Lumbar Spinal Fusion Surgery

Lumbar spinal fusion is a major surgery designed to stop the motion at a painful vertebral segment in the low back. 

The objectives of spinal fusion are to:

• Attain a solid bony fusion that immobilizes the segment
• Improve spinal stability
• Correct anatomical deformities
• Relieve nerve compression

Spinal fusion is the preferred surgical approach for treating degenerative spine disorders and may be performed via the traditional open surgical method or minimally invasive techniques. 

How Spinal Fusion Works in the Lower Back

The lumbar spine (low back) has 5 mobile spinal levels from L1 to S1, also known as motion segments. At each spinal level, motion is controlled by a disc and a pair of facet joints. The disc and motion segment are named by the vertebral body above and below; for example, the disc and motion segment related to the L4 and L5 vertebrae are called the L4-L5 disc and the L4-L5 motion segment.

How spinal fusion sets up

A lumbar fusion surgery stops the motion at a painful motion segment. The fusion is not actually done at the time of the surgery; rather, the surgery sets up the conditions for the bone to heal across the spinal segment to form a bone to replace the joint. The bone healing process takes several months to over a year to fully set up.

After a spinal fusion surgery is performed, the following processes occur:

• A living bone bridge is formed between the two surrounding vertebrae.
• Depending on the surgical approach, this bridge develops either behind the disc between the posterior bony elements, through the disc space, or both. 
• The bridge stiffens that segment in the spine and stops any motion at the fused motion segment. 
• Spinal instrumentation (typically screw and rod fixation) is commonly used to secure the segments while the bony fusion forms.

Spinal fusion surgery may also include fusing the spinal facet joints for added stability. 

Using a Bone Graft in Spinal Fusion

It is common to use a bone graft to bridge the vertebral bones. The bone graft facilitates bone growth through and around the disc, fusing the spinal bones (vertebrae), and aiding in immobilizing the motion segment. 

Bone graft materials can be the patient’s own bone (autograft), donor bone from a bone bank (allograft), or synthetic materials commonly populated with a patient’s bone marrow. 

Due to their efficacy and safety, autografts are considered the gold standard for spinal fusions. However, there is some morbidity associated with bone graft harvest, and there is a limited supply of graft bone from the patient.

The Use of Cage Implants in Spinal Fusion

Interbody cage implants are designed to stop motion at the fusion segment to promote bone healing for fusion. They help support the front (anterior) part of the spinal segment, which bears 80% of the spinal loads, and dissipate forces placed on the rods and screws at the back.

Spinal cages come in different shapes and sizes depending on the surgical approach and indication for spine fusion.

• Anterior spinal cages are used in anterior spinal approaches. They are available as a single piece and cover the entire disc space. They come in different sizes and wedge shapes to precisely fit into the disc space and reconstruct the normal spine shape. Some cages are designed to be implanted in a compressed state and expand once inside the disc space.
  • Anterior cages can be implanted from the side of the spine (lateral approach) and from a modified anterior approach (anterior to the psoas muscle). The shapes of these cages are modified because of anatomic constraints but perform similarly to pure anterior cages.  
• Posterior interbody cages are designed for the posterior (back) approach. They can be straight or crescent-shaped and expandable or fixed.  

The goals of these implants are to stabilize the spine in an anatomic alignment, promote bone healing for fusion, indirectly decompress the nerves, and prevent injury to the normal tissues. Spinal cages can be placed by open or minimally invasive techniques.

Read more about Interbody Cages for Spine Fusion

The surgical decisions regarding approach and implants comprise several considerations. These include the reason for surgery (indication), the patient’s anatomy, prior surgery or medical intervention (eg, radiation therapy), the surgeon’s skill, and hospital/surgical center capabilities.

Spinal fusion surgery may be considered when abnormal and excessive motion at a vertebral segment results in severe pain and inability to function. The surgery aims to stabilize the spine in a position that is close to normal, thereby preventing any abnormal rotation, nerve compression, and pain.

Indications for spinal fusion include:

• Spondylolisthesis
• Spondylolysis
• Spinal stenosis
• Degenerative disc disease 
• Discogenic pain or pain originating from a spinal disc
• Spinal instability during surgery or from a past decompressive surgery, such as lumbar laminectomy
• Medical emergencies, such as a tumor and certain types of traumas

Spine fusion is also indicated to treat spinal deformities, such as scoliosis. Unless a medical emergency, a series of nonsurgical treatments are usually tried before spinal fusion surgery is considered. 

Interbody Fusions of the Lumbar Spine

An interbody spinal fusion involves removing the intervertebral disc and inserting an implant or bone graft in the disc space. This implant or bone graft helps restore disc height, relieve nerve compression, and facilitate bone growth for fusion.

Lumbar interbody fusion can be performed through various approaches:

• Posterior lumbar interbody fusion (PLIF): the spine is approached through the back 
• Anterior lumbar interbody fusion (ALIF): the spine is approached through the abdomen
• Transforaminal lumbar interbody fusion (TLIF): the spine is approached from the back through the hollow bony openings (foramina) between adjacent spinal segments
• Extreme lateral interbody fusion (XLIF): the spine is approached from the side

Interbody fusion surgeries are among the most common types of spinal fusion surgery.

Posterolateral Gutter Fusion

A posterolateral gutter fusion is performed via a posterior (back) approach. In this method, the bone graft is placed in a region outside the spine, near the paired facet joints and the intertransverse gutter. This approach allows clear surgical access over multiple spinal levels.

Due to its position, the bone graft in a posterolateral approach is not load-bearing but rather placed under tension.

An interbody fusion may be performed along with the posterolateral gutter surgery if restoration of disc height is needed.

Anterior and Posterior Spinal Fusion

The anterior and posterior fusion procedure, also called a 360° or circumferential fusion, involves fusing both the front and back of the spine to provide a high degree of stability and a large surface area for the bone fusion to occur. 

Multilevel Spinal Fusion

A multilevel spinal fusion involves fusing two or more levels of the spine, such as the L4-L5 and L5-S1 spinal segments. Multilevel fusions considerably limit the normal motion in the lower back and place more stress across the remaining mobile joints.

Watch Stages of Bone Healing in Lumbar Spine Fusion Surgery Video

Fusing 3 or more levels of the spine is rare and usually reserved for the treatment of scoliosis or lumbar deformity.

See Multilevel Fusion Risks

Spinal Instrumentation to Secure the Fused Vertebrae

Spinal fusion typically involves the use of some form of spinal instrumentation, which helps provide additional spinal stability, acting as an internal brace while the bony fusion heals.

Common surgical implants used in spine fusion include spinal interbody cages, anterior plates, pedicle screws and rods, hooks, and wires.

Success Rates of Lumbar Spinal Fusion Surgery

Research indicates that 65% to 95% of lumbar spinal fusions are successful.

The posterior lumbar interbody fusion (PLIF) approach typically has the highest rate of successful fusion and the lowest rate of complications compared to the other approaches.

See PLIF Potential Advantages and Disadvantages

However, recent lumbar fusion studies demonstrate the superiority of ALIF, XLIF, and minimally invasive TLIF surgeries in regard to surgical outcomes, including pain relief, function, patient satisfaction, and recovery.

Success rates based on specific conditions

The effectiveness of spinal fusion surgery varies depending on the underlying condition.

• Favorable outcomes are generally reported when spinal fusion is used to treat spinal deformities and spondylolisthesis.
• Modest outcomes have been reported when spinal fusion is used to treat degenerative disc disease and disc-related pain.

The vast majority of fusion surgeries are typically considered for the treatment of degenerative spondylolisthesis, a condition where a vertebra slips over the vertebra below it due to age-related changes in the spine.

Factors That Influence a Successful Fusion

Obtaining a successful result from a spine fusion requires several factors, including:

• Presurgical factors: 
  • An accurate diagnosis of the underlying condition
  • A technologically adept, skilled surgeon
  • Appropriate patient selection, taking into consideration the patient’s age, concomitant medical conditions, and lifestyle (healthy weight, does not smoke or use nicotine products)
  • History of previous surgeries
• Surgical factors: 
  • Extent and type of surgery
  • The use of hardware and instrumentation
  • Number of levels fused
• Postsurgical factors:
  • Compliance with postsurgical protocols
  • How closely the care instructions are followed

Additionally, patients with malnutrition, depression, long-standing use of opioids before surgery, and use of chronic steroid medications, including prednisone, may be at risk of slower recovery after fusion surgery.

Patients and caregivers are advised to discuss the surgical procedure and recovery process in detail with the surgeon to get a thorough understanding of what to expect before and after surgery.