Abstract
Understanding the biomechanical behavior of the intact intervertebral disc just rostral to the most commonly fused level in the lumbar spine (L4-5) is of great importance when studying disc disease. Experimental data describing detailed sub-regional biomechanical behavior of the intact lumbar IVD during multi-directional mechanical loading are lacking.
The purpose of this study was to quantify principal strains on the surface of different regions of an intact L3-4 IVD during multi-directional loading using 3D DIC.
Lateral view surface strains of the L3-4 intact IVD during multi-directional loading was assessed using 3D DIC technology with sub-regional post-processing capabilities.
There were 14 healthy human L3-S1 spine segments [6F/8M, mean(±SD) age: 45±13years; BMD: 0.916±0.120 g/cm2].
Mean principal strains (Pmax and Pmin) were determined and compared across the surface of 4 similarly sized quarters of the L3-4 IVD during multiple directions of loading.
Fourteen healthy human L3-S1 spine segments 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 (400 N). A 3D DIC system with sub-regional post-processing analysis capabilities (Vic-3D) was utilized to assess principal strains (Pmax and Pmin) across the disc surface, with cameras positioned laterally (left side). The L3-4 IVD including upper and lower endplates was divided into four similar sized quarters, and mean principal strains from rest to peak load in each quarter were determined for each case. Analysis of variance of mean principal strains within each quarter was performed with statistical significance set at p<0.05.
There were statistically significant differences in mean principal strains between disc quarters (Pmax all directions of loading: p<0.035; Pmin all directions of loading: p<0.003 [except RLB, p=0.525]). The quarter with the largest Pmax strain (tensile) was dependent on direction of loading, with the greatest magnitude overall occurring posteriorly (Q4) during RLB (Pmax of 108023±49815uE, followed by LAR (Pmax of 51707±32952 uE in Q1, anteriorly), and FL (Pmax of 42222±22862 uE in Q1). Pmax decreased in magnitude from posterior (Q4) to anterior (Q1) during RLB, and was significantly smaller towards the center (Q2 and Q3) compared to anterior (Q1, p<0.006) and posterior (Q4, p=0.020) during FL. Pmax during LAR was greater anteriorly (Q1) with significance compared to Q2 (p=0.043), but without significance compared to remaining quartiles (p>0.09). Pmax during RAR was greater anteriorly (Q1), but only with significance compared to Q3 (p=0.004). The quarter with the largest Pmin strain was dependent on the direction of loading, with the greatest magnitude occurring mid-anteriorly (Q2) during FL (-47984±19477uE), followed by LAR (Q2:-34547±15393uE), RAR (Q1:-38843±16894uE) and RLB (Q2:-25236±16166uE). The largest magnitude Pmin during compression and EX was seen posteriorly (Q4:-26096±14538uE and -18263±8828uE, respectively). There were significant differences in mean principal strain direction among quarters during all directions of loading (p<0.045), except during RAR (p=0.243). As seen from the left side, LAR resulted in the most vertically oriented Pmax direction (Q2 and Q3, Fig. 2), while compression (Q2 and Q3) and FL (Q1 and Q2) resulted in the most horizontally oriented Pmax directions.
Sub-regional analysis of principal strains across the intact L3-4 disc assessed using 3D DIC technology showed that different directions of load result in measurably and significantly different strain distribution patterns across the anterior-posterior disc gradient.
This abstract does not discuss or include any applicable devices or drugs.