Anatomic/physiologic (indirect) decompression

Introduction

Low back pain is a common condition affecting up to 80% of adults in the United States over the course of their lives. This pain is often caused by lumbar spinal stenosis (LSS), in which nervous structures such as the spinal cord or nerve roots are compressed due to degenerative disc disease, disc herniation, or osteophytic or ligamentous hypertrophy. Compression of nervous structures can also be caused by degenerative spondylolisthesis and scoliosis. These conditions can be treated through direct removal of structures that compress nerves, but the removal of disc, facet overgrowth, or elements of the posterior column can also result in iatrogenic damage to nerves and instability in some cases. Another approach to nerve decompression is indirect decompression, in which the disc space of a spinal segment is increased, resulting in greater neuroforaminal space and decompressing affected nerves. Spinal interbody fusion is a type of indirect decompression in which an interbody bone graft or device is placed into the disc space following discectomy to restore disc height and expand the foramen. The placement of an interbody device loaded with biologic results in the fusion of consecutive vertebrae with an increased disc height, resulting in increase of foraminal and lateral recess space and alleviation of symptoms such as pain and radiculopathy.

Traditional lumbar fusion has been performed using an open midline technique associated with substantial blood loss, high rates of complication, and a prolonged recovery period. Minimally invasive surgical (MIS) methods of interbody fusion are becoming more frequently utilized as they effectively alleviate symptoms of stenosis while reducing iatrogenic surgical morbidity. MIS approaches to spinal fusion vary widely, with technologies being developed to access the disc space with anterior, lateral, and posterior approaches. In this chapter, we will discuss four different surgical methods of performing interbody fusion. Oblique lateral lumbar interbody fusion (OLLIF) is a relatively new method of lumbar interbody fusion that approaches the disc space at a 45-degree angle to the spine through the Kambin triangle, an anatomical space that permits approach without significant retraction of neural structures. Minimally invasive direct lateral interbody fusion (MIS-DLIF) approaches the disc space laterally and enters the interbody space anterior to the exiting nerve root. Minimally invasive direct thoracic interbody fusion (MIS-DTIF) is used in the thoracic region and approaches the disc space with a lateral approach. Transfacet OLLIF (TF-OLLIF), the final technique discussed, is a modification of the OLLIF that is used at the L5–S1 level in order to access a disc space through the Kambin triangle when the approach is obstructed by osteophytic changes.

Indications

OLLIF, MIS-DLIF, and TF-OLLIF are indicated for lumbar pathologies, and MIS-DTIF for thoracic pathologies, in skeletally mature patients for the treatment of low back pain and radiculopathy in patients who meet the following criteria:

1.

Have undergone and failed to respond to a minimum 6 months of intensive nonoperative treatment that includes medication optimization, activity modification, and active physical therapy.
2.

Severe degenerative disc disease, spondylolisthesis, discogenic stenosis, and disc reherniation are diagnosed clinically and on preoperative imaging including MRI, X-ray of the lumbar spine with flexion and extension, and computerized tomography with discogram in many cases.
3.

Presence of scoliosis and other deformities, if a surgeon has sufficient experience.

Relevant contraindications

OLLIF, MIS-DLIF, TF-OLLIF and MIS-DTIF are NOT indicated in any of the following, except in specific circumstances when other pathologies have been investigated separately and ruled out as a source of pain:

1.

Any case that does not fulfill ALL of the criteria given earlier.
2.

Active systemic infection or infections localized to the site of the proposed implantation are contraindications to implantation.
3.

Severe osteoporosis is generally a relative contraindication for all spinal fusions because postoperative healing is impeded.
4.

Any condition that significantly affects the likelihood of fusion may be a relative contraindication (e.g., cancer).
5.

Comorbidities such as diabetes, osteomalacia, heavy smoking, and morbid obesity, are relative contraindications for all methods of fusion, but are smaller factors in minimally invasive fusions like those discussed in this chapter.
6.

These procedures can be relatively contraindicated in the following cases depending on surgeon level of training and expertise : bony obstruction, significant osteogenic spinal canal stenosis, large facet hypertrophy, grade II listhesis, and other gross deformities.

Preoperative considerations

The patient should be induced followed by Foley catheter placement for longer cases. Patient is placed in the prone position on a Jackson table. Two C-arms are placed to obtain lateral and anterioposterior (AP) X-rays of the patient. The surgical site is cleaned with povidone-iodine prior to draping of the operation site. The patient is draped, and the C-arms are draped. Skin is marked as indicated in each procedure.

Intraoperative medication includes:

1.

Skin injection of 1% lidocaine with epinephrine and 0.25% Marcaine plain half/half at the injection site.
2.

Lumbar epidural steroid injection (1 cc of 0.25 mg Marcaine plain with 40 cc Kenalog at the end of surgery).
3.

Up to 20 cc of 0.75 mg Marcaine or Exparel in paraspinal muscles at the end of surgery.

Postoperative care

The patient is usually discharged on the same day for smaller fusions with additional nights spent at the hospital depending on the levels fused and patient comorbidities. Patient is discharged with pain medication and muscle relaxants.

Complications

Interbody fusion is associated with several possible complications:

1.

Infection of the surgical site is possible, but in our experience only occurred in 0.3% of patients.
2.

Nerve root irritation and damage to neural structures.
- a.
  
  A trans-Kambin approach as in our experience has a rate of nerve root irritation of 7.2%, usually involving temporary L5 numbness, decreasing to 5% after 1 year.
3.

Failure to treat stenosis in 1.3% of cases, requiring patients to undergo repeat surgery.
4.

Revision of posterior instrumentation is required due to screw failure occurring in a number of patients, oftentimes associated with a fall or motor vehicle accident. We found this rate to be 2% at 1-year follow-up.

OLLIF: Oblique lateral lumbar interbody fusion

Background

The oblique lateral lumbar interbody fusion (OLLIF) is a minimally invasive fusion technique that approaches the intervertebral disc space at roughly a 45-degree angle from the posterior midline. OLLIF is different from other posterior approaches in that it accesses the disc space through the Kambin triangle ( Fig. 9.1 ), an electrophysiologically silent window formed by the exiting nerve root, the superior articular process of the inferior vertebra, and the superior endplate of the inferior vertebral body. The procedure is truly minimally invasive, being performed using a ∅10-mm access portal inserted through a ∼15-mm incision. The approach is guided by biplanar fluoroscopy and electrophysiological monitoring.

Room setup

The patient is placed in the prone position on a Jackson table. The table can be rotated 3–5 degrees away from the surgeon until after the cage is placed to facilitate the oblique angle of approach, but fluoroscopy must be adjusted for this ( Fig. 9.2 ).

The endplates of the target level should be aligned in the lateral view. In the AP view, the disc should be visible, and the pedicles should be equal distances from the spinous process.

Neuromonitoring

Electrophysiological monitoring electrodes are placed on the major muscle groups and the patient’s skull to monitor somatosensory evoked potentials (SSEP) and electromyogram (EMG).

Targeting

Determination of the incision point is performed with the use of fluoroscopic imaging. It is critical to confirm that the imaging is oriented correctly on the target level. Confirm that the AP image is properly centered over the vertebral body. This can be achieved by laying a guidewire or other radiopaque instrument on the midline to confirm that the AP image shows the pedicles are equally spaced on each side of the midline. Mark midline when fluoroscopy is centered ( Fig. 9.3 , red line). Next, the location of the target disc(s) should be identified, and a mark placed across the skin corresponding to the center of the disc on fluoroscopy (see Fig. 9.3 , orange line).

The incision point is determined using the lateral view, with the vertebral endplates perfectly aligned. Using an opaque object to determine location, mark a line along the angle of the disc on the patient’s side (see Fig. 9.3 , green line). The distance from the center of the disc to the vertex of the curve of the flank is measured, and this distance is transferred to find the distance from the midline where the incision should be made ( Fig. 9.4 ). This will create a theoretical right triangle with the end of the hypotenuse in the center of the disc ( Fig. 9.5 ). There may be some overlap in the lengths of these lines, and the incision point should be in the approximate center of this overlap. The location of the incision is usually 10–13 cm from midline with variation based on patient disc height. The typical entry point for the OLLIF in comparison with other minimally invasive fusion approaches is displayed in Fig. 9.6 .

To confirm the incision point is in a place that will lead to the Kambin triangle without obstruction, a spinal needle may be placed to confirm the trajectory.

Approach

After confirming the trajectory, make a 10-mm incision in the skin and through the lumbar fascia. The electrode is stimulated at 3 mA during the approach to locate the silent window in the Kambin triangle. The neuromonitoring probe is inserted through the incision, passing through the retroperitoneal space and bluntly piercing the iliopsoas fascia ( Figs. 9.7–9.9 ). A blunt neuromonitoring probe with sleeve is gently maneuvered through the retroperitoneal space until it is positioned on the anterior aspect of the pedicle bellow, then moved along the upper side of the inferior pedicle until reaching the Kambin triangle. The electrode is stimulated at 4 mA after contacting the disc to detect possible contact with the nerve root ( Figs. 9.10 , 9.11 ). Our current data show the threshold of 3 mA is acceptable. Four of four twitches (no paralytics) is required for acceptance of the electrophysiological data. The final placement of the probe is correct when the tip is between the medial and lateral aspect of the pedicle and in the inferior section of the neural foramen ( Fig. 9.12 ).

After completing the navigation to the disc, the neuromonitoring sleeve is pressed forward onto the disc and the electrode removed. An 18-inch guidewire is placed through the neuromonitoring probe sleeve past the midline into the disc ( Figs. 9.13 , 9.14 ).

Once the guidewire is correctly placed in the disc, the neuromonitoring sleeve is removed. The dilator is placed over the guidewire and fluoroscopy is used to confirm that the tip is near the center of the disc on AP and lateral images ( Figs. 9.15 , 9.16 ). Insertion of the dilator should increase disc space and foraminal size, increasing the size of the silent window.

The guidewire can be removed after the dilator has entered the disc space with the correct trajectory ( Figs. 9.17 , 9.18 ).

The guidewire and the dilator handle are removed. The access portal is inserted over the dilator until the end of the portal is secured inside the disc space ( Figs. 9.19 , 9.20 ). The impact sleeve can be used to facilitate this placement. The access portal should be placed so that it is medial to the pedicle in AP view ( Fig. 9.21 ) and roughly 0.5 cm into the disc in the lateral view ( Fig. 9.22 ).