الفهرس 
? Anatomy of the Lumbosacral and Spinopelvic RegionsOnly 14 pages are availabe for public view
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Abstract
L umbosacral pelvic fixation and fusion procedures have been used to treat back pain caused by lumbar instability at the level of L5-S1; and coronal or sagittal deformities and pelvic obliquity to achieve balanced spine; also, when it is needed to increase rigidity of fixation in long fusions for degenerative reasons. (9)(33)(53) The lumbosacral pivot point is that point at the middle osteoligamentous column between the last lumbar vertebra and the sacrum. Only those devices that extend anterior to this pivot point provide a significant biomechanical advantage regarding rigidity of fixation. The farther that the implants extend anterior to this point, the greater the stiffness of the construct is. (8)(33) There are many clinical indications for sacropelvic fixation, including long fusions extending to the sacrum, flat-back deformity requiring corrective osteotomy, correction of pelvic obliquity, high-grade (Grade III or higher) spondylolisthesis, sacrectomy, sacral fractures with spinopelvic dissociation, and substantial osteoporosis in the setting of lumbosacral fusion. (29) Many different types of instrumentation and fixation devices are available for lumbosacral and spinopelvic fixation. Some are only of historical interest, whereas others are used frequently in the current armamentarium of spinal surgeons. Properly applied spinal instrumentation maintains alignment and shares spinal loads until a solid, consolidated fusion is achieved.(11) The concept of intrasacral rods has been introduced depending on the iliac buttress effect described by Jackson in 1993. So the rods are implanted in the area of the sacrum buttressed by the ilium, which results in an improved resistance to flexion bending moment. This system has the advantage of not crossing the sacroiliac joint. However, it is not an option for patients who do not have large enough sacral masses or those with an insufficient iliac overhang to buttress the intrasacral rods. It is also technically difficult to insert the intrasacral rods and allow attachment of bilateral S1 pedicle screws. Although its superiority than other sacral fixation methods is questionable.(11)(8) The Luque system introduced the concept of segmental spinal instrumentation with multiple points of fixation by means of sublaminar wires as opposed to correction by means of distraction with cephalad and caudad hooks. Luque instrumentation allowed correction of coronal and sagittal deformities and avoided flat-back syndrome. However, biomechanically, it lacked torsional stability and the ability to resist flexion at the lumbosacral junction and become an obstacle to flexion and extension; also, posterior position of the construct in relation to the lumbosacral pivot point increase stresses and so increase failure rate. It was noted that pseudarthrosis rates with Luque instrumentation were lower than those with Harrington instrumentation. Nerve root injury, particularly at the sacral level, has been reported with the passage of the sublaminar wires.(11)(33 Many of the complications and problems with, caudad lumbosacral fixation that were associated with previous instrumentation systems were diminished with the advent of the Galveston technique; which was developed by Allen and Ferguson in the 1980s. The major improvement was the incorporation of the ilium into the instrumented fusion. Biomechanically, Luque-Galveston technique is more effective than previous Luque instrumentation due to anterior position of the intra-iliac part of the rod in relation to the lumbosacral pivot point.(11) Iliac screw fixation is a logical advancement from the development of Galveston iliac fixation as it is well known that the purchase of screw is much better than that of the rod. (33) Actually, the iliosacral screw is a sacral screw but passes through ilium to increase its purchase. Compared with S1 pedicle screws, iliosacral screws offer increased caudad purchase and strength by passing through both cortices of the iliac crest and the S1 pedicle. Also, they gains better direction and they have longer part anterior to the lumbosacral pivot point increasing biomechanical advantage and resistance to pullout forces. As well as, sacroiliac screws offer the advantage for correction of the pelvic obliquity and for revision surgery and do not violate the sacroiliac joint.(8)(33) S2 Alar Iliac Screws allows a single rod to be used without the need for cumbersome connectors and has the potential to minimize the complexity of the procedure. Decreased implant prominence is one of the advantages of this technique, because the starting point is approximately 15-mm deeper than that for entry to the posterosuperior iliac spine. (29) Sublaminar devices include wires, cables and hooks; do not provide sufficient biomechanical strength in long fusions ending at the sacrum. The implants lie dorsal to the lumbosacral pivot point and add little biomechanical strength to the construct. However, they can be used as adjunct to augment the construct.(11)(33) Many sacropelvic fixation techniques have been attempted, but only a few are still widely used. Some of those techniques are associated with high rates of complications, which can be minimized by paying close attention to the regional anatomy, minimizing soft tissue dissection, and choosing low-profile implants and techniques. To add anterior structural support, anterior fusions should be considered in long fusion that extend to the upper thoracic spine, which will remove some of the stresses from the posterior implants and enhance and allow early bony fusion. Spine surgeons performing complex spinal reconstruction should be familiar with the currently available techniques, including their potential risks and complications. Surgical treatment decisions should be based on an individual patient’s anatomy and abnormalities and on the surgeon’s experience (29).