Strategies to Minimize Invasiveness and Optimize Success: T10-Pelvis

51 Strategies to Minimize Invasiveness and Optimize Success: T10-Pelvis

Neel Anand, Alisa Alayan, and Sheila Kahwaty

Summary

This chapter provides a step-by-step description of patient evaluation and surgical execution of degenerative spinal deformity correction with circumferentially minimally invasive approach.

Keywords: deformity correction circumferential minimally invasive MIS ante-psoas multilevel OLIF LLIF

Case Example

51.1 Preoperative Presentation

A 71-year-old male—competitive tennis player—presented with progressive low back pain and leaning forward posture over the last several months prior to being seen. He had L5–S1 transforaminal interbody fusion (TLIF) 4 years prior and initially did well postoperatively, but slowly began developing low back pain. He did not have radicular symptoms on presentation. His pain limited his desired activities, especially within the last year prior to seeking consultation. He attempted conservative measures such as physical therapy, exercises, and massage. He had partial relief from nonsteroidal anti-inflammatory drugs (NSAIDs) such as Celebrex and Toradol. Past medical history included cardiac stent placement and prostate surgery, but no active problems. On examination, he had full strength in his lower extremities and no gait instability. Posture was observed to have positive sagittal balance and mid back kyphosis.

51.2 Imaging Studies

a)Standing 36-inch scoliosis X-rays to assess global alignment and spinopelvic parameters:

1.In this patient, we observed degenerative lumbar dextroscoliosis, with apex at around L3. There was mild shift to the left, but overall balanced coronally. Prior L5–S1 hardware was noted. Significant multilevel disc collapse was observed: L4–L5 collapsed to right; T12–L1, L1–L2, L2–L3, and L3–L4 collapsed to left; T11–T12 collapsed to the right. On the lateral film, loss of lumbar lordosis (LL) is observed, with kyphosis at T12–L1. L1–L2 retrolisthesis is also noted (see Fig. 51.1).

2.Pelvic incidence (PI) 70.8 degrees, pelvic tilt (PT) 37.7 degrees, LL 50.7 degrees, sagittal vertical axis (SVA) 114.5 mm, PI-LL mismatch 20.1 degrees.

b)Computed tomography (CT) thoracic and lumbar spine without contrast to assess bony anatomy and rule out spondylolysis or bony fusion of interbody segments or facet joints.

c)In this case, since the patient had previous surgery at L5–S1, we observed the bilateral L5 and S1 screws in appropriate position. We also noted an interbody graft with no evidence of bridging bone across the levels, suggesting pseudarthrosis at the L5–S1 level. The facets at L5–S1, as well as levels above, did not appear fused. We noted presence of gas in each lumbar disc space (see Fig. 51.2).

d)Magnetic resonance imaging (MRI) lumbar spine without contrast to assess stenosis, disc quality, spinal anomalies, and soft tissue anatomy. Most importantly, MRI allows the team to study the access corridor to the disc through the ante-psoas approach and evaluate the vascular anatomy:

1.In this patient, we observed multilevel central and lateral recess stenosis at T10–T11, T11–T12, T12–L1, L1–L2, L2–L3, L3–L4, and L4–L5. No large central or far-lateral disc herniation was observed (see Fig. 51.3).

2.Bone density scan of the hips and spine to assess bone quality:

e)The femoral neck T-score for this patient was −0.3. The T-score for the lumbar spine was 2.1.

Fig. 51.1 (a) Anteroposterior AP) and (b) lateral standing scoliosis radiographs. Previous L5–S1 fusion hardware is noted. (b) Degenerative lumbar dextroscoliosis, with apex at around L3 is noted. (b) Loss of lumbar lordosis is observed, with kyphosis at T12–L1. Overall positive sagittal balance. The global deformity measurements include: Cobb angle 25, pelvic incidence (PI) 70.8, pelvic tilt (PT) 37.7, lumbar lordosis (LL) 50.7, sagittal vertical axis (SVA) 114.5 mm, PI-LL mismatch 20.1.

Fig. 51.2 (a) Sagittal view of the lumbar spine demonstrating the multilevel degeneration. Presence of gas is noted at L5–S1, L4–L5, L3–L4, L2–L3, and T12–L1 levels on this particular cut. (b) Sagittal, axial, and coronal cuts demonstrating the pseudarthrosis at L5–S1 with presence of interbody graft. (c) Sagittal, axial, and coronal cuts demonstrating open facet joints posteriorly at L5–S1.

Fig. 51.3 (a, b) Sagittal and axial views of the lumbar spine at L3–L4 disc space, demonstrating clear ante-psoas access from the left side. The axial images also show no large central disc herniation. Each instrumented level is examined in this manner.

51.3 Decision-Making for MIS

The patient appeared healthy enough to be a surgical candidate with realistic goals and significant impairment of his desired activities. He had exhausted conservative measures. He had progressive sagittal imbalance, measuring 114.5 mm. He had presence of gas in all the lumbar disc spaces on the CT scan, suggesting mobility of the discs. This reassured us that we would be able to elevate the disc spaces and achieve some degree of deformity correction, lordosis, and indirect decompression with interbody grafts at each level. These are the foundation of the corrective forces in this specific MIS technique. Finally, we looked on the MRI for open corridors between the psoas and the vessels, making sure we could place the interbody grafts safely in an ante-psoas MIS fashion.

51.4 Factors Favoring Open Surgery

a)Previous complex abdominal surgery preventing the ante-psoas and MIS L5–S1 oblique lateral interbody fusion (OLIF) approach.

b)High-risk medical comorbidities and osteoporosis (bone density scan T score of –3.0 or worse).

c)Multiple fused segments on CT/prior multilevel fusion surgery.

d)Aberrant vessels visualized on MRI which prevent safe access to the disc spaces safely.

51.5 Details of Surgery

Medtronic instrumentation is used for both stages by the senior author.

Somatosensory evoked potential (SSEP) monitoring not required for stage 1.

51.5.1 Stage 1

1.Positioning: Right lateral decubitus position (left side up) on a flat top Jackson table, with an axillary roll under the right axilla. A pillow is placed under the right knee to protect the peroneal nerve. The kidney rest is elevated to open the left flank. Tape is placed across the iliac crest, chest, greater trochanter, and legs. The C-arm is parked at the patient’s back and the surgeon stands in front of the patient. The retractor system is attached on the table rail behind the patient at the level of the shoulder.

2.Approach to L5–S1:
Mark the anterior and posterior margins of the disc space at L5–S1 with lateral view X-ray. Draw a diagonal line toward the pubis in line with the disc space. Draw a second line from the posterior aspect of the disc space extending perpendicular to the body. An oblique incision is made between these lines, approximately 2 finger breadths anterior to the anterior superior iliac spine (see Fig. 51.4).

a)A vascular surgeon makes the incision in the left lower abdominal quadrant. The transversalis fascia is cut lateral to the rectus sheath, accessing the retroperitoneal space. The peritoneum and the ureter are carefully identified and mobilized as needed. The left iliac vessels and middle sacral vessels may need to be mobilized to gain access to the L5–S1 disc space.

b)A table-mounted tubular retractor system is used to maintain the access. Three blades are positioned: one superiorly retracting the left common iliac vein and artery, one blade retracting the bifurcation cephalically, and one inferiorly by the right common iliac vein and artery.

c)A lateral X-ray is taken to confirm the level and ascertain a clear view of the end plates is available. Some Ferguson tilt with the C-arm may be needed to achieve this. A linear incision is then made within the disc space and a straight, large, long-handled Cobb elevator is employed to enter the disc space all the way to the posterior margin.

d)Discectomy continues with all long-handled instruments: large Cobb elevators, straight and angled curettes, rasps, pituitary rongeurs, and Kerrisons. X-ray is used to confirm depth.

e)The posterior longitudinal ligament (PLL) is released using small straight and angled curettes under lateral fluoroscopy.

f)The Medtronic DLIF Clydesdale trials are used next to dilate the disc space, starting with an 8-mm height trial, followed by 10- and 12-mm trials. Lateral X-ray is used to check the depth and angle of the trials and that the posterior height of the disc space is increasing appropriately (see Fig. 51.5).

g)Next, the Medtronic OLIF Divergence trials are used, beginning with a medium-sized trial with 10 mm of height and 12 degrees of lordosis. As the height is progressively increased, it is important to select a trial that provides at least 4 to 6 mm of posterior height. Anteroposterior (AP) X-ray is used to confirm the position of the trial and the chosen PEEK spacer is inserted with an anterior plate under lateral fluoroscopy.

1.The PEEK spacer is packed with approximately 4 mg rhBMP-2 and Grafton putty.

2.A long-handled screwdriver, with a guide for the screws, is mounted obliquely to the plate and spacer prior to insertion. This guide is a safe tool for lumbar and sacral screw placement across the anterior plate.

3.Grafton putty is packed on either side of the spacer.

h)In this particular case, the previously implanted TLIF graft at L5–S1 was found to be loose without any evidence of bony fusion. A Cobb elevator was used around the graft and then the graft was removed completely from the space. The steps above were then followed.

3.Ante-psoas approach to levels above L5–S1:

a)L4–L5 and L3–L4 can be accessed through one skin incision, while L2–L3 and L1–L2 through another (see Fig. 51.4). The external oblique muscle and the internal oblique muscle are split in line with their fibers. The transversalis fascia is entered with finger dissection. The finger dissection is used to sweep under the iliac crest and under the 12th rib. The peritoneum is swept anteriorly, while palpating for the psoas muscle.

b)With gentle superficial hand-held retraction and mobilization of the psoas muscles, the psoas minor tendon can be visualized and is often a landmark for the docking site at the anterior disc space.

c)A probe is placed onto the anterior one-third of the disc space under direct visualization. Once the position is confirmed on lateral X-ray, the probe is then advanced into the disc space, half the length of the disc space. Check this on AP view X-ray.

d)Sequential dilators are carefully passed over the initial probe and an appropriate size retractor is chosen. The final retractor blades are attached to the table-mounted post. The retractor blades are then opened in the cephalad-caudal direction and all the dilators, except for the initial probe, are removed. The initial probe acts as a guide for the anterior-posterior point of entrance into the disc space.

e)Once the disc surface is cleared off with a Penfield #4 and the anterior longitudinal ligament (ALL) visualized, a linear incision is done with a long 15 blade scalpel just behind the ALL. The initial probe can be removed at this point.

f)A small long-handled Cobb elevator is inserted into the disc space all the way to the contralateral margin (but not through the contralateral annulus), under AP fluoroscopy. It is rotated gently to help open up the disc space. Same is repeated with a large Cobb elevator.

g)Discectomy continues with long-handled instruments: Uterine curette, straight double-sided rasp, pituitary and Kerrison rongeurs.

h)Medtronic DLIF Clydesdale trials are used next, starting with an 8-mm height, followed by a 10-mm trial. AP view fluoroscopy is used to check the trajectory of the trial (see Fig. 51.6).

i)Medtronic combo tool is used next to prepare the end plates. A 12-mm height trial is impacted into the disc space and the position checked with a lateral X-ray.

j)Usually, a 12-mm height × 50-mm length × 12 degrees lordosis spacer containing approximately 4 mg rhBMP-2 and Grafton putty is then inserted into the irrigated disc space under AP fluoroscopy. Final X-rays are taken to confirm the position of the graft (see Fig. 51.7).

4. Closure:

a)Running 1-PDS or 0-Vicryl for fascial layer. Interrupted 2–0 Vicryl for subcutaneous layer, and 3–0 Vicryl for the dermal layer.

b)Steri-Strips and dry gauze dressing.

5. Imaging:

a)Standing AP and lateral X-rays are obtained after patient ambulates post stage 1 (see Fig. 51.8).

b)MRI or CT only indicated if patient has new radicular pain/weakness or if the patient complains of persistent preoperative radicular symptoms.