Changes in Adjacent Segment Biomechanics After Laminectomy and Laminotomy in Lumbar Spine 1Elmasry, S; 1Asfour, S; 2Gjolaj, J; 3Latta, L; 2Eismont, F; +1Travascio, F 1Biomech. Research Lab, Dept. Industrial Engr., Univ. Miami, Coral Gables, FL 2Dept. of Orthop., Univ. Miami, Miami, FL 3Max Biedermann Instit. Biomech., Mount Sinai Med. Center, Miami Beach, FL INTRODUCTION: Lumbar spinal stenosis (LSS), a disease of epidemic proportions in the Nation [1], is characterized by the constriction of the spinal canal at one or multiple spine levels This disease is often treated surgically by decompressing the spinal nerve. However, longitudinal studies reported the occurrence of degeneration in spinal segments adjacent to those operated [2, 3] We hypothesize that surgical procedures for LSS, by altering the anatomy of the spine, elicit changes in adjacent segment biomechanics which may contribute to adjacent segment disease (ASD) Laminectomy & laminotomy are decompressive surgeries for LSS typically performed when there are no indications of pre-operative spinal instability [4]. However, little is known about their implications on the adjacent segments [5, 6]. The objective of this study was to investigate biomechanical changes in adjacent segment due to these procedures. Results: It was found that laminectomy procedures caused the largest changes in the rotational range of motion of the adjacent segment: more than 100% during flexion with respect to the ‘intact spine’ case (Figure 1) Laminectomy procedures were also characterized by the largest increases in intradiscal pressure: more than 100% in NP and more than 50% in AF when compared to the ‘intact spine’ case (Figure 2) After unilateral and bilateral laminotomy, changes in adjacent segment kinematics and intradiscal pressure were less than 20% and less than 2%, respectively Discussion: Post-operative increase in spine range of motion is indicative of spine instability, which may be detrimental for the adjacent segment health [1]. In agreement with clinical studies [9], the computational model predicted changes in spine kinematics after laminectomies that were dramatically larger than those found after laminotomies (Figure 1). laminectomy procedures produced higher ranges of motion due to removing interspinous and supraspinous ligaments. Such ligaments withstand the highest tensile forces during spine flexion [10]. Intradiscal pressure increase may negatively affect intervertebral disc metabolism, potentially leading to disc degeneration [11, 12]. Similar to kinematics results, the model predicts negligible changes in intradiscal pressure after either unilateral or bilateral laminotomy In contrast, after laminectomy procedures, intradiscal pressure increased up to one fold (Figure 2). Similar trends with different magnitudes were found in an in-vitro study on calf spine [6] METHODS: A 3D nonlinear finite elements model of the lumbar spine (from L1 to L5) was reconstructed via CT scan of a healthy male subject (Visible Human Project®). The model was validated by comparing its output with in-vitro study [5] Lumbar vertebrae were schematized as rigid bodies, while intervertebral discs were modeled as inhomogeneous biphasic materials [7]. Cartilage at facet joints and major lumbar spine ligaments were also included into the model Finite element software (FEBio 1.8.0, M-S Research Lab., Univ. Utah) was used to simulate 4 post-operative scenarios: unilateral laminotomy, bilateral laminectomy, facet-sparing laminectomy, and laminectomy with facetectomy For each scenario, the operated segment was L4-L5, and the changes to spine anatomy associated with each surgical procedure were implemented as reported in previous studies [5, 8] In the simulations, a follower load of 400 N, together with a pure flexion-extension bending moment (8 Nm in flexion and 6 Nm in extension) were applied to the spine The analysis focused on post-operative alterations of the biomechanics of the adjacent segment L3-L4 in terms of rotational range of motion in the sagittal plane, and intradiscal pressure SIGNIFICANCE: Laminotomy represents a better approach than laminectomy for reducing potential risks of developing either spine instability or mechanically-accelerated disc degeneration in adjacent segments Figure 1: Post-operative changes in rotational range of motion of the adjacent segment. Data are compared to the ‘intact spine’ case. REFERENCES [1] Arbit & Pannullo (2001) Clin Orthop Relat R 384:818-825. [2] Lee (1988) Spine 13:375-7. [3] Rahm & Hall (2008) J Spinal Disord 9:392-400. [4] Thome et al. (2005) Spine 3:129-41. [5] Lee et al., (2010) Spine 35:1789-1793. [6] Rao et al. (2002) Spine J 2:320-6. [7] Mow et al. (1980) J Biomech Eng 102: 73-84. [8] Zander et al. (2003) Eur Spine J 12:427-434. [9] Fu YS et al., (2008) Spine 31:514-518 [10] Goel et al. (1985) Spine 10:516-523. [11] Stokes & Iatridis (2004) Spine 29:2724-32. [12] Iatridis et al. (2006) JBJS 88:41-6. ACKNOWLEDGEMENTS: Study supported by funds donated to the Biomechanics Research Group of the University of Miami Figure 2: Post-operative changes in intradiscal pressure of the adjacent segment. Data are compared to the ‘intact spine’ case.