P8. Correlations between sagittal plane disc dimensions and principal surface strains across the L3-4 intact IVD during in vitro multidirectional loading

BACKGROUND CONTEXT Understanding the biomechanical behavior of the intact intervertebral disc (IVD) is of great importance when studying disc disease. Experimental data describing the relationship between disc size and sub-regional principal strains of the intact lumbar intervertebral disc during multi-directional loading are lacking. PURPOSE The purpose of this study was to investigate possible relationships between lateral view disc dimensions and principal surface strains across different regions of an intact L3-4 disc assessed using digital image correlation (DIC) during multi-directional loading. STUDY DESIGN/SETTING Correlation analysis of dimensional data obtained from lateral X-rays of intact L3-4 lumbar discs at rest and principal surface strains of the same discs obtained from digital image correlation analysis during in vitro loading. PATIENT SAMPLE There were 14 cadaveric spine segments including 6F/8M, mean(±SD) age: 45±13years; BMD: 0.916±0.120 g/cm2. OUTCOME MEASURES Correlation coefficients (and p-values) between disc dimensions (sagittal view disc height and area) and principal surface strains during multi-directional loading, in sub-regions of intact L3-4 IVD. METHODS The mean height and depth of the L3-4 IVD of 14 seemingly healthy human spine segments at rest were determined using lateral view X-rays and ImageJ. The IVDs were part of L3-S1 spine segments that were tested using non-destructive loading (7.5 Nm) in flexion (FL), extension (EX), right lateral bending (RLB) right/left axial rotation (RAR/LAR), followed by compression (Comp, 400 N). Mean principal strains (Pmax and Pmin) in four similarly sized quarters of the L3-4 IVD were assessed using 3D DIC (Vic-3D) during loading with cameras positioned directly lateral on the specimen's left side. Relationships between sagittal view disc dimensions at rest and mean principal strains per lateral view disc quarter [Q1(ant)-Q4(post)] during loading were studied using Pearson Correlation analysis (SigmaPlot v14 with p RESULTS Disc height correlated significantly and positively with Pmax (tensile/stretching strain) mid-anteriorly (Q2) during Comp (R=0.545, p=0.044). There were no other significant correlations between disc height and principal strains in any other region of the disc during any direction of loading (p>0.05). In the mid-posterior disc region (Q3), Pmax correlated significantly and negatively with sagittal plane disc area during FL (R=-0.538, p=0.047) and RLB (R=-0.592, p=0.033, Fig.), showing that a larger disc (taller and deeper) bulges/stretches less during flexion and right lateral bending than a smaller disc (narrow disc height combined with shorter vertebral depth, anterior-posteriorly), mid-posteriorly. Pmin (compressive strain) correlated significantly and positively with sagittal plane disc area in the mid-posterior disc region during Comp (Q3: R=0.650, p=0.012; and Q4: R=0.619, p=0.018), indicating that a larger disc (taller and deeper) shrinks less vertically than a small disc posteriorly during compression. CONCLUSIONS Significant relationships were found between disc dimensions and mean principal strains in sagittal view sub-regions of the L3-4 intervertebral disc, during different directions of loading. These relationships aid in understanding intact disc biomechanical behavior during loading and will help improve the quality of finite element models of lumbar spine segments. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.