General
- This combined approach is required because the unique anatomy of the lower lumbar spine presents technical challenges to a purely posterior approach, primarily due to the presence of the iliac wing and the critical need to preserve the lumbosacral plexus nerves.
Indication
- Complex spinal tumors located in the lower lumbar spine, typically at the levels of L3 to L5.
- Dealing with Type 5 or 6 tumors (paravertebral or adjacent vertebral extension) where major vessels are compressed or involved.
- This staged procedure minimizes the high risk of vascular injury associated with posterior-only approaches in the lower lumbar region.
Surgical steps
Posterior Approach (Preparation and Stabilization)
- Exposure: A posterior midline incision is made, and the paraspinal muscles are dissected and retracted.
- Laminectomy: En bloc laminectomy (resection of the posterior element) is performed, typically using a T-saw pediculotomy.
- Nerve Root Dissection:
- Lumbar nerve roots at the involved level(s) are preserved, unless they are involved by the tumor.
- The nerve roots are meticulously dissected from the vertebral body to their conjunction with the neighboring lumbar nerves.
- Dural Mobilization:
- The dural tube is dissected from the posterior longitudinal ligament (PLL) or the epidural tumor. Ligamentous tissues between the dural tube/lumbar nerves and the PLL are cut off.
- Psoas Dissection:
- The psoas muscle is dissected from the lateral wall of the vertebral body.
- Posterior Half Osteotomy (Pre-cutting):
- The posterior halves of the craniocaudal adjacent discs of the tumor vertebra are excised. If the cutting level is at the vertebral body, a cutting line is made into the posterior half of the vertebral body using a high-speed drill.
- Nerve Protection:
- An artificial sheet (e.g., Gore-Tex Patch) is placed between the lumbar nerves and the tumor vertebral body to separate them, serving as a landmark for the subsequent anterior approach.
- Temporary Stabilization:
- Posterior instrumented segmental fixation (typically 2 levels above and 2 levels below) is performed to maintain stability for the anterior stage.
Anterior Approach (En Bloc Corpectomy)
- Timing: This stage is often performed after a period of time following the posterior stage.
- Access Route: The approach differs based on the level:
- Above L4/L5: An anterolateral extraperitoneal approach is generally indicated.
- L5 (or L4) Level: An anterior midline transperitoneal approach is indicated.
- Vascular and Nerve Management:
- Major Vessel Dissection: Major vessels (descending aorta, inferior vena cava, and common iliac arteries/veins) are meticulously dissected from the tumor and retracted. A vascular surgeon may be required to dissect vessels if the tumor adheres to or involves them.
- Segmental Vessels: The bilateral segmental vessels of the corresponding level(s) are ligated and cut off.
- Anterior Half Osteotomy:
- The anterior halves of the craniocaudal adjacent discs (or vertebral body) are excised or cut off using a high-speed drill at the precutting level established in Step 1.
- En Bloc Removal:
- The tumor vertebral body(ies) is(are) removed en bloc while retracting the major vessels aside.
- Anterior Reconstruction:
- A vertebral spacer (e.g., titanium mesh cylinder with bone graft) is properly inserted into the defect to provide anterior column support.
Posterior Approach (Finalization and Compression)
- Reconstruction Adjustment: If a titanium cage was used for anterior reconstruction, the posterior approach is performed again (Step 3).
- Spinal Shortening: The posterior instrumentation is adjusted to slightly compress the inserted vertebral spacer. This process of spinal shortening increases the spinal stability of both the anterior and posterior columns and has been linked to an increment in spinal cord blood flow.
- Connector Devices: If two or three vertebrae were resected, the application of a connector device between the posterior rods and the anterior spacer is recommended to secure spinal stability.
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