Laminar Thickness: Correlation Against Symptoms of Spinal Stenosis and Changes with Age Hamed Shalikar, MD 1, Sean L. Borkowski, MS 2, Juan Pablo Villablanca, MD 1, Sophia N. Sangiorgio, PhD 2, Edward Ebramzadeh, PhD 2, Arya N. Shamie, MD 1. 1 UCLA, Los Angeles, CA, USA, 2 Orthopaedic Institute for Children/UCLA, Los Angeles, CA, USA. Disclosures: H. Shalikar: None. S.L. Borkowski: None. J. Villablanca: None. S.N. Sangiorgio: 5; Zimmer, DePuy, TriMed, Extremity Medical, Biomet, NuVasive. E. Ebramzadeh: 5; Zimmer, DePuy, TriMed, Extremity Medical, Biomet, NuVasive. A.N. Shamie: 1; Seaspine. 3B; Biomet. 4; SI Bone, Vertiflex. Introduction: Spinal stenosis is a significant cause of low back pain and a leading reason for orthopaedic visits and subsequent surgery [1]. Despite its large burden on medical care costs, the pathogenesis of spinal stenosis is not fully understood. Spinal lamina may become thicker due to Wolff s law [2], that is, stress over a patient s lifespan, potentially contributing to narrowing of the spinal canal, resulting in spinal stenosis; however, this hypothesis has not been tested previously. The purposes of this study were to measure the laminar thickness in a retrospective cohort of stenosis and non-stenosis patients, to evaluate the effects of laminar thickness on canal size, and to correlate laminar thickness measures to patient gender and age. Methods: Following IRB approval, we retrospectively analyzed lumbar spine computed tomography (CT) scans from a blinded database of patients in a large academic hospital setting, acquired over a one year period (3/1/12-3/1/13), regardless of the indication. Patients with previous lumbar vertebral surgery, vertebral metastasis, and/or severe scoliosis were excluded. Additionally, patients younger than 18 years old or older than 80 years old were excluded. Patients with pain/fatigue and either an aggravating factor or alleviating factor, were included in the spinal stenosis group. Based on these criteria, two groups were defined: stenosis (n=18) and non-stenosis patients (n=133). Patients had a mean age of 53 years old (18-80 years). All CT scans were reviewed to ensure standardized, reliable and repeatable measurements from each patient. The procedure included the helical acquisition of 3mm thick sections in the axial plane, with coronal and sagittal reformations. The field of view was 170mm, with a matrix size of 512 x 512, bone window (40Hs) kernels. Soft tissue kernels (B30, medium smooth) and bone window kernels (B60, sharp) were used. Using Vitrea software in the Vitals Workstation (Vital Images, Inc., Minnetonka, Mn), a 3D reconstruction of a given patient s spine was created using CT source data. Following 3D reconstruction, a custom axial oblique slice of the spine was obtained which passed through the axial plane of the intervertebral disc of interest, and was parallel to the vertebral endplates. This process was repeated separately for both the L4-L5 and the L5-S1 levels of each patient. Then, the laminae were measured in six locations: left and right spinous process-lamina junction, left and right juxta-cortical lamina, and left and right mid-lamina. Statistical analyses were performed using SPSS 19.0 statistical software (IBM, Armonk, NY). The input variables were presence of spinal stenosis symptoms, gender, age, and measurement location. The primary output variable was laminar thickness. For each level, that is L4-L5 and L5-S1, three separate multivariate general linear models were created to evaluate the effects of stenosis symptoms, gender, and age, on laminar thickness at each of the measurement locations: (1) the left+right spinous processlamina junction; (2) the left+right juxta-cortical lamina; and (3) the left+right mid-lamina. Paired samples
t-tests were performed to compare the laminar thicknesses between the left and right lamina at each of the three measurement locations. The Pearson correlation coefficient was calculated to quantify the correlations between laminar thickness and patient age. Finally, separate Pearson correlation analyses were performed to evaluate the repeatability and reliability of the CT laminar thickness measurements. Results: Among the 151 measured patients, the largest laminar thicknesses were found at the juxtacortical lamina locations. In general, laminar thickness at different locations was larger in the patients with stenosis (n=18) compared with the patients without stenosis (n=133), though not all locations were statistically significant. Specifically, mean laminar thickness ranged from 8.5-17.4mm in stenosis patients, compared to only 7.7-14.9mm in non-stenosis patients. The results varied by lamina thickness measurement location, with significantly larger thicknesses found in the left juxta-cortical lamina, and the left and right spinous process-lamina junction of L4-L5 (Figure 1 and 2). At the L5-S1 level, significantly larger thicknesses were found at the right and left juxta-cortical lamina locations (Figure 3).There were positive correlations between age and laminar thickness in all measurement locations at both the L4-L5 and L5-S1 levels. With the exception of the left spinous process-lamina junction of L4-L5 (p=0.095), all locations demonstrated significant positive correlations, with Pearson correlation coefficients ranging from 0.137 to 0.452 (p<0.01). There were no significant differences between male and female patients. The intraobserver and interobserver measurements were significantly correlated at all measurement locations, with Pearson correlation coefficients ranging from 0.638 to 0.954 (p<0.02). Discussion: Laminar thickness was larger in patients with stenosis symptoms compared to those without stenosis symptoms. Furthermore, laminar thickness increased with aging. As such, laminar thickness may be a potential factor in the pathogenesis of lumbar spinal stenosis. By establishing the associations between laminar thickness, a readily available and quantifiable parameter, and clinical factors, including stenosis, age and gender, high risk groups in the population may be identified. Identifying these groups may allow clinicians to improve patient treatment through early conservative interventions, potentially delaying future surgery or preventing it altogether. Significance: Despite the large burdens associated with spinal stenosis, this is the first study to evaluate the potential role of laminar thickness in the pathogenesis of stenosis. The increased thickness reported in the present study suggests its role in this pathogenesis, and will lead to future studies of the factors contributing to spinal stenosis, ultimately improving a clinicians understanding, and in turn, a clinicians ability to treat patients with these conditions.
ORS 2015 Annual Meeting Poster No: 1629