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follows the ligaments at the rim of the upper and lower
vertebra and can eventually encapsulate the disk.
The growth of these bony protrusions may fully bridge the
vertebras where ligament once was along side the disk. This
advanced condition is termed "bamboo spine," as an x-ray displays
this vertebral column as a continuous structure of bone shaped
like bamboo with vertebra and bulbous growth of bone between
them. Other lesser developed ossification is termed "postage
stamp" because of the x-ray visible bony protrusions that
follow the ligament's fibrous strands that run between the
vertebra. This abnormal ossification is what fuses the vertebral
column and gives it its rigid nature.
The typical vertebral joint consists of the vertebras, the
disk, the ligaments, and muscle. Among the ligaments
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necessary are those associated with the outer portion of
the vertebral disk that are called the anulus fibrosi. This
ligament is vital
in the disk's attachment to the vertebrae and spans every
intradisk space.
Prior to ossification, the ligament's attachment
at the rim of the vertebra becomes inflamed.
Lesions form on the vertebra rim at the sites of this inflammation,
a deteriating process known as enthesopathy. The reason for
this inflammation is unknown. This inflammatory condition
exists sporadically for many years, causing pain and some
stiffness. This enthesopathy is known to occur along the anterior
rim of the vertebra rim (the side
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facing the abdomen). The inflammation eventually causes
bone to erode at the rim where the inflamed ligament is attached.
Findings indicate that bone cells fill in the fibrous tissue
of the ligament to repair the defect caused by the eroded
bone.
This new bone is woven into the inflammed fibrous ligament
tissue,
joining the underlying bone of the vertebra with the fibrous
tissue of the ligament, thus causing the bone surface to protrude
outside the original vertebral surface.
The result of the inflammation's healing process are bony
protrusions at the vertebra's original ligament attachment.
Over time, these protrusions grow and tend to fuse with one
another along the length of the spine. This process usually
occurs at several places on the vertebra and may also develop
some distance away from the ligament's attachment at the vertebra
rim.
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