Prevention Strategy of Intra-articular Screw Penetration During Internal Fixation of Femoral Neck Fracture

doi:10.21203/rs.3.rs-2578184/v1

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Prevention Strategy of Intra-articular Screw Penetration During Internal Fixation of Femoral Neck Fracture

https://doi.org/10.21203/rs.3.rs-2578184/v1

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Objective: This study obtains a specific fluoroscopic view by using geometric methods, which can detect whether there is unrecognized joint penetration (UJP) during the operation.

Methods: A retrospective analysis was conducted including 52 patients with femoral neck fractures who underwent internal fixation with cannulated screw at the Department of Orthopedics of the xxx from January 2021 to June 2021. The specific fluoroscopic view that can detect the UJP is obtained by using the geometric method and correction formula. The accuracy and effectiveness of this special fluoroscopic view acquisition method were verified by preparing four femoral models of UJP.

Results: There were 21 patients (40.38%) with unrecognized screw penetration, and 5 patients (9.62%) occurred UJP. Among them, 3 patients occurred in the anterosuperior (AS) area (5.77%), 1 patient in the posterosuperior (PS) area, and 1 patient in the posteroinferior (PI) area (1.92%). In the research and verification of special fluoroscopic views, the lateral view was set as 0°, and the specific fluoroscopic view θ= arctan (M₁O ′/M₂O ′), if the screw is located in the anteroinferior (AI) and PS regions of the femoral head, it is a - θ °rollunder lateral view; If the screw is located in the area of AS and PI femoral head, it is a θ °rollover lateral view. In the validation experiment, using the above method, the UJP model of the four regions can find screw penetration in the specific fluoroscopic view.

Conclusion: In this study, a special fluoroscopy view can detect whether there is screw penetration during internal fixation of femoral neck fracture and effectively reduce the incidence of UJP.

Health sciences/Diseases

Health sciences/Diseases/Trauma

fracture

femoral neck fracture

internal fixation

cannulated screw

intraoperative fluoroscopy

unrecognized joint penetration

Hip fractures cause 4.5 million disabilities globally every year, of which femoral neck fractures account for about 53%¹. Similarly, femoral neck fracture is a common injury in orthopedics. For elderly patients with non-displaced fractures and young patients who are not suitable for joint replacement, closed reduction and internal fixation with cannulated screws is the best treatment. This surgical method usually uses 3 screws placed in a parallel inverted triangle configuration, which has always shown good results in terms of minimally invasive and early rehabilitation and has certain advantages^2,3. The postoperative effect of internal fixation is generally affected by many factors, including reduction, internal fixation position, fixation time, and other factors. Typically, the depth of screw insertion is considered to be a critical factor in determining the stability of reduction and the maintenance of reduction. Biomechanical studies suggest that the ideal implantation depth is still controversial. It is widely accepted that a tip-apex distance of less than 25mm can provide stable fixation⁴. Several studies have demonstrated that the biomechanical properties of long screws provide superior fixation in young patients with femoral neck fractures^5,6. However, proximity to the subchondral surface increases the risk of screw penetration out of the femoral head.

In regions of complex anatomies, such as the hip and spine, bony structures superimpose on one another, thus complicating orientation and correct assignment. Many publications have discussed misplaced implants in these areas, e.g., those by Hernigou et al. and Mao et al. on misplaced screws in the femoral neck^7,8, Rommens et al⁹. on iliosacral screw fixation, and Marc et al.¹⁰ on pedicle screw placement in lumbar vertebrae, Jia et al.¹¹ on pedicle screw placement in the proximal humerus. In internal fixation with cannulated screws for femoral neck fracture, generally, surgeons use the AP and lateral fluoroscopic views to determine whether there is screw penetration, whether intraoperative or postoperative. However, using only these two views is limited, and not all screw penetration can be detected. When the screw appears to be in the head and very close to the surface of the head on fluoroscopy, the screw may have penetrated through the head into the joint. Previous literature described the situation of UJP during the operation and reported its incidence of 8% and 8.3%, respectively^7,12. UJP during the operation leads to cartilage injury, iatrogenic intra-articular penetration, secondary hip osteoarthritis, and osteonecrosis, resulting in hip pain and functional disability^7,12−15. The occurrence of UJP is also encountered in our clinical practice.

The placement of screws during the operation is usually evaluated by C-arm fluorescence views. However, the AP and lateral X-ray images routinely used can only show two-dimensional information about three-dimensional objects, and the femoral head will inevitably form a "shadow part" in the AP and lateral view¹⁶. We simplified the femoral head into a sphere, which in AP and lateral views was the projection of two cylindrical images, respectively. The overlap between two identical vertically intersecting cylinders formed Steinmetz Solid (SS)⁷. Screws contained in the head in the AP and lateral views are necessarily located in the SS but are not necessarily limited to the femoral head itself, while the head is an inscribed sphere of the SS, and therefore, it can cause the situation of intraoperative UJP. (See Fig. 1)

For stability of fixation, the currently accepted technique is to place the screws as close as possible to the subchondral bone, and we cannot shorten the length of the screws or decrease the number of screws to prevent UJP. Therefore, it is necessary to find reliable fluorescence techniques to detect screw penetration. However, there is no objective, reproducible and reliable method for intraoperative verification of whether the cannulated screw penetrates the femoral head and femoral neck. The purpose of this study was to find out which specific fluorescence view can accurately assess whether the screw penetrates the femoral head into the joint cavity.

Clinical Information

This study was approved by the Clinical Research Ethics Committee. The data of 52 patients with femoral neck fractures who underwent internal fixation with cannulated screw in department of orthopedics from January 2021 to June 2021 were collected, including general information about the patient, preoperative, intraoperative, and postoperative AP and lateral radiographs, and postoperative CT scans. Postoperative CT scans (including 2D and 3D) were the gold standard for detecting whether the screws penetrated the femoral head. (See Fig.2)

Exploration of specific fluoroscopic views of UJP

To simplify the geometric analysis and reproducibility, we consider the femoral head as a sphere¹⁷. At the same time, we defined the AP and lateral views of the hip joint. The femoral was placed horizontally and the posterior femoral condyle was placed flush with the horizontal plane, and the image intensifier was placed according to the 45° insertion angle routinely used intraoperatively. AP view is defined as the view of the hip with the image intensifier perpendicular to the plane formed by the femoral neck axis and the axis of the femoral shaft. The lateral view is defined as the view in which the femoral head, femoral neck axis, and axis of the femoral shaft are in a straight line. Thus, the influence of the femoral anteversion angle is eliminated and the angle of the lateral view is defined as 0°. All special fluoroscopic views were obtained by rotating the lateral 0° view with the femoral neck as the axis. Positive values were utilized to define rollover views, and negative values were used to define rollunder views.

To correlate the AP and lateral 0° views, a magnification correction is required, TOD=TOD_m (TOD is the actual distance from the screw tip to the femoral neck axis, TOD_m is the distance from the screw tip to the femoral neck axis measured on the radiograph, Da is the actual diameter of the screw, and Dm is the screw diameter measured on the radiograph).

UJP can only occur from four regions: the anterior superior（AI）, anterior inferior（AS）, posterior superior（PI）, and posterior inferior（PS）of the femoral head. （See Fig.3A）Let the center of the ball of the femoral head be O, the tip of the screw be point M, and L is the axis of the femoral neck. The plane S is perpendicular to both the AP and lateral views, and S is also a transverse view of the femoral neck axis. In AP view, the projection of the screw tip point M is set as point M₁, and the femoral neck axis L₁ past the center of the circle (sphere), makes the vertical line from point M₁ to line L₁ and intersects at point O′; therefore, points M, M₁, and O′ are in the plane S. Similarly, in the lateral view, let the projection of point M be M₂, make a parallel line L₂ of the femoral neck axis over the center of the circle (sphere), make a vertical line from point M₂ to line L₂ and intersect at point O′′. The parameters of AP and lateral views are combined by the magnification correction formula, so O′′ is O′, L₁ and L₂ are L, and the points M, M₁, M₂, O′ are in the plane S, and a rectangle can be formed by these four points, and the lengths of M₁O′ and M₂O′ are the distances from the tip of the screw to the neck axis after correction and magnification, respectively, and the lengths of M₁O′ and M₂O′ can be measured intraoperatively. At the same time, the C-arm rotates on the axis of the femoral neck (x-axis) and the rays are parallel to the plane S. Therefore, we can expand the mathematical algorithm in this plane and use trigonometric functions to calculate the tangential direction of the point M in the sphere, and the angle of this direction is the specific fluoroscopic view for detecting UJP. (See Fig.3B)

Verify the feasibility and accuracy of special fluoroscopic view

To verify the practicality and accuracy of this detection method, we used a 3.5-mm K-wire to place the artificial femoral and penetrate the head according to the routine intraoperative operation and established four models of UJP in four regions, AI, AS, PI, and PS, respectively, while the K-wire of all four models was contained within the head under the standard AP and lateral 0°views. In the verification process, the above method is used to calculate a special fluoroscopic view according to the corrected and enlarged parameters of the standard AP and lateral 0°views of established models to verify whether UJP can be detected in this view. (See Fig.4 A and B)

Clinical data analysis

All femoral neck fractures were treated with closed reduction and internal fixation. Three cannulated screws were placed in an inverted triangle. A total of 52 patients were collected in this study, with a mean age of 63 years (27-92 years), of whom 21 patients presented with UJP and partial extraosseous of the femoral neck ("in-out-in"; IOI), 8 males and 13 females. There were 6 cases of high-energy injury (collision) and 14 cases of low-energy injury (fall); 1 case of punch injury (combined with ipsilateral femoral fracture) and 20 cases of simple femoral neck fracture; 12 cases on the left side. Postoperative AP and lateral views showed that the cannulated screws were contained within the head, while CT identified screw penetration through the femoral head. The incidence of cannulated screw penetration was 40.38%, of which 5 cases (9.62%) showed UJP, 3 cases occurred in the AS region (5.77%), and 1 case each in the PS and PI regions (1.92%). In addition, 4 cases (21.15%) of FNFs patients with UJP were AO/OTA 31-B1.1 and 31-B1.2, 1 case was 31-B3.3.

Special fluoroscopic view and their verification

We use the mathematical algorithm, in the plane S formed by M, M₁, M₂, O′, the line through the point M and perpendicular to O′M is the desired tangential direction. Let the lateral view direction be 0°, then the angle of special fluoroscopic view is θ = arctan (M₁O′/ M₂O′) that can detect UJP (M₁O′ and M₂O′ are the corrected distance from the screw tip to the femoral neck axis in the AP and lateral view, respectively) (Note: arctan is the basic arctangent function, which can be found in one step by the intraoperative assistant using a simple calculator). If the screw is located in the AI and PS regions of the femoral head, it is a - θ° rollunder lateral view; if the screw is located in the AS and PI regions, it is a θ° rollover lateral view. (See Fig.3B) In the validation experiment, a special fluoroscopic view was calculated using the above method based on the correction and magnification parameters of the standard AP and lateral 0° view of the established model, using which UJP could be detected. (See Fig.4)

In recent years, the aging of society and the rapid development of the transportation industry have led to the rising incidence of femoral neck fractures in elderly and young patients. Internal fixation with cannulated screws has become the main treatment for elderly patients with non-displaced fractures and young patients who are not suitable for joint replacement. Intraoperative fluoroscopic visualization is a prerequisite for ensuring a safe screw trajectory. Through clinical practice and analysis, we found that the two-dimensional images provided by fluoroscopy fail to display the three-dimensional information completely intraoperatively, which can cause screws to penetrate the femoral head or femoral neck without being known, and UJP is a common complication of this internal fixation modality, which can cause significant limitation of motion, hip pain, osteoarthritis, and femoral head necrosis. Noordeen et al. ¹² earlier found that the incidence of intraoperative unrecognized screw penetration out of the femoral head was 8%. Hernigou et al. ⁷ found that the incidence of unrecognized screw penetration during surgery was 25%, of which the incidence of UJP was 8%, plus a 7% incidence of screw tips in the articular cartilage. UJP is more common in Garden-I hip fractures. Karray et al. ¹⁸ analyzed 91 cases of hip fracture treated with internal fixation and found that the incidence of UJP was 9.9%. In our study, the incidence of unrecognized screw penetration was 40.38%. The incidence of UJP was 9.62%, 5.77% in AS area, and 1.92% in PS and PI. In addition, the incidence of IOI was 30.77%. Therefore, the results of the clinical data showed that the AP and lateral views were insufficient to evaluate the head and cortical destruction by posterosuperior screws and other screws.

It is well known that UJP can cause cartilage damage, iatrogenic intra-articular penetration, secondary hip osteoarthritis, and osteonecrosis, resulting in hip pain and functional limitation. In addition, screw penetration may also lead to femoral head necrosis by interfering with the vascularization of the subchondral bone¹⁵. In addition, articular disruption subjects the subchondral bone of the femoral head to the pressure of hemarthrosis, which is a potential risk factor for osteonecrosis^13,14. In addition, there was a cartilage layer with a thickness of (2.4 ± 0.36) mm on the surface of the normal femoral head¹⁹. When the tip of the screw penetrates the subchondral bone but does not penetrate the cartilage layer, although it may not cause obvious hip pain and limited mobility in the early stage, the wear of the local cartilage may eventually make the tip of the screw actually penetrate through the joint cavity.

In general, whether intraoperative or postoperative, surgeons use the AP and lateral fluoroscopic views to determine whether there is screw penetration. However, using only these two views is limited, and not all screw penetration can be detected. Many scholars have identified this problem and tried to detect unidentified screws intraoperatively in a simple and effective way. Scott et al.²⁰ reported a case of unexplained hip pain in which no screw penetration of the femoral head was detected on both AP and lateral views, and then a special fluoroscopy view using a 25° posterior rotation of the contralateral pelvis was used to detect screw penetration of the femoral head. However, this special fluoroscopy view can only correctly and effectively identify screw penetration in this patient, and it cannot be applied to UJP of all patients. Nooredee et al.¹² reviewed 50 cases of hip fractures treated with internal fixation and found that up to 8% of patients may have UJP. They suggested placing the screws only 2/3 of the center of the femoral head to prevent penetration, but this is inconsistent with placing the screw within 3 mm of the endosteal surface of the neck cortex for better mechanical advantage^21–23. Mao et al.⁷ proposed an appropriate TED (TED = 7 mm) to reduce the risk of penetration by analyzing the geometric basis, which resulted in a near-zero risk of UJP. However, in internal fixation with cannulated screw for femoral neck fracture, the tip of the screw needs to reach within 5 mm of the subchondral bone to improve the fixation strength. Although this may be useful to reduce the risk of head perforation, it cannot delineate real-time intraoperative screw perforation. Zhang et al. used multiple fluoroscopes from different angles to detect the presence of UJP during intraoperative, but this method can only improve the detection rate, is not accurate, and also greatly increases the time of operation and intraoperative radiation exposure²⁴.

In our study, a special fluoroscopic angle was obtained using a geometric algorithm, and the presence of UJP was clarified by adding a fluoroscopic view of this special angle intraoperatively. This approach significantly reduces the incidence of screw penetration and significantly reduces radiation does and the time of operation. However, our approach still has certain shortcomings: first, the femoral head is considered as a sphere; second, intraoperative AP and lateral 0°view are not completely standard. Of course, intraoperative CT can solve this problem well, but the radiation dose to the patient and surgeon will be significantly higher. In addition, intraoperative CT technology is still limited in primary hospitals.

In conclusion, a special fluoroscopy view can detect whether there is screw penetration during internal fixation of femoral neck fracture and effectively reduce the incidence of UJP.

Acknowledgements

We appreciate all co-authors for their contributions to this study and the writing of this manuscript.

Authors' contributions

All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by Xiaopei Xu and Xin Lv. Xiaopei Xu wrote the first draft of the manuscript and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

Supported by Beijing Key Clinical Specialty Project

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Ethics committee approval was received for this study from the Orthopaedic Ethics Committee of Second hospital of Shanxi Medical University. The authors announce that all methods were performed in accordance with the relevant guidelines and regulations.

Informed Consent:

Written informed consent was obtained from the patients.

Consent for publications

Not Applicable (NA)

Competing interests

The authors declare that they have no competing interests.

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No competing interests reported.

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Prevention Strategy of Intra-articular Screw Penetration During Internal Fixation of Femoral Neck Fracture

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