My Spine - Lumbar
The proper fusion is achieved through bone growth. The bone is placed
between and around certain segments of the adjacent vertebrae, which then
grow together. These may be the spinous processes of the vertebrae (inter-
spinous fusion), the laminae of the vertebrae (posterior fusion), the transverse
processes (inter-transverse postero-lateral fusion) or between the vertebral
bodies themselves (interbody fusion). Of these techniques the inter-transverse
postero-lateral fusion and the interbody fusion are the most common forms of
posterior fusions performed.
Many of the interspinous devices do not constitute a proper fusion as the aim
is not bony growth, but rather to keep the distance between the spinous
processes and allow for the spinal canal to be capacious, thus reducing nerve
compression due to a narrowing of the canal.
The interbody fusions are divided according to the method of introducing the
bone between the vertebral bodies into posterior lumbar interbody fusion
(PLIF) and transforaminal lumbar interbody fusion (TLIF). The traditional
posterior lumbar interbody fusion (PLIF) places bone blocks or cages
between the vertebrae from both sides, which necessitates operating from
both sides of the spinal canal. The more recent operation of a TLIF places a
single spacer well forward between the vertebrae and this is introduced from
one side only. In both cases the remaining space between the vertebrae is then
filled with bone.
These operations often need bone to be harvested from the iliac crest (the hip)
of the patient through usually a separate incision, because at this stage the use
of the patient's own bone for fusion is still regarded as the gold standard.
Sometimes the decompression operation yields enough excised bone that can
be collected and prepared to be used for the bone graft. Allograft from a bone
bank or synthetic material (inducing bone growth) is also used by some spe-
cialists for this purpose.
The main aim of the fusion operation is to achieve bony fusion. If this is not
achieved, then the operation has failed and if the patient continues to have
symptoms, another operation might have to be performed in the future. Bone
growth is variable and depends on many factors. These vary from person to
person.
127