Modular femoral component for a total knee joint replacement for minimally invasive implantation

Description of equivalent WO 2004037119 A2

TITLE: MODULAR FEMORAL COMPONENT FOR A TOTAL KNEE JOINT REPLACEMENT FOR MINIMALLY INVASIVE IMPLANTATION

RELATIONSHIP TO OTHER APPLICATIONS

[0001] This application claims the benefit of U.S.

Provisional Application No. 60/420,299, filed October 23,

2002, the entire disclosure of which is incorporated herein

by reference.

BACKGROUND OF THE INVENTION

Field of the Invention:

[0002] This invention relates to joint replacement

prostheses for the knee, and more particularly to such

prostheses that can be implanted by minimally invasive

surgical techniques.

Brief Description of the Prior Art:

[0003] Replacement of diseased or damaged knees with

suitable prostheses has become a common surgical procedure.

The outcome of such surgery has been found to be favorable

in most cases, and the surgery has come to be regarded as a

very favorable surgical intervention for restoring function

to knees damaged by trauma or degenerative disease. Each

year more than 650,000 patients worldwide undergo operations in which either part or all of their knee joints

is replaced, and the resulting implants typically operate

well for 10 or more years. Typically, current designs

consist of a metallic component made from a cobalt-based

alloy to replace the bearing surfaces of the femur. This

femoral prosthesis bears upon an ultra-high molecular

weight polyethylene component implanted upon the proximal

end of the tibia. Additionally a second polyethylene

implant is used to replace the undersurface of the patella

so that it slides upon the central region of the metallic

femoral implant. To minimize the problem of wear in the

joints, the metallic component is polished to a very fine

mirrored surface and the bearing surfaces are designed with

a high degree of conformity to reduce contact stresses.

[0004] One of the major problems with the conventional

procedure, however, is that the prostheses are relatively

large, and, accordingly, must be inserted through

relatively long incisions. Specifically, the large metal

component that comprises the femoral implant is generally

about four inches wide and about three inches high, which

requires a correspondingly large incision for implantation.

Such large incisions tend to disrupt the tissues associated

with the joint and its joint capsule, requiring long healing and rehabilitation periods after the operation

before the patient can return to normal activities.

Although surgeons have recognized the desirability of

minimizing the size of the incisions, the large size of the

prostheses of current design have frustrated attempts to

use smaller incisions, e.g., 1-2 inches in length.

[0005] U.S. Published Patent Application No.

2003/0158606, to Coon et al . , discloses a knee arthroplasty

prosthesis wherein a femoral component of a total knee

joint replacement is made in more than one piece. The

pieces are inserted separately and assembled within the

surgical site. The separate pieces of the femoral

component are provided with mating surfaces generally

formed at an angle to a plane oriented in an anterior-

posterior direction and proximal distal direction with

respect to the femur. However, the multi-piece prosthesis

of Coon is disclosed as requiring a surgical incision of

three inches .

[0006] Accordingly, a need has continued to exist for a

knee joint prosthesis that can be inserted using minimally

invasive surgical techniques. SUMMARY OF THE INVENTION

[0007] The problem of excessive trauma to the knee joint

during implantation of a knee prosthesis has now been

alleviated by the modular femoral component for a total

knee joint replacement of this invention, which is capable

of being inserted and implanted through surgical procedures

that are significantly less invasive than the conventional

procedures .

[0008] According to the invention the femoral component

of the total knee joint replacement is provided in multiple

segments or modules that can be separately inserted through

minimally invasive incisions and subsequently assembled

within the joint to form a functioning unit.

[0009] Accordingly it is an object of the invention to

provide a modular femoral component for a total knee joint

replacement .

[0010] A further object is to provide a femoral

component for a total knee joint replacement that can be

inserted using minimally invasive surgical techniques.

[0011] A further object is to provide a femoral

component for a total knee joint replacement that can be

inserted through a relatively small incision. [0012] A further object is to provide a femoral

component for a total knee joint replacement that can be

inserted through a relatively small incision and assembled

within the joint to form a functioning prosthesis.

[0013] A further object is to provide a femoral

component for a total knee joint replacement that is less

traumatic to the knee joint than currently used prostheses.

[0014] A further object is to provide a femoral

component for a total knee joint replacement that permits

faster rehabilitation after surgery.

[0015] Further objects of the invention will become

apparent from the description which follows .

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1A illustrates a modular femoral component

for a total knee joint replacement of one embodiment of the

invention in a disassembled state.

[0017] Figure IB illustrates a modular femoral component

for a total knee joint replacement of the embodiment of

Figure 1A in an assembled state.

[0018] Figure 2A illustrates a modular femoral component

for a total knee joint replacement of another embodiment of

the invention in a disassembled state. [0019] Figure 2B illustrates a modular femoral component

for a total knee joint replacement of the embodiment of

Figure 2A in an assembled state.

[0020} Figure 3A is a front elevational view of the

femoral component of Figure IB showing the articulation of

the prosthesis with the undersurface of the patella or an

undersurface patellar implant.

[0021] Figure 3B is an enlarged view of the assembled

femoral component of Figure IB showing the recessed or

beveled interface between adjacent modules.

[0022] Figure 4A illustrates a modular femoral component

for a total knee joint replacement of another embodiment of

the invention wherein the central segment is present only

in the upper portion of the femoral component, while the

outer segments are joined together in the lower portion of

the femoral component .

[0023] Figure 4B illustrates a modular femoral component

for a total knee joint replacement of the embodiment of

Figure 4A in an assembled state.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS [0024] The present invention comprises a design of a

total knee prosthesis in which the femoral component is

provided in multiple pieces or modules sized for insertion

through a minimally invasive incision and capable of

assembly within the joint to form a single functioning

unit. The individual modules are provided with alignment

structure, e.g., mating projections and recesses. The

modules are held together by fastening structures, e.g.,

screws, interfitting joints, interference joints, and the

like.

[0025] Accordingly, the femoral prosthesis of the

invention for use as a component of an artificial knee

joint comprises a plurality of segments or modules, each of

said segments having a femoral fixation surface adapted to

be positioned on a distal end of a femur and at least one

assembly surface adapted to be joined to an assembly

surface of an adjacent one of said segments or modules.

[0026] The modular prosthesis of the invention may

comprise any convenient number of modules that, when

assembled within the surgically prepared region of the

joint, will form a functional prosthesis on the distal end

of the femur. At least some of the individual modules of

the modular prosthesis have a femoral fixation surface that is adapted to contact the surgically prepared distal end of

the femur and be attached by conventional methods such as

an appropriate cement, mechanical fastener or the like.

[0027] Although the modular prosthesis of the invention

may comprise any convenient number of modules, preferred

embodiments may include two or three modules as illustrated

in the drawings . Not all modules have to have a femoral

fixation surface; some of the modules may serve as spacers

between other modules, as is illustrated in Figures 2A

and 2B, discussed in more detail below.

[0028] The side of the module generally opposite to the

femoral fixation surface is a bearing surface that contacts

a corresponding prosthesis affixed to the proximal end of

the tibia in order to bear the weight imposed on the joint

and transfer the force to the tibia. The bearing surface

of each module is shaped and configured to provide a

generally conventional femoral prosthetic surface when the

modular prosthesis is assembled. The bearing surface is

also provided with the conventional highly polished surface

in order to minimize friction within the joint.

[0029] Each module is also provided with at least one

assembly or mating surface that contacts and mates with a

corresponding assembly or mating surface of an adjacent module. The assembly surfaces of adjacent modules are

shaped and configured so that a secure and rigid fastening

therebetween is possible. Any conventional structure for

holding such mating surfaces together may be used. For

example, the mating surfaces can be generally planar and

the modules can be provided with holes or passageways

through which alignment pins or screws can be passed to

align and/or fasten the modules securely together.

Adjacent mating faces may be provided with projecting

alignment pins, lugs, or the like, adapted to mate with

corresponding recesses on the mating face of an adjacent

module. Alternatively, the mating faces can be provided

with joining features that both align and secure the

modules, such as dovetail joints, interference fit joints,

and the like. Instead of discrete lugs, the entire mating

surfaces of adjacent modules can be designed as male and

female lugs. Such an arrangement with large contacting

alignment surfaces may be expected to increase the shear

strength of the joint and thereby contribute to the

rigidity of the prosthesis. The mating surfaces need not

be planar. The mating surfaces are generally of

complementary shape over a sufficient portion of their

surface areas in order to provide for a secure and rigid assembly of the modules. It is preferred to design the

assembly surfaces so that they are self-aligning as they

are assembled within the surgically prepared knee joint.

Such self-aligning mating surfaces can be achieved, for

example, by providing tapered alignment lugs, pins, or the

like, on one of the mating surfaces that fit into similarly

tapered recesses in the complementary mating surface.

Alternatively the mating surfaces can deviate somewhat from

strict planarity, with complementary surface profiles so

that they will assume a single orientation as they are

pressed together. For example, one of the assembly

surfaces may have a relatively shallow broad based V-shape

configuration, extending over the entire surface or a

portion of the area thereof, while the mating surface may

have a complementary V-shaped depressed configuration, so

that the surfaces would gradually slip into their final

alignment as they are brought together within the surgical

site. Such self-aligning configuration of the assembly

surfaces enhances the ease of assembly within a surgical

site that is confined and not subject to easy direct

observation. Other such mechanisms for achieving self-

aligning mating surfaces are readily visualized by those

skilled in the art. [0030] The dimensions of the segments of the femoral

component of the invention are set so that the assembled

femoral component has a size within the conventional size

range of integral currently used femoral components of

total knee joint replacement prostheses. To this end the

individual segments have dimensions proportioned to the

dimensions of standard femoral components (which are

provided in various sizes to accommodate different-sized

individual patients) . Thus for a two-segment femoral

component of the invention the individual segments may

range in width between about one-third and about two thirds

of the lateral dimensions of a standard one-piece femoral

component. The basis for the variation may involve

relative ease of insertion. For example it may be easier

to insert a smaller segment deep into the surgical site and

follow with a somewhat larger segment. The basis for the

variation may also involve the location chosen by the

surgeon to place the articulation between the segments,

e.g., exactly in the center of the patellar groove, or

somewhat to one side of the center, as may be required or

desirable in an individual patient. Accordingly in a

three-segment femoral component according to the invention

the segments may range in width from about somewhat less than one-third of the width of a conventional unitary

femoral component to about as much as two-thirds of the

width of a conventional femoral component. For example,

the width of the central segment may be chosen to be

somewhat greater than one-third of the width of a

conventional one-piece femoral component or somewhat less

than about one-third of the width of a conventional femoral

component .

[0031] If separate fasteners are used for securing the

modules together they may be of any conventional type, such

as screws, rivets, or the like.

[0032] The mating surfaces can be formed at any

convenient angle to the femoral fixation surfaces and/or

the bearing surfaces. However, for convenient assembly

during the surgical procedure it is preferred that the

mating surfaces are oriented generally perpendicularly to

the femoral fixation surfaces and bearing surfaces and

extend generally in the proximal-distal direction relative

to the femur. Such a preferred orientation is illustrated

in the accompanying drawings .

[0033] In general, the articulation between two segments

of the femoral component of the invention, i.e., the line

at a surface, e.g., a bearing surface, of the femoral component where the mating surfaces meet should be

positioned and aligned to minimize contact with the

overlying patella or patellar component of the knee joint

replacement. In preferred embodiments the articulation is

located away from the peak of the condylar portion of the

femoral component and preferably in the groove between the

condylar portions. It is also preferred that the

articulation be arranged in a longitudinal direction with

respect to the femur, i.e., in a proximal-distal direction,

to minimize motion of the patella or patellar component

transverse to the line of articulation as the total knee

replacement is flexed and extended. This requirement is

highly preferred for those areas of the femoral component

wherein the pressure of the overlying patella or patellar

component is relatively great. The condition can be

somewhat relaxed in those areas of the femoral component

where the patellar pressure is somewhat less. In such

areas, the articulation may be oriented to permit some

cross-motion, especially if other benefits, e.g., greater

strength or rigidity or greater ease of assembly can be

achieved.

[0034] In an alternate embodiment wherein the femoral

component of the invention is assembled from three segments, a central segment may be present which extends

only partway along the height of the femoral component .

The two outer segments may then be joined to one another

via mating surfaces extending the remainder of the height

of the femoral component. Such an embodiment is

illustrated in Figures 4A and 4B, discussed in more detail

below.

[0035] The modular prosthesis of the invention may be

made of any conventional material used in such prostheses.

Thus, the individual modules may be made of metal such as

titanium, or a cobalt-based alloy or the like, or of a

ceramic such as alumina, zirconia, or the like.

[0036] The modules of the prosthesis may be manufactured

by any appropriate conventional techniques for processing

metal or ceramic objects such as machining, casting,

forging, hot isostatic pressing, sintering, grinding, or

the like.

[0037] The modular prosthesis of the invention will be

illustrated by the accompanying drawings which illustrate

certain embodiments and features of the invention, but are

not intended to limit the scope of the invention which is

defined solely by the appended claims . [0038] Figure 1A illustrates one embodiment 100 of the

modular prosthesis of the invention in a disassembled

configuration. The modular prosthesis 100 comprises a

first module 102, having a femoral fixation surface 104, a

bearing surface 106 for contacting an opposed mating

surface on a tibial prosthesis (not shown) , and a mating

face 108 for mating with a corresponding mating face of the

second module 112. The femoral fixation surface 104 is

provided with one or more locating and fixing projections

110 which fit into corresponding recesses surgically formed

in the distal end of the femur. The second module 112 of

the modular prosthesis 100 comprises a femoral fixation

surface 114, a bearing surface 116 for contacting an

opposed mating surface on a tibial prosthesis (not shown) .

The second module also has a mating face (not visible) for

mating with the corresponding mating face 108 of the first

module 102. The first module 102 of the modular prosthesis

100 is also provided with one or more alignment pins 120

for engaging corresponding alignment recesses or holes (not

shown) in the mating face of the second module 112, and

with one or more fastener screws 122 for holding the

assembled modules 102, 112 of the prosthesis 100 securely

together. [0039] Figure IB shows the modular prosthesis 100 of

Figure 1A in its assembled configuration, wherein mating

surface 108 of the first module 102 and the corresponding

mating surface (not shown) of the second module 112 are

held securely together by fastener screw 102 as indicated

by mating line 124.

[0040] Figure 2A illustrates another embodiment 200 of

the modular prosthesis of the invention in a disassembled

configuration. The modular prosthesis 200 comprises a

first module 202, having a femoral fixation surface 204, a

bearing surface 206 for contacting an opposed mating

surface on a tibial prosthesis (not shown) , and a mating

face 208 for mating with a corresponding mating face of the

third module 220. The femoral fixation surface 204 is

provided with one or more locating and fixing projections

210 which fit into corresponding recesses surgically formed

in the distal end of the femur. The second module 212 of

the modular prosthesis 200 comprises a femoral fixation

surface 214, a bearing surface 216 for contacting an

opposed mating surface on a tibial prosthesis (not shown) .

The second module also has a mating face (not visible) for

mating with the corresponding mating face 222 of the third

module 220. The first module 202 of the modular prosthesis 200 is also provided with one or more alignment pins 220

for engaging corresponding alignment recesses or holes (not

shown) in the mating face of the third module 220, and the

third module 220 is provided with one or more alignment

pins 226 for engaging corresponding alignment recesses or

holes in the mating face (not shown) of the second module

212. One or more fastener screws 228 hold the assembled

modules 202, 212, and 220 of the prosthesis 100 securely

together.

[0041] Figure 2B shows the modular prosthesis 200 of

Figure 2A in its assembled configuration, wherein mating

surfaces 208 of the first module 202 and 222 of the third

module 220 are held securely together with the

corresponding mating surfaces (not shown) of the third

module 220 and the second module 212, respectively, by

fastener screw 228 as indicated by mating lines 232.

[0042] Figure 3A shows a front elevational view of the

modular prosthesis 100 of Figures 1A and IB, illustrating

the interaction of the bearing surfaces 106 and 116 with

the mating or contacting surface 304 of the patella 302.

In order to prevent contact of any tissue or plastic

covering associated with the surface 304 of the patella 302

with a sharp or rough exposed edge of a mating surface 108 of the first module 102 or the corresponding mating surface

of second module 112, the edges 126, 128 of the mating

surfaces are provided with beveled or radiused corners 306

so that the mating line 124 is depressed below the bearing

surfaces 102 and 112. This construction assures that

adjacent tissue may move over the mating line 124 of the

modules 102 and 112 without being torn, abraded, or

otherwise injured and that any plastic covering, e.g., of

polyethylene or the like, associated with the lower surface

of the patella will not be roughened or abraded.

[0043] Figure 4A illustrates another embodiment 400 of

the modular prosthesis of the invention in a disassembled

configuration. In this embodiment 400 the central segment

contacts the side segments with assembly surfaces that

extend partway down the height of the femoral component of

the invention. The modular prosthesis 400 comprises a

first module 402, having a femoral fixation surface 404, a

bearing surface 406 for contacting an opposed mating

surface on a tibial prosthesis (not shown) , and a mating or

assembly face 408 for mating with a corresponding mating

face of the third module 420. The femoral fixation surface

404 is provided with one or more locating and fixing

projections 410 which fit into corresponding recesses surgically formed in the distal end of the femur. The

second module 412 of the modular prosthesis 400 comprises a

femoral fixation surface 414, a bearing surface 416 for

contacting an opposed mating surface on a tibial prosthesis

(not shown) . The femoral fixation surface 404 is provided

with one or more locating and fixing projections 418 which

fit into corresponding recesses surgically formed in the

distal end of the femur. The second module also has a

mating face (not visible) for mating with the corresponding

mating face 422 of the third module 420. The first module

402 of the modular prosthesis 400 is also provided with one

or more alignment pins 424 for engaging corresponding

alignment recesses or holes (not shown) in the mating face

of the third module 420, and the third module 420 is

provided with one or more alignment pins 426 for engaging

corresponding alignment recesses or holes in the mating

face (not shown) of the second module 412. One or more

fastener screws 428 hold the assembled modules 402, 412,

and 420 of the prosthesis 400 securely together.

[0044] Figure 2B shows the modular prosthesis 400 of

Figure 2A in its assembled configuration, wherein mating

surfaces 408 of the first module 402 and 422 of the third

module 420 are held securely together with the corresponding mating surfaces (not shown) of the third

module 420 and the second module 412, respectively, by

fastener screw 228 as indicated by mating lines 432.

[0045] The invention having been disclosed above in

connection with certain embodiments it is to be understood

that all changes and modifications that conform to the

disclosure and spirit of the invention are to be considered

as included therein, the scope of the invention being

defined by the appended claims.