PHYSICIANS ROUND TABLES

Low Profile Sacral Alar-Iliac Pelvic Fixation

S2 Iliac Technique for Lumbopelvic Screw Placement: A Report of Two Cases

Kai-Uwe Lewandrowski, MD and Nicholas Ransom, MD, Tucson Arizona

Background

Distal fixation in thoracolumbar spine surgery is important in many clinical scenarios. 1,2 Higher pseudarthrosis rates have been associated with poor clincial outcomes when using S1 promontory screws without supplemental pelvic fixation.2–5

Anchoring long constructs at the lumbopelvic is often challenging. Several techniques include transiliac bars, iliac post bolts, and iliosacral screws have been widely used. Studies have shown that iliac screws are biomechanically superior at least in vitro.6 Two commonly used techniques are the Galveston and iliac screw techniques. These latter two techniques, however, can present with additional clinical problems. For example, iliac fixation may require a separate facial or skin incisions and the use of additional side- or offset connectors may become necessary. 7–10 Dissection in the area of the posterior superior iliac spine or the iliiac wing may compromise the integrity and vascularity of muscle and skin layers in this area and lead to tissue necrosis, skin break down, and infection. Cross- and side connectors are often prominent and may become symptomatic prompting removal at some later point in time.

Therefore, alternative methods of lumbopelvic fixation are attractive. The S2 iliac technique has been described by Dr. Sponseller and Dr. Kebaish. 1 We present two cases where this technique was successfully employed.

Case 1

The patient is a 28-year-old male who complained of lower back pain following an instrumented posterolateral L4-S1 spinal fusion which he had done 2 years prior to presentation after a failed L4-S1 Laminectomy at another institution. The posterolateral fusion surgery was complicated by a postoperative wound infection with Methicillin Resistant Staphylococcus Areus (MRSA). The patient had failed over one year of non-operative management and was requiring escalating doses of oral narcotics. On initial presentation to our clinics, he had the following imaging studies:

Preop AP (Left), and Lateral (Right) showing a failed instrumented L4-S1 posterolateral fusion with broken S1 pedicle screws and a high-grade L5/S1 slip.

Revision surgery was performed in three stages:

1. Posterior revision laminectomy and removal of spinal instrumentation.
2. Anterior L5/S1 fusion with a fibulur strut allograft and L4/5 ALIF with PEEK spacer, bone graft, and tension band plating using locking screws.
3. Posterior instrumented fusion L4-S2 by placing pedicle screws into L3, L4 and S1, and by placing S2-ilium screws.

Postop AP xray (Left) showing a true S2-ilium screw on the left side and a shorted S2-pedicle screw not crossing the SI Joint on the right. Lateral postop xray (Right) showing ALIF at L4/5, instrumented L3-S2 pedicle screw fusion, and anterior fibular strut allografting from L5 into S1.

Postop Sagittal (Left) and coronal (Right) CT scan of the fibular strut graft crossing from the L5 into the S1 vertebral body to facilitate fusion at the lumbosacral junction in the setting of a high-grade slip.

The lower anchor points of the sacropelvic fixation were long pedicle screws placed through the S2 pedicle in an outward distal trajectory across the non-articulating portion of the Sacroiliac Joint (SI Joint) aiming for the lower portion of the ilium above the greater sciatic notch. The starting point is approximately 20 mm distal to the center of the S1 pedicle. The top of the S1 endplate may also be used as a reference point. These screws can average between 50 and 110 mm in length. The S2-ilium screws used in the case were 55 mm screws on the left side and 75 mm screws on the right side. The left-sided S2 pedicle-ilium screw did not cross the SI joint.

Coronal and Sagittal CT scans of the S2-ilium pedicle screws.

Top: Coronal views showing the left-sided screw crossing the lower non-articulating portion of the SI joint, whereas the right screw remains in the sacrum without exiting. Bottom: Sagittal views showing the both the left- and right-sided screws traversing the S2 pedicle.

Outcome

The patient did ultimately well from the three-stage revision surgery. He did not have a postoperative wound infection. At the time of this report, he is 7 months postop. His ODI and VAS pain score decreased from preop 55 and 6 to 28 and 3, respectively.

Case 2

The patient is a 66-year-old female who presented with increasing low back pain with ambulation due to flat back and iatrogenic sagittal imbalance. She had a T4-L2 instrumented posterolateral fusion done 18 months prior to presenting to our clinic at another facility. At the time of the index procedure, she required a revision fusion with extension to L4 within one week from her index procedure for failed instrumentation and pulled-out pedicle screws. Her posteropative recovery was initially uneventful but she then increasingly complained about flat-back-related symptoms. She had failed 9 months of non-operative management and was requiring escalating doses of oral narcotics. Upon initial evaluation, the following imaging studies were obtained:

Preop AP (Left), and Lateral (Right) thoracic and lumbar xrays showing a long-segment fusion from T4 - L4 that at initial presentation. There is radiographic evidence of adjacent level disease at L4/5, and L5/S1 with loosening of the distal pedicle screws suggestive of non-union.

Revision surgery was performed in three stages:

1. L4/5, and L5/S1 ALIF with PEEK spacers, bone graft and anterior tension band fixation with locking screws to achieve anterior interbody fusion.
2. Removal of posterior spinal instrumentation from T12 - L4, reinsertion of pedicle screws T12 - L4 and insertion of pedicle screws L5 - S2-ilium.
3. L3-Pedicle Substraction Osteotomy with 40 degree restauration of lumbar lordosis, and completion instrumented posterolateral spinal fusion by connecting the pedicle screws from T12 - S2-ilium with titanium rods and posterolateral bone grafting using end-to-side connectors at T12 to connect to the proximal fusion construct.

Postop AP xray (Left) and neutral, extension & flexion lateral views showing an L3 substraction pedicle osteotomy and L4-S1 ALIF with PEEK spacers, bone graft, and anterior tension band plate. The posterior instrumentation goes down to the S2 level with a S2-ilium screws both of which cross the distal portion of the SI Joint where no cartilage is present.

The lower anchor points of the sacropelvic fixation were long pedicle screws placed through the S2 pedicle in an outward distal trajectory across the non-articulating portion of the Sacroiliac Joint (SI Joint) aiming for the lower portion of the ilium above the greater sciatic notch. The starting point is approximately 20 mm distal to the center of the S1 pedicle. The top of the S1 endplate may also be used as a reference point. These screws can average between 50 and 110 mm in length. The S2-ilium screws used in this case were 65 mm on both sides. Both S2 pedicle-ilium screw did cross the SI joint. The right-sided screw ended within the ilium. The left-sided screw exited anteriorly just after crossing the SI joint.

Coronal and Sagittal CT scans of the S2-ilium pedicle screws.

Top 2 rows of panels: Coronal views showing the left-sided screw crossing the S2 pedilce into the lower non-articulating portion of the SI joint and exiting anterior to it, whereas the right screw remains in the sacrum and without exiting exiting the ileum. Bottom: Sagittal views showing the both the left- and right-sided screws after having crossed the SI joint ending within the ilium. On the left, the tip of the S2-ilium screw ends right above the greater sciatic notch.

Patient 6 months postop with improved sagittal balance.

Outcome

The patient did well from the anterior procedures (L4-S1 ALIF), but had a complicated postoperative course following her first posterior procedure. The posterior portion had to be staged due to high-blood loss, and intraoperative coagulopathy requiring ICU stay. She stabilized quickly after the T12 - L4 hardware removal, and reinsertion of pedicle screws from T12 - S2-ilium. A third surgery, was required to complete the posterior portion with L3 pedicle subtraction osteotomy, and completion instrumented posterolateral fusion from T12 to S2. The patient had a prolonged hospital and rehab stay after her three-staged surgery was completed. She ultimately did well and did not develop a postoperative wound infection. At the time of this report, she is 6 months postop. Her ODI and VAS pain score decreased from preop 61 and 7 to 24 and 4, respectively. Click here to watch this patient's video .

Conclusions

The S2 iliac technique is an attractive alternative method of lumbopelvic fixation. The S2-ilium low-profile pedicle screw is in-line with the remaining lumbosacral screws and offers great advantage with respect to wound healing, posteroperative infections, and distal points of fixation. We had no wound infections, or skin break-down. The complexity of the preoperative condition leading up to surgery requiring distal lumbopelvic fixation impacts the postoperative course. Postoperative complications should be expected.

Literature

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