Iliac Screw Fixation: Radiographic and Clinical Outcomes of Unilateral vs. Bilateral Placement

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Iliac screw fixation improves construct strength and stability but extends operative times and may require a separate procedure for removal due to irritation. Biomechanical studies have suggested that unilateral iliac screw placement may be as effective as bilateral placement, but no study to date has fully explored the clinical and radiographic outcomes between these two methods.


The purpose of this study is to compare the clinical and radiographic outcomes as well as the complications of unilateral vs. bilateral iliac screw fixation for lumbosacral fusions.


Retrospective analysis of prospectively-collected database


Consecutive adult patients undergoing primary lumbosacral fusion involving the use of one or more pedicle screws


Visual-analog pain scale, Oswestry Disability Index; Radiographic outcome: X-rays


67 consecutive adults at one center underwent unilateral (n=33) or bilateral (n=34) iliac screw fixation as part of their lumbosacral fusion. Diagnoses were spondylolisthesis (n=8), degenerative scoliosis (n=23), idiopathic scoliosis (n=12), kyphoscoliosis (n=20), and other degenerative disorders (n=4). Clinical outcomes included the visual-analog pain scale (VAS) and the Oswestry Disability Index (ODI) at pre-op, 1 year, 2 year, and latest follow-up.


Unilateral and bilateral groups had similar clinical scores for both VAS (pre-op: 5.0 vs 5.7, p=0.282; 1yr: 3.3 vs 3.4, p=0.989; 2yr: 3.2 vs 4.0, p=0.388) and ODI (pre-op: 25.1 vs 25.0, p=0.932; 1yr: 14.8 vs 17.2, p=0.352; 2yr: 18.5 vs 16.4, p=0.726). All radiographic parameters, including alignment and balance, were similar between the groups except for iliac screw halo signs, which occurred only in unilateral fixation (4[12.1%] vs 0[0%], p=0.05). Complications between unilateral and bilateral groups were similar and included non-union (1[3.0%] vs 1[2.9%]), symptomatic screw (4[12.1%] vs 6[17.6%]), infection (5[15.2%] vs 2[5.9%]), screw fracture (0[0%] vs 2[5.9%]), rod fracture (0[0%] vs 3[8.8%]), spinal imbalance (3[9.1%] vs 1[2.9%]), and screw removal (2[6.1%] vs 4[11.8%]).


Unilateral iliac screw fixation produces good results in fusions down to the sacrum. Despite having more radiographic signs of screw loosening, the overall rate of union, coronal and sagittal balance, and functional outcomes were not significantly different with unilateral fixation compared with bilateral fixation. Unilateral screws required removal with approximately half the frequency of bilateral fixation.