U.S. patent application number 11/095232 was filed with the patent office on 2006-10-12 for orthopaedic cutting instrument and method.
This patent application is currently assigned to Zimmer Technology, Inc.. Invention is credited to Robert D. Krebs, Justin J. May, Charles D. Persons.
Application Number | 20060229624 11/095232 |
Document ID | / |
Family ID | 37084034 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060229624 |
Kind Code |
A1 |
May; Justin J. ; et
al. |
October 12, 2006 |
Orthopaedic cutting instrument and method
Abstract
An orthopaedic cutting instrument and associated methods are
presented.
Inventors: |
May; Justin J.; (Warsaw,
IN) ; Persons; Charles D.; (Columbia City, IN)
; Krebs; Robert D.; (Warsaw, IN) |
Correspondence
Address: |
ZIMMER TECHNOLOGY - REEVES
P. O. BOX 1268
ALEDO
TX
76008
US
|
Assignee: |
Zimmer Technology, Inc.
|
Family ID: |
37084034 |
Appl. No.: |
11/095232 |
Filed: |
March 31, 2005 |
Current U.S.
Class: |
606/79 |
Current CPC
Class: |
A61B 2034/2051 20160201;
A61B 2017/320032 20130101; A61B 34/20 20160201; A61B 17/32002
20130101 |
Class at
Publication: |
606/079 |
International
Class: |
A61B 17/00 20060101
A61B017/00 |
Claims
1. An orthopaedic cutting instrument comprising: a drive mechanism;
a cutter coupled to the drive mechanism; means for driving the
drive mechanism to produce oscillating rotary motion of the cutter;
and means for adjusting the angular amplitude of the oscillating
rotary motion.
2. The instrument of claim 1 further comprising: means for driving
the drive mechanism to produce continuous rotary motion; and means
for changing from oscillating rotary motion to continuous rotary
motion.
3. The instrument of claim 1 further comprising: means for
combining oscillating rotary motion and continuous rotary motion to
oscillate the cutter while simultaneously rotating the cutter.
4. The instrument of claim 1 wherein the drive mechanism comprises
a motor and further wherein the means for driving the drive
mechanism to produce oscillating rotary motion comprises a sending
a drive signal to the motor that oscillates from positive to
negative signal values.
5. The instrument of claim 4 wherein the means for adjusting the
angular amplitude comprises adjusting the amplitude of the
oscillating drive signal.
6. An orthopaedic cutting instrument comprising: a handpiece
including a motor; an elongated shaft extending from the handpiece
and defining a shaft centerline, the shaft being coupled to the
motor to transmit rotary motion from the motor; a cutter coupled to
the shaft; and a control unit for driving the motor to produce
oscillating rotary motion of the cutter about the shaft
centerline.
7. The instrument of claim 6 wherein the shaft comprises a flexible
shaft.
8. The instrument of claim 6 wherein the shaft includes a rigid
portion.
9. The instrument of claim 8 wherein the shaft includes a curved
portion.
10. The instrument of claim 8 wherein the shaft includes a
steerable portion movable relative to the shaft centerline to
change the angle of the cutter relative to the shaft
centerline.
11. The instrument of claim 6 wherein the shaft comprises fluid
delivery and aspiration channels to transmit fluid to and away from
the cutter.
12. An orthopaedic cutting instrument comprising: a drive
mechanism; a cutter coupled to the drive mechanism; and means for
driving the drive mechanism to preferentially cut relatively hard
tissue and spare relatively soft tissue.
13. The instrument of claim 12 wherein the drive mechanism
comprises a handpiece containing a motor and an elongated shaft
defining a longitudinal centerline coupled to the motor and
extending from the handpiece, and further wherein the means for
driving comprises a control unit that sends an oscillating drive
signal to the motor to cause the cutter to oscillate rotationally
in a plane about the shaft centerline.
14. The instrument of claim 13 wherein the cutter includes a
plurality of teeth having an angular spacing measured in the cutter
rotation plane, the cutter oscillating with an angular amplitude
that is greater than the angular spacing of the teeth.
15. The instrument of claim 13 wherein the cutter includes a
plurality of teeth having an angular spacing measured in the cutter
rotation plane, the cutter oscillating with an angular amplitude
that is less than the angular spacing of the teeth.
16. The instrument of claim 15 wherein the control unit further
sends a constant drive signal combined with the oscillating drive
signal to the motor to cause the cutter to oscillate while
simultaneously rotating.
17. The instrument of claim 13 wherein the shaft includes a portion
that is steerable to change the angle of the cutter relative to the
shaft.
18. The instrument of claim 12 wherein the cutter comprises a
circular blade having teeth formed around its perimeter.
19. The instrument of claim 18 wherein the cutter comprises a
plurality of circular blades mounted on a common shaft, the blades
having graduated diameters.
20. The instrument of claim 12 wherein the cutter comprises a
hollow shell having an interior and an outer surface, the shell
having teeth formed on its outer surface, the shell including
openings from the outer surface to the inner surface adjacent the
teeth.
21. The instrument of claim 12 wherein the cutter comprises a
hemispherical body defining a pole and an equator, the body
defining longitudinally oriented and circumferentially spaced teeth
extending from the pole to the equator.
22. The instrument of claim 12 wherein the cutter comprises an
expandable cutter head formed from a flexible material with cutting
teeth attached to its outer surface.
23. An orthopaedic cutting instrument for cutting tissue at a
surgical site, the surgical site being defined within a surgical
navigation coordinate system, the instrument comprising: a drive
mechanism; a cutter coupled to the drive mechanism; means for
tracking the cutter within the surgical navigation coordinate
system; means for defining a cut zone within the surgical
navigation coordinate system corresponding to a portion of the
surgical site; means for driving the drive mechanism to cause the
cutter to cut tissue when the cutter is within the cut zone; and
means for stopping the drive mechanism to cause the cutter to cease
cutting tissue when the cutter is outside of the cut zone.
24. The instrument of claim 23 wherein the means for driving causes
the cutter to oscillate rotationally.
25. The instrument of claim 23 wherein the means for driving causes
the cutter to oscillate rotationally while simultaneously
rotating.
26. The instrument of claim 23 wherein the drive mechanism
comprises a handpiece including a motor and a control unit coupled
to the handpiece to send a drive signal to the motor, the means for
tracking being coupled to the control unit to modify the drive
signal to cause the motor to stop when the cutter is outside of the
cut zone.
27. The instrument of claim 23 further comprising means for
steering the cutter to cause the cutter to change position within
the cut zone.
28. The instrument of claim 27 wherein the means for steering
comprises actuators coupled to the means for tracking, the means
for tracking transmitting a signal to the actuators to cause the
cutter to change position within the cut zone.
29. The instrument of claim 23 wherein the means for tracking is
able to produce an output indicating areas with the cut zone
through which the cutter has not yet passed.
30. A method of cutting tissue at a surgical site comprising:
introducing a cutter into a surgical site; driving the cutter to
preferentially cut relatively hard tissues as opposed to relatively
soft tissues; and manipulating the cutter within the surgical site
to morselize relatively hard tissues.
31. The method of claim 30 wherein the cutter is mounted on a
curved shaft and further wherein manipulating the cutter comprises
moving the shaft from side to side and rotating the shaft to cause
the cutter to sweep an area larger than the cutter diameter.
32. The method of claim 30 wherein the cutter is mounted on an
elongated shaft and the shaft includes a steerable portion,
manipulating the shaft comprising steering the steerable portion to
cause the cutter to change position relative to the shaft.
33. The method of claim 30 wherein driving the cutter comprises
moving the cutter in an oscillating rotary motion.
34. The method of claim 33 further comprising: adjusting the
oscillation amplitude to adjust the cutting characteristics of the
cutter.
35. The method of claim 33 further comprising: adjusting the
oscillation frequency to adjust the cutting characteristics of the
cutter.
36. The method of claim 30 wherein driving the cutter comprises
moving the cutter in a continuous rotary motion.
37. The method of claim 30 wherein driving the cutter comprises
moving the cutter in an oscillating rotary motion while
simultaneously rotating the cutter in a continuous rotary
motion.
38. The method of claim 30 wherein introducing a cutter into a
surgical site comprises moving the cutter in a continuous rotary
motion to form an access portal and driving the cutter comprises
moving the cutter in an oscillating rotary motion.
39. The method of claim 30 wherein introducing a cutter into a
surgical site comprises forming a portal through a femur from the
lateral side of the femur to the hip joint.
40. The method of claim 39 wherein driving the cutter selectively
removes the femoral head.
41. A method of cutting tissue at a surgical site comprising:
introducing a cutter into a surgical site; tracking the position of
the cutter with a surgical navigation system; and driving the
cutter with cutter position dependent drive inputs.
42. The method of claim 41 further comprising: defining a cut zone
within the surgical navigation system, driving the cutter
comprising driving the cutter to cut tissue when the cutter is
within the cut zone.
43. The method of claim 41 wherein introducing a cutter into a
surgical site comprises forming a portal through a femur from the
lateral side of the femur to the hip joint.
44. The method of claim 43 wherein driving the cutter selectively
removes the femoral head.
Description
FIELD OF THE INVENTION
[0001] The invention relates to orthopaedic cutting instruments
used in orthopaedic surgery. In particular, the invention relates
to powered instruments used to resect tissue.
BACKGROUND
[0002] Orthopaedic surgical procedures exist to treat a wide
variety of conditions of the bones and joints of the human body.
For example, procedures exist to remove damaged or diseased tissues
such as bone tumors. Procedures also exist to replace damaged or
diseased tissues such as joint replacement surgery in which the
articular ends of the bones forming a joint are removed and
replaced with prosthetic bearing components. During such
procedures, tissue is removed from the surgical site using tissue
cutting instruments such as saws, drills, shavers, and
grinders.
[0003] Many surgical procedures are now performed with surgical
navigation systems in which sensors detect tracking elements
attached in known relationship to an object in the surgical suite
such as a surgical instrument, implant, or patient body part. The
sensor information is fed to a computer that then triangulates the
position of the tracking elements within the surgical navigation
system coordinate system. Thus the computer can resolve the
position and orientation of the object and display the position and
orientation for surgeon guidance. For example, the position and
orientation can be shown superimposed on an image of the patient's
anatomy obtained via X-ray, CT scan, ultrasound, or other imaging
technology.
SUMMARY
[0004] The present invention provides an orthopaedic cutting
instrument and methods.
[0005] In one aspect of the invention, an orthopaedic cutting
instrument includes a drive mechanism, a cutter coupled to the
drive mechanism, means for driving the drive mechanism to produce
oscillating rotary motion of the cutter; and means for adjusting
the angular amplitude of the oscillating rotary motion.
[0006] In another aspect of the invention, an orthopaedic cutting
instrument includes a handpiece including a motor, an elongated
shaft extending from the handpiece and defining a shaft centerline,
the shaft being coupled to the motor to transmit rotary motion from
the motor, a cutter coupled to the shaft, and a control unit for
driving the motor to produce oscillating rotary motion of the
cutter about the shaft centerline.
[0007] In another aspect of the invention, an orthopaedic cutting
instrument includes a drive mechanism, a cutter coupled to the
drive mechanism, and means for driving the drive mechanism to
preferentially cut relatively hard tissue and spare relatively soft
tissue.
[0008] In another aspect of the invention, an orthopaedic cutting
instrument includes a drive mechanism, a cutter coupled to the
drive mechanism, means for tracking the cutter within a surgical
navigation coordinate system, means for defining a cut zone within
the surgical navigation coordinate system corresponding to a
portion of the surgical site, means for driving the drive mechanism
to cause the cutter to cut tissue when the cutter is within the cut
zone, and means for stopping the drive mechanism to cause the
cutter to cease cutting tissue when the cutter is outside of the
cut zone.
[0009] In another aspect of the invention, a method of cutting
tissue at a surgical site includes introducing a cutter into a
surgical site; driving the cutter to preferentially cut relatively
hard tissues as opposed to relatively soft tissues; and
manipulating the cutter within the surgical site to morselize
relatively hard tissues.
[0010] In another aspect of the invention, a method of cutting
tissue at a surgical site includes introducing a cutter into a
surgical site; tracking the position of the cutter with a surgical
navigation system; and driving the cutter with cutter position
dependent drive inputs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Various examples of the present invention will be discussed
with reference to the appended drawings. These drawings depict only
illustrative examples of the invention and are not to be considered
limiting of its scope.
[0012] FIG. 1 is an exploded perspective view of an illustrative
orthopaedic cutting instrument according to the present invention
including a set of modular cutter heads;
[0013] FIG. 2 is a cross sectional view taken along line 2-2 of
FIG. 1;
[0014] FIG. 3 is a front elevation view of a controller for the
orthopaedic cutting instrument of FIG. 1;
[0015] FIG. 4 is a diagram showing a drive input for producing
oscillating cutter head motion;
[0016] FIG. 5 is a diagram showing a drive input for producing
rotating cutter head motion;
[0017] FIG. 6 is a diagram showing a drive input for producing
combined oscillating and rotating cutter head motion;
[0018] FIG. 7 is a perspective view of one of the cutter heads of
FIG. 1;
[0019] FIG. 8 is a cross sectional view of the cutter head of FIG.
7;
[0020] FIG. 9 is a side elevation view of a blade of the cutter
head of FIG. 7;
[0021] FIG. 10 is perspective view of tissue cut by the cutter head
of FIG. 7; and
[0022] FIG. 11 is a side elevation view of the instrument of FIG. 1
in use to prepare a femoral bone to receive an implant.
DESCRIPTION OF THE ILLUSTRATIVE EXAMPLES
[0023] Embodiments of orthopaedic cutting instruments according to
the present invention include a powered cutter for removing tissue
at a surgical site. The surgical site may include such sites as a
hip joint, knee joint, vertebral joint, vertebral body, shoulder
joint, elbow joint, ankle joint, digital joint of the hand or foot,
fracture site, tumor site, and/or other suitable surgical site. The
instrument may include a powered handpiece containing a motor and a
cutter head. The cutter head may be a separate modular cutter head
engageable with the handpiece. The cutter head may include a
circular blade, a convex burr, a grating shell, and/or other
suitable cutter head configurations. The handpiece may drive the
cutter head in oscillating motion and/or rotary motion. The cutter
head motion may range from oscillation only to rotation only and
combinations of oscillation and rotation. For example, the
handpiece may drive the cutter head in a rotary motion mode to
create an access portal in drill-like fashion and then be switched
to an oscillating motion mode to selectively remove tissue at an
accessed surgical site. An oscillating motion component may be
controlled in amplitude and frequency so that the cutter head
cutting action may be tailored to different tissues and to produce
differing effects. For example, the oscillations of the cutter head
may be configured to morselize relatively hard tissues while having
no destructive effect on relatively soft tissues.
[0024] The handpiece may be driven pneumatically, hydraulically,
electrically, or by other suitable means. For example, the
handpiece may be driven by an electrical signal. The handpiece may
be configured to turn in one direction with a first electrical
polarity and in an opposite direction with the reverse polarity.
Oscillatory motion may be achieved by inputting a step function
that varies from positive to negative. Rotary motion may be
achieved by supplying a constant voltage. Oscillatory and rotary
motion may be combined by inputting an alternating step function
overlaid with a constant direct current offset.
[0025] The entire instrument may be insertable into a surgical site
or a portion of the instrument may remain outside of the surgical
site while the cutter head is positioned within the surgical site.
For example the handpiece may include an elongated barrel to
facilitate accessing a surgical site. The barrel may be curved
and/or may include a flexible portion to further facilitate
accessing a surgical site. The barrel may be rotatable relative to
the handpiece to position the barrel curve relative to the
handpiece to facilitate reaching a particular surgical site.
Furthermore, the barrel may be intraoperatively rotatable while the
cutter head is positioned within the surgical site to cause the
cutter head to sweep out an area larger than the cutter head. For
example, an elongated barrel may be used to introduce the cutter
head using a minimally invasive surgical approach through a small
incision and along an access portal to a surgical site. For
example, the cutter head may be introduced into a skeletal joint
through a portal formed in a bone. The cutter head may then be
driven to morselize bone adjacent the joint to prepare the joint to
receive an implant. With the cutter head driven in oscillatory
motion to preferentially morselize relatively hard tissues, the
cutter head may be manually manipulated within the bone to remove
the relatively harder bone without cutting the relatively softer
cartilage and capsular tissues. Positioning of the cutter head may
be further facilitated by use of fluoroscopic or other surgical
imaging techniques.
[0026] A flexible portion may be steerable to guide the cutter head
to a desired location and/or to sweep the cutter head back and
forth to remove bone from a particular region. For example, a
flexible portion may include embedded cables connected to an
actuator such that moving the actuator steers the cutter head.
[0027] The instrument may include fluid delivery and/or fluid
evacuation to expand soft tissue surrounding the surgical site to
facilitate movement of the cutter head, to facilitate removal of
resected tissue from the surgical site, and/or to cool the cutter
head and tissue being cut. For example, the barrel may be
cannulated and include a fluid delivery channel for delivering
fluid to the surgical site. The fluid may include gases such as
carbon dioxide and other suitable gases to insufflate the surgical
site to provide more room to manipulate the cutter head. The fluid
may include liquids such as saline and other suitable liquids to
irrigate the surgical site to provide more room and/or to flush
away resected tissues. The barrel may further include a fluid
aspiration channel for allowing fluids to egress from the surgical
site to facilitate controlling the pressure at the surgical site
and also for removal of resected tissues. Fluid delivery and fluid
evacuation channels may also be provided separately from the
instrument such as with separate portals used in arthroscopy and
endoscopy.
[0028] The instrument may include tracking elements detectable by a
surgical navigation system such that the three dimensional position
of the tracking elements can be related to a surgical navigation
coordinate system. For example, a surgical navigation system may
include multiple sensors at known locations that feed tracking
element position information to a computer. The computer may then
use the position information from the multiple sensors to
triangulate the position of each tracking element within the
surgical navigation coordinate system. The surgical navigation
system can then determine the position and orientation of the
cutter head by detecting the position and orientation of the
tracking element and then resolving the position and orientation of
the cutter head from the known relationship between the tracking
array and the cutter head. Tracking elements may be detectable by
imaging, acoustically, electromagnetically, and/or by other
suitable detection means. Furthermore, tracking elements may be
active or passive. Examples of active tracking elements may include
light emitting diodes in an imaging system, ultrasonic emitters in
an acoustic system, and electromagnetic field emitters in an
electromagnetic system. Examples of passive tracking elements may
include elements with reflective surfaces.
[0029] When used with a surgical navigation system, the instrument
controller may be interfaced with the surgical navigation system to
provide location dependent drive inputs to the handpiece. For
example, a particular area within the surgical site may be
identified within the surgical navigation system coordinate system
as a cut zone and/or another area may be identified within the
surgical navigation system coordinate system as a no-cut zone.
Thus, with the surgical navigation system activated, the cutter
head may be driven to resect tissue at the surgical site. If the
cutting envelope of the cutter head begins to exit a cut zone
and/or enter a no cut zone, a signal from the surgical navigation
system to the instrument controller may cause the handpiece to stop
the cutter head. Thus, the cutter head can be manually manipulated
within the surgical site and the cutter head will only resect
tissue when the cutting envelope of the cutter head is within a
predefined area to be resected. The precise location of the cutter
head may not be visible to the surgeon. However, the surgeon can
manipulate the cutter head with confidence knowing that it will
only be driven to resect tissue when it is in the predefined cut
zone. Alternatively, the surgical navigation system may display a
computer image showing the location of the cutter head relative to
the patient's anatomy.
[0030] A steerable cutter head may be configured such that one or
more actuators are motorized and coupled to a surgical navigation
system. In such a system, the cutter head may be steered by the
surgical navigation system to automatically manipulate the cutting
envelope of the cutter head within a predefined cut zone to resect
a particular region of the surgical site. Surgical navigated
steering and surgical navigated cut/no-cut zones may be utilized
together.
[0031] FIGS. 1-10 show an illustrative orthopaedic cutting
instrument and its use in an illustrative surgical technique. The
illustrative instrument includes a handpiece 100, modular cutter
heads 200, 260, 280, and a control unit 300. The handpiece 100
includes a body 102 having a dependent grip 104, and a forwardly
projecting barrel 106. The handpiece 100 houses a motor 108 coupled
to a flexible drive shaft 110 extending from the motor 108, through
the barrel 106, and terminating at a drive chuck 112. The drive
chuck 112 receives the modular cutter heads 200, 260, 280 in torque
transmitting relationship. The cutter heads 200, 260, 280 each
include a cylindrical drive shaft 202, 262, 282 having a axial
locking groove 204, 264, 284 and a "D"-shaped driving portion
having a flat drive surface 206, 266, 286. The drive chuck has a
complementary configuration including a "D"-shaped recess
engageable with the driving portion and a ball detent for engaging
the axial locking groove 204, 264, 284 to retain the cutter heads
200, 260, 280 as is known in the art. The motor 108 drives the
drive shaft 110 in rotary motion which in turn drives the cutter
heads 200, 260, 280 in rotary motion. In the illustrative
instrument, the handpiece 100 defines a pistol grip with the body
102 defining a first axis 103 and the grip 104 defining a second
axis 105 transverse to the body axis 103. The angle 107 between the
two axes 103, 105 facilitates a comfortable grip while permitting
natural pointing of the handpiece 100 and applying pressure to
advance the handpiece 100 and cutter heads and move the cutter
heads about within the surgical site. The angle 107 may be
established to suit a particular surgical approach. However, an
angle between 90.degree. and 120.degree. is generally suitable.
Preferably the angle is approximately 110.degree..
[0032] The illustrative handpiece 100 includes an elongated barrel
106 extending from the body 102 to facilitate access to surgical
sites deep within a patient's body. The barrel 106 includes a
centerline 109. The barrel 106 may be straight or curved. The
illustrative barrel 106 includes a rigid curved portion 114 and a
steerable portion 116. The curved portion 114 facilitates placing
the cutter head in a surgical site that is not aligned with the
body axis 103 when the handpiece is conveniently positioned. The
barrel 106 is rotatable relative to the handpiece to position the
curved portion 114 rotationally relative to the handpiece 100 to
facilitate reaching a particular surgical site. An indexing wheel
115 is mounted on the barrel 106 and can be gripped and rotated to
rotate the barrel 106. A ball detent 117 mounted in the body 102
engages the indexing wheel 115 to maintain the barrel 106 in a
desired position. The cutter head may be moved within a surgical
site to cut tissues by rocking the handpiece 100 back-and-forth
and/or rotating the handpiece 100. The indexing wheel 115 may be
used intraoperatively to rotate the barrel 106 and cause the cutter
head to sweep out an area larger than the cutter head. The
steerable portion 116 includes a flexible material such as an
elastomer, a coil spring, and/or other suitable flexible materials
that allow the steerable portion 116 to bend elastically. A pair of
cables 118 attach to the steerable portion 116 and to an actuator
120 mounted in the handpiece 100. Pivoting the actuator 120 causes
one of the cables 118 to pull on the steerable portion 116 and bend
the steerable portion 116 causing the drive chuck 112 and attached
cutter head to change orientation. The steerable portion 116
permits changing the angle of the cutter head relative to the
barrel centerline 109 to achieve greater movement or the cutter
head within the surgical site. The illustrative handpiece 100 has a
pair of cables 118 permitting control of the steerable portion 116
in one plane. However, it is contemplated that any number of cables
and/or other linkages may be used to permit control of the
steerable portion 116 in any number of planes. For example, four
cables 118 may be used with two actuators 120 to bend the steerable
portion 116 in three dimensions. The illustrative actuator 120 is
shown as a manually operated thumb lever projecting from the body
102. However, it is contemplated that the actuator 120 may be
powered, such as by a motor.
[0033] The illustrative barrel is cannulated to provide fluid
delivery and aspiration to and from the surgical site. Fluid is
transmitted from a fluid reservoir (not shown) through supply line
122, through fluid delivery portal 124 and out the drive chuck 112.
Fluid and debris are transmitted from the surgical site through the
drive chuck 112, through aspiration portal 126 and out suction line
128. The cutter heads 200, 260, 280 may optionally be cannulated so
that fluid delivery and aspiration occur through the cutter
heads.
[0034] The handpiece further includes a trigger 130 coupled to the
motor 108 to permit operator control of the motor 108. The control
signal for the motor 108 is provided by a control unit 300 which
may be part of the handpiece 100 or a separate unit as shown in
FIG. 3. The control unit 300 includes a power input 302 and a power
output 304. The power output 304 connects to the handpiece 100 and
drives the motor 108. The power input 302 and output 304 may be
pneumatic, hydraulic, and/or electric. In the illustrative example,
the power is electric. The trigger 130 interrupts the power
connection from the power output 304 to the motor 108 in the rest
position such that activating the trigger permits the motor 108 to
operate. Optionally, the trigger can be configured to vary the
amplitude of the control signal from zero when the trigger 130 is
at rest to the maximum output control signal when the trigger 130
is fully depressed.
[0035] The control unit 300 includes controls for adjusting the
power output 304 to produce a desired cutter head action. FIGS. 4-6
depict resulting illustrative power output 304 signals 400, 420,
440 for driving the motor 108. The illustrative signals are
characterized by step functions having positive values (positive
polarity in an electrical system, positive pressure in pneumatic
and hydraulic systems) that cause the motor 108 to rotate clockwise
and negative values (negative polarity in an electrical system,
negative pressure in pneumatic and hydraulic systems) that cause
the motor to rotate counterclockwise. Referring to the signal
depicted in FIG. 4, the time for the signal to cycle from the start
of one positive step to the start of the next positive step is the
period 402 of the signal. The inverse of the period 402 is the
frequency. The height 404 of each step determines the rotational
speed of the motor and the length of each step 406 determines how
long the motor 108 is driven in each direction. The height 404 and
length 406 together determine how far the motor 108 rotates in each
direction and thus controls the angular amplitude of the motor and
cutter head. Increasing either of the height 404 and length 406
will increase the angular amplitude and decreasing either of the
height 404 and length 406 will decrease the angular amplitude. In
the illustrative signals, the length 406 of the steps is kept
constant and the height 404 is adjustable. Referring to FIG. 5, a
constant positive signal 420 is illustrated which will cause the
motor 108 to rotate constantly clockwise. The height 422 of the
signal will determine the rate of rotation. FIG. 6 illustrates a
signal 240 combining the oscillating characteristics of FIG. 4 with
a constant positive offset 442 like that of FIG. 5. The effect of
this combined signal 440 is that the motor 108 will oscillate while
rotating clockwise.
[0036] The control unit 300 of FIG. 3 includes a period control
knob 306 that is rotated to adjust the period 402 of the motor
oscillations, an amplitude control knob 308 that is rotated to
adjust the height 404 of the step function and thus the amplitude
of angular oscillation, and a rotation control knob 310 that
introduces a constant offset. Rotating the rotation control knob
310 clockwise increases the offset in the positive direction.
Rotating the rotation control knob 310 counterclockwise increases
the offset in the negative direction. A power switch 312 turns the
control unit on an off. An infinite variety of control signals can
be produced by adjusting the control knobs 306, 308, 310. For
example, setting the oscillation control knobs 306 and 308 to zero
and adjusting the rotation control knob 310 clockwise will provide
a constant positive drive signal upon trigger 130 activation to
turn the cutter head. In this mode, the handpiece will act like a
drill. The rotational speeds can advantageously range from
0-100,000 rpm or more. Larger cutting heads are advantageously
driven at slower speeds while smaller cutter heads are
advantageously driven at faster speeds. For example a large cutter
head or drill bit may be driven between 100 and 1000 rpm to create
an access portal through a bone. In another example, setting the
rotation control 310 to zero and adjusting the oscillating controls
306 and 308 to non-zero values will cause the handpiece 100 to
oscillate the cutter head. The oscillation angle can range from
0.degree. to any value. Advantageously the oscillation angle is
between 0.degree. and 180.degree.. Having all three controls 306,
308, 310 set to non-zero values will cause the handpiece 100 to
oscillate and rotate the cutter head simultaneously.
[0037] As long as the offset 442 of FIG. 6 is less than the
relative height 444 of the steps, the motor will oscillate in both
directions as it rotates. However, in the example of FIG. 6, the
motor will rotate clockwise at a faster rate, and thus further
angularly, than it will counterclockwise because the net positive
signal height 446 resulting from adding in the offset 442 is
greater than the net negative signal height 448. If the offset 442
equals or exceeds the relative height 444 of the steps, the motor
will not actually oscillate but will pulse in one direction as it
turns.
[0038] Different tissues respond differently to different cutter
head motions and blade configurations. For example, different
tissues can tolerate different amounts of lineal displacement
before they begin to tear, fracture, or otherwise become disrupted.
The amount of lineal displacement of a cutter head tooth and
consequently the amount of lineal displacement to which tissue
abutting the tooth is subjected is a function of the angular motion
of the cutter head and the radius from the rotational axis to the
tooth. The control unit 300 may include markings and/or preset
switches corresponding to predetermined values indicating optimum
control settings for different types of cutter heads and different
tissues. For examples there may be a predetermined optimum setting
for a circular blade style cutter head 200 and cortical bone and
another optimum setting for a grater style cutter head 280 and
cartilage.
[0039] FIGS. 7-9 illustrate the circular blade style cutter head
200 of FIG. 1 in more detail. The cutter head 200 includes a
cylindrical drive shaft 202 having an axial locking groove 204 and
a "D"-shaped driving portion having a flat drive surface 206 as is
known in the art. The cutter head 200 further includes a plurality
of blades 208 spaced along the shaft 202. Each blade 208 includes a
central bore 210 that slips over the shaft 202. Spacers 212 fit
between the blades 208 to space them from one another. A key 214
fits within a keyway 216 in the shaft 202 and engages a notch 218
in each blade to rotationally lock the blades 208 to the shaft 202.
An end cap 220 presses the spacers and blades together axially and
is secured with a bolt 222 threaded into the shaft 202. The end cap
220 defines a blunt nose on the cutter head. The blades 208 include
a plurality of teeth 224 spaced around their perimeters.
Preferably, the teeth 224 are set in an alternating pattern to
provide for chip clearance and more efficient cutting. In the
illustrative example, the blades 208 have graduated diameters
increasing from a relatively small diameter blade near the end cap
220 to a relatively large diameter blade spaced from the end cap
220. The graduated blades 208 define a frustoconical cutting
envelope. However, it is contemplated that the blades 208 may vary
in diameter in other patterns or may all be the same diameter. The
modular nature of the illustrative example permits the blade
configuration to be easily changed by the user.
[0040] When the cutter head 200 is used in an oscillating mode the
blades 208 tend to cut relatively hard tissues, such as bone,
aggressively while relatively soft tissues such as meniscal
cartilage and capsular ligaments are not cut. It is believed that
since hard tissues are less mobile local to the teeth 224, the
oscillating motion of the blades 208 fractures the bone and thereby
morselizes it. Conversely, relatively soft tissues are more mobile
local to the teeth 224 and tend to move back and forth with the
teeth 224 without being cut. As long as the lineal displacement of
the teeth 224 is within the range of displacement that the soft
tissue can tolerate without being cut, oscillating the cutter head
200 in an environment including both soft and hard tissues will
tend to morselize the hard tissue while leaving the soft tissue
intact. The lineal displacement of a tooth 224 is equal to twice
the product of the radius 229 from the rotational axis to the tooth
tip and the oscillation amplitude 226 in radians. Furthermore,
during oscillation, soft tissues do not wrap around the blade or
otherwise entangle it. The present investigators have found that
when the oscillating amplitude 226 exceeds the tooth angular
spacing 228, the blades 208 cut much more aggressively in hard
tissues such as bone. Likewise, when the oscillating amplitude 226
is less than the tooth angular spacing 228, the blades cut much
less aggressively. For example, it has been found that with the
illustrative blade shown in FIGS. 7-9, a blade radius 229 of 0.3
inches with a tooth spacing of 8.degree. and an oscillation
amplitude of 10.degree. produces good cutting results in bone while
not cutting adjacent soft tissues.
[0041] An optional cutter head 260 is also depicted in FIG. 1. This
cutter head 260 includes circumferentially spaced longitudinal
teeth 268 extending along the other surface of the cutter head 260
from the cutter head pole 270 to its equator 272. This cutter head
260 is end cutting and can be used to penetrate tissue and form an
access portal. It can also be configured as a collapsible cutter
head to permit it to fit through a small, preformed access portal
and then be expanded at the surgical site. For example, the cutter
head 260 may be formed from a flexible material with cutting teeth
268 attached to its outer surface. In the collapsed state, the
teeth 268 are closely spaced and the cutter head 260 occupies a
first volume. When it is expanded, the cutter head 260 occupies a
second, larger volume and the teeth 268 are more widely spaced. The
cutter head 260 may be formed of an elastic or inelastic flexible
material such as an elastomer, fabric, film, foil, and/or other
suitable material. The teeth may be formed of metal, polymer,
ceramic, and/or other suitable material. For example, an
elastomeric cutter head 260 may be in the form a hollow molded
synthetic rubber cylinder with metal teeth 268 embedded in its
outer surface. The cutter head 260 may be inserted through a
relatively small access portal and then expanded by inflating it
with air, saline, and/or other suitable fluid into its
hemispherical cutting shape. After the cutter head 260 has been
used, it may be deflated and withdrawn. Alternatively, an
inflatable core can be covered with a woven mesh similar to chain
mail to provide an abrading and/or cutting surface. Likewise, an
expandable cutter head may include a mechanical arrangement of
hinged blades and or other mechanism that permits the cutting
diameter to be varied.
[0042] Another optional cutter head 280 is also depicted in FIG. 1.
This cutter head 280 includes a hollow shell 288 having an outer
surface and an inner surface. Grater style teeth 290 project
outwardly from the outer surface of the shell 288. The shell 288
includes openings 291 communicating from the outer surface to the
inner surface to allow tissue cut by the teeth 290 to pass to the
inside of the head where it can be easily aspirated or where it can
be retained for subsequent removal. This cutter head 280
facilitates the collection of tissue for purposes of tissue
grafting, laboratory assay, and/or other purposes. The illustrative
grater style cutter head 280 has teeth that all face in the same
rotational direction such that it cuts in one direction only. To
cut tissue, the cutter head 280 may be oscillated, pulsed, or
rotated. When driven in reverse rotary mode, the cutter head 280
will not cut tissue but can be used to smooth and consolidate
tissues.
[0043] FIG. 10 illustrates the effects of varying the relationship
of the tooth angular spacing 228 and the oscillation amplitude 226.
As the cutter head 200 is oscillated against a relatively hard
tissue 230 such as bone, the teeth 224 will cut into the tissue
230. If the oscillation amplitude 226 is less than the tooth
angular spacing 228, the teeth will cut grooves 232 in the tissue
separated by uncut areas 234. This may be desirable, for example,
to score a bone to produce bleeding bone to stimulate bone growth
or to roughen a bone to accept bone cement. As the oscillation
amplitude 226 is increased relative to the tooth spacing 228, the
grooves 232 will widen and the uncut areas 234 will become more
narrow until the oscillation amplitude 226 is equal to or greater
than the tooth spacing 228 in which case the tooth will remove all
of the bone between adjacent teeth 224. Thus, for efficient tissue
removal, it is advantageous for the oscillation amplitude 226 to
exceed the tooth spacing 228. However, in some instances it may be
advantageous to have relatively widely spaced teeth and relatively
small oscillation amplitude 226. For example, with the grater style
cutter head 280, it may be difficult to produce a cutter head with
closely spaced teeth. In another example, it may be desirable to
have widely spaced teeth in order to cut the tissue into larger
pieces. Furthermore, it may be more efficient to drive the cutter
head with high frequency and low amplitude oscillations. In any
situation where the tooth spacing 228 is greater than the
oscillation amplitude 226, complete removal of tissue between
adjacent teeth 224 may be accomplished by rotating the cutter head
in addition to oscillating it to cause the teeth to progress across
the surface of the tissue. A relatively slow rotation velocity is
sufficient.
[0044] In use, the instrument may be used to excise bone by
inserting it into a surgical site and relying on the preferential
cutting characteristics of a particular cutter head and operation
mode to remove the desired tissue. For example, in a hip joint
application as shown in FIG. 11, the cutter head 200 is introduced
through a portal 501 defining a longitudinal portal axis in the
lateral side 502 of the femur 500. The portal 501 can be
pre-drilled with a conventional drill bit or it can be produced
with the present instrument by using an end cutting cutter head,
such as the cutter head 260 (FIG. 1) and running the handpiece 100
in rotating mode. The cutter head 200 is advanced to the surgical
site and then oscillated to morselize the femoral head 504 and neck
506. However, soft tissues 508, such as the joint cartilage and
capsular ligaments, are not cut by the oscillating cutter head 200
and thus contain the cutting action to the bone of the head 504 and
neck 506. The cutter head 200 is manipulated within the surgical
site by rocking the handpiece 100 and barrel 106 back-and-forth to
move the cutter head 200 off of the portal axis 503. Rotating the
handpiece 100 about the body axis 103 causes the cutter head 200 to
sweep out an area larger than the cutter head 200 around the portal
axis 503. To further aid in reaching the entire surgical site, the
cutter head 200 can be steered using the actuator 120 to change the
angel of the cutter head to the barrel centerline 109. Morselized
bone is mobilized and removed by irrigating and aspirating the
surgical site with saline introduced and removed through the
cannulated barrel 106. The instrument may be used blindly relying
on its preferential cutting ability. Alternatively, a visualization
system may be used to monitor the progress of the cutter head 200.
For example, a fluoroscopic imaging system may be used to visually
track the cutter head 200.
[0045] Optionally, the cutter head may include a tracking element
trackable by a surgical navigation system. For example, the end cap
220 may include a tracking element in the form of an
electromagnetic coil. By detecting the position of the coil, the
surgical navigation system can resolve the location of the cutting
envelope defined by the moving blades 208. The position of the
cutting envelope may be combined with other patient data such as
that from x-rays, MRI scans, CT scans, and/or other sources and
displayed for surgeon guidance. Furthermore, the control unit 300
may be interfaced with the surgical navigation system to provide
location dependent drive inputs to the handpiece 100. For example,
a particular area within the surgical site such as the femoral head
504 and neck 506 may be identified within the surgical navigation
system coordinate system as a cut zone and another area, such as
the acetabulum and/or joint capsule, may be identified within the
surgical navigation system coordinate system as a no-cut zone.
Thus, with the surgical navigation system activated, the cutter
head 200 may be driven to resect tissue at the surgical site. If
the cutting envelope of the cutter head 200 begins to exit a cut
zone and/or enter a no-cut zone, a signal from the surgical
navigation system to the instrument controller 300 will cause the
handpiece to stop the cutter head 200. Thus, the cutter head 200
can be manually manipulated within the surgical site and the cutter
head 200 will only resect tissue when the cutting envelope of the
cutter head 200 is within a predefined area to be resected. The
precise location of the cutter head 200 may not be visible to the
surgeon. However, the surgeon can manipulate the cutter head 200
with confidence knowing that it will only be driven to resect
tissue when it is in the predefined cut zone. This navigated
control option also permits the use of more aggressive cutter heads
and operation modes while protecting tissues in the no-cut zones.
The cutter head may be driven in any mode including rotating,
oscillating, and mixed rotating and oscillating mode. However,
driving the cutter head in an oscillating mode advantageously
permits rapid stopping of the cutter head since it may develop less
angular momentum and the cutter head is already being frequently
stopped and reversed to produce the oscillating motion. The
surgical navigation system can also be configured to indicate
portions of the cut zone that the cutting envelope has not yet
passed through so that the cutter head 200 can be repositioned in
these uncut areas until all of the desired tissue has been cut.
[0046] A steerable configuration may include one or more motorized
actuators 120 coupled to the surgical navigation system. In such a
system, the cutter head 200 may be steered by the surgical
navigation system to automatically manipulate the cutting envelope
of the cutter head within the predefined cut zone to efficiently
resect the cut zone.
[0047] The cutter head 200 may have tracking elements attached at
other locations. Furthermore, tracking elements may be attached
outside of the surgical site as long as the relationship of the
tracking elements to the cutter head 200 is known. For example,
where the relationship of the cutter head 200 to the barrel 106 or
handpiece 100 is known, the tracking elements may be attached to
the barrel 106 or handpiece 100. Any type of tracking element may
be used.
[0048] Although examples of an orthopaedic cutting instrument and
its use have been described and illustrated in detail, it is to be
understood that the same is intended by way of illustration and
example only and is not to be taken by way of limitation. The
invention has been illustrated in the context of a handpiece,
controller, and modular cutter head and has been shown in use to
resect a femoral head and neck in a minimally invasive procedure.
However, the orthopaedic cutting instrument may be alternatively
configured and may be used to remove other types of tissue at other
locations within a patient's body. Accordingly, variations in and
modifications to the orthopaedic cutting instrument and its use
will be apparent to those of ordinary skill in the art, and the
following claims are intended to cover all such modifications and
equivalents.
* * * * *