Overview
The surgical management of sacral fractures is challenging. Although they are rare injuries, they often present with a wide variety of injury and fracture patterns. Presentations vary from high-energy traumatic mechanisms to low-energy stress insufficiency fractures in elderly patients with osteoporosis. In the setting of trauma, sacral fractures often occur with pelvic and lower extremity fractures, with or without concomitant neurologic dysfunction.
Sacral fractures occur in approximately 45% of pelvic injuries. The treatment of sacral fractures is influenced not only by the many fracture patterns of the sacrum itself but also by injuries to the pelvis and lumbar spine. Late sequelae of untreated, unstable sacral fractures can lead to significant morbidity and dehabilitation. In this chapter, we review the surgical management of a variety of sacral fractures, injury patterns, and outcomes.
Anatomy
The sacrum plays an integral role in lumbopelvic alignment and stability via strong osseous and ligamentous structures. In addition, the sacrum serves as a weight-bearing platform for the spine and protects the lumbosacral plexus. The sacrum has an overall kyphotic sagittal alignment, from zero to 90 degrees. In conjunction with the sacral inclination angle, this alignment helps determine the compensatory lordosis of the lumbar spine.
The sacrum encases the cauda equina, which passes through the sacrum. Each of the sacral nerve roots passes through individual foramina. The average foraminal diameter increases moving caudally in the sacrum; this helps explain why foraminal entrapment is more common in the upper sacral nerve roots (S1 and S2) compared with the lower roots (S3 and S4).
The anterior rami of sacral roots two through five provide parasympathetic innervation and allow for important bowel, bladder, and sexual function. Unilateral sacral root S2−S4 function is important for maintaining these functions. Bilateral nerve root involvement is more likely to cause neurologic dysfunction. Sympathetic ganglia of the inferior hypogastric plexus extend anterolaterally from the L5 and S1 vertebral bodies to the anterior and medial margins of the foramina from S2 through S4. Posterior rami contribute sensory fibers to the cluneal nerves. In a study of 44 patients with sacral fractures, Gibbons also noted that unilateral root injuries did not affect sphincter tone.
In contrast to the thicker, soft tissue structures in the lumbar spine, only a thin lumbosacral fascia and the multifidus muscles lie posterior to the sacrum. This thin, soft-tissue envelope does not provide the same level of coverage for spinal instrumentation as seen in the thoracolumbar spine.
Diagnosis
Initial assessment should include a history and physical examination, with particular emphasis on checking for neurologic deficits and associated soft tissue injuries. Sacral fractures are often missed in patients with multiple traumatic injuries. Denis and colleagues showed that patients were more likely to be diagnosed with sacral fracture if an associated neurologic deficit was present. In their study, 51% of patients without neurologic deficit had sacral fracture correctly identified (76% of patients with neurologic deficit).
One factor that affects missed diagnoses is the difficulty in assessing sacral fractures with standard radiographs. In most instances, a computed tomographic (CT) scan with coronal and sagittal reconstructions can help identify most patterns, in conjunction with any associated lumbar and pelvic ring injuries ( Fig. 51-1 ). Magnetic resonance imaging (MRI) may help in cases of occult fractures. In the assessment of sacral fractures, attention should be directed to the level and type of sacral fracture, involvement of the lumbosacral junction and sacroiliac joint, and any pelvic ring injury.
Patterns and associated pelvic CT views that are important in the diagnostic assessment of sacral fractures are listed below.
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Axial CT view: anteroposterior (AP) sacral fracture displacement
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Coronal CT view: vertical sacral fracture displacement
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Sagittal CT view: AP translation and kyphotic angulation
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Axial, coronal, and sagittal CT views: degree of central canal involvement and foraminal encroachment
Classification: Sacral Fractures
Several classification systems are used to describe sacral fratures. For the purposes of this chapter, the Denis classification system and subsequent subtypes are used and are shown in Figure 51-2 .
Denis Classification
The Denis classification system (see Fig. 51-2 ) was developed after studying sacral anatomy in 39 cadaveric specimens in conjunction with a retrospective study of 236 patients with sacral fractures. This retrospective multicenter study remains the largest study to date to assess sacral fractures. The Denis system is based on the direction, location, and level of the sacral fracture and is divided into three anatomic zones: zone 1 fractures are lateral to the neural foramen, zone 2 fractures involve the neural foramen, and zone 3 fractures are medial to the neural foramen. Fractures in zone 1 include the region of the ala and are reported to be the most common. In the multicenter study by Denis and colleagues, approximately 50% of the fractures were zone 1 fractures. In 6% of the cases, zone 1 fractures resulted in neurologic injury to the lower lumbar nerve roots; zone 2 fractures involve the neuroforamina. In the study by Denis and colleagues, the zone 2 fracture pattern was the second most common pattern (34%), but it had a higher rate of associated neurologic injury (28%) that often involved the L4, S1, and S2 nerve roots. Zone 3 fracture patterns are those that affect the central sacral canal. In the study by Denis and colleagues, zone 3 fractures were the least common (16%) but had the highest rates of associated neurologic injury (57%).
The Denis classification does not specifically include the level of the sacral fracture, which plays a significant role in neurologic function. Upper transverse fractures that involve S1−S3 have a greater likelihood of urologic dysfunction compared with lower transverse sacral fractures at S4−S5. One postmortem and pathoanatomic study showed the presence of transsected sacral nerve roots in 35% of displaced transverse sacral fractures. Transverse fractures, discussed subsequently, are considered to be a subtype of Denis zone 3 injuries.
Roy-Camille Subclassification and Strange-Vognsen and Lebech Modification
The Roy-Camille subclassification and subsequent modification by Strange-Vognsen and Lebech divides the Denis zone 3 category into transverse fracture types in the sagittal plane on the basis of angulation and displacement. This classification is shown in Figure 51-2, C , and it categorizes injuries from the least severe (type 1), involving simple angulation, to the more severe patterns, with angulation and complete displacement (type 3). The type 4 pattern includes pure axial-loading injuries and was added by Strange-Vognsen and Lebech.
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Type 1: Fractures that are angulated but without translation
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Type 2: Fracture patterns that are both angulated and translated
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Type 3: Injuries that show complete translation and displacement
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Type 4: Comminuted fractures secondary to axial compression
Isler Classification of Lumbosacral Injuries
Lumbosacral injuries usually are a result of high-energy trauma. Patterns may range from subluxation injuries to complete dissociation. Lumbosacral injuries should be considered in patients who come to medical attention with displaced transforaminal fractures, and patients should be evaluated with CT scans. Isler classified lumbosacral injuries ( Fig. 51-3 ) on the basis of a major fracture line involving the lumbosacral junction in relation to the L5−S1 facet, thus potentially affecting lumbosacral stability. In this classification, type 1 fractures are lateral to the facet, type 2 fractures pass through the facet, and type 3 fractures are medial to the facet. Type 1 fractures are usually stable, but type 3 fractures are associated with instability and often necessitate operative intervention.
Surgical Management
Treatment of sacral fractures should address mechanical instability and neurologic impairment. Although most sacral fractures can be treated nonoperatively, for unstable fracture patterns, several surgical options are available, the goals of which are to provide early mobilization and pain relief. Broadly speaking, management consists of surgical stabilization and/or neural decompressive procedures ( Table 51-1 ). Surgical treatment is usually performed in patients with unstable sacral fracture patterns, a concomitant pelvic ring injury, and/or neurologic dysfunction with radiographic evidence of compression ( Fig. 51-4 ). In certain cases, surgery may be considered for patients with multiple traumatic injuries, if surgery can assist with early rehabilitation. Goals of treatment include fracture stabilization and realignment, improved neurologic function, and reduction of morbidity.
| Surgical Goal | Surgical Procedure |
|---|---|
| Posterior stabilization |
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| Neural decompression |
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| Anterior sacral and pelvic stabilization |
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Surgical stabilization procedures (see Table 51-1 ) traditionally included open reduction and internal fixation with sacroiliac plating or bars. Percutaneous iliosacral screw fixation and lumbopelvic stabilization are now more commonly used as surgical options. In cases of neurologic compromise, the surgeon may perform a limited laminotomy/foraminotomy, laminectomy, or neurolysis as needed.
Because of the morbidity associated with anterior approaches, most surgical treatments for sacral fractures can be addressed via minimally invasive percutaneous or open posterior approaches. Pelvic ring injuries that have associated unstable sacral fractures should first have the anterior pelvic ring injury addressed surgically before embarking on posterior stabilization techniques (see Fig. 51-4 ).
Surgical Timing
The timing of surgery in patients with sacral fractures is largely based on the patient’s overall medical condition, associated extremity injuries, and soft tissue status. Delayed surgical stabilization may affect the surgeon’s ability to obtain quality reduction. In cases of closed reduction and percutaneous fixation for pelvic ring disruptions, Routt and colleagues showed that delaying surgery for more than 5 days for unstable Denis zone 1 and 2 fractures resulted in less accurate closed reduction.
Approach to Surgical Stabilization
Any pelvic ring injuries should be addressed before posterior sacral stabilization procedures are performed. Reduction of the sacroiliac joints is provided by anterior pelvic plating when needed. This also allows for stability when the patient is placed in the prone position for formal posterior sacral stabilization procedures. Once the pelvic ring is stabilized, deciding on the appropriate sacral stabilization procedure largely depends on the sacral fracture pattern.
Although posterior iliac screws can be useful in treating vertical sacral fractures and sacroiliac joint disruptions, they are less suitable for horizontal unstable sacral fracture patterns, which are more amenable to lumbopelvic stabilization. Open lumbopelvic stabilization allows for concomitant neural decompression in cases of nerve compression from bone impaction. Percutaneous sacroiliac screw fixation should not be performed if reduction is not achieved via closed means.
Use of isolated percutaneous sacroiliac fixation techniques in unstable sacral fractures may not effectively prevent the development of a kyphotic deformity alone. However, percutaneous sacroiliac screws placed in conjunction with lumbopelvic procedures for vertical unstable fractures may provide additional stability. This technique, described as triangular osteosynthesis, was studied by Schildhauer and colleagues. The biomechanical study showed that for unstable transforaminal sacral fractures, triangular osteosynthesis provided greater stability than iliosacral screw constructs alone. In a retrospective study, this combined technique allowed for early weight bearing. In a 1-year follow-up study of 58 vertically unstable transforaminal sacral fractures treated by this method, operative reduction was maintained at follow-up in 95% of patients. Late complications noted were asymmetric L5 tilting and L5−S1 facet joint distraction. Sacral screw fixation and sacroiliac screw techniques are a focus of Chapters 53 and 54 , respectively.
Posterior Stabilization Techniques
Lumbopelvic Stabilization
Lumbopelvic stabilization is a treatment option for unstable injuries involving the sacrum. The goal is to transfer weight loads from the trunk to the iliac wings of the pelvis, thereby reducing the forces at the sacrum. Proximal stability is provided by pedicle screws into L5 and often into L4. This construct is linked distally to the sacrum via S1 screws. Two long iliac screws are placed into the pelvis between the posterior superior iliac spine (PSIS) and anterior superior iliac spine (ASIS) from posterior to anterior. Iliac screws help stabilize the lumbosacral segment relative to the pelvis. Cadaveric studies have shown superior biomechanical strength of lumbopelvic constructs compared with sacroiliac screw constructs.
Indications
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Sacral fractures in conjunction with unstable pelvic ring injuries
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Stable Denis zone 1, 2, and 3 injuries
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Unstable sacral fracture patterns
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Roy-Camille type 2, 3, and 4 injuries
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Sacral fractures in conjunction with lumbar spine fractures
Operative Setup and Equipment
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Position: prone on an Jackson table
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Neuromonitoring: somatosensory evoked potentials (SSEPs), electromyography (EMG)
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Equipment: fluoroscopy
Surgical Technique: Open Lumbopelvic Stabilization
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Surgical approach: A standard posterior midline incision is made from the distal lumbar spine to the sacrum, with lateral exposure of the transverse processes of L5 and L4. The sacral ala and PSIS are identified for S1 and iliac screw fixation, respectively.
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Pedicle screws, lumbar spine: Top-loading polyaxial screws are placed into L5; depending on the degree of sacral instability, they may also be placed into L4 for a stronger construct.
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Pedicle screws, sacrum: Top-loading polyaxial screws are placed into the sacral ala bilaterally.
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Iliosacral screws: C-arm fluoroscopy is placed for the obturator outlet view; the x-ray beam is perpendicular to the plane of the sacrum and is then tilted 35 degrees cephalad. The starting point should take into account the position of the L4−S1 screws, thus allowing ease of rod passage. To avoid neuroforaminal compromise, these screws are fully threaded transfixation screws and are not placed in compression. The longest possible screws are selected to allow for maximum purchase within the ilium ( Fig. 51-5, A ). Figure 51-5, B , shows an example of lumbopelvic fixation.
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