Orthopedic Robot-Assisted Femoral Neck System in the Treatment of Femoral Neck Fracture

Summary

This article introduces a method of robot-assisted orthopedic surgery for screw placement during the treatment of femoral neck fracture using the femoral neck system, which allows for more accurate screw placement, improved surgical efficiency, and fewer complications.

Abstract

Cannulated screw fixation is the main therapy for femoral neck fractures, especially in young patients. The traditional surgical procedure uses C-arm fluoroscopy to place the screw freehand and requires several guide wire adjustments, which increases the operation time and radiation exposure. Repeated drilling can also cause damage to the blood supply and bone quality of the femoral neck, which can be followed by complications such as screw loosening, nonunion, and femoral head necrosis. In order to make fixation more precise and reduce the incidence of complications, our team applied robot-assisted orthopedic surgery for screw placement using the femoral neck system to modify the traditional procedure. This protocol introduces how to import a patient’s X-ray information into the system, how to perform screw path planning in software, and how the robotic arm assists in screw placement. Using this method, the surgeons can place the screw successfully the first time, improve the accuracy of the procedure, and avoid radiation exposure. The whole protocol includes the diagnosis of femoral neck fracture; the collection of intraoperative X-ray images; screw path planning in the software; precise placement of the screw under the assistance of the robotic arm by the surgeon; and verification of the implant placement.

Introduction

Femoral neck fracture is one of the most common fractures in the clinic and accounts for about 3.6% of human fractures and 54.0% of hip fractures¹. For young patients with femoral neck fractures, surgical treatment is performed to reduce the risk of nonunion and femoral head necrosis (FHN) by anatomical reduction and rigid internal fixation and to restore their function to the preoperative level as much as possible². The most commonly used surgical treatment is fixation by three cannulated compression screws (CCS). With the increase in patient requirements, especially in young patients, the femoral neck system (FNS) is gradually being used, which combines the advantages of angular stability, minimal invasiveness, and better biomechanical stability than CCS for unstable femoral neck fractures³.

Traditionally, the screws were placed freehand by surgeons under fluoroscopic intraoperative guidance. The freehand method has many shortcomings, such as inability to plan the path intraoperatively, difficulty in controlling the direction of the guide wire during drilling, damage to the bone and blood supply due to repeated drilling, and penetration of the screw through the cortex due to improper positioning. These factors can directly or indirectly cause postoperative complications, such as fracture nonunion, FHN, and internal fixation failure, which influence the functional prognosis⁴. The freehand method has also been associated with increased radiation injury to patients and surgeons from frequent fluoroscopies⁵. Therefore, determining the optimal screw entry point and precise screw placement during pre-operative planning are key to the success of the operation. In recent years, robot-assisted minimally invasive internal fixation has been used with increasing frequency in orthopedic surgery⁶, and it is widely accepted by orthopedic surgeons because of its high precision and its ability to reduce the operation time and radiation injury. We applied the robot-assisted orthopedic surgery system to assist in FNS fixation for the treatment of femoral neck fractures, which resulted in a more accurate and efficient screw placement process, a higher success rate of the screw placement, and better functional recovery.

Protocol

The present study was approved by the ethics committee of Honghui Hospital Xi'an Jiaotong University. Informed consent was obtained from the patients.

1. Diagnosis of femoral neck fracture by X-ray fluoroscopy

1. Identify patients who have a femoral neck fracture with tenderness or percussed pain around the hip joint, shortening of the lower extremity, limitation of the hip joint, etc.
2. Use an antero-posterior (AP) view and a lateral view of an X-ray fluoroscopy or CT scan to diagnose the femoral neck fracture.
3. Order FNS treatment for patients who are less than 60 years old and diagnosed with femoral neck fracture. Use these additional criteria for inclusion: fracture with a clear history of trauma; no history or evidence of metabolic diseases or pathological fractures; well-developed hip joint, with no manifestations of FHN and no deformity; a diagnosis of femoral neck fracture by an X-ray or CT scan.

2. Fracture close reduction, X-ray examination, and preparation of the robot-assisted orthopedic surgery system

1. After general anesthesia, conduct closed reduction of fracture by manual traction and adjustment.
   1. Restore the length of the affected limb by longitudinal traction with the surgeon holding the limb for traction, and restore the alignment of the fracture gap through limb rotation.
   2. Fix the limb to the traction bed (a kind of operation table that provides continuous limb traction) for continuous traction during the operation.
2. Examine the quality of the closed reduction by X-ray fluoroscopy. Restore the neck-shaft angle and alignment of the cortex in the AP and lateral views, and ensure that no angular deformities occur.
3. Before the operation, connect the components of the robot-assisted orthopedic surgery system-the workstation, the optical tracking system, and the robotic arm-with the C-arm X-ray machine. Log into the system, and record the patient's medical records.

3. Disinfection, image collection, and surgical path planning

1. After routine surgical disinfection, place a Schanz pin on the ipsilateral iliac wing, and fix the patient's tracer on the pin.
2. Put sterile protective sleeves on the robotic arm and C-arm. Assemble the positioning ruler (with the 10 identification points on the positioning ruler for the robot positioning system) with the robotic arm.
3. Position the C-arm X-ray machine centrally to the femoral neck, and put the robotic arm with the positioning ruler between the C-arm and the patient. Ensure that there is no obstruction of the optical tracking system, including the patient tracer and the robotic arm.
4. Collect AP view (the X-ray image intensifier is perpendicular to the plane of the patient) and lateral view (the X-ray image intensifier is perpendicular to the femoral neck channel plane) X-ray images containing the 10 identification points of the positioning ruler.
5. Import the AP and lateral view images into the workstation; the images must clearly contain 10 identification points and the entire proximal femur.
6. Perform surgical screw path planning on the software of the workstation.
   1. Locate the screw channel in the center of the femoral neck, with a neck-shaft angle of 130° and parallel to the long axis of the femoral neck on the AP and lateral views.
   2. Locate the tip of the screw 5 mm under the cartilage of the femoral head.

4. FNS placement and verification

1. Replace the positioning ruler to the sleeve on the robotic arm. Run the robotic arm to the position of the entry point according to the planned path. Make a 3 cm incision on the skin along the long axis of the femur with a knife, blunt separate the subcutaneous tissue, and insert the sleeve to contact the bone cortex.
2. Confirm the entry point and direction of the sleeve in accordance with the planned path. Fine-tune the path if necessary.
3. Drill the guide wire into the bone through the sleeve until it is 5 mm from the subchondral bone. Remove the robotic arm, and check the position of the guide wire by X-ray.
4. Ream the hole along the guide wire using a hollow drill bit, and insert the bolt and plate into the femoral head. Place the anti-rotation screw and locking screw.
5. Apply dynamic compression using the compression design of the FNS. The fluoroscopy verifies the FNS placement, with the bolt in the center of the femoral neck both on the AP and lateral views and 5 mm from the subchondral bone, and with the plate fitting the bone.
6. Suggest assisted passive hip flexion activities and active exercise of the knee and ankle joints post-operation. Perform follow-ups at 4 weeks, 8 weeks, 12 weeks, 24 weeks, 36 weeks, and 48 weeks postoperatively, with the weight-bearing time depending on the follow-up.

Representative Results

The robot-assisted orthopedic surgery system simulates the screw path virtually and assists in the precise placement of the screw, meaning this system has the advantages of being highly stable, having improved surgical precision and success rate, and having a lower risk of surgical trauma and radiation injury. Finally, the accuracy of the screw fixation results in a better clinical prognosis and a lower incidence of complications.

Patients diagnosed with a femoral neck fracture received surgery. Prophylactic anti-infection and anticoagulation treatments were used after the surgery. The patients carried out assisted passive hip flexion activities and instructed lower-limb strength training. Within 2 weeks after the surgery, the patients were allowed to perform active bending of the hip joint in bed. The patients could perform non-weight-bearing movements with the help of a walking stick after 4 weeks. X-ray examination was conducted at the follow-ups every 4 weeks; if the fracture line was blurred, the patients could carry out partial weight-bearing exercise. The patients could attempt full weight-bearing walking when the X-ray imaging showed that the fracture had healed. The hip function was assessed according to the Harris hip score system at the final follow-up (Table 1).

The pre-operation X-ray images of the femoral neck fracture are shown in Figure 1 (Figure 1A: AP view; Figure 1B: lateral view). Figure 2 illustrates that the fracture was reduced by closed reduction (Figure 2A,B) to a proper position (Figure 2C,D). The prepared robot-assisted orthopedic surgery system is shown in Figure 3. The collected X-ray images using the patient tracer (Figure 4A) and the positioning ruler (Figure 4B), with the positioning ruler between the C-arm and the patient (Figure 4C,D) are demonstrated, as well as the fluoroscopy images containing the positioning ruler (Figure 4E,F). Surgical path planning was performed on the software, and the screw channel was virtually displayed (Figure 5). The robotic arm ran in the planned direction (Figure 6A), the robotic arm assisted with the placement of the guide wire (Figure 6B), and the position of the guide wire was checked by X-ray (Figure 6C). Figure 7 shows the structure of the FNS (Figure 7A), the reaming process (Figure 7B,C), the placement of the bolt and plate, the anti-rotation screw, and the locking screw (Figure 7D–F). Figure 8 presents the verification X-ray images (Figure 8A: AP view, Figure 8B: lateral view) and the small incision on the skin (Figure 8C).

Figure 1: X-ray images of the patient. The pre-operation X-ray images of the femoral neck fracture of the patient. (A) AP view; (B) lateral view. Please click here to view a larger version of this figure.

Figure 2: Manual closed reduction of the fracture. The images show (A,B) manual reduction of the affected hip and (C) the AP view and (D) the lateral view of the X-ray images after reduction. Please click here to view a larger version of this figure.

Figure 3: The robot-assisted orthopedic surgery system. The system consists of the workstation (left), the optical tracking system (middle), and the robotic arm (right). Please click here to view a larger version of this figure.

Figure 4: Image collection. (A) The patient tracer; (B) the positioning ruler with the robotic arm; (C,D) the relative position between the optical tracking system (including the patient tracer and the robotic arm), the C-arm X-ray machine, and the positioning ruler; (E) the AP view and (F) lateral view X-ray images with the positioning ruler. Please click here to view a larger version of this figure.

Figure 5: Surgical path planning. Display of the virtual screw channel on the software. Please click here to view a larger version of this figure.

Figure 6: Robot assistance in the placement of the guide wire. (A) The robotic arm with the sleeve moves in the planned direction. (B) The guide wire is drilled into the bone through the sleeve by the surgeon. (C) Examination of the placement of the guide wire by X-ray. Please click here to view a larger version of this figure.

Figure 7: FNS placement. (A) The FNS consists of the bolt and plate (yellow), the locking screw (green), and the anti-rotation screw (blue). (B,C) Reaming along the guide wire. (D,E,F) The bolt and plate is inserted into the femoral head, and the locking screw and anti-rotation screw are placed. Please click here to view a larger version of this figure.

Figure 8: X-ray verification. The figure shows (A) the AP view and (B) the lateral view X-ray images of the fracture after dynamic compression. (C) The appearance of the wound. Please click here to view a larger version of this figure.

Table 1: Patient details. The table shows the characteristics, surgical information, and postoperative follow-up of all the patients. Fractures are classified according to the Garden classification⁷, and hip function is assessed using the Harris scoring system⁸. Please click here to download this Table.

Discussion

FNS is a method for fixing femoral neck fractures, which has the advantages of angular stability of the sliding hip screws and minimal invasiveness of the placement of the multiple cannulated screws. This method is less prone to screw cutting and irritation of the surrounding soft tissues. In Tang et al.'s study⁹, compared with the CCS group, patients in the FNS group had lower rates of no or mild femoral neck shortness, shorter healing times, and higher Harris scores. Biomechanical studies have shown that FNS has better biomechanical properties than CCS³. FNS is similar to CCS intraoperatively in that both require accurate screw placement through the femoral neck. In traditional surgery, the screw is placed freehand by surgeons under fluoroscopy; intraoperatively, the percutaneous manipulation, visual deviation, and freehand instability could lead to an error of the actual position from the ideal position. Repeated radiology exposure increases the radiation damage to both patients and surgeons. Furthermore, complications in younger patients, such as nonunion, FHN, and early implant failure, are associated with fixation techniques, and these have an incidence rate of up to 28%¹⁰. The accuracy of screw fixation directly affects the strength of screw fixation and the healing rate of femoral neck fractures¹¹.

With the development of computer navigation systems and medical imaging presentation technology, researchers have achieved good clinical prognosis through computer navigation systems, especially in robot-assisted orthopedic surgery system fixation for femoral neck fractures, which is superior to the traditional procedure in terms of having better surgical precision and a higher success rate, as well as reducing surgical trauma and radiation injury^12,13.

The robot-assisted orthopedic surgery system has the advantage of accurate navigation and positioning. The critical steps in the operation are image collection, surgical path planning, and guide wire insertion. The identification points and the intraoperative biplanar X-ray fluoroscopic images are digitized to form a spatial correspondence so that the surgeon can intuitively plan the path of the screw in the software. Additionally, the robotic arm provides precise spatial positioning for the placement of the screw, with accuracy up to the millimeter level. Zwingmannm et al.^14,15 found that the malposition rate of the conventional method was 2.6% and the revision rate was 2.7%, while the malposition rate of the navigation-assisted technique was 0.1% to 1.3%, and the revision rate was 0.8% to 1.3%. Meanwhile, robotic navigation implantation is highly stable, with a safety boundary in the operation, which greatly reduces the risk of vascular and nerve injuries caused by deviations in the screw placement.

We used the robot-assisted orthopedic surgery system to assist the FNS placement process, and the screw was placed into the corresponding anatomical site accurately and stably. With the assistance of the robot, the resident surgeons could place the screw more quickly and accurately. The learning curve can be shortened with the help of the robot, and individuals can become skillful in the robot-assisted technique through several surgeries. Additionally, the difference in surgical results due to differences in the technical levels of the surgeons can be eliminated. The length and diameter of the screws can be planned in advance to avoid injury to the joint and blood vessels caused by the screws penetrating the femoral head. This reduces the incidence of postoperative traumatic arthritis and FHN.

In the future, we will use the robot-assisted orthopedic surgery system to assist the placement of internal fixation screws in situations such as a high Pauwels grade, posterior inferior comminution, and combined deformities, which make the biological and biomechanical environment for fracture healing more challenging¹⁶. In these situations, precise fixation is required to reduce the incidence of postoperative complications. With the application of the robot-assisted orthopedic surgery system for the internal fixation of screws for femoral fractures, the surgeon dominates the operation planning, obtains the best surgical path, and achieves the highest accuracy and efficiency for implant placement. This method is more conducive to fracture healing, allowing early rehabilitation and a good prognosis for overcoming minor surgical injuries.

However, there are some limitations to robot-assisted internal fixation placement of femoral neck fracture screws. First, the surgeon needs to have experience in traditional surgical techniques (open/closed reduction and internal fixation), so that unexpected situations can be resolved without robot assistance. Second, the basic principles of robot work and the correct completion of image collection require a period of training. The surgeons need to work together to complete the programmed steps, and the operating time could be reduced by improving proficient cooperation. Third, the sleeve receives high lateral stress by the soft tissue and may lead to deviation in the entry point¹³. The tension of the soft tissue around the sleeve could be reduced by blunt separation before the sleeve insertion. Finally, accurate screw placement depends on the spatial position of the surgical site matching the image; various factors can lead to a change in the spatial position or the relative displacement of the patient tracer and the surgical site, which is called image drift¹⁷. The surgeon should be aware of image drift during the operation and verify it. The images need to be collected again if necessary.

Orthopedic robot-assisted FNS for femoral neck fractures is a time-efficient and less invasive procedure with a low rate of postoperative complications. This method could improve the precision of screw placement and reduce the radiation damage during surgery while shortening the learning process for young surgeons.

Materials

C-arm X-ray	Siemens	CFDA Certified No:20163542280	Type: ARCADIS Orbic 3D
Femoral neck system	DePuy, Synthes, Zuchwil, Switzerland	CFDA Certified No: 20193130357	Blot:length (75mm-130mm,5mm interval), diameter (10mm); Anti-rotation screw:length (75mm-130mm,5mm interval,match the lenth of the blot), diameter (6.5mm); Locking screw:length(25mm-60mm,5mm interval),diameter(5mm)
Robot-assisted orthopedic surgery system	Tianzhihang, Beijing,China	CFDA Certified No:20163542280	3rd generation
Traction Bed	Nanjing Mindray biomedical electronics Co.ltd.	Jiangsu Food and Drug Administration Certified No:20162150342	Type:HyBase 6100s