This is a retrospective cohort non-inferiority study conducted on three hospital in Jakarta, Indonesia. Data were collected from January 2016-April 2020; all patients were followed up until one year duration. On that period, we found 202 patients eligible for interbody fusion procedure. The inclusion criteria were grade 1 or 2 single level degenerative spondylolisthesis with mechanical back pain and neurological symptoms. Exclusion criteria were operation other than interbody fusion, previous spinal instrumentation, spinal tumor, fracture or infection pathology, failed to be followed up until one year or patients refused to be involved as a research subject.
All patients had already underwent conservative management for at least 3 months with no improvement in clinical symptoms. Pre-operative examination consists of anteroposterior, lateral and dynamic (flexion and extension) lumbar xray, non-contrast lumbar magnetic resonance imaging.
Evaluation of clinical parameter using back and leg visual analog scale (VAS), Oswestry Disability Index (ODI) and SF-36. All clinical parameter was evaluated before surgery, 3rd, 6th, and 12th months after surgery. Radiological examination of lumbar anteroposterior, lateral and dynamic xray were conducted concurrent with the clinical evaluation. On the 12th months after surgery we did CT scan to evaluate fusion.
Of the 170 patients eligible for TLIF procedure, 14 patients refused to be research subject. There were 80 patients underwent conventional MIS TLIF and 76 patients underwent unilateral biportal endoscopic lumbar interbody fusion (ULIF) procedure. On final followed up, there were 73 patients on conventional MIS TLIF group and 72 patients on ULIF group, the rest of the patients were loss to be followed up.
Surgical Techniques For Unilateral Biportal Endoscopic Interbody Fusion
Position, anesthesia and approach
Patients were positioned prone with 2 bolsters lying transverse on the chest and the anterior superior iliac spine. This position helps us opening the interlaminar window at the beginning of the procedure by jacking up the table and maintaining lumbar lordosis by neutraling the table at the end of procedure while inserting the interbody cages. In our center we mostly use general anesthesia for the procedure, even though in several patient with not good medical condition we sometimes use regional anesthesia. We think that general anesthesia provides more comfort for the patients and easier for mean arterial pressure maintenance during surgery.
We use biportal technique, in which the viewing portal and working are positioned at the level of pedicle above and below level of fusion. (Fig. 1) Two transverse half centimeters incision are made, for the right handed person, portal in the right hand side is used for working portal and in the left hand side is used for viewing portal. Working space on the subperiosteal space are created using periosteal elevator inserted on the working portal and scope trocar are introduced through the viewing portal. The triangulation maneuver is completed after trocar and periosteal elevator meet on the edge of lamina. The next step would be irrigating the water from the trocar into the working space and the water should be coming out from the working portal. (Fig. 2)
Flavectomy and foraminectomy
Decompression are started with drilling the inferior edge lamina until insertion of flavum ligament, base of spinous process, and inner cortex of contralateral lamina until the contralateral facet joint. Drilling is done only to thin out and decorticate the outer cortex of the lamina. The next step would be doing the laminotomy and foraminectomy using combination of Kerrison punch and chisel to have solid bone graft for fusion. Foraminectomy is started by removing inferior articular process (IAP) until seeing base of superior articular process (SAP), medial part of SAP which is also the roof of lateral recess is also resected using either kerisson punch or chisel. The tip of SAP is also removed to create bigger space on the foraminal area for easier discectomy, endplate removal and cage insertion.
Flavectomy is started only after all the bony work finish, this is can be done either en bloc resection or piece by piece using Kerrison punch. (Fig. 3) We do not routinely do total flavectomy, it is depends complains of the patients, the severity of flavum thickening and location of the stenosis. Complete decompression would have sign of pulsating thecal sac, traversing nerve root and exiting nerve root.
Discectomy, endplate removal and cage insertion
Radiofrequency probe is used to expose the disc, usually there are a lot of epidural veins and some adhesion of the dura to the disc. Using the nerve retractor inserted from the working channel we can mobilize the traversing nerve root and the thecal sac towards medial side. Annulotomy is started using radiofrequency probe and continue with discectomy using shaver, currettes, forceps and endplate remover. (Fig. 4) Endplate preparation is finish until we can see multiple spot of bone bleeding, this bone bleeding can only be seen by the aid of endoscopy because the lens can go to the disc space. (Fig. 5) The next step would be trying the cage until the appropriate size, this cage trial are inserted through the working channel. (Fig. 6) Insertion of the cage for the right handed person is preferably done through the right side of the patients, especially on the level L45 or L5S1, because the working portal is located on the rostral side and in these level the intervertebral space are tilted towards the caudal side. (Fig. 7,8,9)
Pedicle screw insertion and listhesis reduction
Supplementation pedicle screw fixation are done using percutaneous technique under florouscopic guidance. (Fig. 10) In order to reduce the listhesis, there are several technique that we can do :
- The rostral pedicle screw are inserted deeper in order to help reducing the listhesis.
- Patients are position on extension by neutraling the table
- Inserting the rod for cantilever maneuver by tightening the caudal screw and then tightening the rostral screw.