# Patent

## Title
Method and apparatus for aligning bone screw holes

## Abstract

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.

## Background
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.

## Claims

1. 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, comprising:
an electronic transmitter operable to transmit a wave into a proximal cortical bone layer, through a cancellous bone layer, and to an inner surface of a distal cortical bone layer from a selected position;
an electronic receiver operable to receive the wave at the selected position after the wave has been reflected from the inner surface of the distal cortical bone layer;
an electronic circuit operable to:
identify the wave as having been reflected by the inner surface of the distal cortical bone layer based on properties of the wave as influenced by densities of the bone;
ignore a wave as having been reflected by the proximal cortical bone layer; and
determine a distance from the depth gauge to the inner surface of the distal cortical bone layer based on times at which the wave is transmitted and received by:
taking a difference between a transmit time and a receipt time;
dividing the difference by two to obtain a quotient; and
multiplying the quotient by a predetermined velocity corresponding to a sound wave travelling through the bone; and


a display operable to display the distance from the depth gauge to the inner surface of the distal cortical bone layer.

2. The depth gauge of claim 1, further comprising a handle that includes the circuit and the display.

3. The depth gauge of claim 1, further comprising an electronic user interface operable to activate the depth gauge.

4. The depth gauge of claim 1, wherein the wave is an ultrasound wave.

5. The depth gauge of claim 1, wherein the transmitter and the receiver are in a single housing.

6. The depth gauge of claim 1, wherein the depth gauge is handheld.

7. The depth gauge of claim 1, wherein the circuit is operable to estimate the at least one of the fastener-hole depth and the fastener length based on the times at which the wave is transmitted and received.

8. The depth gauge of claim 7, wherein the display is operable to display the at least one of the fastener-hole depth and the fastener length.

9. 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, comprising:
a handle having a proximal end and a distal end;
an electronic transmitter mounted to the distal end of the handle and operable to transmit an ultrasound wave into a proximal cortical bone layer, through a cancellous bone layer, and to a distal cortical bone layer;
an electronic receiver mounted to the distal end of the handle and operable to receive the ultrasound wave after the ultrasound wave has been reflected by an inner surface of the distal cortical bone layer;
an electronic circuit disposed inside the handle and operable to determine a distance from the depth gauge to the inner surface of the distal cortical bone layer based on times at which the ultrasound wave is transmitted and received;
a display located on the handle and operable to display the distance to the inner surface of the distal cortical bone layer; and
an electronic user interface located on the handle and operable to activate the depth gauge.

10. The depth gauge of claim 9, wherein the transmitter and the receiver share common circuitry.

11. The depth gauge of claim 9, wherein the transmitter and the receiver are separate from each other.

12. The depth gauge of claim 9, wherein:
the ultrasound wave includes multiple waves; and
the circuit identifies which ones of the multiple waves are reflected by at least one of the proximal cortical bone layer and the distal cortical bone layer based on properties of the multiple waves.

13. 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, comprising:
an electronic transmitter operable to transmit an ultrasound wave into a proximal cortical bone layer, through a cancellous bone layer, and to an inner surface of a distal cortical bone layer;
an electronic receiver operable to receive the ultrasound wave after the ultrasound wave has been reflected by the inner surface of the distal cortical bone layer;
an electronic circuit operable to determine a distance from the depth gauge to the inner surface of the distal cortical bone layer based on times at which the ultrasound wave is transmitted and received;
a display operable to display the distance to the inner surface of the distal cortical bone layer; and
an electronic user interface operable to activate the depth gauge, wherein:
the ultrasound wave includes multiple waves;
the circuit identifies which ones of the multiple waves are reflected by at least one of the proximal cortical bone layer and the inner surface of the distal cortical bone layer based on properties of the multiple waves;
the circuit identifies a first wave and a second wave as reflected by the at least one of the proximal cortical bone layer and the inner surface of the distal cortical bone layer;
the circuit identifies the one of the first wave and the second wave having an earlier receipt time as reflected by the proximal cortical bone layer; and
the circuit identifies the one of the first wave and the second wave having a later receipt time as reflected by the inner surface of the distal cortical bone layer.

14. The depth gauge of claim 13, wherein the circuit determines the distance from the depth gauge to the distal cortical bone layer based on the one of the first wave and the second wave that is reflected by the distal cortical bone layer.

15. A depth gauge for estimating a fastener-hole depth and a fastener length prior to forming a hole in a bone, comprising:
an electronic transmitter operable to transmit a wave into a proximal cortical bone layer, through a cancellous bone layer, and to an inner surface of a distal cortical bone layer;
an electronic receiver operable to receive a first wave after the wave has been reflected by the inner surface of the distal cortical bone layer and a second wave after the wave has been reflected by the proximal cortical bone layer; and
an electronic circuit operable to:
determine a distance from the depth gauge to the inner surface of the distal cortical bone layer based on times at which the first wave is transmitted and received;
determine a distance from the depth gauge to the proximal cortical bone layer based on times at which the second wave is transmitted and received;
estimate the fastener-hole depth based on a difference between the times at which the first wave is transmitted and received after being reflected by the inner surface of the distal cortical bone layer and the times at which the second wave is transmitted and received after being reflected by the proximal cortical bone layer; and
estimate the fastener length based on the times at which the first wave is transmitted and received after being reflected by the inner surface of the distal cortical bone layer.

16. The depth gauge of claim 15, further comprising a display operable to display the distance to the distal cortical bone layer.

17. The depth gauge of claim 16, further comprising a transducer that includes the transmitter and the receiver.

18. The depth gauge of claim 17, further comprising a user interface operable to activate the depth gauge.

19. The depth gauge of claim 18, wherein:
the user interface includes a button;
the user interface activates the circuit when the button is depressed; and
the circuit activates the transducer and the display when the circuit is activated.

20. 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, comprising:
an electronic transmitter operable to transmit a wave into a proximal cortical bone layer, through a cancellous bone layer, and to an inner surface of a distal cortical bone layer;
an electronic receiver operable to receive the wave after the wave has been reflected by the inner surface of the distal cortical bone layer;
an electronic circuit operable to:
determine a distance from the depth gauge to the inner surface of the distal cortical bone layer based on times at which the wave is transmitted and received; and
estimate the at least one of the fastener-hole depth and the fastener length based on the times at which the wave is transmitted and received;
a display operable to display the distance to the inner surface of the distal cortical bone layer; and
an electronic transducer that includes the transmitter and the receiver, wherein the circuit activates the display when the transducer detects that a distance between the depth gauge and an object is less than a predetermined distance;
wherein the transducer is configured to mate within a fastener hole in a bone plate.