Intervertebral Disk Replacement - Keivan Anbarani's Electronic ...

Figure 3. Intervertebral Disc
Source: Spine Universe, 2010
When standing up or sitting, the spine is loaded in which the nucleus pulposus is
compressed creating a pressure inside that will force the water out (Figure 5). Similarly, no
load on the spine exists when lying down there and the water will flow back in. Overtime,
as the body ages, more water leaves the disc than enters-­‐ causing spinal disc degeneration
and increased lower back pain among older people.
Figure 4. Intervertebral Disc under Compression
Source: ICORD, 2010
The vertebrae bone is divided into three different sections: cervical, thoracic and
lumbar (Figure 7). Each section is named using the first initial of the section name followed
by a sequential numbering system starting from the top at number one and increasing to
the number of vertebrae of that section. The last bone after L5 is sacrum and is usually
referred as S1. Due to a higher load and stress concentration on the lower back area,
biomechanical analysis will focus on the lumbar vertebrae (discs L1 to L5). This higher
level of stress concentration is a result of the force applied by the majority of upper body
weight. During spinal cord bending, flexion and extension, creates the biggest moment arm
at the lumbar vertebrae (Figure 6).
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