Modulator knee prosthesis system

A modular knee joint prosthesis using variably sized components for joining a variably resected tibia bone and a femur bone, having a tibial platform defining peripheral edges on its bottom surface for engaging beveled edges of the plates or spacers. The platform has an upraised boss on a top surface for engaging a tibial insert which can be locked in place with a lock key. The tibial insert serves as an articulating surface for a femoral component. An implantable stem extends below the platform and may be complementarily joined to a second stem; the stems lock together using a Morse taper and a locking bolt. Full-sized or half-sized extension plates have beveled edges on a top surface to engage complementing edges on the bottom surface of the tibial base plate. The plates act as a spacer or cap to the resected tibia and act to distribute load or make up for bone deficits.

This invention in general relates to prosthetic devices and implants such 
as artificial joints, and more particularly knee joints. 
The knee joint is where the distal end of the femur and the proximal end of 
the tibia meet. Incorporated by reference herein are the background of the 
invention sections of the following U.S. Pat. No. 4,257,129 to Robert G. 
Volz and U.S. Pat. No. 4,714,474 to John G. Brookes, Jr. et al which 
disclose the particularities of the natural knee joint, problems 
associated with its replacement and discussions surrounding implantation 
of knee joint prostheses. 
The main problem associated with knee joint implantation is that most 
prostheses restrict the surgeon to where resection of the tibia bone must 
take place. Furthermore, most prostheses do not allow for much 
adjustability to best accommodate the patient, thereby losing the ability 
to make a natural joint connection between the femur and the tibia. 
The prosthetic device disclosed herein provides the greatest flexibility to 
the implanting surgeon offering the patient a prosthetic knee joint best 
simulating the natural knee joint. These results, as well as others, will 
be apparent from the hereinafter following commentary. 
SUMMARY OF THE INVENTION 
The present invention is directed to an improved knee joint prosthesis 
which offers a great degree of surgical flexibility at the time of 
implantation. The invention incorporates a modular system which allows the 
surgeon to structure and orient a knee prosthesis to best suit the 
patient. 
More particularly, the knee joint prosthesis of the present invention 
allows the variable use of components to join a variably resected tibia 
bone to a femur bone. The system employs a tibial platform or base plate 
defining a top surface having an upraised boss. Along the periphery of the 
platform's bottom surface is an engaging and beveled lip. Extension plates 
of a variety of sizes may be placed under the tibial base plate. Also, a 
half-sized spacer may be used. The extension plates or half-sized spacers 
have beveled edges which engage the engaging and beveled lip assuring 
secure engagement. 
A tibial insert providing an articulating surface for a femoral component 
engages the boss holding the tibial insert to the tibial base plate. A top 
surface of the base plate has a pair of engaging lips to prevent the 
tibial insert from sliding off the tibial platform. A lock key is used to 
lock the insert to the boss. 
On the bottom side of the base plate is a concentrically narrowing stem 
which is axially located and which engages a modular stem which may have 
fins or anti-rotation grooves. The modular stem is implantable within the 
resected tibia bone. The engagement between the stem and modular stem 
utilizes a Morse taper fit on engagement. Also, a bolt may be incorporated 
through the stem for engagement to the modular stem. 
Other aspects and advantages of the present invention will become apparent 
from the following description of the preferred embodiment, taken in 
conjunction with the accompanying drawings, which illustrate, by way of 
example, the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings wherein like numerals identify like elements, the 
invention is embodied in a prosthetic knee joint 7. The joint 7 is 
implantable into a human leg 9, between the femur 10 and the tibia 12 
bones. A femoral component 14 may be used to cap-off the distal end of the 
femur 10. 
The joint 7 comprises a design and configuration which offers a great 
degree of modularity of components. The components comprise a tibial 
insert possibly a tibial extension plate 13 or modular half-spacer 21, a 
tibial platform or base plate 15, a stem bolt 17, a lock key 19, and a 
modular stem 22 or keel stem 23. Securing screws 25 may be utilized to 
secure the tibial extension plate 13 or the modular half spacer 21 to a 
bottom surface 31 of the tibial base plate 15. The screws 25 pass through 
the tibial base plate 15 to engage the extension plate 13 or modular half 
spacer 21. 
A primary component is the tibial base plate or platform 15. The base plate 
or platform 15 has a kidney-shaped configuration having a top surface 29 
and the bottom surface 31. An interrupted and upraised boss 33, primarily 
centered along the top surface 29 of the tibial base plate 15, is provided 
to operatively engage the tibial insert 11. A slot 35 along an 
undersurface of the tibial insert 11 is of a complementary shape and size 
to the boss 33. This allows a surgeon to easily slide the tibial insert 11 
over the top surface 29 of the tibial base plate 15 to operatively engage 
the boss 33. The slot 35 has lateral and paralled grooves 39 on opposite 
and opposing walls 37. The engagement is snug and sufficient to prevent 
the insert 11 from sliding off the boss 33 or to cause shimming. 
Furthermore, the tibial base plate 15 has a pair of peripheral lips 64 on 
its top surface 29 which prevent anterior-posterior and medial-lateral 
movement of the tibial insert 11 upon assembly with the tibial base plate 
15. 
The lock key 19 has a circumferential shape and thickness adapted to slide 
into the grooves 39 of the slot 35. The lock key 19 has dual prongs of a 
type commonly known in the art of clips. 
The tibial key 19 clips to the boss 33 in such a fashion, once the insert 
11 is assembled upon the tibial base plate 15, so as to operatively and 
securely retain the insert 11 to the tibial base plate 15. 
The tibial insert 11 can be selected from a large number of different ones 
varying in thickness, shape and design so long as the insert 11 has the 
requisite slot 35 and grooves 39 as described above. 
Additionally, a standard or customized tibial extension plate 13 may be 
optionally positioned on the bottom surface 31 of the tibial base plate 
15. The extension plate 13 may serve as both a spacer and a cap for the 
top of the resected tibia 12. The modular half-spacer 21, may be 
optionally placed on the bottom surface 31 instead of or in addition to 
the tibial extension plate 13 to act as on partial spacer, as shown in 
FIG. 2. 
Extending downwardly from the bottom surface 31 of tibial base plate 15 is 
stem 41 centrally located and having a cylindrical and tapering end 43. 
The stem 41 engages a modular stem 22 shown in phantom line in FIGS. 1 and 
2 or a keel stem 23 either of which may be implanted within the tibia 12 
to be joined with the femur 10. The keel stem 2 has a receiving end 42 
which is cylindrical and tapering inwardly to mate with the tapering end 
43 of stem 41. When in an assembled condition, the stem 41 and keel stem 
23 (or modular stem 23) form a Morse taper association to securely 
associate both stems 41 and 23. The keel stem 23 is often used in 
cementless surgical implanting techniques. 
Alternatively, stem 22 the modular stem 22 shown in phantom line in FIGS. 1 
and 2, may have a clover-leaf cross-section with anti-rotation grooves 24 
and a receiving end 42 and functions similar to the keel stem 23. The 
modular stem 22 is used in cementing surgical implanting techniques. 
A bore 47 extends axially through the tibial base plate 15 and the stem 41 
of the tibial base plate 15 and is of sufficient size to receive stem bolt 
17. Stem bolt 17 has a threaded end 49 and an enlarged head 51 with a 
hexagonal recess 53 for engagement by a tool not shown. The bolt 17 passes 
through bore 47 and threadedly engages threads 50 within the interior of 
receptacle end 42 of keel stem 23 (or end 42 of the modular stem 22). The 
enlarged head 51 of bolt 17 is too large to pass through the bore 47 
entirely, thereby securing the tibial base plate 15 to the keel stem 23 or 
modular stem 22. 
The mid-section of the boss 33 is interrupted or discontinuous allowing a 
top opening 55 of the bore 47 to be exposed at a level flush with the top 
surface 29 of the tibial base plate 15. This allows the bolt 17 to be 
associated with the tibial base plate 15 and the keel stem 23 or modular 
stem 22 prior to the assembly of the tibial insert 11. Of course, as shown 
in FIG. 4, the bore 47 may be wider at its top opening 55 sufficient to 
allow the enlarged head 51 of the bolt 17 to fully recess into the bore 
47, yet still retain the tibial base plate 15 to the keel stem 23 or the 
modular stem 22. 
The boss 33, additionally, has corresponding grooves 57 positioned so as to 
allow the lock key 19 to slide into locking engagement with the boss 33 
and the grooves 39 within the slot 35 of the tibial insert 11. Extending 
and curved surfaces on a bottom surface, not shown, of the boss's grooves 
57 provide a locking feature, wherein the complementary curved surfaces 58 
and 61 of the lock key 19 engage those surfaces on the boss 33 once the 
lock key 19 is slid into position. 
The extension plate 13 or tibial base plate 15 may be asymmetrical or its 
periphery may be customized based upon a single cat scan (CT) slice of 
cross-sectional information so that the tibial base plate 15 or extension 
plate 13 fully covers the tibial bone 12. This configuration may achieve 
better loading on the proximal end of the tibial bone 12 to encourage 
proper healing. Customization may also take place using a variety of other 
imaging techniques to define the limits of the patient's bones. The image 
defined by the patient's, bones (primarily the proximal end of the tibia 
12) dictates or defines the geometry of the extension plate 13 and/or the 
tibial base plate 15. 
In more detailed aspects of the extension plate 13, the extension plate 13 
has a kidney-shape configuration like the top surface 29 of the tibial 
base plate 15. However, the extension plate 13 may be slightly larger to 
act as an extending cover over the top of the resected tibia 12 in the 
event the tibial base plate 1 is not wide enough to satisfactorily cap off 
the end of the tibia 12. The extension plate 13 may range in thickness 
depending upon the patient encountered. Beveled edges 59 peripherally and 
uniformly circumscribed are located on a top surface 62 of the extension 
plate 13. 
Although the extension plate 13 may come in a variety of sizes, the shape 
and size of the beveled edges 59 are uniform to allow modularity between 
different sized extension plates 13 and tibial base plates 15. The beveled 
edges 59 may have an inward inclination of 30.degree. from lips 63 of the 
bottom surface 31 of the tibial base plate 15 in an assembled condition. 
The lips 63 may create a complementary angle or bevel from the horizontal 
or an angle so as to complement and engage the beveled edges 59 of the 
extension plate 13. The combination of lips 63 and edges 59 not only 
provides some degree of locking engagement, but also serves as a cement 
dam when cement is used to further secure the extension plate 13 to the 
bottom surface 31 of tibial base plate 15. The top surface 62 and a bottom 
surface 67 of the plate 13 may have an irregular surface for purposes of 
providing a better surface for engaging the component using cement. 
The extension plate 13 defines a centrally located and rectangular cut-out 
section 69 with rounded corners which allows the extension plate 13 to be 
assembled on the bottom surface 31 of the tibial base plate 1 and allows 
the stem 41 to protrude through the extension plate 13. 
The extension plate 13 may have positioning holes 74 uniformly positioned 
through the extension plate 13. Pegs or screws (not shown) can be 
positioned into the top of the tibia bone 12. The extension plate can be 
placed on the tibia bone 12 with the pegs or screws (not shown) passing 
through the holes 74 to position the extension plate 13. The tibial base 
plate 15 can then be positioned on the extension plate 13 to allow 
fastening of the tibial base plate 15 to the extension plate 13. 
Additionally, slots 71 may interrupt the sides of the rectangular cut-out 
section 69 to accommodate the geometry or cross-section of the keel stem 
23. 
Also, screw holes 73 are evenly distributed across the extension plate 13 
to allow the screws 25 to pas through the complementary spaced and sized 
holes 75 on the top surface 29 of the tibial base plate 15 and engage the 
extension plate 13 or half-spacer 21. 
The half-spacer 21 is similar to the extension plate 13, but covers only 
half the area, has beveled edges 79 on a top surface 81 and engages lips 
63 on the bottom surface 31 of the tibial base plate 15. A bottom surface 
91 may have similar beveled edges for greater modularity. Screws 25 and 
cement may, likewise, secure the half-spacer 21 to one side of the bottom 
surface 31 or the other of the tibial base plate 15. The holes 75 in the 
tibial base plate 15 pass all the way through the tibial base plate so as 
to allow screw attachment via the top surface 29. 
The modular half-spacer 21 may be optionally fastened to the tibial base 
plate 15 which allows the proper orientation of the tibial base plate 15, 
to the tibia 12, especially after a non-uniform or slanted resection of 
the tibia 12. The modular half-spacer 21 is attached to the tibial base 
plate 15 like the extension plate 13. 
The half-spacer 21 may come in a variety of sizes, thicknesses, and angular 
cross-sections, however, its beveled edges 79 and holes 73 and 74 are 
uniformly positioned for modularity, fitting with a variety of different 
sized tibial base plates 15. Top and bottom surfaces 89 and 91 of the 
half-spacer 21 may also be irregular for cementing purposes. The 
half-spacer 21 allows the surgeon to buttress the tibial base plate 15 
where the tibia bone 12 has not been resected perpendicularly to its 
longitudinal axis. This type of resection is often required where the 
proximal end of the tibia bone 12 has deteriorated due to disease or 
trauma or prior surgery. 
Due to the modularity of the invention, the extension plate 13 could be 
positioned and attached to the bottom surface 31 of the tibial base plate 
15 like the half-spacer 21. 
The keel stem 23 or modular stem 22 can come in a variety of lengths, sizes 
and configuration. However, the receptacle ends 42 and 42 are of a uniform 
size as is the stem 41 of the tibial base plate 15 for purposes of 
interchangeability between components of different sizes. Also, threadings 
50 shown within the interior of the receptacle end 42 of the keel stem 23 
are of a uniform size to assure complete modularity. 
In the preferred embodiment, the keel stem 23 is cylindrical with extending 
fins 95 which help stabilize the prosthesis 7 when implanted within the 
tibia bone 12. This stability helps prevent twisting disassociation of the 
prosthesis 7 from the tibia bone 12. 
As mentioned, the tibial insert 11 is similar to those inserts as described 
by those tibial inserts described in the incorporated by reference 
patents, with the exception of the unique slot 35 and groove 39 
configuration allowing for locking engagement with the boss 33 of the 
tibial base plate 15 using the lock key 19. 
The materials used and their manufacture for each of the components are the 
same materials and methods of manufacture as those corresponding 
structures in the incorporated by reference patents, namely implantable 
cobalt chrome or titanium and ultra high molecular weight polyethylene 
plastic. 
Implantation of the prosthesis 7 is similarly accomplished by the surgeon 
as current knee prostheses, however the surgeon has much greater 
flexibility in changing the overall fit, design, and attributes of the 
knee prosthesis once the implantation operation has started. After the 
surgeon has resected the tibia bone 12, he can quickly and easily build a 
prosthesis 7 to accommodate any situation he encounters. Also, the fit of 
the prosthesis can be enhanced with the variability of components and 
options that are available. 
Furthermore, the present invention promotes greater bone surface to surface 
contact of the prosthesis. This contact distributes the stress of walking 
at the end of the joined bones, thereby acting to reduce resorption of the 
surrounding tissue away from the prosthesis. 
In view of the foregoing, it should be appreciated that the present 
invention provides an improved modular knee joint prosthesis, which is 
simple in construction, completely modular and interchangeable, and 
superiorly effective. 
Although the present invention has been described in detail with reference 
only to the presently-preferred embodiment, it will be appreciated by 
those of ordinary skill in the art that various modifications can be made 
without departing from the invention. Accordingly, the invention is 
limited only by the following claims.