Poster Presentation 51st International Society for the Study of the Lumbar Spine Annual Meeting 2025

Development of a reproducible in vivo model of ligamentum flavum hypertrophy through induced spinal instability (#191)

Rahul Ramanathan 1 , Christopher Como 1 , Sean Nguyen 1 , Yunting Tang 1 , Anthony Oyekan 1 , Nam Vo 1 , Joon Lee 1 , Gwendolyn Sowa 1 , Peter Alexander 1
  1. University of Pittsburgh, Pittsburgh Township, PA, United States

 

INTRODUCTION 

Lower back pain continues to contribute to poor quality of life and rising annual healthcare costs in the US1. Lumbar spinal stenosis (LSS) is linked to back pain/disability and has received attention in both surgical and nonsurgical spine care2. The ligamentum flavum (LF) is a ligament anterior to the lamina juxtaposing the spinal canal. Hypertrophy of this ligament (LFH) has been the subject of many investigations recently due to its contribution to canal stenosis3. Complex mechanisms have been identified in the pathogenesis of LFH, including inflammation, fibrosis, and biomechanical instability4. Multiple groups have attempted to develop an in vivo animal model of LFH5. These models are limited by incomplete induction of instability, aggressive soft tissue dissection, and/or use of advanced equipment and extensive training for reproducibility. We aim to establish an in vivo rat model of LFH induced by spinal instability that spares the surrounding musculature using basic surgical instruments and skills for reproducibility.  This rat model is intended to replicate the complexities of LFH and allow small animal therapeutic testing and behavioral analysis of pain during the development of LFH.  

METHODS 

16 adult male Fischer 344 6-month-old rats were randomly divided into two groups – instability (n=8) and sham (n=8). All rats underwent surgery approved under IACUC protocol #20087679 according to their respective groups. For the instability group, bilateral pars defects were created at the L4-L5 level with resection of inferior articular processes. In the sham group, paraspinal muscles were retracted away from midline to expose lamina and facet joints at L4-L5, but no bony structures were resected. Behavioral analysis involved open-field behavior and analysis of grooming, rearing and distance traveled as previously described8 at 2, 4, 6, and 8 wks. Rats were sacrificed 12 weeks post-surgery and spines dissected and fixed in paraformaldehyde for imaging (MRI, microCT).  

RESULTS 

Behavioral analysis revealed that rats in the instability group demonstrated on average 17.2 (SEM +/- 2.4) seconds less in a rearing position and groomed on average 44.05 (SEM +/- 7.46) seconds more compared to the sham group (p>.05, n=8 instability, n=8 sham) during a 10-minute testing interval. Two instability specimens were analyzed with MRI, comparing canal dimensions at nonsurgical (Figure 1) and surgical (Figure 2) levels. Both instability specimens demonstrated successful pars defects at the surgical level. Only two instability specimen MRIs were available for current analysis. T2-weighted MRI at 46 cubic micron voxel resolution demonstrated central stenosis with average (n=2) cross-sectional area of 2.04mm2 at the surgical level, and 5.99mm2 at the nonsurgical control level.  

DISCUSSION 

Current in vivo small animal models for studying the pathogenesis of LFH suffer from compromised soft tissue from aggressive surgical technique and incomplete induction of instability.  Preliminary results of our LFH model herein demonstrate surgical induction of spinal stenosis identifiable by MRI and are accompanied by behavioral changes. Further analysis will compare ligamentum flavum thickness at surgical and nonsurgical levels through histological examination, potentially establishing a reliable and efficient model for evaluating therapies to mitigate spinal stenosis caused by LFH. 

 

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