e-Poster Presentation Sydney Spinal Virtual Symposium 2020

Bone Remodelling Signal Changes in the Endplates Following Lumbar Discectomy: A Finite Element Modelling Study (#13)

Alessandro G. Larosa 1 , Vivek A.S. Ramakrishna 2 3 , Uphar Chamoli 1 3
  1. School of Biomedical Engineering, Faculty of Engineering and Information Technology, University of Technology Sydney, Ultimo, New South Wales, Australia
  2. School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Kensington , New South Wales, Australia
  3. Spine Labs, St. George & Sutherland Clinical School, University of New South Wales, Sydney, Kogarah, New South Wales, Australia

Morphological changes in the intervertebral disc following discectomy may elicit bony endplate remodelling following Wolff’s law, due to the alterations in natural stress transmission patterns. Previously published computational modelling research lacks necessary detail in endplate geometry required to examine bony endplate remodelling following discectomy.

This study aimed to compare the effect of aggressive and conservative surgical approaches for lumbar discectomy on the bone remodelling (BRM) of superior and inferior bony endplates at the index level using finite element (FE) analysis.

A three-dimensional ligamentous, non-linear FE model of the lumbosacral spine (L1-S1) was assembled using computed tomography (CT) scans. Three models were developed representing intact, conservative, and aggressive discectomy at the L4-L5 intervertebral disc. Models were pre-loaded with 1200N compression along the follower load path and simulated in flexion and extension with 10Nm moments. The BRM algorithm (shown below) was based on strain energy density (SED) comparison between the intact and discectomy models. The thresholds for formation and resorption signals were 0.75 and -0.75, respectively.

BRM Signal = (SEDDiscectomy - SEDIntact)/SEDIntact 

Larger volumes of BRM were observed in the aggressive (Agg) discectomy model compared to conservative (Cons). (Cons [fx = 1.67%, ex = 0.45%],  Agg [fx = 3.01%, ex = 1.41%]).  Bony endplate regions adjacent to discectomy (directly above and below) experienced bone resorption (Average BRM signal; Cons [fx = -0.41, ex = -0.15], Agg [fx = -0.39, ex = -0.15]) and changes in the residual regions were insignificant. Notably, L4 caudal bony endplates experienced larger volumes of bone formation and resorption (Cons [fx = 2.67%, ex = 0.72%], Agg [fx = 5.08%, ex = 1.50%]) compared to L5 cephalad bony endplates (Cons [flex = 0.68%, ext = 0.18%], Agg [fx = 0.94%, ex = 1.32%]).

The reported differences in BRM between aggressive and conservative discectomies warrant clinical validation and investigation of endplate pathology mechanisms in addition to a comparison of superior and inferior endplate morphology at the index level.