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Case Study 4
S1 Failure in an Elderly Female
Christopher I. Shaffrey, MD
Professor, Department of Neurological Surgery
University of Virginia
Charlottesville, VA
History
Three years ago, the patient, a 72-year-old female, was treated for spinal stenosis and scoliosis. At another institution, she had a T10-S1 spinal fusion.
Although the patient did well for the two months following the T10-S1 fusion, after two months, her back pain increased again. Her posture also changed. When the patient presented at this institution, she was 5'2" tall and weighed 252 pounds.
Examination
The patient has no neurological deficits upon examination.
Images
The patient's lateral supine x-ray (Figure 1A) and AP supine x-ray (Figure 1B) are below. (Both are before a T10-S1 fusion at another institution.)
Diagnosis
Failure of S1 fixation and likely multi-level pseudarthrosis. The patient has significant positive sagittal imbalance.
Treatment
At a different institution, the patient underwent a L4-L5 and L5-S1 ALIF and re-instrumentation with T10 to iliac fusion. (Figures 6A, 6B)
Outcome
At one-year, the patient had marked improvement in posture, mild reduction of low back pain, and an Oswestry Disability Index score of 34.
Case Discussion
Lawrence G. Lenke, MD
The Jerome J. Gilden Professor of Orthopedic Surgery
Co-Chief Pediatric & Adult Spinal, Scoliosis & Reconstructive Surgery
St. Louis, MO
This long adult spinal reconstruction highlights many important points that create a very difficult and complicated surgical course for some of our patients.
Figures 1A and 1B shows the pre-operative films of a 72-year-old female with a mild degenerative scoliosis and multilevel degenerative sagittal plane alignment. Of importance is that these short films do not allow visualization of the entire spinal column from the cervical spine to the pelvis. Also, these x-rays are taken supine and not upright, so there is no information on what the overall sagittal balance is pre-operative. Surgeons contemplating long spinal reconstructions, from the thoracolumbar junction to L4, L5 or the sacrum, need to obtain pre-operative upright long cassette AP and lateral radiographs. Such radiographs enable the surgeon to fully assess the entire spinal column, pelvis, and alignment to optimize postoperative alignment and balance.
Figures 2A and 2B shows again short cassette AP and lateral supine x-rays with a pedicle screw/rod construct for the thoracolumbar junction to S1. Of note, is the S1 screws are placed in a straight-ahead position on the AP x-ray and are short of being bicortical on the lateral x-ray. It is imperative to obtain strong bicortical purchase of S1 screws at the end of long constructs.
Also, acquiring long cassette x-rays to assess overall alignment and balance should be accomplished before the patient leaves the hospital. The ability of S1 screws alone to remain secure in this type of construct, without being supported by S2 or iliac screws posteriorly, or any interbody support of L5-S1 anteriorly, is very challenging.
Predictably, the S1 screws will migrate/loosen in a cantilever flexion type of moment arm, especially when such a tall L5-S1 disc is encountered. The unfortunate sequelae is noted clinically in Figure 3, which shows a mid-length lateral x-ray with the S1 screws nearly completely pulled out of the sacrum. The CT scans (Figures 4 and 5) confirm this. Now, a situation more difficult than the original problem presents in that a revision reconstruction is needed to realign and re-instrument the posterior spine.
Figures 6A and 6B finally shows long cassette AP and lateral x-rays following a revision ASF/PSF with interbody allograft spacers placed at L4-5 and L5-S1 and a revision PSF to the sacrum, including iliac screws. The lumbosacral region is much more secure, but the continued anterior global sagittal imbalance is still worrisome. This produces tremendous cantilever forces on the distal L5-S1 construct during standing and gait (often 6 to 7 times the patient's body weight), with the posterior fusion bone in continuous tension.
Also, no mention is made of the type of bone graft utilized in the most recent reconstruction. In a manuscript from our institution several years ago, our pseudarthrosis rate, at L5-S1 in long constructs to the sacrum/ilium, was greater than 25%. (1) Thus, Figures 7A and 7B, which shows the 1-year postoperative x-rays, demonstrates broken L5-S1 rods and suspected lumbosacral pseudarthrosis with recurrent sagittal imbalance. This is a combination of failed lumbosacral instrumentation/pseudarthrosis and proximal junctional kyphosis above the prior thoracic fusion levels. This was appropriately treated with a revision PSF with implant removal, L2 PSO and PSF from the upper thoracic spine to the sacrum/ilium.
Figures 9A and 9B, 1-year postoperative x-rays, show improved sagittal balance, but with a persistent and approximate 8-10 cm sagittal vertical axis. The outcome scores are improved, but a fair amount of disability remains.
Also, it is imperative to follow these patients for at least 5, if not 10, years after surgery. Many adult pseudarthrosis patients will be demonstrated after 2 years, and many after 5-years follow up, as shown in the paper by Kim et al JBJS, 2006 (1).
So, although the alignment and construct are quite satisfactory at the latest follow-up, this now mid-70-year-old lady, who has had 2 prior lumbosacral reconstructions for pseudarthrosis, and implant failure is not without risk of further problems, will require longer follow-up. This case demonstrates many of the challenges of long spinal reconstructions in an elderly age group. In addition, when ending a long construct from the thoracic spine to sacrum, the use of only 2 S1 screws, without any backup posterior fixation, such as iliac screws, or any interbody support placed via a TLIF or ALIF route, is also quite prone to clinical failure.
At the 2008 Scoliosis Research Society meeting, we presented a series of 33 patients who had been revised at our institution for S1 screw failures/L5-S1 pseudarthrosis in long adult spinal reconstructions (2). We reported that 17 of 19 patients with only S1 screws and no other distal fixation had screw failure at L5 and/or S1.
Even if the L5-S1 interspace had been structurally grafted, 4 of 6 bone grafts collapsed and 2 of 12 cages subsided.
Patients with bilateral S1 and/or bilateral S2 or iliac screws had rod failure at only L5-S1, demonstrating lumbosacral pseudarthrosis.
All patients revised in the study had bilateral bicortical S1 screws and at least 1 iliac screw. Usually, they had 2 iliac screws placed.
Fifteen of twenty-one revisions ultimately healed. However, 6 needed more surgery to become fully solid.
This study therefore shows the difficulty associated with this patient population.
References:
1. Kim YH, Bridwell KH, Lenke LG, Cho SK, Edwards II CC, Rinella AS: Pseudarthrosis in Adult Spinal Deformity Following Multisegmental Instrumentation and Arthrodesis. JBJS 2006: 88-A(4): 721-8.
2. Harimaya K, Mishirao T, Lenke LG, Bridwell KH, Koester L, Sides B: Etiology and Revision Surgical Strategies in Failed Lumbosacral Fixation of Adult Spinal Deformity Constructs. Scoliosis Research Society Annual meeting, Paper # 23, Salt Lake City, UT, September 2008.
Courtesy of Spine Universe
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