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The current main techniques of Posterior Lumbar Interbody Fusion (PLIF) surgery
all incorporate a supplementary intervertebral implant:
• Threaded cylindrical cages made of titanium, cortical allograft (donor
bone) or synthetic bone.
• Impacted cages made of titanium, carbon-fiber reinforced or plain
PEEK polymer (Polyetheretheketone).
• Impacted wedges made of carbon-fiber reinforced PEEK, plain PEEK polymer
or cortical allograft.
• Inserted and rotated wedges made of carbon-fiber reinforced PEEK or
plain PEEK polymer.
They all involve an initial laminectomy and a variable amount of removal of
the facet joints (medial facetectomy). The latter, which may require complete
removal of the facet joints, will depend upon the choice and size of implant,
as well as the surgical level. Following decompression of the spinal canal,
intervertebral disc space spreaders are used to correct coronal plane deformity
(scoliosis) and restore disc space and foraminal height (Figure 2).
Supplementary pedicle screw instrumentation may then be used to complete the
correction of any spondylolisthetic deformity (spondylolisthesis) (Figures 3
and 4).
Figure 3. Spondylolisthesis reduction using a screw
thread to apply a powerful posterior translation force.
Figure 4. Complete reduction and PLIF
in a 15 year old boy with Grade III spondylolisthesis
Most modern techniques rely on supplementary pedicle screw instrumentation
to assist the stabilization / deformity correction although some surgeons still
regard the distraction (separation)/ compression stabilization achieved by the
implants to be satisfactory.
In the case of threaded cylindrical cages, bilateral holes are then made, centered
upon the disc space and removing several millimeters of the adjacent vertebral
end plates. The holes are tapped and the implants, filled with bone graft are
screwed into the holes. Care must be taken to avoid injury to the adjacent nerve
roots during preparation of the holes and implantation of the cages as these
devices.
With impacted cages / wedges, the posterior disc space is usually over-distracted
(separated) to enable an implant of sufficient anterior height to be inserted.
A broach (a surgical instrument) may be used to prepare a path through the posterior
disc space. The disc space contents and cartilaginous end plates are removed
to facilitate fusion. In the case of impacted wedges, bone graft is after loaded
into the disc space beside the wedges.
The Insert and Rotate technique is similar to the Impacted wedge technique
but does not require over-distraction (separation) or involve the cutting of
any channel through the posterior end plates. It separates the load bearing
and stabilization role from the fusion role. The bone graft is after loaded
and placed to either side of the implants. The implant may be made quite lordotic
to facilitate restoration of Lordosis (natural inward spinal curvature), especially
of the lumbosacral (lumbar / sacrum) segment. Care must be taken to preserve
the vertebral end plates upon which the implant will rest. It requires minimal
dural / neural retraction (Figure 5). Supplementary pedicle screw instrumentation
must be used.
Figure 5. Schematic representation of the difference in the neural retraction
required for Threaded Cylindrical, Impacted and Insert and Rotate implant techniques.
Both the Impacted and Insert and Rotate techniques are suitable for use with
minimal access techniques.
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