Screw Corridors Research Articles

The infraacetabular screw - anatomy, radiology, biomechanics and clinics.

Acetabular fracture surgery follows the primary aim of anatomic reduction and rigid stable fixation of the fracture. Infraacetabular screws (IAS) allow for an increased stability of the acetabular fixation by closing the periacetabular fixation frame without requiring an additional posterior approach. The osseous screw corridor for infraacetabular screws use the transition zone between the acetabular ring and the obturator ring. The infraacetabular screw corridor (IAC) shows a double-cone shape with an isthmus located near the acetabular fovea. The iliopectineal eminence (IE) is mainly used as a clinical landmark for the intraoperative assessment of the entry point of IAS. The inlet view, the combined obturator oblique outlet view and a 1/3 iliac oblique outlet view may be used for the intraoperative radiological assessment for both the entry point and the screw trajectory of IAS. Several biomechanical studies have shown that IAS increase the stiffness of the internal fixation. Scientific proof for an improved clinical outcome is still missing.

Dependable Automated Approach for Measuring the Retrograde Superior Ramus Screw Corridor in Pelvic Fracture Fixation.

Precise measurement of the intraosseous corridor within the superior pubic ramus is essential for the accurate percutaneous placement of a retrograde superior ramus screw (SRS). However, conventional manual measurement methods are often subjective, leading to variations in results among observers. Our goal was to develop an automated and dependable method for determining the retrograde SRS corridor. We developed an automated technique that utilized a computed tomography (CT) image-based search algorithm to identify the retrograde SRS corridor with the maximum diameter. We evaluated the reliability of this automated approach in comparison to a manual method using 17 pelves. Subsequently, we used both methods to measure the diameter, length, and orientation of the retrograde SRS corridor in 204 pelves in a Chinese population and assessed the intra- and interobserver agreement of each method by calculating the root-mean-square error (RMSE) and constructing Bland-Altman plots. We determined the screw applicability (percentages of hemipelves that could be treated with specific sizes of screws) for each method. Additionally, we investigated potential factors influencing the corridor, such as sex, age, height, and weight, through regression analysis. The intra- and interobserver intraclass correlation coefficients (ICCs) for the automated method (0.998 and 0.995) were higher than those for the manual approach (0.925 and 0.918) in the assessment of the corridor diameter. Furthermore, the diameter identified by the automated method was notably larger than the diameter measured with the manual method, with a mean difference and RMSE of 0.9 mm and 1.1 mm, respectively. The automated method revealed a significantly smaller corridor diameter in females than in males (an average of 7.5 and 10.4 mm, respectively). Moreover, use of the automated method allowed 80.6% of the females to be managed with a 4.5-mm screw while a 6.5-mm screw could be utilized in 19.4%, surpassing the capabilities of the manual method. Female sex had the most substantial impact on corridor diameter (β = -0.583). The automated method exhibited better reliability than the manual method in measuring the retrograde SRS corridor, and showed a larger corridor diameter for screw placement. Females had a significantly smaller corridor diameter than males. Given the intricate nature of the automated approach, which entails utilizing different software and interactive procedures, our current method is not readily applicable for traumatologists. We are working on developing integrated software with the goal of providing a more user-friendly solution for traumatologists in the near future. Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Optimization of S2-alar-iliac screw (S2AI) fixation in adult spine deformity using a comprehensive genetic algorithm and finite element model personalized to patient geometry and bone mechanical properties.

To optimize the biomechanical performance of S2AI screw fixation using a genetic algorithm (GA) and patient-specific finite element analysis integrating bone mechanical properties. Patient-specific pelvic finite element models (FEM), including one normal and one osteoporotic model, were created from bi-planar multi-energy X-rays (BMEXs). The genetic algorithm (GA) optimized screw parameters based on bone mass quality (BM method) while a comparative optimization method maximized the screw corridor radius (GEO method). Biomechanical performance was evaluated through simulations, comparing both methods using pullout and toggle tests. The optimal screw trajectory using the BM method was more lateral and caudal with insertion angles ranging from 49° to 66° (sagittal plane) and 29° to 35° (transverse plane). In comparison, the GEO method had ranges of 44° to 54° and 24° to 30° respectively. Pullout forces (PF) using the BM method ranged from 5 to 18.4kN, which were 2.4 times higher than the GEO method (2.1-7.7kN). Toggle loading generated failure forces between 0.8 and 10.1kN (BM method) and 0.9-2.9kN (GEO method). The bone mass surrounding the screw representing the fitness score and PF of the osteoporotic case were correlated (R2 > 0.8). Our study proposed a patient-specific FEM to optimize the S2AI screw size and trajectory using a robust BM approach with GA. This approach considers surgical constraints and consistently improves fixation performance.

PELVİS TİPLERİNİN TRANS-SAKRAL VİDA KORİDOR ÇAPINA ETKİSİNİN DEĞERLENDİRİLMESİ (BİLGİSAYARLI TOMOGRAFİ VERİLERİ KULLANILARAK YAPILAN RETROSPEKTİF ANALİZ.)

Aims: The aim of this study was to investigate the effect of pelvis type on the trans-sacral(TS) screw corridor diameter.
 Methods: Pelvis computed tomography (CT) scans between 2017 and 2020 were retrospectively reviewed. Age, gender, height, weight and body mass index (BMI) of the patients were determined during the CT examination. Pelvic CT scans were examined using the imaging system's multi-plane reconstruction (MPR) mode, and the TS screw corridor was measured for both the upper and second sacral segments. In addition, pelvic incidence (PI), sacral tilt (SS), and pelvic tilt (PT) values were measured. Pelvis typing was performed using the large transverse diameter, anteroposterior diameter, interspinous, intertuberocytosis, transverse outlet diameter, sagittal mid-pelvic diameter, and sagittal outlet values.
 Results: 81(38%) male and 132(62%) female patients were included in the study. Gynecoid pelvis type was more common in females and android pelvis in males (p < 0.001). The largest diameters in the TS screw corridor at the S1 level belonged to the anthropoid pelvis type. However, in the TS corridor at the S2 level, there was a significant difference between the pelvis-type groups in the mean values of AP and CC (p < 0.001). The effect of gender difference on the TS screw corridor width at the S1 and S2 levels was significant. An adequate corridor width for the TS screw corridor was detected in 50.8% of females and 67.9% of males at the S1 level, while in 21.2% of females and 70.4% of males at the S2 level.
 Conclusions: There is a significant difference in the dimensions of the trans-sacral screw corridor according to the pelvis type and gender, with the largest diameter observed in the anthropoid pelvis type and males. In critical situations, especially in males and individuals with android-anthropoid pelvis, the trans-sacral screw option should be considered primarily not only for the S1 trans-sacral corridor but also for the S2 trans-sacral corridor in pelvic posterior ring injuries

Navigation Template Design and the Anatomic Measurement for Anterograde Transpubic Screws.

For pelvic ring fractures, screw fixation became a popular technique for its good biomechanical performance. The safe insertion of anterograde the transpubic screw is important for patients with anterior pelvic ring fractures. This paper is to research the anatomical parameters of the anterograde transpubic screw corridor and evaluate the safety of anterograde transpubic screw placement assisted by the assembled navigation template. Fifty subjects with normal pelvic, 25 men and 25 women, age from 20 to 60 were enrolled, and their ilium were 3D reconstructed. The ilium was divided into zone I, zone II and zone III. Zone I and zone III was defined as medial and lateral to the obturator foramen, respectively. Zone II is located between zones I and III. The corridor A is formed by zone I and zone II and corridor B is formed by zone I, zone II and zone III. The diameter and length of the inner circle, the distance from the center of the inner circle to the posterior superior and to the inferior iliac spine of corridor A and corridor B were measured, respectively. Nine patients with pelvic fractures underwent anterograde transpubic screw and transverse sacroiliac screw placement assisted by the assembled navigation template and were retrospectively analyzed. Operation time, blood loss, incision length and fluoroscopy times were recorded. Grading score and Matta score were evaluated after surgery. In the 50 subjects, the diameter of corridor A was 11.16 ± 2.13 mm, and that of corridor B was 8.54 ± 1.52 mm. The length of corridor A was 86.39 ± 9.35 mm, and that of corridor B was 117.05 ± 5.91 mm. The surface distance from the screw entry point to the posterior superior iliac spine in corridor A was 109.31 ± 11.06 mm, and that in corridor B was 127.86 ± 8.23 mm. The surface distance from the screw entry point to the posterior inferior iliac spine in corridor A was 91.16 ± 10.34 mm, and that in corridor B was 106.92 ± 7.91 mm. A total of 18 sacroiliac transverse screws and 11 anterograde transpubic screws were inserted assisted by assembled navigation templates for nine patients. The average operation time was 108.75 ± 25.71 min, the blood loss was 141.11 ± 50.21 ml, the incision length was 14 ± 4.62 cm, and the intraoperative fluoroscopy was 17.89 ± 4.01 times. Transpubic screw corridor can be obtained by 3D reconstruction. For the majority of patients, the anterograde pubic ramus corridor accommodated a 6.5 mm diameter screw. It is safe to use anterograde transpubic screw placement assisted by an assembled navigation template.

A Novel C2 Screw Corridor Parallel to the Sagittal Plane for Transpedicular Fixation - A 3D-CT Study.

A 3D-CT Study. To research the feasibility and advantages of screw corridors parallel to the sagittal plane (SPC) of the C2 for transpedicular fixation. A total of 125 patients were enrolled for analysis, and the 3D model of the C2 for the 125 patients were reconstructed and analyzed. The SPC screw and the corridor of the general pedicle (GPC) screw of both sides were inserted into these C2 models. The anatomic parameters of the SPC and GPC, including the inner circle diameter, length of the corridors, medial angle and cephalad angle, were measured and compared. The anatomic location of the entry point for the SPC screw was evaluated. The diameter of the SPC averaged 5.5±1.8mm; 81.2% (203/250) were larger than 4mm. There was no significant difference between the SPC and GPC in diameter or percentage of diameter greater than 4mm. There was a significant difference between the length of the SPC (25.3±2.4mm) and the GPC (27.4±2.2mm). The cephalad angle was 51.6±6.9° for the SPC and 43.3±4.4° for the GPC, and there was a significant difference between the SPC and GPC. The entry point of the SPC screw was located on the cortical crest at the lower 1/4 of the lamina and located to the lower and inner side of the GPC screw entry point. It is feasible for most patients to accommodate an SPC screw with a diameter of 3.5mm. All SPC screws crossed the pedicle completely. The optimal entry point of the SPC screw was located on the cortical crest of the axial lamina.

Risk factors for screw breach and iatrogenic nerve injury in percutaneous posterior pelvic ring fixation

BackgroundPercutaneous screw fixation of the posterior pelvic ring is technically demanding and can result in cortical breach. The purpose of this study was to examine risk factors for screw breach and iatrogenic nerve injury. MethodsA retrospective review at a single level-one trauma center identified 245 patients treated with 249 screws for pelvic ring injuries with postoperative computed tomography (CT) scans. Cortical screw breach, iatrogenic nerve injury, and associated risk factors were evaluated. ResultsThere were 86 (35%) breached screws. The breach rate was similar between screw types (33% S1-iliosacral (S1-IS), 44% S1-transsacral (S1-TS), 31% S2-IS, and 30% S2-TS) and was not associated with patient characteristics, Tile C injuries, or corridor size or angle. The overall rate of screw revision for screw malpositioning was 1.2% (3/249). Iatrogenic nerve injuries occurred in 8 (3.2%) of the 249 screws. Screws that caused iatrogenic nerve injuries had greater screw breach distances (5.4 vs. 0 mm, MD 5, CI 2.3 to 8.7, p < 0.0001), were more likely to be S1-IS screws (88% vs. 47%, PD 40%, CI 7 to 58%, p = 0.006), more likely to be placed in Tile C injuries (75% vs. 44%, PD 31%, CI -3 to 55%, p = 0.04), and there was a trend for having a screw corridor size <10 mm (75% vs. 47%, PD 28, CI -6 to 52%, p = 0.06). Of the 7 iatrogenic nerve injuries adjacent to screw breaches, two nerve injuries recovered after screw removal, three recovered with screw retention, and two did not recover with screw retention. ConclusionScrew breaches were common and iatrogenic nerve injuries were more likely with S1-IS screws. Surgeons should maintain a high degree of caution when placing these screws and consider removal of any breached screw associated with nerve injury.

Accuracy and Safety of Neuronavigation for Minimally Invasive Stabilization in the Thoracolumbar Spine Using Polyaxial Screws-Rod: A Canine Cadaveric Proof of Concept

The main aim of this study was to evaluate the feasibility of minimally invasive stabilization with polyaxial screws-rod using neuronavigation and to assess accuracy and safety of percutaneous drilling of screw corridors using neuronavigation in thoracolumbar spine and compare it between an experienced and a novice surgeon. Feasibility of minimally invasive polyaxial screws-rod fixation using neuronavigation was first performed in the thoracolumbar spine of two dogs. Accuracy and safety of drilling screw corridors percutaneously by two surgeons from T8 to L7 in a large breed dog using neuronavigation were established by comparing entry and exit points coordinates deviations on multiplanar reconstructions between preoperative and postoperative datasets and using a vertebral cortical breach grading scheme. Feasibility of minimally invasive stabilization was demonstrated. For the experienced surgeon, safety was 100% and mean (standard deviation) entry point deviations were 0.3 mm (0.8 mm) lateral, 1.3 mm (0.8 mm) ventral and 0.7 mm (1.8 mm) caudal. The exit points deviations were 0.8 mm (1.9 mm) lateral, 0.02 mm (0.9 mm) dorsal and 0.7 mm (2.0 mm) caudal. Significant difference in accuracy between surgeons was found in the thoracic region but not in the lumbar region. Accuracy and safety improvement are noted for the thoracic region when procedures were repeated by the novice. This proof of concept demonstrates that using neuronavigation, minimally invasive stabilization with polyaxial screws-rod is feasible and safe in a large breed dog model.

Iliosacral screw corridors in Japanese subjects: a study using reconstruction CT scans.

Objectives:To investigate the characteristics of iliosacral (IS) screw corridors of Japanese pelves.Methods:Computer tomography images of 42 adult Japanese subjects without any pelvic injury were analyzed at a workstation. Using the manual reconstruction function, the width of a simulated horizontal corridor for an IS screw on the true coronal and true axial planes in the upper (S1), second (S2), and the third (S3) sacral segments was measured. For pelves without an adequate S1 corridor, a cranially tilted corridor was sought. A corridor was defined as “adequate” if its width on both planes was 10 mm or more.Results:An adequate horizontal corridor was found in S1 in 17 (40.5%) subjects, in S2 in 29 (69.0%) subjects, and in S3 in no subject. An independent factor affecting the adequacy of the S1 corridor was the adequacy of the S2 corridor (OR: 0.09). Similarly, an independent factor affecting S2 adequacy was S1 adequacy (OR: 0.10). A tilted, 10 mm diameter corridor was found in all 25 subjects who did not have an adequate horizontal corridor in the S1 segment. The angle required to obtain a 10 mm diameter corridor inversely correlated with the diameter of a horizontal corridor on the true coronal plane (R = −0.713, P = .000).Conclusions:The characteristics of IS screw corridors in the 42 Japanese subjects were similar to those reported in previous studies conducted in the West. The importance of preoperative planning using reliable techniques, such as three-dimensional reconstruction, should be emphasized.Level of evidence: Diagnostic Level III. See Instructions for Authors for a complete description of level of evidence.

Anatomical evaluation of the transpubic screw corridor based on a 3D statistical model of the pelvic ring

Retrograde transpubic screw fixation is a common procedure for the treatment of anterior pelvic ring fractures. With its sparing surgical approach and significant pain relief after screw fixations allowing early mobilisation, it has gained importance especially in the treatment of insufficiency fractures in elderly patients. However, positioning of transpubic screw osteosynthesis is not always possible due to narrowness and curvature of the screw corridor. The aim of the present study was to evaluate availability and length of the screw corridor using a 3D statistical model of the pelvic ring consisting out of 150 uninjured pelves. Virtual bore probes with a diameter of 7.5 mm were analysed as to accessibility, length and grey value distribution in Hounsfield Unit (HU). A transpubic corridor with a diameter of ≥ 7.5 mm was available in 185 of 300 investigated superior pubic rami with mean screw length of 131.7 mm. Accessibility of the screw corridor was higher in males than in females. However, screw length showed no systematic differences between the sexes or ethnicities. Analysis of the grey value distribution demonstrated the strongest bone to be located at the lateral ilium and the supraacetabular region.

Analysis of trans-sacral corridors in stabilization of fractures of the pelvic ring.

Percutaneous screw fixation combined with pelvic reduction is a surgical technique used to stabilize fractures of the posterior pelvic ring. This is the standard surgical treatment of unstable posterior pelvic ring injuries. The primary goal of this treatment is an anatomic reduction and stable fixation. This has been shown to reduce pain and improve the patients' long-term well-being. The aim of this analysis was to determine the possible screw lengths and the positioning of the screws in the S1 and S2 sacral segments. A population of 697 pelvises from the Stryker Orthopaedic Modeling and Analytics database were analyzed. The dimensions of the S1 and S2 screw corridors were determined and after assessing for sacral dysmorphism, the correct screw placement was chosen to determine the necessary screw length for surgical treatment. The measurements of the screw lengths show a Gaussian distribution for the analyzed population. The percentage of dysmorphic pelvises for the S1 screw corridor was 31.3% and for the S2 corridor 8%. Average screw length for S1 was 163.8 ± 16.2 mm and for the S2 137.3 ± 9.5 mm. The results show that the S1/S2 axis cannot be used for a trans-sacral screw placement in every patient. The study shows that intraosseous screw corridors are present in 68.7% of the patients in the S1 position and in 92% at the S2 level where an intended implant can be placed fully intraosseous.

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

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. 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. 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). 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.

Two-Dimensional Visualization of the Three-Dimensional Planned Sacroiliac Screw Corridor with the Slice Fusion Method.

Insertion of sacro-iliac (SI) screws for stabilization of the posterior pelvic ring without intraoperative navigation or three-dimensional imaging can be challenging. The aim of this study was to develop a simple method to visualize the ideal SI screw corridor, on lateral two-dimensional images, corresponding to the lateral fluoroscopic view, used intraoperatively while screw insertion, to prevent neurovascular injury. We used multiplanar reconstructions of pre- and postoperative computed tomography scans (CT) to determine the position of the SI corridor. Then, we processed the dataset into a lateral two-dimensional slice fusion image (SFI) matching head and tip of the screw. Comparison of the preoperative SFI planning and the screw position in the postoperative SFI showed reproducible results. In conclusion, the slice fusion method is a simple technique for translation of three-dimensional planned SI screw positioning into a two-dimensional strict lateral fluoroscopic-like view.

Infra-acetabular screw exited between ischial tuberosity and ischial spine is more suitable for Asian population: a 3D morphometric study

BackgroundRecently, the infra-acetabular screw has been proposed for use in treatment of acetabular fractures as a part of a periacetabular fixation frame. Biomechanical studies have shown that an additional infra-acetabular screw placement can enhance the fixation strength of acetabular fracture internal fixation. Currently, the reported exit point of the infra-acetabular screw has been located at the ischial tuberosity (Screw I). However, our significant experience in placement of the infra-acetabular screw has suggested that when the exit point is located between the ischial tuberosity and the ischial spine (Screw II), the placement of a 3.5 mm infra-acetabular screw may be easier for some patients. We conducted this study in order to determine the anatomical differences between the two different IACs.MethodsThe raw datasets were reconstructed into 3D models using the software MIMICS. Then, the models, in the STL format model, were imported into the software Geomagic Studio to delete the inner triangular patches. Additionally, the STL format image processed by Geomagic Studio was imported again into MIMICS. Finally, we used an axial perspective based on 3D models in order to study the anatomical parameters of the two infra-acetabular screw corridors with different exit points. Hence, we placed the largest diameter virtual screw in the two different screw corridors. The data obtained from this study presents the maximum diameter, length, direction, and distances between the entry point and center of IPE.ResultsIn 65.31% males and 40.54% females, we found a screw I corridor with a diameter of at least 5 mm, while a screw II corridor was present in 77.55% in males and 62.16% in females. Compared to screw I, the length of screw II is reduced, the angle with the coronal plane is significantly reduced, and the angle with the transverse plane is significantly increased.ConclusionsFor East Asians, changing the exit point of the infra-acetabular screw can increase the scope of infra-acetabular screw use, especially for females.

Anterior supra-acetabular external fixation for tile C1 pelvic fractures: a digital anatomical study and a finite element analysis.

Investigating the anatomical characteristics of supra-acetabular screw corridor as well as comparing the biomechanical stability between semi- and full-length screw external fixations for Tile C1 pelvic fractures. 50 male and 50 female uninjured pelvic CT data were converted into three-dimensional models and the supra-acetabular corridors were reconstructed by the Mimics software. The horizontal slice was redefined passing through the bilateral anterior inferior iliac spine and bilateral posterior superior iliac spine at the same time. On every horizontal slices, a 5mm diameter virtual screw was placed along with the unilateral anterior narrowing to posterior narrowing of the supra-acetabular corridor, and the relevant parameters of the semi- and full-length screw fixations were measured from inferior to superior at an interval height of 2.5mm until the width of the corridor was less than 5mm. Thus, the insertion position was located, as well as the inclination angle ranges were measured. The same procedure was done on a bilateral supra-acetabular corridor for each patient. Last, a Tile C1 pelvic finite element model was simulated and fixed with either semi- or a full-length anterior supra-acetabular external fixator. A 500N loading was tested on the model with three directions (cranial-caudal, anterior-posterior and lateral-medial) and the stiffness was determined by the max displacements. The insertion points of supra-acetabular screw for 66% (66/100) of men and 78% (78/100) of women were located at the outer lower part of the anterior inferior iliac spine (AIIS) (p < 0.001). The medial inclination angles of the screw were 29.50 ± 4.05° for men and 28.00 ± 3.78° for women (p = 0.007). The cranial inclination angles of the screw were 29.40 ± 5.38° for men and 28.57 ± 6.01° for women (p = 0.306). The safe inclination angle ranges of the semi-length screw were 3°-6° bigger than the full-length screw. For semi-length corridor, the widths were 14.07 ± 2.39mm for men and 11.29 ± 1.81mm for women (p < 0.001) and the depths were 71.77 ± 5.96mm for men and 69.26 ± 5.21mm for women (p < 0.001). For full-length corridor, the widths were 10.61 ± 2.10mm for men and 8.44 ± 2.03mm for women (p < 0.001) and the depths were 133.37 ± 7.60mm for men and 129.01 ± 8.12mm for women (p < 0.001). In the finite element analysis, the max displacements of the pelvis under three loading modes (cranial-caudal, anterior-posterior and lateral-medial) for semi-length fixation were 0.772mm, 0.409mm and 0.331mm and for full-length fixation were 0.727mm, 0.385mm and 0.262mm. The outer lower part of AIIS is recommended as an insertion point of the supra-acetabular screw with about 30° medial and cranial inclination angles, and the semi-length screw is safer for placing and has satisfactory biomechanical stability by compared with a full-length screw.

The three-dimensional bone mass distribution of the posterior pelvic ring and its key role in transsacral screw placement

To optimize the placement of iliosacral screws in osteoporotic bone it is essential to know where to find the best purchase. The aim of this study was to determine and visualize the distribution of bone mass in the posterior pelvic ring by using a color-coded thermal map, to differentiate the bone distribution patterns in normal pelvises and in pelvises with impaired bone density and to identify zones in S1 and S2 with particularly good bone quality, in both healthy and osteoporotic pelvises. A total of 324 pelvises were included. The bone density of the posterior pelvic ring, the fifth lumbar vertebral body (L5) and screw corridors S1 and S2 were visualized. Each individual pelvis was measured with a 3D automated program. Two groups were selected - patients with mean bone density in L5 of ≤100 HU (group 1, n = 52) and those with mean bone density >100 HU (group 2, n = 272). Color-coded thermal maps are presented of the bone density distribution in the pelvises. Bone density in L5 correlated significantly with S1 and S2; bone density was significantly higher in the S1 than in the S2 corridor (p < 0.001). Bone was denser in the posterior and upper parts of the S1 body. Bone density was significantly lower in group 2 than in group 1 (p < 0.001). The color-coded “thermal” maps of bone mass distribution can help surgeons to decide where sacroiliac screws are likely to find optimal purchase.

COMPARISON OF X-RAY AND CT METHODS FOR ASSESSING SACRAL SHAPE VARIANTS AND IDENTIFYING A SECURE SACROILIAC SCREW FIXATION CORRIDOR

Sacroiliac screw fixation is the only minimally invasive technique for stabilizing unstable posterior pelvic ring fractures. X-ray/CT methods identify sacral shape variants, which influence screw fixation feasibility at sacral segment S1. As no reliability analysis was previously published, this study analyzed four X-ray/CT-based screw corridor evaluation methods. CT datasets of 80 human pelvises (♂[Formula: see text][Formula: see text], ♀[Formula: see text][Formula: see text], [Formula: see text] years, [Formula: see text][Formula: see text]cm, [Formula: see text][Formula: see text]kg) were used. CTs were post-processed using Amira 5.2 software to generate 3D models and analyzed for S1 transverse 7.3[Formula: see text]mm screw corridors using a C++ program. CT-slices and radiograph-like images were generated per each classification’s requirements. Five surgeons independently assessed sacral shape and transverse screw insertion feasibility. Sensitivity, specificity, and positive/negative predictive values were calculated. C++ analysis indicated feasible screw insertion in 66 cases (82%). Sensitivities were 86% (Mendel), 75% (Routt), 74% (Carlson), and 67% (Kim). Specificities were 73% (Mendel) and 79% (Kim). Mean positive predictive value spanned from 54.6% (Mendel) to 26.2% (Carlson); negative predictive value spanned from 94.5% (Kim) to 90.4% (Carlson). No significant differences existed between surgeons. Mendel’s classification provides reliable and reproducible assessment via the lateral sacral triangle, without additional CTs like Carlson or Routt or the subjectivity of Kim’s method.

Clinical application of 3D printing technology to the surgical treatment of atlantoaxial subluxation in small breed dogs.

Atlantoaxial instability (AAI)/subluxation commonly occurs in small breed dogs. Ventral stabilization techniques using screws and/or pins and a plate or, more commonly, polymethylmethacrylate are considered to provide the most favorable outcome. However, the implantation of screws of sufficient sizes for long-term stability becomes challenging in toy breed dogs (e.g. <2 kg). We herein report the application of 3D printing technology to implant trajectory planning and implant designing for the surgical management of AAI in 18 dogs. The use of our patient-specific drill guide templates resulted in overall mean screw corridor deviations of less than 1 mm in the atlas and axis, which contributed to avoiding iatrogenic injury to the surrounding structures. The patient-specific titanium plate was effective for stabilizing the AA joint and provided clinical benefits to 83.3% of cases (15/18). Implant failure requiring revision surgery occurred in only one case, and the cause appeared to be related to the suboptimal screw-plate interface. Although further modifications are needed, our study demonstrated the potential of 3D printing technology to be effectively applied to spinal stabilization surgeries for small breed dogs, allowing for the accurate placement of screws and minimizing peri- and postoperative complications, particularly at anatomical locations at which screw corridors are narrow and technically demanding.

Secure corridor for infraacetabular screws in acetabular fracture fixation\u2014a 3-D radiomorphometric analysis of 124 pelvic CT datasets

BackgroundAcetabular fracture surgery is directed toward anatomical reduction and stable fixation to allow for the early functional rehabilitation of an injured hip joint. Recent biomechanical investigations have shown the superiority of using an additional screw in the infraacetabular (IA) region, thereby transfixing the separated columns to strengthen the construct by closing the periacetabular fixation frame. However, the inter-individual existence and variance concerning secure IA screw corridors are poorly understood.MethodsThis computer-aided 3-D radiomorphometric study examined 124 CT Digital Imaging and Communications in Medicine (DICOM) datasets of intact human pelves (248 acetabula) to visualize the spatial IA corridors as the sum of all intraosseous screw positions. DICOM files were pre-processed using the Amira® 4.2 visualization software. Final corridor computation was accomplished using a custom-made software algorithm. The volumetric measurement data of each corridor were calculated for further statistical analyses. Correlations between the volumetric values and the biometric data were investigated. Furthermore, the influence of hip dysplasia on the IA corridor configuration was analyzed.ResultsThe IA corridors consistently showed a double-cone shape with the isthmus located at the acetabular fovea. In 97% of male and 91% of female acetabula, a corridor for a 3.5-mm screw could be found. The number of IA corridors was significantly lower in females for screw diameters ≥ 4.5 mm. The mean 3.5-mm screw corridor volume was 16 cm3 in males and 9.2 cm3 in female pelves. Corridor volumes were significantly positively correlated with body height and weight and with the diameter of Köhler’s teardrop on standard AP pelvic X-rays. No correlation was observed between hip dysplasia and the IA corridor extent.ConclusionIA corridors are consistently smaller in females. However, 3.5-mm small fragment screws may still be used as the standard implant because sex-specific differences are significant only with screw diameters ≥ 4.5 mm. Congenital hip dysplasia does not affect secure IA screw insertion. The described method allows 3-D shape analyses with highly reliable results. The visualization of secure IA corridors may support the spatial awareness of surgeons. Volumetric data allow the reliable assessment of individual IA corridors using standard AP X-ray views, which aids preoperative planning.

Three-dimensionally-navigated cross-cannulated screw fixation for traumatic pubic symphysis diastasis: an anatomical study

The aim of this study was to design and optimize the secure corridor of cross-cannulated screw implantation in pubic symphysis through Orbic 3D (Siemens Medical Solutions, Erlangen, Germany) computerized navigation and to provide an anatomic basis through the study of regional anatomy. Fifteen embalmed adult cadavers (8 males, 7 females) were used in this study. All pelvic specimens were placed in the supine position on a radiolucent carbon fiber table. The ideal angle of screw placement, appropriate screw diameter, and perfect attachment point were determined by the computerized navigation system. According to the above data, cross-cannulated screws 6.5 mm in diameter were implanted by the guide pins. Based on detailed local dissection, the entry-exit points of double screws were exposed in the pelvis. The distances were measured between the entry-exit points and the major structures. Radiographs and computed tomography (CT) scans of the pelvis were performed to reassess the position of screws. The trajectory of the first screw originated from the trailing edge of the pubic tubercula to the anterior-lower corner of the contralateral pubic tubercula. The second screw was directed from the base of the pubic tubercula to the junctional zone between the pubic tubercula and inferior ramus of the pubis of the opposite side of the body. Both screws maintained a safe distance from the surrounding major structures. All screw corridors were found intact without any damage under X-ray and CT images. The Orbic 3D computer navigation system is a reliable and new method of achieving a secure corridor for screw implantation in the pubic symphysis.