The patient is placed in prone position on the operating table. To simplify the approach, the patient is tilted away from the surgeon by 3-5º until after the cage is inserted. Then, the patient is planed back into a true prone position. To enable quick readjustment, 3M Ioban (3M Center, St. Paul, MN) transparent plastic draping is used to help the surgeon get a sense of the patient’s positioning. setup is very similar to OLLIF setup ( reference to OLLIF paper)
Next, bilateral fluoroscopy is set up. The endplates of the target level should line up well in lateral view. In the anterior-posterior (AP) view, the disk needs to be visible but not necessarily completely aligned, and the spinous process should be centered between the pedicles. Electrophysiological monitoring is set up on the major muscle groups and the skull. The somatosensory evoked potential (SSEP) and electromyogram (EMG) is checked and monitored throughout the surgery. TcMEP is obtained.
The posterior axillary line is projected on the level in question and lines are drawn on the back region. In the AP view the midline and each disk are marked. A vertical line showing the midpoint of each disk is marked in the lateral view.
The incision is close to posterior axillary line, multiple levels can be approached through the same incision by shifting the skin or approaching the disk at a slight angle. But this mobility is much less than in lumbar region because of the limitation of the motion of the ribs, still skin can be pushed on rib above and below.
A two centimeter (cm) incision is placed on the posterior axillary line. The rib is identified and, just superior to the rib, a small incision is placed. A blunt probe is entered into pleural space, kept along the rib in the pleural space, and then walked to the head of the rib. The probe is then positioned directly in the interested disc space.
This position is confirmed via biplanar fluoroscopic imaging. The probe is cannulated, at this point, a K-Wire with a sharp tip is introduced into the cannulated blunt probe and entered into the disc space. Next, the probe is tapped with a mallet into the disc space and the K-Wire removed. Then a working tube is placed over the blunt probe and entered into the disc space. A series of specialized tools are then used, including a fanning curette. A ring curette is placed over the tube into the disc space and used in conjunction with a multiple rongeur.
These instruments are all introduced over the tube and a discectomy is performed. During entire procedure there is a direct connection through a tube of 10mm from outside of skin to disk space which is sealed by skin and intercostal tissue. There is no need for collapsing the long like in regular thoracotomy .
Disk material is removed first with a drill and then with a rotating cutter, ring curette and long pituitary, all delivered through the access portal. The endplates are prepared with serial dilation of the rotating curette. Tactile feedback from the curette indicates when the endplates are reached and free. Next, the disk space is packed with tricalcium phosphate (Berkeley Advanced Biomaterials Inc., 901 Grayson St., Berkeley, CA) soaked in autologous bone marrow aspirate drawn from a Jamshidi needle in one of the pedicles. A K-wire is placed and the access portal and then the portal is removed.
Next, the cone-shaped cage (PEEK Zeus-O cage manufactured by Amendia) is inserted over the K-wire aided by fluoroscopy. Biplanar fluoroscopic imaging confirms adequate positioning. The cage is introduced into the pleural space, positioned on the top of the disc, and entered into the disk in the proper position (in AP and lateral view) with a mallet. With mallet taps the cage is entered until 1/3 of the cage is past the midline. Then, the insertion device is removed and the pleural space is sutured in two layers.
After cage placement, all patients undergo percutaneous posterior pedicle screw fixation. Savannah-T posterior instruments and high top screws manufactured by Amendia were used. Jamshidi needles have already been placed in one level at the beginning of the surgery to allow tricalcium phosphate to be saturated with bone marrow aspirate.
Once the cage is inserted, all pedicles are tapped with Jamshidi needles that are stimulated up to 30mA to assure there is no contact to neural structure. All stimulation results above 18mA were accepted. It is necessary to ensure all Jamshidi needles are positioned correctly because repositioning is easiest at this point. K-wires are then placed through the Jamshidi needles, and once the positioning of all K-wires is confirmed, the AP fluoroscopic arm is removed to ease screw placement.
An osteotome with a groove is slid down the K-wire and the facets are bare boned aided by lateral fluoroscopy. A small amount of dry tricalcium phosphate is placed in the just created space on the facets. To complete the surgery, the screws are inserted and the rod is placed as described by Foley.3
Anesthesia/surgery times, blood loss and fluoroscopy times were recorded for all patients by clinic staff and entered into the EMR database immediately after surgery. Blood loss was measured by weighing sponges and subtracting dry weight. Routine follow-up was done within 3 months, 6 months and 9-12 months post-surgery.
Pre-operative imaging included MRI, x-ray of the thoracic spine with flexion and extension and in many cases a discogram and computerized tomography (CT). MIS-DTIF is indicated for thoracic disc herniation after conservative therapy has failed.
All patients have gone through a full course of conservative therapy before being considered candidates for surgery. Patient surgical indications are Degenerative Disk Disease, Herniated Disks, Spondylolisthesis, Scoliosis, & Spinal Stenosis