U.S. patent application number 15/351021 was filed with the patent office on 2017-03-02 for automated systems for manufacturing patient-specific orthopedic implants and instrumentation.
The applicant listed for this patent is ConforMIS, Inc.. Invention is credited to Philipp Lang, John Slamin, Daniel Steines, Alexey Zhuravlev.
Application Number | 20170056183 15/351021 |
Document ID | / |
Family ID | 42199981 |
Filed Date | 2017-03-02 |
United States Patent
Application |
20170056183 |
Kind Code |
A1 |
Steines; Daniel ; et
al. |
March 2, 2017 |
Automated Systems for Manufacturing Patient-Specific Orthopedic
Implants and Instrumentation
Abstract
Disclosed herein are devices, systems and methods for the
automated design and manufacture of
patient-specific/patient-matched orthopedic implants. While the
embodiments described herein specifically pertain to
unicompartmental resurfacing implants for the knee, the principles
described are applicable to other types of knee implants
(including, without limitation, other resurfacing implants and
joint replacement implants) as well as implants for other joints
and other patient-specific orthopedic applications.
Inventors: |
Steines; Daniel; (Lexington,
MA) ; Zhuravlev; Alexey; (Canton, MA) ;
Slamin; John; (Wrentham, MA) ; Lang; Philipp;
(Lexington, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ConforMIS, Inc. |
Bedford |
MA |
US |
|
|
Family ID: |
42199981 |
Appl. No.: |
15/351021 |
Filed: |
November 14, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13561696 |
Jul 30, 2012 |
9495483 |
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15351021 |
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12712072 |
Feb 24, 2010 |
8234097 |
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13561696 |
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11671745 |
Feb 6, 2007 |
8066708 |
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12712072 |
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11002573 |
Dec 2, 2004 |
7534263 |
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11671745 |
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10724010 |
Nov 25, 2003 |
7618451 |
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11002573 |
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10305652 |
Nov 27, 2002 |
7468075 |
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10724010 |
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10160667 |
May 28, 2002 |
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10305652 |
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10728731 |
Dec 4, 2003 |
7634119 |
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11671745 |
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10681750 |
Oct 7, 2003 |
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11671745 |
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61208440 |
Feb 24, 2009 |
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61208444 |
Feb 24, 2009 |
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60765592 |
Feb 6, 2006 |
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60785168 |
Mar 23, 2006 |
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60788339 |
Mar 31, 2006 |
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60293488 |
May 25, 2001 |
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60363527 |
Mar 12, 2002 |
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60380695 |
May 14, 2002 |
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60380692 |
May 14, 2002 |
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60431176 |
Dec 4, 2002 |
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60467686 |
May 2, 2003 |
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60416601 |
Oct 7, 2002 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2002/3895 20130101;
A61B 2034/108 20160201; A61F 2002/30952 20130101; G06F 30/00
20200101; A61F 2002/30948 20130101; A61B 17/1675 20130101; A61F
2002/30878 20130101; A61F 2002/30943 20130101; A61B 17/1662
20130101; A61F 2/3859 20130101; A61B 2017/00526 20130101; A61F 2/38
20130101; A61F 2/30942 20130101 |
International
Class: |
A61F 2/30 20060101
A61F002/30; A61F 2/38 20060101 A61F002/38; G06F 17/50 20060101
G06F017/50 |
Claims
1. A method for automated design of a femoral component of a knee
implant system, comprising: a. sketching, using an automation
system, a sulcus line on a condylar surface of a virtual model of a
patient's distal femur; b. creating a profile view and
automatically sketching an implant contour using the profile view
and completing a center line of the implant contour; and c.
designing the femoral component by projecting the implant contour
onto the virtual model, and designing an inner surface and an outer
surface of the femoral component, wherein the outer surface is
defined by sweep an arc of a constant radius and angle along the
center line.
Description
RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 13/561,696, filed Jul. 30, 2012, which
in turn is a continuation application of U.S. patent application
Ser. No. 12/712,072, filed Feb. 24, 2010, which in turn claims
priority to U.S. Provisional Application 61/208,440, filed Feb. 24,
2009, entitled "Automated Systems for Manufacturing
Patient-Specific Orthopedic Implants and Instrumentation."
[0002] U.S. patent application Ser. No. 12/712,072 also claims
priority to U.S. Provisional Application 61/208,444, filed Feb. 24,
2009, entitled "Automated Systems for Manufacturing
Patient-Specific Orthopedic Implants and Instrumentation."
[0003] U.S. patent application Ser. No. 12/712,072 also is a
continuation-in-part application of U.S. patent application Ser.
No. 11/671,745, filed Feb. 6, 2007, entitled "Patient Selectable
Joint Arthroplasty Devices and Surgical Tools", which in turn
claims the benefit of U.S. Ser. No. 60/765,592 entitled "Surgical
Tools for Performing Joint Arthroplasty" filed Feb. 6, 2006; U.S.
Ser. No. 60/785,168, entitled "Surgical Tools for Performing Joint
Arthroplasty" filed Mar. 23, 2006; and U.S. Ser. No. 60/788,339,
entitled "Surgical Tools for Performing Joint Arthroplasty" filed
Mar. 31, 2006.
[0004] U.S. Ser. No. 11/671,745 is also a continuation-in-part of
U.S. Ser. No. 11/002,573 for "Surgical Tools Facilitating Increased
Accuracy, Speed and Simplicity in Performing Joint Arthroplasty"
filed Dec. 2, 2004 which is a continuation-in-part of U.S. Ser. No.
10/724,010 for "Patient Selectable Joint Arthroplasty Devices and
Surgical Tools Facilitating Increased Accuracy, Speed and
Simplicity in Performing Total and Partial Joint Arthroplasty"
filed Nov. 25, 2003 which is a continuation-in-part of U.S. Ser.
No. 10/305,652 entitled "Methods and Compositions for Articular
Repair," filed Nov. 27, 2002, which is a continuation-in-part of
U.S. Ser. No. 10/160,667, filed May 28, 2002, which in turn claims
the benefit of U.S. Ser. No. 60/293,488 entitled "Methods To
Improve Cartilage Repair Systems", filed May 25, 2001, U.S. Ser.
No. 60/363,527, entitled "Novel Devices For Cartilage Repair, filed
Mar. 12, 2002 and U.S. Ser. Nos. 60/380,695 and 60/380,692,
entitled "Methods And Compositions for Cartilage Repair," (Attorney
Docket Number 6750-0005p2) and "Methods for Joint Repair,"
(Attorney Docket Number 6750-0005p3), filed May 14, 2002.
[0005] U.S. Ser. No. 11/671,745 is also a continuation-in-part of
U.S. Ser. No. 10/728,731, entitled "Fusion of Multiple Imaging
Planes for Isotropic Imaging in MRI and Quantitative Image Analysis
using Isotropic or Near-Isotropic Imaging," filed Dec. 4, 2003,
which claims the benefit of U.S. Ser. No. 60/431,176, entitled
"Fusion of Multiple Imaging Planes for Isotropic Imaging in MRI and
Quantitative Image Analysis using Isotropic or Near Isotropic
Imaging," filed Dec. 4, 2002.
[0006] U.S. Ser. No. 11/671,745 is also a continuation-in-part of
U.S. Ser. No. 10/681,750, entitled "Minimally Invasive Joint
Implant with 3-Dimensional Geometry Matching the Articular
Surfaces," filed Oct. 7, 2003, which claims the benefit of U.S.
Ser. No. 60/467,686, entitled "Joint Implants," filed May 2, 2003
and U.S. Ser. No. 60/416,601, entitled Minimally Invasive Joint
Implant with 3-Dimensional Geometry Matching the Articular
Surfaces," filed Oct. 7, 2002.
[0007] Each of the above-described applications is hereby
incorporated by reference in their entireties.
[0008] This application relates to U.S. patent application Ser. No.
12/398,753, filed Mar. 5, 2009, entitled "Patient Selectable Joint
Arthroplasty Devices and Surgical Tools," which in turn claims
priority to U.S. Provisional Patent Application No. 61/034,048,
filed Mar. 5, 2008, entitled "Patient Selectable Joint Arthroplasty
Devices and Surgical Tools," and U.S. Provisional Patent
Application No. 61/034,048, filed Mar. 5, 2008, entitled "Patient
Selectable Joint Arthroplasty Devices and Surgical Tools," each of
these above-described applications hereby incorporated by reference
in their entireties.
BACKGROUND
[0009] Technical Field
[0010] The embodiments described herein relate to automated systems
for designing and manufacturing patient-specific orthopedic
devices, such as implants and instrumentation, based on data, such
as imaging data, representing an existing joint.
[0011] Description of the Related Art
[0012] Personalized medicine is one of the fastest growing trends
in the healthcare industry. While this trend has mainly been seen
in the drug sector, medical device manufacturers have also
recognized the benefits of individualizing their products to meet
the needs of different patient groups. The orthopedic implant
manufacturers have recently launched implants optimized for
different genders or geographies, or combining patient-specific
instruments with standardized implants. However, these are not
truly personalized, patient-specific or patient-matched approaches.
Technological advances now allow for the design and manufacture of
implants and associated instrumentation optimized for a specific
individual. Such implants fall on a spectrum from, e.g., implants
that are based on one or two aspects or dimensions of a patient's
anatomy (such as a width of a bone, a location of a defect, etc.)
to implants that are designed to conform entirely to that patient's
anatomy and/or to replicate the patient's kinematics.
[0013] One example of such patient-specific or patient-matched
technology is the ConforMIS iFit.RTM. technology used in the
iUni.RTM. (unicompartmental knee resurfacing implant) and iDuo.RTM.
(dual compartmental knee resurfacing implant). This technology
converts Computed Axial Tomography ("CT") or Magnetic Resonance
Imaging ("MRI") scans into individualized, minimally invasive
articular replacement systems capable of establishing normal
articular shape and function in patients with osteoarthritis. By
starting with imaging data, the approach results in implants that
conform to bone or cartilage, and reduce the need for invasive
tissue resection. The implant is made to fit the patient rather
than the reverse. By designing devices that conform to portions of
the patient's anatomy, the implants allow the surgeon to resurface
rather than replace the joint, providing for far more tissue
preservation, a reduction in surgical trauma, and a simplified
technique.
[0014] The image-to-implant process begins with the patient having
a medical image such as a CT or MRI scan, which can be done on
commonly available machines, using a standardized protocol that
ensures the data needed to design the implant is captured properly.
The image data is then combined with computer-aided design (CAD)
methods to generate a patient-specific model of the knee from which
a patient-specific implant and/or patient-specific instrumentation
can be designed and manufactured. The electronic design file
created during this process is used to fabricate the
patient-specific implant and custom instrumentation, which is a
process that takes approximately four to six weeks.
[0015] The development and manufacture time associated with all
types of patient specific devices could be significantly reduced if
some or all aspects of the design and manufacture process were
fully automated or more fully automated. Automation of some or all
aspects of the process, including, without limitation, imaging,
diagnosis, surgical planning, instrumentation design, implant
design, manufacture, quality systems and distribution could result
in, among other advantages, faster and less costly production,
which could result in patient's being able to have surgery sooner
and at a lower cost. Additionally, such systems could improve
productivity of designers, which would have several advantages such
as improving profitability of manufacturing such implants. Further,
such systems would both directly and indirectly improve the quality
of such implants by, example, providing defined rules to ensure
patient-specific implant designs meet specification, and also
indirectly by improving the cost effectiveness of skilled
designers, which makes the technically skilled employees found in
more developed countries such as the United States more
economically competitive and thereby reducing the impetus to
outsource such production to countries with less technically
skilled but cheaper labor that may result in reduced quality in the
design process.
SUMMARY
[0016] Some embodiments described herein include new computer-based
methods used to generate the designs for personalized joint
implants that are custom-tailored to a patient's individual
anatomy. The anatomic information is derived from medical images,
such as CT or MRI scans. Other types of images also could be used,
including, without limitation, x-ray images. A variety of
segmentation methods can be applied to extract the relevant
anatomic information.
[0017] In one embodiment, the anatomic information resulting from
the segmentation can be composed of individual points, surface
information, or solid bodies, preferably in 3 or more dimensions.
In another embodiment, the anatomic information results in a
virtual model of the patient's anatomy.
[0018] The processing of the anatomic information and the
generation of the custom-fit implant design can have different
degrees of automation. It can be fully automated, thus not
requiring any user input. It can provide default settings that may
be modified and fine-tuned by the operator. In any automated step
performed by the system, constraints pertaining to a specific
implant model, to a group of patients or to the individual patient
may be taken into account. For example, the maximum implant
thickness or allowable positions of implant anchors may depend on
the type of implant. The minimum implant thickness can depend on
the patient's bone quality.
[0019] In another embodiment, the system supports the operator by
guiding him/her through the design workflow and prompting the user
for required input. For example, the system follows a predefined
step-by-step design protocol. It performs automated calculations
whenever possible. For certain steps that require operator
intervention, the system presents the operator with all information
necessary to provide his input. This can include, without
limitation, showing the design status from a specific viewpoint
that allow the operator to best make the required decision on the
particular design step. Once the information has been entered by
the operator, the system can continue the automated design protocol
until further operator interaction becomes necessary.
[0020] In another embodiment, the system uses anatomic landmarks to
generate an implant design. The system can, for example, merge the
patient's anatomic information with a generic atlas or model
containing the landmark information. By merging the two pieces of
information, the landmark information is transferred into the
patient information, thus allowing the system to use the landmark
information as reference in the implant design. Alternatively, the
landmark information may be derived directly from the patient's
anatomical data, for example and without limitation, by locating
curvature maxima or minima or other extrema.
[0021] In another embodiment, the system automatically finds the
best viewpoint to allow the user to perform a design step. This can
be facilitated by using the landmark information derived from the
patient's anatomical information. For example, the system can find
the best view to allow the operator to define the implant's outer
profile or contour.
[0022] In another embodiment, the implant profile is defined using
a virtual template. The template may be fitted automatically to the
patient's anatomical model, for example, by using the generic
atlas, which may have the virtual template integrated into it. The
anatomical model can be represented by a series of 2D images or a
3D representations. The model typically, but not always, will have
at least one of bone or cartilage already segmented.
[0023] Alternatively, the virtual template can be user-adjustable.
The system can provide an initial default fit of the template and
then allow the user to make adjustments or fine-tune the shape or
position. The system can update the implant as the operator makes
adjustments to the template, thus providing real-time feedback
about the status of the implant design. The adjustments can be
made, for example, for irregularities of the articular surface
including osteophytes or subchondral cysts, or flattening of an
articular surface.
[0024] The virtual template can be a 3D template. In another
embodiment, the virtual template is a 2D template that is projected
onto a 2D or 3D anatomical model of the patient's anatomy. The
template can be a composite of standard geometric shapes, such as
straight lines, arcs or other curved elements in 2D and planes,
spherical shapes or other curved elements in 3D. Alternatively, the
template may have an irregular, free-form shape. To adjust the
shape of the template, the system or the operator can move the
standard shapes or adjust the radius of the curved elements. In
another embodiment, the virtual template may have a number of
control points that can be used to adjust its shape. In yet another
embodiment, the center line of the profile can be used to adjust
its shape.
[0025] In another embodiment, the final implant includes one or
more bone cuts. The cut planes for these bone cuts can be
automatically determined by the system, for example using
anatomical landmarks. The cut planes can also be built into a
generic virtual atlas that is merged with the patient's anatomical
information. Optionally, the cut planes can be adjusted by the
operator.
[0026] The system can also construct the implant surfaces. Surfaces
may be composed of different elements. In one embodiment, elements
of the surfaces will conform to the patient's anatomy. In these
situations the system can build a surface using the patient's
anatomical model, for example by constructing a surface that is
identical with or mostly parallel to the patient's anatomical
surface. In another embodiment, the system uses geometric elements
such as arcs or planes to construct a surface. Transitions between
surfaces can be smoothed using tapers or fillets. Additionally, the
system may take into account constraints such as minimum or maximum
thickness or length or curvature of parts or aspects of the implant
when constructing the surfaces.
[0027] In another embodiment, the system can automatically or
semi-automatically add other features to the implant design. For
example, the system can add pegs or anchors or other attachment
mechanisms. The system can place the features using anatomical
landmarks. Constraints can be used to restrict the placement of the
features. Examples of constraints for placement of pegs are the
distance between pegs and from the pegs to the edge of the implant,
the height of the pegs that results from their position on the
implant, and forcing the pegs to be located on the center line.
[0028] Optionally, the system can allow the user to fine-tune the
peg placement, with or without enforcing the constraints.
[0029] In another embodiment, the additional features are embedded
with the generic virtual atlas and merged with the patient-specific
anatomical information, thus overlaying the information about the
position of the feature embedded in the atlas on top of the
patient's anatomical model.
[0030] In other embodiments, devices that are tailored to only one
or a few dimensions or aspects of a patient's anatomy are designed
using automated processes.
[0031] The principals can also be applied to other devices, such as
the design and manufacture of patient-specific instruments, such as
jigs used in orthopedic surgeries or other instrumentation.
Similarly, the concepts can be applied to portions of the design of
an implant or instrument, such as the design of an articular
surface of a patient-specific and/or patient-engineered articular
implant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a graphic representation of a virtual model
illustrating a front perspective view of a proximal portion of a
tibia;
[0033] FIG. 2 is a graphic representation of a virtual model
illustrating a front perspective view of a portion of the tibial
bone of FIG. 1 to be removed along a cutting place;
[0034] FIG. 3 is a graphic representation of a virtual model
illustrating a front perspective view of the tibia of FIG. 1 with a
portion of bone removed;
[0035] FIG. 4 is a graphic representation of a virtual model
illustrating a side perspective view of the tibia of FIG. 3 with
the portion of bone removed;
[0036] FIG. 5 is a graphic representation of a virtual model
illustrating a top perspective view in an axial direction of the
tibia of FIG. 3;
[0037] FIG. 6 is a graphic representation of a virtual model
illustrating a top perspective view of the tibial of FIG. 3 and an
implant placed where the portion of bone was removed;
[0038] FIG. 7 is a graphic representation of a virtual model
illustrating an end perspective view of a condyle portion of a
femur;
[0039] FIG. 8 is a graphic representation of a virtual model
illustrating an end perspective view in an axial direction of the
femur of FIG. 7 with an initial form of an implant placed on one of
the condyles of the femur;
[0040] FIG. 9 is a graphic representation of a virtual model
illustrating a side perspective view of the initial form of the
implant of FIG. 8
[0041] FIG. 10 is a graphic representation of a virtual model
illustrating a side perspective view of the implant of FIG. 8 in a
later stage of design;
[0042] FIG. 11 is a graphic representation of a virtual model
illustrating a side perspective view of the implant of FIG. 11 in a
later stage of design;
[0043] FIG. 12 is a graphic representation of a virtual model
illustrating a side perspective view of the implant of FIG. 10 in a
still later stage of design and attached to the femur of FIG.
7;
[0044] FIG. 13 is a graphic representation of a virtual model
illustrating a side perspective view of the final design of the
implant;
[0045] FIG. 14 is a schematic view of a unicompartmental
implant;
[0046] FIG. 15 is a cross-sectional schematic view in the coronal
plane of a femoral component of the implant of FIG. 14;
[0047] FIG. 16 is a cross-sectional schematic view in the coronal
plane of an alternate embodiment of a femoral component of a
unicompartmental implant;
[0048] FIG. 17 is a cross-sectional schematic view in the coronal
plane of an alternate embodiment of a femoral component of a
unicompartmental implant;
[0049] FIG. 18 is a cross-sectional schematic view in the coronal
plane of an alternate embodiment of a femoral component of a
unicompartmental implant;
[0050] FIG. 19 is a cross-sectional schematic view in the coronal
plane of an alternate embodiment of a femoral component of a
unicompartmental implant;
[0051] FIG. 20 is a graphic representation of a virtual model
illustrating a side perspective view of a condyle of a femur having
an implant contour on a profile plane superimposed;
[0052] FIG. 21 is a graphic representation of a virtual model
illustrating a side perspective view of the condyle of the femur of
FIG. 20 having an implant contour superimposed on the femur
surface;
[0053] FIG. 22 is a graphic representation of a virtual model
illustrating a side perspective view of the condyle of the femur of
FIG. 20 having cross-sections of the condyle in an anterior taper
zone of the implant superimposed;
[0054] FIG. 23 is a graphic representation of a virtual model
illustrating a side perspective view of the condyle of the femur of
FIG. 20 showing an alternative view of the anterior taper zone
shown in FIG. 22;
[0055] FIGS. 24A and 24B graphic representations of a virtual model
illustrating a front and a side perspective view respectively of a
surface of a condyle of FIG. 20 for use in designing an
implant;
[0056] FIG. 25 is a graphic representation of a virtual model
illustrating a side perspective view of the condyle of the femur of
FIG. 20 having a set of arcs superimposed to loft an outer surface
of an implant from the surface of the condyle;
[0057] FIG. 26 is a graphic representation of a virtual model
illustrating a side perspective view of inner and outer surfaces of
an implant derived from the condyle of FIG. 20;
[0058] FIG. 27 is a graphic representation of a virtual model
illustrating a side perspective view of an implant in an initial
stage of design and having the inner and outer surfaces of FIG.
26;
[0059] FIG. 28 is a graphic representation of a virtual model
illustrating a side perspective view of an outline of the implant
of FIG. 27 having a cross section noted by a lighter-colored
line;
[0060] FIG. 29 is a graphic representation of a virtual model
illustrating a bottom schematic view of the outline of FIG. 27 in a
later stage of development during which pegs are added to the
implant;
[0061] FIG. 30 is a graphic representation of a virtual model
illustrating a side perspective view of the implant of FIG. 27 in a
later stage of development with the pegs added; and
[0062] FIG. 31 is a graphic representation of a virtual model
illustrating a side perspective view of the implant of FIG. 30 in
final form and with fillets added around the pegs.
DETAILED DESCRIPTION
[0063] Various embodiments of the invention can be adapted and
applied to implants and other devices associated with any
anatomical joint including, without limitation, a spine, spinal
articulations, an intervertebral disk, a facet joint, a shoulder
joint, an elbow, a wrist, a hand, a finger joint, a hip, a knee, an
ankle, a foot and toes. Furthermore, various embodiments can be
adapted and applied to implants, instrumentation used during
surgical or other procedures, and methods of using various
patient-specific implants, instrumentation and other devices.
[0064] One embodiment is a nearly-fully automated system to design
a patient-specific implant that requires minimal input from a
designer or other operator and that is capable of designing an
implant in a small fraction of the time it takes for a designer to
design such an implant using computer aided design (CAD) tools.
Automated Design of a Patient-Specific Unicompartmental Femoral
Implant
[0065] Referring to FIGS. 1-13 below, an exemplary patient-specific
implant is illustrated, including references to the bone cuts made
to implant the device. The implant is designed based on a medical
image, such as a CT scan of a particular patient, and includes both
a resurfacing component that attaches to the femoral condoyle of
the patient and a tibial tray component that attaches to the top of
the tibia as illustrated. When implanted, the unicompartmental
resurfacing component and the tibial tray form an articular surface
of the knee joint in the patient.
[0066] Such an implant can be designed and manufactured using
traditional CAD-based design rules. However, in the present
embodiment, it is designed using an automated system that, for
example, partially automates the design process. The specifics
attributes of such a system are more fully described below.
Similarly, other devices, such as patient-specific instrumentation,
other types of knee resurfacing devices, other types of knee joint
replacement devices, and other orthopedic implants and
instrumentation for other joints or other parts of the anatomy can
be designed and manufactured using such partially or fully
automated design and manufacturing processes.
[0067] FIGS. 1-6 illustrate the design process for an exemplary
tibial component of a patient-specific unicompartmental knee
implant. The image data from the CT scan is transferred to the
system and used to build a virtual model of the patient's anatomy.
Referring to FIG. 1, the virtual model includes the tibial surface
200 of the patient, which is derived from the image data. An image
of the surface of the tibia 200 can be generated from the virtual
model and displayed on a computer screen during the design
process.
[0068] Referring also to FIG. 2, the tibial surface 200 can be used
to define mathematically the natural slope of the patient's tibia.
In this embodiment, the slope is graphically illustrated by a plane
210. Referring to FIG. 3, a horizontal cut is then designed. First,
an anatomical axis 230 of the tibia is determined, and the
positions of a horizontal cut 240 and vertical cut 250 are
determined. In the coronal plane, the horizontal cut 240 preferably
is perpendicular to the anatomical axis 230, but many other
orientations and positions are possible. As shown in FIG. 4, with
respect to the sagittal plane, the horizontal tibial cut 240 can be
derived with respect to the patient's slope 260. Preferably, the
cut 240 is approximately 11.5 degrees relative to the patient's
existing tibial slope 250 in the sagittal plane.
[0069] Referring to FIGS. 5 and 6, the resulting cut leaves a shelf
260 upon which the tibial component 270 of a unicondylar knee
implant will be placed. The tibial component 270 preferably is
designed to maximize coverage of the tibial shelf 260. In some
embodiments, a tibial component can be designed to exactly match a
perimeter of the tibial shelf.
[0070] Referring to FIGS. 7-13, a femoral component of the
patient-specific unicompartmental knee implant is also designed
using automated design principles. As with the tibial, the surface
300 of the patient's femur is derived from the image data,
including a virtual representation of the condyle 320 of the femur.
Referring to FIG. 8, a coronal profile 310 of the implant can be
superimposed on the condyle 320 of the femur to assess the
orientation and sizing of the implant to be designed.
[0071] As shown in FIGS. 9-10, a virtual interim implant 330 is
used to design a posterior cut into the implant. The virtual
interim implant 330 allows the system to optimize the placement of
the posterior cut, and includes a posterior cut surface 350 to
align the posterior cut on the virtual model of the condyle. Once
the posterior bone cut surface 350 is properly positioned, a
posterior tray 360 is filled in on the virtual implant and trimmed
to optimize the design of the implant. As shown in FIG. 11,
fixation pegs 370 and 380 can then be added. Preferably, the pegs
370 and 380 are positioned in a flexed position relative to the
mechanical axis and/or the primary direction of the forces on the
knee applied by the femur.
[0072] Referring to FIG. 12, the virtual model of the femoral
component of the unicompartmental implant 390 is then fit to the
virtual model of the condyle 320, and the proper orientation of the
implant relative to the condyle is finalized. A tapering portion
400 is included in an anterior portion of the implant to provide a
gradual transition from an articular surface 410 of the implant and
an articular surface 420 of the implant.
[0073] Referring to FIG. 13, a virtual model of the final femoral
component 440 is created by position a cement pocket 450 in a
bone-facing surface 460 of the posterior tray 360.
Automated Design of an Implant with a "Patient-Engineered"
Articular Surface
[0074] Preferably, patient-specific implants include articular
surface and other attributes that are engineered from the patient's
own anatomy, but that provide an improved function. For example, an
articular surface can create a healthy and variable "J" curve of
the patient in the sagittal plane and a constant curvature in the
coronal plane that is based on the patient's specific anatomy, but
that does not seek to mimic or precisely recreate that anatomy, may
be preferred. For example, referring to FIGS. 14-15, in another
exemplary embodiment of a patient-specific device, a
unicompartmental resurfacing implant has an enhanced articular
surface that is engineered based on the specific anatomy of a
patient. A unicompartmental implant 10 similar to the device in
Example 1, having a femoral resurfacing component 20 and a tibial
tray component 30, is designed based on patient-specific data. An
inner, femoral-facing surface 40 of the resurfacing component 20
conforms to the corresponding surface of the femoral condoyle.
However, the outer, articular surface 50 of the resurfacing
component 20 is enhanced to incorporate a smooth surface having a
nearly constant radius in the coronal plane. The corresponding
articular surface 70 of the tibial tray 30 has a surface contour in
the coronal plane that is matched to the outer articular surface
50. In this embodiment, the articular surface 70 has a radius that
is five times the radius of outer articular surface 50.
[0075] The design of implant 10 has several advantages. First, the
design of articular surface 50 allows the thickness of femoral
component to be better controlled as desired. For example,
referring to FIG. 16, if a curve of an articular surface 80 of a
femoral component 90 is too large, the thickness of the femoral
component may be too thick along a centerline 100 of the implant,
thereby requiring an excessive amount of bone to be removed when
the implant is placed on the femoral condoyle. On the other hand,
referring to FIG. 17, if the same curve 80 is applied to a device
having an appropriate centerline thickness 110, the margins or
sidewalls 120 and 130 of the device may be too thin to provide
proper structural support. Similarly, referring to FIG. 18, if the
curve of the outer articular surface 120 of a femoral component 130
is too flat, the device will not exhibit the tapering from a
centerline 140 to the margins or sidewalls 150 and 160 of the
device and may not function well.
[0076] Referring again to FIGS. 14 and 15, a second advantage of
the implant 10 over certain other embodiments of patient-specific
devices is that the smooth articular surface 50 is thought to
provide better kinematics than a true representation of the surface
of the patient's femoral condoyle may provide.
[0077] For example, referring also to FIG. 19, one method of making
patient specific implants is to use a simple offset, in which a
femoral component 170 is designed using a standard offset from each
point of the modeled surface of the patient's femoral condoyle.
Using such a design, the thickness of the device will remain
essentially constant, and an outer surface 180 will essentially
match or conform to the underlying inner femoral-facing surface
190, as well as the modeled surface of the femoral condoyle on
which it is based. While this provides a truly patient-matched
outer surface, it is not necessarily optimal for the kinematics of
the resulting implant, due to, for example, rough areas that may
produce higher, more localized loading of the implant. By using a
smooth surface with an essentially pre-determined shape, the
loading of the implant can be better managed and distributed,
thereby reducing the wear on the tibial tray component 30.
[0078] The third advantage, which is also related to the loading
and overall kinematics of the implant, is in the matching of the
tibial articular surface 70 to the femoral articular surface 50 in
the coronal plane. By providing a radius that is predetermined,
e.g., five times the radius of the femoral articular surface 50 at
its centerline in the present embodiment, the loading of the
articular surfaces can be further distributed. Thus, the overall
function and movement of the implant is improved, as is the wear on
the tibial tray, which is polyethylene in this embodiment. While
the present embodiment uses a ratio of five times the radius of the
outer surface at its centerline (note that the radius of the outer
surface may be slightly different at other locations of the outer
surface 50 away from the centerline), other embodiments are
possible, including an outer tibial surface that, in the coronal
plane, is based on other ratios of curvature, other curvatures,
other functions or combinations of curves and/or functions at
various points. Additionally, while the embodiments shown in FIGS.
16-19 are not considered to be optimal designs generally, they are
embodiments that can be generated using automated systems and may
have preferable characteristics in some instances.
An Exemplary Automated System for Designing Patient-Specific
Implants
[0079] The implants described in both Examples 1 and 2 can be
designed and manufactured using CAD-based design rules or other
largely manual procedures, i.e., procedures that are either
entirely manual, or that may contain certain automated components
but that are still predominately manual in nature.
[0080] Alternatively, those implants, as well as essentially any
type of patient-specific implant, can be designed and manufactured
using an automated system that, for example, partially or fully
automates the design process. Such an automated process is more
fully described below. Similarly, other devices, such as
patient-specific instrumentation, other types of knee resurfacing
devices, other types of knee joint replacement devices, and other
orthopedic implants and instrumentation for other joints or other
parts of the anatomy can be designed and manufactured using such
partially or fully automated design and manufacturing processes. In
the following example, an embodiment of an automated process is
described. This embodiment is one of many potential embodiments
that may vary in many ways, each having its own specifications,
design goals, advantages and tradeoffs.
Automated Design of a Femoral Component
[0081] a. Sketching a Sulcus Line
[0082] Referring to FIGS. 20-31, a sulcus line can be sketched as a
curve on a condylar surface of a femur before sketching a femoral
implant contour. The sulcus point can be viewed more easily in a
view other than a profile view. It is preferable to start sketching
the sulcus line in a view where the sulcus point is easily visible
and then change the view with each new segment, finally making the
line visible in the profile view.
[0083] The automation system constructs the curve segment by
segment, interpolating the sketch points by a local cubic spline.
The spline does not lie on the surface, and typically will not be
close to it. The curve will pass near the surface on the outside
part of it to make it highly visible in any view. To do this, the
spline segments are interpolated, and, for each intermediate point,
a ray extending from an essentially infinitely distant point and
perpendicular to the screen plane intersects with the surface. As
the view can be different for each segment, the directions of
projects may also be different for each segment.
[0084] When a new sketch point is added, the spline is changed only
at its last created segment. But the sketch points and the
directions of projection are kept until the curve construction is
complete. This allows the system to reject as many segments as the
system wants and redefine the spline until the system has developed
a satisfactory shape using an iterative process.
[0085] The cubic spline is a local cubic spline with a special rule
of defining tangent vectors of interpolating points. By way of
example in this particular embodiment:
[0086] Suppose there are n+1 points p0, p1, . . . , pn.
[0087] For inner points (i=1, . . . , n-1), the system defines
tangent vector as a bisect of a triangle formed by two neighbor
chord vectors starting from the point:
v 0 = p i - p i - 1 incoming chord ( a ) v 1 = p i + 1 - p i
outgoing chord ( b ) h 0 = v 0 length of the incoming chord ( c ) h
1 = v 1 length of the outgoing chord ( d ) tn i = h 1 * v 0 + h 0 *
v 1 h 0 + h 1 tangent at the inner point ( e ) ##EQU00001##
[0088] For the first and the last points the system define the
tangent vector from the constraint of zero curvature at the end
points:
v 0 = p 1 - p 0 first chord ( f ) tn i = 3 * v 0 - tn 1 2 first
tangent ( g ) v n - 1 = p n - p n - 1 last chord ( h ) tn n = 3 * v
n - 1 - tn n - 1 2 last tangent ( i ) ##EQU00002##
[0089] The interpolation inside each segment is done according a
classic cubic segment formula:
f0=1-3u.sup.2+2u.sup.3 (j)
f1=3u.sup.2-2u.sup.3 (k)
g0=u.sup.3-2u.sup.2+u (l)
g1=u3-u.sup.2 (m)
pt=f.sub.0*pt.sub.0+g.sub.0*tn.sub.0+ (n)
f.sub.1*pt.sub.1+g.sub.1*tn.sub.1 (o)
[0090] When the system has sketched the sulcus line 520, it then
begins to develop the curve of the shape of the implant. This is
performed by an object that interpolates points lying close to the
surface. In the present embodiment, the spline or the projection
directions array is not used for this purpose, but many other
implementations are possible. This curve serves as an indicator of
approximate position where the femoral implant should stop.
b. Making Profile View
[0091] In the next phase of the design, a profile view is created.
The system defines the profile view using the following steps:
[0092] Set bottom view [0093] Rotate it 180 degrees around the
z-axis [0094] Rotate it 15 degrees around x-axis [0095] Find common
tangent to both condoyles in that view [0096] Change the view to
make the common tangent horizontal [0097] Offer class for making
additional rotations around x-axis and z-axis
[0098] In the present embodiment, all steps except the last one are
done automatically. (But, this step could also be automated.) Here,
the user interface for making additional rotations is done using a
UI class derived from CManager. The view can be rotated around
x-axis and around z-axis either by moving the sliders or by setting
the rotation angles in the toolbar edit boxes. This allows the
designer to better view and examine the implant surfaces during the
automated design process. When a designer, customer or other user
clicks "Accept" in the toolbar, the system stores the entity of the
view information in the document. The entity contains the view
parameters and two correction angles.
c. Sketching Implant Contour
[0099] Referring to FIG. 20, the profile view discussed above is
used to sketch the implant. Designing the contour occurs in three
steps: [0100] Sketch the original contour [0101] Preview the
contour in 3d [0102] Modify the contour The second and third steps
can be repeated until the contour shape is acceptable.
[0103] The initial implant contour 500 is sketched in the profile
plane of condyle 510 of the femur of the patient. The contour is
projected onto the femur surface orthogonally to the screen plane
(profile plane). To close the contour on the posterior side, there
are two points on the vertical edges of the contour which are the
closest to a so-called 93 degrees plane. The system computes the
cutting plane as the plane passing through those two points and
forming minimal angle with 93 degrees plane. Making a cross-section
by the cutting plane allows us to close the implant contour.
[0104] The two dimension contour to be projected on the femur
surface consists of lines and arcs. There are two vertical lines,
two slopped parallel lines, one horizontal line, two fillet arcs
and two 90 degrees arcs on the top, forming one 180 degrees arc.
Each of these arcs and lines is called a contour element; the
contour consists of nine elements. The system also considers
center-line elements, including two center lines and two points
(shown as bold markers on the screen).
[0105] The members of this data structure are called "defining
elements." The system can uniquely compute contour elements based
on this information. When the software stores the profile contour
in an external file, the software stores the defining elements. The
defining elements can include those listed below in Table 1, but
other embodiments are possible.
TABLE-US-00001 TABLE 1 Exemplary Defining Elements Used In
Automated Design Process Defining Element Definition pt0, pt1, pt2
ends of two center lines, from bottom to top h1 half distance
between two vertical lines h2 half distance between two slopped
lines r0 and r1 radii of fillet arcs bFixedRad Boolean flag True
means preserving the radii during modification False re-compute the
radii after modifications
[0106] If the system wants to adjust fillets, the system sets a
flag to true. The system then leaves the radii being to the
original value and does not re-compute them automatically.
[0107] The initial sketching starts with indicating the upper point
of the first vertical line. Then the system indicates the upper end
of the first slopped line and makes the first fillet automatically.
The last action in the initial sketching is indicating the upper
point of the second slopped line--the rest of the contour can be
uniquely defined automatically with the assumption that h1=h2. This
condition can be changed during modification phase. After the
initial sketch is complete, the contour is projected on the femur
surface and is displayed.
[0108] In most cases the contour built after the initial sketch
requires some modification, which can be automated using an
iterative process that checks against a predefined set of rules and
compares to a specification. Alternatively, a designer can
intervene to check to progression of the automated design. To
switch to modification phase, the user clicks a "Modify" button in
the toolbar. When a user moves the mouse over some contour element,
the element is highlighted by displaying in bold lines. The user
can drag the element along the direction, associated with each
element, by pressing left button, moving the mouse and releasing it
in a new position. The whole contour will be rebuilt
accordingly.
[0109] When the contour shape, which serves as the footprint and
starting point of the implant, is satisfactory, the user clicks the
button "Make" in the toolbar and the process of constructing the
implant starts.
d. Making Implant
[0110] Constructing of the implant is done by the following main
steps of the process: [0111] Projecting the contour on femur
surface [0112] Making vertical sections [0113] Computing posterior
cutting plane [0114] Making posterior section [0115] Making the
contour on femur surface [0116] Making a center line [0117] Making
side lines [0118] Approximating inner surface [0119] Constructing
an outer surface [0120] Making the implant BREP [0121] Marking
inner and outer surfaces [0122] Cutting by posterior cylinder
[0123] Flattening the cutting area [0124] Filleting
[0125] In the present embodiment, the process starts with
projecting the sketched contour on the femur surface. This function
does two things. First, it traverses all contour elements, computes
30 points on each of them and projects them onto femur BREP.
Second, it takes two center line elements, extends the top one up
to the top arcs, makes a fillet between the two lines and projects
the resulted center line onto femur BREP. This is a first step in
constructing the femur center line.
[0126] When the system projects contour and center line points onto
the femur BREP, some points may miss the surface. This happens on a
portion of a region where the contour elements are vertical lines.
As the system constructs the contour on the femur in this area, the
system will make cross-sections of the femur by those vertical
lines. The system also finds the "lowest" (the closest to the 93
degrees plane) points on the side sections.
[0127] When the system calculates the two "lowest" points on the
side sections, the system computes the cutting plane. It computes a
temporary plane passing through the two lowest points perpendicular
to the 93 degrees plane and then makes a cutting plane as passing
through two lowest points perpendicular to the temporary plane. As
the result, the cutting "profile" plane forms a minimal angle of 93
degrees from all planes passing through the two lowest points.
[0128] The next step is cutting the femur with the profile plane.
The function finds a cross-section as an array of curves, discards
the ones belonging to the other condoyle, approximates the best
curve with a single spline and re-orients it so that it has the
same direction at the starting lowest point as the projected
contour.
[0129] The final step in making the contour on the femur is
assembling all aspects together. This is done by a function that
forms the contour from the main portion of the projection, i.e.,
the two segments of the vertical sections which start where the
projection portion finishes and end at the "lowest" points, and the
portion of the cutting plane cross-section.
[0130] FIG. 21 shows the resulting contour 530 superimposed on the
condyle 510 of the femur. Now, when the system has the implant
contour, it completes the center line. So far the system has the
center line in the form of a point array on the femur from one end
of the contour to the other. The function extends this array behind
both ends along the corresponding cross-sections and approximates
the resulted array with a relatively large tolerance (e.g., 0.5). A
larger tolerance leads to a smoother outer-femoral curve, which is
a design goal of the present embodiment (although other embodiments
may have different implementations and/or design goals). However,
while using a larger tolerance in the approximation make a smoother
outer curve, but it may result in deviation from the vertical
center line. To accommodate this phenomenon, a function is
implemented that corrects the control points of the center line
B-spline--adjusting them into the vertical line starting at some
point.
[0131] As shown in FIGS. 22-23, the system then computes the
tapering arcs 550. Two functions compute the arcs 550 lying on the
outer surface 560 of condyle 510. The arcs 550 are not connected to
the center line 570, which passes closer to the inner surface of
the implant being designed.
[0132] The system then computes the side rails of the implant by
extending the side lines of the contour behind the end points to
provide good intersection of the inner and outer surfaces with the
cutting surfaces.
[0133] Referring also to FIGS. 24A and 24B and 26, the system then
constructs the inner and outer surfaces 580 and 590. The inner
surface 580 is constructed by a function that computes 15 points on
the portion of a center line 600 between the end point of anterior
taper and the end of the center line 570. For each of these points
it makes a cross-section of the femur BREP by the plane, passing
through the point and perpendicular to the center line. This
cross-section is trimmed by the side rails, extended a little
behind the side rails and added as single B-spline curve to the
section array. Now, the system adds the cross-sections in the
tapered zone. To do that, the system takes the first computed
cross-section and creates additional sections. The system inserts
the additional sections in the beginning of the section array.
[0134] Referring to FIGS. 25-26, the system then constructs a loft
surface 620 using an array of cross-sections. A center line 630 and
cross-sections 640 are used for making the outer surface 580 of the
implant.
[0135] The outer surface 590 is constructed by sweeping an arc of
the constant radius and angle along a center line trajectory. The
trajectory is defined by the center line curve and an offset value.
The ending portions of the trajectory are defined by the tapering
arcs. The system function assumes that the arc radius and the
offset value are given; for example, the system may use a
radius=25.0 and offset=3.5.
[0136] The function then determines the angle of the sweeping arc.
To find the angle, the system uses a heuristic approach. It
computes several (e.g., 10) points on the center line in between
tapering zones. For each of these points the system makes a plane
perpendicular to the center line and find two points where the
plane intersects with two side curves. Then the system computes the
"center" by offsetting the point on the center line against the
surface normal by a value equal the difference (radius--offset).
The system then makes two lines from the center to the points on
side curves and computes the angle between them. This angle
approximates the possible sweeping arc angle at this cross-section.
The system sets the angle of the sweeping arc to the maximum of
those arcs angles.
[0137] Once the system determines the sweeping arc angle, it
processes the anterior taper arc, the portion of the center line
between taper zones, and the posterior taper arc. For taper arcs,
the system computes an array of points on the curve and constructs
an arc of the given radius and angle, lying in the plane
perpendicular to the curve and having the calculated point as its
middle point. The center line that the system processes is almost
the same, except that the system offsets the point on the curve
along the femur normal to the offset value. This results in a set
of arcs as shown. Thus, the outer surface 590 is created as a loft
surface using the set of created arcs as cross-sections.
[0138] Referring now to FIG. 27, after the system has designed the
inner and the outer surfaces 580 and 590, it creates the side walls
650 of the implant. The system generates the side wall 650 by
making two additional surfaces: a tabulated cylinder passing
through the implant contour with an axis perpendicular to the
profile plane, and a half of a regular cylinder with an axis
perpendicular to the 93-degree plane.
[0139] Ideally, in this embodiment, the radius of the cylinder
should be the half of the distance between the side lines, although
other embodiments may employ different implementations. The
implementation of this embodiment allows the cylinder to be
tangential to the walls of the tabulated cylinder, and thus to
create a smooth side surface.
[0140] The system then eliminates the angles of the side surfaces.
The system can do this either by filleting the angles, or by using
Boolean subtraction. Boolean operation will provide a more exact
result, but risks instability in some cases. The system then
flattens the posterior area 660 of the inner surface.
e. Measuring Thickness
[0141] Referring to FIG. 28, the next step after the implant is
created is controlling its thickness. With a sweeping arc radius
that is small enough (e.g., 25 mm), the thickness may need to be
altered in some portions. If the system keeps the thickness of the
implant along the spine of the implant at about 3.5 mm, the
thickness may be too small thickness along the edges. Generally,
the thickness of the implant along the center line should be bigger
than at the edges, but neither the center line nor the edges of the
implant should get too thick or too thin. The design rules may
result in such a condition, however, in the process of constructing
other parts of the implant. Thus, the system checks the final
thickness and makes adjustments to ensure the thickness meets the
specifications of the implant.
[0142] In this embodiment, a functions to check the implant
thickness is provided as a menu item that a user can select, but
the feature could be automated to run automatically. As shown in
FIG. 28, the menu item allows the system to move an implant
cross-section 670 along a center line 690 and to move a line across
that section and measure the distance between inner and outer
surfaces along that line.
[0143] When the system begins to measure the implant thickness, it
can display the implant in wireframe mode 680 and display the
cross-section 670 in some initial position. The cross-section 670
is displayed, for example, in white, and the center-line 690 is
displayed, for example, in red. The initial position of the
cross-section is at the point on the center line 690 where anterior
taper begins. The cross-line default position is in the middle of
the cross-section 670.
f. Making Attachment Pegs
[0144] Referring to FIGS. 29 and 30, the system provides a function
for positioning of pegs 700, 705 for attachment of the implant 710
to bone. The system allows a user to control the distances and the
pegs heights, but these aspects could also be automated in other
embodiments.
[0145] When started, the class displays the implant in the
wireframe mode in the profile view and suggests default positions
720, 730 for the pegs, marked on the screen as circles:
[0146] The user can move the pegs by dragging them. The pegs are
moved along the center lines keeping constant distance between
them. The toolbar displays the distances between the cutting plane
and the first peg (d1), between the two pegs (d2), and between the
second peg and the apex point of the implant contour (d3). It also
displays the pegs heights.
[0147] The pegs 700, 705 can be pre-viewed with dynamic view
changing by clicking button Preview and made with filleting their
intersection with the implant inner surface by clicking Accept.
[0148] The class automatically computes initial positions of the
pegs, trying to make equal all three distances d1, d3, d3. The
distance d2 should be integer number, so it is rounded to the
nearest integer. The other two, d1, and d3, are updated
accordingly. A user can set the distance d2 right in the toolbar;
again, the other two distances will be updated.
[0149] The toolbar has a button "Constraints". Clicking on this
button invokes a modal dialog with a set of conditions. It sets the
minimum value for d1 (11), the min/max values for d2 (11-18) and
the min/max values for pegs heights (11-12). If one (or more) of
conditions is violated, the corresponding value is displayed in red
and moving the pegs produces an alarm.
[0150] The system requires that the distances from pegs apex points
to the profile plane be equal. Although many other embodiments are
possible. For every position of the pegs, the system extends them
up to a plane, parallel to the profile plane and measure their
heights, h1 and h2. Then the system adjusts them so that (h1+h2)/2
becomes 11.5. This allows the system to place both of pegs in the
range 11-12 and their heights differ from 11.5 the same
distance.
g. Inserting a Cement Pocket
[0151] Referring to FIG. 31, a cement pocket 740 is then placed in
the posterior section of the implant 710 as shown below.
[0152] The embodiments disclosed herein are exemplary only, and one
skilled in the art will realize that many other embodiments are
possible, including, without limitation, many variations on the
embodiments described above as well as other entirely different
applications of automated systems for designing patient specific
implants of various types and for various joints and other parts of
a patient's anatomy. The embodiments described herein are not
intended to limit the scope of the claims.
* * * * *