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Lumbosacral fixation using sacroiliac buttress screws: a modification to the Jackson technique with intrasacral rods
© Fukuda et al.; licensee BioMed Central Ltd. 2014
Received: 23 May 2014
Accepted: 1 July 2014
Published: 12 July 2014
The use of intrasacral rods has been previously reported for posterior lumbosacral fixation. However, problems associated with this technique include poor stability of the rod in the sacrum, difficulty in contouring the rod to fit the lateral sacral mass, and the complicated assembly procedure for the rod and pedicle screws in the thoracolumbar segments after insertion of the rod into the sacrum.
We used a screw with a polyaxial head instead of an intrasacral rod, which was inserted into the lateral sacral mass and assembled to the rod connected cephalad to pedicle screws. The dorsal side of the screw was stabilized by the sacral subchondral bone at the sacroiliac joint with iliac buttress coverage, and the tip of the screw was anchored by the sacral cortex.
Three different cases were used to illustrate lumbosacral fixation using intrasacral screws as an anchor for the spinal instrumentation. Effective resistance of flexural bending moment and fusion were achieved in these patients at the lumbosacral level.
An intrasacral screw can be stabilized by subchondral bone with iliac buttress coverage at the dorsal and ventral sacral cortex. Posterior spinal fusion with this screw technique enables easier assembly of the instrumentation and presents better stabilization than that provided by the previously reported intrasacral rod technique for correction and fusion of thoracolumbar kyphoscoliosis.
Posterior spinal fusion at the lumbosacral junction remains challenging because this surgery is associated with a high rate of complications, such as pseudarthrosis and instrumentation failure[1, 2], particularly in patients requiring correction for long fusion segments and/or severe deformities. Bilateral bicortical screws at the S1 segment are not sufficient as distal foundations for long fusions; thus, an additional anchor at the sacrum and/or ilium is required. Several surgical techniques have been developed to overcome this problem, including the use of iliac rods or screws[3–5], iliosacral screws, and intrasacral rods.
Jackson and McManus reported that the placement of intrasacral rods is a useful technique for posterior lumbosacral fixation, in which rods are inserted into the lateral sacral mass and attached to segmental pedicle screws. The rods are stabilized by the subchondral bone of the sacrum at the sacroiliac joint with iliac buttress coverage. This buttress effect provides resistance to flexural bending at the lumbosacral level. One of the difficulties of this technique is in contouring rod to fit the lateral sacral mass and spinal curvature. The procedure of attaching the rod to the S1 pedicle screw and every level cephalad is technically demanding, particularly in patients with severe spinal deformities. To overcome this difficulty, we modified the methods of Jackson and McManus by way of using a screw with a polyaxial head instead of the intrasacral rod for a good distal foundation and easy assembly of the instrumentation. In this report, we introduce a surgical technique based on a modification to the Jackson procedure.
We use intrasacral screws with polyaxial heads that allow a wide range of angulation formed between the head and screw axes; the ZODIAC® Spinal Fixation System (Alphatec Spine, Inc., Carlsbad, CA, USA) and the EXPEDIUM™ Dual Innie System (DePuy Synthes Spine, Inc., Raynham, MA, USA) or the CD HORIZON® SOLERA™ Spinal system (Medtronic, Inc. TN, USA). Screws are less than 7 mm in diameter because there is insufficient space in the lateral sacral mass in approximately 8% of patients to accommodate a 7-mm rod.
Representative case presentation
The connection of an intrasacral rod to pedicle screws is one of the techniques for lumbosacral fixation reported by Jackson and McManus. Theoretically, the ilium and sacroiliac ligaments provide a buttress effect to the rods against a flexural load. One of the difficulties of this procedure is in contouring the rod to fit the lateral sacral mass and spinal curvature. In addition, the procedure to assemble the rod to S1 and pedicle screws cephalad to it is technically demanding. Here we introduced an intrasacral screw as an alternative for a part of the rod. The use of this alternative technique with screws with polyaxial heads enables easier assembly of the rod and screws compared with previous techniques. This intrasacral screw technique is indicated for patients with kyphoscoliosis at the lumbosacral level.
Modification of rod insertion to the intrasacral screw has another advantage. The construct with an intrasacral screw is more stable than that with an intrasacral rod against pull- and/or back-out forces because the screw threads interdigitate with the subchondral bone under iliac buttress coverage with the dorsal and ventral cortex of the sacrum. Kuklo et al. reported a similar modification of the Galveston iliac rod to the screw and Schwend et al. performed a mechanical test in a cadaver model and demonstrated that iliac screws were more than three times stronger than iliac rods.
Posterior spinal fusion at the lumbosacral junction remains challenging because of the complex anatomy and poor bone quality of the sacrum. Several techniques have been reported to achieve distal foundation of the instrumentation[11, 12]. Sacroiliac screws from the S2 alar crossing the sacroiliac joint to the ilium are considered to form a stronger foundation than the presented technique. However, the impact of sacroiliac screws on the sacroiliac joint remains uncertain in long-term follow-ups.
Limitations of this study include the small number of cases, short follow-up periods, and lack of biomechanical data. Furthermore, intrasacral screws may not provide a sufficient foundation for some patients who require a more extensive force to correct curvature. The combination of distal foundation techniques of instrumentation, use of an orthosis, and temporary limited postoperative activities can help to achieve successful fusion.
The placement of an intrasacral rod by the Jackson and McManus technique can be modified to accommodate an intrasacral screw with a polyaxial head connected to the rod. This modification may contribute to stronger distal foundation and easy assembly of the instrumentation for posterior spinal fusion at the lumbosacral junction.
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