Adjustable drill gauge

A drill stop apparatus for use with an elongated drill bit is provided. The drill bit has a drilling end that is used to drill a hole of a specified, predetermined depth. The bit also has a plurality of circumferentially extending, axially spaced grooves formed on its outer surface. The drill stop includes a body having a first end and formed to include an axially extending bore that is sized to receive the drill bit to permit the bit to be moved axially within the body. The body also has a cavity that extends substantially perpendicularly through the bore. A plunger is provided that is sized to be received in the cavity for releasably engaging one of the plurality of grooves in the drill bit to lock the drill bit against axial movement within the body member such that a specified length of the drill bit extends beyond the first end of the body member. This specified length of the drill bit defines a specified operable drilling length between the first end of the stop apparatus and the drilling end of the drill bit.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to a drill for boring a hole of a specified 
depth in bone. More particularly, the present invention relates to an 
adjustable stop member mounted on the drill that is selectively movable to 
different positions along the drill shaft to provide a positive stop to 
control the depth of penetration of the drill bit. The adjustable stop 
member of the present invention can be used to control the depth of any 
drilling operation in bone, including depth drilling for tibial tray screw 
fixation and drilling for femoral screw implant. 
One example of the use of a bone drill is in the surgical treatment of 
fractures of the neck of the femur. Such treatment generally requires 
reduction of the fracture by means of a screw implant. The implant is 
designed to bring the fractured surfaces together, and to stabilize the 
fractured surfaces in proper alignment for healing. Before such a screw 
implant can be inserted into the bone, a hole must be drilled into the 
bone. Generally, the hole has a diameter somewhat smaller than the 
diameter of the screw implant. The screw implant is generally provided 
with self-tapping threads which screw into the smaller diameter hole to 
firmly embed the implant in the bone. In order for the screw implant to be 
anchored properly in the bone, it is desirable to drill the hole as deeply 
as possible through the neck and into the head of the femur, but not to 
pass entirely through the opposite surface of the head of the femur. 
To drill the hole into the neck and head of the femur, a drill assembly is 
normally used that includes some type of stop collar to limit the 
penetration of the drill bit into the bone. Normally, drilling of the hole 
is preceded by the placement of a conventional guidewire, for example a 
1/8 inch guide pin. The guide pin is generally placed in the bone by the 
use of an alignment device that assures that the pin will be placed at the 
proper angle. The guide pin is normally placed in the bone to extend from 
the outer, or lateral portion of the femur through the fracture, and into 
the head of the femur to a point near the surface of the head. The guide 
pin is generally inserted using x-ray information to determine when the 
pin has reached the desired position and depth. After the pin has been 
inserted to the proper depth, the protruding remainder of the pin is 
measured with a measuring device that permits the surgeon to determine the 
length of the hole to be drilled into the bone. Once this length, or depth 
of the hole, is determined, the drill assembly is adjusted so that a hole 
of the proper depth can be drilled. Generally, the drill assembly will 
have a cannulated drill bit to permit the drill bit to be inserted 
directly over the guide pin so that the hole can be drilled with the wire 
in place. Drilling the hole over the guide pin insures that the hole will 
be drilled at the proper angle, and at the proper position in the bone. 
One type of tool for drilling a hole of a specified depth in a bone is 
disclosed in U.S. Pat. No. 4,341,206 to Perrett et al. U.S. Pat. No. 
4,341,206 discloses a tool that includes a drill to form a small diameter 
hole with a reamer portion to form a slightly larger diameter hole 
disposed over the drill. The drill and the reamer portion are axially 
adjustable relative to each other, with the reamer portion acting as a 
stop collar for the drill. The shank of the drill has a number of annular 
grooves with calibration marks. A locking device is attached to the reamer 
portion to lock the reamer portion against movement with respect to the 
drill. The locking device is in the form of a sleeve that extends axially 
away from the reamer portion. The sleeve has a plurality of cuts that are 
parallel to the longitudinal axis of the drill to form four tongues that 
extend in the longitudinal direction of the drill and resiliently engage 
the grooves of the shank of the drill. A threaded nut is provided that 
engages the tongues to lock the tongues in a preselected groove to 
determine the amount of extension of the drill bit beyond the end of the 
reamer portion. 
One problem with the device disclosed in U.S. Pat. No. 4,341,206 is that 
the adjustable locking device on the reamer portion is difficult to adjust 
axially along the shank of the drill. To adjust the drill with respect to 
the reamer, or stop collar, the threaded nut must be first disengaged from 
the tongues. After the nut is disengaged, the operator must grasp the 
reamer portion with one hand, and the shank of the drill with the other 
hand, and move the shank of the drill within the reamer portion. A 
substantial amount of force is required to move the two components 
relative to each other because of the resilient locking characteristics of 
the tongues in the groove. 
Another problem with the tool disclosed in U.S. Pat. No. 4,341,206, is that 
the threaded nut is removed from the locking device by rotation. Because 
of this rotational activation of the threaded nut, it is possible for the 
nut to become disengaged from the locking device during operation of the 
drill. This can possibly result in movement of the reamer portion along 
the shank of the drill during the drilling procedure, which can possibly 
lengthen the amount of the drill extending beyond the reamer portion. This 
may cause the drill to protrude through the surface of the neck of the 
femur. 
One object of the present invention is to provide a drill assembly that 
includes a stop member that is easily adjustable along the shank, or shaft 
of the drill. Preferably, the stop member will be adjustable by the use of 
one hand only. 
Another object of the present invention is to provide a drill assembly in 
which the locking capability of the stop member is not affected by 
rotation of the drill bit. 
According to the present invention, a drill stop apparatus for use within 
an elongated drill bit having a drilling end used to drill a hole of a 
specified, predetermined depth, is provided. The drill bit has a plurality 
of circumferentially extending, axially spaced grooves formed on its outer 
surface. The stop apparatus includes a body having a first end and formed 
to include an axially extending bore that is sized to receive the drill 
bit to permit the drill bit to be moved axially within the body. The body 
also has a cavity that extends substantially perpendicularly through the 
bore. Means are disposed in the cavity for releasably engaging one of the 
plurality of grooves in the drill bit to lock the drill bit against axial 
movement within the body member such that a specified length of the drill 
bit extends beyond the first end of the body member. This specified length 
of the drill bit defines a specified operable drilling length between the 
first end of the stop apparatus and the drilling end of the drill bit. 
One feature of the foregoing structure is that the body member is formed to 
include a cavity that extends substantially perpendicular to the drill bit 
receiving bore. Means are disposed in the cavity for releasably engaging 
one of the plurality of grooves in the drill bit to lock the drill bit 
against axial movement within the body member. One advantage of this 
feature is that the engaging means operates along an axis substantially 
perpendicular to the axis of the drill bit. Thus, the engaging means, or 
locking mechanism for the body member, can be completely disengaged simply 
by moving the engaging means along this substantially perpendicular axis. 
In preferred embodiments of the present invention, the engaging means 
comprises a plunger that is sized to be movably received within the body 
member cavity. The plunger is formed to include a transverse opening that 
is sized to receive the drill bit and an upstanding ridge that is 
configured to engage selectively one of the grooves in the drill bit. One 
feature of the foregoing structure is that the groove-engaging ridge is 
connected to the movable plunger. One advantage of this feature is that by 
simply moving the plunger, the ridge may be disengaged from the groove to 
permit the body member to move with respect to the drill bit to adjust the 
operable length of the bit. 
Also in preferred embodiments of the present invention, spring means are 
provided for yieldably urging the plunger into a groove-engaging position. 
When in the groove-engaging position, a portion of the plunger extends 
beyond the outer surface of the body member, with the extending portion 
adapted to be depressed by a force to move the plunger into a 
groove-disengaged position. One feature of the foregoing structure is that 
the plunger is normally biased into the groove-engaging position, and the 
plunger is depressed to the groove-disengaged position by a force acting 
substantially perpendicular to the axis of the drill. One advantage of 
this feature is that the engagement of the grooves by the plunger is 
unaffected by rotation of the drill bit about the drill bit longitudinal 
axis. The plunger is disengaged from the appropriate groove only by a 
force that is applied about the axis substantially perpendicular to the 
axis of rotation of the drill bit. 
Also in preferred embodiments of the present invention, the body member 
includes a frustaconically-shaped portion that terminates at the first 
end. One feature of the foregoing structure is that the first end, the 
depth limiting end, has a smaller diameter than the overall diameter of 
the body member. One advantage of this feature is that the smaller 
diameter depth limiting end does not block the surgeon's view of the drill 
bit and hole as the first end approaches the bone surface to stop the 
penetration of the drill bit. 
The present invention provides a drill assembly that includes an adjustable 
drill stop that is easily moved and adjusted along the length of the drill 
bit to control the depth of penetration of the drill bit into a bone. The 
adjustable stop is operated by a force applied along an axis substantially 
perpendicular to the axis of the drill bit. Rotation of the drill bit 
about its axis does not affect in any manner the locking capability of the 
adjustable stop member. The adjustable drill stop of the present invention 
is adaptable for use for many types of bone drills, including drills 
having a reamer and chamfer portion. 
Additional objects, features, and advantages of the invention will become 
apparent to those skilled in the art upon consideration of the following 
detailed description of a preferred embodiment exemplifying the best mode 
of carrying out the invention as presently perceived. A detailed 
description particularly refers to the accompanying figures in which:

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring now to the drawings, and particularly to FIG. 1, FIG. 1 shows the 
drill assembly 10 of the present invention. The drill assembly 10 includes 
an elongated drill bit 12 that includes a conventional drilling end 14. 
The drill bit 12 also includes a shank portion 16 with a plurality of 
circumferentially extending, axially spaced grooves 20 formed therein. 
Numerical indicators 22 (FIG. 2) are provided adjacent every other groove 
20, the use of which will be discussed later. The drill bit 12 also 
includes an engaging end 24 that is configured to be received in, and 
driven by a conventional drill bit driving device (not shown). 
An adjustable stop collar 26 is disposed over the shank portion 16 of the 
drill bit 12. The stop collar 26 is configured to move axially along the 
shank portion 16, and to be locked at a selected position on the shank 
portion 16 to limit the depth of penetration of the drill bit 12 into the 
material to be drilled. 
FIG. 2 shows the stop collar 26 in more detail. The stop collar 26 includes 
a body portion 28. The body portion 28 includes a generally 
cylindrically-shaped center portion 29 that includes a roughened outer 
surface that is adapted to aid an operator (not shown) in gripping the 
stop collar 26. The body portion 28 also includes a frusticonically-shaped 
section 30 that terminates in a front, depth-limiting end 32. As best seen 
in FIG. 1, the depth-limiting end 32 is oriented toward the drilling end 
14 of the drill bit 12. The body portion 28 also includes an indicating 
end 34 that is oriented away from the drilling end 14. 
A bore 38 is formed to extend axially through the center of the body 
portion 28. The bore 38 is sized to have a diameter slightly greater than 
the diameter of the shank portion 16 of the drill bit 12 to permit the 
shank portion 16 to be movably received within the bore 38. A cavity 40 is 
formed in the center portion 29 of the body portion 28. The cavity 40 is 
oriented to be perpendicular to the bore 38, and extends into the body 
member 28 through the bore 38 to a depth somewhat greater than one-half 
the diameter of the center portion 29. The orientation and depth of the 
cavity 40 is best shown in FIGS. 3 and 4. 
A generally cylindrically-shaped plunger 44 is provided that is sized and 
shaped to be movably received into the cavity 40. FIG. 2 shows the plunger 
44 removed from the cavity 40 for clarity. The plunger 44 includes an 
opening 46 that extends transversely therethrough. The opening 46 is 
oriented to align with the bore 38 when the plunger 44 is placed within 
the cavity 40. The orientation of the opening 46 and the bore 38 is best 
shown in FIG. 4. An upstanding ridge 48 is formed on the lower portion of 
the opening 46. The ridge 48 is sized and shaped to be partially received 
into any one of the grooves 20 in the shank portion 16. The plunger 44 
also includes at one end an upper surface 50 that extends somewhat beyond 
the outer surface of the center portion 29 of the body portion 28 when the 
plunger 44 is fitted into the cavity 40 (FIGS. 3 and 4). A reduced 
diameter portion 52 is formed on the end of the plunger 44 opposite the 
upper surface 50. The reduced diameter portion 52 and the main portion of 
the plunger 44 cooperate to define a downwardly facing shoulder 54. 
A coil spring 60 is provided to be disposed within the cavity 40 to 
cooperate with a bottom surface 62 of the cavity 40 to bias the plunger 44 
upwardly. The spring 60 is sized to mate with the shoulder 54 on the 
plunger 44 to provide this biasing force. It will be understood that the 
spring 60 could be attached to the shoulder 54 of the plunger 44 rather 
than being separate. FIG. 2 also shows a passage 64 that is formed axially 
through the drill bit 12. The use of the passage 64 will be described in 
detail later. 
FIG. 3 shows the plunger 44 disposed within the cavity 40 in a position of 
use with the shank portion 16 of the drill bit 12 extending through the 
bore 38 and the stop collar 26 and the opening 46 in the plunger 44. The 
ridge 48 is shown in an engaging position in one of the grooves 20. It 
will be understood that the plunger 44 is biased to this groove-engaging 
position by the spring 60. FIG. 3 also shows clearly that the opening 46 
is sized somewhat larger than the diameter of the shank portion 16. 
Specifically, the opening 46 is sized to permit the shank portion 16 to 
axially move through the opening 46 when the ridge 48 is disengaged from 
the groove 20. 
FIG. 4 shows in greater detail the engagement of the groove 20 by the ridge 
48. As discussed previously, the ridge 48 is sized to fit within the 
groove 20 with very close dimensional tolerance. Because of this close 
tolerance, when the ridge 48 is engaged with the groove 20, axial movement 
of the shank portion 16 with respect to the plunger 44 is negligible. As 
can be seen in FIG. 4, the dimensional tolerance between the plunger 44 
and the cavity 40 is also substantially close to prevent movement of the 
plunger 44 within the cavity 40 transverse to the axis of cavity 40. Thus, 
when the ridge 48 is engaged with one of the grooves 20 on the shank 
portion 16, relative axial movement between the stop collar 26 and the 
drill bit 12 is prevented. 
To disengage the ridge 48 from the groove 20, the plunger 44 must be 
depressed against the biasing force of the spring 60 within the cavity 40. 
Illustratively, FIG. 4 shows a force applied against the upper surface 50 
of the plunger 44 depicted by the arrow 66. In use, the upper surface 50 
would normally be depressed by an operator (not shown) in the direction of 
the arrow 66 to disengage the ridge 48 from the groove 20. Once the 
plunger 44 has been depressed to disengage the ridge 48 from the groove 
20, the shank portion 16 of the drill bit 12 can be axially moved within 
the stop collar 26 to reposition the drilling end 14 of the bit 12 with 
respect to the depth limiting end 32 of the stop collar 26. 
To determine accurately the length of the drill bit 12 that extends beyond 
the depth limiting end 32 to the drilling end 14, the markings 22 on the 
shank portion 16 are used in conjunction with the indicating end 34 of the 
stop collar 26. The marking 22 immediately adjacent the indicating end 34 
serves as an indication of the exposed length of the drill bit 12 between 
the depth limiting end 32 and the drilling end 14 of the drill bit 12. 
This exposed length of the drill bit 12 will correspond to the depth of 
the hole that can be drilled by the drill bit 12 when the stop collar 26 
is so oriented. 
FIG. 5 shows the drill assembly 10 of the present invention in a position 
of use in the upper portion of a femur bone 68. Specifically, the drill 
assembly 10 is shown oriented to drill a hole in the upper portion of the 
femur 68 from the lateral portion of the femur 68 below the greater 
trochanter, through the neck 70, and into the head 72 of the femur 68. 
Illustratively, the hole will be used for the placement of an implant 
screw (not shown) to stabilize the head 72 and neck 70 with respect to the 
remaining portion of the femur 68 to reduce a fracture indicated by the 
fracture line 78. 
Before using the drill assembly 10 to drill the pilot hole for the implant 
screw, a guidewire 80 is first placed within the femur 68 in the same 
orientation and direction as the desired hole to be drilled. 
Illustratively, the guidewire 80 is a 1/8 inch diameter guide pin. It will 
be understood that other types of guide devices could be used. The 
guidewire 80 is conventionally placed within the femur 68 using a guiding 
device (not shown) that insures that the guidewire 80 will be properly 
guided and oriented in the bone 68. The depth of penetration of the 
guidewire 80 into the head 72 is determined by conventional x-ray 
techniques. It will be understood that the depth of penetration of the 
guidewire 80 is critical because of the importance of not penetrating 
through the outer surface 74 of the head 72. Ideally, the guidewire 80 is 
placed as deeply as possible into the head 72 without penetrating the 
outer surface 74. Once the guidewire 80 is in place, a separate instrument 
(not shown) is used to determine the depth of penetration of the guidewire 
80 into the femur 68. It will be understood that the depth of penetration 
of the guidewire 80 when in place corresponds to the desired depth of the 
hole to be drilled by the drill assembly 10. Such a corresponding depth 
will permit the drill assembly 10 to drill a hole extending into the head 
72 of the femur 68 without penetrating the outer surface 74. 
After the guidewire 80 has been placed within the femur 68, and a depth of 
penetration of the guidewire 80 ascertained, the stop collar 26 is 
adjusted over the shank portion 16 until the indicating end 34 is adjacent 
a marking 22 that corresponds to the depth of penetration of the guidewire 
80. The adjustment of the stop collar 26 is conducted by depressing the 
upper surface 50 of the plunger 44 to disengage the ridge 48 from the 
groove 20. With the plunger 44 in this position, the shank portion 16 of 
the drill bit 12 can be axially moved within the stop collar 26 until the 
indicating end 34 is aligned with the marking 22 corresponding to the 
desired depth of the hole to be drilled. Once the stop collar 26 is in the 
correct position, the plunger 44 is released. The biasing force provided 
by the spring 60 then urges the ridge 48 into the appropriate groove 20 to 
lock the stop collar with respect to the drill bit 12. 
To drill the hole within the femur 68, the axial passage within the drill 
bit 12 is placed over the guidewire 80, and the drilling end 14 is brought 
into contact with a lateral bone surface 76 on the femur 68. A 
conventional driving device (not shown) is attached to the engaging end 24 
of the drill bit 12 to rotate the bit 12. It will be understood that the 
guidewire 80 remains in place to guide the drilling end 14 to insure that 
the hole formed by the drill bit 12 extends in the appropriate orientation 
and direction through the neck 70 into the head 72. As the depth limiting 
end 32 of the stop collar 26 nears the bone surface 76, the 
frusticonically-shaped section 30 permits the operator to view the bone 
surface 76 adjacent the hole being formed to accurately determine when 
contact between the depth limiting end 32 and the bone surface 76 is 
eminent. Once the depth limiting end 32 contacts the bone surface 76, the 
operator knows that the hole has been formed to the correct depth. The 
drill bit 12 is then conventionally removed from the hole, followed by 
removal of the guidewire 80. The hole is then prepared for receipt of the 
implant device (not shown) to reduce the fracture. 
Applicants' invention provides a drill assembly having an easily adjustable 
depth limiting device to limit the depth of penetration of a hole in a 
bone. The depth limiting stop collar 26 is accurately adjustable along the 
drill bit 12, and is not suspectible to dislodgment due to rotation of the 
drill bit 12. 
Although the invention has been described in detail with reference to a 
preferred embodiment and specific examples, variations and modifications 
exist within the scope and spirit of the invention as described and 
defined in the following claims.