Introduction: Use of supplemental lateral plating and/or integrated lateral screw fixation with lateral lumbar interbody fusion (LLIF) can be effective in diminishing the need for extensive/invasive posterior instrumentation. However, additional lateral fixation often requires wider exposure and prolonged retraction of the psoas. Accordingly, adjunctive lateral fixation achieved via a pure in-line lateral trajectory is clinically advantageous. The goal of this in-vitro biomechanics study was to assess stability of a novel LLIF device possessing zero-profile, intra-discal, integrated fixation deployed within the margins of the disc space (Fig.1).
Methods: Six ligamentous lumbar cadaveric spines (L1-S1) were tested. Specimens were screened radiographically to confirm integrity. The L1 and S1 vertebral bodies were potted for subsequent test apparatus attachment. Each spine was first tested in an intact state, followed by sequential iterative construct instrumentation (L4/5) and testing.
Testing Sequence:
1. Intact
2. LLIF+PS (PS=bilateral pedicle screw fixation)
3. LLIF+IPF (IPF=interspinous process fixation)
4. LLIF+IF+IPF (IF=integrated lateral plate fixation)
5. LLIF+IF+PS
6. LLIF+IF
7. LLIF+IF* (*superior plate removed)
Each specimen was tested in Flexion /Extension (8/6Nm) (‘FE’) without preload (0N), then with a 400N preload, and then in Lateral Bending (±6 Nm) (‘LB’) and Axial Rotation (±5 Nm) (‘AR’) without preload. Loading moments were applied to the specimen via arms fixed to the L1 vertebrae. Segmental range-of-motion (ROM) was tracked using a motion analysis system. Mean ROM reduction (% intact) was calculated. Comparisons between test iteration #2 and #3, 4, 6 were made using a repeated measures ANOVA with Bonferroni correction (p<0.05).
Results: See Figures 2 and 3.
Conclusions: The LLIF+IF+IPF construct supported robust ROM reduction in all principle motions, performing well in comparison to traditional LLIF+PS. Given the minimally disruptive nature of IPF posteriorly, coupled with the zero-profile footprint of the integrated lateral device, the LLIF+IF+ISPF technique presents as a synergistic circumferential construct.
Patient Care: The ability to reduce the duration and extent of retraction during LLIF is critical in decreasing risk of lumbar plexus injury. The device studied herein allows for secondary lateral stability while keeping retraction at the disc margins. In considering this minimally invasive characteristic, the added stability provided by the integrated fixation may be clinically advantageous over traditional LLIF cage only and lateral plate constructs with respect to patient safety.
Learning Objectives: Following this session, participants should be able to:
1. Discuss whether the zero-profile, integrated lateral device supports added supplemental stability in comparison to traditional LLIF techniques
2. Discuss what clinical benefits may be associated with a zero-profile, integrated lateral device
3. Discuss potential patient demographics for which the novel LLIF+IF+ISPF technique may be suitable for