Sequential fluoroscopic rollover images reliably identify "in-out-in" posterosuperior screws during percutaneous fixation of femoral neck fractures

Intraoperative angulation of the C-arm for X-ray of each curved surface of the femoral neck wall: a cadaveric study

BACKGROUND

C-arm fluoroscopy is the main method assisting surgical reduction and internal fixation of the femoral neck, as traditional anteroposterior and lateral fluoroscopy is insufficient for visualizing the irregular anatomical structure of the femoral neck. We analysed the anatomy of the femoral neck to ascertain the optimal position and angle of the C-arm for adequate visualization of the femoral neck during fluoroscopy.

METHODS

The femoral neck was divided into anterior, posterosuperior and posteroinferior surfaces. These surfaces and the coronal plane of the femur formed the anterior surface coronal angle (ACA), posterosuperior surface coronal angle (PSCA) and posteroinferior surface coronal angle (PICA), respectively. Three angles of 32 dried femoral samples were measured. In the aluminium model, steel wires penetrated the femoral neck wall, whereas, in the wire model, three Kirschner wires penetrated the femoral neck wall. The C-arm was rotated 5° for a 0°-180° fluoroscopic view of each curved surface. Each specimen was imaged, totalling 111 frames. The optimal angle for fluoroscopic imaging of each surface was ascertained, and fluoroscopic features of the Kirschner wire penetrating the femoral neck cortex at three different angles on fluoroscopy and anteroposterior and lateral radiographs were observed.

RESULTS

The femoral neck is irregularly shaped and cylindrical, with the anterior surface longer than the posteroinferior surface. The ACA, PSCA and PICA were 31 ± 4.589°, 67.813 ± 5.052° and 168.688 ± 3.206°, respectively. The optimal angles for visualizing the anterior, posterosuperior and posteroinferior surfaces of the steel wire aluminium foil model under fluoroscopy were 30.781 ± 5.464°, 67.969 ± 3.721°, and 167.813 ± 4.319°, respectively. There was no significant difference in the measurements of the corresponding surface coronal angles (P > 0.05). Kirschner wires penetrating the femoral neck wall were difficult to visualize on traditional anteroposterior and lateral films. Increasing the angle to 30°, 70° or 170° for fluoroscopy allowed clear visualization of Kirschner wires penetrating the femoral cortex.

CONCLUSION

Traditional anteroposterior and lateral fluoroscopic views are insufficient for clear visualization of the true structure of the femoral neck. Additionally, increasing the angle to 30°, 70° or 170° for fluoroscopy allows observation of the fracture reduction quality from the anterior surface, posterosuperior surface and posteroinferior surface of the femoral neck and the damage to the corresponding cortical bone caused by internal fixation.

LEVEL OF EVIDENCE

Level II.

Screw Configuration Does Not Significantly Alter Neck Shortening After Valgus-Impacted Femoral Neck Fracture (OTA Type 31B1.1)

OBJECTIVES

To compare 3 different cancellous screw configurations used for Garden 1 femoral neck fractures (FNFs).

METHODS

DESIGN

Retrospective review.

SETTING

A large urban academic medical center.

PATIENT SELECTION CRITERIA

All patients with Orthopaedic Trauma Association 31B1.1 FNF who underwent in situ fixation with cancellous screws between 2012 and 2021 were included. Patients were divided into 3 groups: 2 screws placed in a parallel fashion, 3 screws placed in an inverted triangle configuration, and 3-screw fixation with placement of 1 "out-of-plane" screw perpendicular to the long axis of the femur.

OUTCOME MEASURES AND COMPARISONS

Postoperative femoral neck shortening (mm) was the primary outcome, which was compared among the 3 groups of different screw configurations.

RESULTS

Sixty-one patients with a median follow-up of 1 year (interquartile range 0.6-1.8 years) and an average age of 72 years (interquartile range 65.0-83.0 years) were included. All fractures demonstrated bony healing. Overall, 68.9% of the cohort had ≤2 mm of femoral neck shortening. There was no difference between groups in the proportion of patients who experienced greater than 2 mm of shortening (P = 0.839) or in the amount (mm) of femoral neck shortening (Kruskal-Wallis χ2 = 0.517, P = 0.772).

CONCLUSIONS

Although most patients with valgus-impacted FNF treated with screw fixation do not experience further femoral neck shortening, some patients demonstrated continued radiographic shortening during the healing process. The development of further femoral neck shortening and the amount of shortening that occurs do not differ based on implant configuration. Multiple different screw configurations seem to be acceptable for achieving healing and minimizing further femoral neck impaction.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Accuracy of radiographic projections to guide cephalic screw position in pertrochanteric fracture: a cadaveric study

PURPOSE

The aim of this study was to evaluate the relationship between the Löwenstein Lateral view and the True Lateral view for the positioning of the cephalic hip screw, through a cadaveric study.

MATERIALS AND METHODS

We placed two Kirschner wires in eight femur specimens using an Antero-Posterior view, Löwenstein Lateral view and True Lateral view. The distances between the Kirschner wires and the anterior, posterior, superior and inferior cortex were measured in all projections. The head of the femur was then sectioned, and the same macroscopic distances were measured. Finally, we could calculate the accuracy of the two radiographic lateral projections.

RESULTS

When the Kirschner wire was placed in the center of the head using the Antero-Posterior and the True Lateral view, the accuracy of Antero-Posterior view was 0.9705 while the accuracy of True Lateral view and Löwenstein Lateral view was 1.1479 and 1.1584, respectively. When the Kirschner wire was placed superior on the Antero-Posterior and centrally on the True Lateral view, the accuracy of Antero-Posterior view was 0.9930 while the accuracy of True Lateral view and Löwenstein Lateral view was 1.1159 and 0.7224, respectively.

CONCLUSION

When the Kirschner wire was positioned proximal in Antero-Posterior view and central in True Lateral view, only the True Lateral view showed high accuracy.

Can "In-Out-In" posterosuperior screws meet nutrient foramina in patients with femoral neck fractures?

BACKGROUND

The "In-Out-In" (IOI) posterosuperior screw was common in screw fixations of femoral neck fractures. The impacts of the IOI screw on the blood supply of the femoral head have not yet been clarified. The nutrient foramen was damaged when the screw was present in their corresponding cortex surface. This study aimed to evaluate the damage degrees of the nutrient foramina in the femoral neck as the IOI posterosuperior screw was placed in different posterosuperior locations.

METHODS

One hundred and eight unpaired dry human cadaveric proximal femurs were scanned by a three-dimensional scanner. Digital data obtained from the proximal femur surface were employed for subsequent analysis. All nutrient foramina in the femoral neck were identified and marked in each subject. A simulation of the anteroposterior, lateral, and axial views was then performed, and regions of interest (ROIs) for IOI posterosuperior screws, with 6.5 mm diameter, were determined in the posterosuperior femoral neck on the axial graphs. Nutrient foramina were counted and analyzed in ROIs and femoral neck, and its damage from the IOI posterosuperior screw was also calculated in different conditions of screw placement. Paired t-tests were used for comparative analyses before and after damage.

RESULTS

Most nutrient foramina were located in the subcapital region and the least in the basicervical region in the femoral neck, while the most were located in the transcervical and the least in the subcapital in the ROIs. In addition, most nutrient foramina in ROIs were located in the superior-posterior area of the femoral neck. There were four main locations of IOI posterosuperior screws where the decrease in the nutrient foramina was statistically significant (P < 0.01). The risk zone determined by these locations was located in a posterosuperior square of ROIs with an edge length of 9.75 mm.

CONCLUSION

To minimize iatrogenic damage to the blood supply of the femoral head, screw positions could be assessed in anteroposterior and lateral radiographs using a risk zone. The IOI posterosuperior screw in ROIs can be applied to fix femoral neck fractures when feasible in clinical practice. This study could provide surgeons with more alternatives for screw placement in the posterosuperior femoral neck.

The Use of the Piriformis Fossa Radiographic Landmark to Predict "In-Out-In" Placement of the Posterosuperior Femoral Neck Screw

OBJECTIVES

To investigate the correlation between a screw's radiographic relationship to the piriformis fossa with position on CT in the clinical setting.

METHODS

Intraoperative fluoroscopic images of patients treated with cannulated screw fixation of a femoral neck fracture, who also had a postoperative CT scan, were retrospectively evaluated by 4 fellowship-trained orthopaedic trauma surgeons. The posterosuperior screw on the AP fluoroscopic view was determined to be above the piriformis fossa (APF) or below the piriformis fossa (BPF). Using CT scan to determine IOI placement, the ability to predict IOI position based on fluoroscopic imaging was evaluated by calculating accuracy, sensitivity, specificity, and interobserver reliability.

RESULTS

73 patients met inclusion criteria. The incidence of IOI screw placement was 59% on CT evaluation. The use of the PF landmark accurately predicted CT findings in 89% of patients. A screw placed APF was 90% sensitive and 88% specific in predicting cortical breach, with near-perfect interobserver agreement (κ = 0.81).

CONCLUSION

The use of the PF radiographic landmark is highly sensitive and specific in predicting the placement of an IOI posterosuperior femoral neck screw.

LEVEL OF EVIDENCE

Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Orientated-quantitative computed tomography study on individualized axial safety target area of femoral neck screw channel and establishment of a stable spatial coordinate system based on anterior cortex of femoral neck basilar

BACKGROUND

Frequent in-out-in femoral neck screws were reported potential huge iatrogenic-injury risks, related to axial safe target area (ASTA) of femoral neck screws channel. However, orientated-quantitative ASTA based on stable coordinate system was unreported before.

METHODS

Three-dimensional reconstruction was performed on computed tomography (CT) images of 139 intact normal hips, and the intersection area, defined as ASTA, was obtained by superimposing the axial CT images of each femoral neck. Taking anterior cortex of femoral neck basilar (AC-FNB) as landmark, a coordinate system was established to measure the anterior-posterior diameter (D-AP), the superior-inferior diameter (D-SI) and the oblique angle respectively. Each intersection was overlaid up to the axial CT images to determine the coronal location of the ASTA boundaries.

RESULTS

Each ASTA presented an inclined rounded triangle with a flat anterior base coincided with AC-FNB. There were significant sex differences in D-SI (male: 33.6±2.3 vs. female: 29.4±1.9 mm) and D-AP (male: 25.3±2.1 vs. 21.9±1.9 mm), P <0.001. D-SI was found to be positively correlated with D-AP ( R2 =0.6). All fluoroscopic visible border isthmus completely matched the corresponding ASTA boundaries. The oblique angle was 5-53° (male: 28.1±10.3°, female: 27.1±8.2°) without significant difference between sexes.

CONCLUSION

The intersection method was employed to conveniently acquire orientated-quantitative individualized ASTA. Under this coordinate system, x-ray data of screws could be converted to axial coordinates in CT ASTA, which could help surgeons design combined screws configuration preoperatively and evaluate quantitatively their axial position intraoperatively.

Orientated-quantitative computed tomography study on individualized axial safety target area of femoral neck screw channel and establishment of a stable spatial coordinate system based on anterior cortex of femoral neck basilar

Background:

Frequent in-out-in femoral neck screws were reported potential huge iatrogenic-injury risks, related to axial safe target area (ASTA) of femoral neck screws channel. However, orientated-quantitative ASTA based on stable coordinate system was unreported before.

Methods:

Three-dimensional reconstruction was performed on computed tomography (CT) images of 139 intact normal hips, and the intersection area, defined as ASTA, was obtained by superimposing the axial CT images of each femoral neck. Taking anterior cortex of femoral neck basilar (AC-FNB) as landmark, a coordinate system was established to measure the anterior–posterior diameter (D-AP), the superior–inferior diameter (D-SI) and the oblique angle respectively. Each intersection was overlaid up to the axial CT images to determine the coronal location of the ASTA boundaries.

Results:

Each ASTA presented an inclined rounded triangle with a flat anterior base coincided with AC-FNB. There were significant sex differences in D-SI (male: 33.6±2.3 vs. female: 29.4±1.9 mm) and D-AP (male: 25.3±2.1 vs. 21.9±1.9 mm), P<0.001. D-SI was found to be positively correlated with D-AP (R 2=0.6). All fluoroscopic visible border isthmus completely matched the corresponding ASTA boundaries. The oblique angle was 5–53° (male: 28.1±10.3°, female: 27.1±8.2°) without significant difference between sexes.

Conclusion:

The intersection method was employed to conveniently acquire orientated-quantitative individualized ASTA. Under this coordinate system, x-ray data of screws could be converted to axial coordinates in CT ASTA, which could help surgeons design combined screws configuration preoperatively and evaluate quantitatively their axial position intraoperatively.

A new posterosuperior screw placement strategy to avoid in-out-in screws in femoral neck ractures

Objective

The inverted triangle configuration of the three cannulated screws is the classic fixation method most commonly performed for undisplaced femoral neck fractures in young and geriatric patients. However, the posterosuperior screw has a high incidence of cortical breach, known as an in-out-in (IOI) screw. In this study, we present a novel posterosuperior screw placement strategy to prevent the screw from becoming IOI.

Methods

Using computed tomography data and image-processing software, 91 undisplaced femoral neck fractures were reconstructed. The anteroposterior (AP), lateral, and axial radiographs were simulated. To simulate the intraoperative screw placement process, participants used three screw insertion angles (0°, 10°, and 20°) to place the screw on the AP and lateral views of the radiograph according to the three established strategies. On the AP radiograph, a screw was placed abutting (strategy 1), 3.25 mm away from (strategy 2), or 6.5 mm away from (strategy 3) the superior border of the femoral neck. On the lateral radiograph, all the screws were placed abutting the posterior border of the femoral neck. Axial radiographs were used to evaluate the screw position.

Results

In strategy 1, all the placed screws were IOI regardless of the screw insertion angle. In strategy 2, 48.3% (44/91) of IOI screws occurred at a 0° screw insertion angle, 41.7% (38/91) of IOI screws occurred at a 10° screw insertion angle, and 42.9% (39/91) of IOI screws occurred at a 20° screw insertion angle situation. In strategy 3, no IOI screw occurred, and the screw insertion angles did not affect the safety and accuracy of screw placement.

Conclusions

Screws placed according to strategy 3 are safe. The reliability of this screw placement strategy is unaffected by a screw insertion angle of less than 20 degrees.

The application of the 150° oblique tangential fluoroscopic view to detect the posterosuperior femoral neck screw in-out-in intraoperatively

This study investigates the application of the 150° tangential fluoroscopic projection as a novel fluoroscopic view to detect the posterosuperior screw in–out–in (IOI) in the cannulated screws fixation of femoral neck fractures. A retrospective analysis was conducted including 33 patients with femoral neck fractures enrolled from April to November 2021. All patients underwent closed reduction and internal fixation with cannulated screws under intra-operative C-arm fluoroscopy. The posterosuperior femoral neck screw position (whether in–out–in and the distance to the femoral neck cortex) was evaluated from the standard anteroposterior (AP), lateral view, and tangential view images. Postoperative computed tomography (CT) scan results are considered the gold standard for detecting the femoral neck screw locations. Of 33 patients, no femoral neck screws were found to be placed IOI under the standard AP and lateral views. The tangential view revealed the posterosuperior screw was IOI in 8 patients, whereas the average distance between the posterosuperior screw and the posterior femoral neck cortex was 2.73 ± 1.06 mm under the standard lateral view. Postoperative CT verified that posterosuperior screw was placed IOI in these 8 patients. In the other 25 patients with the tangential view showed the posterosuperior screw completely contained in the femoral neck, the average distance between the posterosuperior screw and the posterior femoral neck cortex was 5.48 ± 1.26 mm under the standard lateral view and 2.76 ± 1.08 mm under the tangential view, with a statistically significant difference between the two groups (p < 0.05). Post-operative CT demonstrated that the femoral neck screws were completely contained in the femoral neck in these 25 patients. Intra-operative tangential view of 150° can effectively identify the posterosuperior screw IOI in the cannulated screws fixation of femoral neck fractures. Based on our study, we highly recommend the tangential view as a routine intraoperative fluoroscopic angle to detect the posterosuperior screw IOI.

A Novel Fluoroscopic View for Improved Assessment of the Safety of the Posterosuperior Screw in Femoral Neck Fracture Fixation

BACKGROUND

The purpose of the present study was to determine specific fluoroscopic views of the femoral neck to accurately identify partially extraosseous ("in-out-in"; IOI) placement of the posterosuperior screw for fixation of femoral neck fractures.

METHODS

A 3.2-mm guide pin was placed in the posterosuperior aspect of 2 synthetic femur models: 1 entirely intraosseous and 1 IOI. Sequential fluoroscopic images were made at 5° intervals in order to identify which fluoroscopic projections identified IOI guide pin placement. These images were utilized to inform screw placement and assessment in the second phase of the study, which involved the use of cadaveric specimens. In Phase II, the posterosuperior screw of the inverted triangle was placed in 10 cadaveric specimens with use of a standard posteroanterior fluoroscopic view and 1 of 2 lateral views, either (1) neck in line with the shaft, i.e., 0° lateral; or (2) a -15° rollunder view. The final fluoroscopic views (i.e., the posteroanterior and multiple lateral and oblique views) were randomized and blinded for review by 10 orthopaedic residents and 5 attending orthopaedic traumatologists. Specimens were stripped of soft tissue and inspected for screw perforation.

RESULTS

Overall accuracy of respondents was 68.8%, with no difference between the attending traumatologists (71.8%) and resident surgeons (67.4%; p = 0.173). Interobserver reliability was moderate (κ = 0.496). Dissection identified that 4 (40%) of 10 screws were extraosseous. All of the extraosseous screws were placed with use of the 0° lateral view. The -15° rollunder lateral view was the most sensitive (81.7%) and specific (92.2%) view for identifying IOI screw placement.

CONCLUSIONS

Surgeons often utilize the standard posteroanterior and 0° lateral fluoroscopic views to safely place screws; however, many of these screws are IOI. The addition of a -15° rollunder lateral view significantly improved identification of IOI screws in the posterosuperior femoral neck. Unidentified IOI screw placement may result in damage to the blood supply of the femoral head.

Avoid the In-Out-In Posterosuperior Femoral Neck Screw: The Use of the Piriformis Fossa Radiographic Landmark

OBJECTIVES

The most common screw placement across the femoral neck is the inverted triangle. The posterosuperior screw has a high incidence of cortical breach, creating an in-out-in (IOI) screw. This study examined the use of the radiographic landmark of the piriformis fossa (PF) to prevent screws being placed IOI. The hypothesis was that posterior screws placed below the PF inferior margin would prevent femoral neck cortex breach.

METHODS

Five bilateral cadaveric specimens were used to place 10 screws along the femoral neck posterosuperior cortex. On the AP view, 5 screws were placed in a traditional manner, below the femoral neck superior cortex but above the inferior margin of the PF (APF screws), and 5 were placed below the inferior margin of the PF (BPF). All 10 screws were placed inside the posterior cortex on the lateral view. After screw placement, each hip was dissected, and the femoral necks were evaluated for signs of cortical breach.

RESULTS

All screws placed below the PF inferior margin were contained within the femoral neck with no incidence of being IOI. All screws placed above the PF inferior margin breached the cortex to a varying degree. All screws were similar in relation to their distance from the posterior cortex on the lateral view, with the APF screws averaging 1.98 mm and the BPF screws averaging 1.82 mm (P value = 0.46).

CONCLUSIONS

Placing the posterosuperior screw of the inverted triangle caudal to the PF inferior margin on the AP view seems to avoid cortical breach during percutaneous screw fixation of femoral neck fractures.

Modified radiographic views to prevent the anterosuperior and posterosuperior bony violation during screw fixation of femoral neck fractures

INTRODUCTION

The standard anteroposterior and lateral fluoroscopic projections used during femoral neck fracture fixation provide a two-dimensional representation of the cephalocaudal and anteroposterior extents of the femoral neck. The radiographic representation differs from the actual extent of the femoral neck. The anterosuperior (AS) and posterosuperior (PS) surfaces of the femoral neck are at risk of bony breach by the fixation screws and that may get easily missed with standard fluoroscopic views. The current study aims at investigating the special fluoroscopy views, based on the orientation of the AS and PS surface of the femoral neck, that can help in the safe placement of screws near these surfaces without bony breach.

METHOD

A computed tomography-based analysis of fifty intact proximal femora was performed. The longitudinal axis of the proximal femoral shaft and the center of the femoral head were aligned along a common horizontal plane. The cephalocaudally constricted zone of the femoral neck was identified along its axis. The surface inclinations of the AS surface and the PS surface at the constricted zone of the femoral neck were measured in relation to the horizontal plane. The mean, standard deviation, overall range, interquartile ranges and gender-based variation of each of the two surface inclinations were measured.

RESULTS

The mean surface inclinations of the AS surface and the PS surface with reference to the horizontal plane were 55° ± 7.76° and 123.32° ± 7.88°, respectively. There were no significant side to side and male to female differences.

CONCLUSIONS

The modified radiographic views based on the surface inclinations of the AS and the PS surfaces can help in the localization of the critical zones of these surfaces which are at risk of bony breach with screw placement close to the surface. A prior fluoroscopic evaluation of these surfaces before guidewire placement can help in preventing the surface violation.

High incidence of "in-out-in" posterosuperior screws after cannulated screw fixation of femoral neck fractures

INTRODUCTION

Cadaveric models have demonstrated a high incidence of extraosseous "in-out-in" (IOI) posterosuperior screws after cannulated screw fixation of femoral neck fractures. The purpose of this study was to determine the incidence of IOI screws in vivo and to evaluate their association with osteonecrosis and revision surgery.

METHODS

A total of 104 patients with 107 hips with a pelvis computed tomography (CT) scan after cannulated screw fixation of a femoral neck fractures were included. Screw position was evaluated on postoperative radiographs and CT scan to determine if screws were IOI or all-in. Osteonecrosis and revision surgeries were documented.

RESULTS

IOI posterosuperior screws were identified on CT scan in 58 (54%) hips. On postoperative AP and lateral radiographs, IOI screws were a median (interquartile range) of 10 mm (7-11 mm) and 3 mm (0-4 mm) from the cortex, respectively. The sensitivity and specificity of radiographs to detect IOI screws was 39% and 92%, respectively. The incidence of osteonecrosis and revision surgeries in hips, with and without IOI screws, was 6% versus 6% [Odds ratio (OR) 1.1, 95% confidence interval (CI) 0.2-5.3] and 10% versus 10% (OR 1.0, CI 0.3-3.1), respectively; a true clinical difference cannot be excluded due to the width of the confidence intervals.

CONCLUSIONS

There was a high incidence of IOI posterosuperior screws on CT scans. Postoperative radiographs had a poor sensitivity for detecting IOI screws. A larger sample size is necessary to evaluate the association of IOI screws with osteonecrosis and revision surgery.

LEVEL OF EVIDENCE

Level III, comparative cohort study.