Sacral Fractures: Current Strategies in Diagnosis and Management

Posted on October 11, 2009

by David J. Hak, MD, MBA; Sean Baran; Philip Stahel, MD

While many sacral fractures can be treated nonoperatively with restricted weight bearing, unstable fractures and fractures with associated nerve injury may require surgical management.

Sacral fractures can result from a range of injury mechanisms. While sacral fractures typically result from high-energy injuries, there is increasing identification of low-energy insufficiency fractures of the sacrum and pelvis in elderly and osteoporotic patients. The pattern, location, and stability of the fracture also vary greatly. Stable nondisplaced fractures are usually treated nonoperatively, while significantly displaced fractures require reduction and internal fixation.

Sacral fractures occur in approximately 45% of all pelvic fractures.1 The pattern of the associated pelvic fracture has a significant impact on the location, stability, and treatment of the sacral fracture. The sacral fracture associated with lateral compression pelvic fractures is usually stable, since there is impaction of the sacrum. In contrast, sacral fractures associated with vertical shear pelvic fractures are usually unstable patterns. Sacral fractures may involve injury to the lumbosacral junction and result in varying degrees of lumbosacral instability or even lumbosacral dissociation.

The close association of the lumbosacral plexus places the neurologic structures at risk of a traction injury or transection in high-energy displaced fractures. Neurologic injury associated with sacral fractures can range from an incomplete injury of a single nerve root to involvement of the entire cauda equina.

Imaging

Sacral fractures can often be difficult to visualize on an anteroposterior (AP) radiograph because of the inclination angle of the sacrum. Improved visualization can be obtained with inlet and outlet radiographs.2 While the outlet view provides a better AP view of the sacrum, the inlet view provides better visualization of the sacral spinal canal. In addition, a lateral view of the sacrum can be useful to identify displacement in the sagittal plane, however surrounding soft tissue often limits the image quality. A 2- to 3-mm thin cut computed tomography (CT) scan with coronal and sagittal reconstruction provides the optimal imaging to identify and evaluate sacral fractures (Figure 1). Magnetic resonance imaging, while not commonly required, can be used to evaluate associated neural compromise in selected cases.

Classification

The wide range of sacral fracture patterns, and their frequent association with pelvic and lumbar fractures, mandates a number of different fracture classification systems.

Denis Classification

Sacral fracture patterns are commonly categorized using the Denis classification system.3 The Denis classification divides the sacrum into 3 zones (Figure 2).

  • Zone 1 fractures are lateral to the neural foramina,
  • Zone 2 fracture pass through the foramina, and
  • Zone 3 fractures are medial to the foramen and involve the spinal canal.

Descriptive Classification of Transverse Sacral Fractures

Transverse sacral fractures are uncommon, occurring in <5% of sacral fractures.4 Because they traverse the spinal canal they are classified as Denis 3 fractures, but the fracture line often traverses all 3 zones. Transverse fractures of the sacrum have also been described based on the pattern morphology as H, U, lambda and T-shaped fractures (Figure 3).5

Roy-Camille/Strange-Vognsen and Lebech Classification of Transverse Sacral Fractures

Both Roy-Camille et al6 and Strange-Vognsen and Lebech7 have further classified transverse Denis zone 3 fractures. In this classification, type I fractures show only kyphotic angulation at the fracture. Type 2 fractures have both kyphosis and partial anterior translation. Type 3 fractures have kyphosis along with complete translation. Type 4 fractures have segmental comminution of the S1 body due to axial compression (Figure 4).

Isler Classification

Fractures involving the lumbosacral junction generally occur from high-energy injuries. The Isler classification is based on the location of the major fracture line relative to the L5-S1 facet, which impacts the potential for lumbosacral instability (Figure 5). Fractures of the lumbosacral junction that are lateral to the facet are classified as type I and are unlikely to impair lumbosacral stability but may impact the stability of the pelvic ring. Fractures of the lumbosacral junction that exit through the L5-S1 facet are classified as type II. Fractures of the lumbosacral junction that exit medial to the facet are classified as type III. Type III fractures are usually associated with significant instability of the lumbosacral junction. Bilateral type III injuries may represent lumbosacral dissociation.

Neurologic Injury

Fractures of the sacrum may result in a neurologic injury in up to 25% of cases.1 The nerve injury may involve >1 nerve roots, and be unilateral or bilateral depending on the fracture pattern and location. The injury can range from a neuropraxic injury due to nerve contusion or shearing injury, to transection of individual nerve roots, or even complete transection of the cauda equina.

The L5 nerve root traverses the anterosuperior border of the S1 vertebral body and sacral ala. It can be injured by fractures in this region and during surgical approaches or internal fixation. Sympathetic ganglia of the inferior hypogastric plexus are present along the anterior surface of the L5 vertebral body and sacrum. Anterior rami of S2 to S5 provide contributions to the parasympathetic nerves that control sexual, bladder, and rectal function.

Associated neurologic injury, especially of the lower sacral plexus, may not always be appreciated unless a thorough examination is performed. Injuries to the S2 to S5 nerve roots can be easily overlooked since they do not supply motor or sensory supply to the lower leg. S2 innervates the musculature that forms the external urethral and anal sphincters. S4 and S5 give sensation to the penis, labia, urethra, posterior scrotum, and anal canal. The bladder and rectum are innervated primarily by the pelvic splanchnic autonomic nerves from S2 to S4. Continence and sexual function require at least unilateral preservation of the S2 and S3 nerve roots.4 The presence of a Foley catheter, and confounding variables, can often initially mask voiding problems, which not uncommonly are attributed to other causes resulting in a delayed diagnosis of sacral nerve root injury.

Therefore clinical examination of patients sustaining sacral fractures requires more than just routine examination of lower extremity sensory and motor function. Additional examination is required to identify injuries to the lower sacral plexus. A rectal examination must be performed to evaluate sphincter contraction and to exclude an open pelvic fracture. Light touch and pinprick sensation should be assessed for the perianal dermatomes of S2 to S5. In addition the perianal wink, bulbocavernosus, and cremasteric reflexes should be assessed.

The location of the fracture has been found to be a good predictor of neurologic injury deficits. Denis zone 3 fractures, while less frequent, are associated with the highest rate of nerve injury. In a retrospective review of 236 fractures, Denis et al3 noted that 57% of patients with zone 3 injuries had a neurologic deficit. While Denis zone 1 injuries are the most frequent, they have the lowest rate of associated nerve injury. Six percent of patients with zone 1 fractures had a neurologic injury, which was localized to the sciatic nerve or L5 nerve root.3

Zone 2 fractures are intermediate in their frequency and rate of associated nerve injury. In the series by Denis et al,3 the incidence of zone 2 fractures was 34% and the rate of neurologic injury was 28%. Unilateral injury of the L5, S1 or S2 nerve roots were noted in the zone 2 fractures.

In a case series of transverse sacral fractures, Robles4 reported that 97% of patients presented with some neurologic injury that ranged from radiculopathy to bowel and bladder disturbance. Complete nerve root transection has been reported in 35% of transverse sacral fractures.5 However, the neurologic injury seen in transverse sacral fractures may be easy to overlook if the examination is limited simply to lower extremity motor and sensory function that primarily focuses on the L5 and S1 nerve root distribution.

Treatment of Sacral Fractures

Most sacral fractures can be treated nonoperatively. These include stable, nondisplaced sacral fractures without a significant associated pelvic ring disruption, fractures not involving the lumbosacral junction, and fractures without neurologic injury. Patients’ weight bearing is limited to touchdown weight bearing on the affected side for approximately 8 weeks.

Sacral Fracture Fixation

Displaced or unstable sacral fractures are best treated by closed or open reduction and internal fixation. Following anatomic reduction, sacral fractures can be fixed with percutaneously placed screws, posterior sacral “tension band” plating, or posterior iliac rods. Surgical stabilization of any associated anterior pelvic ring injury is essential to improve the fixation stability.

Percutaneous Iliosacral Screws

Percutaneously placed iliosacral screws are commonly used for the fixation of sacroiliac joint disruptions and for sacral fractures (Figure 6). The ideal screw trajectory is more horizontal for the fixation of sacral fractures than for fixation of a sacroiliac joint disruption. Caution is exercised when fixing comminuted Denis 2 fractures to avoid compression of the foramen that may result in iatrogenic neural injury. For this reason, fully threaded screws are usually used to fix sacral fractures, rather than partially threaded screws that are used to fix sacroiliac joint disruptions. Adequate experience and intraoperative imaging is necessary to safely insert these screws, since the safe corridor for placement is fairly small. In some patients, such as those with a dysmorphic sacrum, this safe corridor is even smaller and may preclude the placement of an iliosacral screw. In one review, 14.5% of trauma patients undergoing CT scan were found to have sacral dysmorphia.8

Posterior Sacral Tension Band Fixation

Transiliac posterior tension band fixation, while less commonly used than iliosacral screws, offers an alternative method for stabilization of the posterior pelvic ring.9 It is indicated in vertically unstable comminuted sacral fractures, for which iliosacral screws may be insufficient. It is also indicated in patients with a dysmorphic sacrum in whom there is no safe corridor for placement of iliosacral screws. Threaded rods or a posterior plate may be secured to the posterior ilium (Figure 7). Disadvantages of this fixation is the need for a larger surgical dissection, which has a greater risk of wound breakdown and infection, especially in the presence of a severe associated soft tissue injury, such as the Morel-Lavallée internal degloving injury.

Lumbopelvic Fixation

Surgical management is indicated for those sacral fractures with associated lumbosacral instability, such as the Isler 3 classification. Also, the H- and U-type descriptive patterns of transverse sacral fractures may represent spinopelvic dissociation with only the body of S1 or S2 attached to the spine.

While Nork et al10 reported on the successful stabilization of 13 U-shaped transverse sacral fractures with iliosacral screws alone, other surgeons have expressed concern that iliosacral screws alone may not be successful in preventing a kyphotic deformity following this injury. A kyphotic deformity can occur with iliosacral screws alone because the pelvis can flex in relation to the spine along the axis of the SI screws.

Lumbopelvic fixation consists of pedicle screws placed in L5 and or L4 that are connected to fixation placed into the ilium from posterior to anterior just cephalad to the sciatic notch (Figure 8).

Schildhauer et al11 reported on the use of lumbopelvic fixation in 19 patients with Roy-Camille type 2 four sacral fractures with spinopelvic instability and cauda equina injuries. All of the sacral fractures successfully healed and none of the patients had loss of reduction. Fifteen of the 19 patients had full or partial recovery of bowel and bladder deficits. They reported that complete recovery of cauda equina function was more likely in patients with continuity of all sacral roots and in injuries where the initial deficit was incomplete.

Triangular Osteosynthesis

The term triangular osteosynthesis has been coined to describe fixation constructs that involve placement of pedicle screws in the lower lumbar and the posterior ilium in conjunction with iliosacral screws.12 In a biomechanical study, triangular osteosynthesis was shown to be superior to iliosacral screws alone for fixation of unstable transforaminal sacral fractures.13 Sagi et al14 reported on the use of triangular osteosynthesis in 58 patients with vertically unstable transforaminal sacral fractures. Patients were allowed full weight bearing at 6 weeks, with only a 5% malunion rate. The authors noted a high rate of prominent and painful hardware (95%). Additional problems included iatrogenic L5 nerve injury in 13%, delayed union in 25%, and pronounced tilting of the L5 vertebral body with distraction of the L5/S1 facet joint ipsilateral to the fixation in 15%.

Neural decompression

Neural decompression may be achieved indirectly by fracture reduction, or directly through a laminectomy or foraminotomy. However, the indications for and outcome from neural decompression of injured sacral nerves remains a topic of debate. In general, 80% of initial nerve injuries will improve regardless of treatment.3 Nerve injury due to neuropraxia due to fracture translation, angulations, or direct compression has a good chance for recovery. Nerve transection of nerve root avulsion is less commonly seen, but offers no prospect for recovery.

Conclusion

The relative ease with which sacral fractures and associated neural compromise can be missed on initial evaluation of the trauma patient necessitates that the examiner maintain a high index of suspicion. Obtaining appropriate imaging, including pelvic inlet and outlet views as well as pelvic CT, can assist the surgeon in diagnosing potential sacral fractures, however these modalities should not be considered a replacement for complete neurologic assessment of the lower lumbar and sacral nerve root distributions. Confounding factors often occurring in multiple injured patients, including the presence of a Foley catheter and altered mental status, mandate a high index of suspicion and thorough physical examination.

Sacral fractures can be classified based on anatomic and morphologic characteristics. This classification serves an important purpose in that it helps the surgeon identify fractures more commonly associated with neural compromise as well as those fractures requiring surgical fixation. While many sacral fractures can be treated nonoperatively with restricted weight bearing, unstable fractures and fractures with associated nerve injury may require surgical management. The selected surgical treatment option should be tailored to the individual fracture pattern, the patients associated injuries, and the surgeons expertise.

References

  1. Mehta S, Auerbach JD, Born CT, Chin KR. Sacral fractures. J Amer Acad Orthop Surg. 2006; 14(12):656-665.
  2. Routt ML Jr, Simonian PT, Swiontkowski MF. Stabilization of pelvic ring disruptions. Orthop Clinic North Am. 1997; 28(3):369-388.
  3. Denis F, Davis S, Comfort T. Sacral fractures: An important problem: Retrospective analysis of 236 cases. Clin Orthop Relat Res. 1988; (227):67-81.
  4. Robles LA. Transverse sacral fractures. Spine J. 2009; 9(1):60-69.
  5. Vaccaro AR, Kim DH, Brodke DS, et al. Diagnosis and management of sacral spine fractures. Instr Course Lect. 2004; 53:375-385.
  6. Roy-Camille R, Saillant G, Gagna G, Mazel C. Transverse fracture of the upper sacrum: Suicidal jumper’s fracture. Spine. 1985; 10(9):838-845.
  7. Strange-Vognsen HH, Lebech A. An unusual type of fracture in the upper sacrum. J Orthop Trauma. 1991; 5(2):200-203.
  8. Hasenboehler EA, Stahel PF, Williams A, et al. Prevalence of sacral dysmorphia in a prospective trauma population: Implications for a “safe” surgical corridor for SI-screw placement. Presented at: 75th Annual meeting of the American Academy of Orthopaedic Surgeons; March 5-9, 2008; San Francisco, CA.
  9. Suzuki T, Hak DJ, Ziran BH, et al. Outcome and complications of posterior transiliac plating for vertically unstable sacral fractures. Injury. 2009; 40(4):405-409.
  10. Nork SE, Jones CB, Harding SP, Mirza SK, Routt ML Jr. Percutaneous stabilization of U-shaped sacral fractures using iliosacral screws: Techniques and early results. J Orthop Trauma. 2001; 15(4):238-246.
  11. Schildhauer TA, Bellabarba C, Nork SE, Barei DP, Routt ML Jr, Chapman JR. Decompression and lumbopelvic fixation for sacral fracture-dislocations with spino-pelvic dissociation. J Orthop Trauma. 2006; 20(7):447-457.
  12. Schildhauer TA, Josten Ch, Muhr G. Triangular osteosynthesis of vertically unstable sacrum fractures: a new concept allowing early weight-bearing. J Orthop Trauma. 2006; 20(1 Suppl):S44-51.
  13. Schildhauer TA, Ledoux WR, Chapman JR, Henley MB, Tencer AF, Routt ML Jr. Triangular osteosynthesis and iliosacral screw fixation for unstable sacral fractures: A cadaveric and biomechanical evaluation under cyclic loads. J Orthop Trauma. 2003; 17(1):22-31.
  14. Sagi HC, Militano U, Caron T, Lindvall E. A comprehensive analysis with minimum 1-year follow-up of vertically unstable transforaminal sacral fractures treated with triangular osteosynthesis. J Orthop Trauma. 2009; 23(5):313-321.

Authors

Drs Hak and Stahel and Mr Baran are from Denver Health/University of Colorado, Denver, Colorado.

Drs Hak and Stahel and Mr Baran have no relevant financial relationships to disclose.

Correspondence should be addressed to: David J. Hak, MD, MBA, Department of Orthopedic Surgery, 777 Bannock St, MC 0188, Denver, CO 80204.

doi: 10.3928/01477447-20090818-18

Posted in Trauma