Bicortical S1 Screw Fixation May Obviate The Need for Iliac Screws in Minimally Invasive Surgery for Adult Spinal Deformity

Presented at SMISS Annual Forum 2014
By Joseph Zavatsky MD
With David Briski MD, Brandon Cook MD, MHA,

Disclosures: Joseph Zavatsky MD B; Amendia, Biomet, Depuy, Stryker. D; Innovative Surgical Solutions, Safe Wire, Vivex. F; Biomet. David Briski MD None, Brandon Cook MD, MHA None,

Introduction:
Minimally Invasive Surgery (MIS) allows for the maintenance of the spine’s soft tissue envelope, preserving many of its stabilizing structures. Lumbosacral stability increases when S1 screws are placed in a bicortical fashion. MIS techniques, along with bicortical S1 screw placement may obviate the need for iliac screw fixation in the treatment of Adult Spinal Deformity (ASD).

Aims/Objectives:
To evaluate fusion rates in long deformity constructs in patients with ASD with and without iliac screw fixation utilizing bicortical S1 fixation.

Methods:
A retrospective review from 2009 to 2014 included all patients with ASD treated using MIS techniques. Lateral Interbody Fusion (LIF) was performed for all lumbar interbody fusion levels. Transforaminal Lumbar Interbody Fusion (TLIF) was performed at all L5-S1 levels. Patients were divided into 2 groups. Group 1 (Hybrid) had open pedicle screws with bilateral iliac screw fixation. Group 2 (MIS) had percutaneous pedicle screws without iliac screws. All S1 pedicle screws were placed in a bicortical fashion in both groups. CT scans were obtained at one-year post-op. Two independent board-certified radiologists assessed fusion.

Results:
Twenty-three patients met inclusion criteria and were 1-year out from surgery. Group 1 included 10 patients; Group 2 included 13 patients. There was no difference in age, height, weight, BMI, number of lateral levels fused, pre-operative Cobb angle, or peri-operative complications between the 2 groups. There was a statistical difference in the mean length of the posterior construct between Group 1 and Group 2 (10 vs 6 levels, p<0.05), mean blood loss between Group 1 and Group 2 (1600 vs 566, p=0.006), as well as mean operative times (520 vs 338 minutes, p=0.003). CT scans were available for 21 of the 23 patients and both radiologists agreed there was solid fusion at all interbody levels including L5-S1 (100% fusion rate). Two patients, one from each group, had full-length scoliosis x-rays that demonstrated fusion, without evidence of hardware failure, radiolucency, or migration

Conclusions:
MIS techniques preserve many of the spine’s stabilizing structures in the treatment of ASD. Addition stability is observed when S1 screws are placed bicortically and may obviate the need for iliac screw fixation. These techniques may provide the added stability decreasing pseudoarthrosis / failure rates without the need for iliac screw fixation.