Patent Publication Number: US-9901376-B2

Title: Method and apparatus for aligning bone screw holes

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 13/014,893 filed Jan. 27, 2011. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The following relates to aligning bone screw holes, and more specifically, relates to a gauge for non-invasively estimating bone screw trajectories. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and does not constitute prior art. 
     Bone screws and bone plates are used to fix bone fragments when repairing complex fractures. Typically, when inserting a bone screw into a bone, a hole is drilled into a bone at a desired depth and a bone screw is inserted into the hole. To determine if the desired depth has been reached, a surgeon either uses tactile feedback while drilling into the bone or uses a depth gauge after drilling into the bone. Using tactile feedback while drilling into the bone can be inaccurate due to variations in bone density. Using a depth gauge after drilling into the bone can be inaccurate since the drill depth is not determined until after the hole has been drilled. 
     Thus, there is need for procedures and depth gauges that enable estimating screw trajectories, such as a screw-hole depth or a screw length, prior to forming a hole in a bone. In addition, there is a need for procedures and depth gauges that minimize the amount of fluoroscopy necessary for bone screw insertions, thereby reducing the time and costs required for bone screw insertions. 
     SUMMARY 
     A depth gauge for estimating at least one of a fastener-hole depth and a fastener length prior to forming a hole in a bone can include a transmitter, a receiver, a module, and a display. The transmitter can be operable to transmit a wave into a bone from a selected position. The receiver can be operable to receive the wave at the selected position after the wave has been reflected from tissue in the bone. The module can be operable to determine a distance from the depth gauge to the tissue in the bone based on times at which the wave is transmitted and received. The display can be operable to display the distance to the tissue in the bone. 
     A method for estimating at least one of a fastener-hole depth and a fastener length prior to forming a hole in a bone can include selecting a position on a proximal side of a proximal cortical bone layer for forming the hole, transmitting a transmitted wave into the bone from the selected position, and receiving a reflected wave at the selected position after the transmitted wave has been reflected by a distal cortical bone layer. The method can further include determining a distance from the selected position to the distal cortical bone layer based on times at which the transmitted wave is transmitted and the reflected wave is received, and estimating the at least one of the fastener-hole depth and the fastener length based on the distance to the distal cortical bone layer. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a perspective view of a depth gauge according to various teachings of the present disclosure; 
         FIG. 2  is a side view of the depth gauge of  FIG. 1  indicating a distance from a distal end of the depth gauge to a distal cortical bone; 
         FIG. 3  is a side view of the depth gauge of  FIG. 1  positioned normal to a longitudinal axis of a bone plate and indicating a distance from the distal end of the depth gauge to the distal cortical bone; 
         FIG. 4  is a side view of the depth gauge of  FIG. 1  angled with respect to the longitudinal axis of the bone plate and indicating a distance from the distal end of the depth gauge to the distal cortical bone; 
         FIG. 5  is a side view of a fastener-hole based on the distance; and 
         FIG. 6  is a side view of a bone fastener based on the distance. 
     
    
    
     DESCRIPTION OF VARIOUS EMBODIMENTS 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Referring to  FIG. 1 , a depth gauge  10  is illustrated according to various exemplary embodiments of the present disclosure. The depth gauge  10  can be handheld and can include a proximal end  12 , a distal end  14 , a transducer  16  adjacent to the distal end  14 , and a handle  18  extending from the transducer  16  to the proximal end  12 . The transducer  16  and the handle  18  can be integral or separate. 
     The transducer  16  can be trapezoidal, as shown, or can have a different shape. The transducer  16  includes both a transmitter and a receiver, further discussed herein. The transducer  16  can be a transceiver in which the transmitter and receiver are combined and share common circuitry or a single housing. Alternatively, the transducer  16  can be a transmitter-receiver in which the transmitter and receiver are separate. 
     The handle  18  can be rectangular, as shown, or can have a different shape. The handle  18  can include a module  20 , a display  22 , and a user interface  24 . The module  20  can be in communication with the transducer  16 , the display  22 , and the user interface  24 . The display  22  can display values digitally. The user interface  24  can be a button that allows a user to activate the depth gauge  10 . The user interface  24  can be omitted, and the depth gauge  10  can be activated when the transducer  16  detects that the depth gauge  10  is in close proximity with an object. 
     Referring to  FIGS. 2 through 4 , operation of the depth gauge  10  will now be described. The depth gauge  10  estimates a hole depth or a length associated with a fastener, such as a screw or a pin, prior to forming a hole in a bone  26 . The bone  26  includes a proximal outer cortical bone layer  28 , an inner cancellous bone layer  30 , and a distal outer cortical bone layer  32 . The cortical bone layer  28  includes an outer surface  34  and an inner surface  36 . The cancellous bone layer  30  includes a proximal inner surface  38  and a distal inner surface  40 . The cortical bone layer  32  includes an inner surface  42  and an outer surface  44 . The cortical bone layers  28 ,  32  are on proximal and distal sides, or opposite sides, of the bone  26 . The cancellous bone layer  30  is between the inner surfaces  36 ,  42  of the cortical bone layers  28 ,  32 . 
     The depth gauge  10  can be used before fixing bone fragments of the bone  26  to an unbroken portion of the bone  26  using fasteners and/or plates. In this regard, prior to forming holes in the bone  26 , a position can be selected on the proximal side of the bone  26  for forming a hole in the bone  26 . The hole can be formed before inserting a fastener or while inserting a self-tapping fastener. 
     The distal end  14  of the depth gauge  10  can be placed at the selected position. The selected position can be directly on the outer surface  34  of the cortical bone layer  28  ( FIG. 2 ). Alternatively, a bone plate  46  having proximal and distal surfaces  48 ,  50  can be placed on the proximal side of the bone  26 , and the selected position can be within or near a plane including the proximal surface  48  of the bone plate  46  ( FIGS. 3 and 4 ). To this end, the bone plate  46  can include holes  52 , and the selected position can be at a proximal end of one of the holes  52 . The selected position can correspond to a proximal surface of a fastener when the fastener is placed in one of the holes  52  and in the bone  26 . The bone  26  and the bone plate  46  can be separated by a gap  54  across which the fastener must extend. 
     The depth gauge  10  can be positioned normal or perpendicular to a longitudinal axis x of the bone plate  46  when the distal end  14  of the depth gauge  10  is placed at the selected position ( FIG. 3 ), such as over one of the holes  52 . Alternatively, the depth gauge  10  can be angled with respect to the longitudinal axis x of the bone plate  46  when the distal end  14  of the depth gauge  10  is placed at the selected position ( FIG. 4 ). In this regard, the depth gauge  10  can be aligned with a desired fastener trajectory. 
     Actions can be taken to activate the depth gauge  10  using the user interface  24 . For example, if the user interface  24  is a button, the user interface  24  can be depressed. In turn, the user interface  24  can activate the module  20 , which can activate the transducer  16  and the display  22 . Alternatively, the transducer  16  and the module  20  can remain active, and the module  20  can activate the display  22  when the transducer  16  detects an object in close proximity with the depth gauge  10 . 
     With continued reference to  FIGS. 2 through 4 , the transducer  16  can transmit a wave into the bone  26  from the selected position. The wave can be a wave used in medical imaging, including a sound wave, such as ultrasound or Doppler, a light wave, a radio wave, or a gamma ray. As indicated by the dashed line and the distal arrow, the transmitted wave travels from the distal end  14  of the depth gauge  10 , through the cortical bone layer  28  and the cancellous bone layer  30 , and to the cortical bone layer  32 . The module  20  can instruct the transducer  16  to transmit the transmitted wave and can record a transmit time, or the time at which the wave is transmitted, based on this instruction to the transducer  16 . 
     The inner surface  42  of the cortical bone layer  32  reflects the wave at a normal incidence. As indicated by the dashed line and the proximal arrow, the reflected wave travels from the inner surface  42  of the cortical bone layer  32 , through the cancellous bone layer  30  and the cortical bone layer  28 , and to the distal end  14  of the depth gauge  10 . If the selected position is within or near a plane including the proximal surface  48  of the bone plate  46  ( FIGS. 3 and 4 ), the transmitted and reflected waves can also travel through one of the holes  52  in the bone plate  46 . 
     The transducer  16  can receive the reflected wave at the selected position after the transmitted wave has been reflected by the inner surface  42  of the cortical bone layer  32 . The transducer  16  can communicate properties of the reflected wave to the module  20 , including frequency, amplitude, and velocity. The module  20  can determine a receipt time, or the time at which the reflected wave is received, based on this communication from the transducer  16 . 
     The transmitted wave can also be reflected by the cortical bone layer  28 , the cancellous bone layer  30 , and the bone plate  46 . To this end, the transducer  16  can receive multiple waves that have been reflected by the bone  26  or the bone plate  46 . The module  20  can identify which of the multiple waves has been reflected from the cortical bone layer  32  based on the wave properties and the receipt times. Each of the bone layers  28 ,  30 , and  32  has a different density. The cortical bone layers  28 ,  32  have a greater density than the cancellous bone layer  30 . The module  20  can identify the reflected waves that have been reflected by the cortical bone layers  28 ,  32  based on the wave properties. In addition, the module  20  can ignore the earlier receipt time of the wave reflected by the cortical bone layer  28 , and can use the later receipt time of the wave reflected by the cortical bone layer  32 . 
     The module  20  can determine a distance from the selected position to the cortical bone layer  32  based on the transmit time and the receipt time. The module  20  can determine this distance taking a difference between the transmit time and the receipt time, dividing this difference by two, and multiplying this quotient by a predetermined velocity. The predetermined velocity can correspond to a sound wave travelling through bone in the radial direction (e.g., approximately 3300 m/s). 
     The module  20  can estimate the fastener-hole depth and/or the fastener length based on the distance to the cortical bone layer  32 . The fastener-hole depth and/or the fastener length can be equal to the distance to the inner surface  42  of the cortical bone layer  32 . Alternatively, the fastener-hole depth can be equal to a difference between the distance to the inner surface  42  of the cortical bone layer  32  and the distance to the outer surface  34  of the cortical bone layer  28 . The module  20  can determine the distance to the cortical bone layer  28  in the same manner that the module  20  determined the distance to the cortical bone layer  32 . 
     The display  22  can display the distance to the cortical bone layer  32 , the fastener-hole depth, and/or the fastener length based on communication with the module  20 . If the display  22  displays the distance to the cortical bone layer  32  only, the fastener trajectories can be estimated by the user based on the displayed distance. The insertion angle of the fastener with respect to the bone  26  can be estimated based on the angle of the depth gauge  10  with respect to the bone  26 . 
     Referring to  FIG. 5 , using a drill bit  56  to drill holes  58  into the bone  26  based on the estimated fastener-hole depth will now be described. The drill bit  56  can be adjusted in a drill (not shown) such that the drill bit extends into the bone  26  to the estimated fastener-hole depth when the drill chuck abuts a proximal surface, such as the outer surface  34  of the cortical bone layer  28  or the proximal surface  48  of the bone plate  46 . Alternatively, the drill can have depth markings used to determine when the drill bit has reached the estimated fastener-hole depth. 
     Referring to  FIG. 6 , sizing fasteners  60  based the estimated fastener length and inserting the fasteners  60  into the bone  26  will now be described. Sizing the fasteners  60  can include selecting the fasteners  60  from various fasteners having various lengths and/or cutting the fasteners  60 . The fasteners  60  can be sized to have a distal end at the inner surface  42  of the cortical bone layer  32 , as shown, or can be shorter. The fasteners  60  can be perpendicular to a longitudinal axis of the bone  26  and/or the longitudinal axis x the bone plate  46 , or can be angled therefrom. The fasteners  60  can be inserted into the holes  58  in the bone  26 , or the fasteners  60  can be self-tapping and inserted into the bone  26  without drilling the holes  58 . The depth gauge  10  allows for predetermining the fastener-hole depth and/or the fastener length prior to drilling the holes  58 . 
     The foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.