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

(a) (b) (c)
Fig. 1. The three representative degrees of kyphosis: (a) 37°, (b) 50° and (c) 70° for the normal, moderate and severe
case. The thoracic vertebral bodies are removed for better visualisation. The red spheres represent the 6 DOF
connection between two neighbouring vertebral bodies.
(a) (b) (c) (d)
Fig. 2. Pelvis, sacrum and vertebral bodies with; (a) erectus spinae muscle, (b) multifidus muscle, (c) semispinalis
muscle and (d) abdominal muscle group
To evaluate the influence of kyphosis on spinal loading, the compression and shear
forces between the vertebral bodies for the three degrees of kyphosis were computed
and compared. Similarly, the compression and shear forces between the vertebral bodies
for the different sarcopenia stages were computed and compared, to investigate the
influence of sarcopenia on spinal loading. To validate the model, we took the ratio of
the compression force from the flexed to the upright posture (normalisation to standing).
These normalised spinal loads are compared to three different in vivo measurements
from the literature; direct measurement with an instrumented vertebral body
replacement (VBR), spinal force calculated from direct intradiscal pressure
measurement (IDP) and spinal force derived from muscle activation patterns (EMG)
[11,12,13].
4. RESULTS
The predictions of spinal loading for varying degrees of kyphosis showed a good
agreement with literature values for compression forces between T6 and T9. The most
severe kyphosis curvature (70°) lead to an increase in segmental compression forces at
these levels of approximately 20%, compared to the model with a normal curvature. For