U.S. patent application number 16/865976 was filed with the patent office on 2020-08-27 for method for producing a customised orthopaedic implant.
The applicant listed for this patent is Royal Melbourne Institute of Technology. Invention is credited to Milan Brandt, Peter Choong, Martin Leary, Darpan Shidid.
Application Number | 20200269516 16/865976 |
Document ID | / |
Family ID | 1000004816352 |
Filed Date | 2020-08-27 |
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United States Patent
Application |
20200269516 |
Kind Code |
A1 |
Shidid; Darpan ; et
al. |
August 27, 2020 |
METHOD FOR PRODUCING A CUSTOMISED ORTHOPAEDIC IMPLANT
Abstract
A customised orthopaedic implant is provided, the implant being
formed of metal, the implant being substantially comprised of a
lattice-type geometry that has a periodic arrangement and is
conformal to a configuration of a region of bone that was resected
to remove bone that is diseased and is optimised to substantially
restore a biomechanical function of a bone from which the region of
bone was resected on implantation of the customised orthopaedic
implant in consideration of the anatomical function and of the
properties of a bone type corresponding to the region of bone that
was resected, together with patient-specific parameters and
anticipated loads to which the implant will be subjected during
various typical activities and movements.
Inventors: |
Shidid; Darpan; (Jalgoan,
IN) ; Leary; Martin; (Altona, AU) ; Brandt;
Milan; (Templestowe, AU) ; Choong; Peter;
(Kew, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Royal Melbourne Institute of Technology |
Melbouren |
|
AU |
|
|
Family ID: |
1000004816352 |
Appl. No.: |
16/865976 |
Filed: |
May 4, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15123024 |
Sep 1, 2016 |
10688726 |
|
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PCT/AU2015/000124 |
Mar 4, 2015 |
|
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16865976 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B33Y 50/00 20141201;
A61F 2002/3092 20130101; A61F 2002/30263 20130101; A61F 2/28
20130101; A61F 2002/30948 20130101; B29L 2031/7532 20130101; A61F
2002/3093 20130101; A61F 2002/30011 20130101; B29C 64/153 20170801;
B33Y 80/00 20141201; A61F 2002/3097 20130101; A61F 2002/30952
20130101; A61F 2/30942 20130101; A61F 2002/30014 20130101; B33Y
10/00 20141201; A61F 2002/30006 20130101; A61F 2002/30985 20130101;
A61F 2240/002 20130101; A61F 2002/30962 20130101; B29C 64/393
20170801 |
International
Class: |
B29C 64/393 20060101
B29C064/393; A61F 2/28 20060101 A61F002/28; B33Y 10/00 20060101
B33Y010/00; B29C 64/153 20060101 B29C064/153; A61F 2/30 20060101
A61F002/30 |
Claims
1. A customised orthopaedic implant formed of metal, the implant
formed by a method comprising the following steps: a. scanning a
bone, the bone being a diseased bone from which a region of bone
that is diseased is to be resected to obtain a three dimensional
digital image of an unresected volume of the diseased bone; b.
resecting the region of bone that is diseased to leave a remaining
volume of the bone from which the diseased region has been
resected; c. scanning the remaining volume of bone after the region
of bone that is diseased has been resected to obtain a
corresponding three dimensional digital image of the remaining
volume of bone; d. comparing the three dimensional digital image of
the unresected volume of bone to the corresponding three
dimensional digital image of the remaining volume of bone to
estimate a volume of the region of bone that has been resected; e.
using the estimate of the volume of the region of bone that has
been resected to generate a three dimensional computer model that
substantially conforms to a configuration of the volume of the
region of bone that was resected and is topologically optimised to
substantially restore a biomechanical function of the bone on
implantation of a customised orthopaedic implant corresponding to
the optimised three dimensional computer model; and f.
manufacturing the customised orthopaedic implant from the optimised
three dimensional computer model, wherein the implant is configured
for insertion into the region of the remaining bone from which the
diseased region of bone has been resected in step b., wherein the
customised orthopaedic implant is substantially comprised of a
lattice-type geometry that has a periodic arrangement and that is
conformal to the resected volume of bone and is optimised to
substantially restore the biomechanical function of the bone in
consideration of the anatomical function and of the properties of
the bone type corresponding to the region of diseased bone that has
been resected, together with patient-specific parameters and the
anticipated loads to which the implant will be subjected during
various typical activities and movements.
2. A customised orthopaedic implant according to claim 1, wherein a
porosity of the lattice-type geometry is varied at a region of the
implant configured to interface with the remaining volume of the
bone so as to enhance bone ingrowth.
3. A customised orthopaedic implant according to claim 1, wherein
said implant is manufactured using additive technology.
4. A customised orthopaedic implant according to claim 3, wherein
the step of manufacturing using additive technology involves
selective laser melting.
5. A customised orthopaedic implant according to claim 3, wherein
said implant is optimised to meet additive manufacturing
constraints.
6. A customised orthopaedic implant according to claim 1, wherein
the diseased region of bone is affected by osteosarcoma.
7. A customised orthopaedic implant according to claim 1, wherein
steps a. to f. occur consecutively during a period of time in which
a patient is under anaesthesia.
8. A customised orthopaedic implant formed of metal, the implant
being substantially comprised of a lattice-type geometry that has a
periodic arrangement and is conformal to a configuration of a
region of bone that was resected to remove bone that is diseased
and is optimised to substantially restore a biomechanical function
of a bone from which the region of bone was resected on
implantation of the customised orthopaedic implant in consideration
of the anatomical function and of the properties of a bone type
corresponding to the region of bone that was resected, together
with patient-specific parameters and anticipated loads to which the
implant will be subjected during various typical activities and
movements.
9. A customised orthopaedic implant according to claim 8, wherein a
porosity of the lattice-type geometry is varied at a region of the
implant configured to interface with a volume of bone remaining
after the region of bone has been resected to remove bone that is
diseased so as to enhance bone ingrowth.
10. A customised orthopaedic implant according to claim 8, wherein
said implant is optimised to meet additive manufacturing
constraints.
11. A customised orthopaedic implant according to claim 8, wherein
said implant is manufactured using additive technology.
12. A customised orthopaedic implant according to claim 11, wherein
manufacturing using additive technology involves selective laser
melting.
Description
PRIORITY CLAIM
[0001] The present application is a continuation of U.S.
application Ser. No. 15/123,024, titled "A METHOD FOR PRODUCING A
CUSTOMISED ORTHOPAEDIC IMPLANT," filed Sep. 1, 2016, which claims
the benefit of priority of International Application Serial No.
PCT/AU2015/000124, titled "A METHOD FOR PRODUCING A CUSTOMISED
ORTHOPAEDIC IMPLANT," filed Mar. 4, 2015, which is incorporated
herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to methods for designing and
manufacturing customised orthopaedic implants. More particularly,
the method relates to design and production of patient-specific
orthopaedic implants for insertion into a resected region of
bone.
BACKGROUND OF INVENTION
[0003] Osteosarcomas are a class of cancer originating from the
bone, mainly affecting children or young adults. Prior to the
1970s, amputation was the sole means of treatment available.
Amputation results in poor outcomes for patients in terms of
quality of life and accordingly current trends are directed toward
trying to salvage the affected limb while resecting the tumour in
its entirety to reduce the risk of local recurrence and to maximise
the prospects of survival. Once the tumour is resected, further
surgery is typically required to reconstruct the limb.
[0004] Efforts to salvage the limb often involve the insertion of
orthopaedic implants to reconstruct the bone or replacement of
natural joints with prosthesis. Conventional orthopaedic implants
generally have a solid construction intended to structurally
stabilise the resected bone to which they are attached. To
stabilise small tumour resections, solid metallic plate type
implants may be fixed to the bone tissue using multiple screws.
These implants are available in standard shapes and sizes and the
surgeon usually adjusts the implant contour to align with the bone
during surgery using trial and error. For tumours located near
joints, a total joint replacement prosthesis is used. These
implants are substantial in design to improve fatigue life and
accordingly require significant removal of bone tissue from the
affected as well as the unaffected region to accommodate the
prosthesis. In the case of young patients whose bones have not
matured, an expandable prosthesis may be used requiring repeat
visits to biomechanics laboratories for lengthening. Once the bones
reach maturity the expandable prosthesis is replaced with permanent
joint replacement prosthesis, resulting in further surgery and
rehabilitation for the patient. For elderly patients, the chances
of prosthesis failure are greater, due to reduced physical activity
and other age related complications such as osteoporosis. Moreover,
the placement strategy for such prosthesis tends to focus on the
configuration of the standard orthopaedic implant and how the
existing bone needs to be shaped to conform to the implant, rather
than focusing on the anatomical function of the bone and what is
required to maintain optimal biomechanical function of the
limb.
[0005] The disparity in stiffness between the existing bone and the
orthopaedic implant can lead to bone resorption and subsequent
loosening of the orthopaedic implant. While in some cases,
conventional orthopaedic implants do provide a satisfactory result
that allow the patient to return to an active lifestyle, in others,
use conventional orthopaedic implants has resulted in extended
rehabilitation, pain, discomfort, and lack of mobility. Therefore,
there is need for the development of customised orthopaedic
implants that are optimised to loading conditions of the affected
region, are affordable and can be rapidly produced.
[0006] It would therefore be desirable to be able to design and
manufacture an orthopaedic implant which is customised for a
patient and specific to a diseased skeletal element. In particular,
it would be desirable to be able to automate design of orthopaedic
implants which offer a suitable compromise to the bone's inherent
biomechanical function and enhance bone in-growth rate. Finally, it
would be desirable to optimise the entire process of designing and
manufacturing customised orthopaedic implants to enable orthopaedic
implant design, manufacture and placement to take place within the
time constraints of surgery.
SUMMARY OF INVENTION
[0007] According to an aspect of the present invention, there is
provided a customised orthopaedic implant formed of metal, the
implant formed by a method comprising the following steps: a.
scanning a bone, the bone being a diseased bone from which a region
of bone that is diseased is to be resected to obtain a three
dimensional digital image of an unresected volume of the diseased
bone; b. resecting the region of bone that is diseased to leave a
remaining volume of the bone from which the diseased region has
been resected; c. scanning the remaining volume of bone after the
region of bone that is diseased has been resected to obtain a
corresponding three dimensional digital image of the remaining
volume of bone; d. comparing the three dimensional digital image of
the unresected volume of bone to the corresponding three
dimensional digital image of the remaining volume of bone to
estimate a volume of the region of bone that has been resected; e.
using the estimate of the volume of the region of bone that has
been resected to generate a three dimensional computer model that
substantially conforms to a configuration of the volume of the
region of bone that was resected and is topologically optimised to
substantially restore a biomechanical function of the bone on
implantation of a customised orthopaedic implant corresponding to
the optimised three dimensional computer model; and f.
manufacturing the customised orthopaedic implant from the optimised
three dimensional computer model, wherein the implant is configured
for insertion into the region of the remaining bone from which the
diseased region of bone has been resected in step b., wherein the
customised orthopaedic implant is substantially comprised of a
lattice-type geometry that has a periodic arrangement and that is
conformal to the resected volume of bone and is optimised to
substantially restore the biomechanical function of the bone in
consideration of the anatomical function and of the properties of
the bone type corresponding to the region of diseased bone that has
been resected, together with patient-specific parameters and the
anticipated loads to which the implant will be subjected during
various typical activities and movements.
[0008] Design of the customised orthopaedic implant to
substantially restore the biomechanical function of the bone
involves consideration of one or more typical loading conditions on
a bone type which corresponds to the bone that has been resected.
For instance, this may involve a consideration of the anatomical
function of the bone type in question and the anticipated bone
loading during various typical activities.
[0009] Design of the customised orthopaedic implant preferably
involves consideration of typical maximum stress and deflection to
which the bone type which corresponds to the resected bone is
subjected. That is, taking into account the physique of the
patient, the loads incurred by the bone type during typical
activities such as walking, running, jumping and external impact
can be modelled.
[0010] The density of the lattice-type geometry is configured to
enhance bone ingrowth and is optimised to neutralise stresses
developed at the bone-implant interface. The lattice-type geometry
is preferable since it offers a favourable strength to weight
ratio, reduces stress shielding and can be manufactured using
additive technology. The lattice-type geometry includes a periodic
arrangement. Such an arrangement provides more predictable
mechanical properties and behaviour and accordingly, provides
greater control over the ultimate performance of the customised
orthopaedic implant in-situ. That is, varying the porosity of the
lattice structure at a bone/implant interface can be used to
enhance bone ingrowth or increase implant stiffness. A porosity of
the lattice-type geometry is varied at a region of the implant
configured to interface with the remaining volume of the bone so as
to enhance bone ingrowth.
[0011] The customised orthopaedic implant is preferably
manufactured using additive manufacturing technology. The additive
manufacturing technology may involve selective laser melting.
[0012] In one form of the invention, scanning a bone to obtain a
three dimensional digital image involves obtaining a plurality of
two dimensional digital images and constructing a three dimensional
digital image therefrom.
[0013] During the design process, the implant may be optimised to
meet additive manufacturing constraints.
[0014] In one particular embodiment, the diseased region of bone is
affected by osteosarcoma.
[0015] In a preferred form of the invention, the steps of the
method for producing a customised orthopaedic implant occur
consecutively during a period of time in which the patient is under
anaesthesia.
[0016] According to another aspect of the present invention, there
is provided a 8.
[0017] A customised orthopaedic implant formed of metal, the
implant being substantially comprised of a lattice-type geometry
that has a periodic arrangement and is conformal to a configuration
of a region of bone that was resected to remove bone that is
diseased and is optimised to substantially restore a biomechanical
function of a bone from which the region of bone was resected on
implantation of the customised orthopaedic implant in consideration
of the anatomical function and of the properties of a bone type
corresponding to the region of bone that was resected, together
with patient-specific parameters and anticipated loads to which the
implant will be subjected during various typical activities and
movements.
[0018] A porosity of the lattice-type geometry may be varied at a
region of the implant configured to interface with a volume of bone
remaining after the region of bone has been resected to remove bone
that is diseased so as to enhance bone ingrowth.
[0019] The implant may be optimised to meet additive manufacturing
constraints
[0020] The implant is manufactured using additive technology.
Manufacturing using additive technology may involve selective laser
melting.
BRIEF DESCRIPTION OF DRAWINGS
[0021] The invention will now be described in further detail by
reference to the accompanying drawings. It is to be understood that
the particularity of the drawings does not supersede the generality
of the preceding description of the invention.
[0022] FIG. 1 is a flowchart showing the method for producing a
customised orthopaedic implant according to an embodiment.
[0023] FIGS. 2A to 2C show a more detailed flowchart showing the
method for producing a customised orthopaedic implant.
[0024] FIG. 3A is a schematic of a diseased bone showing the amount
of tissue to be removed.
[0025] FIG. 3B is shows a 3D comparison between the diseased bone
and a normal bone to assist in surgical planning.
[0026] FIG. 3C shows the diseased bone of FIG. 3A with osteosarcoma
tissue removed.
[0027] FIGS. 4A and 4B show the output of two different STL file
comparisons to estimate the amount of tissue removed from diseased
bone of different bone types.
[0028] FIGS. 5A to 5C show stepwise rendering of customised
orthopaedic implant to replace the amount of tissue removed from
the diseased bone shown in FIGS. 4B and 5A.
[0029] FIGS. 6A and 6B are schematic representations showing
determination of loads and stresses incurred by a resected femur
during walking.
[0030] FIG. 7A shows example of a lattice structure which is
optimised for the loading conditions, but is not manufacturable
using additive manufacturing.
[0031] FIG. 7B shows a lattice structure which is optimised for the
loading conditions and further optimised for manufacture using
additive manufacturing processes.
[0032] FIGS. 8A and 8B show an example of a periodic lattice
structure generated using direct import of an STL file.
[0033] FIGS. 9A to 9D are exemplary lattice structure unit cells
that may be used in a suitable periodic lattice structure.
[0034] FIGS. 10A and 10B show the application of a functionally
gradient structure to the lattice geometry.
[0035] FIGS. 11A to 11C shows a series of schematics illustrating
the customised orthopaedic implant inserted to replace the removed
tissue.
DETAILED DESCRIPTION
[0036] Referring firstly to FIG. 1, there is shown a flowchart
illustrating the method 100 for producing a customised orthopaedic
implant. At step 110, a bone from which a diseased region of bone
will be resected is scanned to obtain a three dimensional digital
image of an unresected volume of bone. At step 120, the same bone
from which a diseased region of bone has been resected is scanned
to obtain a three dimensional digital image of a resected volume of
bone. At step 130, a three dimensional digital image of the
unresected volume of bone is compared to the corresponding three
dimensional digital image of the resected volume of bone to
estimate the volume of bone that has been resected. At step 140,
the estimate of the volume of bone that has been resected is used
to design a customised orthopaedic implant which substantially
corresponds to a configuration of the resected volume of bone.
Modelling is performed to ensure proposed customised orthopaedic
implant should substantially restore the biomechanical function of
the bone. At step 150, the customised orthopaedic implant is
manufactured. Finally, at step 160, the customised orthopaedic
implant is provided for insertion into the resected region of
bone.
[0037] It is to be understood that the steps of the method take
place while the respective patient is in surgery and generally
under anaesthesia. Moreover, the invention is herein described in
the context of designing and manufacturing orthopaedic implants to
replace sections of tissue surgically resected to remove an
osteosarcoma. However, it is to be understood that the method of
producing customised orthopaedic implants may have broader
application than that in the context of which the invention is
herein described.
[0038] Manufacture of customised implants within surgical time
constraints can be achieved using additive or three dimensional
printing techniques as subsequently described.
[0039] The method will now be described in more detail with
reference to the flowchart provided in FIGS. 2A to 2C. Referring
now to FIG. 2A, at step 205, the surgical team acquires medical
imaging data of the disease affected bone by scanning the bone
using, for example, a laser or computed tomography (CT) scanner.
Imaging a bone to obtain three dimensional models requires
obtaining a plurality of two dimensional digital images and
constructing a three dimensional digital image therefrom. Once
scanning is complete, at step 210, the medical imaging data is
processed in order to identify relevant features and attributes of
the instant bone such as the anatomical position of the
osteosarcoma within the bone, and the shape and size of the
osteosarcoma. At step 215, the surgical team examines the medical
imaging data of the diseased bone, as shown for example in FIG. 3A,
to determine the region of bone to be resected to remove the
osteosarcoma, using a three dimensional comparison of diseased and
normal bone as shown for example in FIG. 3B. At this stage, the
surgical team determines how the customised orthopaedic implant
will be fixed to the bone, so that the preferred fixation strategy
can be taken into account during orthopaedic implant design.
Surgical data, as shown in FIG. 3C, is sent to the engineering team
in real-time during the surgical procedure.
[0040] At step 220 the processed scan data is reviewed by an
engineering team and the orthopaedic implant design process
commences. The medical image data files typically comprise CT scan
data that are converted into three dimensional stereo lithography
(STL) files as shown for example in FIG. 3A. The STL files of the
resected volume of bone can be imported directly into the design
algorithm, avoiding any requirement for decimation of medical
imaging data or the use of finite element mesh creation software.
This ultimately results in enhanced optimal geometric integrity of
the customised implant and a more precise fit.
[0041] The resulting virtual three dimensional model is used
compare models of the unresected volume of bone with the models of
the resected volume of bone to provide an estimate of the volume of
bone that will be resected as shown for example in FIGS. 4A and
4B.
[0042] FIGS. 5A to 5C further illustrate how the STL files can be
used to model the amount of tissue to be resected 510, as shown in
FIG. 5B. The resected region of bone 510 is then precisely filled
using CAD modelling constrained by the pre-resection medical image
data to provide a generalised shape of the proposed orthopaedic
implant 520 as shown in FIG. 5C.
[0043] Since the aim of limb salvage surgery is to fill the
resected region with a customised orthopaedic implant which
substantially corresponds to not only to the configuration of the
resected volume of bone, but also to ensure that the orthopaedic
implant substantially corresponds to the biomechanical properties
of the surrounding bone, the orthopaedic implant design must take
into account the properties of the surrounding bone. These
properties can be calculated using Young's Modulus-bone density
relationship using a bone density library and well established
theoretical models at step 225.
[0044] Use of high resolution STL files enables accurate assignment
of patient specific loads and boundary conditions such as tendon
and ligament attachments that can be discerned from medical imaging
data. The patient specific loads and boundary conditions are
typically ascertained from magnetic resonance imaging (MRI) data or
similar, whilst the resected bone volume determinations may be
based on computed tomography (CT) data, laser scanner or the
like.
[0045] At step 230, a variety of physical activities and movements
are simulated whilst taking into account the patient's age and
physique, i.e. height, weight etc., in order to determine the loads
that will be incurred by the customised orthopaedic implant post
fixation. Such activities may include walking, running, jumping and
external impact. Each activity will subject the orthopaedic implant
to different load magnitudes and directions.
[0046] An example of a simulation is shown in FIG. 6A, wherein the
loads on a femur whilst walking are illustrated. These loads may be
estimated using OpenSim software tool (Delp S L, Anderson F C,
Arnold A S, Loan P, Habib A, John C T, Guendelman E, Thelen D G.
OpenSim: Open-source Software to Create and Analyze Dynamic
Simulations of Movement. IEEE Transactions on Biomedical
Engineering. (2007)) or similar. The estimated loads are applied to
a three dimensional model of the femur to illustrate the loads on
different areas of the femur as shown in FIG. 6B. Different
activities will subject the orthopaedic implant to different load
magnitudes and directions dependent on the physique of the
patient.
[0047] Referring now to FIG. 2B, a digital model of the orthopaedic
implant comprising of lattice structure that is conformal to the
resected volume of the bone is developed at step 235. This step is
carried out using a custom designed algorithm, which automatically
imports the implant volume and converts it into a periodic lattice
structure. At this stage features such as density gradient, choice
of unit cell are interactively selected via a graphic user
interface (GUI).
[0048] At step 240, the resulting digital model of the customised
orthopaedic implant is adjusted to accommodate the requisite
surgical features that are necessary to enable the orthopaedic
implant to be suitably located and fixed to the bone. Such surgical
features include custom surgical guides, fixation brackets and
tailored screws.
[0049] Later at step 245, the proposed orthopaedic implant
configuration is assessed to determine whether it can be
manufactured using additive technology. Typical additively
manufactured parts use structural supports to brace the part
against the loads generated while laying and solidifying the
preceding layers. These structures are difficult to remove,
especially for complex geometries such as lattice structures. Hence
it is desirable to avoid use of support structures within the part.
If the proposed orthopaedic implant is not able to be manufactured
without the use of support structures, using additive technology at
250, then the proposed orthopaedic implant configuration is
modified to meet the manufacturing constraints at step 253. Some
examples of suitable modifications include changing a feature
thickness, modifying an inclination of a feature, adding or
removing support features. Residual stresses owing to the thermal
gradient between the lattice and fixation brackets are compensated
by generating additional removable struts.
[0050] Development and optimisation of the digital implant model
takes into account the anatomical function of the bone, the
properties of the bone, e.g. density gradient and corresponding
variation in stiffness, and the anticipated load that the
orthopaedic implant will be subject to during typical activities
and movements.
[0051] Once the manufacturability of the implant is ensured at step
255, the lattice geometry or truss structure 700, 750 as generally
shown in FIGS. 7A and 7B can be automatically optimised to take
specified stresses, deflections and loading conditions as
determined at step 230
[0052] The lattice structure 750 shown in FIG. 7B is optimised to
neutralise all possible forms of loading conditions and transmit
the load to the load bearing bone and lends itself to manufacturing
by additive technology. The lattice structure 700 shown FIG. 7A
shows example of an optimised lattice structure that is not
manufacturable using additive manufacturing and accordingly not
suitable for rapid manufacture of customised orthopaedic implants
within surgical time constraints.
[0053] A lattice structure with a periodic arrangement is
preferred, i.e. a periodic layout of nodes and struts, since it
results in predictable mechanical properties and behaviour. A
periodic arrangement enables utilisation of a unit cell based
topology wherein the user can assign different types of unit cells
according to the structural requirements of the implant. An example
of such a periodic lattice structure 800 is shown in FIG. 8A.
[0054] In contrast, aperiodic structures have non-organised
arrangement of struts and nodes, making prediction of mechanical
behaviour difficult. Currently, two strategies are employed to
generate conformal lattice structures. Using the most common
method, the organic volume to be filled is intersected by a
periodic arrangement of lattice unit cells. Due to periodic nature
of the lattice structure and aperiodic surface contour,
intersection of lattice structure at nodes is not guaranteed.
Accordingly, the structural integrity of such structures is
compromised and the purpose of using a periodic structure is not
fulfilled. Such structures are also difficult to optimise using
available optimisation tools. Using another method of generating
conformal lattice structures, the organically shaped volume is
decimated using STL processing software and the corresponding
arrangement of nodes and vertices is converted into a lattice
structure. Due to aperiodic placement of triangles on a STL file,
the resulting structure is also aperiodic. Furthermore, as a result
of shape deformation during decimation, accurate application of
muscle loads and boundary conditions is difficult. The presently
proposed algorithm takes into account the potential shortcomings
and aforementioned issues. The ensuing lattice structure is
generated directly from a high resolution STL file, enabling
accurate assignment of loading conditions. Furthermore, all nodes
are located on the surface of the STL, ensuring that the loads are
applied at nodes and optimisation process for such structure is
computationally efficient.
[0055] FIGS. 9A to 9D illustrate examples of unit cell types that
can be applied to a periodic lattice structure 810 as shown in
FIGS. 8A and 8B, for example. FIG. 9A shows a body centred cubic
cell, FIG. 9B shows a face centred cubic cell with vertical struts,
FIG. 9C shows a face and body centred cubic with vertical struts,
and FIG. 9D shows face and body centred cubic with horizontal and
vertical struts. The body centred cubic (BCC) type cells as shown
in FIG. 9A are effectively employed in impact absorption
applications due to their compliance. In contrast, the face centred
cubic (FCC) type cells as shown in FIG. 9B are stiffer under
compressive loading and accordingly useful for energy absorption.
FCC type cells tend to be stronger when loaded in the Z direction,
compared to the X and Y directions. This property makes them useful
for load bearing implants since the resulting structure can exhibit
increased stiffness in the loading direction, compared to other
directions, enabling a reduction in the weight of the implant. The
addition of horizontal elements to the unit cell, see for example
the unit cell shown in FIG. 9D, increases the resistance of the
structure to torsion and shear loading when compared with any of
the other illustrated unit cell types.
[0056] Referring now to FIGS. 10A and 10B, periodicity of the
lattice structure also enables application of a functionally
gradient structure to permit regulation of stiffness and/or enhance
osseointegration (bone-ingrowth) by varying the density of the
lattice structure near the bone/implant interface. FIG. 10B FIG.
shows a change in density of the lattice structure towards the
implant interface by employing different unit cell types and a
larger strut diameter when compared to the rest of the structure.
Varying the density in this way near the implant interface enables
bone ingrowth to be enhanced whilst at the same time maintaining a
lightweight structure. The periodicity of the lattice structure
provides precise control over the pore geometry and size.
Accordingly, porosity of the structure will be easy to vary
depending on whether enhancement of bone ingrowth or controlling
stiffness of the implant is prioritised.
[0057] The customised orthopaedic implant is passed through an
iterative process of its design involving topological optimisation
to identify the optimal geometry to fill the space left by the
removed tissue within the constraints provided by the anatomical
features of the instant bone and the physique of the patient for
whom the orthopaedic implant is being customised from step 260 to
264. If the structure does not meet the stress and deflection
criterion, the geometry is modified and the structure is reassessed
until optimal solution is achieved. Modification of geometry
includes either reduction or increase in strut diameter.
[0058] Once the structure is optimised based on loading conditions
at step 264, the three dimensional computer model of the proposed
orthopaedic implant configuration is processed for additive
manufacture at step 265. Typically this will involve conversion to
a file format suitable for transmitting direct to a three
dimensional printer or selective laser melting machine. The
orthopaedic implant is then manufactured at step 270 using additive
technology.
[0059] At step 275, the manufacturing process is monitored to
ensure that in-situ process control measures are met. For example,
such in-situ control measures might include a check of the build
temperature and the manufactured geometry. If the control measures
are not within acceptable limits at 280, then the proposed geometry
and/or processing is modified at step 285. Suitable modifications
might include adding support structure(s), altering the location or
orientation of the part on the machine platform or changing the
processing parameters.
[0060] If the in-situ control measures are within acceptable limits
at 290, then the manufactured customised orthopaedic implant is
subject to post processing at step 295, as required. Necessary
post-processing may include but is not limited to mechanical and/or
chemical processing to enhance the surface finish of the
orthopaedic implant, removal of loose powder particles, and/or
sterilisation of the customised orthopaedic implant in preparation
for insertion into the patient.
[0061] Finally, at step 298, the manufactured customised
orthopaedic implant is delivered to the surgical team together with
the relevant instructions for implantation. Referring now to FIGS.
11A to 11C, there is shown in FIG. 11A the unresected bone 1110, in
FIG. 11B the resected bone 1120 is shown with the customised
orthopaedic implant comprising a periodic lattice structure 1130
fixed thereto and in FIG. 11C a "skin" 1140 is provided over the
orthopaedic implant 1130 which has optimally sized pores to enable
flow of essential nutrients and promote bone osseointegration i.e.
bone in-growth.
[0062] Various software and tools may be employed in implementing
the method for producing a customised orthopaedic implant and
particularly during the design process. These may include but are
not limited to Mimics, Geomagic Studio/VX Elements with laser
scanning, Solidworks, Abaqus, Matlab, Haptic Device/Freeform
Modelling Plus and Magics/Autofab.
[0063] It is a particular advantage of the present invention, that
not only is it possible to provide a customised orthopaedic implant
specific to a patient and specific to a particular bone and the
manner in which that bone has been resected, within a relatively
short time frame. In particular, it appears that the customised
orthopaedic implant could be produced in accordance with the method
described herein within a period of time in which the patient is
under anaesthesia. This suggests a significant improvement over
method for producing customised orthopaedic implants which often
require multiple surgical interventions before the orthopaedic
implant can be inserted and hence result in a much longer recovery
and rehabilitation time for the patient as well as often
sub-optimal outcomes owing to the difficulty of suitably
customising the orthopaedic implant.
[0064] While the invention has been described in conjunction with a
limited number of embodiments, it will be appreciated by those
skilled in the art that many alternative, modifications and
variations in light of the foregoing description are possible.
Accordingly, the present invention is intended to embrace all such
alternative, modifications and variations as may fall within the
spirit and scope of the invention as disclosed.
* * * * *