ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

a moderate kyphotic curvature (50°), the increase in compression was approximately
10%, compared to the normal curvature. The compression forces in the lumbar spine
were similar for all three different kyphotic curvatures; the load had even a slightly
opposite trend to that predicted in the literature. The predicted shear forces in the
lumbar spine were almost the same for all kyphotic curvatures. In the upper thoracic
spine, the shear forces increased with the degree of kyphosis. In the lower thoracic
spine, the opposite was observed; the normal curvature produced the highest, and the
most severe curvature the lowest shear force (Fig. 3). For the investigation of the
influence of sarcopenia on spinal loading, the predicted compression force increased in
the lower lumbar spine with stronger erector spinae muscles. In the thoracic spine, the
compression forces were similar for the different muscle strengths. The compression
maximum was at the intervertebral disc between T12 and L1. The predicted shear forces
in the thoracic spine were again similar for all muscle strengths. However, strong
erector spinae muscles induced higher shear forces in the lower lumbar spine. For the
weakest muscles (ES-Factor 0.1), the shear forces between L3 and T10 acted in the
opposite direction than for the other muscle strengths. This effect was most pronounced
for the 70° kyphosis (Fig. 4).
Fig. 3. Comparison of the compression and shear forces of different kyphosis angles. For the erector spinae scaling
factors 0.1 and 0.84.
Fig. 4. Comparison of the compression and shear forces for different degrees of sarcopenia for both the 30° and 70°
thoracic curvature.
5. DISCUSSION
The first goal of this study was to evaluate the influence of kyphosis on local spinal
segment loading. Our model demonstrated an increase of the compression forces