Elsevier

Spine Deformity

Volume 7, Issue 4, July 2019, Pages 509-516
Spine Deformity

Review
Sacropelvic Fixation: A Comprehensive Review

https://doi.org/10.1016/j.jspd.2018.11.009Get rights and content

Abstract

Sacropelvic fixation is indicated in various clinical settings, most notably long spinal arthrodesis, reduction of high-grade spondylolisthesis, and complex sacral fractures. The sacropelvis is characterized by complex regional anatomy and poor bone quality. These factors make achieving solid fusion across the lumbosacral junction challenging. However, a better understanding of spinal biomechanics at that level has led to much higher fusion rates than those of the past. The newer fixation techniques are biomechanically superior to previous methods mainly because they achieve bony purchase anterior to the pivot point—first described by McCord et al. in 1994. Today, the two most widely used fixation techniques are iliac screws and S2-alar-iliac screws. Although these techniques are associated with very high rates of fusion, instrumentation-related pain and reoperation remain problematic. This review provides an overview of the regional anatomy and biomechanics at the lumbosacral junction, as well as a summary of fixation techniques with an emphasis on the most widely used techniques today.

Level of Evidence

IV.

Section snippets

Overview

The lumbosacral junction has complex anatomic features that make it a unique area of the spine [1]. It is the most mobile lumbar segment in the sagittal plane; however, its range of motion in the coronal plane is the narrowest of all spinal levels [2]. The lordotic curvature of the lumbar spine results in the lumbosacral segment having the most steeply angulated disc [3]. Load vectors in the setting of these unique anatomic parameters create the largest translational shear forces generated in

Anatomy

A comprehensive understanding of the spinopelvic anatomy and its variations is valuable in understanding and performing the various sacropelvic fixation techniques. The lumbar vertebrae are the largest of the human spine. They are characterized by a reniform shape, which is deeper and thicker ventrally than dorsally [15]. They differ from the thoracic spine in that they have transverse processes instead of lateral facet articulation with the ribs and a larger pedicle diameter [1], [2]. The fact

Classification of Pelvic Fixation Zones

The most widely used classification system for sacropelvic fixation was described by O'Brien et al. [22] in 2004. They divided the sacropelvis into three zones of fixation (Fig. 2). Zone I consists of S1 and the cephalad sacral alae, zone II encompasses the sacral alae below and S2, and zone III is the bilateral ilia. Zone I fixation with S1 screws or rods is the least biomechanically stable because of the high risk of facet fracture and screw pull-out [22], [23]. Zone II is noted for having

Pelvic Parameters

Spinal sagittal alignment is largely defined by the relationship of the spine to the pelvis. Analysis of the pelvis in the sagittal plane is typically assessed with three angular measurements: pelvic tilt (PT), pelvic incidence (PI), and sacral slope (SS) (Fig. 3) [29]. PT is defined as the angle between the vertical reference line and the line connecting the femoral head to the midpoint of the sacral plate. PT is usually elevated in the setting of sagittal imbalance as a compensatory

Indications

The most common indication for pelvic fixation in spine surgery is a long fusion to the sacrum. The tremendous flexion and cantilever moments at the lumbosacral junction require a rigid foundation to support the cephalad construct (Fig. 4). Cunningham et al. [33] showed that long fusions above L3 significantly increase the strain on S1 screws; therefore, augmenting the distal fixation with iliac screws helps protect the S1 screws. The cephalad fusion level at which sacropelvic fixation is

Preoperative Planning

Preoperative planning should involve the use of radiographs to formulate a three-dimensional scheme and determine the optimal screw path and positioning. Posteroanterior and lateral 36-inch radiographs should be part of the preoperative planning for all cases requiring sacropelvic fixation. These two views allow for the assessment of sagittal and coronal realignment and presence of pelvic obliquity, all of which are crucial factors in the correction of a spinal deformity [52]. Pelvic inlet and

Harrington Technique

Before the era of spinal instrumentation, sacropelvic fixation was attempted using whole-body casting. However, high pseudoarthrosis rates, complications of immobility, and inadequate correction led to the development of Harrington instrumentation [8], [57]. The Harrington technique consists of spinal distraction with cephalad and caudal hooks attached to the transverse processes or laminae while connected to a ratcheted rod [58]. Pseudoarthrosis rates were found to be high with this technique,

Conclusion

Sacropelvic fixation has evolved substantially since the advent of body casting in the 1960s. The two most widely used methods today, S2AI and iliac screw fixation techniques, offer comparable biomechanical stability and rates of fusion. Recent studies of the S2AI technique show significantly lower rates of instrumentation-related complications and reoperation rates compared with iliac screw fixation. Both methods are skill-dependent, but allow for rigid pelvic fixation and are interchangeable

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    Author disclosures: MHED (none), MR (none), LO (none), KMK (personal fees and other from DePuy Synthes; personal fees from K2M and Orthofix, outside the submitted work).

    IRB approval: Institutional review board approval was not required for this study.

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