Biomedical Engineering Reference
In-Depth Information
Fig. 5.41 a FE-modelling of the vertebrae connection between vertebra L4 and L5 via a
connector definition, b moment-angle characteristics prescribing a (counter) moment at a given
relative angle
5.3.3.2 Kinematics of the Spine
The degrees of freedom of the spine can be divided into the three following motions:
(1) Sagittal flexion, composed of ventral flexion (forward bending) and dorsal flexion
(backward bending) (cf. Fig.
5.40
b), (2) Lateral flexion from the neutral position to
the left or right and back (cf. Fig.
5.40
c) and (3) Rotation about the ''longitudinal
axis'' of the spine, from left to right and back to neutral (cf. Fig.
5.40
d).
The required stability and mobility of the spine is provided by the intervertebral
discs,
the
ligaments,
the
muscles
and
small
vertebral
joints
connecting
the
vertebrae.
With the exception of the first and second cervical vertebra (C1 and C2), as well as
the vertebrae of the os sacrum and the coccyx, contiguous vertebrae are connected by
a vertebral disc. The vertebral discs consist of fibrocartilage with a colloidal soft core
(nucleus pulposus) and a fibrous outer ring (anulus fibrosus). The discs provide
damping and shock absorbing properties to the human body. The iliac bone, the
pelvis and the os sacrum are connected via a bony joint (sacroiliac—SI—joint).
Every motion of these anatomical structures of the spine is a consequence of complex
interaction between muscle tension of the abdomen, the diaphragm, back muscles
and respiratory muscles, while permanently overcoming gravitational force.
5.3.3.3 FE-Modelling of the Spine
Based on imaging techniques (MRI and/or CT) acquisition, FE-representation of
the spine including single vertebrae, discs and muscles can be achieved. Such a
model does not contain kinematic information. Modelling of complex interactions
combined with biological variability is not feasible at present since research on
continuum mechanical modelling of active muscles in connection with FEM is still
in progress. Modelling of such complex behaviour in a simplified manner, suitable
