22.2.1 Anterior Approach

Lumbar spine pathologies have been addressed via an anterior approach for decades. ³ The transperitoneal and retroperitoneal ALIF are widely used techniques for degenerative disk disease as well as deformity correction.

The anterior approach to the lumbar spine has many advantages. A large graft can be inserted, as there is access to the entirety of the anterior disk space. This allows for restoration of disk height and lordosis, as well as providing a large fusion surface. Releasing the anterior longitudinal ligament, which is required to access the disk, also assists with deformity correction. The amount of lordosis gained from a single interbody fusion alone is typically between 4° and 10°. ^{4 ,​ 5 ,​ 6} The disk height restoration has the added benefit of indirectly decompressing the neural foramen, increasing foraminal height by up to 18%. ⁷

The Food and Drug Administration (FDA) approved the use of bone morphogenic protein (BMP) in ALIF. The large fusion surface provided by the ALIF, along with the use of BMP, can give fusion rates greater than 90% at 12 months. ⁸ Combining this approach with posterior decompressions and fusions can give dramatic deformity corrections and improved patient-reported outcomes. ⁹

Both the transperitoneal and retroperitoneal approaches may involve mobilizing major vasculature. This may necessitate the use of an approach surgeon. The L5-S1 disk can typically be accessed in the bifurcation of the iliac veins. Above L5-S1, the vena cava and aorta will likely have to be mobilized laterally. Care must be taken to avoid tearing the iliolumbar vein on the left when exposing L4-L5, as it can retract and cause significant bleeding. While vascular injuries are rare with this approach, they are a possibility and the patient must be counseled about the risks. ¹⁰ Manipulation and prolonged retraction of these vessels can also lead to an increased deep vein thrombosis rate. ^{10 ,​ 11} The use of neuromonitoring and pulse oximetry on the foot can alert the operating team to intraoperative ischemia from vessel retraction.

Abdominal surgery carries a higher risk of postoperative ileus. This complicates pain management as it can be aggravated by opioid analgesics. Patients’ diets should be advanced slowly after this procedure. Even more serious is acute colonic pseudo-obstruction, which occurs after manipulation of the sacral plexus and disrupts colonic autonomic function. This uncommon condition can lead to cecal perforation. This can be treated by bowel rest, nasogastric suctioning, enemas, neostigmine, and, if needed, colonoscopic decompression. ¹¹

Injury to the superior hypogastric plexus can cause retrograde ejaculation in male patients. The rates have been reported from 1% to 45%. ^{8 ,​ 12} These rates may be increased with BMP usage and laparoscopic approaches. ^{12 ,​ 13 ,​ 14} Other complications can include abdominal hernia, wound infection, ureter injury, retroperitoneal hematoma, and lymphocele. ^{5 ,​ 15}

Fig. 22‑1 demonstrates an example of a 77-year-old female who presented with low back pain and was found to have degenerative scoliosis and spondylolisthesis. She underwent an anterior retroperitoneal approach, and she had 8° cages placed at L2-L3 and L3-L4, a 15° cage placed at L4-L5, and a 20° cage placed at L5-S1. BMP was used for fusion. The cages were secured with anterior screw fixation, and she had posterior instrumentation via an MIS approach using intraoperative computed tomography (CT) and navigation. She also had MIS laminoforaminotomies at L1-L2, L2-L3, and L4-L5.

22.2.2 Transpsoas Lateral Approach

The transpsoas lateral technique provides access to the lumbar disk space without many of the complications associated with the anterior procedure. By dissecting through the psoas muscle, the lateral lumbar spine can be accessed. This allows for interbody grafts to be inserted that span the apophyseal ring.

This procedure is done from the lateral position in a completely retroperitoneal trajectory. The approach is perpendicular to the spine and patient positioning is key to ensure this angle. If fluoroscopy is to be used, the patient must be positioned in a true lateral position. This helps ensure perpendicular trajectories, decreases the chances that anterior structures will be injured, and provides clear fluoroscopic guidance. Navigation can also be used for this approach, which decreases the amount of radiation exposure.

If L4-L5 is to be fused, standing radiographs must be examined preoperatively as iliac crest height will determine accessibility. If the iliac crest height is above the disk space, another approach should be considered, as it may be difficult to access the disk space.

Another benefit to the lateral approach is correction of coronal deformity. Approaching from the concavity of the curve allows for asymmetric disk degeneration to be addressed. Upward of 20° of coronal correction are reported in the literature with the use of a lateral approach. ¹⁶

Whereas coronal correction is achieved with the lateral approach, it may not have the same benefit as the anterior approach with respect to lordosis. ¹⁷ This is because the approach does not routinely release the anterior longitudinal ligament, as the ALIF does. However, if anterior column release is added to the lateral approach, better lumbar lordosis (LL) correction can be achieved as well. ^{18 ,​ 19}

Härtl et al showed a lower overall complication rate with lateral approaches in a meta-analysis comparing it to the ALIF. However, the transpsoas lateral approach did have a higher rate of neurologic complications. ¹⁰ This is because of the various nerves that run superficial to or within the psoas muscle, the most commonly injured or stretched being the femoral or genitofemoral nerves.

Injuries to these nerves can lead to anterolateral thigh/groin pain and numbness or hip flexor/quadriceps weakness. These nerves lie in the posterior third of the plexus and can be avoided either with triggered electromyography monitoring or by dissecting them under direct visualization. ²⁰ Even with these techniques, thigh numbness can occur in up to 40% of patients and weakness in up to 55%. ²¹ A meta-analysis by Joseph et al ²² showed a 9.4% transient and 2.5% permanent deficit with the transpsoas lateral approach, along with a 27.1% rate of sensory deficits.

Other complications secondary to this approach include injuries to the retroperitoneal structures. While the lateral approach has fewer incidents of this than the anterior approach, injuries to the great vessels and even abdominal viscera are still possible. ^{23 ,​ 24} Distortions of the anatomy as a result of the degenerative scoliosis can increase the chances of this. ²⁵ Pseudohernia is also a possible complication. ²⁶

Fig. 22‑2 demonstrates an example of deformity correction via the lateral approach. The patient presented with degenerative scoliosis and lumbar stenosis, and underwent an L2-L3, L3-L4, and L4-L5 lateral retroperitoneal exposure and interbody fusion. Neuromonitoring was used. The patient underwent a minimally invasive posterior instrumentation as a separate procedure.