Advances in Surgical Techniques for Lumbar Interbody Fusion

One of the most common musculoskeletal conditions is lumbar spinal disorders. The occurrence rate for first-time episodes of low back pain (LBP) ranges from 6.3% to 15.4%, with 3/4 to 4/5 of adults experiencing LBP at some point in their lives.

LBP can be primary (non-specific/idiopathic) or secondary, resulting from known causes. Non-surgical approaches are mainly used for primary LBP, while surgery is often considered for secondary LBP that doesn’t respond to conservative treatments.

Lumbar interbody fusion/arthrodesis (LIF) is a treatment method that involves stabilizing the painful motion segment, correcting deformity, restoring lordosis, and providing indirect decompression of the neural elements.

There are various surgical techniques available for lumbar interbody fusion (LIF), including the anterior approach known as anterior LIF (ALIF) and the posterior approach called posterior LIF (PLIF). The TLIF technique has become more popular than PLIF due to its advantage of involving less nerve retraction.

Alternative methods such as extreme or lateral LIF (XLIF/LLIF) and oblique LIF (OLIF) have been developed and used to reduce spinal and paraspinal muscle dissection. Recently, minimally invasive approaches like MI-TLIF have been developed and gained popularity in clinical practice.

Advancements in surgical technology and interbody fusion cage design have led to an increase in the number of lumbar fusions performed over the past decades. Non-union or pseudarthrosis after lumbar interbody fusion (LIF) remains a major surgical complication, with rates ranging from 7 to 20%.

Patients with osteoporosis have been reported to have a non-union rate of 29% even in one-level lumbar interbody fusion (LIF).Autogenous iliac crest bone grafting (ICBG) has been utilized as a means to improve bony fusion, however, it comes with significant risks and complications.

Surgical Techniques And Clinical Outcomes

To perform LIF, the intervertebral body space is prepared and a bone graft or cage containing osteogenic materials is inserted to cover the bony endplates. The interbody cage or graft is braced and compressed by “wires” on three sides, acting as a central pole.

Most surgeons typically add supplementary posterior or anterior fixation to provide additional stabilization to the construct. Recent studies discuss different surgical techniques for lumbar fusion, their advantages and disadvantages, indications, and outcomes.

Posterior LIF (PLIF)

Indications

The PLIF is a LIF technique that involves accessing the intervertebral disc through posterior laminectomy. It is beneficial for certain patients with segmental instability, recurrent disc herniation, symptomatic spinal stenosis, and pseudarthrosis. However, it has contraindications, including extensive epidural scarring, arachnoiditis, and active infection.

The PLIF technique involves decompression, complete removal of the intervertebral disc, and spinal fusion with or without additional stabilization using transpedicular screw/rod. The fusion is accomplished by using iliac crest autograft, allograft, or cages that are filled with bone graft.

• Advantages: this method provides a broad view of the posterior area and allows for the complete release of pressure on the nerve elements without needing a separate incision as the spine is already exposed for decompression. The fusion process involves applying pressure.
• Disadvantages: Epidural bleeding, cage displacement, particularly without posterior instrumentation, cage sinking due to excessive removal of the endplate during surgery, formation of scar tissue around nerves causing ongoing pain in the back and/or legs, and impairment of the nervous system.

Surgical and Clinical Outcomes

The attainment of solid spinal fusion is possible in a large number of cases, which can be identified by the presence of a characteristic radiographic indicator known as the “sentinel sign.”

The presence of persistent pain, development or progression of deformity, loss of disc height, vertebral displacement, implant failure, haloing, migration or resorption of the bone graft, pedicle screw loosening, and movement on flexion/extension views are potential indicators of pseudarthrosis or non-union.

Adjacent segment degeneration (ASD) is a possible long-term complication of PLIF that may result in the need for reoperation. According to literature, symptomatic ASD may require reoperation and reported reoperation rates increase over time: 9.6% at 5-year follow-up, 24.6% at 10-year follow-up, and 37.5% at 15-year follow-up.

Some studies have proposed that decreased disc space height at the adjacent segment does not impact patient-reported outcomes, including pain and disability. The redistribution of stress at the neighboring level, which can increase mobility and intradiscal pressure, is thought to be the underlying mechanism of ASD. ASD may also be observed in other types of lumbar interbody fusion (LIF) approaches.

Transforaminal LIF (TLIF)

TLIF is a surgical approach that combines anterior/posterior fusion techniques and is recommended for treating several degenerative pathologies. TLIF accesses the disc through the posterolateral section of the vertebral foramen and restores lumbar lordosis with an interbody spacer and pedicle screw fixation.

Unilateral laminectomy, inferior facetectomy, and partial resection of the superior facet are performed at the level of fusion to access the intervertebral disc while preserving the contralateral facet joint.

TLIF is similar to PLIF in terms of discectomy, endplate preparation, and cage insertion, but it involves less or no traction on the dura and nerve roots. However, TLIF is unsuitable for patients with significant epidural scarring, arachnoiditis, fused or conjoined nerve roots, or osteoporosis.

• Advantages: The interlaminar surface of the contralateral side is preserved in TLIF, which can be used as an additional surface area for the fusion mass. Also, it can reduce risk of incidental neural complications because it only requires exposure of the ipsilateral neural foramen, unlike other techniques. TLIF is a safer technique above the L3 level with minimal risk of injuring the conus and is well-suited for reoperations where there is significant epidural fibrosis, as it only requires a lateral dural exposure on one side.
• Disadvantages: Experienced surgeons can usually avoid the uncommon disadvantages of TLIF, such as incomplete removal of the intervertebral disc, incomplete preparation of the vertebral endplate, and potential injury to the exiting nerve root. However, TLIF is unable to decompress the contralateral nerve root in the classic approach.

Surgical and Clinical Outcomes

TLIF is a more effective treatment for patients with degenerative lumbar scoliosis, as compared to posterolateral lumbar fusion. It achieves better restoration of lumbar lordosis and spinal sagittal balance by using interbody distraction and resecting posterior facet joints.

It is the preferred surgical approach for lumbar spinal fusion due to its lower risk of violating the spinal canal and causing morbidity, as compared to PLIF and ALIF. Despite a 14% complication rate, which includes problems such as haematoma, nerve root lesions, dural tears, and intraoperative pneumothorax, these issues can be effectively managed with drainage and appropriate follow-up.

Anterior LIF (ALIF)

The surgical technique of anterior lumbar interbody fusion (ALIF) was introduced in 1948 and is considered a salvage technique for patients experiencing painful pseudarthrosis following posterior lumbar fusion. While the anterior approach is an effective method for accessing the L5-S1 level, it is less efficient for levels above L3-L4.

• Advantages: direct visualization, enabling easier and complete discectomy, better distraction leading to higher fusion rates, and reduced iatrogenic trauma.
• Disadvantages: the drawbacks of ALIF include complications related to the surgical approach, such as hernias, bowel obstruction, venous thrombosis, urological injury, and retrograde ejaculation. Additionally, a separate posterior incision is required for decompression or fixation.

Surgical and Clinical Outcomes

ALIF is associated with higher interbody fusion rates compared to posterolateral approaches, as reported by Jackson et al., who observed ALIF fusion in 95.3% of patients with only minor complications.

According to a randomized controlled trial in the literature, changes in the whole lumbar lordosis were not found to be dependent on changes in the segmental angle at the fused segment during a 10-year follow-up period.

Extreme lateral LIF (LLIF/XLIF)

The use of the LLIF approach is considered a safe and effective alternative to the anterior or posterior approaches for lumbar fusion. The LLIF approach can be used to treat several conditions, such as degenerative disc disease, adult scoliosis, spondylolisthesis, and adjacent segment disease.

The LLIF approach involves three surgical pathways: lateral flank, retroperitoneal, and transpsoas, and it is important to have knowledge of critical structures such as the lumbar plexus. The LLIF approach permits the realignment of the spine in cases of de novo scoliosis in both the coronal and sagittal planes.

• Advantages: One of the advantages of the LLIF technique is its ability to access the anterior and middle columns of the lumbar spine through a small incision with minimal blood loss during surgery. With the LLIF technique, it is possible to access multiple levels from T11 to L4 through a transpsoas approach while preserving the posterior musculature and longitudinal ligaments of the spine.
  This approach is relatively easy to use, compared to others, and has the advantage of preserving these important structures. LLIF also offers the advantage of avoiding direct trauma to important structures such as the abdominal viscera, peritoneum, great iliac vessels, and sympathetic chain. Moreover, LLIF offers minimally invasive lumbar spine access, shorter operating times, and shorter hospital stays in comparison to other techniques.
• Disadvantages: The use of the LLIF technique is limited in cases of severe central stenosis and anatomical variations that may obstruct access to L4-5. Furthermore, due to the obstruction caused by the iliac crest, LLIF cannot be performed at the L5-S1 level.
  Furthermore, the LLIF approach has been associated with post-operative hip flexion weakness and thigh/groin pain, which may occur as a result of stretching or injury of the genitofemoral nerve during the procedure, according to reports.

Surgical and Clinical Outcomes

With optimal technique, LLIF has shown fusion rates similar to those of anterior and posterior approaches. There were no statistically significant differences observed between the different types of graft used to fill the cages.

LLIF is associated with a common post-operative side effect, known as thigh symptoms, which affects around 20% of patients. These symptoms include paresthesia, numbness, and motor weakness that affects hip flexion. The majority of these symptoms are temporary, with a recovery rate of 50% after three months and 90% after one year.

Oblique LIF (OLIF)

The OLIF approach, which stands for oblique trajectory anterior to psoas, uses a retroperitoneal plane to reach the disc through a corridor located in front of the iliac crests, between the major abdominal vessels and the psoas muscle.

The OLIF approach, unlike LLIF, does not involve the dissection and splitting of the psoas muscle, which could potentially reduce post-operative pain. The OLIF approach, which accesses the disc through a retroperitoneal plane anterior to the iliac crests between the psoas muscle and major abdominal vessels, is suitable for cases of degenerative disc disorders, discitis, pseudoarthrosis at L5-S1, and isthmic spondylolisthesis.

The approach involves inserting an intervertebral cage after disc space preparation and can be followed by posterior stabilization via open or percutaneous procedures, depending on the underlying condition.

• Advantages: The oblique trajectory utilized in the oblique trajectory anterior to psoas (ATP) approach (OLIF) allows for the avoidance of surgical trauma to the psoas and lumbosacral plexus, while enabling efficient clearance of the disc space and placement of a large interbody device for foraminal decompression.
  Additionally, the oblique trajectory of the OLIF approach offers a distinct angle that allows for visualization of the epidural space, aiding in the removal of ventral osteophytes and disc herniation.
  The OLIF approach is viewed as a possible solution to the challenges posed by ALIF (such as the risk of injury to the iliac vessels and peritoneum) and LLIF (which requires splitting of the psoas muscle and provides limited access to the lower lumbar spine).
• Disadvantages: Post-operative numbness, pain, and leg weakness are potential complications of OLIF. If the retroperitoneal oblique corridor (ROC) is narrow, greater psoas retraction may be necessary, which increases the likelihood of postoperative neurological complications in OLIF.

Surgical and clinical outcomes of OLIF

The success rate of achieving fusion with OLIF is high at 84% or more, and the surgery typically takes between 55 to 145 minutes with blood loss ranging from 67.8 to 260 ml.

However, there is a relatively high occurrence of perioperative complications such as endplate fracture/subsidence (18.7%), temporary psoas weakness and thigh numbness (13.5%), segmental artery injury (2.6%), surgical site infection (1.9%), and reoperation (1.9%). Permanent damage from the surgery is rare.