Modified unilateral iliac screw fixation with partial reduction in the treatment of high-grade spondylolisthesis at L5/S1 in adult patients: introduction of key technique, report of clinical outcomes and analysis of spinopelvic parameters

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Study design: Prospective non-randomized study. Background: Management of high-grade spondylolisthesis (HGS) remains challenging. Spinopelvic fixation such as iliac screw (IS) wasdeveloped to deal with HGS. However concerns regarding constructs prominence and increased infection-related revision surgery have complicated it’s use. We aim to introduce the modified iliac screw (IS) technique in treating high-grade L5/S1 spondylolisthesis (HGS) and it’s clinical and radiological outcomes. Methods: Patients with L5/S1 HGS who underwent modified IS fixation were enrolled. Pre- and postsurgical upright full and lumbar spine radiographs were obtained to analyze sagittal imbalance, spinopelvic parameters, pelvic incidence-lumbar lordosis mismatch (PI-LL), slip percentage, slip angle (SA), lumbosacral angle (LSA) and fusion status. Visual analogue scale (VAS), Oswestry disability index (ODI) were evaluated pre- and postoperatively for clinical outcomes assessment. Estimated blood loss, operating time, perioperative complications and revision surgery were documented. Results: From Jan 2018 to March 2020, 32patients (15 males) with mean age of 58.66 ± 7.77 years were included. The mean follow-up period was 49 months. The mean operation duration was 171.67 ± 36.66 min. At the last follow-up: 1) the VAS and ODI score were significantly improved (p<0.05), 2) PI increased by an average of 4.3°, the slip percent, SA and LSA were significantly improved (p<0.05), 3) four patients (16.7%) with sagittal imbalance recovered a good sagittal alignment, PI-LL within ± 10° was observed in all patients. One patient experienced wound infection. One patient underwent a revision surgery due to pseudoarthrosis at L5/S1. Conclusion The modified IS technique is safe and effective in treating L5/S1 HGS. Sparing use of offset connector could reduce hardware prominence, leading to lower wound infection rate and less revision surgery. The long-term clinical affection of increased PI value is unknown.