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.

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 surger...

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 ha...

Materials

Name	Company	Catalog Number	Comments
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