POSTERIOR LUMBAR INTERBODY FUSION (PLIF) and TRANSFORAMINAL LUMBAR INTERBODY FUSION (TLIF)
Spinal fusion is a surgical procedure used to correct problems with the small bones in the spine (vertebrae). It is essentially a “welding” process. The basic idea is to fuse together the painful vertebrae so that they heal into a single, solid bone.
One method of fusing the lumbar spine involves removing the intervertebral disc. When the disc space has been cleared out, a metal, plastic, or bone spacer is implanted between the two adjoining vertebrae.
These spacers, or “cages”, usually contain bone graft material. This promotes bone healing and facilitates the fusion. After the cage is inserted, surgeons often use metal screws, plates, and rods to further stabilize the spine.
An interbody fusion can be performed using a variety of different approaches:
Posterior lumbar interbody fusion (PLIF). A spacer may be inserted from the back of the spine. With this approach, your surgeon gains access to your spine by removing the bone (lamina) and retracting the nerves. Then the back of the disc can be removed and a spacer inserted.
Transforaminal lumbar interbody fusion (TLIF). With this technique, the surgeon approaches the spine a little bit from the side. This requires less movement of the nerve roots. More recently, it has even been possible to take a direct side approach and center the incision over the patient’s flank. With this approach, the surgeon can reach the disc without moving the nerves and opening the back muscles (AAOS, 2015).
The ALIF approach is advantageous in that, unlike the PLIF and posterolateral gutter approaches, both the back muscles and nerves remain undisturbed.
Another advantage is that placing the bone graft in the front of the spine places it in compression, and bone in compression tends to fuse better.
Lastly, a much larger implant can be inserted through an anterior approach, and this provides for better initial stability of the fusion construct.
TLIF and PLIF back surgeries are done through the back part of the spine.
- Surgical hardware is applied to the spine to help enhance the fusion rate. Pedicle screws and rods are attached to the back of the vertebra and an interbody fusion spacer is inserted into the disc space from one side of the spine.
- Bone graft is placed into the interbody space and alongside the back of the vertebra to be fused. Bone graft is obtained from the patient’s pelvis, although bone graft substitutes are also sometimes used.
- As the bone graft heals, it fuses the vertebra above and below and forms one long bone.
Doing a pure PLIF surgery has the advantage that it can provide anterior fusion of the disc space without having a second incision as would be necessary with an anterior/posterior spine fusion surgery. However, it has some disadvantages:
- Not as much of the disc space can be removed with a posterior approach (from the back).
- An anterior approach (an ALIF, from the front) provides for a much more comprehensive evacuation of the disc space and this leads to increase surface area available for a fusion.
- A larger spinal implant can be inserted from an anterior approach, which provides for superior stabilization.
- In cases of spinal deformity (e.g. isthmic spondylolisthesis) a posterior approach alone is more difficult to reduce the deformity.
- There is a small but finite risk that inserting a cage posteriorly will allow it to retro pulse back into the canal and create neural compression.
TLIF procedure has several theoretical advantages over some other forms of lumbar fusion:
- Bone fusion is enhanced because bone graft is placed both along the gutters of the spine posteriorly but also in the disc space.
- A spacer is inserted into the disc space helping to restore normal height and opening up nerve foramina to take pressure off the nerve roots.
- A TLIF procedure allows the surgeon to insert bone graft and spacer into the disc space from a unilateral approach laterally without having to forcefully retract the nerve roots as much, which may reduce injury and scarring around the nerve roots when compared to a PLIF procedure.
As with all forms of lumbar spine fusion, prior to TLIF surgery medical clearance is obtained. Smoking should be stopped. Patients may require pre-donation of blood to be used at the time of surgery.