Anterolateral approaches to the lumbar spine provide direct access to the disc space. These techniques facilitate thorough discectomy, which is essential for successful arthrodesis. They improve segmental lordosis without osteotomy and indirectly decompress neural elements in carefully selected patients. Benefits include shorter operative times, reduced blood loss, and rapid postoperative mobilization compared to posterior approaches. Each technique has specific advantages and limitations, thus none is inherently superior to another. Detailed knowledge of these techniques is essential for modern spine surgeon to provide personalized operative plan for each patient.
Key points
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Anterolateral interbody techniques allow large interbody placement without extensive posterolateral bony work. Advantages include optimal lordosis, indirect decompression, and high arthrodesis rate with low subsidence risk.
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Anterior lumbar interbody fusion is especially useful at L5 to S1, requiring an access surgeon and repositioning for posterior instrumentation.
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Lateral lumbar interbody fusion (LLIF) is transpsoas, reducing vascular injury risk but increasing transient psoas dysfunction and lumbar plexopathy risk. The lumbosacral junction is not accessible via LLIF. Anterior column realignment with anterior longitudinal ligament resection is a potent LLIF variant for sagittal correction.
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Oblique lumbar interbody fusion (OLIF) can access the entire lumbar spine, including the lumbosacral junction, using a prepsoas corridor. An access surgeon at L5 to S1 is needed to prevent vascular complications. The OLIF approach is limited to the left side to avoid manipulating venous structures. The prepsoas approach minimizes, but does not eliminate, psoas and lumbar plexus injury.
Introduction
Historically, lumbar interbody fusions were done using a posterior approach, needing direct neural decompression and small grafts through Kambin’s triangle. Anterior lumbar interbody fusion (ALIF) and lateral approaches, either prepsoas oblique lumbar interbody fusion (OLIF) or transpsoas lateral lumbar interbody fusion (LLIF), offer direct disc space access without posterior bony work. These anterolateral approaches, free from constraints of Kambin’s triangle and posterior neural elements, enable comprehensive discectomy and larger graft insertion, enhancing segmental lordosis and indirect neural decompression. Spine surgeons must intimately know each technique to use them appropriately. This article overviews each surgical technique, their advantages and disadvantages, specific indications, and unique complications.
Anterior lumbar interbody fusion
Technique
Described in the 1930s by Capener, the ALIF technique provides maximum anterior access to the disc space. It allows for extensive discectomy and resection of the anterior longitudinal ligament (ALL) to enhance lordosis, and the placement of large interbody grafts.
A general or vascular surgeon is typically required to mobilize the peritoneum and vasculature to gain spinal access. With the patient supine, a transverse Pfannenstiel incision is made. For levels above L4 to L5 or multiple levels, a paramedian vertical incision is used. The anterior and posterior rectus sheath and muscles are mobilized. Peritoneum is bluntly swept revealing the retroperitoneum, which contains the iliac vessels. The iliac bifurcation occurs proximal to L5 to S1, providing a midline corridor for lumbosacral junction access, whereas lateral mobilization of the iliac vessels is necessary above this level. Once the spine is reached, retractors are positioned to protect the vessels and peritoneum. Wide discectomy is completed, followed by endplate preparation. After trialing, an appropriately sized interbody is placed and secured to the vertebral bodies using screw fixation or a plate.
Advantages and Disadvantages
The ALIF technique offers multiple advantages, including thorough discectomy and endplate preparation due to direct visualization and a relatively large working space, promoting arthrodesis and reducing subsidence risk. The incision of the ALL allows for the placement of large, hyperlordotic interbody grafts, which enable large segmental lordosis and indirect foraminal decompression through distraction across the disc space. ALIF has several disadvantages. Although some spine surgeons forgo an access surgeon, we advocate for access surgeons due to the risk of visceral and vascular complications. Repositioning the patient prone for posterior instrumentation prolongs operative times.
Indications/Contraindications
Indications for ALIF include degenerative disc disease, spondylolisthesis, spondylosis, and adult spinal deformity correction. Due to the iliac bifurcation, L5 to S1 is the most common level for ALIF. Imaging review is necessary to identify vascular anomalies. In multilevel fusion including L5 to S1, ALIF may be preferred, provided an access surgeon can safely mobilize proximal vessels. Other favorable indications include failed prior direct decompressions with persistent radiculopathy, complicated posterior approaches, and distal adjacent segment disease affecting L5 to S1.
Contraindications to ALIF include general spine fusion concerns, such as obesity, uncontrolled diabetes, and osteoporosis. Specific ALIF considerations include truncal obesity, retroperitoneal scarring (from prior abdominal surgery, radiation, or infection ), and severe vascular disease (eg, aortic atherosclerosis).
Complications and Avoidance
ALIF-specific complications are associated with the anterior approach. Rarely, direct vascular injury can occur, leading to significant blood loss. Large bore suction and cell saver in ALIF procedures facilitates rapid volume replacement if necessary. Risk of vascular injury requiring repair ranges from 1.9% to 4.6%, , with opioid use and multilevel ALIF as independent predictors. Excessive and/or prolonged vessel compression resulting from retraction may lead to vessel occlusion, causing either deep venous thrombosis in veins or limb ischemia in arteries. Use of pulse oximetry on lower extremities can alert the surgical team to potential limb ischemia. Retrograde ejaculation arising from injury to the superior hypogastric plexus, especially at L5 to S1, may occur in 0.3% to 9.8% of patients. , Although it can resolve spontaneously, counseling is essential for patients, especially young male individuals who may be planning to start a family. Female sexual dysfunction is poorly characterized; nonetheless, we recommend limiting electrocautery to mitigate this risk. Ileus is a significant complication, resulting from surgical manipulation of the intestines with incidence ranging from 2.9% to 10.2%. Ileus mitigation following surgery includes early mobilization, early diet, scheduled bowel regimen, multimodal pain control with narcotics minimization, and pharmacologic intervention with peripheral mu-receptor antagonists.
Case Example of Anterior Lumbar Interbody Fusion: Grade II L5 to S1 Spondylolisthesis
This is a case of a woman in her 40s with a long history of back and leg pain. Preoperative imaging ( Fig. 1 A–C ) showed transitional anatomy and grade II isthmic spondylolisthesis at L5 to S1. After failing conservative management, she was counseled for L5 to S1 ALIF with percutaneous pedicle screw fixation. Her history of laparoscopic cholecystectomy was not a contraindication for ALIF. Preoperative MRI (see Fig. 1 C, inset) indicated a favorable operative corridor, and a vascular surgeon assisted. The spondylolisthesis was reduced without osteotomies, and segmental lordosis improved from 28° to 36° ( Fig. 1 D, E). Her postoperative course was uneventful, and she was discharged after 2 days. At 6 month follow-up, she reported persistent improvement in her symptoms.
Lateral lumbar interbody fusion
Technique
The classification of lateral techniques for lumbar interbody fusion is based on the approach corridor relative to the psoas muscle. LLIF denotes the transpsoas technique, performed with the patient in the lateral decubitus (lateral transpsoas), or prone position (prone transpsoas). In this discussion, we focus on the lateral transpsoas approach, referred to as LLIF. Specific considerations related to the prone transpsoas technique will be provided where applicable.
Historically, lateral retroperiotoneal techniques required large incisions to directly visualize the psoas, before gaining access to the disc space, and were used as a last resort. However, the modern technique, described Ozgur and colleagues in 2006, utilized real-time neuromonitoring with smaller incisions and less disruptive dissection, leading to widespread adoption.
In LLIF, the patient is placed in a lateral decubitus position with gentle hip and knee flexion to relax the psoas muscle and reduce lumbar plexus tension. The iliac crest is positioned at the table break, with a small roll above it acting as a fulcrum. The patient is secured with tape. The incision is centered around the middle of the disc space visualized on anteroposterior (AP)/lateral views fluoroscopically.
An access surgeon is not typically needed. After skin incision and fascial opening, electrocautery is no longer used. The external and internal oblique and transversus abdominis muscles are dissected bluntly. The retroperitoneal space is entered by piercing the transversalis fascia and sweeping the peritoneal fat anteriorly off the psoas muscle with finger dissection. The psoas muscle striations should be palpated without intervening fat. Posteriorly, the quadratus lumborum and transverse process can be palpated to approximate the introduction point for dilation. The dilator is docked shallowly over the disc space, avoiding psoas disruption. Lateral fluoroscopic confirmation is necessary to adjust the position of the dilator. Electromyography is used to place the retractor anterior to the lumbar plexus. A guide wire is used to enter the disc space, followed by sequential dilators. A specialized lateral retractor is placed over the final dilator and secured with a docking shim. Discectomy is completed, with opening of bilateral annuli with a Cobb elevator, followed by careful endplate preparation. After trialing, an appropriate interbody is placed.
A lateral plate does not replace the need for pedicle screw fixation if stabilization is required. Biomechanical studies demonstrate lateral plates offer minimal advantage, mainly in decreased lateral bending. If the ALL is inadvertently compromised, the plate is necessary for graft stabilization. Anterior column release (ACR, or anterior column realignment) is a variation of LLIF whereby the ALL is intentionally released. ACR-LLIF is a powerful technique for the correction of adult spinal deformity through focal hyperlordosis, akin to ALIF, and can be combined with posterior osteotomies for further correction. In this technique, a blunt retractor anterior to the ALL protects vasculature while a sharp blade incises the ALL. When the ALL is thinned, distraction across the disc space allows full release. Due to the destabilizing nature of ACR-LLIF, a lateral plate is necessary to secure the interbody graft.
Advantages and Disadvantages
The modern LLIF approach offers several advantages. It eliminates the need for an access surgeon and allows easy access to the disc space for thorough discectomy and large interbody placement. This results in indirect decompression and high fusion rates. LLIF is a powerful tool for correcting segmental and regional coronal and sagittal malalignment, with enhanced sagittal correction when combined with ACR. The prone transpsoas technique further increases segmental lordosis due to gravity and allows simultaneous access to the posterior column, improving operating room efficiency by eliminating the need for repositioning. LLIF can be performed from the left or right, unlike OLIF, which is restricted to the left to avoid venous injury.
Modern LLIF uses a small incision, reducing tissue disruption and speeding recovery. However, it poses unique disadvantages with poor visualization and unfamiliarity with retroperitoneal anatomy, making visceral injury subtle and vascular injury life-threatening. Identifying a safe corridor in the psoas, which contains the lumbar plexus, is crucial, especially at L4 to L5 due to the anterior location of the femoral nerve. Early adoption of this technique saw a high nerve palsy at 4.8% for L4 to L5, but 1.7% across all levels. Improved understanding of electromyography (EMG), and the addition of motor-evoked potential (MEP) and somatosensory-evoked potential (SSEP), has enhanced LLIF safety. In the prone position, the psoas migrates posteriorly, enlarging the safe corridor. A high-rising iliac crest may inhibit L4 to L5 access; our preferred method involves entering the disc space at an angle permitted by the iliac crest, then pivoting the retractor around the shim for near orthogonal orientation to the disc space. We use angled instruments to maintain parallel orientation to the endplates. LLIF is unsuitable for the lumbosacral junction due to the iliac crest and the anterior location of the psoas and neurovascular structures.
Indication/Contraindication
LLIF is suitable for a broad range of spinal pathologies, including spinal stenosis, degenerative disc disease, spondylolisthesis/spondylosis, and adjacent segment disease. It is effective for adult deformity correction and lordosis induction, especially when combined with ACR and posterior osteotomies. LLIF can be used for corpectomy in infectious, traumatic, and oncologic conditions in the lumbar and thoracic spine and is arguably the most versatile anterolateral approach.
Contraindications to LLIF are those applicable to any interbody fusion. Indirect decompression is less effective with bony or hypertrophic ligament stenosis. Truncal obesity is a relative contraindication to prone transpsoas. Other contraindications specific to LLIF include unfavorable vascular anatomy, anteriorly transposed psoas muscle, and prior retroperitoneal surgery on the side of the intended approach. Some authors report high-grade spondylolisthesis as a contraindication for LLIF due to bony compression in the lateral recess, which may not respond to indirect decompression. However, in carefully selected patients, LLIF can still yield successful outcomes.
Complications and Avoidance
The LLIF approach poses a unique set of risks and complications. Visceral or vascular injury is rare, but can occur due to the proximity of these structures to/within the retroperitoneal space. Abdominal wall pseudohernia may result from iatrogenic nerve injury to the subcostal, iliohypogastric, or ilioinguinal nerves during the approach, resulting in bulging of the abdominal wall without an actual muscle defect. The extent of abdominal wall muscle dissection and electrocautery current setting are contributory. Pseudohernias often resolve with reinnervation of abdominal wall muscles. True incisional hernia involves an actual defect in the abdominal wall and, thus, has the potential to entrap bowel loops and lead to bowel obstruction or strangulation. Proper diagnosis and differentiation between pseuodhernia and hernia are crucial for appropriate management.
LLIF can cause transient psoas muscle weakness, often mistaken for neurologic injury, due to stretch trauma or inflammation, which typically recovers spontaneously within 2 to 6 weeks. Peritoneal, ureteral, and major vessels injuries are rare but serious. Neurologic complications in LLIF are classified as either transient or persistent. Transient symptoms result from compression or traction of the lumbar plexus include thigh pain, numbness, weakness, and often resolve within 6 weeks to 6 months. Compression may occur when retractor blades are opened perpendicular to the long axis of a nerve, while traction occurs when they are opened parallel to it. Persistent neurologic deficits are rare and have become less prevalent with improved neuromonitoring techniques.
The most common peripheral nerve injury involves the femoral nerve, particularly at L4 to L5, and presenting with hip flexion and knee extension weakness. Femoral nerve injury can occur intraoperatively without changes in neuromonitoring modalities, especially electromyography. Other neuromonitoring modalities, including MEP and saphenous nerve SSEP, may confer an advantage, but no modality has been shown to be 100% sensitive and/or specific. It is impossible to distinguish transient (neuropraxia) versus persistent (axonotmesis/neurotmesis) nerve injury immediately after surgery. Therefore, close monitoring of the symptoms is necessary, and nerve injury is better characterized at 6 to 12 weeks with electromyography. Persistent injury to the femoral nerve causes significant quadriceps atrophy, leading to ambulatory difficulty.
Case Example of Lateral Lumbar Interbody Fusion: Grade I L4 to L5 Spondylolisthesis
This case involves a man in his 60s with a long history of back pain and neurogenic claudication. Preoperative imaging ( Fig. 2 A–D ) showed degenerative grade I spondylolisthesis at L4 to L5 with severe stenosis. After conservative management failed, he was advised to undergo L4 to L5 LLIF with percutaneous pedicle screw fixation. With no history of retroperitoneal surgery, his anatomy was suitable for the LLIF approach from either side (see Fig. 2 D, inset). The right side was chosen due to better orientation and less collapse in the coronal plane (see Fig. 2 C), allowing easier maneuvering around the iliac crest. The OLIF was not chosen due to the less favorable left-sided approach, and ALIF was unsuitable due to unfavorable vascular anatomy at L4 to L5 and the need for a vascular surgeon. The spondylolisthesis was reduced successfully without osteotomies, and indirect decompression relieved the stenosis ( Fig. 2 E–H). His postoperative course was uneventful, and he was discharged after 1 day. At the 9 month follow-up, he reported persistent improvement in back pain and resolution of neurogenic claudication.
