12.5.2 Initial Working Space and Bone Working (Fig. 12.3 and Video 12.1)
After positioning the endoscope and the semi-tubular retractor through each portal, the initial working space is made under endoscopic guidance. Coagulate the soft tissue overlying the cranial lamina using an RF probe to identify the inferior edge of the cranial lamina and the interlaminar space (Fig. 12.3a). Perform ipsilateral laminotomy using a Kerrison punch or round cutting burr, collecting autogenous bone for grafting, while leaving the ligamentum flavum (LF) as a protective barrier against neural injury. Continue the laminotomy until the cranial end of the LF is exposed (Fig. 12.3b, c).
Remove the inferior articular process (IAP) of the upper vertebra using multiple osteotomies to preserve autograft material (Fig. 12.3d, e). Ensure bone chips are appropriately sized for removal through the working portal to avoid paraspinal muscle injury. Perform bone work on the contralateral side through a sublaminar approach, removing the base of the spinous process and contralateral lamina using a round cutting burr or osteotome (Fig. 12.3f). Sufficiently remove the base of the spinous process to allow proper instrument and endoscope manipulation. Conduct contralateral facetectomy through a sublaminar approach to facilitate spondylolisthesis reduction and lordosis formation (Fig. 12.4a). In cases of prominent facet joint osteophytes or significant spondylolisthesis, create new portals on the contralateral side for total IAP removal (Fig. 12.4b).
12.5.3 Partial Removal of Superior Articular Process and Identification of Disc Space (Fig. 12.5 and Video 12.2)
Remove the superficial layer of ipsilateral LF to identify the upper portion of the caudal lamina and the medial aspect of the superior articular process (SAP) (Fig. 12.5a, b). Partially remove the upper portion of the caudal lamina using a Kerrison punch, continuing along the medial margins of the SAP, and detach the deep layer of the LF (Fig. 12.5c). Adequately resect the medial aspect of the SAP to provide sufficient space for cage insertion, ensuring a minimum distance of 8 mm from the lateral margin of the thecal sac to avoid retraction-related neurapraxia (Fig. 12.5d).
Once the deep layer of the ipsilateral LF is partially removed, identify the lateral margin of the thecal sac, ipsilateral traversing nerve root, pedicle of the lower vertebra, and disc space (Fig. 12.5e). Avoid fully exposing the ipsilateral exiting nerve root before cage insertion to protect it from neural injury during the procedure.
12.5.4 Annulotomy and Endplate Preparation (Fig. 12.6 and Video 12.2)
After exposing the ipsilateral disc space, coagulate the epidural vessels above the annulus using an RF probe. Perform an annulotomy with the RF probe, taking care to protect the thecal sac and nerve root (Fig. 12.6a). Use a Kerrison punch to remove the annulus fibrosus, facilitating further release of the disc space (Fig. 12.6b).
Remove the nucleus pulposus and cartilaginous endplate using angled endplate removers and pituitary forceps, ensuring meticulous endplate preparation to avoid bony endplate injury and prevent cage subsidence into the vertebral body. Detach the cartilaginous endplate from the bony endplate using various angled endplate removers (Fig. 12.6c). Adequately remove disc material and cartilaginous endplate on the contralateral side to ensure proper cage insertion. Utilize angled endplate removers and curved pituitary forceps for contralateral endplate preparation under endoscopic guidance. The 30° scope is beneficial for enhancing contralateral endplate preparation. Typically, 70%–80% of the disc space can be prepared for fusion with ULIF.
In patients with high-grade spondylolisthesis or significant disc narrowing, endplate preparation and cage insertion may be challenging. In such cases, remove the upper edge of the lower vertebral body with an osteotome to create a larger entry (Fig. 12.6d). The magnified endoscopic view ensures precise and complete endplate preparation (Fig. 12.6e).