Lumbar Fusion and Stabilization (PLF/PLIF/TLIF/OLIF/ALIF/XLIF)
Overview: In patients with instability (abnormal mobility between spinal bones causing pain) stabilization with implants may be requires. This is usually combined with a fusion procedure (laying bone graft) which fuses two bones and prevents abnormal movement.
This surgery has two aspects – a. Fusion and b. Stabilization. These steps are usually performed in conjunction with Posterior Lumbar decompression/ LaminectomyOnly in cases where in the surgeon relies on indirect decompression [OLIF/ALIF/XLIF] or in cases where only stabilization is required (fractures without neural compression) the decompression procedure is not done. These are Minimally Invasive Techniques where Stabilization is done with Percutaneous Pedicle Screw Fixation.
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The primary indication of Fusion and Stabilization is instability. Instability due to any cause- infection, trauma, tumour, deformity, etc is treated with this procedure. Instability causes abnormal movement between bones giving rise to back pain, thus fusion is indicated.
Fusion literally means fusing/ joining/ welding two bones together. The fusion material used is bone graft and its substitutes. Bone grafts come from many sources. Each type has advantages and disadvantages.
Autograft bone comes from you. The surgeon takes your own bone cells from the hip (iliac crest). This graft has a higher rate of fusion because it has bone-growing cells and proteins. The disadvantage is the pain in your hipbone after surgery. Harvesting a bone graft from your hip is done at the same time as the spine surgery.
Allograft bone comes from a donor (cadaver). Bone-bank bone is collected from people who have agreed to donate their organs after they die. This graft does not have bone-growing cells or proteins, yet it is readily available and eliminates the need to harvest bone from your hip.
Bone graft substitute comes from man-made plastic, ceramic, or bioresorbable compounds. Often called cages, this graft material is packed with shavings of living bone tissue taken from your spine during surgery.
Rh BMP- This is recombinant Bone Morphogenetic Protein. These proteins are bone forming proteins which are produced with genetic engineering techniques. These have bone fusing potential as much as autograft except that it is costly. It does not require bone to be harvested from the hip. It is combined with locally acquired bone or bone substitutes to promote fusion.
Fusion in lumbar spine can be done from various approaches i.e from the front (anterior) or back (posterior). Traditionally posterior approaches are more commonly used. With advances in Minimally Invasive Techniques anterior techniques are now being utilized. Interbody fusion techniques have better stability and fusion rates. The approaches used for fusion can be:
- Postero-Lateral Fusion (PLF): Bone graft is laid over the postero-lateral gutters on either sides of laminae (bone covering spinal canal) after removing them – Laminectomy
- Posterior Lumbar Interbody Fusion (PLIF): Bony graft is laid in the disc space along with PEEK (polyether ether ketone) or metallic (titanium) spacers after removing the disc material. The disc space is reached after retracting the spinal cord. This retraction of spinal cord may cause post operative nerve pain and inflammation. Hence TLIF technique evolved.
- Transforaminal Lumbar Interbody Fusion (TLIF): Bone graft is laid in the disc space along with PEEK (polyether ether ketone) or metallic (titanium) spacers after removing facet joints and disc material, without retracting the spinal cord. This procedure can also be done through Minimally Invasive Techniques – MIS TLIF
- Anterior Lumbar Interbody Fusion (ALIF): Bone graft is laid in the disc space along with PEEK (polyether ether ketone) or metallic (titanium) spacers after removing the disc material. The space is accessed through the front of the abdomen. After the spacer is inserted, decompression if required is done and screws are inserted from the back.
- Xtreme Lateral/ Lateral Lumbar Interbody Fusion (XLIF): Bone graft is laid in the disc space along with PEEK (polyether ether ketone) or metallic (titanium) spacers after removing the disc material. The space is accessed through the side of the abdomen. After the spacer is inserted, decompression if required is done and screws are inserted from the back.
- Oblique Lumbar Interbody Fusion (OLIF): Bone graft is laid in the disc space along with PEEK (polyether ether ketone) or metallic (titanium) spacers after removing the disc material. The space is accessed through the side of the abdomen. After the spacer is inserted, decompression if required is done and screws are inserted from the back.
OLIF and XLIF ate Minimally Invasive Techniques which are in vogue recently. They rely on Indirect Decompression where compression of neural structures is relieved without Laminectomy. Percutaneous Pedicle Screw Fixation through multiple small holes rather than open technique.
Fusion procedure provides long term stability. However, bones take anywhere from 3 months to 1 year to fuse. During this time to provide stability implants like screws and spacers are inserted. These enable the surgeon to make the patient walk earlier as compared to conventional techniques where bed rest and activity modification were advised. They are can be inserted through Minimally Invasive Techniques also. See PPF.
Implant related complications: Since implants are foreign materials they may cause reactions which are extremely rare situations. They are also a source of infection. However, they are bio inert and compatible and do not require removal usually. They are also MRI compatible. In a few patients, they can be malpositioned when they can cause neural compression and need to be repositioned. To improve this, Navigation and Robotic Techniques have been introduced. If the bone fail to fuse, the implant may fail in few patients particularly those who are heavily built and have osteoporosis. Failure of fusion (pseudoarthrosis) is another complication where bone does not fuse and cause persistent back pain. In such patients, a revision surgery may be required.
Adjacent Segment Degeneration (ASD): This happen when the segment has solid fusion and biomechanical stresses are placed on the level above and below and they may degenerate earlier. To avoid this, Artificial Disc Replacement may be used in some patients to maintain segment motion
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