Posterolateral Gutter Spine Fusion Surgery

Posterolateral fusion is the most common type of lumbar spinal fusion surgery. It is considered by many surgeons to be the "tried and true" method of spinal fusion.

It is called posterolateral gutter fusion because the fusion occurs by placing bone graft in the spinal “gutter” – a shallow groove on either side of the spine.

What Is Posterolateral Spinal Fusion?

The essentials of a posterolateral gutter fusion are:

• It is primarily indicated for treating spinal instability and localized back pain caused by degenerative conditions or aging-related spinal changes, such as degenerative disc disease and spinal osteoarthritis.
• A stand-alone posterolateral fusion does not involve the removal of any spinal structures, such as the disc or bone, and fuses the spinal level(s) in their natural state.
• Fusion is achieved by placing bone grafts in the lateral gutter of the spine, where a rich bed of blood vessels stimulates bone growth and healing for the fusion to take place. This space is near the vertebrae’s transverse process - the bony projections on either side of the vertebrae. As the bone graft grows and adheres to the vertebrae’s transverse processes, spinal fusion is achieved and motion at that segment is stopped.
• Posterolateral fusion is generally recommended after several months of unsuccessful non-surgical treatments to improve persistent or worsening lower back pain and disability.
• It can be performed on up to 4 consecutive spinal levels from L1-L2 at the top of the lumbar spine (lower back) through L5-S1 at the very bottom.

A solid fusion is not always achieved in this surgery.

Goals of Posterolateral Fusion Surgery

The primary goals of posterolateral gutter fusion surgery are to:

Stabilize the spine by preventing movement and reducing instability in the affected area.

Reduce localized back pain and improve function by alleviating symptoms associated with abnormal motion and muscle spasms.

Combining Spinal Fusion Surgeries

Posterolateral gutter fusion is often combined with one or more lumbar spine surgeries to treat a broader range of symptoms and conditions, including leg pain caused by spinal nerve compression. The number of levels fused and the need for additional surgical techniques depends on the severity of the condition being treated.

The combined approach enhances the reinforcement and stability of the painful motion segment. All the procedures are performed at the same time during the same surgical session.

Common examples of surgeries combined with a posterolateral fusion include lumbar interbody spinal fusion (ALIF, PLIF, TLIF, or XLIF), laminectomy, facetectomy, or microdiscectomy.

Posterolateral Spinal Fusion vs Interbody Lumbar Spinal Fusion

Both procedures aim to improve spinal stability by fusing the motion segment, but the way fusion is achieved and the parts of the spine that are fused are different:

Both types may require additional devices for stability, such as rods and screws, while the fusion sets up.

Conditions Treated

As a stand-alone procedure, this surgery is used to treat spinal instability caused by degenerative spinal conditions without any symptoms or signs of nerve root or spinal cord compression, such as:

• Degenerative disc disease: The spinal discs degenerate and become flatter, stiffer, and less capable of absorbing loads, causing abnormal movement and muscle spasms in the affected motion segment.
• Degenerative spondylolisthesis: One vertebra slips forward over another due to degeneration and weakening of the spinal discs and facet joints in the motion segment, causing instability and a misalignment in the affected segment.
• Isthmic spondylolisthesis: A spinal vertebra slips forward on the one below it due to structural defects in the vertebral bone - causing instability and a misalignment in the motion segment.
• Spinal osteoarthritis: Wear and tear on the spinal facet joints causes the joint cartilage to break down, resulting in inflammation and pain during spinal movement.
• Spinal fracture with instability: Break in the vertebral bone causing instability in the affected motion segment.

In cases where the above conditions cause nerve root compression or other issues like spinal stenosis is present, a posterolateral fusion may be combined with additional procedures to address the specific problem as discussed below.

Posterolateral Spinal Fusion with Lumbar Interbody Fusion

The procedure is combined with an interbody spinal fusion when the disc is degenerated or herniated, and there is a diagnosis of nerve root or spinal cord compression.

Interbody fusion addresses nerve root or spinal cord compression by removing the problematic disc and inserting a bone graft into the evacuated disc space. This procedure sets up the conditions for new bone to grow and fuse the adjacent vertebral bones into one long, stable bone. It also helps restore the height of the disc space, relieving nerve compression in the area.

A posterolateral fusion is then performed to provide additional stability on the sides of the spine.

A 360-degree fusion is achieved by combining an anterior lumbar interbody fusion (ALIF), which fuses the spine from the front, with a posterolateral fusion. This approach creates a complete fusion of the motion segment from all sides.

Posterolateral Spinal Fusion with Microdiscectomy

The surgery is combined with a microdiscectomy procedure to address nerve compression from a herniated disc, specifically in cases where multiple recurrent herniation occurs (the herniation keeps recurring after being surgically treated).

Microdiscectomy surgery involves removing the herniated portion of the disc to relieve pressure on the nerve. The remaining disc is left as-is.

A posterolateral fusion is then performed to fuse the motion segment and improve spinal stability.

Posterolateral Spinal Fusion with Laminectomy or Facetectomy

A posterolateral fusion is combined with decompression procedures like laminectomy or facetectomy when there’s instability from a degenerative condition like a degenerated disc in addition to nerve compression due to overgrown bone and narrowing of space in the spinal canal (spinal stenosis).

A laminectomy involves removing a portion of the lamina, a bony arch that covers the spinal canal from the back and is typically used to relieve pressure on the spinal cord.

A facetectomy involves trimming the facet joints, which are located on the back of the vertebrae, to relieve spinal nerve root compression caused by overgrown bone in this area.

The posterolateral fusion component of the procedure stabilizes the spine and reduces pain associated with the degenerated disc by limiting movement in the affected area.

Success Rates

Research shows that most patients have favorable outcomes after posterolateral fusion surgery.¹Levin JM, Tanenbaum JE, Steinmetz MP, Mroz TE, Overley SC. Posterolateral fusion (PLF) versus transforaminal lumbar interbody fusion (TLIF) for spondylolisthesis: a systematic review and meta-analysis. Spine J. 2018;18(6):1088-1098. doi:10.1016/j.spinee.2018.01.028^,2Endler P, Ekman P, Möller H, Gerdhem P. Outcomes of Posterolateral Fusion with and without Instrumentation and of Interbody Fusion for Isthmic Spondylolisthesis: A Prospective Study. J Bone Joint Surg Am. 2017;99(9):743-752. doi:10.2106/JBJS.16.00679

Posterolateral fusion may not always result in a solid fusion (non-union), which can increase the risk of future pain due to failed spinal fusion.

As with most types of spinal fusions, non-union is more common in the L5-S1 segment due to a higher degree of stress and loads on this segment. Multi-level fusions involving more than three levels also carry a higher risk of non-union.³Guppy KH, Royse KE, Norheim EP, et al. Operative Nonunion Rates in Posterolateral Lumbar Fusions: Analysis of a Cohort of 2591 Patients from a National Spine Registry. World Neurosurg. 2021;145:e131-e140. doi:10.1016/j.wneu.2020.09.142

Successful fusions typically set up within three months and continue to get stronger over a period of one to two years.

Posterolateral gutter spinal fusion surgeries are elective, meaning it’s up to the patient to decide whether or not to have surgery.

The procedure is performed by an orthopedic surgeon or neurosurgeon who specializes in spine surgery.