Tze-Hong Wong

Electromagnetic/Magnetic-Coupled Targeting System for Screw-Hole Locating in Intramedullary Interlocking-Nail Surgery

At present, intramedullary interlocking nails are widely used for bone-fracture fixation in orthopedic surgeries. Surgeons often use X-ray imaging to find the actual location of the distal screw-holes of the nail after the nail is inserted into the medullary canal of a bone for fixation. Thus, the patients and medical team are inevitably exposed to radioactivity. In this paper, we report a radiation-free electromagnetic/magnetic-coupled targeting system to locate the distal screw-holes of the nail used in interlocking-nail surgery. The targeting system consists of a c-shaped electromagnet with a pick-up coil, a highly permeable curved silicon-steel strip embedded on the nail, a guiding mechanism, and electronic measuring instruments. An alternative current is applied to the electromagnet to generate a uniform magnetic field/flux in the electromagnets air gap. When the nail inserted into the medullary canal of a bone is scanned through or rotated in the air gap of the electromagnet, the magnetic flux in the air gap is influenced by the silicon-steel strip embedded on the nail. The variation of the magnetic flux induces a voltage response in the pick-up coil due to electromagnetic induction. The pattern of the voltage response is analyzed to establish a criterion for screw-hole targeting. The results obtained using this criterion reveal that the maximum targeting error of the location and orientation targeting for a screw-hole with a diameter of 5 mm is <;2 mm and 10°, respectively. Thus, the system/approach is sufficiently simple and accurate to be used by surgeons in clinical surgery.

An electromagnetic-induction approach for screw-hole targeting in interlocking-nail surgery

We report a novel approach for targeting screw-holes of an intramedullary nail in a long-bone fracture surgery. The approach utilizes the electromagnetic induction to avoid over exposure of radioactivity which is the critical issue in conventional X-ray-imaging targeting method. Based on the approach, we fabricate a targeting system. The targeting system consists of a c-shaped electromagnet, detecting-coil, guiding-mechanism, and measurement electronics. When a voltage is applied to the electromagnet, magnetic flux is generated in the air gap of the electromagnet and subsequently detected by the coil. When the flux is detected by the coil, a voltage response is induced in the coil. When a nail in a bone is scanned through the air gap of the electromagnet, the flux is influenced due to a discrepancy of the permeability between the location with and without the hole of the nail. The influenced flux induces different voltage response in the coil. Through analyzing the voltage response, we establish a criterion for targeting the holes. By the criterion, the experimental result shows the maximum error of targeting a hole with a diameter of 5 mm is less than 2.5 mm.

A novel guiding device for distal locking of intramedullary nails

This paper presents the prototype of a new remote guiding device to find the accurate screw hole position for drilling and direction for locking in intramedullary nailing surgery. The device consists of three magnetic pins and an electrical conductive board. The three symmetrically placed magnetic pins can rotate freely and point to the permanent magnet inside the nail. The drilling position and screwing direction can be obtained by moving the device with those magnetic pins to align with the magnet in the nail. The alignment condition is indicated by a LED. When the device is not aligned with the magnet in the nail properly, either in position or direction, the pins then will contact with the board to trigger a light-emitting diode for alarming.

Novel Passive Two-Stage Magnetic Targeting Devices for Distal Locking of Interlocking Nails

Interlocking nailing is a common surgical operation to stabilize fractures in long bones. One of the difficult parts of the surgery is how to locate the position and direction of a screw hole on the interlocking nail, which is invisible to the naked eye after insertion of the nail into the medullary canal. Here, we propose a novel two-stage targeting process using two passive magnetic devices to locate the position and direction of the screw hole without radiation for the locking screw procedure. This involves a ring-shape positioning magnet inside the nail to generate a magnetic field for targeting. From the accuracy test results of these two-stage targeting devices, the search region can be identified in less than 20 seconds by the 1st-stage targeting device, while the total targeting time to locate the drilling position and direction takes less than 4 minutes, with 100% successful rate in 50 attempts. The drilling test further combines the two-stage targeting process and drilling process on the swine tibia, and it is shown that a 100% successful rate is achieved in all 10 attempts, where the total time needed is less than 5 minutes.

Electromagnetic Coil/Inductance-Based Nondestructive Methods for Locating Distal Screw-Holes of an Intramedullary Interlocking-Nail

We report an electromagnetic inductance/coil-based non-destructive method to target distal screw-holes in an intramedullary interlocking-nail surgical operation for fixing a long-bone fracture. The method is a radiation-free approach addressing the over-exposure issue of radioactivity caused by the typical X-ray-imaging approach. According to the method, we fabricate a targeting-system consisting of an internal inductance, external coil, guiding-mechanism, and driving/measurement electronics. When a voltage is applied to the internal inductance embedded in one of the distal screw-holes of a nail inserted in a bone, a directional magnetic flux is generated by the internal inductance due to the electromagnetic induction. Subsequently, the directional magnetic flux penetrates the nail and bone. When the external coil outside the bone scans along the axial and angular directions of the nail/bone, different amount of the generated magnetic flux is detected by the coil and consequently corresponding voltage response is induced in the coil due to the electromagnetic induction. In contrast to the magnetic flux generated and detected by the inductance and coil, respectively, we also investigate the reverse physics-behavior of the flux transmission (i.e., flux generated and detected by the coil and inductance) in order to improve the approach. Finally, by correlating the induced-voltage responses with the scanned axial-locations along the nail/bone, correlation curves are plotted. Through analyzing the curves, a criterion for predicting the location of the screw-holes of the nail is established. When compared the predicted location with the actual location of the screw-hole, the maximum targeting error is 2 mm for locating a screw-hole with a diameter of 5 mm. The result shows the targeting-method is accurate, fast, and easy for the surgeons and significantly simplifies the existed interlocking-nail surgical procedures.