locking screw nail = magnet - tracker - upto 20mm - gren light red light =



  1. https://www.blogger.com/blogger.g?blogID=1600717268638399529#editor/target=post;postID=5853913611032932414
  2.  magnet in nail - they call it positioning magnet














  3.  targeting device


  4. The 2nd-Stage Targeting
    The 2nd-stage targeting device consists of a transparent baseboard with three aligning lines, conductive rings, three magnetic pins with rotary joints, and an indicator, as shown in Figure 3(a). The three symmetrically placed magnetic pins can rotate freely and point to the positioning magnet inside the nail. The three magnetic pins act as three mechanical switches in operation, which are linked to the indicator by conductive rings and used to indicate alignment or misalignment by a light signal. Each magnetic pin can rotate to the strongest gradient direction of the nearby magnetic field from the positioning magnet inside the nail. The magnetic pin has two equal parts with a rotary joint in the middle to eliminate the gravity effect in operation, which can provide a flexible and unrestricted operation method in surgery. The transparent baseboard with three aligning lines provides a clear field of vision to observe the motion of the magnetic pins, which is used to guide the device to rapidly and accurately identify the alignment status. The indicator consists of two light-emitting diodes (LEDs) and a relay with DC voltage through a simple circuit, as shown in Figure 3(b), to indicate the alignment (green light) or misalignment (red light) state directly. The LED signal can help the user to determine alignment state in a more intuitive way.
    In the proposed design, when the 2nd-stage targeting device misaligns with the positioning magnet either in position or direction, one or more pins will contact with the conductive ring on the transparent baseboard to turn on the red LED, as shown in Figures 4(a) and 4(b), respectively. By moving the guiding device around the positioning area identified by the 1st-stage targeting device, once three magnetic pins reach to symmetrical positions without contacting the conductive ring on the upper transparent baseboard, as shown in Figure 4(c), the green LED instead of red will be switched on. The 2nd-stage targeting device is considered to be aligned with the positioning magnet inside the nail. Then, the drilling process can be performed through the drilling hole at the center of the 2nd-stage targeting device.
    The transparent baseboard with alignment lines can provide a clear field of vision to observe the motion of the magnetic pins. When the guiding device aligns with the invisible positioning magnet in the nail, the projection of the three magnetic pins should overlap the aligning lines, as shown in Figure 5(a). When the guiding device misaligns with the magnet either in position or direction, one or more pins will deviate from the aligning line on the transparent baseboard, as shown in Figure 5(b). Then, the adjustment of the device should be continued.

    3. Detail Design

  5. Due to the space limit of the interlocking nail, the positioning magnet made of NdFeB (N52, Asia Magnets Co. Ltd.) with a 9 mm outer diameter, a 5 mm inner diameter, and 7 mm high is designed to place into a commercial interlocking nail with inner radius of 10 mm and outer radius of 12 mm. The following designs and tests on the 1st-stage and the 2nd-stage targeting devices are all based on this positioning magnet. However, the maximum operating temperature of the positioning magnet used in this work should be less than 140°C [20, 21]. Therefore, in the sterilization process of the positioning magnet, the operating temperature should be less than 140°C to main the strength of positioning magnet. For example, some clinical low-temperature sterilization processes, such as EO sterilization, activated glutaraldehyde sterilization, and plasma sterilization, are operating below 140°C
  6. IMPLANTING IN PIG TIBIA




     
  7. The two-stage targeting with drilling tests is conducted by two different persons with five attempts each, and 100% successful rate is achieved in all these 10 attempts. The time to finish the 1st-stage targeting process, the 2nd-stage targeting process, and the drilling process is between 7–11 seconds, 29–215 seconds, and 38–40 seconds, respectively, as listed in Table 2. The total time used in the entire process is between 95–300 seconds, less than 5 minutes.
  8. The 2nd-stage targeting device can accurately identify both the position and direction of the screw hole. From the accuracy tests, the experimental results show that alignment accuracy of the proposed 2nd-stage targeting device in position is ±2.1 mm and in direction is ±7 degrees.
  9. However, the proposed devices can be further improved, such as the working distance. Currently, the maximum working distance is around 20 mm, which may be sufficient for nailing surgery with thin soft tissue, such as tibia nailing, but not enough for nailing surgery with thick soft tissue, such as femoral nailing
    1. BUT TIBIA NAIL IS OFTEN 8 MM DIAMETER AND MAGNET MAYNOT FIT INSIDE NAIL 


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