Abstract
PurposeSpinopelvic fixations involving the S2-alar-iliac (S2AI) and iliac screws are commonly used in various spinal fusion surgeries. This study aimed to compare the biomechanical characteristics, specifically the risk of screw and adjacent bone failures of S2AI screw fixation with those of iliac screw fixation using a finite element analysis (FEA).MethodsA three-dimensional finite element (FE) model of a healthy spinopelvis was generated. The pedicle screws were placed on the L3-S1 with three different lengths of the S2AI and iliac screws (60 mm, 75 mm, and 90 mm). In particular, two types of the S2AI screw, 15°- and 30°-angled polyaxial screw, were adopted. Physiological loads, such as a combination of compression, torsion, and flexion/extension loads, were applied to the spinopelvic FE model, and the stress distribution as well as the maximum von Mises equivalent stress values were calculated.ResultsFor the iliac screw, the highest stress on the screw was observed with the 75-mm screw, rather than the 60-mm screw. The bones around the iliac screw indicated that the maximum equivalent stress decreased as the screw length increased. For the S2AI screw, the lowest stress was observed in the 90-mm screw length with a 30° head angle. The bones around the S2AI screw indicated that the lowest stress was observed in the 90-mm screw length and a 15° head angle.ConclusionsIt was found that the S2AI screw, rather than the iliac screw, reduced the risk of implant failure for the spinopelvic fixation technique, and the 90-mm screw length with a 15° head angle for the S2AI screw could be biomechanically advantageous.
Highlights
Degenerative spinal diseases are one of the most frequently reported chronic health problems affecting the adult population owing to aging
The highest stress on the screw was observed with the 75-mm screw, rather than the 60-mm screw
For the S2AI screw, the lowest stress was observed in the 90-mm screw length with a 30 ̊ head angle
Summary
Degenerative spinal diseases are one of the most frequently reported chronic health problems affecting the adult population owing to aging. Adult spinal deformities have increased owing to the growing elderly population. These spinal conditions lead to an imbalance in the structural support of the spine. With the development of surgical techniques and supporting surgical skills, spinal deformity surgeries have become more frequent. Because of the poor bone quality of most elderly patients, implantation-related problems are frequent, especially in the lumbosacral area. Kim et al [1] reported a pseudoarthrosis rate of 24% at the L5-S1 junction in adult scoliosis surgery. Many studies have shown that long instrumentation to the sacrum without pelvic fixation is susceptible to implant failure [2,3,4]
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