A novel device for accurate placement of guide wire in cannulated screw xation of femoral neck fracture: A pilot study

Background: Accurate placement of cannulated screws is the key to stable xation of the femoral neck fracture. A novel device was developed to improve the accuracy of screw placement. Methods: 20 synthetic femoral bones were divided into conventional technique group and the experimental group. Three Kirschner wire were inserted into the femoral neck fracture by conventional technique or by the novel guide device. The operative time, total drilling attempts and uoroscopic frequency were evaluated. Results: By using the guide device, the uoroscopy and operation time of the experimental group were shorter that of the conventional method. The total drilling attempts with the novel guide device were signicantly lower than the conventional technique group. Conclusion: This device can help trauma surgeons shorten the surgical time and reduce radiation exposure time. The use of this guide device can make screw xation for femoral neck fracture easier.


Background
Femoral neck fracture is a common hip fracture in orthopedics. Internal xation is preferred for femoral neck fracture in young people and non-displaced femoral neck fracture in elderly people with good physical condition [1,2]. Cannulated screws has been an accepted implant among several implants which have been used for femoral neck fracture [3,4,5]. Placing three cannulated screws in parallel with the inverted triangle can provide better biomechanical stability [6]. However, it is not easy for the surgeons to place screws at the right position. Accurately to insert guide wires accounts for a signi cant proportion of the total uoroscopy and operative time.
In this study, the authors designed a novel device for accurate placement of guide wires in cannulated screw xation of femoral neck fracture. The purpose of this study was to demonstrate the effectiveness of the device.

Materials And Methods
The device consists of two parts, the aiming part and the xing part (FIG. 1). The aiming component is a 50-degree angle structure welded by two small stainless steel plates. Two mesh plates with equal size are vertically welded on the surface of a small steel plate. The holes in mesh plates are arranged in parallel columns and rows. The hole diameter is 2.5mm, and the hole margin is 2mm. The corresponding holes of the mesh plates form parallel guide channels go pass guide pin. The other plate is welded with a 3.5mm Kirschner wire. The xing assembly is made of two steel buckle welded vertically.
Twenty synthetic right femur specimens with similar bone structure and mechanical characteristics to human bone were obtained from Hangzhou Osborn Technology Co., LTD. The femurs were covered with sponge to simulate soft tissue. They were randomly divided into conventional technology group and experimental group. All operative procedures were performed by two attending orthopaedic surgeons.

Surgical Technique
In the conventional technology group: the rst guide pin was drilled into the femoral neck at the insertion point 5cm below the femoral greater trochanter. Based on anteroposterior and lateral images, the guide pin was adjusted until it was in the inferocentral position of the femoral neck. Then use a parallel guide to place the posterosuperior and anterosuperior pins.
In the experimental group: a 3.0mm Kirschner wire was drilled vertically into the lateral cortex of the upper femur, connecting the guide device and the reference guide pin (Figure 2A). Fluoroscopic imaging was performed to ensure that the reference guide pin was in perfect position on anteroposterior view ( Figure   2B) and parallel to the central axis of the femoral neck on lateral view ( Figure 2C This was carried out using SPSS18.0 software (SPSS Inc., Chicago IIIiosi) using chi-squared testing. Data are presented as mean± standard deviation or numbers, as appropriate The level of signi cance was set as a p value<0.05.

Results
The results were presented in the Table1.The operative time with the novel device were signi cantly lower than the operation with the conventional technique (p 0.05). The uoroscopic frequency and total drilling attempts were also signi cantly lower in the operation with the novel device (p 0.05 ).

Discussion
Closed reduction and internal xation have become the standard methods for the treatment of femoral neck fractures in patients 60 years of age or younger. Fixation with three parallel cannulated screws placed in an inverted triangle con guration, is a common method for femoral neck fracture [7]. If complication didn't occur, the patient can resume normal activities. The inverted triangle con guration is effective in reducing the rate of nonunion and implant failure [8]. However, accurate guide wire placement necessitates high requirement for the surgeon and requires more uoroscopic and operative time. So, we developed this device to make it easier.
The conventional method of screw placement for femoral neck fractures is mainly performed by surgeons with experience under fluoroscopic monitoring. During the screw xation of femoral neck fracture with closed reduction, the femoral neck was not exposed and the desired position was not easily obtained due to the lack of necessary reference during the placement of the rst guide pin, which often requires multiple drilling for success. Multiple drilling not only resulted in prolonged operation time, increased tissue damage, and increased doctor-patient exposure time to the X-ray radiation, but also can affect the mechanical strength of femoral neck fracture xation [9].
By using the guide device, the uoroscopy and operation time of the experimental group were shorter that of the conventional method. This is because in the experimental group, the three guide wires in the femoral neck can be inserted and observed at the same time with one uoroscopy, while in the control group, each guide wire needs to be uoroscopy separately. This present study demonstrated three advantage of the device. The rst advantage is that the guide wires were accurately inserted in the femoral neck at one time in the experimental group. The hole spacing is 2mm in the device, so the position of the guide wires can be slightly adjusted to achieve the best position. The guide channels in the device are parallel. This ensures that the guide wire can be placed in a parallel inverted triangle con guration to the femoral neck. A second advantage is programmed surgical procedures. The surgeon's experience was not important in the experimental group. When the reference guide wire is in the exact position, the guide wire passing through the guide channel must be parallel to the central axis of the femoral neck. The surgeon only needs to select the right channel to insert the three guide wires onto the lateral cortex of the femur in an inverted triangle con guration. The third advantage is that the femoral cortex was not drilled frequently in the experimental group. Drill attempts on the femoral cortex were no more than three times. So the device was easy to operate.
Other researchers have developed guides to accurately place Kirschner wires. Yin et al. demonstrated a novel guidewire aiming device to improve the accuracy of guidewire insertion [10]. However, the operation was complicated. The navigation systems could improve accuracy [11,12,13], but the higher costs of the special instruments and increased radiation and operative time limited their clinical use [14].

Conclusions
This guide device can signi cantly improve the accuracy of injection, reduce tissue damage, shorten the operation time and reduce the amount of X-ray radiation. The operator's experience was not important.
The use of this device can make percutaneous compression cannulated screw xation for femoral neck fracture easier.
We believe this guide device can help to promote screw xation technique in third world countries. This is helpful for an inexperienced hand. However, the utility of this device should be further veri ed in clinical practice. Table   Table 1: Comparison of results in the two groups. The values are given as the mean and the standard deviation. Statistical significance was defined for p≤0.05.

Result
Experimental group Conventional group P