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Description  |
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FIELD OF THE INVENTION
The present invention relates to apparatus and methods applicable in
surgical situations in which the precise positioning of a tool in relation
to a patient is an integral part of the surgery. More particularly, the
present invention utilizes a programmable robot in a system for
determining a reference position for certain surgical tasks, precisely
determining the position for a specific tool relative to the reference
position, positioning the tool, and rigidly holding the tool to aid the
surgeon in a more efficient and accurate completion of the task.
BACKGROUND OF THE INVENTION
During orthopedic surgery, it is often the case that surgeons are required
to make surgical alterations to bone. Such alterations include but are not
limited to making cuts in bone, drilling holes in bone, and affixing a
plate, screw, nail, or prosthesis to bone.
When making such alterations, it is desirable that the alteration be
realized in a manner which precisely conforms to the operative plan of the
surgeon. Among the aspects of a surgical alteration which require careful
control are: (1) the alignment of the cut, hole, plate, screw, nail, or
prosthesis with respect to the anatomy of the patient; (2) if there is
more than one bone cut and/or hole, the relative alignment of the cuts and
holes with respect to each other; and (3) if a plate, screw, nail, or
prosthesis is to be fixed to bone, the alignment of the cuts and/or holes
with respect to the plate, screw, nail or prosthesis.
Current surgical techniques utilize limited mechanical means to assist the
surgeon in making bone alterations. However, existing techniques do not
suffice to ensure that perfect or nearly perfect alterations can be
achieved routinely. Where practical, it is desirable to enhance the
surgeon's decision-making process by providing accurate solutions to
purely geometric problems posed by surgery, while leaving final
positioning decisions up to the surgeon. When the surgeon is provided with
accurate geometric solutions, the quality of the overall subjective
evaluation should be improved.
An example of a surgical procedure that requires accurate geometric
solutions, as well as the evaluation of specific patient physiological
characteristics, is total knee arthroplasty (TKA), which is a total knee
reconstruction surgery. The anatomic knee is a remarkable mechanism.
Contrary to first impression, it is not a simple hinge. Rather, the femur
and tibia move relative to each other with a complex mixture of rolling
and sliding motions. The stability of the joint comes entirely from soft
tissue structures, not from bone geometry. The major stabilizing ligaments
are the medial and lateral collateral ligaments, and the anterior and
posterior cruciate ligaments.
In total knee arthroplasty, the distal femur and the proximal tibia are
resected and are replaced by prosthetic components made of metal and
plastic. The most successful designs are unconstrained prostheses that
closely mimic the natural anatomy of the knee. Like the anatomic knee,
unconstrained designs allow the femur and tibia to roll and slide relative
to each other. They depend on the natural ligamentous structures of the
knee to stabilize the reconstructed joint.
Total knee reconstruction surgery is conceptually simple. The knee is
flexed, the patella moved to one side to give access to the joint, and the
degenerated surfaces of the femur and tibia are cut away. The bone cuts
are made to fit femoral and tibial prosthetic components, which are
available in a wide variety of sizes and styles. These are generally
cemented into place, using polymethyl methacrylate (PMMA). One new
technique uses no cement. Rather, bone grows into a porous backing on the
prosthetic component. This is termed porous-ingrowth fixation.
Each year, approximately 100,000 people undergo a TKA. TKAs are often
performed in people whose knees have become so painful, because of
progressive arthritic changes, that they are unable to rise from a chair,
walk, or climb stairs. For these people, total knee arthroplasty can
provide a return to near-normal, pain-free life.
A great deal of developmental technology has gone into perfecting the femur
prostheses used in TKAs. However, the technology for positioning the
prosthesis properly on the femur has not similarly advanced. Ideally, the
bone cuts should be (1) an exact press-fit to the components, and (2) in
proper alignment with respect to bones and soft tissues. Failure to
achieve these goals will result in poor knee mechanics and/or loosening of
the components, leading eventually to failure of the reconstruction.
At present, the surgical instrumentation used in total knee arthroplasty
consists of hand-held saws which are guided by simple cutting blocks and
mechanical jig systems. There is abundant evidence in the literature that
these tools do not suffice to do a good job. First, most prosthetic
components are not put in with perfect alignment, and misalignment of
three to five degrees or more is not uncommon. Second, prosthetic
components do not fit perfectly on the bone, and there are inadvertent
gaps between the cut surface of the bone and the prosthesis. Third, there
is a learning curve associated with arthroplasty technique. The first
fifty knees a surgeon does are not as good as subsequent knees.
The primary goals of the surgeon during total knee arthroplasty are: proper
alignment of the reconstructed knee, stability of the reconstructed knee,
and press-fit of the components to the bone. With respect to alignment,
the knee should neither be knock-kneed or bowlegged, to ensure that the
medial and lateral sides of the components bear equal loads. Asymmetric
loading leads to early failure. In addition, the ligaments of the knee
should provide stability at all angles of flexion, as they do in the
anatomic knee. If the ligaments are too tight, they will restrict the
motion of the knee. If they are too loose, the knee will "give way" during
use.
Finally, if a prosthetic component is even slightly loose, then each step
will "rock" the component against the bone. The bone soon gives way, and
the reconstruction fails. Ideally, the prosthesis is a press-fit to the
cut bone at the time of surgery. This minimizes micro-scale rocking
motions. Press-fit is especially important for a porous ingrowth
prosthesis, since even a one-millimeter gap between prosthesis and bone is
too large for the ingrowth process to bridge.
These goals are simple to state, but difficult to achieve in the operating
room. To understand the problems, consideration should be given to all the
ways malalignment can occur. There are three different ways a component
can be malaligned in orientation. These correspond to rotations of the
component away from the desired orientation along the internal/external,
varus/valgus, and flexion/extension axes. Similarly, there are three
different ways to malposition a component by translation along an axis.
These correspond to translations along the medial/lateral,
proximal/distal, and anterior/posterior axes.
Thus, to achieve good alignment and good ligament balance, surgeons must
mentally manipulate three translational and three orientational variables
for each of the femoral and tibial components, or twelve spatial variables
in all. Margins for error are small. Repositioning the prosthetic
component by even one millimeter has an appreciable effect on the
stability of the knee. Moreover, each knee presents its own special
problems. It is frequently the case that the knee has a preexisting
deformity which must be taken into account.
In addition, the surgeon must also take care that the bone surfaces are
press-fit to the component. This involves five cut planes and two drill
holes for a typical femoral component, and one cut plane and two drill
holes for a typical tibial component, for a total of ten separate cutting
operations. In each case, imprecision of one millimeter or less can have
significant consequences, especially for porous-ingrowth prostheses.
It is a remarkable fact that present-day surgical instruments for total
knee arthroplasty could have been manufactured in the nineteenth century.
The essential features of present-day instrumentation systems are their
reliance on hand-held oscillating saws to make bone cuts, and mechanical
jigs with slots and cutting blocks to help align the cuts. Considerable
ingenuity has been applied to optimizing instrumentation systems of this
type, and there are dozens of variations on the market. Nonetheless, poor
alignment and inaccurate cuts are common problems when using these
mechanical instrumentation systems.
Poor alignment occurs when femoral and tibial cutting jigs are not properly
aligned with respect to the hip, the ankle, and the stabilizing soft
tissues of the knee. This can happen because the surgeon is mislead by the
anatomic landmarks used by a given system, because the landmarks are
concealed by fat and muscle, because preoperative deformities exist, or
because the jig has shifted slightly during the procedure. The best test
of alignment is flexion of the newly reconstructed knee. Unfortunately, by
the time such a test can be made, the bone cuts have been made, and it is
too late to change the alignment of the components.
Inaccurate cuts occur when the various cuts and drill holes do not
precisely mate with the surfaces of the prosthetic components, possibly as
the result of errors which accumulate during placement and removal of the
various cutting blocks. Also, there is inherent inaccuracy associated with
a flexible, oscillating saw blade resting on a cutting block or in a slot.
The blade tends to "sky" when it encounters a dense section of bone. This
tendency is resisted by canting the handheld saw in a downward direction.
There is ample evidence in the published literature that the present state
of total knee arthroplasty is not satisfactory. Cameron H. U., Hunter G.
A. in: Failure in Total Knee Arthroplasty, 170 Clinical Orthopaedics and
Related Research: pp. 141, 146, 1982, noted, "[t]he results of total knee
arthroplasty range from an acceptable 5.4% failure rate at five years to
an abysmal 70% failure rate at three years. Failure rates of this
magnitude indicate that many revisions are being performed." Bryan R. S.,
Rand M. J. in: Revision Total Knee Arthroplasty, 170 Clinical Orthopaedics
and Related Research: pp. 116-122, 1982, state that, "[p]roper component
alignment is of critical importance" and that "[f]ailure to obtain
appropriate component orientation, axial alignment, and soft tissue
balance predisposes implants to loosening and failure." Hood R. W., Vannie
M., and Install J. N., as noted in, The Correction of Knee Alignment in
255 Consecutive Total Condylar Knee Replacements, 160 Clinical
Orthopaedics and Related Research: pp. 94-105, 1981, found in a series of
255 knees that, "[e]leven percent of the knees in this series were outside
the alignment limits selected. This may reflect extremes of body habitus
but, more importantly, indicates that deficiencies in instrumentation
still remain." Hvid I., Nielsen S. in: Total Condylar Knee Arthroplasty,
55 Acta Orthop Scand 55: pp. 160-165, 1984, found in a study of 138 knees
that although "the aim was to place the tibial component at right angles
to the tibial axis," only "53 percent were within four degrees of tilt in
any direction." Some of their components were eight degrees or more out of
alignment. In summary, there is ample evidence that with existing
instrumentation surgeons cannot obtain good alignment routinely in total
knee arthroplasty.
As is evident from the less-than-satisfactory clinical results, the theory
and practice of jig-assisted knee surgery are two different things. In
practice, total knee arthroplasty is largely a seat-of-the-pants
procedure. Surgeons recruit every pair of eyes in the operating room to
judge how a contemplated cut "looks" from a variety of angles. Equally
important is a steady and practiced hand on the cutting saw, and a sound
understanding of the biomechanics of the knee joint.
The conventional TKA requires that the surgeon attempt to achieve exact
physiologically correct relationships and to make geometrically exact cuts
with inexact methods. As discussed above, both the position and quality of
the cuts and bores greatly affect the success of the operation. While the
background of a TKA has been described, numerous types of surgeries
present the same problem of integrating geometric analysis with a
subjective evaluation of physiological factors. Examples of such surgeries
are osteotomies and ligament repairs. In the majority of these operations,
certain mechanical devices, such as the jig systems described above, have
been developed to aid in the operation. The exactness of these mechanical
devices varies and, thus, so do the efficiencies resulting from their use.
However, most surgical procedures that are not solely based on subjective
medical decisions will suffer from some inaccuracies based on the fact
that surgeons have a limited capacity for making independent exact
geometric calculations and carrying out tasks based on those calculations.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a system and method for
facilitating the performance of a surgical bone alteration task by
accurately positioning a tool relative to the patient's bone. The
illustrative example of a total knee arthroplasty (TKA) of a femur is
used.
In one preferred embodiment, a system according to the present invention
comprises bone immobilization means and a robot. The bone immobilization
means supports the patient's bone in a fixed position with respect to a
reference structure. The robot comprises a base, a mounting member and a
manipulator. The base is fixed in position with respect to the reference
structure. The manipulator connects the mounting member to the base so as
to permit relative movement between the mounting member and the base. The
robot also includes attachment means for securing a tool to the mounting
member. Finally, the system includes means for causing the mounting member
to move relative to the reference structure in response to movement
commands, so that the tool can be moved to a position to facilitate
performance of the task. The movement commands are preferably provided by
task control means that includes memory means for storing data and control
programs, and control processing means for processing the control programs
to generate the movement commands.
Preferably the system also includes a template attachable to the mounting
member. The template may be positioned such that a predetermined feature
of the template is in a desired position relative to the bone. For a TKA
procedure, the template feature may represent a surface of a prothesis to
be mounted on the patient's bone. With the template in the desired
position, the reference position of the template is recorded in a "world"
coordinate system that is fixed with respect to the reference structure.
The reference position may therefore be combined with a geometric database
that includes data representing the geometric relationships relevant to
the performance of the task, to generate movement commands that cause the
robot to move surgical tools into desired tool positions during subsequent
stages of the operation. Preferably, the reference position is determined
by placing the robot in a passive mode in which the mounting member may be
moved manually by an operator. The operator can then mount the template to
the mounting member, move the template and mounting member such that the
template is properly positioned with respect to the bone, and then cause
the system to record the reference position. The robot can then be
returned to an active mode in which the mounting member moves in response
to movement commands.
In another preferred embodiment, the present invention provides a bone
immobilization device to be used in a surgical procedure requiring the
rigid positioning of a bone throughout the procedure. The bone
immobilization device rigidly secures a bone in relationship to a
reference structure such as an operating table. The bone is inserted
through a frame and rigidly suspended relative to the frame by fixation
means attached to the frame and the exposed bone. The frame is secured
relative to the reference structure by an adjustable support means. The
frame can be disassembled into an upper section and a lower section for
ease of positioning the bone as well as for removal of the bone in case of
an emergency.
In accordance with further aspects of this invention, the fixation means
include two coacting gripping components attached to, and extending
radially into, the frame. The components include a pointed shaft and a
contact element having a serrated contoured contact surface. The point of
the shaft contacts and slightly enters the bone, thereby providing a force
against the bone coaxial with the shaft axis. The contact element is
adjustably mounted on the shaft and the angle of the contact surface is
adjusted relative to the shaft axis so that the bone surface is contacted
by the contact surface. The contact element is secured against the bone to
provide a force against the movement of the bone parallel to the shaft
axis. In this manner, a two-point suspension system is provided that
minimally contacts the exposed bone and minimally interferes with the area
of the bone to be operated on.
The present invention further provides a prosthesis template for aiding in
the determination of the desired position and orientation of a prosthesis
relative to a bone. The prosthesis has an exterior surface that simulates
the exterior surface of the bone and an interior surface comprised of one
or more relatively planar surfaces to which the prepared bone must
conform. The prosthesis template has a functional interior surface defined
by at least three contour lines. This functional interior surface
corresponds to the exterior surface of the prosthesis so that when the
template is positioned near the bone it provides a means for evaluating
the position and orientation of the prosthesis exterior surface relative
to the bone.
In accordance with additional aspects of this invention, the prosthesis
template includes cut guide marks on the template. The cut guide marks lie
in the various planes that correspond to the interior surfaces of the
prosthesis, and thus correspond to the bone cuts that must be made in
order to prepare the bone for the prosthesis. The relationship between the
cut guide marks and the functional interior surface of the template
correspond to the relationship between the interior surface and the
exterior surface of the prosthesis. Thus, when the template is positioned
near the bone, it provides a means for evaluating the position and
orientation of the prosthesis interior and exterior surfaces relative to
the bone.
In accordance with other aspects of this invention, the template includes
rod alignment tabs positioned on the anterior side of the template. A
reference rod can be attached to the alignment tabs. In this manner, the
rod provides an additional reference between the position of the template
and the longitudinal axis of the bone. Additionally, the template includes
mounting means for rigidly securing the template relative to the bone.
An additional object of the present invention is to provide an orthopedic
saw guide for confining the blade of a surgical saw to movement in a
single plane while allowing translational and rotational movement of the
blade within the plane. A pair of elongated guide plates are secured
together at either end to form a partially enclosed space. The distance
between the inner surfaces of the guide plates is adjustable, and is
preferably adjusted to be slightly greater than the thickness of the
specific blade to be used. Mounting means for rigidly securing the saw
guide relative to the bone, so that the plane defined by the space between
the inner surfaces corresponds to the cut plane, is provided.
In accordance with still further aspects of this invention, the inner
surfaces of the guide plates include guide liners that are comprised of a
low-friction material. The liners may be permanently secured to the guide
plates or removable and disposable. The guide plates are curved in the
plane of the guide surfaces so that the saw guide can be mounted close to
the end of a bone to provide maximum access to the bone with the closest
possible positioning of the guide.
In accordance with additional aspects of this invention, a stabilizing
device is provided for creating a rigid link between the mounting member
and the reference structure, in addition to the link provided by the
manipulator. Any compliance of the end of the saw guide is thus prevented
so that, for example, the inner surface of the guide is held rigidly
within the cut plane throughout the cutting task. The stabilizing device
permits use of a smaller and more compact robot in the surgical system.
In accordance with other aspects of this invention, the stabilizing device
is incorporated into a safety feature of the task control means. When the
mounting member, tool, stabilizing device, and the article to which the
stabilizing device is attached are made of electrically conductive
materials, the attachment of the mounting member to the stabilizing device
produces a simple circuit. The task control means detects when the circuit
is complete and will not allow manipulator movement during that time.
Thus, the robot will never inadvertently move when the mounting member is
stabilized.
In accordance with still further aspects of this invention, the template
and tools used in the system include a tool identification pattern that
uniquely identifies each tool. An identification device is included in the
attachment means so that when the template or tool is mounted, the
identification pattern can be read and transferred to the task control
means. The identification is then compared to the identification for the
template or tool that is appropriate for the task. An error message is
generated and displayed if the incorrect template or tool is attached.
In accordance with still other aspects of this invention, the robot base
includes a tiltable safety stand, including a means of communicating to
the task control means the status of the stand. The safety stand is
configured so that if the robot encounters a rigid object while it is
moving, the stand will tilt away from the object, thereby preventing the
continued force against the object. When the stand tilts, a safety signal
is generated that is received by the task control means and is indicative
of the need to shut off the power to the robot.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this
invention will become more readily appreciated as the same becomes better
understood by reference to the following detailed description, when taken
in conjunction with the accompanying drawings, wherein:
FIG. 1 is an isometric view of a prosthesis and a bone, with the end of the
bone prepared to receive the prosthesis;
FIG. 2 is a side view of a bone with a prosthesis press fit thereon, with
the bone partially cut away to show the prosthesis anchoring stud;
FIG. 3 is a pictorial view of the system of the present invention including
a patient positioned on an operating table;
FIG. 4 is an isometric view of the bone immobilization device of the
present invention with a representative femur suspended by the device;
FIG. 5 is a side view of the bone immobilization device with the frame and
fixation components shown adjusted to a raised position relative to the
base of the device;
FIG. 6 is an exploded view of one fixation component of the bone
immobilization device;
FIG. 7 is an isometric view of a robot used in the system illustrated in
FIG. 3;
FIG. 8 is an isometric view of the robot illustrated in FIG. 7 showing the
movement capabilities of the robot;
FIG. 9 is an isometric view of the wrist and the mounting flange of the
robot with the tool-coupling device of the present invention exploded away
from the mounting flange;
FIG. 10 is an isometric view of the wrist and coupling device illustrated
in FIG. 9 with a sample tool attachment flange shown exploded away from
the coupling device;
FIG. 11 is an isometric view of the robot safety stand used in the system
illustrated in FIG. 3;
FIG. 12 is a side view of the robot safety stand with portions of the upper
plate and one spring assembly cut away to show the compliance features of
the stand;
FIG. 13 is a top view of the top plate of the robot safety stand to show
the configuration of the upright supports and the spring assemblies;
FIG. 14 is a block diagram of the robot and peripherals, controller, and
supervisor of the system of the present invention;
FIG. 15 is an isometric view of a use of the prosthesis template of the
present invention attached to the robot and positioned near an immobilized
bone;
FIG. 16 is an isometric view of the template illustrated in FIG. 15;
FIG. 17 is a side view of the template attached to the robot and positioned
near the end of an uncut bone;
FIG. 18 is a top view of the template with the top portion cut away to show
the relationship between the horizontal plate and an uncut bone;
FIG. 19 is an isometric view of a use of the saw guide of the present
invention positioned near the immobilized bone;
FIG. 20 is an exploded view of the saw guide;
FIG. 21 is a top view of the saw guide with a saw blade positioned between
the guide plates;
FIG. 22 is a front view of the saw guide;
FIG. 23 is a sid | | |
