Sacral fractures after multi-segmental lumbosacral fusion: a series of four cases and systematic review of literature

Management of C0 Sacral Fractures Based on the AO Spine Sacral Injury Classification: A Narrative Review

The Arbeitsgemeinschaft fur Osteosynthese fragen Spine Sacral Injury Classification hierarchically separates fractures based on their injury severity with A-type fractures representing less severe injuries and C-type fractures representing the most severe fracture types. C0 fractures represent moderately severe injuries and have historically been referred to as nondisplaced "U-type" fractures. Injury management of these fractures can be controversial. Therefore, the purpose of this narrative review is to first discuss the Arbeitsgemeinschaft fur Osteosynthese fragen Spine Sacral Injury Classification System and describe the different fracture types and classification modifiers, with particular emphasis on C0 fracture types. The narrative review will then focus on the epidemiology and etiology of C0 fractures with subsequent discussion focused on the clinical presentation for patients with these injuries. Next, we will describe the imaging findings associated with these injuries and discuss the injury management of these injuries with particular emphasis on operative management. Finally, we will outline the outcomes and complications that can be expected during the treatment of these injuries.

Treatment for sacral insufficiency fractures: A systematic review

Intro

Sacral insufficiency fractures after lumbosacral fusion continue to establish themselves as a rare complication after surgery. The diagnosis can often be missed due to inconclusive imaging and non-specific symptoms. In the literature, the treatment of sacral insufficiency fractures varies from non-operative and conservative management to surgical intervention with lumbopelvic fixation.

Methods

We performed a systematic review searching the PubMed database using sacral insufficiency fracture treatment after lumbosacral fusion and sacral insufficiency fracture after posterior spinal instrumentation as keywords.

Results

This search strategy identified 32 publications from the PubMed database for literature review. After evaluating the inclusion and exclusion criteria, a total of 17 articles were included in the review. 65% of sacral insufficiency fractures were managed surgically with 35% of patients proceeding with non-operative, conservative management only. Revision surgery always involved sacropelvic fixation which typically led to immediate resolution or reduction of symptoms, with the exception of 2 cases that did not receive adequate reduction of symptoms. Five cases reported failed non-operative management that subsequently responded to revision surgery.

Conclusion

Outcomes after non-operative management usually leads to symptom resolution; however has a slower symptom relief time as well as a higher chance of failed treatment. Operative outcomes, generally with a variation of sacropelvic fixation lead to immediate symptom resolution and very rarely failed treatment. Clinicians must always maintain a high index of suspicion of new onset lower back or sacral pain after lumbosacral surgery and order a CT scan to rule out a potential insufficiency fracture.

Objectives

The objective of this study was to review the literature to examine treatment options for sacral insufficiency fractures after lumbosacral fusion in order to improve clinical practice and management. This systematic review of the literature regarding treatment of sacral insufficiency fractures will assist clinicians in making the accurate diagnosis and devise a strategic treatment plan for patients with sacral insufficiency fractures after spinal instrumentation.

Early postoperative sacral fracture after short-segment posterior lumbar interbody fusion for L5/S1 isthmic spondylolisthesis: A case report

Background:

Early postoperative sacral fractures are extremely rare complications of single-level posterior lumbar interbody fusions (PLIFs).

Case Description:

A 71-year-old female presented with lower back pain and right S1 radiculopathy attributed to MR-documented L5/S1 isthmic spondylolisthesis. Following a L5 laminectomy and bilateral L5/S1 PLIF, she experienced sacral pain while sitting. When the MR showed a sacral insufficiency fracture with anterolisthesis at L5/S1, a secondary posterior fusion was extended to the pelvis, utilizing bilateral iliac screws. Following this reoperation, the patient did well and went on to achieve arthrodesis.

Conclusion:

Early postoperative sacral fractures that occur following single-segment L5/S1 PLIF for isthmic spondylolisthesis warrant fusion to the pelvis with bilateral iliac screws.

Sacral insufficiency fracture after instrumented lumbosacral fusion: Focusing pelvic deformation -A retrospective case series

The purpose of this study was to report the characteristics of SIFs after ILSF and discuss its management focusing on pelvic deformation. We retrospectively reviewed all consecutive patients who underwent ILSF for degenerative disc diseases during the period between 2000 and 2017 and were diagnosed as SIF at our institute. The clinical and radiographic data were reviewed on their medical charts. Treatment outcomes for SIF were also investigated. Eight patients (all females) were included in this study. Mean age at SIF diagnosis was 72 years, and the mean follow-up period was 3.8 years (range 1-7 years). SIF developed average 7.5 years (range 1 month-17 years) after the index ILSF. Fracture patterns were unilateral vertical in four, bilateral vertical in three, and horizontal in 1 patient. Unlike patients with unilateral vertical SIF, patients with bilateral vertical or horizontal SIF showed a marked increase of pelvic incidence (PI) by mean 17.0°±5.0° and sagittal vertical axis (SVA) by mean 4.5 ± 2.2 cm, compared to the respective values before the onset of abrupt pain. All patients with unilateral vertical SIF were treated favorably by conservative management, however sacropelvic fixation was inevitable in patients with bilateral vertical or horizontal SIF. Bilateral vertical or horizontal SIF showed marked changes on sagittal radiographic parameters including PI and SVA. Although unilateral vertical SIF has benign courses that responded well to conservative management, bilateral vertical or horizontal SIF is likely to need surgical treatment. Treatment plan should be determined depending on fracture pattern and pelvic deformation.

A Case Series That Supports the Application of the S2AI Technique for Fractures and Failures After Lumbosacral Fusion

BACKGROUND

Sacral fractures and failures are uncommon after lumbosacral fusion but have received increasing attention in the surgical literature. They can be difficult to diagnose, making timely treatment difficult. No consensus has been reached on the characteristics of these complications or on optimal treatment.

QUESTIONS/PURPOSES

The goal of this retrospective case series is to contribute additional cases of these uncommon complications of lumbosacral fusion to the surgical literature to help clinicians to anticipate, diagnose, characterize, manage, and treat sacral fractures and failures after lumbosacral fusion.

METHODS

The medical records of five patients who experienced a sacral fracture or failure after lumbosacral fusion between January 2012 and November 2017 were identified and reviewed retrospectively. Records were reviewed for age, sex, clinical presentation, previous management, outpatient clinical records, imaging, and post-operative course.

RESULTS

Four patients in the series experienced a sacral fracture and one experienced hardware failure. All patients presented with elevated pain and underwent revision surgery. Radiographic detection of the fracture or failure occurred at a mean of 11.2 weeks (range, 3 to 24 weeks) after initial surgery, and the mean age of patients was 68.2 years (range, 63 to 80 years). Of the five patients, four were female; two had been diagnosed with osteoporosis and two with osteopenia. In our case series, the S2-alar-iliac (S2AI) technique was used with success in all five cases.

CONCLUSION

Fractures and failures after lumbosacral fusion can be difficult to diagnose because of delayed presentation, nonspecific presenting symptoms, and a lack of identifiable mechanism. A high index of suspicion is required to detect these uncommon complications, and patients have responded well to both conservative and surgical treatments.

Sacral insufficiency fractures after lumbosacral arthrodesis: salvage lumbopelvic fixation and a proposed management algorithm

OBJECTIVE

Sacral insufficiency fracture after lumbosacral (LS) arthrodesis is an uncommon complication. The objective of this study was to report the authors' operative experience managing this complication, review pertinent literature, and propose a treatment algorithm.

METHODS

The authors analyzed consecutive adult patients treated at their institution from 2009 to 2018. Patients who underwent surgery for sacral insufficiency fractures after posterior instrumented LS arthrodesis were included. PubMed was queried to identify relevant articles detailing management of this complication.

RESULTS

Nine patients with a minimum 6-month follow-up were included (mean age 73 ± 6 years, BMI 30 ± 6 kg/m2, 56% women, mean follow-up 35 months, range 8-96 months). Six patients had osteopenia/osteoporosis (mean dual energy x-ray absorptiometry hip T-score -1.6 ± 0.5) and 3 received treatment. Index LS arthrodesis was performed for spinal stenosis (n = 6), proximal junctional kyphosis (n = 2), degenerative scoliosis (n = 1), and high-grade spondylolisthesis (n = 1). Presenting symptoms of back/leg pain (n = 9) or lower extremity weakness (n = 3) most commonly occurred within 4 weeks of index LS arthrodesis, which prompted CT for fracture diagnosis at a mean of 6 weeks postoperatively. All sacral fractures were adjacent or involved S1 screws and traversed the spinal canal (Denis zone III). H-, U-, or T-type sacral fracture morphology was identified in 7 patients. Most fractures (n = 8) were Roy-Camille type II (anterior displacement with kyphosis). All patients underwent lumbopelvic fixation via a posterior-only approach; mean operative duration and blood loss were 3.3 hours and 850 ml, respectively. Bilateral dual iliac screws were utilized in 8 patients. Back/leg pain and weakness improved postoperatively. Mean sacral fracture anterolisthesis and kyphotic angulation improved (from 8 mm/11° to 4 mm/5°, respectively) and all fractures were healed on radiographic follow-up (mean duration 29 months, range 8-90 months). Two patients underwent revision for rod fractures at 1 and 2 years postoperatively. A literature review found 17 studies describing 87 cases; potential risk factors were osteoporosis, longer fusions, high pelvic incidence (PI), and postoperative PI-to-lumbar lordosis (LL) mismatch.

CONCLUSIONS

A high index of suspicion is needed to diagnose sacral insufficiency fracture after LS arthrodesis. A trial of conservative management is reasonable for select patients; potential surgical indications include refractory pain, neurological deficit, fracture nonunion with anterolisthesis or kyphotic angulation, L5-S1 pseudarthrosis, and spinopelvic malalignment. Lumbopelvic fixation with iliac screws may be effective salvage treatment to allow fracture healing and symptom improvement. High-risk patients may benefit from prophylactic lumbopelvic fixation at the time of index LS arthrodesis.

BMI and gender increase risk of sacral fractures after multilevel instrumented spinal fusion compared with bone mineral density and pelvic parameters

BACKGROUND CONTEXT

Sacral fractures are a rare but potentially devastating complication. Long-fusion constructs, including the sacrum, that do not extend to the pelvis may result in sacral fractures. Besides established risk factors including gender, age, and number of levels fused, body mass index (BMI), pelvic parameters, and bone mineral density (BMD) have also been proposed as potential risk factors for postoperative sacral fractures. The literature supporting this, however, is limited.

PURPOSE

The aim of the present study was to assess whether preoperative pelvic parameters, BMI, or BMD of patients with sacral fracture are different compared with age, gender, and fusion level-matched non-fracture controls.

STUDY DESIGN/SETTING

This is a case-control study.

PATIENT SAMPLE

Patients undergoing posterior instrumented fusion at a single academic institution between 2002 and 2016 were included in the study.

OUTCOME MEASURES

The outcome measure was occurrence of a postoperative sacral fracture.

METHODS

Patients with sacral fractures after posterior instrumented spinal fusion, including the sacrum, were retrospectively identified and matched 2:1 with non-fracture controls based on gender, age, and number of levels fused. Patients with concurrent spinopelvic fixation or missing preoperative computed tomography (CT) imaging were excluded. Preoperative sagittal balance was assessed using lateral radiographs. Quantitative computed tomography (QCT) assessment included standard measurements at L1/L2 and additional experimental measurements of the S1 body and sacral ala.

RESULTS

Twenty-one patients with sacral fracture were matched to non-fracture controls. The majority of the patients with sacral fracture was female (76.2%) and of advanced age (mean 66.4 years). Fracture and control groups were well matched with respect to gender, age, and number of levels fused. Standard measurements at L1/L2 showed no significant difference in BMD between the fracture and the control groups (109.9 mg/cm³ vs. 116.4 mg/cm³, p=.414). Similarly, there was no significant BMD differences between the groups using the experimental measurements of the S1 body (183.6 mg/cm³ vs. 176.2 mg/cm³, p=.567) and the sacral ala (8.9 mg/cm³ vs. 4.8 mg/cm³, p=.616). Mean preoperative pelvic incidence-lumbar lordosis mismatch and pelvic tilt were not significantly different between the groups. Univariate conditional logistic regression analysis revealed that the odds of experiencing a sacral fracture was approximately six times higher for obese patients compared with normal or underweight patients. After controlling for BMI in multivariate conditional logistic regression models, BMD was still not significantly associated with the odds of experiencing sacral fractures.

CONCLUSIONS

To our knowledge, this is the first study to assess the association of preoperative BMD measured by QCT, pelvic parameters, and BMI with postoperative sacral fractures in a large patient cohort. Interestingly, our data do not show any difference in preoperative pelvic parameters and BMD between the groups. This is in line with previous reports that indicate only a few patients with sacral fracture after fusion surgery have clear evidence of osteoporosis. Bone mineral density as a measure of bone quantity, rather than bone quality, may not be as important in these fractures as previously thought. Obesity, however, was associated with higher odds of experiencing postoperative sacral fractures. The present study thereby challenges the widespread concept that obesity is a protective factor against fractures in the elderly. In summary, our results suggest that BMI and gender, more than pelvic parameters and BMD, are risk factors for postoperative sacral fractures.

Vertebral Compression Fractures after Lumbar Instrumentation

Lumbar spinal stenosis (LSS) is primarily found in an older population. This is a similar demographic group that develops both osteoporosis and vertebral compression fractures (VCF). This report reviewed a series of patients treated for VCF that had previous lumbar surgery for symptomatic spinal stenosis. Patients that only underwent laminectomy or fusion without instrumentation had a similar distribution of VCF as the non-surgical population in the mid-thoracic, or lower thoracic and upper lumbar spine. However, in the patients that had previous short-segment spinal instrumentation, fractures were found to be located more commonly in the mid-lumbar spine or sacrum adjacent to or within one or two spinal segments of the spinal instrumentation. Adjacent-level fractures that occur due to vertebral osteoporosis after long spinal segment instrumentation has been discussed in the literature. The purpose of this report is to highlight the previously unreported finding of frequent lumbar and sacral osteoporotic fractures in post-lumbar instrumentation surgery patients. Important additional factors found were lack of preventative medical treatment for osteoporosis, and secondary effects related to inactivity, especially during the first year after surgery.

A novel technique to repair a transverse sacral fracture in a previously fused lumbosacral spondylolisthesis

BACKGROUND

Transverse fractures of the sacrum are rare, and surgical treatment for these fractures ranges from conservative to challenging. Transverse stress fractures of the sacrum after placement of lumbar-to-sacral instrumentation have been previously described. We report a new technique to repair a transverse Type-2 Roy-Camille fracture with spondylolisthesis of S1 over S2 in a previously fused instrumented high-grade L4-L5, L5-S1 spondylolisthesis.

CASE DESCRIPTION

A 64-year-old female who previously had an L4-L5, L5-S1 fusion for spondylolisthesis presented with excruciating lower back pain and radiculopathy for over 6 months. She was found to have an S1-S2 transverse fracture caused by previous implantation of pedicle screws. She underwent repositioning of several failed right lumbar and sacral screws and then had bilateral S1-S2 screws placed directly across the fracture line. The patient had an unremarkable postoperative course. She discontinued most of her pain medications within 6 weeks postoperatively. In the months following surgery, she reported only minimal lower back pain and no radiculopathy with the last appointment 5 years postoperatively.

CONCLUSIONS

We describe a novel technique to reduce an iatrogenic transverse type-2 Roy-Camille fracture at S1-S2 in a previously instrumented high-grade L4-L5, L5-S1 spondylolisthesis. The patient's fracture achieved adequate reduction and fusion with symptomatic relief.

Sacral stress fracture after lumbar and lumbosacral fusion. How to manage it? A proposition based on three cases and literature review

Sacral fracture after lumbosacral instrumentation could be a source of prolonged pain and a late autonomy recovery in old patients. Diagnosis remains difficult and usually delayed. No clear consensus for efficient treatment of this complication has been defined. Aim of this study was to determine how to manage them. Three patients who sustained sacral fracture after instrumented lumbosacral fusion performed for degenerative disease of the spine are discussed. History, physical examinations' findings and radiographic features are presented. Pertinent literature was analyzed. All patients complained of unspecific low back and buttock pain a few weeks after index surgery. Diagnosis was done on CT-scan. We always choose revision surgery with good functional results. Sacral stress fracture has to be reminded behind unspecific buttock or low back pain. CT-scan seems to be the best radiological test to do the diagnosis. Surgical treatment is recommended when lumbar lordosis and pelvic incidence mismatched.

Incidence, diagnosis, and management of sacral fractures following multilevel spinal arthrodesis

BACKGROUND

Fractures of the sacrum are a rare complication following instrumented spinal fusion, with only 34 cases previously reported in the literature. Previous series have generally been limited to less than five cases.

PURPOSE

The purpose of this study is to determine the incidence of sacral fractures caudal to instrumented spinal fusion constructs, identify risk factors for fracture and for failure of conservative management, and describe strategies for surgical treatment of these fractures.

STUDY DESIGN

This is a retrospective review.

PATIENT SAMPLE

Patients undergoing instrumented posterior spinal arthrodesis between 2002 and 2011 were included in the sample.

OUTCOME MEASURES

Clinical and radiographic data from hospital and surgeon records comprise outcome measures.

METHODS

Methods include a review of clinical and radiographic data from a prospectively collected patient database recording all adjacent segment fractures during the study period.

RESULTS

Twenty-four patients developed sacral fractures caudal to instrumented spinal fusion constructs during the study period. The overall incidence was 6.1% and was significantly greater in fusions greater than four levels (14.5%). The mean time from index surgery to fracture was 4.3 months. Only one fracture was evident on plain radiography at the onset of symptoms. Computed tomography, magnetic resonance imaging, and nuclear scintigraphy can all be used to establish the diagnosis. Eight patients were successfully treated conservatively. The mean time to fracture union was 21 weeks. Anterolisthesis of the fracture greater than 2 mm and kyphotic angulation were significantly associated with failure of conservative management. Surgical intervention included posterior extension of the fusion construct to S2 and the iliac wings with sacroiliac joint fusion. In 10 cases, a combined anterior and posterior approach was used that consisted of either revision anterior lumbar interbody fusion or transsacral posterior lumbar interbody fusion.

CONCLUSIONS

Sacral fractures following instrumented posterior spinal fusion are an uncommon complication; that is often unrecognized on plain radiographs. Risk factors include osteoporosis and long spinal fusions. Anterolisthesis and kyphosis of the fracture is associated with failure of conservative management.

Sacral fracture after instrumented lumbosacral fusion: analysis of risk factors from spinopelvic parameters

STUDY DESIGN

Retrospective comparative study.

OBJECTIVE

To examine the incidence and characteristics of key spinopelvic parameters that are correlated with sacral fracture development after lumbosacral fusion.

SUMMARY OF BACKGROUND DATA

Sacral fracture is a possible complication of instrumented lumbosacral fusion and this has recently been documented in the literature. Preoperative awareness of risk factors concerning spinopelvic parameters and sacral fracture may aid in surgical planning to prevent its occurrence.

METHODS

All patients who underwent instrumented lumbosacral fusion from L2 or above, between 2010 and 2011 at Gakkentoshi Hospital, were included.

RESULTS

A total of 116 patients (47 men and 69 women) were evaluated in this study. Average age at surgery was 71 years, and the average follow-up period was 19 months. The average number of fixed segments was 5, and the average time interval between index surgery and sacral fracture development was 42 days. Notably, sacral fractures were identified in 5 patients (4.3%), all of whom were women. We, therefore, compared the 2 groups of female patients (fracture group, n = 5 vs. nonfracture group, n = 64). The fracture group had a substantially higher mean pelvic incidence (PI) than the nonfracture group (72° ± 8° vs. 51° ± 12°, respectively, P < 0.01). The fracture group also had a larger postoperative lumbar lordosis (LL)-PI mismatch than the nonfracture group (-26° ± 7° vs. -7° ± 18°, respectively, P < 0.01).

CONCLUSION

The current review of our patients informs appropriate preoperative planning in cases involving lumbosacral fusion for postmenopausal women with a high PI. Surgeons should plan to achieve large increases in LL to restore not only spinopelvic harmony but also to avoid postoperative sacral fracture. For such patients, because it is difficult to consistently achieve a sufficiently large LL, we recommend prophylactic iliosacral fixation to protect the sacrum.

LEVEL OF EVIDENCE

4.

Should symptomatic iliac screws be electively removed in adult spinal deformity patients fused to the sacrum?

STUDY DESIGN

Retrospective, single-institution review of adult deformity patients who underwent iliac screw (IS) removal placed during fusion to the sacrum.

OBJECTIVE

To demonstrate whether IS removal offered benefit in terms of hip/buttock pain overlying the IS and whether IS could be removed without significant complications.

SUMMARY OF BACKGROUND DATA

ISs are effective at countering cantilever forces imparted on sacral pedicle screws. Despite the efficacy of IS fixation, pain or implant prominence can lead to elective IS removal. There has been no study about IS removal in adult spinal deformity patients.

METHODS

A total of 395 consecutive walking adult spinal deformity patients fused to the sacrum with IS fixation and minimum 2-year follow-up met study inclusion criteria. Clinical/radiographical data were analyzed. Because there is no validated pain outcomes instrument specific to this situation, an 8-question IS removal questionnaire was designed and used for the sole purpose of this inquiry, within which a universally accepted numeric rating scale for pain was included. RESULTS.: Twenty-four of 395 (6.1%) patients (2 men and 22 women) with mean age of 50.5 ± 10.8 years underwent elective IS removal at mean 2.6 ± 1.3 years from index surgery. Mean follow-up from initial surgery was 6.3 ± 4.0 years. Symptoms included hip/buttock pain in all 24 patients and IS prominence in 5 patients (20.8%). Screw removal was bilateral in 18 (75%) patients and unilateral in 6 (25%) patients. Using a numeric rating pain scale (0-10), hip/buttock pain improved after IS removal: preoperative 6.9 ± 1.8, postoperative 2.0 ± 2.7 (P < 0.05). Patients reported hip/buttock symptoms post-IS removal as "much improved" (78.3%), "somewhat improved" (8.7%), and "unchanged" (13.0%). Two of 24 (8.3%) patients sustained complications from IS removal (wound infection, n = 1; coronal/sagittal imbalance, n = 1). Presented with the same set of circumstances, 22 of 24 (91.7%) patients would have their IS removed again, including one of the patients who had a complication.

CONCLUSION

Of 395 consecutive walking patients who had ISs placed during fusion to the sacrum for adult spinal deformity, 24 (6.1%) underwent elective removal. Patients had a statistically significant improvement in hip/buttock pain after IS removal, and a low prevalence of complications after the procedure was observed.

Sacral fractures after lumbosacral fusion: a characteristic fracture pattern

OBJECTIVE

The purpose of this study was to describe the radiologic pattern of sacral fractures after lumbosacral fusion and to identify clinical characteristics relevant to the radiologic diagnosis.

MATERIALS AND METHODS

A search of CT, nuclear medicine, and MRI radiology reports over a 5-year period at our institution revealed a total of 23 patients with sacral fractures after lumbosacral fusion. Two radiologists reviewed all of the images to determine the sacral fracture pattern. The clinical records of these patients were reviewed for interval after surgery, fusion length, hardware, approach, preoperative diagnosis, symptoms, treatment, and risk factors.

RESULTS

All 23 sacral fractures were horizontal through the sacral body, involved the screw holes, and exited through the posterosuperior sacral alae. The fractures occurred within 3 months of fusion in 19 of 23 patients. All 23 patients had symptoms at the time of fracture. Seventeen of 23 fusions were long (more than four vertebrae). Four of 23 patients had osteoporosis. Eleven of 23 fractures healed without surgery, and 12 were managed with transiliac fixation.

CONCLUSION

Sacral fractures after lumbosacral fusion have a characteristic transverse pattern through the sacral screw holes that differs from the configuration of more common sacral insufficiency fractures. Most of these fractures occur within 3 months after surgery, and many of the patients need additional surgical fixation. Because few of the patients had osteoporosis and most underwent long fusion, the fractures might have been caused by hardware-related stress raisers in the sacrum.

The effect of sacral decortication on lumbosacral fixation in a calf spine model

STUDY DESIGN

Animal cadaveric biomechanical study.

OBJECTIVE

We hypothesized that increasing bony destabilization of a bovine cadaveric sacrum by anterior pedicle screw penetration and bilateral alar decortication would decrease the amount of load necessary for failure of the construct and result in failure through the decortication sites.

SUMMARY OF BACKGROUND DATA

Fusion to the sacrum has become commonly used for treatment of neuromuscular scoliosis and fusions in osteoporotic patients. Fixation failure after attempted fusion to the sacrum may be attributed to iatrogenic causes such as S1 screw penetration and sacral ala decortication.

METHODS

Sixteen fresh-frozen 6- to 8-week-old calf spines were tested after instrumentation with pedicle screws and bilateral rods from L2 to S1 using four constructs: (1) S1 screws with posterior-only purchase; (2) S1 screws with bicortical purchase; (3) S1 screws with bicortical purchase and sacral alar decortication; and (4) S1 screws with bicortical purchase, decortication, and iliac fixation. A destructive flexural bending load was applied at L2 to each construct. Ultimate failure moment (Nm) was compared among the four groups, using a one-way analysis of variance combined with Holm-Sidak post hoc test.

RESULTS

No significant difference in failure moment was found among groups 1, 2, and 3. The addition of iliac fixation (group 4) significantly increased bending load to failure (P < 0.01), and iliac screw dislodgement was the dominant mechanism of failure. All specimens in group 3 failed with fractures extending through the decortication site. Groups 1 and 2 specimens failed by fracturing through the S1 body.

CONCLUSION

Sacral alar decortication and anterior pedicle screw purchase did not decrease the failure moment in long instrumentation to the sacrum. Pattern of failure was affected, with alar decortication being the site of fracture in each construct in which it was performed. Iliac fixation increased the failure moment under catastrophic loading conditions even when combined with sacral alar decortication and bicortical pedicle screw purchase.