Sacral Fracturesp

Jens R. Chapman, MD, Thomas A. Schildhauer, MD, and Carlo Bellabarba, MD O

1. What is the role of the sacrum?

The sacrum connects the lumbar spine and the left- and right-sided iliac wings by means of well-developed ligaments with little inherent bony stability. The sacrum is kyphotically aligned in the sagittal plane in a variable dimension ranging from 0° to over 90°. The sacrum distributes the torso load from the lumbar spine mainly through its S1 segment into the sacroiliac joints and distally to the hip joints.

2. Who is affected by sacral fractures?

Basically two distinct patient groups are affected by sacral fractures:

1. High-energy injury mechanisms: These patients require assessment and treatment as polytrauma victims (e.g. motor vehicle accidents, falls from a height, crush injuries)

2. Low-impact insufficiency fractures: These patients require comprehensive metabolic and neoplasia workup (osteoporosis, previously undiagnosed neoplastic disorder)

3. How are sacrum fractures diagnosed?

Subjective symptoms of patients with sacrum fractures are notoriously vague and usually consist of back pain aggravated by sitting, standing, and walking. A detailed patient history including mechanism of injury and associated injuries is critical. Physical examination is important and consists of inspection and palpation of the patient's back side and thorough examination of neurologic function. Specific imaging and electrodiagnostic tests are critical.

4. Describe the components of the neurologic examination for patients with a sacral fracture.

Regardless of the patient's cognitive status, an evaluation consistent with the Guidelines of the American Spinal Injury Association is performed. A detailed rectal examination is performed. Components of this evaluation include assessment for blood in the rectal vault, as well as presence of the prostate in the expected position. From a neurologic perspective, rectal assessment should include four components:

1. Presence of spontaneous anal sphincter tone

2. Maximum voluntary anal sphincter contractility

3. Perianal sensation to light touch and pinprick

4. Presence of anal wink and bulbocavernosus reflex

Postvoid residuals (PVR) can be used as a follow-up test for patients with neurogenic bladder to assess for reinnervation. In female patients, examination of the vaginal vault is also important.

5. What imaging tests are helpful in assessing sacral fractures?

The basic radiographic assessment starts with an anteroposterior (AP) pelvis radiograph. Due to the inclined nature of the sacrum, visualization of the sacrum is limited. Attention to subtle details, such as disruption of the foraminal lines, is important in screening for sacral fractures. If a fracture is suspected, further radiographs should be ordered, including pelvic inlet and outlet views and a lateral sacral radiograph. If a pelvic ring fracture is suspected, a pelvic computed tomography (CT) is ordered to assess the three-dimensional complexities of the fracture. If a significant sacral fracture is diagnosed, a sacral CT including sagittal and coronal reformatted images is required. Magnetic resonance imaging (MRI) is not routinely necessary but is helpful for diagnosis of insufficiency or stress fractures and to evaluate unclear neurologic injuries. MRI neurography is useful to localize known root or plexus injury. Technetium bone scans with single-photon emission computed tomography (SPECT) images are helpful in identifying insufficiency fractures of the sacrum.

6. What electrodiagnostic tests are helpful in assessing patients with sacral fractures and neurologic injuries?

• Electromyogram (EMG) of L5 and S1 innervated muscles • Pudendal sensory-evoked potentials (pudendal SEPs)

• Anal sphincter EMG • Cystomyography (CMG)

• Somatosensory-evoked potentials (SSEPs) of tibial and peroneal nerves

Pudendal SEPs are helpful for patients with impaired cognitive status or unclear physical examination findings and suspected lumbosacral root injury. Pudendal SEPs are useful in the assessment of the acutely injured patient. In contrast, conventional EMG is limited to assessment of the L5 and S1 roots and usually has a delay time of 3 weeks before injury-related changes are detectable. Anal sphincter EMG and CMG can diagnose lower sacral root damage but are not useful in the immediate postinjury period. CMG has been used as a follow-up study for patients with neurogenic bladder and may demonstrate bladder reinnervation.

7. Why is the diagnosis of sacral fractures frequently overlooked or delayed?

The diagnosis of sacral fractures is overlooked or delayed in up to half of cases. Causes for missed injuries range from vague physical symptoms and findings to difficulties in interpreting an AP pelvis radiograph for sacral abnormalities. This can be especially challenging in obese patients and in the presence of an osteopenia or osteophytes. In multiply-injured patients, a challenging resuscitation setting can distract diagnostic attention from the posterior pelvic ring. A high index of suspicion is important to avoid potential secondary damage from a missed sacral fracture.

8. What are possible consequences of a missed sacral fracture?

• Chronic pain with weightbearing

• Sacral or posterior pelvic malunion

• Secondary neurologic deficits from progressive fracture displacement and/or neural element impingement

• Posterior soft tissue breakdown from progressive sacral kyphosis

9. How are sacral fractures classified?

The wide range of sacral fracture patterns and their frequent association with pelvic fractures has led to development of many different fracture classification systems. The Denis classification is the most helpful general classification of sacral fractures because of its significant implications regarding incidence and type of associated neurologic injury. It uses the most medial fracture extension to distinguish three types of fractures (Fig. 58-1):

• Zone 1 fractures remain lateral to the sacral foramina. This is the most frequent fracture type and is associated with the lowest rate of neurologic injury (5%). Neurologic injury in Zone 1 fractures is limited to the L5 root or sciatic nerve

• Zone 2 fractures extend through the sacral foramina. These are the second most frequent fracture type. Associated lumbo-sacral root injuries occur in one quarter of patients

• Zone 3 fractures involve the central sacral spinal canal. These are the least common injury type but have the highest rate of neurologic injuries (>50%) ranging from sacral root deficits to cauda equina transection with associated bowel and bladder control deficits

The Denis classification, however, does not specifically address zone 3 transverse fractures. The Roy-Camille classification provides a helpful subclassification system (Fig. 58-2) to address these injuries. It differentiates simple kyphotic fractures (type 1), kyphotically and partially translated fractures (type 2), fully displaced fractures (type 3), and segmentally comminuted fractures (type 4, as described by Strange-Vognsen).

L5-S1 facet joint disruption may occur in association with sacral fractures and can compromise pelvic ring stability and influence treatment. The Isler classification distinguishes three injury types: type 1 (lateral to the facet joint), type 2 (fracture line passes through the L5-S1 facet joint), and type 3 (fracture line passes medial to the L5-S1 facet joint). Type 1 fractures are least likely to disrupt lumbosacral stability.

Figure 58-1. Three-zone system of Denis: zone I injuries remain lateral to the neuroforamina; zone II fractures involve the neuroforamina but do not involve the central spinal canal; zone III injuries extend into the central spinal canal.

Figure 58-2. Subclassification of Denis zone III fractures as suggested by Roy-Camille. Type 1 injuries are angulated but not translated, whereas type 2 injuries are angulated and translated. Type 3 injuries show complete translational displacement of upper and lower sacrum, whereas type 4 injuries are segmentally comminuted due to axial impaction (as suggested by Strange-Vognsen). (From Chapman JR, Mirza SK. Sacral fractures. In: Fardon D, Garfin S, et al, editors. Orthopaedic Knowledge Update: Spine 2. Rosemont, IL: American Academy of Orthopaedic Surgeons, 2002.)

Figure 58-2. Subclassification of Denis zone III fractures as suggested by Roy-Camille. Type 1 injuries are angulated but not translated, whereas type 2 injuries are angulated and translated. Type 3 injuries show complete translational displacement of upper and lower sacrum, whereas type 4 injuries are segmentally comminuted due to axial impaction (as suggested by Strange-Vognsen). (From Chapman JR, Mirza SK. Sacral fractures. In: Fardon D, Garfin S, et al, editors. Orthopaedic Knowledge Update: Spine 2. Rosemont, IL: American Academy of Orthopaedic Surgeons, 2002.)

Sacral fractures associated with pelvic ring injuries require additional classification. Standard pelvic injury classifications (e.g. Tile classification, Young Burgess classification) are utilized to assess stability, injury mechanism, and associated injuries.

10. What factors influence selection of treatment options for sacral fractures?

Decision making regarding management of patients with sacral fractures is multifactorial. Variables include presence/ absence of multiple injuries, open vs. closed fracture, associated soft tissue compromise, neurologic injury, and injury mechanism. There are no simple treatment algorithms.

11. What are the nonoperative treatment options for sacral fractures?

Criteria for nonoperative management include (1) stable, nondisplaced, closed, single-system injury; (2) no associated pelvic ring injury or L5-S1 facet joint disruption; and (3) intact neurologic status. Nonoperative management options include:

• Early, protected weightbearing

• Immobilization with a thoracolumbosacral orthosis (TLSO) with a unilateral or bilateral thigh extension or pantaloon spica cast

• Prolonged bed rest with recumbent skeletal traction

12. What surgical treatment options exist for sacral fractures?

Surgical interventions can be classified as decompression procedures and procedures that provide fracture reduction and stabilization.

13. When is a surgical decompression indicated after a sacral fracture?

In presence of lumbosacral or sacral nerve deficits or sacral radicular pain, surgical decompression within 2 weeks of injury has been associated with improved outcome compared with nonsurgical management. Decompression can be accomplished with direct decompression through a dorsal midline laminotomy and foraminotomy or with indirect decompression via fracture disimpaction or fracture reduction and stabilization.

14. What drawbacks are associated with surgical decompression of sacral fractures?

Surgical decompression may be ineffective in presence of traumatic sacral neural transsection. Approximately 35% of displaced transverse sacral fractures are associated with transected sacral roots based on autopsy study. Unfortunately, no imaging or electrophysiologic studies can conclusively establish the presence of transected sacral roots. Other risks associated with decompression surgery for sacral fractures include wound healing problems, persistent cerebrospinal fluid leakage, and additional fracture destabilization.

15. When is surgical stabilization of a sacral fracture indicated?

There are few strict guidelines for surgical sacral fracture stabilization. Typically, fracture displacement of 1 cm or more is considered to be consistent with fracture instability. Injuries that disrupt significant ligamentous lumbopelvic support structures usually have a poor prognosis for healing. Most patients who require surgical decompression of lumbosacral neural elements should also be considered for surgical stabilization to prevent further fracture displacement and enhance chances of neural recovery.

16. What are the options for surgical stabilization of sacral fractures (Table 58-1)?

All sacral fractures should be evaluated in the context of their effect on posterior pelvic ring and spinopelvic junction stability. Anterior pelvic ring stabilization has a supplemental role in sacral fracture stabilization, which can be achieved with anterior external fixation or symphyseal plating. Posterior pelvic ring fixation has undergone considerable evolution. Percutaneous sacroiliac screw placement has been reported to have a high success rate in the treatment of noncomplex sacral fractures. This technique allows effective indirect fracture reduction and stabilization when applied within 2 to 3 days from injury and has a relatively low incidence of reported complications. It is, however, limited in its biomechanical stability, especially for vertically displaced fractures and high-grade Denis zone 3 injuries. The most stable sacral fracture stabilization consists of lumbopelvic stabilization using lumbar pedicle and iliac screw fixation. This technique allows comprehensive stabilization of the sacrum through a posterior midline exposure.

Table 58-1. Options for Surgical Stabilization of Sacral Fractures

ANTERIOR (INDIRECT METHODS)

POSTERIOR

Symphyseal plating

Sacroiliac screw fixation (open or closed)

Anterior external fixation

Posterior tension band plating

Retrograde superior ramus screw fixation

Sacral alar plating (Roy-Camille technique)

Lumbopelvic instrumentation

Combined procedures

17. What is the optimal time for surgical intervention for a sacral fracture?

Optimal timing of surgical intervention for sacral fractures is multifactorial. Posterior exposures usually require a posterior midline approach with the patient in the prone position. Truly emergent open surgical decompression and stabilization of sacral fractures are rarely indicated. Because of the risk of significant blood loss, emergent surgical intervention using the open approach in the prone position is frequently postponed in favor of a delayed postprimary procedure within the first 2 weeks after injury. Additional factors to consider are presence of soft tissue deglovement (Morel-Lavalle lesion), open sacral fractures, and posterior soft tissue compromise caused by prominent bony fragments.

18. How are percutaneous sacroiliac screws placed?

Intricate knowledge of pelvic anatomy and high-quality intraoperative C-arm is prerequisite. Satisfactory closed reduction is achieved by skeletal traction or percutaneous manipulation. Radiographic anatomy should be reviewed to rule out the presence of congenital sacroiliac bony anomalies. Typically, a 7.0-mm large fragment cannulated screw system is used for unilateral or bilateral fixation. With the patient positioned supine on a fluoroscopy table, appropriate percutaneous starting points and guide-pin trajectories are determined using sacral lateral, as well as inlet and outlet projections on C-arm. Intraoperative screw placement under computed tomography (CT) guidance can be used as an imaging alternative. However, this approach is not feasible for polytraumatized patients or if intraoperative fracture manipulation is required. Screws are usually advanced over guidewires into the vertebral body of the S1 segment. Compression screws can be used in the presence of noncomminuted fractures. Fully threaded screws are preferred for patients with comminuted zone 2 fractures.

19. How is lumbopelvic instrumentation accomplished?

The ideal instrumentation system for lumbopelvic fixation is low profile and biomechanically stable, possesses a simple screw-linkage mechanism, and is adaptable to individual needs (Fig. 58-3). The instrumentation technique for lumbopelvic fixation differs significantly among various implant makers. Using side-loading implants, such as the Universal Spine System (Synthes), bilateral L5 pedicle fixation is obtained. If the S1 segment is intact, additional pedicle screws are placed into this segment. After decompression of the sacrum from the L5 segment downward, reduction of the sacral segments and the iliac wings can be accomplished with temporary threaded pins. Rods are then contoured to connect from the L5 and S1 screws to the region of the posterior iliac crest overhang and the posterior sacral ala. Using the outer iliac table as an inclination guide, one or two drill holes are then placed just lateral to the rod under lateral C-arm visualization. A starting point is selected approximately 2 cm inferior to the posterior superior iliac spine and aiming toward the anterior inferior iliac spine. The thickened portion of the ilium within 2 to 3 cm above the sciatic notch offers the most predictable passageway for such pelvic anchoring devices. Screws of up to 130 mm in length and 8 mm in diameter have been shown to be safely anchored in the iliac wing using this technique.

20. What is triangular osteosynthesis?

The term triangular osteosynthesis is used to denote implant constructs that combine longitudinal vertebropelvic fixation (i.e. pedicle screw-rod fixation between the lower lumbar pedicles and iliac column or sacral ala) with horizontal fixation using an iliosacral screw. Triangular osteosynthesis provides greater stability than isolated iliosacral screw constructs. It is intended to facilitate early progressive weight-bearing for patients with vertically unstable sacral fractures.

Figure 58-3. Insertion of lumbopelvic fixation. Comprehensive stabilization of the sacrum and complete decompression of the sacrum can be achieved with the insertion of long iliac screws that are attached to conventional, caudally extended lumbosacral rods.

Key Points

1. A high index of clinical suspicion, targeted physical examination, and appropriate imaging studies are required for timely diagnosis of sacral fractures.

2. Sacral fractures may result in posterior pelvic ring instability, spinopelvic instability, or combined instabilities.

3. Surgical treatment is indicated for sacral fractures associated with neurologic deficit, instability, or deformity.

Websites

Sacral fractures: Current strategies in diagnosis and management: http://www.orthosupersite.com/view.asp?rID=44034 Sacral insufficiency fracture: http://rheumatology.oxfordjournals.Org/cgi/content/full/40/9/1065 Sacrum and sacral fractures: http://www.wheelessonline.com/ortho/sacrum_and_sacral_fractures

BiBLiOGRAPHY

1. Denis F, Davis S, Comfort T. Sacral fractures: An important problem: retrospective analysis of 236 cases. Clin Orthop 1988;227:67-81.

2. Nork S, Jones CB, Harding SP, et al. Percutaneous stabilization of U-shaped sacral fractures using iliosacral screws: Technique and early results. J Orthop Trauma 2001;15:1236-44.

3. Schildhauer TA, Bellabarba C, Nork SE, et al. Decompression and lumbopelvic fixation for sacral fracture-dislocations with spino-pelvic dissociation. J Orthop Trauma 2006;20:447-57.

4. Schildhauer TA, Josten C, Muhr G. Triangular osteosynthesis of vertically unstable sacrum fractures: A new concept allowing early weight-bearing. J Orthop Trauma 2006;20:S44-S51.

5. Schildhauer TA, McCullough P, Chapman JR, et al. Anatomic and radiographic considerations for placement of transiliac screws in lumbopelvic fixations. J Spinal Disord Tech 2002;15(3):199-205.

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