Sacral Dysmorphism Research Articles

Simple mathematical model of sacroiliac screws safe-zone-Easy to implement by pelvic inlet and outlet views.

Percutaneous sacral screw fixation is the mainstay of posterior pelvic ring fixation. This study quantifies the accuracy of fluoroscopic screw placement using post-operative CT scans and redefines the fluoroscopic safe zone using a mathematical calculation obtained from Inlet and outlet images. The authors hypothesized that a mathematical calculation of screw placement within the ala will improve accuracy of screw placement. A retrospective review of consecutive patients admitted to a level 1 trauma center with pelvic fractures fixed with iliosacral screws from January 2011 to December 2014 was performed. Accuracy of screw placement was determined by comparing fluoroscopy to post-operative CT scans. A mathematical calculation of screw position within the sacral ala was applied to determine assess screw position and compared to CT findings. Ninety-four patients with 156 screws met inclusion criteria, of which 50 (32.0%) had a cortical breech on CT. The sensitivity and specificity of the inlet-outlet safe zone using mathematical calculation were 97.1% and 84.0%, respectively. The positive and negative predictive values were 92.7% and 93.3%, respectively. Overall accuracies of the radiographic inlet-outlet and lateral safe zones were 92.9% and 70.0%, respectively (p-value = 0.004). Sacral dysmorphism was not found to be associated with sacral cortical breech. A Simple mathematical calculation (screw position relative to percentage of bone width) on the inlet-outlet provides an accurate way to predict the accuracy of sacroiliac screws. The method is easy to implement, part of the surgery work-flow, and provides higher accuracy than relying on subjective interpretation of inlet, outlet, and lateral images. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1478-1484, 2017.

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

BackgroundPercutaneous 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 methodsCT 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.ResultsA 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 %.DiscussionThis 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.

CT-based bone density assessment for iliosacral screw trajectories

Introduction: Sacroiliac screw placement is one standard treatment option for stabilization of posterior pelvic ring injuries encountering high intra- and inter-individual variations of bone stock quality as well as a vast variety and prevalence of sacral dysmorphism. An individual, easy-to-use preoperative bone stock quality estimation would be of high value for the surgeon. Materials and Methods: We analyzed 36 standard computed tomography datasets with the uninjured pelvic ring. Using a two-plane cross-referencing technique, we assessed the Hounsfield unit (HU) mean values as well as standard deviation and minimum/maximum values within selected region of interests (ROIs) at five key areas: os ilium left and right, massa lateralis of os sacrum left and right, and central vertebral body on levels S1 and S2. Results: Results showed no difference in mean HU at any ROI when comparing male and female data. For all ROIs set on S1 and S2, there was an age-related decline of HU with a calculated slope significantly different from zero. There was no statistical difference of slopes when comparing S1- and S2-level with respect to any distinct ROI. Comparison of levels S1 and S2 revealed differences at the vertebral body and at the right os ilium. The right and left massa lateralis of os sacrum had lower bone density than the center of the vertebral body, the right, or left os ilium on S1; right and left massa lateralis density did not differ significantly. On level S2, results were comparable with no difference of massa lateralis density. Conclusion: With our easy-to-use preoperative assessment of bone density of five key areas of sacroiliac screw anchoring we were able to find the lowest bone density in both the left and right massa lateralis on levels S1 and S2 with high inter- and intra-individual variations. Significantly lower bone density was found in the center of the vertebral bodies S2 in comparison to S1, which both are crucial for iliosacral screw placement. We thus recommend priority use of level S1 in screw placement and careful consideration of sole massa lateralis short-screw anchoring.

Investigation of bone quality of the first and second sacral segments amongst trauma patients: concerns about iliosacral screw fixation.

BackgroundIliosacral screw fixation has become a common method for surgical stabilization of acute disruptions of the pelvic ring. Placement of iliosacral screws into the first sacral (S1) body is the preferred method of fixation, but size limitations and sacral dysmorphism may preclude S1 fixation. In these clinical situations, fixation into the second sacral (S2) body has been recommended. The objective of this study was to evaluate the bone quality of the S1 compared to S2 in the described “safe zone” of iliosacral screw fixation in trauma patients.Materials and methodsThe pelvic computed tomography scans of 25 consecutive trauma patients, ages 18–49, at a level 1 trauma center were prospectively analyzed. Hounsfield units, a standardized computed tomography attenuation coefficient, was utilized to measure regional cancellous bone mineral density of the S1 and S2. No change in the clinical protocol or treatment occurred as a consequence of inclusion in this study.ResultsA statically significant difference in bone quality was found when comparing the first and second sacral segment (p = 0.0001). Age, gender, or smoking status did not independently affect bone quality.ConclusionIn relatively young, otherwise healthy trauma patients there is a statistically significant difference in the bone density of the first sacral segment compared to the second sacral segment. This study highlights the need for future biomechanical studies to investigate whether this difference is clinically relevant. Due to the relative osteopenia in the second sacral segment, which may impact the quality of fixation, we feel this technique should be used with caution.Level of evidenceIII

Three-Dimensional Navigation Is More Accurate than Two-Dimensional Navigation or Conventional Fluoroscopy for Percutaneous Sacroiliac Screw Fixation in the Dysmorphic Sacrum

To evaluate the accuracy of computer-assisted sacral screw fixation compared with conventional techniques in the dysmorphic versus normal sacrum. Review of a previous study database. Database of a multinational study with 9 participating trauma centers. The reviewed group included 130 patients, 72 from the navigated group and 58 from the conventional group. Of these, 109 were in the nondysmorphic group and 21 in the dysmorphic group. Placement of sacroiliac (SI) screws was performed using standard fluoroscopy for the conventional group and BrainLAB navigation software with either 2-dimensional or 3-dimensional (3D) navigation for the navigated group. Accuracy of SI screw placement by 2-dimensional and 3D navigation versus conventional fluoroscopy in dysmorphic and nondysmorphic patients, as evaluated by 6 observers using postoperative computerized tomography imaging at least 1 year after initial surgery. Intraobserver agreement was also evaluated. There were 11.9% (13/109) of patients with misplaced screws in the nondysmorphic group and 28.6% (6/21) of patients with misplaced screws in the dysmorphic group, none of which were in the 3D navigation group. Raw agreement between the 6 observers regarding misplaced screws was 32%. However, the percent overall agreement was 69.0% (kappa = 0.38, P < 0.05). The use of 3D navigation to improve intraoperative imaging for accurate insertion of SI screws is magnified in the dysmorphic proximal sacral segment. We recommend the use of 3D navigation, where available, for insertion of SI screws in patients with normal and dysmorphic proximal sacral segments. Therapeutic level I.

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.

Anatomic Determinants of Sacral Dysmorphism and Implications for Safe Iliosacral Screw Placement.

Upper sacral segment dysplasia increases the risk of cortical perforation during iliosacral screw insertion. Dysmorphic sacra have narrow and angled upper osseous corridors. However, there is no validated definition of this anatomic variation. We hypothesized that pelves could be quantitatively grouped by anatomic measurements. One hundred and four computed tomography (CT) scans and virtual outlet views of uninjured pelves were analyzed for the presence of the five qualitative characteristics of upper sacral segment dysplasia. CT scans were reformatted to measure the cross-sectional area, angulation, and length of the osseous corridor. Principal components analysis was used to identify multivariable explanations of anatomic variability, and discriminant analysis was used to assess how well such combinations can classify dysmorphic pelves. The prevalences of the five radiographic qualitative characteristics of upper sacral segment dysplasia, as determined by two reviewers, ranged from 28% to 53% in the cohort. The rates of agreement between the two reviewers ranged from 70% to 81%, and kappa coefficients ranged from 0.26 to 0.59. Cluster analysis revealed three pelvic phenotypes based on the maximal length of the osseous corridor in the upper two sacral segments. Forty-one percent of the pelves fell into the dysmorphic cluster. The five radiographic qualitative characteristics of dysmorphism were significantly more frequent (p < 0.007) in this cluster. A combination of upper sacral coronal and axial angulation effectively explained the variance in the data, and an inverse linear relationship between these angles and a long upper sacral segment corridor was identified. A sacral dysmorphism score was derived with the equation: (first sacral coronal angle) + 2(first sacral axial angle). An increase in the sacral dysmorphism score correlated with a lower likelihood of a safe transsacral first sacral corridor. No subjects with a sacral dysmorphism score >70 had a safe transsacral first sacral corridor. Sacral dysmorphism was found in 41% of the pelves. The major determinants of sacral dysmorphism are upper sacral segment coronal and axial angulation. The sacral dysmorphism score quantifies dysmorphism and can be used in preoperative planning of iliosacral screw placement.

Reexamination of Pelvic Inlet and Outlet Images Using 3-Dimensional Computed Tomography Reconstructions

Inlet and outlet views are essential in the evaluation of patients with pelvic injuries. The optimal angles that should be used to obtain these views are still debated. Computed tomography scans of 70 patients without pelvic ring injuries were analyzed. Using the raw data from the computed tomography images, virtual pelvic x-rays were generated. The images were rotated 1 degree at a time and a total of 360 images were generated. The same procedure was repeated to create solid 3-dimensional (3D) reconstructions. Two trauma-trained orthopaedic surgeons then reviewed all 360 images to select inlet and outlet views as described in previous literature. Intraclass correlation coefficients were calculated for each inlet and outlet value. The average inlet angle (caudal tilt) that was required to achieve a view where the promontory overlaps the S1 body was found to be 26.7 degrees (95% confidence interval, 25-29) with virtual x-rays and 24.3 degrees (95% confidence interval, 22-26) with 3D reconstructions. The average outlet angle (cephalad tilt) that was required to achieve a view where the superior border of the pubic symphysis overlaps the S2 body was 43.7 degrees (95% confidence interval, 42-45) with virtual x-rays and 43.8 degrees (95% confidence interval, 42-45) with 3D reconstructions. There was no difference in these angles based on gender, whereas sacral dysmorphism increased the angle needed to obtain the outlet view by an average of 5 degrees. This study demonstrated that the ideal angle to obtain inlet views should be approximately 25 degrees and to obtain outlet views should be approximately 45 degrees during screening x-rays to evaluate patients who were diagnosed with pelvic injuries. Application of these new values in the clinical practice would provide higher rates of adequate studies and further prospective clinical studies should be performed to validate these parameters.

Variations in Sacral Morphology and Implications for Iliosacral Screw Fixation

Posterior pelvic percutaneous fixation following either closed or open reduction is a popular procedure. Knowledge of the posterior pelvic anatomy, its variations, and related imaging is critical to performing reproducibly safe surgery. The dysmorphic sacrum has several key characteristics. The upper portion of the sacrum is relatively colinear with the iliac crests on the outlet radiographic view. Other characteristics include the presence of mammillary bodies (ie, underdeveloped transverse processes) at the sacral mid-alar area, anterior upper sacral foramina that are not circular, residual upper sacral disks, an acute alar slope oriented from cranial-posterior-central to caudal-anterior-lateral on the outlet and lateral views of the sacrum, a tongue-in-groove sacroiliac joint surface visualized on CT, and cortical indentation of the anterior ala on the inlet radiographic view. The surgeon must be knowledgeable about individual patient anatomy to ensure safe iliosacral screw placement.

Radiographic Quantification and Analysis of Dysmorphic Upper Sacral Osseous Anatomy and Associated Iliosacral Screw Insertions

To quantify upper sacral dysmorphic osseous anatomy and assess its impact on second sacral segment iliosacral screw insertion. Retrospective evaluation of a prospective trauma database. Regional Level I trauma center. Twenty-four patients with unstable posterior pelvic ring disruptions and sacral dysmorphism were evaluated radiographically and second segment (S2) screws were placed using a standard technique. The sacral osseous pathway limits were measured using preoperative pelvic computed tomography at the upper and second sacral segments. The S2 screw location relative to the sacral nerve root tunnels and the maximum possible screw lengths for both S1 and S2 screws were evaluated with postoperative pelvic computed tomography. The S2 screw positions were graded as intraosseous, juxtaforaminal, or extruded. Preoperative and postoperative peripheral neurologic examinations were documented. The dysmorphic S1 width available for screw insertion averaged 13.2 mm. The S2 pathway width averaged 15.2 mm. The maximum potential screw length for the dysmorphic S1 averaged 100.8 mm and for S2 measured 151.9 mm. Twenty of 24 patients with S2 screws were intraosseous and in four patients were juxtaforaminal. There were no extruded screws. There were no neurologic injuries. Dysmorphic S1 segments are anatomically competent for routine screw fixation. The S2 segment provides a larger osseous site for screw insertion than S1 in dysmorphic sacrums. Significantly longer screws are possible in S2 compared with the dysmorphic S1 segment. S2 iliosacral screws can be safely and accurately accomplished using a standard technique in patients with unstable posterior pelvic ring disruptions and sacral dysmorphism. Safe screw insertions avoid iatrogenic nerve root injuries.

Quantification of the Upper and Second Sacral Segment Safe Zones in Normal and Dysmorphic Sacra

To quantify the obliquity and dimensions of the upper and second sacral segment iliosacral screw safe zones and to determine the differences between normal and dysmorphic sacral morphology. Retrospective cohort. University Level I trauma center. Fifty patients with pelvic computed tomography scans. All sacra were characterized as normal or dysmorphic based on plain pelvic radiographs and previously described criteria. Multiple computed tomography scan reconstructions were viewed and manipulated simultaneously with 6 degrees of freedom to allow for custom visualization in any plane. In each patient, a unique reconstruction plane was created perpendicular to the safe zone axis. The narrowest safe zone cross-sectional area was measured. Next, on simulated pelvic outlet and inlet views, safe zone obliquity and width were measured. Finally, the space available for a transverse screw was assessed. Measurements were performed for both upper and second sacral segment. Values for normal and dysmorphic safe zones were compared. Sacral dysmorphism was identified in 22 patients. In these sacra, the upper sacral segment safe zone cross-section was 36% smaller than in normal sacra (P < 0.001). No transverse screws could be placed, but accommodating for the caudal to cranial obliquity (30° versus 21° in normals, P < 0.001) and posterior to anterior obliquity (15% versus 4% in normals, P < 0.001) of the safe zone, an iliosacral screw at least 75 mm in length could be placed safely in 91% of patients. A transverse screw could be placed in 75% of normal sacra. In the second segment safe zone, the cross-sectional area was more than twice as large in dysmorphic sacra compared to normals (220 mm versus 109 mm, P < 0.001). The obliquity was not different on either the inlet or outlet views between groups. A transverse screw could be placed at this level in 95% of those with dysmorphic sacra and in only 50% of normal sacra. Sacral dysmorphism occurred in 44% of patients in this consecutive series. Many anatomic differences were consistently found between the two morphologies with clinical relevance to iliosacral screw placement. Specifically, the dysmorphic upper sacral segment safe zone is significantly smaller and more obliquely oriented but is still large enough to accommodate an iliosacral screw in nearly all patients. The second sacral segment safe zone is approximately transversely oriented in both sacral types but is more than twice as large in dysmorphic sacra. This segment may be a primary fixation opportunity in patients with sacral dysmorphism.

Placement of percutaneous iliosacral screws under computed tomographic guidance

This report discusses the technique and results of computed tomographic-guided placement of sacroiliac screws using only conscious sedation and local anesthesia. Previous literature found logistic problems with sterility and adequate anesthesia. We have developed and refined the technique of placing sacroiliac screws with a local prep and portable equipment. This technique allows placement of screws in positions not previously accessible with standard fluoroscopic methods and is 100% accurate. There are no visualization problems and variations in lumbosacral morphology or sacral dysmorphism does not preclude its use. In unstable and disiplaced fractures, a preliminary reduction of the anterior pelvis with either an external fixator or plating will often reduce the posterior pelvis to the extent that minor improvements of reduction are possible with reduction screws. There were no adverse events associated with the technique, and a cost analysis found significant savings when compared with intraoperative placement using fluoroscopy. To date, we have not identified any other literature using this particular method, and we find it to be quite useful, safe, and accurate for the indicated patients.