Anatomical study of anterior column screw tunnels through virtual three-dimensional models of the pelvis

A new technique for percutaneous screw fixation for treating FFP IIIa and IIIb fragility fractures of the pelvis

To determine the presence of a consistent osseous corridor from the lateral-posterior aspect of the anterior inferior iliac spine to the sacral wing that could be used for safe trans percutaneous screw fixation for pelvic fragility fractures of the iliac wing and fracture dislocations of the sacroiliac joint (FFP types IIIa and IIIb). Computed tomography (CT) scans were obtained from 100 patients and imported to Mimics software for 3D reconstruction. Then, a cylinder was drawn to imitate the modified LC-II screw and adjusted to a maximum radius and length to obtain the feasible region. Thirteen parameters of the osseous corridor of the modified LC-II screw were measured. Differences between sex groups were compared, and significant statistical correlations were carefully studied to determine potentially important clinical relationships. The records of patients with FFP type IIIa and IIIb fragility fractures of the pelvis were extracted from our hospital. Patients who underwent modified LC-II screw fixation, LC-II screw fixation or reconstruction plate fixation were included. Patients' operative characteristics and complications were recorded at follow-up. Fracture reduction quality was assessed using the Matta standard. Functional outcomes were evaluated using the Majeed grading system. The mean maximum diameters of the osseous corridors of the modified LC-II screw in males and females were 12.73 and 10.83 mm, respectively. The mean maximum lengths of the osseous corridors of the modified LC-II screw in males and females were 96.37 and 93.37 mm, respectively. In the treatment of patients with FFP IIIa and FFP IIIb fractures, the group of treatment by the modified LC-II screws fixation was shown significantly shorter operative time and fewer intraoperative blood loss in comparison to that by the reconstruction plates. In the present study, all the males and females had a complete osseous corridor of the modified LC-II screw. The clinical results of the patients who were treated with modified LC-II screw fixation suggest that the novel method has a good preliminary outcome.

[Digital study of the ideal position of lag screw internal fixation in the anterior column of the acetabulum]

Objective

To find the ideal position of lag screw internal fixation in the anterior column of acetabulum by digital technology, and measure its related parameters, so as to improve the accuracy of lag screw implantation.

Methods

The CT scan data of 266 semi-pelvic raw in 133 cases (78 males and 55 females, aged 18-65 years old with an average age of 42 years) were collected between January 2019 and January 2020 to compose three-dimensional models. According to the relationship between the peripheral bone cortex of the anatomical channel and the lag screw, a new standard for the ideal position of lag screw fixation in the anterior column of acetabulum was proposed to simulate the implantation of the screw. After the screw was in the ideal position, the following indicators were measured: the maximum allowable diameter of the virtual screw (the diameter of the cylinder up to the new standard, R), the length (the distance between the center of the nail point on both sides, L); the position of the retrograde nail point (the interval between the nail insertion points and the midpoint of the pubic symphysis and the pubic tubercle, respectively, D1 and D2) and the position of the antegrade nail insertion point (the distance between the nail insertion point and the anterior superior iliac spine, the major ischial notch, and the vertical distance between the nail insertion point and the apex of the posterior upper edge of the acetabulum, respectively, D3, D4, D5); and the direction of the virtual screw at the ideal position (the angle between the screw and the horizontal plane, sagittal plane, and coronal plane, respectively, ∠β, ∠γ, ∠δ) were calculated.

Results

The maximum allowable diameter of virtual screws was 5.70-14.10 mm for males, with an average of 9.25 mm; for females, it was 4.40-10.40 mm with an average of 7.29 mm. The antegrade insertion point of the anteroposterior acetabular lag screw was located at 2.0-2.5 cm above the apex of the acetabulum, which was almost the same distance from the anterior superior iliac spine and the ischial notch, about 5 cm; the insertion point of the retrograde implant was located at the pubic bone 2.5-3.0 cm below the nodule. When the acetabular anterior column screw was in the ideal position, there was no significant difference in the comparison of ∠β and ∠γ between the male and the female ( P>0.05), and the differences in the other indicators were significant ( P<0.05). Except for D4 and ∠β showing no significant difference between the left and right sides ( P>0.05), the differences in the other indicators were significant ( P<0.05).

Conclusion

In the bony channel of the anterior column of the acetabulum, all males can accommodate screws with a diameter of <5.70 mm, and females can accommodate screws with a diameter of <4.40 mm. The anterograde or retrograde screw insertion points are different for male and female. The use of digital technology to individually measure the appropriate screw parameters can improve the accuracy and stability of the lag screw internal fixation for acetabular anterior column fractures.

Obturator Oblique and Pubic Ramus Inlet Views Can Better Guide the Insertion of an Anterior Column Acetabular Screw

OBJECTIVE

The objective of the present paper was to investigate the value of obturator oblique and pubic ramus inlet views in guiding anterior column acetabular screw insertion.

METHODS

We collected pelvic CT scans at the diagnostic imaging center of our hospital between 2017 and 2019. Virtual three-dimensional (3D) models of the pelvis were created based on the CT scans. Then the transparency was adjusted to 30%. Two identical copies of the 3D model data were made. 3D model replications were divided into a control group and an experimental group. In the control group, the screw was inserted into the anterior acetabular column using obturator-outlet and iliac-inlet views. In the experimental group, the screw was guided under obturator oblique and pubic ramus inlet views. Based on whether the screw penetrated the hip joint and/or exited the pubic ramus, models were divided into three grades. Grade I: the screw travels completely within the anterior column bone corridor; Grade II: the screw exits the superior pubic ramus, but the length of the screw outside the channel does not exceed 1/2 of the anterior column; Grade III: the screw exits the superior pubic ramus and the length of the screw outside the corridor exceeds 1/2 of the anterior column. We compared the screw placement quality of the two groups and analyzed differences between genders. In addition, the distance between the screws and the acetabulum was recorded and compared among the two groups.

RESULTS

A total of 110 hemipelves were selected, including those of 80 men and 30 women, with an average age of 46.76 ± 14.26 years. In the control group, the screw quality of 64 models (58.2%) was Grade I. In the experimental group, 94 models (85.5%) had Grade I screw placement quality. Grade II screw placement quality accounted for 18.2% of the control group and 7.3% of the experimental group. In the control and the experimental groups, there were 26 and 8 cases with Grade III screw placement quality, respectively. The quality of screw placement in the experimental group was significantly better than that in control group, and the difference between the two groups was statistically significant (P < 0.01). The distance between the screw and the acetabulum in the control group and experimental group was 0.92 ± 0.49 mm and 2.78 ± 1.15 mm, respectively. The difference between the two groups was statistically significant.

CONCLUSION

Anterior column acetabular screws can be inserted successfully and more accurately using the obturator oblique and pubic ramus inlet views.

Computer navigation-assisted minimally invasive percutaneous screw placement for pelvic fractures

Pelvic fractures are often caused by high-energy injuries and accompanied by hemodynamic instability. Traditional open surgery has a large amount of bleeding, which is not suitable for patients with acute pelvic fracture. Navigation-guided, percutaneous puncture-screw implantation has gradually become a preferred procedure due to its advantages, which include less trauma, faster recovery times, and less bleeding. However, due to the complexity of pelvic anatomy, doctors often encounter some problems when using navigation to treat pelvic fractures. This article reviews the indications, contraindications, surgical procedures, and related complications of this procedure for the treatment of sacral fractures, sacroiliac joint injuries, pelvic ring injuries, and acetabular fractures. We also analyze the causes of inaccurate screw placement. Percutaneous screw placement under navigational guidance has the advantages of high accuracy, low incidence of complications and small soft-tissue damage, minimal blood loss, short hospital stays, and quick recovery. There is no difference in the incidence of complications between surgeries performed by new doctors and experienced ones. However, computer navigation technology requires extensive training, and attention should be given to avoid complications such as screw misplacement, intestinal injury, and serious blood vessel and nerve injuries caused by navigational drift.

Achievable pin spanning angulation in anterosuperior pelvic external fixation

INTRODUCTION

Pelvic external fixation using anterosuperior pins provides a quick method of stabilization without necessitating fluoroscopic guidance. Various locations, depths, and inclinations have been cited for external fixator pins; however, the existing literature lacks clear indications for the angular difference between pins. Thus, we aimed to determine the greatest degree of sagittal pin spanning angulation (SPSA) between two iliac crest pins and how intraosseous depth (ID) affects these angulations.

MATERIALS AND METHODS

A newly developed computer algorithm produced cross sections of 3D pelvic reconstructions in the sagittal plane in 5° increments. Computer-generated pins with IDs of 60, 75, and 90 mm were positioned in 5° increments transversely. Pins were assessed for cortical containment to define values for SPSA and transverse pin spanning angulation (TPSA).

RESULTS

A bimodal distribution revealed varying degrees of insertion frequency and SPSA, cranially and caudally. The caudal distribution exhibited greater cortical containment with larger values for SPSA and TPSA. The highest insertion frequency (85.7%) and largest SPSA (155°) were observed for the 60-mm ID. Increasing ID resulted in further bony penetration and smaller values for SPSA and TPSA.

CONCLUSIONS

Expanding the degree of SPSA between inserted pins in anterosuperior pelvic external fixation can be challenging due to the thinning of the iliac wing, which affords a narrow corridor for intraosseous pin containment. An ID of 60 mm allows larger degrees of SPSA while maintaining higher rates of cortical pin containment when compared to pins with greater IDs.

Intramedullary Fixation Techniques for the Anterior Pelvic Ring

The superior ramus is an irregularly shaped, undulating, and curvilinear osseous structure that can provide an osseous conduit for intramedullary screws. A wide spectrum of variability between the curve and obliquity of the superior ramus osseous fixation pathway (OFP) exists in both the anteroposterior and the coronal planes. A detailed understanding of the osseous topography and how it correlates with fluoroscopic imaging is mandatory. Obtaining the correct intraoperative inlet and combined obturator oblique-outlet fluoroscopic views specific to each patient's anatomy is necessary for safe implant insertion. Intramedullary screws can be inserted in either an antegrade or a retrograde direction depending on a number of variables, including fracture location, the proximity of patient's external genitalia to the skin insertion side, and the possible impact of thigh girth on the surgeons hand position. Multiple screw insertion techniques are possible, but a simple and reproducible technique is described. The size and number of screws that can be inserted is variable, differs between surgeons, but is ultimately dependent on the cortical limits of the superior ramus OFP. Standard screw insertion techniques are successful in most patients. If the osseous corridor or external anatomy impedes standard insertional techniques, several modifications exist that can allow successful screw insertion. A thorough understanding of each patient's anatomy, injury, and precise surgical technique with the appropriate fluoroscopic views are required to safely place intraosseous intramedullary implants into the superior ramus OFP.

A radiographic simulation study of fixed superior pubic ramus fractures with retrograde screw insertion

OBJECTIVES

The study's aim is to calculate the parameters for retrograde insertion points for fixed superior pubic ramus fractures.

METHODS

From the pubic symphysis, diameter and length of the screw were measured, as well as the angle between the screw axis and the 3 planes.

RESULTS

When the diameter was fixed at 4.5 mm, the maximum lengths were 125 mm and 119 mm.

CONCLUSIONS

When the fracture occurs in Zone I, the penetration point could be selected in the pubic symphysis pubis angle to ensure that medial fracture fragments have sufficient screw channel length.

Comparison of anterograde versus retrograde percutaneous screw fixation of anterior column acetabular fractures

PURPOSE

Percutaneous screw fixation is an effective technique in addressing minimally displaced anterior column acetabular fractures. The aim of this study is to evaluate the ease of percutaneous screw insertion for acetabular anterior column fracture, as it pertains to anterograde versus retrograde insertion techniques.

METHOD

From 2009 to 2013, CT imaging from 30 adult volunteers (15 males, 15 females) without history of pelvic disruption and/or morphologic abnormalities were evaluated. From these images, virtual 3D pelvic models were generated. The differences area of screw starting points, limitation position of anterior column screws, and range of screw directions were analyzed.

CONCLUSION

We found in our analysis that anterograde and retrograde had not only variations in their starting points, but differences in areas of insertion. Typically, anterograde portals have a larger area for insertion. Additionally, given the limitations we noted in screw position and the severity of the acetabular fractures, this will allow the treating surgeon to determine the most optimal technique for percutaneous anterior column screw fixation.

RESULTS

In our analysis, we found two areas for effective percutaneous anterograde insertion and one area for effective retrograde insertion. They both possess geometries with different shapes. Additionally, the area of anterograde insertion is larger than the retrograde area of insertion. The limitations in screw positions were shown in the AP, inlet, outlet, iliac oblique, obturator oblique, and lateral views. The direction range between superior and inferior and between medial and lateral were measured and recorded. In area of anterograde, the angle between the superior and inferior limits was 29.2° ± 2.7°, while the angle limit between medial and lateral was 18.5° ± 1.8°. In area of retrograde, the angle between the superior and inferior limits was 8.32° ± 1.3°, while the angle limit between medial and lateral was 7.5° ± 0.8°

Axial perspective to find the largest intraosseous space available for percutaneous screw fixation of fractures of the acetabular anterior column

OBJECTIVE

To find the largest screw path in the acetabular anterior column using a novel method of axial perspective and test the clinical feasibility of the anterior column axial view projection.

METHODS

3D models with the inner triangular patches deleted were created from the pelvic CT scan data of 58 normal pelvises. The transparency of each 3D model was downgraded at the axial perspective (the view perpendicular to the cross section of the anterior column axis) so that a translucent area was seen clearly. The orientations of each 3D model were adjusted until a triangle-like translucent area that could accommodate the largest virtual screw (Screw I) was present and then an ellipse-like translucent area that could accommodate the two largest virtual screws (Screw II) was present. The maximum diameter, direction of Screw I and the maximum diameter Screw II were measured. Clinical feasibility of the axial view projection was next tested in five cadaveric specimens.

RESULTS

The mean maximum diameters of Screw I and Screw II were 11.20 ± 1.73 (7.80-14.60 mm) and 8.71 ± 0.91 (6.60-10.60 mm), respectively. The angles of Screw I to the transverse, coronal and sagittal planes were 41.16° ± 4.59°, 18.18° ± 1.15° and 44.33° ± 4.31°, respectively. Translucent areas were successfully observed in all the cadaveric hemi-pelves and guide pins were successfully inserted in all the cadaveric hemi-pelves with the assistance of the anterior column axial view projection without cortex penetration or joint violation.

CONCLUSIONS

The acetabular anterior column could safely accommodate not only one 7.3-mm screw, but also two 6.5-mm screws. The anterior column axial projection may be clinically feasible.