Improved control over implant anchorage under the use of the femoral neck system for fixation of femoral neck fractures: a technical note

Abstract

Background: The depth of bolt in Femoral neck system (FNS, DePuy Synthes, Oberdorf, Switzerland) is difficult to finely control as the length of the bolt is in units of 5 mm. Thus, this study introduces a method to control the depth of FNS bolt in analogue scale in patients with femoral neck fracture.

Methods: By the technique of control of reaming and retraction of bolt, the tip of implant could be positioned close to subchondral bone without harming it. The position of implant tip in four cases in which the introduced technique was applied was compared to that of eight cases where the standard technique was performed.

Results: The average tip-apex distance measured in the cases that underwent surgery using the suggested technique in this study was statistically significantly shorter than that measured in the cases that underwent surgery under manufacturer guidelines.

Conclusion: Even though the bolt of FNS is manufactured in the unit of 5 mm, the technique proposed in this study helps surgeons to adjust the depth of bolt for the fixation of femoral neck fracture using FNS.

Keywords: Femoral neck fracture; Femoral neck system; Fixation; Hip; Treatment.

Fig. 1

A Femoral neck system consists of bolt, plate, antirotation screw and locking screw. B Insertion handle and cylinder impactor. The photographs were taken by the authors

Fig. 2

After the depth of central guide wire embedded in the femoral bone is measured, the size of bold is selected which is next longer construction size. The photographs were taken by the authors

Fig. 3

After reaming to target depth under a fluoroscopy, insert bolt and plate by insertion handle. The white arrow indicates black screw which combines the insertion handle, plate, and bolt. The black arrow indicates that plate does not contact with lateral cortex of femur. The photographs were taken by the authors

Fig. 4

Loose the black screw and impact the plate using cylinder impactor. It makes contact between plate and lateral femoral cortex. The white arrow indicates loosen black screw and the black arrow indicates contact between plate and lateral femoral cortex. The photographs were taken by the authors

Fig. 5

Insert distal locking screw, taking care not to insert eccentrically into the subtrochanteric area. The photographs were taken by the authors

Fig. 6

During the impact for contact between plate and lateral femoral cortex, bolt could be pulled out from target depth. In this case, bolt can be inserted back to the target position by tightening the black screw. The white arrow indicates the tightened the black screw. The photographs were taken by the authors

Fig. 7

A Insert antirotation screw. B An immediate postoperative radiograph of in a 54-year-old male patient with femoral neck fracture who was treated with the Femoral neck system. The photographs were taken by the authors

Fig. 8

Indraoperative radiographs of the case shown in Fig. 7B show the surgical procedure for femoral neck fracture using the Femoral neck system. A After closed reduction using a Steinmann pin, a guide pin was inserted and reaming was performed. B The femoral neck system inserted with an insertion handle. According to our technique, the plate could not be contacted with the lateral femoral cortex (white arrow). C To reduce gap between plate and lateral femoral cortex (white arrow), the black screw was loosened and the plate was impacted. D After then, locking screw was inserted. The photographs were taken by the authors

Fig. 9

The radiographs show the connection between plate of FNS and insertion handle by tightening of black screw. A The white arrow indicates the slit for connecting with plate. If the black screw is completely loosened with insertion hand, plate can be disconnected from insertion handle. B The white arrow means that plate slit is blocked by metal portion of black screw. If the black screw is tightened even a little, plate cannot be disconnected from handle. The photographs were taken by the authors

Fig. 10

A The white arrow show plate slit is not blocked by metal when the black screw is completely loosened. B The white arrow show plate slit is blocked by metal when the black screw is tightened even a little. It makes prevention of disconnection between plate and handle. The photographs were taken by the authors