Endoscopic Transforaminal Decompression for Unilateral Radiculopathy

Occasionally, a patient with degenerative scoliosis will complain mainly of leg pain, with only minor back pain. In most cases, the pain is due to neuroforaminal stenosis. Traditionally, this has been treated with hemilaminectomy and foraminotomy. However, there is risk of worsening deformity due to loss of stability when excessive bony resection is necessary and when the activity of the multifidus muscle is disrupted. An extraforaminal approach has been used with good success via a Wiltse-type paramedian approach. A minimally invasive modification of this technique utilizes tubular retractors that dilate the soft tissue and minimize retraction pressures. Although this is still performed with the patient under general anesthesia, the accessibility of the neuroforamen is sufficient. However, it is technically challenging to use the operating microscope because of the angle of the approach.

The endoscopic technique provides another avenue of treatment and it can be performed using local anesthesia.⁵ This is advantageous for patients with significant medical comorbidities that make general anesthesia risky. Furthermore, the endoscopic technique allows a more lateral trajectory to the spine, facilitating deeper entry into the neuroforamen (Figure 60-1).

FIGURE 60-1 Endoscopic Transforaminal Decompression. A 7-mm endoscopic cannula is placed at the extraforaminal opening of the affected level. A combination of bipolar probes (Ellman International, Inc., Oceanside, N.Y.), holmium side-firing lasers (Trimedyne, Inc., Irvine, Calif.), and mechanical trephines (Joimax, Inc., Campbell, Calif.) are used to release the neuroforaminal ligament, superior edge of the facet joint capsule, and lateral edge of the ligamentum flavum as it becomes confluent with the facet joint capsule. Mechanical trephines are used under fluoroscopic guidance to remove the superior edge of the superior articular process. A combination of ligamentous release with a small amount of bony resection decompresses the exiting nerve root. The angled bipolar probe is passed into the spinal canal to manually confirm adequate decompression. A, AP radiograph showing asymmetric disc collapse with narrowing of the left L4 and L5 neuroforamina. B, Left parasagittal T1-weighted MR image showing narrowing of the left L4 and L5 neuroforamina. (open arrows) C, Endoscopic view of the facet joint capsule. D, Endoscopic view of the semicircular removal of superior articular process using trephines. The rough cancellous bone can be seen as a superior dome in the field of view. E, Intraoperative AP C-arm image showing the endoscopic cannula docked at the extraforaminal opening of the left L4 neuroforamen. F, Intraoperative lateral C-arm image showing the endoscopic cannula docked at the extraforaminal opening of the left L4 neuroforamen. Intraoperative AP image showing the endoscopic angled probe passing through the superior (G), middle (H), and inferior (I) aspects of the neuroforamen. The ability to pass the probe through the neuroforamen without resistance confirms an adequate decompression.

Deformity Correction via Direct Lateral Anterior Interbody Fusion

A powerful method of deformity correction is the direct lateral interbody fusion (DLIF) technique (Figures 60-2 through 60-5). This technique was best described by Ozgur and colleagues⁶ using the XLIF system (Nuvasive, San Diego, Calif.). The key feature of the technique is the ability to rest the interbody spacer along the strongest portion of the vertebra endplate, namely, the cortical rim or apophyseal ring. The annulus inserts at this location and the cortex of the vertebral body acts as a vertical support. Because the interbody spacer is placed from the lateral position, the implant may overhang past the edge of the disc space, ensuring that the implant fully rests on the strongest portion of the endplate. If placed from an anterior or anterolateral position, the interbody spacer would enter the canal or the neuroforamen. In addition, the DLIF technique preserves the anterior longitudinal ligament. It is presumed that by keeping the integrity of this structure, the spine maintains a pivot point from which to correct an asymmetrically collapsed disc.

FIGURE 60-2 Lateral Positioning for Direct Lateral Interbody Fusion (DLIF). An important step in the safe application of the DLIF procedure is proper patient positioning. The patient is placed on a breaking radiolucent table. A soft support is placed at the lateral hip at the level of the iliac crest (A). The break in the table is placed at the same area (black oval). The patient is secured to the table using sticky rolls or a moldable beanbag device. Soft tape is placed at the hips (over the greater trochanters) and just below the shoulders. The hips and knees are flexed in a comfortable position at about 45 degrees. Transverse pillows are placed between the legs. A strap is then gently placed above the ankles to maintain this position. The patient must be adequately secured to the table so that the table itself can be rotated (“airplaned”), ensuring that the surgical target site is perfectly lateral relative to the floor. This is best accomplished by using the C-arm under the table flat to the floor. The table is then rolled until a perfect AP image is obtained (B). In most cases of degenerative scoliosis, there is some mild rotation such that the caudal vertebral body and the cephalic vertebral body cannot be in a perfect AP position simultaneously. In this instance, the caudal vertebral body is usually used as the reference level. This process is required at each level to adjust for rotational deformities between levels. The lateral image is used to target the midportion of the disc space (C). At L4-5, the nerve root can be at this position. In such cases, the initial dilator is targeted more anteriorly and thereafter pulled posteriorly to the disc midpoint. This allows the dilator to enter the psoas muscle anterior to the nerve root and by sweeping posteriorly creates a cuff of muscle that separates the dilator from the nerve root. The iliac crest can impede access to the L4-5 disc space (dotted lines). It is important to ascertain before surgery that iliac crest can be pulled out of the way by lateral bending of the patient on the operating table, as described in A.

FIGURE 60-3 Direct Lateral Retroperitoneal Transpsoas Approach. The skin incision is made with the aid of the C-arm in the direct lateral position. Gentle blunt dissection is accomplished with angled Mayo scissors. The muscles of the lateral abdominal wall are entered between muscle fibers (A). Numerous sensory nerves are encountered, which can be swept out of the surgical corridor. The retroperitoneal space is entered by cautious, gentle spreading of the tranversus abdominis fascia, which can be thick in younger patients. Finger dissection is then used to open the potential space of the retroperitoneum. Upon entering the retroperitoneal space, the finger is immediately directed posteriorly to the inner abdominal wall as shown by the dotted lines (B). A back-and-forth motion is used to release thin reticular attachments of the retroperitoneal fat to the abdominal wall. The tip of the traverse process is used as the initial landmark. At L4-L5, the iliolumbar ligament is palpated as well as the anterior aspect of the iliacus muscle. Blunt finger dissection is further taken anteriorly over the psoas muscle, which is very soft and delicate to the touch. Care should be taken to avoid undue maceration of the fragile muscle fibers. The initial dilator is then passed down along the finger and docked gently on the surface of the psoas muscle. The initial dilator is kept in contact with the finger to facilitate safe passage of the tip through the retroperitoneal space and ensure that it does not capture any abdominal structures such as bowel or ureter. Using the C-arm, the tip of the initial dilator is positioned at the disc center and the psoas muscle entered gently using a back-and-forth twisting motion. Because the psoas muscle is soft it will not cause resistance. Neurophysiologic monitoring via free-run and triggered EMG is used to confirm that the nerve root is not in the path of the initial dilator. The safe zone for the transpsoas approach is anterior to the nerve root and posterior to the vena cava (C). The limits of this safe zone suddenly narrow at L4-L5 compared to the more cephalic levels (D).

FIGURE 60-4 Disc Exposure. Once the initial dilator is safely passed through the psoas muscle and positioned on the disc space, a guidewire is inserted into the disc to hold the dilators in place. Serial dilation is then performed with larger tubular rings. At each step, neurophysiologic monitoring is used to avoid the nerve root. After the final dilator, an expandable tubular retractor (A and B) is slid down using a back-and-forth motion (Medtronic Spine, Memphis, Tenn.). Thin fibers of the psoas are often found over the disc space (C). These fibers should be only 1 to 2 mm thick and can be swept aside with the suction tip or a Penfield 4 probe. The blades of the retractor contain slots for bone fixation screws (white arrow, C) that can be used to pass the neuromonitoring probe (NIM, Medtronic, Memphis, Tenn.) down to the bone surface (white arrow, D). The bone fixation screw is inserted through the slots in the retractor (E). It is best to position the bone screw immediately adjacent to the disc space (F). Before insertion of the bone screw, the ball-tip neuromonitoring probe (open arrow, F) is used to ensure that the bony surface is free of neural structures.

FIGURE 60-5 Direct Lateral Discectomy. A key component of the DLIF discectomy is release of the contralateral annulus. This can be accomplished with a Cobb-type periosteal elevator (A). Using a mallet, the elevator is gently tapped until it penetrates the annulus. A palpable release can be appreciated. Although the tip of the elevator may protrude up to 1 cm past the lateral vertebral body line, no known clinical sequelae have been observed. Once a subtotal discectomy, endplate preparation, and contralateral annular release have been accomplished, smooth trials are used to dilate the disc space (B to D). The interbody device of the appropriate size is then tamped into place. Using a wide interbody spacer that rests on the lateral cortical rim of the vertebral body, a dramatic reduction and disc height restoration can be seen (E to G). The specialized retractor provides an optimal view of the surgical corridor before (D) and after insertion (H) of the interbody spacer.

A comparison of interbody fusion techniques shows that the direct lateral interbody technique allows for greater deformity correction than anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF) or posterolateral fusion without interbody fusion. A radiographic comparison of various treatment groups showed that the focal Cobb angle for DLIF was two to four times that for the other treatment methods (Figure 60-6). The main drawback of this technique is approach-related nerve root irritation, which occurs in 3.4% of patients.⁷

FIGURE 60-6 Deformity Correction using the DLIF Technique. A retrospective radiographic review comparing various fusion techniques shows the superiority of the DLIF technique for reduction of focal Cobb angle in patients with degenerative scoliosis (A) and reduction of spondylolisthesis (B).

Minimally Invasive Posterior-Only Approaches

The most common minimally invasive posterior approach is the minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). Utilizing a paramedian approach, a unilateral facetectomy may be performed on the side requiring maximum correction.⁸ Interbody fusion allows for a high fusion rate and provides additional soft tissue release needed for deformity correction. The MIS TLIF strategy is particularly attractive if there is a large disc herniation, facet cyst, and/or severe stenosis requiring a direct decompression.

A key limitation is the difficulty in placing a sufficiently large interbody spacer to restore disc space height. Additionally, each level requires a separate and distinct dissection. In cases in which there are more than three levels to be corrected, this technique can be time-consuming and laborious.

Percutaneous Pedicle Screw Fixation

Multilevel fixation with pedicle screws and rods remains one of the most significant challenges in the minimally invasive treatment of degenerative scoliosis. In contrast to open techniques, the percutaneous rods cannot be reduced into the tulip of the pedicle screws, nor can a rotation maneuver be performed. The method of bringing the rod to the screw relies on screw extension sleeves that serve to guide the rods through each tulip and thereafter reduces the rod into the seat of the tulip so that a fixation nut can be applied (Figure 60-7). The greatest challenge occurs at the lumbosacral junction, where there is a sudden curvature due to the lordotic angle between L4 and S1 (See Figure 60-7H). Extreme care must be exercised to align the height of the tulips. With osteoporotic bone, misalignment can lead to screw pullout during the reduction maneuver. The use of bone cement injected into the pedicles immediately before screw insertion greatly improves fixation strength.⁹

FIGURE 60-7 MIS Pedicle Screw Fixation. Meticulous intraoperative AP (A) and lateral (B) imaging is required to enter the pedicle using percutaneous or mini-open techniques. A sleeve to guide rod insertion is required to facilitate passage of the rod over multiple levels (C, E). The design of the sleeve should provide a relatively large opening to simplify rod insertion and reduction of the rod down to the tulip of the pedicle screw (D, F). The depth of screw insertion should be monitored carefully using lateral C-arm imaging to avoid step-offs, which make rod reduction difficult (G). Careful rod contouring is also necessary, particularly if crossing the lumbosacral junction, where there is a sudden increase in lordosis (H). Pelvic fixation can be accomplished through a small surgical corridor that is immediately adjacent to the L5-S1 exposure (MIS pelvic screw marked by ^∗ in H).

FIGURE 60-8 Case 1: L2-L5 Degenerative Scoliosis with Stenosis. Standing AP (A) and lateral (C) radiographs of a 72-year-old man with constant back pain and neurogenic claudication. Patient avoided surgical treatment because of fear of intraoperative risks of traditional open surgery. Current medical problems include hypertension and mild chronic obstructive pulmonary disease. Patient underwent angioplasty 2 years ago. Surgical treatment was performed in 1 day via stage 1 direct lateral anterior interbody fusion at L2-L3, L3-L4 and L4-L5. Estimated blood loss was 50 ml, and surgical time was 127 min. The patient was repositioned and nonsegmental posterior instrumentation was performed through 18-mm percutaneous incisions. The rod was inserted through proximal stab incisions (F, blue arrow). The navigation patient reference frame was placed percutaneously on the left posterior superior iliac spine (F, white arrow). Decompression was achieved indirectly via deformity correction and disc space height restoration. No laminectomy was performed. Patient was ambulating on postoperative day 1 with resolution of leg pain. He was discharged on postoperative day 3. At 1-year postsurgery, his visual analog scale is 2-3 and his walking tolerance is 2 miles.

MIS Iliac Fixation

The use of iliac screws improves fusion rates at L5-S1 when the construct is long. An important technique in posterior deformity correction is insertion of iliac screws in a minimally invasive fashion.¹⁰ By placing the insertion point of the iliac screws on the medial wall of the posterior superior iliac spine (PSIS) about 2 cm distal to the S1 screw, the tulips of the screws can be aligned so that a rod can be passed through both the S1 screw tulip and the iliac screw tulip (Figure 60-8). Meticulous attention to rod contouring is required to ensure that the construct is not under undue stress.

FIGURE 60-9 Case 2: L2-S1 Degenerative Scoliosis. Standing AP (A) and lateral (B) radiographs of 69-year-old woman with back pain, left posterolateral leg pain, right anterior thigh pain, and neurogenic claudication with walking and prolonged standing. Her walking tolerance was less than 100 feet, limited by worsening bilateral leg pain, left worse than right. A two-stage procedure was performed. On day 1, DLIF was performed at L2-L3, L3-L4, and L4-L5. She tolerated the procedure well with 75 ml, of estimated blood loss. Surgical time was 142 minutes. Two days later, she underwent the stage 2 procedure: left L5-S1 MIS TLIF, mini-open left iliac screw, and percutaneous pedicle screws bilaterally at L2, L3, L4, L5, and S1 (C, D). The rod was passed percutaneously using reduction sleeves (E, F). Decompression was achieved indirectly via deformity reduction and realignment. No laminectomies, except those at L5-S1 during the MIS TLIF, were performed. The iliac screw is inserted on the medial aspect of the posterior superior iliac spine about 2 cm distal to the S1 pedicle screw, such that the base of the screw tulips is aligned to accept a single rod (E to G). Estimated blood loss was 275 ml and total surgery time was 387 minutes. She was ambulatory on postoperative day 1 after stage 2 and discharged to home on postoperative day 4. She has good resolution of her leg pain and mild to moderate back pain (VAS 4-5).

Case Studies

Minimally invasive scoliosis surgery relies on three main technologies: (1) DLIF/XLIF, (2) posterior MIS TLIF, and (3) percutaneous pedicle screw instrumentation. Using a combination of these techniques, deformities of the thoracolumbar spine spanning T10 to the pelvis can be treated. The most common and most straightforward problem is a degenerative scoliosis from L2 to L5 with back pain and neurogenic claudication (Figure 60-8). Using a lateral interbody approach, much of the stenosis can be addressed by correcting the Cobb angle and reestablishing the disc space height. In doing so, an indirect decompression can be achieved in some cases without the need for a posterior laminectomy.

In cases in which there is an oblique takeoff of L5 from the sacrum, L5-S1 fusion can be achieved using an MIS TLIF (see Figure 60-9). A novel and promising strategy for L5-S1 fusion is the use of a transsacral fixation device (Figure 60-10). Added construct stability can be achieved with additional pelvic fixation using the L5-S1 surgical corridor to expose the medial wall of the posterior-superior iliac spine (PSIS) as the entry point for the pelvic screw. This allows the tulip of the pelvic screw to align with the S1 screw so that a single rod can be used (see Figures 60-9 and 60-10).

FIGURE 60-10 Case 3: T10-Pelvis Reconstruction. Standing AP (A) scoliosis films of a 47-year-old woman with seronegative spondyloarthropathy complaining of worsening back pain and right flank pain due to impingement of the 12th rib on the iliac crest. Radiographs from 18 months previously revealed only minimal deformity. Stage 1 DLIF was performed with marked improvement in coronal alignment (B). Two days later, she underwent posterior reconstruction: L5-S1 transsacral fusion, mini-open bilateral iliac screws, mini-open bilateral T10-L1 pedicle screws, and percutaneous pedicle screws bilaterally at L2-L3 with unilateral screws at L4-L5 (C, D). Mini-open exposures for the pedicle screws were used to expose the facet joints and posterior elements of T10-L1, which were decorticated and bone grafted. Long contoured rods were passed through proximal stab incisions and advanced through each of the rod reduction sleeves. The stage 2 procedure was tedious and difficult. Total surgical time was 9 hours, 17 minutes and estimated blood loss was 575 ml. Postoperatively, she was ambulatory on day 2 and discharged home on day 7.