Percutaneous screw placement in acetabular posterior column surgery: gender differences in implant positioning

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.

A standard canulated screw may not fit up to 1/3 of the patients treated percutaneously for anterior column acetabular fractures-A pilot study

A proper evaluation of the narrowings and length of the anterior acetabular column would offer better predictability and precision for implant insertion in the case of an acetabular fracture.

OBJECTIVE

To determine the diameter and length of the safety corridor of the anterior column of the acetabulum in patients with available pelvic computed tomography (CT), analyze the obtained measurements against those of a standard 6.5-mm implant, and verify possible sex differences regarding these measurements. A secondary aim was to develop a method for measurement of the anterior column of the acetabulum based on CT images.

MATERIALS AND METHODS

In 200 CT scans of hemipelvises we measured the diameter of two areas of narrowing and the length of the safety corridor of the anterior column. The images were submitted to multiplanar reformatting adjusted to a plane orthogonal to the bone corridor, drawn at the level of the superior pubic ramus.

RESULTS

Measurement #1 had a mean value of 8.12 (2.27) mm in the overall sample and median values of 9.03 (7.76-10.48) mm in men and 6.77 (5.44-7.19) mm in women. Measurement #2 had a mean value of 7.29 (2.19) mm and median values of 8.23 (7.18-9.82) mm in men and 5.9 (4.65-7.19) mm in women. Measurement #3 had a mean value of 109.53 (13.66) mm in the overall sample and median values of 117.17 (112.9-122.9) mm in men and 100.91 (90.95-111.17) mm in women (p<0.001 all three measurements). Measurement #1 was smaller than 6.5 mm in 22.5% of the patients (of whom 90% were women). Measurement #2 was smaller than 6.5 mm in 35% of the patients (of whom 80% were women).

CONCLUSIONS

This study proposed an anatomic evaluation of the anterior column of the acetabulum using conventional CT images The areas of narrowing in the anterior column had an average of 8.12 mm at the level of the pubic tubercle and 7.29 mm at the level of the acetabular fossa. The mean length of the safety corridor was 109.53 mm. In 35% of the cases, a 6.5 mm percutaneous screw would have violated the cortical bone of the safety corridor.

Use of the iliac-outlet and iliac-inlet combined views in percutaneous posterior column retrograde screw fixation

Posterior column fractures are common acetabular injuries. Although displaced fractures require open reduction and fixation, undisplaced patterns may benefit from percutaneous screw fixation. The combination of iliac oblique with inlet and outlet views offers an intuitive and panoramic rendering of the bony corridor into the posterior column; lateral cross table view completes the sequence of fluoroscopic projections. Herein we describe the use of outlet/inlet iliac views and a detailed procedure for percutaneous retrograde posterior column screw fixation.

The largest secure corridor of the infra-acetabular screw-a 3-D axial perspective analysis

Background

The infra-acetabular screw which is placed from the pubis to the ischium can be used as a special positional screw of the posterior column of the acetabulum. This study was performed to simulate the surgical procedure and obtain the ideal insertion point, diameter, length and angle of the screw through the method of axial perspective in Chinese patients.

Methods

We randomly collected the pelvic computed tomography (CT) scans of 200 adults. DICOM-formatted CT-scan images were imported into Mimics software to establish the 3D digital model of the right semi-pelvic was established. A virtual cylinder representing the screw was placed from the pubis to the ischium to fix the posterior column. The largest secure diameter and length of the virtual screw were measured and the position of the insertion point and the directions of the screw were also researched.

Results

The screw insertion safe zone exhibits an irregular shape of “tear drop” in the reconstructed pelvic model. The mean maximum diameter of screws was 5.01 ± 1.28 mm, and the mean maximum length of screws was 93.99 ± 8.92 mm. The screw insertion corridor with the least diameter 3.5 mm was found in 94 of 100 males (94%) and 86 of 100 females (86%). We found gender-dependent differences for the mean maximum diameter and the maximum length of the screw. There was statistically significant difference between genders in the position of insertion point.

Conclusions

In this study, we suggest an individual preoperative 3D reconstruction simulation to develop better screw placement plans, which provides a valuable guideline for seeking the largest secure corridor of infra-acetabular screw. Further biomechanical studies are needed to verify the function of the screw.

The "safe zone" for infrapectineal plate-screw fixation of quadrilateral plate fractures: An anatomical study and retrospective clinical evaluation

Extra-articular screw placement in the true pelvis for fixing quadrilateral plate fractures remains challenging. We aimed to define the "safe zone" on the quadrilateral surface to facilitate safe plate-screw placement.Twenty cadaveric hemipelves were sectioned and assembled to define the projection of the acetabular boundary on the quadrilateral surface. Three lines (X, Y, and Z) were drawn tangent to the projection, with X parallel to the iliopectineal line, Y perpendicular to the iliopectineal line, and Z parallel to the posterior border of the ischial body. Then, the distances between X and the iliopectineal line (D1), Y and the sacroiliac joint (D2), and Z and the posterior border of the ischium (D3) could be used to determine a "safe zone" on the quadrilateral surface for screw insertion. We included 15 patients whose conditions satisfied the definition of a comminuted quadrilateral plate fracture and applied two-ended buttress plates for treatment in accordance with this "safe zone."The average D1 was 50.0 mm, the average D2 was 30.6 mm, and the average D3 was 12.4 mm. For all 15 patients with comminuted quadrilateral fracture who were treated, no intraoperative or postoperative screw penetration of the acetabulum was identified, and no loss of reduction was observed during an average follow up of 17.7 months.The "safe zone" established in this study simplifies extraarticular screw placement for managing quadrilateral plate fractures in the true pelvis. As a result, two-ended buttress plate fixation in the true pelvis becomes safe, therefore, treatment with two-ended buttress plates may represent a viable alternative to single-ended elastic fixation in the management of comminuted quadrilateral fractures.

The anatomical and imaging study of pes anserinus and its clinical application

BACKGROUND

The pes anserinus was an important graft choice for anterior cruciate ligament (ACL) reconstruction. The infrapatellar branch of the saphenous nerve (IPBSN) might be damaged in this surgery. This study aimed to provide anatomic and ultrasonic measurement data of pes anserinus and superficial nerves.

METHODS

Eighty lower limb specimens of forty adult cadavers were dissected. The length, width, thickness, and the position of the tibial attachment of pes anserinus tendons were anthropometric measured, as well as the distance between the infrapatellar branch of the saphenous nerve and the pes anserinus. Sixty healthy adult participants were enrolled for ultrasonic research. The length, width, thickness of pes anserinus was also measured and the saphenous nerve was also assessed.

RESULTS

Anatomic results showed that there were 3 types of pes anserinus, the infrapatellar branch of the saphenous nerve (IPBSN) was almost paralleled to the upper edge of the pes anserinus tendon, and the average of distance between them was about 0.95 cm. The length of semitendinosus and gracilis tendons were 146.49 ± 12.83 mm and 124.62 ± 8.86 mm, the width of sartorius tendon was 25.58 ± 4.65 mm, wider than other tendons. The classification of pes anserinus tendons and the saphenous nerves could be identified in ultrasonic image. The length of semitendinosus and gracilis tendons were 151.35 ± 9.65 mm and 120.86 ± 8.99 mm, the width of sartorius tendon was 22.84 ± 3.83 mm. And there was no significance difference between anatomic and ultrasonic measurement (P > .05).

CONCLUSION

The morphology of pes anserinus and its peripheral structures could be identified and measured precisely by ultrasound device, a presurgical ultrasonic examination was recommended. The arrangement of pes anserinus tendons was classified into 3 types according to our results. The incision should be performed medial to tibial eminence 1.5 cm and under the tibial tubercle level 2 to 3 cm, an oblique incision formed an angle of 50° with tibial transection was recommend, which was parallel to the direction of pes anserinus tendon.

Anterograde Fixation Module for Posterior Acetabular Column Fracture: Computer-Assisted Determination of Optimal Entry Point, Angle, and Length for Screw Insertion

BACKGROUND The aim of this study was to provide valid data for a plate-screw fixation model for fractured posterior-anterior columns of the acetabulum. MATERIAL AND METHODS Nineteen cadaveric bony hemi-pelvis specimens were obtained and 50 healthy adults were enrolled. The modified Stoppa approach and computed tomography (CT) imaging were used to collect the measured parameter data of the module. RESULTS The measured parameter data were as follows: OP, 0.96±0.32 cm in females and 0.92±0.16 cm in males (P>0.05); PI, 0.98±0.28 cm in females, and 0.75±0.23 cm in males (P>0.05); Ðϴ, 59.68°±6.28° in females and 56.75°±3.22° in males (P>0.05); and Ðφ, 41.27°±2.76° in females and 34.31°±2.78° in males (P<0.05). The corresponding CT image data were as follows: PI, 1.08±0.22 cm in females and 0.85±0.27 cm in males (P>0.05); OP, 1.06±0.29 cm in females and 1.12±0.24 cm in males (P>0.05); Ðϴ, 55.33°±4.00° in females and 55. 50°±3.43° in males (P>0.05); and Ðφ was 39.21°±2.45°in females and 35.58°±2.31°in males (P<0.05). No significant difference with respect to sex and side existed between specimens and healthy adults (P>0.05). CONCLUSIONS The measured parameter data obtained in healthy adults and cadaveric specimens provided an anatomic basis for the designation of the guide module, and thus confirmed the accuracy and safety of screw placement in fractured columns of the acetabulum.

Definition of a safe zone for antegrade lag screw fixation of fracture of posterior column of the acetabulum by 3D technology

The objective of this study was to define a safe zone for antegrade lag screw fixation of fracture of posterior column of the acetabulum using a novel 3D technology. Pelvic CT data of 59 human subjects were obtained to reconstruct three-dimensional (3D) models. The transparency of 3D models was then downgraded along the axial perspective (the view perpendicular to the cross section of the posterior column axis) to find the largest translucent area. The outline of the largest translucent area was drawn on the iliac fossa. The line segments of OA, AB, OC, CD, the angles of OAB and OCD that delineate the safe zone (ABDC) were precisely measured. The resultant line segments OA, AB, OC, CD, and angles OAB and OCD were 28.46mm(13.15-44.97mm), 45.89mm (34.21-62.85mm), 36.34mm (18.68-55.56mm), 53.08mm (38.72-75.79mm), 37.44° (24.32-54.96°) and 55.78° (43.97-79.35°) respectively. This study demonstrates that computer-assisted 3D modelling techniques can aid in the precise definition of the safe zone for antegrade insertion of posterior column lag screws. A full-length lag screw can be inserted into the zone (ABDC), permitting a larger operational error.

Virtual mapping of 260 three-dimensional hemipelvises to analyse gender-specific differences in minimally invasive retrograde lag screw placement in the posterior acetabular column using the anterior pelvic and midsagittal plane as reference

BACKGROUND

Due to complex pelvic geometry, percutaneous screw placement in the posterior acetabular column can pose a major challenge even for experienced surgeons.

METHODS

The present study examined the preformed bone stock of the posterior acetabular column in 260 hemipelvises. Retrograde posterior column screws were virtually implanted using iPlan CMF (BrainLAB AG, Feldkirchen, Germany); maximal implant length, maximal implant diameter and angles between the screw trajectories and the reference planes anterior pelvic plane as well as the midsagittal plane were assessed for gender-specific differences.

RESULTS

The virtual analysis of the preformed bone stock column showed two constrictions of crucial clinical importance. These were located 49.6 ± 3.4 (41.0-60.2) mm (inferior margin of acetabulum) and 77.0 ± 5.6 (66.5-95.3) mm (centre of acetabulum) from the entry point of the implant in men and respectively 43.7 ± 2.3 (38.3-49.3) mm as well as 71.2 ± 3.5 (63.5-79.99) mm in women (men vs. women: p < 0.001). The entry point of the retrograde posterior column screw was located dorsal from the transition of the lower margin of the ischial tuberosity to ramus inferior pointing to the medial margin of the ischial tuberosity. In female patients, the entry point was located significantly closer to the medial margin of the ischial tuberosity. However, 7.3 mm screws can generally be used in men and women. The angle between the screw trajectory and the anterior pelvic plane in sagittal section was 14.0 ± 4.9 (2.5-28.6) °, the angle between the screw trajectory and the midsagittal plane in axial section was 31.1 ± 12.8 (1.5-77.9) ° and the angle between the screw trajectory and the midsagittal plane in coronal section was 8.4 ± 3.8 (1.5-20.0) °. For all angles, significant gender-specific differences were found (p < 0.001).

CONCLUSION

Therefore, the anterior pelvic plane as well as the midsagittal plane can facilitate intraoperative orientation for retrograde posterior column screw placement considering gender-specific differences in preformed bone corridor, implant length as well as angles formed between screw trajectory and these reference planes.

Axial view of acetabular anterior column: a new X-ray projection of percutaneous screw placement

INTRODUCTION

To search for a new radiographic view/projection of the acetabular anterior column to provide a safe guide for percutaneous screw placement for acetabular fractures.

MATERIALS AND METHODS

Eight pelvic specimens taken from normal adult cadavers were positioned in a supine position on the operating table. First, the ipsilateral ilium-oblique view of the observed side was obtained on C-arm fluoroscopy by tilting the C-arm approximately 35° toward the contralateral hip joint. Then, the tilting angle of the C-arm was changed gradually until an oval track image (acetabular anterior column axial view) appeared. The oval shadow was clear only in one position as the angle of the C-arm was changed toward the caudal side of the operating table. A guide pin was put on the skin of the cadaver, and the location and tilting direction of the guide pin were adjusted under C-arm fluoroscopy until the pin's shadow became a point in the center of the oval track. Then, the guide pin was inserted into the bone using a battery-powered drill. The degree of inclination of the guide pin in the cadaver in the frontal and sagittal planes was measured using computed tomography (CT).

RESULTS

Axial views of the anterior column were found successfully in all of the pelvic specimens, and the guide pins were inserted accurately into the acetabular anterior column under C-arm fluoroscopic guidance. On the CT-reconstructed image, the average degree of angle between the guide pin and the sagittal plane was 33.6° (range 29.6°-36.5°). The average angle between the guide pin and the transverse plane was 59.1° (range 56.4°-63.2°).

CONCLUSION

This axial view of the acetabular anterior column is a novel X-ray projection which provides an optimal method for guiding percutaneous insertion of anterior column screws for acetabular fractures.

Retrograde lag screw placement in anterior acetabular column with regard to the anterior pelvic plane and midsagittal plane -- virtual mapping of 260 three-dimensional hemipelvises for quantitative anatomic analysis

Percutaneous screw placement can be used for minimally invasive treatment of none or minimally displaced fractures of the anterior column. The complex pelvic geometry can pose a major challenge even for experienced surgeons. The present study examined the preformed bone stock of the anterior column in 260 hemipelvises (130 male and 130 female). Screws were virtually implanted using iPlan(®) CMF (BrainLAB AG, Feldkirchen, Germany); the maximal implant length and the maximal implant diameter were assessed. The study showed, that 6.5mm can generally be used in men; in women however individual planning is essential in regard to the maximal implant diameter since we found that in 15.4% of women, screws with a diameter less than 6.5mm were necessary. The virtual analysis of the preformed bone stock corridor of the anterior column showed two constrictions of crucial clinical importance. These can be found after 18% and 55% (men) respectively 16% and 55% (women) measured from the entry point along the axis of the implant. The entry point of the retrograde anterior column screw in our collective was located lateral of tuberculum pubicum at the level of the superior-medial margin of foramen obturatum. In female patients, the entry point was located significantly more lateral of symphysis and closer to the cranial margin of ramus superior ossis pubis. The mean angle between the screw trajectory and the anterior pelvic plane in sagittal section was 31.6 ± 5.5°, the mean angle between the screw trajectory and the midsagittal plane in axial section was 55.9 ± 4.6° and the mean angle between the screw trajectory and the midsagittal plane in coronal section was 42.1 ± 3.9° with no significant deviation between both sexes. The individual angles formed by the screw trajectory and the anterior pelvic and midsagittal plane are independent from anthropometric parameters sex, age, body length and weight. Therefore, they can be used for orientation in lag screw placement keeping in mind that the entry point differs in both sexes.