Surgical technique

The patient undergoes general endotracheal anesthesia and is positioned prone on a Jackson table with a Wilson frame. Attention is given to maximize kyphosis of the patient, this may be achieved by raising the Wilson frame or adding rolls underneath the anterior superior iliac spine. Once the patient is prepped and draped, an AP X-ray is obtained to determine the appropriate level and the optimal craniocaudal angle of the surgical corridor. Typically, tilting the C-arm 10–15 degrees caudally from an initial endplate view of the caudal vertebral body allows to minimize removal of the inferior articular process. Utilizing the determined craniocaudal tilt, the skin incision is marked where the inferior margin of the lamina intersects with the middle of the disc space (Figure 3). A stab incision is made through skin and thoracolumbar fascia using an 11-blade. The trocar is advanced through the incision toward the inferior margin of the lamina. The caudal margin of the lamina is palpated with the trocar. Excessive movement of the trocar should be avoided to minimize muscular bleeding. Typically, one more confirmatory AP X-ray is obtained and the c-arm is moved out of the operative field. Then, the working cannula with the bevel facing medially is introduced over the trocar. The working cannula needs to be advanced until the lamina is palapated, insufficient advancement will lead in incomplete retraction of the paraspinal muscles. The trocar is then removed and the endoscope is introduced. The Trigger Flex bipolar electrode and micro punches are utilized to define the inferior margin of the lamina and the medial aspect of the facet joint.

Interlaminar approach. (A) Intraoperative AP X-ray depicting marking for the skin incision for a L4/5 medial facetectomy; (B) cartoon illustrating the lumbar spine; (C) boxed area in panel B depicts a close up of the lateral recess. The green area indicates bone removal of the inferior articular process and the blue area indicated the area of bony resection of the superior articular process. Note that an attempt is made to undercut the inferior articular process.

A high-speed diamond drill is used to resect the caudal portion of the rostral lamina and the medial aspect of the facet joint (Figures 3 and 4A​4A).). At this point, the yellow ligament is identified and dissected along its fibers under using the open micro punches (Figure 4B). Yellow ligament is resected piecemeal using micro punches and kerrison rongeurs. At this point the thecal sac is visualized and the lateral margin of the traversing nerve root is identified (Figure 4C). The high speed diamond drill is used to undercut the facet joint until the lateral margin of the traversing nerve root is decompressed. Given the 25 off axis optics of the endoscope, rotation of the endoscope helps with direct visualization of the nerve root and to undercut the facet joint. At this point the superior articular process is identified. It is resected along the lateral margin of the traversing nerve root together with the most rostral part of the rostral portion of the next level lamina (Figure 4D). Gentle lateral pressure onto the inferior articular process facilitates undercutting of the joint. Once the traversing nerve is visualized it is mobilized using the blunt dissector. Adhesions that cannot be freed by blunt dissection are sharply dissected using the scissors and/or Trigger Flex. The annulus and endplates anterior to the traversing nerve root are visualized. Once the nerve is mobilized a small side biting drill is used to obtain a smooth bony edge lateral to the nerve root. Direct visualization of the traversing nerve root should be obtained from the tip of the superior articulating facet to the midpedicular line of the caudal pedicle, which may be verified using fluoroscopy.

Intraoperative steps for lateral recess decompression. (A) Following resection of the medial portion of the inferior articular process (i) the superomedial aspect of the superior articular process is exposed; (B) resection of the yellow ligament is carried out using micropunches; (C) following resection of the yellow ligament the traversing nerve root (t) is exposed. A small synovial cyst (arrow head) is seen along the medial aspect of the superior articular process (s); (D) complete decompression of the traversing nerve root (t) is achieved by resecting the synovial cyst and medial portion of the superior articular process.

Once hemostasis is achieved the endoscope and working cannula are removed. Closure is carried out in a layered fashion, with 0 Vicryls for the subcutaneous tissue, followed by a subcuticular 4-0 biosyn for the skin. Steri strips are placed to approximate the wound edges and the wound is covered with primapore.