Image-Based Markers Predict Dynamic Instability in Lumbar Degenerative Spondylolisthesis

Neurospine Neurospine 2020;17(1):221-227. https://doi.org/10.14245/ns.1938440.220 Original Article Corresponding Author Alejandro A. Espinoza Orias https://orcid.org/0000-0002-3792-515X Department of Orthopedic Surgery, Rush University Medical Center, 1611 W Harrison Street, Orthopedic Building – Suite 201, Chicago, IL 60612, USA E-mail: Received: December 13, 2019 Revised: February 27, 2020 Accepted: February 28, 2020 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Copyright © 2020 by the Korean Spinal Neurosurgery Society pISSN 2586-6583 eISSN 2586-6591 Image-Based Markers Predict Dynamic Instability in Lumbar Degenerative Spondylolisthesis William Slikker III1,2,3, Alejandro A. Espinoza Orías1,2, Grant D. Shifflett1,2,4, Joe Y.B. Lee1,2,5 Krzysztof Siemionow1,2,6, Sapan Gandhi1,2, Louis Fogg7, Dino Samartzis1,2, Nozomu Inoue1,2, Howard S. An1,2 Department of Orthopedic Surgery, Rush University Medical Center, Chicago, IL, USA International Spine Research and Innovation Initiative, Rush University Medical Center, Chicago, IL, USA 3 Private Practice, San Leandro, CA, USA 4 DISC Sports & Spine Center, Newport Beach, CA, USA 5 Private Practice, Arcadia, CA, USA 6 Department of Orthopedic Surgery, University of Illinois at Chicago, Chicago, IL, USA 7 College of Nursing, Rush University Medical Center, Chicago, IL, USA 1 2 Objective: To identify possible radiographic predictors markers of dynamic instability including disc height (DH), disc degeneration, and spondylosis in the setting of degenerative spondylolisthesis (DS). Methods: A retrospective review with prospectively collected data was performed on 125 patients with L4–5 DS who underwent decompression and fusion. Patients were divided into groups with dynamic instability and those without. Radiographs of the lumbar spine in neutral, flexion, and extension were used to determine degree of slip, DH, translational motion, angular motion, spondylotic changes, and lumbar lordosis. Magnetic resonance imaging (MRI) scans were reviewed to assess disc degeneration. Results: Thirty-one percent of the patients met criteria for dynamic instability. Significant correlations (p < 0.05) were found between preserved DH and dynamic instability; increased spondylotic changes and decreased translational motion; as well as advanced MRI-based disc degeneration scores with decreased angular motion, respectively. Six radiographic parameters were utilized to create a predictive model for dynamic instability, and a receiver operating characteristic curve was able to validate the predictive model (area = 0.891, standard error = 0.034, p < 0.001). Conclusion: In DS patients, preserved DH was significantly related to dynamic instability. This finding may represent a greater potential for slip progression over time in these patients. In contrast, disc degeneration on MRI, and spondylotic changes were inversely related to dynamic instability and may represent restabilization mechanisms that decrease the chance of future slip progression in DS. Keywords: Degenerative spondylolisthesis, Dynamic instability, Intervertebral disc height, Spondylosis INTRODUCTION following degenerative spondylolisthesis have shown that a subsect of untreated patients experience clinical deterioration, even without radiographic slip progression.2 However, the relationship between clinical deterioration, as well as radiographic parameters remain unknown. Strong evidence supports the role of surgical intervention in Although degenerative spondylolisthesis remains one of the most common lumbar pathologies encountered in a clinical spine practice, a complete understanding of its natural history and treatment remains controversial.1 Natural history studies  www.e-neurospine.org 221 Slikker III W, et al. the setting of degenerative spondylolisthesis patients, with longterm studies showing favorable results over nonsurgical management.3 However, the optimal surgical solution remains controversial, particularly regarding the decision of whether or not to perform lumbar arthrodesis in the setting of degenerative spondylolisthesis.1 Authors have found differing clinical outcomes regarding the role of lumbar fusion in the setting of degenerative spondylolisthesis, with some finding favorable results with arthrodesis and others finding no advantage compared to decompression alone.4-6 From these differing results, it is clear that a more complete understanding of degenerative spondylolisthesis is required to assess its natural progression. Dynamic instability is the finding of abnormal motion at a spinal level, defined in the literature as greater than 3 mm of translation or greater than 10° of motion between adjacent vertebral endplates.7-9 From a clinical standpoint, patients with these findings in the setting of degenerative spondylolisthesis may expect to have chronic symptoms of low back and/or leg pain (i.e., greater than 4 years).9 Additionally, when deciding on treatment, patients with dynamic instability in the setting of degenerative spondylolisthesis who undergo decompression alone may be at risk of developing postoperative radiographic instability.10 These patients may benefit additionally from lumbar fusion, rather than decompression alone. Although the role of dynamic instability in the pathogenesis of degenerative spondylolisthesis remains unclear, identifying patients who have dynamic instability, or may be at risk of developing it, may be vital in selecting the optimal treatment for the patient. Kirkaldy-Willis and Farfan11 suggested that the pathomechanics of lumbar spine degeneration occurs in 3 progressive phases. In the early dysfunction stage, biochemical changes occur and microscopic damage accumulates in the intervertebral disc, along with synovitis of the facet cartilage, which likely occurs prior to the development of spondylolisthesis and/or dynamic instability. As degeneration progresses, there is decreased intervertebral disc height and subluxation of the facet joints leading to increased instability between adjacent vertebral bodies. In the final stage, spondylosis occurs from formation of apophyseal disc osteophytes and the facet joints undergo hypertrophic arthropathy. Their model suggests that dynamic instability and subsequent restabilization of the degenerative lumbar segment occur in separate phases and may linked intimately to disc height as well as disc degeneration. Several studies have linked both disc height and degree of disc degeneration to degree of spondylolisthesis.12,13 Given the potential significance of dynamic instability in the 222 www.e-neurospine.org Dynamic Instability Degenerative Spondylolisthesis pathogenesis of degenerative spondylolisthesis, as wel (...truncated)