Lightning Podiums: Smorgasboard - Room 802B

Presented by: I. Bussey


M. Shasti(1), A. Nash(1), I. Bussey(1), S. Koenig(1), N. O'Hara(1), T. Weir(1), D. Gelb(1), S. Ludwig(1)

(1) University of Maryland, Orthopedics, Baltimore, MD, United States


Background: Adjacent segment disease (ASD) is a well-known complication after lumbar fusion. Lateral interbody fusion (LIF) provides a potential way to treat ASD while avoiding associated complications with revision surgery through posterior stabilization (PS). Biomechanical stability of LIF for treating ASD has not been evaluated. This study evaluates the stability of anterior column reconstruction through the less invasive lateral approach technique as well as the additional comparative stabilizing effects of various internal fixation options.

Methods: Eighteen fresh-frozen cadaveric specimens were dissected from L1-Sacrum. Radiographs and DEXA scans were used confirm the absence of deformity, excessive degeneration, or osteoporosis. Specimens were mounted in polymethylmethacrylate (PMMA) and tested quasi-statically in flexion, extension, and lateral bending using pure moment testing protocol. 7.5 Nm was applied in each motion plane for 3 cycles, with the final cycle used in data analysis. The motion segment kinematics at adjacent segments were evaluated using a 3D motion capture camera system. After testing the intact spine, the specimens were divided into three posterior instrumentation groups to replicate a prior fusion at L5-S1 (Group 1), L4-S1 (Group 2), and L3-S1 (Group 3). The specimens within each of the three groups then underwent interbody placement at the level adjacent to the most cephalad fusion level: L4-5, L3-4, and L2-3. After interbody placement, biomechanical testing was conducted on all specimens with varying forms of augmentation: (a) stand-alone LIF; (b) LIF + plate; (c) LIF + single screw-rod (SSR) anterior instrumentation; (d) LIF + PI. The means and standard deviations for the range of motion (ROM) at the adjacent segment level were calculated for each test condition and loading direction. Stability is expressed as the reduction in percentage of ROM as compared to the intact spine. Pair-wise comparisons and Multivariate Analysis of Variance (MANOVA) were utilized to compare stability of the construct.

Results: ROM as a percentage of the intact was consistently similar between LIF + plate and LIF + PSF in all groups (table 1). LIF + plate augmentation provides equivalent stability as compared to LIF + PS during lateral bending. During flexion and extension, LIF + PSF provides superior stability as compared to all other constructs.

Conclusion: The results of this study demonstrate the stability of minimally invasive lateral lumbar interbody fusion supplemented with either lateral plate or lateral screw-rod construct and traditional posterior instrumentation may be comparable. Further studies are indicated to determine if LIF may reduce the morbidity associated with using a posterior approach for the treatment of adjacent segment disease after fusion of the lumbar spine.

Table 1. Average ROM as % of Intact Spine