Prevalence of sacral dysmorphia in a prospective trauma population: Implications for a "safe" surgical corridor for sacro-iliac screw placement

Triangular Screw Placement to Treat Dysmorphic Sacral Fragility Fractures in Osteoporotic Bone Results in an Equivalent Stability to Cement-Augmented Sacroiliac Screws-A Biomechanical Cadaver Study

Background: Sacroiliac screw fixation in elderly patients with pelvic fractures remains a challenging procedure for stabilization due to impaired bone quality. To improve it, we investigated the biomechanical properties of combined oblique sacroiliac and transiliosacral screw stabilization versus the additional cement augmentation of this construct in a cadaver model of osteoporotic bone, specifically with respect to the maximal force stability and fracture-site motion in the displacement and rotation of fragments. Methods: Standardized complete sacral fractures with intact posterior ligaments were created in osteoporotic cadaver pelvises and stabilized with a triangle of two oblique sacroiliac screws from each side with an additional transiliosacral screw in S1 (n = 5) and using the same pelvises with additional cement augmentation (n = 5). A short cyclic loading protocol was applied, increasing the axial force up to 125 N. Sacral fracture-site motion in displacement and rotation of the fragments was measured by optical motion tracking. Results: A maximum force of 65N +/- 12.2 N was achieved using the triangular screw stabilization of the sacrum. Cement augmentation did not provide any significant gain in maximum force (70 N +/- 29.2 N). Only low fragment displacement was observed (2.6 +/- 1.5 mm) and fragment rotation (1.3 +/- 1.2°) without increased stability (3.0 +/- 1.5 mm; p = 0.799; 1.7 +/- 0.4°; p = 0.919) following the cement augmentation. Conclusions: Triangular stabilization using two obliques and an additional transiliosacral screw provides sufficient primary stability of the sacrum. Still, the stability achieved seems very low, considering the forces acting in this area. However, additional cement augmentation did not increase the stability of the sacrum. Given its lack of beneficial abilities, it should be used carefully, due to related complications such as cement leakage or nerve irritation. Improving the surgical methods used to stabilize the posterior pelvic ring will be a topic for future research.

Which screw corridors can be used for bilateral fragility fractures of the pelvis with a transverse fracture component (FFP IVb)?

BACKGROUND

Fragility fractures of the pelvis are becoming increasingly important in an ageing society. However, they are under-represented in the current research literature. In particular, unstable bilateral fragility fractures of the sacrum (FFP IVb) benefit from surgical treatment, but individual fracture patterns need to be considered in the surgical decision. This study describes the sacral anatomy in patients with FFP IVb pelvic fractures, with particular emphasis on the identification and evaluation of possible trans-sacral screw corridors, with particular emphasis on the transverse fracture components.

METHODS

Design: Retrospective clinical study.

SETTING

Level 1 trauma center. Patient Selection Criteria: The study reviewed 100 patients admitted for bilateral FFP with a transverse fracture between 01 / 2013 and 11 / 2023 that had a preoperative computed tomography (CT) of the pelvis including the fifth vertebra, treated with FFP IVb using preoperative multiplanar CT scans to analyze sacral anatomy. Outcome Measures and Comparisons: Sacral types and transitional abnormalities were classified, and corridor dimensions for S1 and S2 were measured, including estimated bone density using Hounsfield units. Bone corridors ≥ 8 mm were considered adequate. In addition, possible trans-sacral screw corridors were evaluated, taking into account the transverse fracture component.

RESULTS

While large trans-sacral screw corridors (≥ 8 mm) for S1 and S2 were identifiable in most cases, the actual feasibility for screw placement was limited due to the transverse fracture component's location, resulting in meaningful corridors in only 80 % for S1 and 47 % for S2. Additionally, in 4 % of patients without an S1 corridor, trans-sacral screw fixation was deemed inadequate due to the fracture line passing through S2.

CONCLUSIONS

These results indicate that not all FFP IVb fractures can be effectively stabilized using trans-sacral screw or bar fixation, necessitating alternative techniques for some cases. Furthermore, precise preoperative planning is essential for the management of these fractures due to complexity of anatomy. To identify the most suitable treatment approaches, further clinical studies are required.

LEVEL OF EVIDENCE

III.

Complete dorsal wall agenesis of the sacral canal in a Greek population: an osteological study

INTRODUCTION

The failure of closure of the dorsal wall of the sacral canal (SC) has been known since the eve of modern osteology, appearing in prehistoric times. Variants include partial or complete absence of the dorsal wall of the SC. SC presents a pathway for minimally invasive therapeutic and diagnostic procedures for spinal diseases and for ensuring analgesia and anesthesia in operations, including labor and genitourinary surgery.

3D-navigation for SI screw fixation - How does it affect radiation exposure for patients and medical personnel?

BACKGROUND

3D-navigation for percutaneous sacroiliac (SI) screw fixation is becoming increasingly common and several studies report great advantages of this technology. However, there is still limited clinical evidence on the efficacy regarding radiation exposure for patient and personnel.

METHODS

This is a retrospective, single-center cohort study. All patients who underwent percutaneous sacroiliac screw fixation for an injury of the posterior pelvic ring from 2014 to 2021 were screened. Inclusion criteria were: conclusive radiation dosage reports, signed informed consent, a twelve month follow up and a complete data set. Patients were stratified in two groups (3D-navigation (Group 3D-N) vs. control (Group F)) based on the imaging modality used. Primary outcomes were radiation exposure for patient and personnel. Secondary outcomes were reoperations, complications, and intraoperative precision.

RESULTS

Of 392 patients screened, 174 patients (3D-N: n = 50, F: n = 124) could be included for final analysis. We noted a significant reduction of the dose corresponding to potential radiation exposure for medical personnel (-15.3 mGy, 95 %CI: -2.1 to -28.5, p = 0.0232), but also a significant increase of the dose quantifying radiation exposure for patients (+77.0 mGy, 95 %CI: +53.3 to +100.6, p < 0.0001), when using navigation. In addition, the rate of radiographic malplacement was significantly reduced (F: 11.3% vs. 3D-N: 0 %, p = 0.0113) despite a substantial increase in transsacral screw placement (F: 19.4% vs. 3D-N: 76 %).

CONCLUSION

Our data clearly suggests that the use of 3D-navigation for percutaneous SI screw fixation decreases radiation exposure for medical personnel, while increasing radiation exposure for patients. Furthermore, intraoperative precision is improved, even in more challenging operations.

Safe surgical corridor for iliosacral screw placement in unstable pelvic fractures: a computed-tomography-guided validation study of the "triangulation method"

BACKGROUND

The percutaneous iliosacral screw technique represents a global standard fixation method for unstable fractures of the posterior pelvic ring. However, the inaccurate positioning of iliosacral screws is associated with a significant risk of severe intra-operative complications. Therefore, this study aimed to investigate the relationship between the skin entry point of the transverse iliosacral screw of the first sacral vertebral body and the anterior superior iliac spine and the greater trochanter of the femur using computed-tomography-guided validation.

METHODS

Overall, 91 consecutive patients admitted to a tertiary referral center in China for posterior pelvic ring fixation via the "triangulation method" using computed-tomography-guided validation between January 1, 2020, and December 31, 2020, were included in this retrospective observational cohort study. Modeling and simulated iliosacral screw placement were performed using the Mimics software. The distance between the three points of interest was measured, and their relationship in a rectangular coordinate system was determined. Patients were categorized according to gender, body mass index, and femoral rotation angle to investigate the factors affecting the positional relationship between the three points.

RESULTS

An equilateral triangular relationship was observed between the positioning points of the transverse iliosacral screw, anterior iliac spine, and greater trochanter. Additionally, 95% of the entry points were within a circle radius centered 12 mm at the apex of an equilateral triangle comprising the anterior superior iliac spine and the greater trochanter as the base. The entry point in the femoral external rotation was more dorsal than that in the internal femoral rotation. Furthermore, the entry point in females was more rostral than that in males, and the entry point in overweight patients was more dorsal than that in normal-weight patients.

CONCLUSIONS

The skin entry point of the percutaneous iliosacral screw can be located by drawing an equilateral triangle from the anterior superior iliac spine and the greater trochanter as the base to the dorsum end of the patient's head. In summary, this retrospective cohort study validated the safety and efficacy of the "triangulation methods" for percutaneous fixation of unstable posterior pelvic ring injuries.

[Sacral H-shaped fractures between traumatic, insufficiency and fatigue fractures : Similarities, differences and controversies]

In the basic entirety of stress fractures, insufficiency fractures are defined as fractures caused by prolonged normal or physiological loading of a bone with insufficient elastic resistance. This clearly distinguishes it from fatigue fractures, in which excessive loads are continuously applied to a bone with normal elastic resistance. According to Pentecost (1964) both entities of stress fracture result from "the inherent inability of the bone to withstand stress applied without violence in a rhythmical, repeated, subthreshold manner". This distinguishes them from acute traumatic fractures. In the clinical routine these differences are not always so clearly presented. The example of the H‑shaped sacral fracture is used to illustrate the relevance of a clear terminology. In this context, current controversies in the treatment of sacral insufficiency fractures are discussed.

Complications of conventional percutaneous sacroiliac screw fixation of traumatic pelvic ring injuries: a systematic review and meta-analysis

OBJECTIVES

The objective of this review was to present a thorough overview of the complications associated with conventional percutaneous sacroiliac screw fixation to identify areas for improvement in surgical technique and patient selection.

METHODS

PubMed/Medline, Web of Science, Embase, Ovid, Cochrane library, and Google Scholar were systematically searched for original human studies reporting on complications of conventional percutaneous sacroiliac fixation in traumatic pelvic ring injuries from January 1, 2000, to April 30, 2022. The main meta-analysis was based on the random effect model to pool all complications reported in the included studies. The results were reported as weighted proportions with 95% confidence intervals. This review was conducted in line with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines.

RESULTS

A total of 56 studies with 3644 screws (2871 procedures) met the inclusion criteria, with a mean age of 40.5 years. The most frequently reported complications were screw malposition with a weighted proportion of 6% (95% CI: 5-9%) and involved 189 out of 3644 screws, persistent pain following the procedure with a weighted proportion of 3% (95% CI: 2-4%) and affected 98 out of 2871 patients, and nerve injury, which had a weighted proportion of 2% (95% CI: 1-3%) and was observed in 41 out of 2871 procedures. The L5 and S1 nerve roots were more frequently affected. Revision surgery was required for 184 out of 2871 patients with a weighted proportion of 5% (95% CI: 3-7%). The primary reason for the revision was persistent pain after the initial procedure, which affected 74 out of 184 patients, with a weighted proportion of 2.0% (95% CI: 1.2-2.8%).

CONCLUSIONS

This study showed that screw malposition, the need for revision surgery, persistent pain, and nerve injuries were the most frequent complications following conventional percutaneous sacroiliac screw fixation. However, these results must be interpreted in context due to confounding factors, including the lack of high-quality studies and the absence of uniformity in defining some complications across studies.

Guidance for dysmorphic sacrum fixation with upper sacroiliac screw based on imaging anatomy study: techniques and indications

OBJECTIVE

This study aimed to investigate the techniques and indications of upper sacroiliac screw fixation for the dysmorphic sacrum.

METHODS

The dysmorphic sacra were selected from 267 three-dimensional pelvic models. The dysmorphic sacra which couldn't accommodate a 7.3 mm upper trans ilio-sacroiliac screw were classified as the main dysmorphic sacra. Then, the size of the bone corridor, the length of the screw in the corridor, and the orientation of the screw were measured. The insertion point on the sacrum was identified by two bone landmarks.

RESULTS

totally, 30.3% of sacra were identified as the main dysmorphic sacra. The inclinations of the screw oriented from posterior to anterior were (21.80 ± 3.56)° for males and (19.97 ± 3.02)° for females (p < 0.001), and from caudal to cranial were (29.97 ± 5.38)° for males and (28.15 ± 6.21)° for females (p = 0.047). The min diameters of the corridor were (16.31 ± 2.40) mm for males and (15.07 ± 1.58) mm for females (p < 0.001). The lengths of the screw in the Denis III zone were (14.41 ± 4.40) mm for males and (14.09 ± 5.04) mm for females (p = 0.665), and in the Denis II+III zones were (36.25 ± 3.40) mm for males and (38.04 ± 4.60) mm for females (p = 0.005). The rates of LP-PSIS/LAIIS-PSIS were (0.36 ± 0.04) for males and (0.32 ± 0.03) for females (t = 4.943, p < 0.001). The lengths of LPM were (8.81 ± 5.88) for males and (-4.13 ± 6.33) for females (t = 13.434, p < 0.001).

CONCLUSION

When the sacrum has the features of "sacrum not recessed" and/or "acute alar slope", the conventional trans ilio-sacroiliac screw couldn't be placed safely. The inclination oriented from posterior to anterior and from caudal to cranial are approximately 20° and 30°, respectively. The bone insertion point locates in the rear third of the anterior inferior iliac spine to the posterior superior iliac spine. The sacroiliac screw is not recommended to fix the fractures in Denis III zone.

Iliac dysmorphism: defining radiographic characteristics and association with pelvic osseous corridor size

INTRODUCTION

Insertion of iliac wing implants requires understanding of the curvilinear shape of the ilium. This study serves to quantitatively identify the area of iliac inner-outer table convergence (IOTC), characterize the iliac wing osseous corridor, and define the gluteal pillar osseous corridor.

METHODS

Computed tomography scans of 100 male and 100 female hemipelves were evaluated. The iliac wing was studied using manual best-fit analysis of the bounds of the inner and outer cortices. The IOTC was defined as the location of the iliac wing with an intercortical width less than 5 mm. The shortest distance from the apex of the iliac crest to the superior border of the IOTC was defined as the iliac wing osseous corridor. Finally, the width of the gluteal pillar corridor from the gluteus medius tubercle to the ischial tuberosity was measured.

RESULTS

The IOTC is an elliptical area measuring 22.3 cm². All ilia had an area where the inner and outer cortices converged to an intercortical width of less than 5 mm; 48% converged to a single cortex. The shortest mean distance from the superior edge of the iliac crest to the beginning of the IOTC was 20.3 mm in men and 13.8 mm in women (p < 0.001). The gluteal pillar diameter averaged 5.3 mm in men and 4.3 mm in women (p < 0.001).

DISCUSSION

All ilia converge to a thin and frequently unicortical central region. A 4.5 mm iliac wing lag screw will not breach the cortex if it remains within 20 mm or 14 mm distal to the cranial aspect of the iliac crest in males and females, respectively. Not only is the gluteal pillar smaller than previously thought, in 41% of males and 73% of females, it is not be large enough for 5 mm implants.

CONCLUSION

This study quantitatively assesses the dimensions of the IOTC, the iliac crest osseous corridor, and the gluteal pillar. Overall, our findings provide improved understanding of the limits for implant use in the iliac wing as well as better appreciation of the complex osteology of the ilium. This will help surgeons to identify safe areas for implant placement and avoid inadvertent cortical penetration.

An evaluation of the inlet obturator oblique view for sacroiliac and transsacral screw placement

INTRODUCTION

Between 2005 and 2017, the number of closed reduction and internal fixation of pelvic ring injuries increased by 1116%. Percutaneous fixation is currently the only minimally invasive technique that can stabilize the posterior elements of the pelvis. The purpose of this study was to investigate the utility of the inlet obturator oblique view (IOO) with the hypothesis that the IOO view will improve the accuracy of sacroiliac and transsacral screw placement in the S1 or S2 body and improve the accuracy of assessing whether the implant is fully seated against the outer cortex of the ilium.

MATERIALS AND METHODS

Ten male pelvic training models were used. Thirty-six screw configurations were inserted by a fellowship trained orthopedic trauma surgeon in appropriately and inappropriately placed sacroiliac and transsacral screw configurations. These configurations were imaged using fluoroscopy in different planes and saved for survey.

RESULTS

Fourteen orthopedic professionals reviewed 313 fluoroscopic images. Interrater reliability demonstrated marked improvement in assessment of whether the screw head was seated against the outer cortex of the ilium with the IOO view (kappa = 0.841, without IOO kappa = 0.027). There was a statistically significant difference in overall accuracy (p value < 0.001, OR = 1.57, 95% CI = 1.35-1.84) and whether the screw head was seated (p value < 0.001, OR = 8.14, 95% CI = 5.52-11.99) when compared with and without the IOO view (accuracy with IOO view: 85%, accuracy without IOO view: 78.26%; screw seated with IOO view: 93.93%, screw seated without IOO view: 65.54%). There was no significant difference (p value 0.465, OR = 1.13, 95% CI = 0.82-1.55) determining if the screw was in a safe position (safe with IOO view: 84.64%, safe without IOO view: 83.04%).

CONCLUSIONS

Our findings demonstrate that misinterpretation of sacroiliac and transsacral screw placement can occur with the standard fluoroscopic imaging. We suggest the addition of the IOO view increases the overall accuracy of screw placement and whether the screw head is fully seated against the outer table of the ilium. This in turn can improve fixation and potentially improve patient outcomes and decrease adverse events.

Ethnic Differences in Western and Asian Sacroiliac Joint Anatomy for Surgical Planning of Minimally Invasive Sacroiliac Joint Fusion

Pain originating in the sacroiliac joint (SIJ) is a contributor to chronic lower back pain. Studies on minimally invasive SIJ fusion for chronic pain have been performed in Western populations. Given the shorter stature of Asian populations compared with Western populations, questions can be raised regarding the suitability of the procedure in Asian patients. This study investigated the differences in 12 measurements of sacral and SIJ anatomy between two ethnic populations by analyzing computed tomography scans of 86 patients with SIJ pain. Univariate linear regression was performed to evaluate the correlations of body height with sacral and SIJ measurements. Multivariate regression analysis was used to evaluate systematic differences across populations. Most sacral and SIJ measurements were moderately correlated with body height. The anterior-posterior thickness of the sacral ala at the level of the S1 body was significantly smaller in the Asian patients compared with the Western patients. Most measurements were above standard surgical thresholds for safe transiliac placement of devices (1026 of 1032, 99.4%); all the measurements below these surgical thresholds were found in the anterior-posterior distance of the sacral ala at the S2 foramen level. Overall, safe placement of implants was allowed in 84 of 86 (97.7%) patients. Sacral and SIJ anatomy relevant to transiliac device placement is variable and correlates moderately with body height, and the cross-ethnic variations are not significant. Our findings raise a few concerns regarding sacral and SIJ anatomy variation that would prevent safe placement of fusion implants in Asian patients. However, considering the observed S2-related anatomic variation that could affect placement strategy, sacral and SIJ anatomy should still be preoperatively evaluated.

Contemplate iliosacral screw in patients with developmental dysplasia of the hip

OBJECTIVES

Our aim in the study was evaluating sacroiliac morphology in patients with DDH and its possible effect on appropriate iliosacral screw fixation.

DESIGN

Retrospective cohort study.

SETTING

Level of evidence 3.

PATIENTS/PARTICIPANTS

We evaluated the anteroposterior pelvis X-ray and pelvic CT scans of patients. We mainly divided the patients into two groups: DDH group (n:105) and control group (n:105).

INTERVENTION

The presence of the five qualitative characteristics of sacral dysplasia evaluated according to Route in both groups. The DDH group was divided into four subgroups according to the degree of hip dysplasia.

MAIN OUTCOME MEASUREMENT

The cross-sectional area, length of the osseous corridor, coronal and vertical angulation evaluated in both groups.

RESULTS

The DDH group also exhibited a significantly higher S1 coronal and axial angulation, lower S1 cross-sectional area and S1 iliosacral screw length than the control group (p:0.033, p:0,002, p:0.006, p:0,019, respectively). According to the Rout classification, 9% were normal, 31% transient, 58% dysplastic in the DDH group. 45.7% were normal, 38% transient, 17% dysplastic in the control groups. These differences between the groups were statistically significant (p < 0.001). When the DDH groups were evaluated within themselves; no statistically significant difference was observed in S1 and S2 cross-sectional area, S1 and S2 maximum estimated iliosacral screw length, S1 and S2 axial and coronal angles assessment.

CONCLUSION

Sacral dysplasia was more common, narrower and more angled osseous canal for the iliosacral screw was found in the DDH group. There was no relation between the degree of hip dysplasia and sacrum morphology in the DDH group. Thus, we suggest the surgeons be aware of iatrogenic injury even in constrained dysplastic hips.

Comparison of Three-Dimensional Navigation-Guided Percutaneous Iliosacral Screw and Minimally Invasive Percutaneous Plate for the Treatment of Zone II Unstable Sacral Fractures

OBJECTIVE

The percutaneous IS screws and the minimally invasive percutaneous plate are the most popular internal methods for Zone II unstable sacral fractures. However, the choice of fixation remains controversial for orthopaedic surgeons. The purpose of study was to evaluate and compare the clinical results of percutaneous iliosacral (IS) screw fixation under three-dimensional (3D) navigation and minimally invasive percutaneous plate fixation in the treatment of Zone II unstable sacral fractures.

METHODS

A retrospective study was performed, including 64 patients with Zone II unstable sacral fractures who underwent percutaneous IS screw fixation under 3D navigation (navigation group) and minimally invasive percutaneous plate fixation (plate group) from January 2011 and March 2021 in our department. The age, gender, fracture type, mechanism of injury, injury severity score (ISS), time from admission to operation, operative time, intraoperative blood loss, hospital stay, incision length, follow-up time, time to clinical healing, and complications were recorded and analyzed. Matta standard was used to assess fracture reduction outcomes. The Majeed function system assessed functional outcomes at the last follow-up.

RESULTS

The average follow-up time was (14.42 ± 1.57) months in the navigation group and (14.79 ± 1.37) months in the plate group. No statistical difference between the two groups in age, gender, fracture type, mechanism of injury, ISS, time from admission to operation, and time to clinical healing. However, significant differences were detected in operative time, intraoperative blood loss, hospital stay, and incision length (p < 0.001). According to Matta standard at 2 days postoperatively, the excellent and good rate was 91.42% in the navigation group, and it was 93.10% in the plate group. There was no significant difference between the two groups (p = 0.961). According to Majeed function system at the follow-up, the excellent and good rate was 97.14% in the navigation group, and 93.10% in the plate group. The difference between the two groups was not statistically significant (p = 0.748). There were no neurovascular injuries associated with this procedure. The incidence of complications was 44.82% (13/29) in the plate group, while 14.28% (5/35) in the navigation group (p = 0.007).

CONCLUSION

This study found that compared with minimally invasive percutaneous plate fixation, percutaneous IS screw fixation under 3D navigation is a suitable option for the treatment of Zone II unstable sacral fractures. This approach is characterized by its shorter operation time, less surgical trauma, less bleeding, less hospital time, and fewer complications.

Supraacetabular osseous corridor: defining dimensions, sex differences, and alternatives

INTRODUCTION

The supraacetabular (SA) corridor extends from the anterior inferior iliac spine to the posterior ilium and can safely accommodate implants to stabilize pelvic and acetabular fractures. However, quantitative analysis of its dimensions and characteristics have not been thoroughly described. This study seeks to define the dimensions, common constriction points, and any alternative trajectories that would maximize the corridor diameter.

METHODS

Computed tomography of 100 male and 100 female hemipelves without osseous trauma were evaluated. The corridor boundaries were determined through manual best-fit analysis. The largest intercortical cylinder within the pathway was created and measured. Alternative trajectories were tested within the SA boundaries to identify another orientation that maximized the diameter of the intercortical cylinder.

RESULTS

The traditional SA corridor had a mean diameter of 8.3 mm in men and 6.2 mm in women. This difference in diameter is due to a more S-shaped ilium in women. A larger alternative SA corridor was found that had a less limited path through the ilium and measured 11.3 mm in men and 9.9 mm in women. These dimensions are significantly different compared to those of the traditional SA corridor in both men and women.

CONCLUSIONS

In men, the SA corridor allows for the safe passage of most hardware used in pelvic and acetabular fractures. However, in women, the SA corridor is restricted by a more S-shaped ilium. An alternative trajectory was found that has a significantly larger mean diameter in both sexes. Ultimately, the trajectory of hardware will be dictated by the clinical scenario. When large implants are needed, especially in women, we recommend considering the alternative SA corridor.

Defining the iliac wing osseous fixation pathways: anatomy and implant constriction points

INTRODUCTION

Insertion of iliac wing implants requires understanding of the curvilinear shape of the ilium. This study serves to quantitatively identify the area of iliac inner-outer table convergence (IOTC), characterize the iliac wing osseous corridor, and define the gluteal pillar osseous corridor.

METHODS

Computed tomography scans of 100 male and 100 female hemipelves were evaluated. The iliac wing was studied using manual best-fit analysis of the bounds of the inner and outer cortices. The IOTC was defined as the location of the iliac wing with an intercortical width less than 5 mm. The shortest distance from the apex of the iliac crest to the superior border of the IOTC was defined as the iliac wing osseous corridor. Finally, the width of the gluteal pillar corridor from the gluteus medius tubercle to the ischial tuberosity was measured.

RESULTS

The IOTC is an elliptical area measuring 22.3 cm². All ilia had an area where the inner and outer cortices converged to an intercortical width of less than 5 mm; 48% converged to a single cortex. The shortest mean distance from the superior edge of the iliac crest to the beginning of the IOTC was 20.3 mm in men and 13.8 mm in women (p < 0.001). The gluteal pillar diameter averaged 5.3 mm in men and 4.3 mm in women (p < 0.001).

DISCUSSION

All ilia converge to a thin and frequently unicortical central region. A 4.5 mm iliac wing lag screw will not breach the cortex if it remains within 20 mm or 14 mm distal to the cranial aspect of the iliac crest in males and females, respectively. Not only is the gluteal pillar smaller than previously thought, in 41% of males and 73% of females, it is not be large enough for 5 mm implants.

CONCLUSION

This study quantitatively assesses the dimensions of the IOTC, the iliac crest osseous corridor, and the gluteal pillar. Overall, our findings provide improved understanding of the limits for implant use in the iliac wing as well as better appreciation of the complex osteology of the ilium. This will help surgeons to identify safe areas for implant placement and avoid inadvertent cortical penetration.

Is the Iliac Cortical Density Similarly Positioned in the Developing Pediatric Pelvis?

OBJECTIVES

The iliac cortical density (ICD) is a critical fluoroscopic landmark for pelvic percutaneous screw placement. Our purpose was to evaluate the ICD as a landmark in pediatrics and quantify the diameter of osseous pathways for 3 screw trajectories: iliosacral (IS) at S1 and transiliac-transsacral (TSTI) at S1 and S2.

METHODS

Two hundred sixty-seven consecutive pelvic CT scans in children 0-16 years of age were analyzed. ICD and S1 vertebral heights were measured at multiple regions along S1. Their height and corresponding ratios, as well as osseous screw corridor dimensions were compared between age groups and by the dysmorphic status.

RESULTS

In the nondysmorphic pelvises, S1 height, ICD height, and the ICD to S1 height ratio increased across age groups for all locations (P < 0.001). All 3 screw pathway diameters increased with age (P < 0.001). In the dysmorphic group, there was no increase in ICD to S1 height ratio with age. Except for the age 0-2 group, the ICD to S1 height ratios were significantly larger in the nondysmorphic group. In the dysmorphic group, S1 TSTI pathway remained narrow with age, whereas IS at S1 and TSTI at S2 had a significant increased diameter with age (P < 0.001).

CONCLUSION

The ICD is a useful fluoroscopic landmark for percutaneous screw placement in the pediatric pelvis. For nondysmorphic pelvises, the ICD to S1 height ratio, as well as osseous corridors for IS, TSTI at S1, and TSTI at S2 screw trajectories increase significantly with age. The margin for safe screw placement in S1 is smaller for younger and dysmorphic pelvises.

Pelvic antropometric measurement in 3D CT for placement of two unilateral iliosacral S1 - 7.3 mm screws

PURPOSE

Stability of the dorsal pelvic ring is important for patient mobilisation and can be restored using several surgical procedures after fracture. Placement of percutaneous iliosacral screws is a reliable and minimal-invasive technique to achieve stabilisation of the dorsal pelvic ring by placement of two screws in the first sacral vertebra. Aim of this study was to evaluate 3D CT scans regarding the anatomical possibility to place two 7.3 mm iliosacral screws for fixation of the dorsal pelvic ring.

METHODS

3D CT datasets of 500 consecutive trauma patients with 1000 hemipelves of a mid-european level I trauma centre with or without pelvic injury were evaluated and measured bilaterally in this retrospective study.

RESULTS

One thousand hemipelvic datasets of 500 patients (157 females, 343 males) with a mean age of 49.7 years (18 to 95) were included in this study. Only 16 hemipelves (1.6%, 11 in females, 5 in males) in 14 patients (2.8%, 9 females = 5.73%, 5 males = 1.5%) showed too narrow corridors so that 7.3 mm screw placement would not be possible (p = 0.001). In women, too narrow corridors occurred 3.9 times as often as in men. Only two females showed this bilaterally.

CONCLUSION

The evaluation of 3D CT scans of the pelvis showed the importance of planning iliosacral screw placement, especially if two 7.3 mm screws are intended to be placed in the first sacral vertebra.

Corridor-diameter-dependent angular tolerance for safe transiliosacral screw placement: an anatomic study of 433 pelves

BACKGROUND

The purpose of this study was to determine the angular tolerance of the S1 and S2 segments to accommodate a transiliosacral screw across both sacroiliac joints.

HYPOTHESIS

We hypothesized that the angular tolerance for transiliosacral screw placement would be more constrained than the angular tolerance for iliosacral fixation in pelves where a safe osseous corridor was measured.

MATERIALS AND METHODS

The cortical boundaries of the S1 and S2 sacral segments in 433 pelvic CTs were digitally mapped. A straight-line path was placed within each osseous corridor and extended across both SI joints past the outer iliac cortices. The diameter of the path was increased until it breached the cortex, geometrically determining maximum diameter (Dmax). Angular tolerance for screw placement was calculated with trigonometric analysis of the Dmax value of the corridor, and the average distance from the termination of the osseous corridor to the site of percutaneous insertion. Gender, age, and BMI were evaluated as independent predictors using binomial logistic regression.

RESULTS

The transiliosacral angular tolerance for the S1 and S2 osseous corridors was 1.53 ± 0.57 degrees and 1.02 ± 0.33 degrees, respectively. 68.9% of S1 corridors and 81.1% of S2 corridors had a safe zone (corridor diameter ≥ 10 mm) for transiliosacral placement, 48.3% of the pelves had a safe zone for both corridors, while 5.1% had no safe zones. Females had a less frequent Dmax ≥ 10 mm at S1, 52% vs 67% (p = 0.001), and at S2, 64% vs 86% (p < 0.001).

DISCUSSION

In conclusion, the angular tolerance of 1.53 and 1.03 degrees for the S1 and S2 segments, respectively, creating a narrow interval for safe passage of the trans-iliac and trans-sacral, with approximately 31.1% of patients not having a viable corridor for screw passage. A correlation exist between S1 and S2 corridors with Dmax ≥ 10 mm and the resulting increase in angular tolerance for safe passage of a transilioscral screw.

LEVEL OF EVIDENCE IV

Level Retrospective Cohort.

Gender-Associated Differences in Sacral Morphology Do Not Affect Feasibility Rates of Transsacral Screw Insertion. Radioanatomic Investigation Based on Pelvic Cross-sectional Imaging of 200 Individuals

STUDY DESIGN

Retrospective radioanatomic single-center cohort study.

OBJECTIVE

To investigate sex-specific differences in transsacral corridor dimensions, determine feasibility rates of transsacral screw placement without extended safety zones around planned screw positions, and develop an index defining sacral dysmorphism (SD) irrespective of transsacral corridor diameters.

SUMMARY OF BACKGROUND DATA

Previously reported SD definitions used radiologically identifiable pelvic characteristics or predefined minimum diameter thresholds of transsacral corridors in the upper sacral segment including safety zones for screw placement. Technical progress of surgical 3D image guidance improved sacral screw insertion accuracy questioning established minimum diameter threshold-based SD definitions.

METHODS

Datasets from cross-sectional pelvic imaging of 100 women and 100 men presenting to a general hospital from July 2018 through August 2018 were included in a database to evaluate transsacral trajectory rates, and dimensions of transsacral corridor lengths, widths (TSCWs), and heights (TSCHs) in sacral segments I to III (S1-3). SD was assumed, if no transsacral trajectory was found in S1 with a corridor diameter of at least 7.5 mm.

RESULTS

Women presented significantly higher rates of transsacral trajectories in the inferior sector of S1 (P = 0.03), and larger transsacral corridor lengths in S2 (superior sector, P = 0.045), and S3 (central position, P = 0.02). In men, significantly higher feasibility rates were found for the placement of two transsacral screws in S2 (P = 0.0002), and singular screws in S3 (P = 0.006), with larger S1- (P = 0.0002), and central S2-TSCWs (P = 0.006). SD was prevalent in 17% of women, and 16% of men (P = 0.85). Calculating TSCW ratios of S1 and S2 was significantly indicative for SD at values below a threshold of 0.8 in women (P < 0.00001), and men (P = 0.0004).

CONCLUSION

SD is independent of sex despite significant differences in sacral morphology. An index defining SD irrespective of absolute transsacral corridor dimensions is presented to reliably differentiate dysmorphic from nondysmorphic sacra in women and men.

LEVEL OF EVIDENCE

2.

Percutaneous removal of sacroiliac screw following iatrogenic neurologic injury in posterior pelvic ring injury: A case report

INTRODUCTION

Percutaneous sacroiliac fixation is an effective minimally invasive method for posterior pelvic ring stabilization. Screw misplacement, and subsequent neurologic injury are two well described complications. Managing those complications however is under-reported.

CASE

A young female, sustained an unstable pelvic ring injury as a victim of motor vehicle collision. Following percutaneous sacroiliac screw fixation, she complained of L5 nerve root radiculopathy, and muscle weakness. Percutaneous removal of the screw after a wait period for fracture union resulted in immediate symptoms relief.

DISCUSSION

Safe sacroiliac screw placement is technically demanding requiring good understanding of sacral complex morphology and its anatomic variants. Risk of screw misplacement, and potential neurologic injury increases in dysmorphic sacra, or with inaccurate fracture reduction. Advances in intraoperative imaging modalities have been introduced in an attempt to improve accurate screw insertion. Literature is scarce with reports discussing removal of sacroiliac screw. Technique of screw retrieval is also controversial.

CONCLUSION

This case addresses management of an iatrogenic neurologic complication following percutaneous sacroiliac screw fixation. Our experience showed that, percutaneous retrieval of an intact misplaced sacroiliac screw is achievable, resulting in complete resolution of neurologic symptoms.

Feasibility of iliosacral screw placement in patients with upper sacral dysplasia

Background

Exact knowledge of the sacral anatomy is crucial for the percutaneous insertion of iliosacral screws. However, dysplastic anatomical patterns are common. In addition to a preoperative computed tomography (CT) analysis, conventional radiographic measures may help to identify upper sacral dysplasia and to avoid damage to surrounding structures. Aiming to further increase safety in percutaneous iliosacral screw placement in the presence of sacral dysmorphism, this study examined the prevalence of previously established radiographic signs and, in addition, defined the “critical SI angle” as a new radiographic criterion.

Methods

Pelvic CT scans of 98 consecutive trauma patients were analysed. Next to assessment of established signs indicating upper sacral dysplasia, the critical sacroiliac (SI) angle was defined in standardized pelvic outlet views.

Results

The critical SI angle significantly correlates with the presence of mammillary bodies and an intraarticular vacuum phenomenon. With a cut-off value of − 14.2°, the critical SI angle detects the feasibility of a safe iliosacral screw insertion in pelvic outlet views with a sensitivity of 85.9% and a specificity of 85.7%.

Conclusions

The critical SI angle can support the decision-making when planning iliosacral screw fixation. The clinical value of the established signs of upper sacral dysplasia remains uncertain.

Space available for trans-sacral implants to treat fractures of the pelvis assessed by virtual implant positioning

INTRODUCTION

The use of trans-sacral implants to treat fractures of the sacrum is limited by the variable pelvic anatomy. We were interested in how many trans-sacral implants can be placed per pelvis? If a trans-sacral implant cannot be placed in S1, where is the cortex perforated, and is the use of sacroiliac screws safe in these pelves?

MATERIALS AND METHODS

3D pelvic models were created from CT scans of 156 individuals without fractures (92 European and 64 Japanese, 79 male and 77 female, mean age 66.7 ± 13.7 years). Trans-sacral implants with a diameter of 7.3 mm were positioned virtually with and without a surrounding safe zone of 12 mm diameter.

RESULTS

Fifty-one percent of pelves accommodated trans-sacral implants in S1 with a safe zone. Twenty-two percent did not offer enough space in S1 for an implant even when ignoring the safe zone. Every pelvis had sufficient space for a trans-sacral implant in S2, in 78% including a safe zone as well. In S1, implant perforation was observed in the sacral ala and iliac fossa in 69%, isolated iliac fossa perforation in 23% and perforation of the sacral ala in 8%. Bilateral sacroiliac screw placement was always possible in S1.

CONCLUSIONS

The use of trans-sacral implants in S1 requires meticulous preoperative planning to avoid injury of neurovascular structures. S2 more consistently offers space for trans-sacral implants.

Preoperative planning and safe intraoperative placement of iliosacral screws under fluoroscopic control

OBJECTIVE

Preoperative planning of the starting point and safe trajectory for iliosacral screw (SI screw) fixation using CT scans for safe and accurate fluoroscopically controlled percutaneous SI screw placement.

INDICATIONS

Transalar and transforaminal sacral fractures. SI joint disruptions and fracture-dislocations. Non- or minimally displaced spinopelvic dissociation injuries.

CONTRAINDICATIONS

Transiliac instabilities. Sacral fractures with neurological impairment requiring decompression. Relevant residual displacement after closed reduction attempts. Insufficient fluoroscopic visualization of the anatomical landmarks of the upper sacrum.

SURGICAL TECHNIQUE

Preoperative planning of the starting point and the safe screw trajectory using CT scans and two-dimensional multiplanar reformation tools. Fluoroscopically guided identification of the starting point using the lateral view according to preoperative planning. Advancing the guidewire under fluoroscopic control using inlet and outlet views according to the planned trajectory. Predrilling and placement of 6.5 mm cannulated screws.

POSTOPERATIVE MANAGEMENT

Weightbearing as tolerated using crutches. Immediate CT scan in case of postoperative neurological impairment. Generally no screw removal.

RESULTS

Fifty-nine screws were placed in 34 patients using the described technique. There were 2 cases of screw malpositioning (anatomical landmarks inadequately identified and fluoroscopically controlled SI screw fixation should thus not have been performed at all; in a case with sacral dysmorphism, preoperative planning suggested a posterior and/or caudal S1 starting point, respectively, but intraoperatively, selection of a different starting point and screw trajectory resulted in screw malpositioning with iatrogenic L5 nerve palsy).

Safe corridor for iliosacral and trans-sacral screw placement in Indian population: A preliminary CT based anatomical study

OBJECTIVES

Nonsurgical management of unstable pelvic ring injuries is associated with poor outcomes. Posterior pelvic ring injuries include sacroiliac joint disruption and sacral fractures or a combination of the two. Morbidity is high in non-operatively managed patients. Screw fixation is being increasingly used to manage unstable posterior pelvic injuries. Limitations include a steep learning curve and potential for neurovascular injury. This is the first study in Indian population to describe the safe corridor for screw placement and check the feasibility of screw in both upper and lower sacral segments.

METHODS

This study involved retrospective analysis of 105 pelvic CT scans of patients admitted to the emergency department of a Level 1 trauma centre. Vertical height at the level of constriction (vestibule) of S1 and S2 was measured in coronal sections and anteroposterior width of constrictions was measured in axial sections. We created a trajectory for 7.3 mm cylinder keeping additional 2 mm free bony corridor around it and confirmed that bony limits were not breached in axial, coronal and sagittal sections. Whenever there was breach in bony limit we checked applicability of 6.5 mm screw.

RESULTS

The vertical height and anteroposterior width of vestibule/constriction of S1 was significantly higher in males, whereas S2 vestibule height and width were similar in males and females. Both male and female pelves were amenable to S1 Trans-sacral and S1 Iliosacral screw fixation with a 7.3 mm screw when a safe corridor of 2 mm was kept on all sides. However, when S2 segment was analysed, only 42.9% of male pelves and 25.7% of female pelves were amenable to insertion of trans-sacral 7.3 mm screw.

CONCLUSION

An individualized approach is necessary and each patient's CT must be carefully studied before embarking on sacroiliac screw fixation in Indian population.

Percutaneous Versus Open Treatment of Posterior Pelvic Ring Injuries: Changes in Practice Patterns Over Time

OBJECTIVE

To determine how the utilization of open versus percutaneous treatment of posterior pelvic ring injuries in early-career orthopaedic surgeons has changed over time.

METHODS

Case log data from surgeons testing in the trauma subspecialty for part II of the American Board of Orthopaedic Surgery examination from 2003 to 2015 were evaluated. Current procedural terminology codes for percutaneous fixation (27216) and open fixation (27218) of the posterior pelvic ring were evaluated using a regression analysis.

RESULTS

A total of 377 candidates performed 2095 posterior ring stabilization procedures (1626 percutaneous, 469 open). Total case volume was stable over time [β = -1.7 (1.1), P = 0.14]. There was no significant change in the number of posterior pelvic ring fracture surgery cases performed per candidate per test year [β = 0.1 (0.1), P = 0.50]. The proportion of posterior pelvic ring cases performed percutaneously increased significantly from 49% in 2003 to 79% in 2015 [β = 1.0 (0.4), P = 0.03]. There was a significant decrease in the number of open cases reported per candidate [β = -0.07 (0.03), P = 0.008].

DISCUSSION AND CONCLUSION

Early-career orthopaedic surgeons are performing more percutaneous fixation of the posterior pelvic ring and less open surgery. The impact of this change in volume on surgeon proficiency is unknown and warrants additional research.

Accuracy of sacroiliac screw placement with and without intraoperative navigation and clinical application of the sacral dysmorphism score

INTRODUCTION

Percutaneously-placed sacroiliac (SI) screws are currently the gold-standard fixation technique for fixation of the posterior pelvic ring. The relatively high prevalence of sacral dysmorphism in the general population introduces a high risk of cortical breach with resultant neurovascular damage. This study was performed to compare the accuracy of SI screw placement with and without the use of intraoperative navigation, as well as to externally validate the sacral dysmorphism score in a trauma patient cohort.

PATIENTS AND METHODS

All trauma patients who underwent sacroiliac screw fixation for pelvic fractures at a level 1 trauma centre over a 6 year period were identified. True axial and coronal sacral reconstructions were obtained from their pre-operative CT scans and assessed qualitatively and quantitatively for sacral dysmorphism - a sacral dysmorphism score was calculated by two independent assessors. Post-operative CT scans were then analysed for breaches and correlated with the hospital medical records to check for any clinical sequelae.

RESULTS

68 screws were inserted in 36 patients, most sustaining injuries from road traffic accidents (50%) or falls from height (36.1%). There was a male preponderance (83.3%) with the majority of the screws inserted percutaneously (86.1%). Intraoperative navigation was used in 47.2% of the patient cohort. 30.6% of the cohort were found to have dysmorphic sacra. The mean sacral dysmorphism scores were not significantly different between navigated and non-navigated groups. Three cortical breaches occurred, two in patients with sacral dysmorphism scores >70 and occurring despite the use of intraoperative navigation. There was no significant difference in the rates of breach between navigated and non-navigated groups. None of the breaches resulted in any clinically observable neurovascular deficit.

CONCLUSION

The sacral dysmorphism score can be clinically applied to a cohort of trauma patients with pelvic fractures. In patients with highly dysmorphic sacra, reflected by high sacral dysmorphism scores, intraoperative navigation is not in itself sufficient to prevent cortical breaches. In such patients it would be prudent to consider instrumentation of the lower sacral corridors instead.

[Treatment of Day type pelvic crescent fracture by using percutaneous cannulated screw fixation technique]

Objective

To evaluate the feasibility and effectiveness of percutaneous cannulated screw fixation for the treatment of Day type Ⅱ pelvic crescent fracture.

Methods

The clinical data of 14 patients with Day type Ⅱ pelvic crescent fractures underwent closed reduction and percutaneous cannulated screw fixation between January 2009 and July 2016 were retrospectively analysed. There were 9 males and 5 females, aged 17-65 years (mean, 38 years). The causes of injury included traffic accident in 8 cases, falling from height in 3 cases, bruise injury in 3 cases; all were closed fractures. According to Tile classification, there were 8 cases of type B, 6 cases of type C. There were 13 cases combined with fracture of the anterior pelvic ring, including 8 cases of superior and inferior ramus of pubis fracture, 1 case of superior ramus of pubis fracture with symphysis separation, and 4 cases of symphysis separation. The interval of injury and admission was 1- 72 hours (mean, 16 hours), and the interval of injury and operation was 3-8 days (mean, 5 days). After operation, the reduction of fracture was evaluated by the Matta evaluation criteria, the clinical function was assessed by Majeed function assessment.

Results

The operation time was 35-95 minutes (mean, 55 minutes), cumulative C-arm fluoroscopy time was 3-8 minutes (mean, 5 minutes), no iatrogenic vascular injury and pelvic organ damage occurred. Postoperative X-ray films at 2 days indicated that 2 cases of vertical shift and 2 cases of mild rotation were not completely corrected. Postoperative CT examination at 3 days indicated that 2 pubic joint screws broke through the obturator bone cortex. None of the pubic ramus screws entered into the acetabulum, but a screw of superior pubic branch broke through the posterior cortical of superior pubic branch, a screw of posterior ilium column broke through the medial bone cortex of the ilium, and no clinical symptom was observed. One patient suffered from wound infection in the pubic symphysis, then healed after 2 weeks of wound drainage, the other wounds healed by first intention. According to Matta criterion for fracture reduction, the results were excellent in 9 cases, good in 4 cases, and fair in 1 case with an excellent and good rate of 92.9%. All patients were followed up 8-24 months (mean, 14 months). All fractures healed at 4 months and restored to the normal walking at 6 months after operation, 3 patients suffered from slight pain in the sacroiliac joints and slight claudication when they were tired or walked for a long time and unnecessary for special treatment. One patient felt pain in the back of the iliac spine when he was lying down. During the follow-up, no screw loosening or other internal fixation failure occurred. At last follow-up, according to Majeed functional evaluation criteria, the results were excellent in 7 cases, good in 5 cases, and fair in 2 cases with an excellent and good rate of 85.7%.

Conclusion

The percutaneous cannulated screw fixation is a safe treatment for Day type Ⅱ pelvic crescent fracture, which has a reliable fixation and good effectiveness.

Use of the S3 Corridor for Iliosacral Fixation in a Dysmorphic Sacrum: A Case Report

CASE

The S1 and S2 corridors are the typical osseous pathways for iliosacral screw fixation of posterior pelvic ring fractures. In dysmorphic sacra, the S1 screw trajectory is often different from that in normal sacra. We present a case of iliosacral screw placement in the third sacral segment for fixation of a complex lateral compression type-3 pelvic fracture in a patient with a dysmorphic sacrum.

CONCLUSION

In patients with dysmorphic sacra and unstable posterior pelvic ring fractures or dislocations, the S3 corridor may be a feasible osseous fixation pathway that can be used in a manner equivalent to the S2 corridor in a normal sacrum.

Critical dimensions of trans-sacral corridors assessed by 3D CT models: Relevance for implant positioning in fractures of the sacrum

Trans-sacral implants can be used alternatively to sacro-iliac screws in the treatment of osteoporosis-associated fragility fractures of the pelvis and the sacrum. We investigated trans-sacral corridor dimensions, the number of individuals amenable to trans-sacral fixation, as well as the osseous boundaries and shape of the S1 corridor. 3D models were reconstructed from pelvic CT scans from 92 Europeans and 64 Japanese. A corridor of <12 mm was considered critical for trans-sacral implant positioning, and <8 mm as impossible. A statistical model of trans-sacral corridor S1 was computed. The limiting cranio-caudal diameter was 11.6 mm (±5.4) for S1 and 14 mm (±2.4) for S2. Trans-sacral implant positioning was critical in 52% of cases for S1, and in 21% for S2. The S1 corridor was impossible in 26%, with no impossible corridor in S2. Antero-superiorly, the S1 corridor was limited not only by the sacrum but in 40% by the iliac fossa. The statistical model demonstrated a consistent oval shape of the trans-section of corridor S1. Considering the variable in size and shape of trans-sacral corridors in S1, a thorough anatomical knowledge and preoperative planning are mandatory using trans-sacral implants. In critical cases, S2 is a veritable alternative. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2577-2584, 2017.

Percutaneous screw fixation of the iliosacral joint: A case-based preoperative planning approach reduces operating time and radiation exposure

INTRODUCTION

A preoperative planning approach for percutaneous screw fixation of the iliosacral joint provides specific entry points (EPs) and aiming points (APs) of intraosseous screw pathways (as defined by CT scans) for lateral fluoroscopic projections used intraoperatively. The potential to achieve the recommended EPs and APs, to obtain an ideal screw position (perpendicular to the iliosacral joint), to avoid occurrence of extraosseous screw misplacement, to reduce the operating time and the radiation exposure by utilizing this planning approach have not been described yet.

METHODS

On preoperative CT scans of eight human cadaveric specimen individual EPs and APs were identified and transferred to the lateral fluoroscopic projection using a coordinate system with the zero-point in the center of the posterior cortex of the S1 vertebral body (x-axis parallel to upper S1 endplate). Distances were expressed in relation to the anteroposterior distance of the S1 upper endplate (in%). In each specimen on one side a screw was placed with provided EP and AP (New Technique) whereas at the contralateral side a screw was placed without given EP and AP (Conventional Technique). Both techniques were compared using postoperative CT scans to assess distances between predefined EPs and APs and the actually obtained EPs and APs, screw angulations in relation to the iliosacral joint in coronal and axial planes and the occurrence of any extraosseous screw misplacement. The "operating time (OT)" and the "time under fluoroscopy (TUF)" were recorded. Statistical analysis was performed by the Wilcoxon signed-rank test.

RESULTS

EPs were realized significantly more accurate using the new technique in vertical direction. The screw positions in relation to the iliosacral joint showed no significant difference between both techniques. Both techniques had one aberrantly placed screw outside the safe corridor. The (mean±SD) "OT" and the (mean±SD) "TUF" were significantly decreased using the new technique compared to the conventional technique (OT: 7.6±2min versus 13.1±5.8min, p=0.012; TUF: 1.5±0.8min versus 2.2±1.1min).

CONCLUSION

The presented preoperative planning approach increases the accuracy in percutaneous screw fixation of the iliosacral joint, reduces operating time and minimizes radiation exposure to patient and staff.

Treatment of massive acetabular bone loss and pelvic discontinuity with a custom triflange component and ilio-sacral fixation based on preoperative CT templating. A report of 2 cases

Revision rates for total hip arthroplasty are increasing and pelvic discontinuity is estimated to be present in 1% to 5% (Berry). Discontinuity is defined as a separation of the cephalad portion of the pelvis from the caudad portion (AAOS Type IV defects). This results from bone loss secondary to osteolysis, infection, fracture, or mechanical loosening. The goals of revision surgery in this setting are to obtain secure fixation of the acetabular component with or without union of the discontinuity. Many methods exist for treating this problem. Results with allograft and cage fixation have generally been poor (Berry, Hansen). More favourable outcomes have been reported using either a cup cage technique or custom triflange (Gross, Christie). The custom Triflange component is designed based on preoperative imaging with CT scan to manufacture a custom titanium implant to address the patient's specific bone loss pattern and obtain secure fixation in the ilium, pubis, and ischium. However, we have encountered cases of acetabular discontinuity with massive pelvic bone loss in which bone stock in the ilium was insufficient to provide support for proximal fixation of a conventional custom triflange component. Currently in the trauma patient population posterior pelvic ring disruptions are being treated with ilio-sacral screw fixation. The sacrum provides a source of secure bony fixation for these injuries. We report on 2 patients with pelvic discontinuity and massive bone loss using a technique to obtain proximal fixation of a custom triflange component into the sacrum.

Transsacral Osseous Corridor Anatomy Is More Amenable To Screw Insertion In Males: A Biomorphometric Analysis of 280 Pelves

BACKGROUND

Percutaneous iliosacral screw placement is the standard procedure for fixation of posterior pelvic ring lesions, although a transsacral screw path is being used more frequently in recent years owing to increased fracture-fixation strength and better ability to fix central and bilateral sacral fractures. However, biomorphometric data for the osseous corridors are limited. Because placement of these screws in a safe and effective manner is crucial to using transsacral screws, we sought to address precise sacral anatomy in more detail to look for anatomic variation in the general population.

QUESTIONS/PURPOSES

We asked: (1) What proportion of healthy pelvis specimens have no transsacral corridor at the level of the S1 vertebra owing to sacral dysmorphism? (2) If there is no safe diameter for screw placement in the transsacral S1 corridor, is an increased and thus safe diameter of the transsacral S2 corridor expected? (3) Are there sex-specific differences in sacral anatomy and are these correlated with known anthropometric parameters?

METHODS

CT scans of pelves of 280 healthy patients acquired exclusively for medical indications such as polytrauma (20%), CT angiography (70%), and other reasons (10%), were segmented manually. Using an advanced CT-based image analysis system, the mean shape of all segmented pelves was generated and functioned as a template. On this template, the cylindric transsacral osseous corridor at the level of the S1 and S2 vertebrae was determined manually. Each pelvis then was registered to the template using a free-form registration algorithm to measure the maximum screw corridor diameters on each specimen semiautomatically.

RESULTS

Thirty of 280 pelves (11%) had no transsacral S1 corridor owing to sacral dysmorphism. The average of maximum cylindrical diameters of the S1 corridor for the remaining 250 pelves was 12.8 mm (95% CI, 12.1-13.5 mm). A transverse corridor for S2 was found in 279 of 280 pelves, with an average of maximum cylindrical diameter of 11.6 mm (95% CI, 11.3-11.9 mm). Decreasing transsacral S1 corridor diameters are correlated with increasing transsacral S2 corridor diameters (R value for females, -0.260, p < 0.01; for males, -0.311, p < 0.001). Female specimens were more likely to have sacral dysmorphism (defined as a pelvis without a transsacral osseous corridor at the level of the S1 vertebra) than were male specimens (females, 16%; males, 7%; p < 0.003). Furthermore female pelves had smaller-corridor diameters than did male pelves (females versus males for S1: 11.7 mm [95% CI, 10.6-12.8 mm] versus 13.5 mm [95% CI, 12.6-14.4 mm], p < 0.01; and for S2: 10.6 mm [95% CI, 10.1-11.1 mm] versus 12.2 mm [95% CI, 11.8-12.6 mm ], p < 0.0001).

CONCLUSIONS

Narrow corridors and highly individual, sex-dependent variance of morphologic features of the sacrum make transsacral implant placement technically demanding. Individual preoperative axial-slice CT scan analyses and orthogonal coronal and sagittal reformations are recommended to determine the prevalence of sufficient-sized osseous corridors on both levels for safe screw placements, especially in female patients, owing to their smaller corridor diameters and higher rate of sacral dysmorphism.

2D versus 3D fluoroscopy-based navigation in posterior pelvic fixation: review of the literature on current technology

PURPOSE

Percutaneous sacroiliac (SI) fixation of unstable posterior pelvic ring injuries is a widely accepted procedure. The complex sacral anatomy with narrow osseous corridors for SI screw placement makes this procedure technically challenging. Techniques are constantly evolving as a result of better understanding of the posterior pelvic anatomy. Recently developed tools include fluoroscopy-based computer-assisted navigation, which can be two-dimensional (2D) or three-dimensional (3D). Our goal is to determine the relevant technical considerations and clinical outcomes associated with these modalities by reviewing the published research. We hypothesize that 3D fluoroscopy-based navigation is safer and superior to its 2D predecessor with respect to lower radiation dose and more accurate SI screw placement.

METHODS

We searched four medical databases to identify English-language studies of 2D and 3D fluoroscopy-based navigation from January 1990 through August 2015. We included articles reporting imaging techniques and outcomes of closed posterior pelvic ring fixation with percutaneous SI screw fixation. Injuries included in the study were sacral fractures (52 patients), sacroiliac fractures (88 patients), lateral compression fractures (20 patients), and anteroposterior compression type pelvic fractures (8 patients). We excluded articles on open reduction of posterior pelvic ring injuries and solely anatomic studies. We then reviewed these studies for technical considerations and outcomes associated with these technologies.

RESULTS

Six studies were included in our analysis. Results of these studies indicate that 3D fluoroscopy-based navigation is associated with a lower radiation dose and lower rate of screw malpositioning compared with 2D fluoroscopy-based systems.

CONCLUSIONS

It may be advantageous to combine modern imaging modalities such as 3D fluoroscopy with computer-assisted navigation for percutaneous screw fixation in the posterior pelvis.

A simple approach for the preoperative assessment of sacral morphology for percutaneous SI screw fixation

BACKGROUND

Percutaneous sacroiliac screw fixation under fluoroscopic control is an effective method for posterior pelvic ring stabilization. However, sacral dysmorphism has a high risk of L5 nerve injury. This study describes a simple method for the preoperative assessment of the sacral morphology using CT scans with widely available tools.

MATERIALS AND METHODS

CT scans of 1000 patients were analyzed. True inlet, outlet, and lateral views of the sacrum were obtained using a two-dimensional reconstruction tool to align the sacrum in a reproducible manner. Corridor morphology in the inlet view was measured to calculate different morphological types: (1) Ascending type, (2) Horizontal type, and (3) Descending type. In a second step, the corridor was analyzed for the presence of an anterior indentation of the sacrum between the SI joint and the midsagittal plane with proximity to the nerve root L5, which, therefore, may be harmed during screw misplacement.

RESULTS

A notch was found in the majority of cases with relative frequencies ranging from 69 % (upper quartile of S1) to 95 % (upper quartile of S2). Descending types were, by far, the most frequent corridor type with one exception: In the upper quartile of S1, the ascending type was the most frequent corridor (71 %). Horizontal types were less frequent with a relative incidence between 2 and 14 %.

DISCUSSION

This study should increase the awareness for sacral dysmorphism, emphasize the importance of a preoperative assessment of the osseous corridor, and provide a simple method for the preoperative assessment with widely available tools.

Supplemental S1 fixation for type C pelvic ring injuries: biomechanical study of a long iliosacral versus a transsacral screw

Background

A single iliosacral screw placed into the S1 vertebral body has been shown to be clinically unreliable for certain type C pelvic ring injuries. Insertion of a second supplemental iliosacral screw into the S1 or S2 vertebral body has been widely used. However, clinical fixation failures have been reported using this technique, and a supplemental long iliosacral or transsacral screw has been used. The purpose of this study was to compare the biomechanical effect of a supplemental S1 long iliosacral screw versus a transsacral screw in an unstable type C vertically oriented sacral fracture model.

Materials and methods

A type C pelvic ring injury was created in ten osteopenic/osteoporotic cadaver pelves by performing vertical osteotomies through zone 2 of the sacrum and the ipsilateral pubic rami. The sacrum was reduced maintaining a 2-mm fracture gap to simulate a closed-reduction model. All specimens were fixed using one 7.0-mm iliosacral screw into the S1 body. A supplemental long iliosacral screw was placed into the S1 body in five specimens. A supplemental transsacral S1 screw was placed in the other five. Each pelvis underwent 100,000 cycles at 250 N, followed by loading to failure. Vertical displacements at 25,000, 50,000, 75,000, and 100,000 cycles and failure force were recorded.

Results

Vertical displacement increased significantly (p < 0.05) within each group with each increase in the number of cycles. However, there was no statistically significant difference between groups in displacement or load to failure.

Conclusions

Although intuitively a transsacral screw may seem to be better than a long iliosacral screw in conveying additional stability to an unstable sacral fracture fixation construct, we were not able to identify any biomechanical advantage of one method over the other.

Level of evidence

Does not apply—biomechanical study.

Biomorphometric analysis of ilio-sacro-iliacal corridors for an intra-osseous implant to fix posterior pelvic ring fractures

It is hypothesized that ilio-sacro-iliacal corridors for a new envisioned pelvic ring implant (trans-sacral nail with two iliacal bolts = ISI-nail: ilio-sacro-iliacal nail) exists on the level of S1- or S2-vertebra in each patient. The corridors of 84 healthy human pelves (42x ♂; 42x ♀, 18-85 years) were measured in high resolution CT scans using the Merlin Diagnostic Workcenter Software. Trans-sacral corridors (≥ 9 mm diameter) on the level of S1 and S2 were found in 62% and 54% of pelves with a mean length [mm ± SD] of 164 ± 12.9 and 142 ± 10.2. Corresponding iliac corridors were present in all specimens in caudally tilted axial planes of 37.8 ± 0.67° and 53.7 ± 0.94° in relation to the operating table plane and divergent angulations of 69.0 ± 0.49° and 70.1 ± 0.32° in relation to the sagittal midline plane. Sacral dysmorphism, with compensatory larger S2 corridors were prevalent in 24% of pelves; ilio-sacro-iliacal osseous corridors for the envisioned implant were found in 88% of pelves on the level of S1 or S2. In the remaining 12% with too narrow corridors for any trans-sacral implant (screws, bars, ISI nail) alternative fixation methods have to be considered. Expected advantages of the envisioned ISI nail compared to available fixation devices are discussed.

When do anterior external or internal fixators provide additional stability in an unstable (Tile C) pelvic fracture? A biomechanical study

PURPOSE

This study aimed at evaluating the additional stability that is provided by anterior external and internal fixators in an unstable pelvic fracture model (OTA 61-C).

METHODS

An unstable pelvic fracture (OTA 61-C) was created in 27 synthetic pelves by making a 5-mm gap through the sacral foramina (posterior injury) and an ipsilateral pubic rami fracture (anterior injury). The posterior injury was fixed with either a single iliosacral (IS) screw, a single trans-iliac, trans-sacral (TS) screw, or two iliosacral screws (S1S2). Two anterior fixation techniques were utilized: external fixation (Ex-Fix) and supra-acetabular external fixation and internal fixation (In-Fix); supra-acetabular pedicle screws connected with a single subcutaneous spinal rod. The specimens were tested using a nondestructive single-leg stance model. Peak-to-peak (P2P) displacement and rotation and conditioning displacement (CD) were calculated.

RESULTS

The Ex-Fix group failed in 83.3 % of specimens with concomitant single-level posterior fixation (Total: 15/18-7 of 9 IS fixation, 8 of 9 TS fixation), and 0 % (0/9) of specimens with concomitant two-level (S1S2) posterior fixation. All specimens with the In-Fix survived testing except for two specimens treated with In-Fix combined with IS fixation. Trans-sacral fixation had higher pubic rotation and greater sacral and pubic displacement than S1S2 (p < 0.05). Rotation of the pubis and sacrum was not different between In-Fix constructs combined with single-level IS and TS fixation.

CONCLUSION

In this model of an unstable pelvic fracture (OTA 61-C), anterior fixation with an In-Fix was biomechanically superior to an anterior Ex-Fix in the setting of single-level posterior fixation. There was no biomechanical difference between the In-Fix and Ex-Fix when each was combined with two levels of posterior sacral fixation.

3D statistical modeling techniques to investigate the anatomy of the sacrum, its bone mass distribution, and the trans-sacral corridors

The complex anatomy of the sacrum makes surgical fracture fixation challenging. We developed statistical models to investigate sacral anatomy with special regard to trans-sacral implant fixation. We used computed tomographies of 20 intact adult pelves to establish 3D statistical models: a surface model of the sacrum and the trans-sacral corridor S1, including principal component analysis (PCA), and an averaged gray value model of the sacrum given in Hounsfield Units. PCA demonstrated large variability in sacral anatomy markedly affecting the diameters of the trans-sacral corridors. The configuration of the sacral alae and the vertical position of the auricular surfaces were important determinants of the trans-sacral corridor dimension on level S1. The statistical model of trans-sacral corridor S1 including the adjacent parts of the iliac bones showed main variation in length; however, the diameter was the main criterion for the surgically available corridor. The averaged gray value model revealed a distinct pattern of bone mass distribution with lower density particularly in the sacral alae. These advanced 3D statistical models provide a thorough anatomical understanding demonstrating the impact of sacral anatomy on positioning trans-sacral implants.

[Percutaneous cement-augmented screw fixation of bilateral osteoporotic sacral fracture]

We describe the case of a 71-year-old woman who presented with persisting painful symptoms of the back and pelvis which had begun 4 weeks previously. A preceding trauma was plausibly excluded. Diagnostics showed a slightly dislocated bilateral sacral fracture with underlying osteoporosis also known as an insufficiency fracture. We performed a percutaneous and cement-augmented bilateral iliosacral joint revision using screws and 6 months after surgery, imaging showed a stable fracture with appropriate screw positions.

Intra- and postoperative complications of navigated and conventional techniques in percutaneous iliosacral screw fixation after pelvic fractures: Results from the German Pelvic Trauma Registry

BACKGROUND

Percutaneous iliosacral screw placement following pelvic trauma is a very demanding technique involving a high rate of screw malpositions possibly associated with the risk of neurological damage or inadequate stability. In the conventional technique, the screw's correct entry point and the small target corridor for the iliosacral screw may be difficult to visualise using an image intensifier. 2D and 3D navigation techniques may therefore be helpful tools. The aim of this multicentre study was to evaluate the intra- and postoperative complications after percutaneous screw implantation by classifying the fractures using data from a prospective pelvic trauma registry. The a priori hypothesis was that the navigation techniques have lower rates of intraoperative and postoperative complications.

METHODS

This study is based on data from the prospective pelvic trauma registry introduced by the German Society of Traumatology and the German Section of the AO/ASIF International in 1991. The registry provides data on all patients with pelvic fractures treated between July 2008 and June 2011 at any one of the 23 Level I trauma centres contributing to the registry.

RESULTS

A total of 2615 patients were identified. Out of these a further analysis was performed in 597 patients suffering injuries of the SI joint (187×with surgical interventions) and 597 patients with sacral fractures (334×with surgical interventions). The rate of intraoperative complications was not significantly different, with 10/114 patients undergoing navigated techniques (8.8%) and 14/239 patients in the conventional group (5.9%) for percutaneous screw implantation (p=0.4242). Postoperative complications were analysed in 30/114 patients in the navigated group (26.3%) and in 70/239 patients (29.3%) in the conventional group (p=0.6542). Patients who underwent no surgery had with 66/197 cases (33.5%) a relatively high rate of complications during their hospital stay. The rate of surgically-treated fractures was higher in the group with more unstable Type-C fractures, but the fracture classification had no significant influence on the rate of complications.

DISCUSSION

In this prospective multicentre study, the 2D/3D navigation techniques revealed similar results for the rate of intraoperative and postoperative complications compared to the conventional technique. The rate of neurological complications was significantly higher in the navigated group.

The influence of sacral morphology on the existence of secure S1 and S2 transverse bone corridors for iliosacroiliac screw fixation

Sacroiliac (SI) screw fixation for unstable pelvic fractures stands out as the only minimally invasive method among all other ORIF procedures. A strictly transverse screw trajectory is needed for central or bilateral fracture patterns up to a complete iliosacroiliac fixation. However, secure screw insertion is aggravated by a narrow sacroiliac bone stock. This study investigates the influence of a highly variable sacral morphology to the existence of S1 and S2 transverse corridors. The analysis contained in this study is based on 125 CT datasets of intact human pelvises. First, sacral dysplasia was identified using the "lateral sacral triangle" method in a lateral 3-D semi-transparent pelvic view. Second, 3-D corridors for a 7.3mm screw in the upper two sacral levels were visualised using a proprietary IT workflow of custom-made programme scripts based on the Amira(®)-software. Shape-describing measurement variables were calculated as output variables. The results show a significant linear correlation between ratioT and the screw-limiting S1 isthmus height (Pearson coefficient of 0.84). A boundary ratio of 1.5 represented a positive predictive value of 96% for the existence of a transverse S1-corridor for at least one 7.3mm screw. In 100 out of 125 pelvises (80%), a sufficient S1 corridor existed, whereas in 124 specimens (99%), an S2 corridor was found. Statistics revealed significantly larger S1 and S2 corridors in males compared to females (p<0.05). However, no gender-related differences were observed for clinically relevant numbers of up to 3 screws in S1 and 1 screw in S2. The expanse of the S1 corridor is highly influenced by the dimensions of the dysplastic elevated upper sacrum, whereas the S2 corridor is not affected. Hence, in dysplastic pelvises, sacroiliac screw insertion should be recommended into the 2nd sacral segment. Our IT workflow for the automatic computation of 3-D corridors may assist in surgical pre-operative planning. Furthermore, the workflow could be implemented in computer-assisted surgery applications involving pelvic trauma.

Trans-iliosacral plating for vertically unstable fractures of sacral spine associated with spinopelvic dissociation: A cadaveric study

BACKGROUND

The treatment algorithm for sacral fracture associated with vertical shear pelvic fracture has not emerged. Our aim was to study a new approach of fixation for comminuted and vertically unstable fracture pattern with spinopelvic dissociation to overcome inconsistent outcome and avoid complications associated with fixations. We propose fixation with well-contoured thick reconstruction plate spreading across sacrum from one iliac bone to another with fixation points in iliac wing, sacral ala and sacral pedicle on either side. Present biomechanical study tests the four fixation pattern to compare their stiffness to vertical compressive forces.

MATERIALS AND METHODS

Dissection was performed on human cadavers through posterior midline paraspinal approach elevating erector spinae from insertion with two flaps. Feasibility of surgical exposure and placement of contoured plate for fixation was evaluated. Ten age and sex matched computed tomography scans of pelvis with both hips were obtained. Reconstructions were performed with advantage windows 4.2 (GE Light Speed QX/I, General Electric, Milwaukee, WI, USA). Using the annotation tools, direct digital CT measurement (0.6 mm increments) of three linear parameters was carried out. Readings were recorded at S2 sacral level. Pelvic CT scans were extensively studied for entry point, trajectory and estimated length for screw placement in S2 pedicle, sacral ala and iliac wing. Readings were recorded for desired angulation of screw in iliac wing ala of sacrum and sacral pedicle with respect to midline. The readings were analyzed by the values of mean and standard deviation. Biomechanical efficacy of fixation methods was studied separately on synthetic bone. Four fixation patterns given below were tested to compare their stiffness to vertical compressive forces: 1) Single S1 iliosacral screw (7.5 mm cancellous screw), 2) Two S1 and S2 iliosacral screws, 3) Isolated trans-iliosacral plate, 4) Trans-iliosacral plate + single S1 iliosacral screw.

STATISTICAL ANALYSIS

Mean of desired angulation for inserting screws and percentage of displacement on biomechanical testing was evaluated.

RESULTS

Mean angulations for inserting sacral pedicel were 12.3° (SD 2.7°) convergent to midline and divergent of 14° (SD 2.3°) for sacral ala screw and 23° (SD 4.9°) for iliac wing screw. All screws needed to be inserted at an angle of 90° to sacral dorsum to avoid violation of root canals. Cross headed displacement across fracture site was measured and plotted against the applied vertical shear load of 300 N in five cycles each for all the four configurations. Also, the force required for cross headed displacement of 2.5 mm and 5 mm was recorded for all configurations. Transmitted load across both ischial tuberosities was measured to resolve unequal distribution of forces. Taking one screw construct (configuration 1) as standard base reference, trans-iliosacral plate construct (configuration 3) showed equal rigidity to standard reference. Two screw construct (configuration 2) was 12% stronger and trans-iliosacral plate (configuration 4) with screw was 9% stronger at 2.5 mm displacing on 300 N force, while it showed 30% and 6%, respectively, at 5 mm cross-headed displacement.

CONCLUSIONS

Trans-iliosacral plating is feasible anatomically, biomechanically and radiologically for sacral fractures associated with vertical shear pelvic fractures. Low profile of plate reduces the risk of hardware prominence and decreases the need for implant removal. Also, the fixation pattern of plate allows to spare mobile lumbosacral junction which is an important segment for spinal mobility. Biomechanical studies revealed that rigidity offered by plate for cross headed displacement across fracture site is equal to sacroiliac screws and further rigidity of construct can be increased with addition of one more screw. There is need for precountered thicker plate in future.

Survival following a vertical free fall from 300 feet: the crucial role of body position to impact surface

We report the case of a 28-year old rock climber who survived an "unsurvivable" injury consisting of a vertical free fall from 300 feet onto a solid rock surface. The trauma mechanism and injury kinetics are analyzed, with a particular focus on the relevance of body positioning to ground surface at the time of impact. The role of early patient transfer to a level 1 trauma center, and "damage control" management protocols for avoiding delayed morbidity and mortality in this critically injured patient are discussed.