Surgery and postoperative imaging
The patient underwent two-stage C-arm-free cMIS. The first surgery comprised L1–S1 C-arm-free oblique lumbar interbody fusion (OLIF), with an operation time of 3 h 57 min and an estimated blood loss of 240 mL. After 1 week, the second PPS fixation was performed and proximal screws (T10, T11) were inserted with a transdiscal approach (T11) and with lower angulation trajectory (T10) to enhance pullout strength (Figure 4). For this second stage, operative time was 3 h 33 min and estimated blood loss was 320 mL. No postoperative complications or neurological compromise was reported.
Follow-up results and imaging
Follow-up radiography showed no PJK or screw loosening (Figure 5). In terms of clinical outcomes, Oswestry Disability Index improved from 56% to 24% and visual analog scale score for neck pain improved from 62 mm to 24 mm by the 1-year follow-up.
First surgery (L1–S1 OLIF)
The patient was placed in the right lateral decubitus position on an adjustable hinged carbon operating table (OSI Axis Jackson table; Mizuho, Union City, CA, USA) to perform CT using an O-arm. An axillary roll was placed to protect the neurovascular structures in the axilla. The patient was secured to the Axis Jackson table with tape, and the table was adjusted to approximately 15° convex. The percutaneous reference frame was attached through the sacroiliac joint. The O-arm was then positioned, and 3-dimensional (3D) reconstructed images were obtained and transmitted to the Stealth station navigation system Spine 7® (Medtronic Sofamor Danek; Minneapolis, MN, USA). After verifying every navigated spinal instrument, the best entry point for each disc was marked by the navigated pinpoint probe. Typically, three oblique skin incisions of approximately 4 cm each are necessary for this technique.
The subcutaneous fat layers were dissected until the abdominal musculature was reached. The external, internal, and transverse abdominal muscles were divided parallel with the alignment of the muscle fibers to avoid cutting the muscle fibers. Both index fingers were inserted inside the retroperitoneal space, and were used to follow the internal abdominal wall posteriorly down to the psoas muscle, which can be visualized. The navigated first direct lateral dilator rested on the anterior border of the psoas muscle at the L5-S1 disc level. Use of a hand-held retractor with illumination placed between the peritoneal contents and the probe was used to minimize the risk of injury to the ureter and vascular structures anteriorly. The retractor assembly was attached to the flexible arm and stability pins were inserted to fix the retractor. Discectomy was performed using a bayoneted knife, Kerrison rongeurs, pituitary forceps, a navigated Cobb elevatorium, a navigated shaver (Figure 5) and navigated curved curettes (Figure 6A, B). After trialing (Figure 6C, D), a mixture of iliac bone and demineralized bone material was inserted into the cage hole. A mallet was then used to gently insert the OLIF cage (Clydesdale PTC®, OLIF51 SovereignTM Spinal 173 System; Medtronic Sofamor Danek) while monitoring placement (Figure 8).
Second surgery -Percutaneous pedicle screw (PPS) fixation
The patient was placed in the prone position on the Axis Jackson table. The reference frame was attached around the T11 spinous process and 3D images were obtained from T10 to L3. After every navigated instrument was verified, PPS was inserted by navigation (Figure 9). The length and diameter of pedicle screw were also measured by navigation. After T10–L3 screws were inserted, the reference frame was reattached to L3, and another 3D image was obtained from L4 to the pelvis. Sacral-alar-iliac (SAI) screws are recommended to enhance the pelvic anchors. The proximal screws (T10, T11) are inserted with a transdiscal approach (T11) (Figure 10) and with lower angulation trajectory (T10) (Figure 11) to enhance pullout strength. This technique results in triangular fixation of the upper instrumented vertebra (UIV) to prevent screw pull-out (Figure 12).
Anteroposterior and lateral radiograms should be obtained to ensure correct placement of pedicle screws and SAI screws. Rods were bent in an appropriate contour and inserted percutaneously. The Axis Jackson table was bent by more than 20° to create good lumbar lordosis. The set screws were gradually tightened to create a greater amount of lumbar lordosis.