H.22 Bone thickness measuring device for accurate bony fixation screw selection
Problem Description
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Internal fixation of the mandible is a surgical procedure often done by head and neck surgeons (including oral and maxillofacial surgery, ENT and plastic surgery) to provide stability of a fractured mandible. A fractured mandible is encountered in the setting of trauma, mandible pathology that requires resection and controlled fracture by the surgeon for repositioning of the mandible. During the fixation stage, we utilize plates and screws to hold the fractured pieces together (Figure 1). One of the challenges in this procedure is to select the correct screw length after the holes are drilled. Our goal is to select the screw length that matches the thickness of the mandible. However, with different patient anatomy and plate location, the screw length is impossible to predict and must be measured in the operating room.
Figure 1: (A) The image on the left showed a fractured mandible fixated by bone plates and screws, (B) The image on the right showed cross section of the mandibular fixation with screws of different lengths.
The current measuring system available is a depth gauge, which is a retractable metal rod with a hock at the end. The rod goes through the pre-drilled hole while the hock hocks onto the inner cortex of the mandible (Figure 2). The gauge must be positioned perpendicular to the mandible for the retractable rod to pass through the pre-drilled holes (Figure 3A). It is not an effective system since the surgical access is usually done through a small incision in the mouth with deep dissection (Figure 3B). Perpendicular placement of the gauge is challenging. The small hock often fail to hold on to the inner cortex of the mandible due to difficult positioning. Despite wanting surgical accuracy, this measuring step is often skipped.
Figure 2: (A) Stryker depth gauge (B) Current depth gauge system being used on a piece of fractured bone.
Figure 3: (A) Using the current measuring system to measure mandible thickness (B) Commonly used surgical access for mandible fixation. The bone plate is secured with screws across the fracture line. The position of this fixation is located below the position of the lower wisdom tooth accessed through the mouth.
The goal of this project is to design a robust measuring device that can be inserted into deep tissue pocket while obtaining measurement of the bone thickness at the level of the pre-drilled hole. The measurement needs to be accurate to within a millimeter and easy to read. The device needs to be able to access any pre-drilled holes in the jawbone regardless of the position and depth from the surgical incision and easily sterilizable for surgery.
