An Imaging Study Of Spinal Pelvic Surgery

Summary of Background:Sacropelvic fixation is now widely used in spinal surgery, especially in the deformity surgery for adults with scoliosis, kyphosis, neuromuscular kyphoscoliosis, high-grade spondylolisthesis (Grade III or higher). Long fusions to the sacrum would add huge flexional, rotary, and compressive moment to the lumbosacral junction。On the other hand, the poor bone quality of the sacrum could not support a stable and rigid anchor in the distal part of the fixation。Rates of instrumentation failure and pseudarthrosis remains high. Iliac Screws provide optimal pelvic fixation which largely reduces the rate of these complications. But its starting point is in the PSIS which is so close to the skin. Instrumentation prominence and pain are the most common complications. Also iliac screw requires much more muscle dissection which may increase the risk of infection.S2AI screw is a newly developed technique which could also provide a stable and stiff pelvic fixation. Besides, it decreases implant prominence as its entrance is approximately15-mm deeper than that of the iliac screw. The complication rate of S2AI was much lower than that associated with other techniques. How to find an optimal placement of S2AI challenges researchers because of its population diversity and complex regional anatomy.The general entry point is1-2mm inferior and1-2mm lateral to the S1dorsal foramen, and its optimal entrance angles varied.Objective:To establish a radiographic method of measurement which is supposed to be scientific and reliable quantitative measurement of optimal placement of posterior second sacral alar iliac (S2AI) screw for instrumentation and fusion of scoliosis.To collect the normal and healthy people’s pelvic CT image Data, and try to find a optimal placement of S2AI screw including optimal starting points and optimal angle in a Chinese population.Methods:S2AI screw trajectories were mapped on three-dimensional computed tomography (3DCT) reconstructions of40normal adult pelvises of men. Three different entry points(S1,S2,S3) and four deferent plans(D0,DX,D1,D2) each side were chosen. Recording to the data review. We simulated a screw with a diameter of7mm inserting into the pelvic in12ways. We mainly measured and analyzed the data including the safe angular dimension, the maximum distance of screw placement, width of the minimum distance of the ilium etc. Then we compared these data between different angles and entry points, to investigate the optimal placement of S2AI.Result:S2AI screw fixation through S3have a larger safe angular dimension,longer maximum distance of screw placement, wider minimum distance of ilium compared to the S1and S2entry point. And the minimum width of the ilium appears further from the starting point.But its average distance in ilium is the shortest. The direction from the starting point to the anterior inferior spine (DO) is optimal of the four.