc normal with Isobar TTL, Discectomy, Discectomy with TTL

FCF

FCF in upright anterior flexion, posterior extension, lateral bending, and rotation were reduced to 4.01%, 0.74%, 3.78%, 3.45%, and 19.7% of the vertical load (400 N), respectively, and the FCF was reduced to 24.99%, 17.23%, 17.0%, 18.40%, and 35.99% of normal, respectively

Lu et al. (2016) [56]

Finite Element

Finite Element

N/A

Intact, Ti rods (L4-S1)

AS angular displacement, IDP

L3–L4 angular displacement of flexion, extension, left bending, right bending, left axial rotation, and right axial rotation were 19.2%, 15.1%, 11.1%, 12.2%, 18.4%, and 22.1%, respectively, lower than Ti rods; were 11.8%, 15.7%, 6.4%, 6.5%, 11.1%, and 10.9%, respectively, higher than intact IDP:

Alexander Yu et al. (2016) [57]

Cadaveric lumbar spines

Displacement controlled loading

6

Intact, Ti rods

ROM, AL, IDP

ROM: no statistical difference in ROM between Isobar and Ti rods in any mode of loading. AL: Under axial compression, Isobar showed increased AL when compared to the Ti rods. IDP: A statistically significant increase in IDP in flexion extension movement with the Isobar compared to Ti rod, and no significance detected during lateral bending, axial torsion and axial compression

Chen et al. (2022) [58]

Finite Element

Finite Element

N/A

Dynesys, 1-level and 2-level static fixator models

ROM, IDP, FCF, stress distribution along screw–vertebral interfaces

Both the Dynesys and Isobar had better performance than the 2-level static fixator in balancing junctional problems The ROMs at L3–L4 in the Dynesys group were 15% higher in flexion, 49% higher in extension, 10% higher in lateral bending, and 8% higher in axial rotation, respectively, than those implanted with Isobar The ROMs and IDP at L2–L3 of the Isobar ranged from 2% (rotation) to 24% (extension) higher and from 2% (lateral bending) to 9% (flexion) higher, respectively, than those of the Dynesys The Isobar afforded the decreased FCF, ranging from 15% (bending) to 41% (rotation), more than the Dynesys did Stresses on rod and near bone–screw interface are lower than that of the Dynesys group