Overview

Anterior lumbar spinal surgery has been performed in various forms for decades. Müller described an anterior approach to the lumbar spine as early as 1906, and the anterior approach was later popularized by Hodgson for the treatment of spinal tuberculosis. In 1948, Lane described a transperitoneal approach specifically designed for anterior lumbar diskectomy and fusion. That approach, however, requires opening the peritoneum and mobilizing the bowel. Harmon later described a modification through the retroperitoneum that enables the operator to access the lumbar spine without intentionally violating the peritoneum.

The desire to access the anterior elements of the lumbar spine has increased because of the possibility of improving fusion rates and gaining better sagittal balance with the application of anterior interbody devices. Classically, the retroperitoneal approach is performed through an incision through the abdominal wall. The incision may be paramedian, midline, or Pfannenstiel. Although the Pfannenstiel incision is the most cosmetic, it is nonextensible and is therefore used for single-level access to L5–S1 alone. In recent years, minimally invasive techniques have been developed that have included laparoscopic and mini–open approaches; however, these techniques are technically challenging, and they have not decreased many of the unwanted complications, nor have they consistently provided significant benefits over open techniques. Because of the perceived benefits of the interbody fusion, however, the search for safer techniques to gain access to the anterior vertebral elements continues.

The latest technique gains exposure via a less invasive lateral approach through the retroperitoneal fat and psoas major muscle. This approach, may circumvent some of the potential complications encountered in the anterior transperitoneal approach, such as visceral, vascular, and ureteral injury and sexual dysfunction in males. Additionally, it can be very useful in revision surgery of the upper lumbar spine to avoid previously operated tissue.

This chapter describes the various retroperitoneal approaches to the lumbar spine and its junctions, using both open and minimally invasive surgical (MIS) techniques.

Anatomy Review

Understanding the classic anatomy is the basis for performing these techniques, but that alone is not sufficient preparation. Evaluating the patient-specific anatomy and potential anatomic variants is absolutely critical to performing these techniques safely.

The open anterior surgical dissection is performed through the anterior abdominal wall, which consists of the skin, subcutaneous fat, Scarpa fascia, rectus abdominis muscle, transversalis fascia, and preperitoneal fat. The linea alba is the fascial condensation encountered at the midline, between the left and right rectus abdominis muscles. The lateral musculature, from superficial to deep, includes the external oblique, internal oblique, and transversus abdominis muscles ( Fig. 37-1 ).

Paramedian approach demonstrates the muscular anatomy of the anterior abdomen.

The umbilicus is generally located at the L3–L4 disk space; the L4–L5 disk space is often located at the level of the iliac crests ( Fig. 37-2 ). Access to L4–L5 and L5–S1 can be gained through an incision from the umbilicus to the pubic symphysis. Access to the upper lumbar disks requires extending the incision proximal to the umbilicus.

Lumbar disk levels with respect to surface anatomy of the abdomen.

The abdominal vault is encountered deep to the abdominal wall, and it houses the peritoneum and the intraperitoneal contents. Posterior to the peritoneum are the retroperitoneal structures. The aorta generally bifurcates into the common iliac arteries at the L4–L5 disk level and into the inferior vena cava bifurcates at the L5 body level. The vena cava is most commonly posterior and to the right of the aorta, and the iliolumbar vein usually drains into the common iliac vein at the level of the L5 vertebral body. The ascending lumbar vein may be present as a branch off the iliolumbar system or as a separate vein that arises directly off of the common iliac vein. The middle sacral vessels run anteriorly along the lowest lumbar vertebra and the sacrum ( Fig. 37-3 ). It is extremely important to review the patient-specific vascular anatomy to determine whether any variation is present that could preclude a safe surgical approach, specifically when access to the L4–L5 level is required.

Venous anatomy in the lumbar region. The inferior vena cava is shown bifurcating at the level of the L5 body. Ascending lumbar veins are visualized arising from the common iliac veins bilaterally, and the middle sacral vein is shown crossing the L5–S1 disk. ( The iliolumbar vein is not shown. )

The psoas muscles run bilaterally along the lateral borders of the lumbar spine, and the ureters lie on the anterior psoas and cross over the common iliac vessels at the level of the sacroiliac joint. The sympathetic trunk runs along the lateral borders of the lumbar vertebral bodies ( Fig. 37-4 ), generally located directly on or near the medial origin of the psoas. The sympathetic trunk is often well fixed to the disk by a very dense, fascialike connective tissue layer at L2–L3, L3–L4, and L4–L5 disk levels, and it is slightly separated from the bony surfaces of the vertebral bodies. Caudad, the sympathetic chain commonly runs vertically to pass beneath the common iliac vein and artery. Injury to the sympathetic trunk blocks normal vasoconstriction of the extremity vasculature, which can result in temperature discrepancies in the lower extremities. The extremity on the affected side will feel warmer as a result of unopposed vasodilation. Nursing staff will often report that the contralateral extremity is cold.

Retraction of the psoas allows visualization of the sympathetic trunk on the lateral borders of the lumbar vertebral bodies.

The superior hypogastric plexus is an extension of the aortic plexus lying in the extraperitoneal connective tissue anterior to the distal aorta and aortic bifurcation. It usually drapes over the L5–S1 disk space as a “leash” of fibers, but it can be present as a single trunk or as parallel strands. Generally, it is located just left of midline before dividing into left and right hypogastric nerves. This plexus mediates contraction of the internal vesicular sphincter during normal ejaculation. Failure of the vesicular sphincter to contract during ejaculation causes retrograde flow of semen into the bladder, a complication known to occur in up to 20% of anterior cases. Retrograde ejaculation may cause infertility in men who have undergone anterior lumbar surgery.

The cisterna chyli is a dilated sac at the end of the thoracic duct that acts as a conduit for lymph from the intestinal tract and lumbar trunks. It is most commonly located on the anterior aspect of the first and second lumbar vertebral bodies just posterior to the aorta and adjacent to the right crus of the diaphragm. Damage to the cisterna chyli can occur with anterior approaches to the upper lumbar and lower thoracic spine. Traumatic injury to the cisterna chyli or thoracic duct within the abdomen can lead to chyloperitoneum, and an injury at a thoracic level can lead to chylothorax. If injury occurs, conservative treatment should be instituted, such as thoracentesis, bowel rest and/or tube drainage, parenteral nutrition, and a restricted-fat diet. If drainage persists, exploration may be required to ligate ducts. Intraoperative discovery of an injury can be treated with ligation or repair; however, ligation of the ducts can lead to lymphedema of the extremities.

Retroperitoneal access to the lumbar spine from the lateral approach is performed through the lateral abdominal wall (i.e., the external and internal oblique and transversus abdominis musculature), the retroperitoneal fat, and the psoas muscle. The superior edge of the iliac crest limits the potential exposure of the inferior lumbar levels. During open dissection anterior to the psoas, the surgeon must again be aware of the location of the ureters overlying the psoas and the sympathetic trunk on the lateral borders of the lumbar vertebral bodies.

During the direct lateral approach, the lumbar plexus anatomy must be carefully considered. The anterior rami of the L1–L4 nerves coalesce within the psoas muscle to form this plexus, which gives rise to the iliohypogastric (T12–L1), ilioinguinal (L1), genitofemoral (L1–L2), lateral femoral cutaneous (L2–L3), obturator (L2–L4), and femoral nerves (L2–L4). All but the genitofemoral nerve pass through the posterior portion of the psoas before exiting. The genitofemoral nerve travels within the psoas in a posterior-to-anterior direction between L3 and L4, exiting the anterior aspect of the psoas then traveling along its anterior aspect. Nerve injuries can occur during the transpsoas dissection, leading to significant thigh and groin numbness and weakness of the iliopsoas and quadriceps muscles.

General Indications

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  Interbody fusion

  
  
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  Spondylolisthesis correction

  
  
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  Pseudarthrosis management

  
  
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  Deformity correction

  
  
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  Fracture

  
  
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  Tumor

  
  
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  Infection

Contraindications