Instrumented reduction of high-grade spondylolisthesis with distal anchorage using iliac screws vs. S2 screws: a comparison of techniques, complications and results

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High grade spondylolisthesis (HGS) can present with significant pain, neurologic deficits and significant deformity. Most advocate decompression along with some amount of instrumented reduction to correct lumbosacral kyphosis and sagittal plane imbalance.



Analyze outcomes and complications arising from gradual instrumented reduction of HGS using distal fixation at S1 (grade 3 only), S2 alar screws, or iliac screws.


Study Design

Retrospective review of prospectively gathered data


Patient Sample

26 consecutive patients (22 Female, 4 Male) with HGS at L5-S1 who underwent surgical correction by a single surgeon from 1993-2010. Average age 31 years (10 - 50 years). Excluded: traumatic or other causes of HGS.


Outcome measures

Visual Analog pain Scores (VAS), Oswestry Disability Index (ODI), Complications



HGS grades: Grade 3- 13, Grade 4- 2, Grade 5– 10. Spondyloptosis (Grade 5) was defined as the entire L5 vertebral body below a horizontal line at the top of the sacrum. All patients underwent posterior only surgery including full Gill laminectomy, gradual incremental correction of lumbosacral kyphosis and HGS, and instrumented posterolateral arthrodesis. Grades 4 and 5 had sacral dome osteotomy and interbody fusion. Grades 4 and 5 also had bilateral contoured temporary alar distraction rods (hooks under L1 distracted from hooks the ala) used during decompression and construct assembly to improve the local lumbosacral kyphosis and loosen the deformity. Grade 3 patients had distal fixation of S1 screws alone. Grades 4 and 5 used either: bilateral S1 and S2 sacral alar screws vs. bilateral S1 pedicle screws and iliac screws. Distal fixation at S1 alone was used in 5 patients (all Grade 3), 9 patients had iliac screw fixation (all grade 4 or 5). Of the 12 patients treated with S2 fixation, 11 had Grade 4 or 5 slips.



Follow up ranged from 2-10 years. Complications included 2 foot drop, 1 temporary quadriceps weakness (resolved by 1 year), and 3 infections. There were no nonunions. All 5 patients with cauda equina syndrome improved after surgery. Screw loosening or hardware failure within 3 months was noted in 4/12 patients with S2 distal fixation, all 4 lost alignment and required revision surgery; 0/9 patients with iliac screws lost fixation. Ten patients had clinical outcomes: VAS averaged 6.2 pre-op, improved to 2.0 at 2 years. Oswestry averaged 35 pre-op improved to 17.2 at 2 years.



After decompression and removal of tethering structures, gradual instrumented reduction of HGS deformity produces good long-term results, with less revision surgery using Iliac screw fixation compared to S2 screws. Bilateral iliac screws are better than S2 alar screws at providing sufficient strength to counter the required reduction forces. Sacral dome osteotomy and temporary alar distraction rods are useful in grade 4 and 5 listhesis. The reliability of pain relief and restoration of lumbosacral alignment make instrumented reduction of HGS with iliac screws an attractive treatment alternative. Long-term outcomes appear durable.