MDCT-Based Finite Element Analyses: Are Measurements at the Lumbar Spine Associated with the Biomechanical Strength of Functional Spinal Units of Incidental Osteoporotic Fractures along the Thoracolumbar Spine?

Abstract

Assessment of osteoporosis-associated fracture risk during clinical routine is based on the evaluation of clinical risk factors and T-scores, as derived from measurements of areal bone mineral density (aBMD). However, these parameters are limited in their ability to identify patients at high fracture risk. Finite element models (FEMs) have shown to improve bone strength prediction beyond aBMD. This study aims to investigate whether FEM measurements at the lumbar spine can predict the biomechanical strength of functional spinal units (FSUs) with incidental osteoporotic vertebral fractures (VFs) along the thoracolumbar spine. Multi-detector computed tomography (MDCT) data of 11 patients (5 females and 6 males, median age: 67 years) who underwent MDCT twice (median interval between baseline and follow-up MDCT: 18 months) and sustained an incidental osteoporotic VF between baseline and follow-up scanning were used. Based on baseline MDCT data, two FSUs consisting of vertebral bodies and intervertebral discs (IVDs) were modeled: one standardly capturing L1-IVD–L2-IVD–L3 (FSU_L1–L3) and one modeling the incidentally fractured vertebral body at the center of the FSU (FSU_F). Furthermore, volumetric BMD (vBMD) derived from MDCT, FEM-based displacement, and FEM-based load of the single vertebrae L1 to L3 were determined. Statistically significant correlations (adjusted for a BMD ratio of fracture/L1–L3 segments) were revealed between the FSU_F and mean load of L1 to L3 (r = 0.814, p = 0.004) and the mean vBMD of L1 to L3 (r = 0.745, p = 0.013), whereas there was no statistically significant association between the FSU_F and FSU_L1–L3 or between FSU_F and the mean displacement of L1 to L3 (p > 0.05). In conclusion, FEM measurements of single vertebrae at the lumbar spine may be able to predict the biomechanical strength of incidentally fractured vertebral segments along the thoracolumbar spine, while FSUs seem to predict only segment-specific fracture risk.

Editorial on Special Issue “Spine Imaging: Novel Image Acquisition Techniques and Analysis Tools”

“…Other articles in this Special Issue have set a focus on the opportunistic use of MDCT data for osteoporosis diagnostics or prediction of incidental osteoporotic VFs (i.e., use of existing imaging data originally acquired for other purposes than osteoporosis screening, such as oncologic staging in cancer patients) [ 19 , 20 , 21 ]. In detail, Burian et al studied the contribution of bone mineral density (BMD) at different vertebral levels, subcutaneous adipose tissue (SAT), and visceral adipose tissue (VAT) regarding the identification of VFs using baseline and follow-up image data from a 64-row MDCT scanner in patients (osteoporotic incidental VFs) and controls (no VFs) [ 20 ].…”

“…The combination of normalized failure load, normalized failure displacement, and normalized BMD increased the AUC up to 0.77 [ 19 ]. Another study evaluated whether lumbar FEA can predict the biomechanical strength of functional spinal units (FSUs), which are given by at least two adjacent vertebrae with the intervertebral disc (IVD) [ 21 ]. Specifically, images acquired with a 64-row MDCT scanner among patients who sustained an incidental osteoporotic VF between baseline and follow-up exams were used to model two FSUs (L1–IVD–L2–IVD–L3 = FSU_L1–L3 and fractured vertebral body at the center of the FSU = FSU_F), followed by extraction of the BMD, the FEA-based displacement, and the FEA-based load [ 21 ].…”

“…Another study evaluated whether lumbar FEA can predict the biomechanical strength of functional spinal units (FSUs), which are given by at least two adjacent vertebrae with the intervertebral disc (IVD) [ 21 ]. Specifically, images acquired with a 64-row MDCT scanner among patients who sustained an incidental osteoporotic VF between baseline and follow-up exams were used to model two FSUs (L1–IVD–L2–IVD–L3 = FSU_L1–L3 and fractured vertebral body at the center of the FSU = FSU_F), followed by extraction of the BMD, the FEA-based displacement, and the FEA-based load [ 21 ]. The study revealed statistically significant correlations between the FSU_F and mean load of L1 to L3 (r = 0.814) and mean BMD of L1 to L3 (r = 0.745), adjusting for a BMD ratio of fracture/L1–L3 segments [ 21 ].…”

“…Specifically, images acquired with a 64-row MDCT scanner among patients who sustained an incidental osteoporotic VF between baseline and follow-up exams were used to model two FSUs (L1–IVD–L2–IVD–L3 = FSU_L1–L3 and fractured vertebral body at the center of the FSU = FSU_F), followed by extraction of the BMD, the FEA-based displacement, and the FEA-based load [ 21 ]. The study revealed statistically significant correlations between the FSU_F and mean load of L1 to L3 (r = 0.814) and mean BMD of L1 to L3 (r = 0.745), adjusting for a BMD ratio of fracture/L1–L3 segments [ 21 ]. However, there were no statistically significant associations between the FSU_F and FSU_L1–L3 or between the FSU_F and the mean displacement of L1–L3 [ 21 ].…”

“…The study revealed statistically significant correlations between the FSU_F and mean load of L1 to L3 (r = 0.814) and mean BMD of L1 to L3 (r = 0.745), adjusting for a BMD ratio of fracture/L1–L3 segments [ 21 ]. However, there were no statistically significant associations between the FSU_F and FSU_L1–L3 or between the FSU_F and the mean displacement of L1–L3 [ 21 ]. Taken together, the opportunistic use of spine MDCT data may have distinct value for fracture prediction, with FEA of single lumbar vertebrae having predictive capabilities regarding biomechanical strength assessments for incidentally fractured vertebral segments along the thoraco-lumbar spine.…”