Tibial prosthesis, template and reamer

Disclosed herein are an improved tibial prosthesis and a template and reamer which are utilized in installing the prosthesis on the proximal end of a surgically prepared tibia. The prosthesis comprises a tibial component including a tray attached to the proximal tibia and an insert attached to the tray and provided to present an articulating surface for bearing engagement with the distal end of the femur or alternatively with a femoral component which has been surgically attached to the distal end of the femur. The tray includes an exterior surface including a plurality of domical contours which interengage with corresponding surfaces formed in the proximal tibia by the surgeon. The tray is preferably attached to the proximal tibia through the use of screw fasteners extending through openings formed in the domical contours. The template is utilized by the surgeon in measuring the exact location and size of the contours which are to be surgically formed in the proximal tibia. The reamer is specifically designed to enable its use during the surgical procedure to surgically create the contours which are formed in the proximal tibia.

BACKGROUND OF THE INVENTION 
The present invention relates to an improved tibial prosthesis, template 
and reamer. The bearing surfaces of the knee joint are vulnerable to 
stress and arthritic and other disease-induced deterioration. Prosthetic 
correction is indicated when the knee joint is so damaged that other less 
drastic techniques have little or no prospect of success. In earlier 
years, hinge-type prostheses were most frequently employed in such cases 
to restore the joint to some degree of normalcy. This was not entirely 
satisfactory due to the complexity of the knee joint movement, the 
desirability of minimal bone removal, the need for preserving potentially 
functional cruciate and collateral ligaments, and the limitations of 
hinge-type prostheses in handling various knee loads and forces without 
being damaged. Hinge-type prostheses are generally limited today to cases 
with severe soft tissue damage. Later and present knee prostheses have 
separate femoral and tibial components attached to the respective femoral 
and tibial condyles so as to provide a prosthesis more in harmony with the 
actual workings of the knee joint. Separate components allow use of the 
existing cruciate and collateral ligaments and permit the prosthesis to 
handle radial and twisting forces on the knee without breaking. 
Although the prior art as embodied in separate tibial and femoral 
components has become more sophisticated as of late, to this time, tibial 
prosthetic components do not ideally replace the bone tissue since their 
shapes and means of attachment do not optimize the uniform spreading of 
forces which are placed on the tibia nor do they adequately oppose lateral 
motions which are inherently placed upon tibial components during normal 
joint movements. Thus, in the prior art, tibial components often loosen 
and must be reattached or replaced with such operations often requiring 
removal of additional bone tissues. 
In a further aspect, many tibial components known at this time are attached 
to the proximal tibia through the use of cementing techniques. This may 
cause problems in the joint since these cementing techniques usually 
result in elevated temperatures during the curing of the cement, which 
elevated temperatures tend to damage body tissues. Thus, a need has 
developed for a tibial prosthesis which may be installed without the use 
of cement but which may consistently achieve firm initial fixation and 
thence may receive bony ingrowth for firm permanent fixation. 
The tibial component of a knee prosthesis is generally cemented to the 
tibial condyle rather than screwed thereto because a satisfactory 
environment for uncemented devices has not been taught by prior art. 
Earlier tibial components such as that which is disclosed in U.S. Pat. No. 
3,728,742 to Averill had serrations and pins on the underside which were 
anchored in the proximal tibial surface by a suitable cement after 
surgical preparation. The problems with cemented prosthesis have been 
discussed hereinabove and components such as those disclosed by Averill 
have been known to be vulnerable to loosening from typical knee forces 
which are placed on the prosthesis. 
In order to avoid the problems of Averill, the configuration of the tibial 
component further evolved to a point where a vertical element extending 
downwardly from the undersurface of the tibial component and into the 
tibia has been used to counteract instability problems. U.S. Pat. No. 
4,205,400 to Shen, et al. discloses a tibial prosthesis having a base 
plate formed with a depending connecting stem which is designed to extend 
distally into the proximal tibial surface into a cavity excavated therein 
by the surgeon. This device is believed to be deficient in that it 
requires a large amount of bone removal and still requires the use of 
cement which has the problems as set forth hereinabove. 
Additionally, the following prior art is known to applicants: 
U.S. Pat. No. Re. 29,757 to Helfet discloses prosthetic joint components 
including double curved surfaces as well as an elongated post for fixation 
purposes. The teachings of Helfet differ from the teachings of the present 
invention mainly because the present invention does not require an 
elongated fixation spike and further because the present invention 
utilizes fixation means which may comprise screws extending through the 
curved surfaces thereof. 
U.S. Pat. Nos. 4,224,696 and 4,224,697 both to Murray, et al., disclose a 
prosthetic knee having femoral and tibia components both of which are made 
of a biologically inert high strength metal such as 
chromium-cobalt-molybdenum. The meniscal plate is a one-piece unit of 
ultra-high molecular weight polyethylene and fixed between the femoral and 
tibial components. The underside of the tibial component include a 
substantially curved surface but also requires an elongated anchoring 
spike. Of course, this anchoring spike renders the tibial prosthesis of 
Murray, et al. vastly different from the teachings of the present 
invention and Murray, et al. also fail to disclose the type of fixation 
utilized in the present invention. 
SUMMARY OF THE INVENTION 
The present invention overcomes the deficiencies found in prior art tibial 
prostheses such as those discussed above and provides an improved tibial 
prosthesis which optimizes prosthesis design and insertion and retention 
techniques. The inventive tibial prosthesis optimizes the design by 
providing a structure which optimally spreads forces in more than one 
direction into the tibia so as to reduce the effects of shock forces and 
lateral joint movements which may occur in normal walking motions. 
Furthermore, the inventive prosthesis increases the surface area of 
engagement between the prosthesis and the bone surface so as to maximize 
the area of the engaging surfaces and thereby maximize the area of 
fixation therebetween. By increasing the surface area through the use of a 
plurality of domical surfaces, lateral motion of the prosthesis with 
respect to the bone is substantially avoided. Furthermore, the present 
invention by eliminating elongated fixation posts reduces the amount of 
bone material which must be removed from the bone during the installation 
of the prosthesis during surgery. 
The present invention includes the following aspects: 
(a) The improved tibial prosthesis forming a part of the present invention 
is made of two general parts. The first part comprises a tray portion 
preferably made of a metallic material. The tray portion includes in the 
preferred embodiment a double domical contour which is designed to face 
the cut surface of the proximal tibia. The domes which define the domical 
contour provide anatomical and physiological interfaces with the bone of 
the proximal tibia as it has been prepared by the surgeon and is distinct 
from the prior art as using large convex undersurfaces to fixate the 
prosthesis to the proximal tibia without the additional use of elongated 
peg-type fastening means. By providing the domical contours, the tray 
portion maximizes the surface area of interengagement between the tray 
portion and the bone surfaces of the proximal tibia over the area which 
would be in interengagement were the contour of the tray portion to be 
made completely flat. This increased surface area enhances bony ingrowth 
fixation and eliminates the need for bone cement where bony ingrowth 
fixation is indicated in particular cases. 
(b) Each of the domes which form the domical contour has, in the preferred 
embodiment, a plurality of holes therein through which fastening devices 
are extended so as to fasten the tray portion to the proximal tibia. In 
the preferred embodiment, these fastening devices consist of headed 
screws, however, if desired, other fixation devices such as nails may be 
utilized. In order to enhance the fixation of the tray portion to the bone 
surfaces, the domical contours may be provided with metallic or 
non-metallic mesh bony ingrowth materials specifically designed to 
interact with the bone tissue of the tibia so that the bone tissue grows 
therein to thereby permanently fixate the tray portion to the bone. These 
factors combined with the fact that the convexities of the undersurface of 
the tray portion are analogous to the normal contours of the sub-chondral 
bone optimizes the firm fixation of the tray portion to the bone. In a 
further aspect, the convexities reproduce the normal distribution of 
stress within the cancellous and cortical bone of the proximal tibia. If 
desired, the above-described metal bony fixation material may instead 
consist of a porous bony ingrowth fixation layer. 
(c) The other part of the tibia prosthesis consists of an articular insert 
preferably made of a low friction plastic material. The insert is designed 
to be attached to the back side of the tray portion in any suitable manner 
such as for example, through a snap fit connection, dove-tail interface or 
through the use of fastening devices such as screws. In another aspect, in 
practice, fastening means to fasten the tray portion and articular insert 
portion together are not necessary since the various knee ligaments and 
tendons, if intact, will hold the portions together. The plastic insert on 
its face which faces away from the tibia includes a bearing surface 
designed to engage the distal end of the femur or, alternatively, distal 
surfaces of a distal femur prosthesis. 
(d) In a further aspect of the present invention, in order to properly 
install the tibial prosthesis on the tibia, the proximal tibia must be 
properly and accurately prepared for the installation of the prosthesis. 
For this purpose, the present invention further includes a template which 
is designed to enable the surgeon to properly locate the areas on the 
proximal tibia where recesses are to be formed so as to enable the 
proximal tibia to snugly receive the domical contours. Thus, the present 
invetion includes such a template which includes a plurality of holes 
therethrough corresponding to the number of domes which are to be included 
in the prosthesis and further includes a peripheral shape corresponding 
closely to the periphery of the bone surface which has been prepared by 
the surgeon. Thus, the template may be placed over the bone surface and a 
reamer device may easily be guided through the template holes and thereby 
used to ream the domical recesses in the proximal tibia. 
(e) In order to ream the domical recesses in the proximal tibia, a special 
reaming device must be utilized since the reaming device will be utilized 
through a body incision during the course of surgery. Thus, the present 
invention further contemplates a special reamer having a drive shaft 
preferably disposed at an angle to the axis of rotation of the reaming 
head. In the preferred embodiment, this angle should be from 45.degree. to 
90.degree., however, other angles may be contemplated by those skilled in 
the art so long as those angles enable the reamer to be utilized through 
an incision in the knee. 
In a further aspect of the present invention, the domical contours of the 
tray portion may take on different types of curvature. Thus, for example, 
the individual domes may be part-spherical or elliptical in nature. It is 
important to note that the present invention solely resides with the 
creation of domical contours of curved configuration since applicants 
believe that such curved configurations optimize the distribution of 
stresses and forces which are created through the use of a knee in normal 
movements thereof. The inventors believe that other types of surfaces such 
as for example conical surfaces, do not properly distribute the forces and 
stresses which are imposed upon a knee joint during normal motions thereof 
and thus such conical surfaces are inferior to the teachings of the 
present invention. In the situation where the domes are made of spherical 
surfaces, it has been found that, optimally, each dome comprises less than 
a hemisphere. This is because completely hemispherical domes would require 
the removal of too much bone tissue from the proximal tibia and would thus 
cause a negative impact thereon. It has been found that spherical surfaces 
describing less than a hemisphere increase the surface area of contact 
between the proximal tibia and the domical contours sufficiently so as to 
render them quite reliable. 
Accordingly, it is a first object of the present invention to provide a new 
and improved tibial prosthesis for an articular knee joint prosthesis. 
It is a further object of the present invention to provide such a 
prosthesis which increases the surface area of engagement between the 
prosthesis and the proximal tibia. 
It is a still further object of the present invention to provide such a 
prosthesis which spreads forces and stresses which are placed on a knee 
joint during normal movements thereof so as to reduce the possibilities of 
lateral motion of the prosthesis with respect to the tibia. 
It is a still further object of the present invention to provide such a 
prosthesis which increases the surface area of interengagement while 
reducing the amount of material which must be removed from the tibia. 
It is a still further object of the present invention to provide such an 
improved tibial prosthesis which increases the surface area of 
interengagement to a sufficient extent so as to avoid the necessity of 
cementing the prosthesis to the proximal tibia and so as to facilitate 
fixation through the use of bolt or screw fasteners. 
It is a yet further object of the present invention to provide a tibial 
prosthesis which substantially duplicates the anatomical configuration of 
the sub-chondral plates in the medial and lateral compartments of a 
healthy knee joint. 
It is a still further object of the present invention to provide a template 
and reamer device which are specifically designed to enable the accurate 
preparation of the proximal tibia for the installation of the improved 
tibial prosthesis of the present invention. 
These and other objects, aspects and features of the present invention will 
be better understood in the following detailed description of the 
preferred embodiments when read in conjunction with the appended drawing 
figures.

SPECIFIC DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference is first made to FIGS. 1, 2, 3 and 4 wherein a first embodiment 
of the present invention is shown in detail. Reference numeral 1 refers 
generally to the tibial prosthesis comprising the major aspect of the 
present invention. As shown in FIGS. 1 and 2, the tibia 3 is adjacent the 
fibula 5 which is the non-weight bearing lower leg bone. As is well known 
and not shown herein, the tibia has a plateau portion made up of a lateral 
plateau and a medial plateau with each plateau having a pronounced 
indentation, which indentations are termed the lateral sub-chondral plate 
and the medial sub-chondral plate. Stress transfer from a load-bearing 
femur to the proximal tibia is by way of the sub-chondral plates named 
above. Thus, the tibial bone structure consisting of cancellous and 
cortical tissue in the areas of the sub-chondral plates is consequently 
denser and stronger than bone tissue in other areas of the tibia. 
As may be seen with particular reference to FIG. 2, in order to prepare for 
installation of the prosthesis of the present invention, the proximal 
tibia has been prepared by the surgeon to have a flat surface 7 thereon 
into which are reamed a plurality of domical recesses, in this example, 
two in number and designated by the reference numerals 9 and 11. The 
number of domical recesses which are prepared in the proximal tibia 
corresponds to the number of domical contours which are included in the 
tray portion of the inventive prosthesis. 
The inventive prosthesis 1 includes a tray portion generally designated by 
the reference numeral 13 and an articular insert portion generally 
designated by the reference numeral 15. 
The tray portion 13 includes an upper surface 17, a lower surface 19 and a 
peripheral surface 21. The upper surface 17 consists of a flat portion 23 
and a plurality of domical recesses each designated by the reference 
numeral 25. As seen in FIGS. 1 and 2, a plurality of holes 27 extend 
through the tray portion 13 which holes 27 originate in the recesses 25. 
The tray periphery 21 is of a substantially C-shaped configuration which is 
specifically designed to match the outer periphery of the proximal tibia 
as it has been prepared by the surgeon for implantation of the prosthesis 
1. This may be seen from comparison of the periphery 21 and the periphery 
of the proximal tibia as best seen in FIG. 2. With reference to FIG. 1, 
the underside surface 19 of the tray portion 13 includes a contoured 
surface comprising, in this example, a pair of domical contours 29 through 
which the holes 27 extend. As stated above, the domical contours 29 are 
characterized by having curved surfaces which may be formed through 
rotation of a curved line about its axis of rotation. In the embodiment 
shown in FIGS. 1-4, the domical contours 29 consits of part spherical 
surfaces. As will be described in greater detail hereinafter, domical 
contours comprising other types of curved surfaces may also be 
contemplated under the purview of the present invention. 
With further reference to FIG. 1, it is seen that in surrounding relation 
to the domical contours 29, the undersurface 19 of the tray portion 13 
includes flat surfaces 31 which extend to the periphery 21. The flat 
surfaces 31 are designed to bearingly engage the flat surfaces 7 of the 
proximal tibia as best seen in FIG. 2 while the domical contours 29 are 
specifically sized and designed so as to interengage in the domical 
recesses 9 and 11 which have been prepared in the poximal tibia. If 
desired, the domical contours 29 may cover as much as 75% of the surface 
area of the tray undersurface 19 or more if desired. In the preferred 
embodiment, screws designated by the reference numeral 33 in FIG. 1 may be 
inserted through the holes 27 within the recesses 25 to the top surface 17 
and thence screwed into the proximal tibia preferably within the domical 
recesses 9 and 11 which have been formed therein to thereby fixate the 
tray portion 13 to the proximal tibia. Of course, the fasteners may extend 
through any portion of the tray portion and thence into the proximal 
tibia. Regardless of where the fasteners are located, the domical contours 
will just as effectively uniformly spread forces placed on the prosthesis 
throughout the tibia. For example, the fasteners could extend through the 
tray portion without intersecting with any of the domical contour 
structure. This equally applies to all embodiments disclosed herein. The 
ability to use the fasteners 33 in this manner will enhance supplemental 
bone grafting as the grafts may be partially secured with the fasteners 
33. 
With reference now to FIGS. 1 and 3, it is seen that the undersurface 19 of 
the tray portion 13, including the domical contours 29 is completely 
covered with a porous bony ingrowth material designated by the reference 
numeral 35 which material may comprise metallic or non-metallic mesh which 
has been firmly fixated to the undersurface 19 in a manner well known to 
those skilled in the art. The purpose for the bony ingrowth material 35 is 
to enhance the fixation of the prosthesis 1 to the proximal tibia by 
virtue of bone material in the proximal tibia ingrowing into the mesh to 
thereby firmly fixate the tray portion 13 and thereby the entire 
prosthesis 1 thereto. The use of the material 35 eliminates the 
requirement for fixation through the use of cement. If, however, the 
surgeon desires to use cement in fixating the prosthesis 1 to the proximal 
tibia, the entire undersurface 19 of the tray portion 13 could be made 
smooth, even in the region of the domical contours 29. However, in the 
preferred embodiment of the present invention, the undersurface 19 is 
completely covered with the porous bony ingrowth material 35 since, as 
stated above, the use of the domical contours 29 sufficiently increases 
the surface area of contact between the tray portion 13 and the proximal 
tibia so as to eliminate the necessity of fixation through cementing 
techniques. 
In the preferred embodiment, the tray 13 may be made of a high-strength 
bio-compatible material such as titanium. However, if desired, other 
high-strength metals such as chromium-cobalt-molybdenum may be utilized. 
Additionally, non-metallic bio-compatible materials may be used. 
With reference, now, to FIGS. 1, 2 and 4, it is seen that the articular 
insert portion 15 includes an upper surface 41, an undersurface 43, and a 
periphery 45. As best seen in FIG. 2, the upper surface 41 includes a pair 
of generally concave indentations designated by the reference numerals 47 
and 49 and which are designed to bearingly receive cooperating condyle 
portions of the femoral prosthesis in a manner well-known to those skilled 
in the art. The indentations 47 and 49 are separated from one another by a 
rib-like structure 51 which is designed to be received between the femoral 
condyles in a manner well known to those skilled in the art. 
The periphery 45 of the articular insert portion 15 is designed to smoothly 
match the periphery 21 of the tray portion 13 so that when the tray 
portion 13 and the articular insert portion 15 are assembled together, the 
edges therebetween are smoothly engaging so as to avoid damage to 
surrounding tissues. 
With further reference to FIGS. 1 and 4, the undersurface 43 of the 
articular insert portion 15 includes a flat surface 55 and a pair of 
domical contours designated by the reference numeral 57. The contours 57 
are designed to snugly fit into the recesses 25 in the top surface 17 of 
the tray portion 13 so as to snugly assemble the components together. In 
the same manner, the flat surfaces 55 of the articular insert portion 15 
are designed to lie against the flat surfaces 23 on the top surface 17 of 
the tray portion 13. It is important to note, with partiuclar reference to 
FIG. 4, that the articular insert portion 15 between said domical contours 
57 and said indentations 47, 49 is of substantially uniform thickness. 
This design causes the portion 15 to substantially uniformly distribute 
forces and stresses placed thereon by normal joint movements. 
With reference to FIGS. 1-4, since the facing surfaces of the tray portion 
13, and the articular insert portion 15 include respective recesses 25 and 
contours 57, these components may not be assembled to one another by 
sliding contact therebetween. Thus, in order to assemble these components 
together, they must be assembled together in a stacking fashion which 
precludes the use of a dovetail type assembly means. Thus, in the 
embodiment of FIGS. 1-4, the components may be assembled together through 
a snap-fit connection or, as shown in FIG. 4, through the use of 
screw-type fastening means 59. 
Reference is now made to FIGS. 5-8 wherein a further embodiment of the 
present invention is shown. For ease of understanding, with respect to the 
embodiment of FIGS. 1-4, like elements will be designated by like primed 
reference numerals. With reference, first to FIGS. 5 and 6, the inventive 
prosthesis 1' is seen in its environemnt of the tibia 3, fibula 5 and 
femur 4 as well as the patella 6. A distal femoral prosthesis 8 is also 
shown but does not form a part of the present invention. As seen with 
reference to FIGS. 5 and 6, the prosthesis 1' includes a tray portion 13' 
and an articular insert portion 15'. The tray portion 13' includes a 
plurality of domical contours 29' through which, preferably but not 
necessarily, fastening devices 33' may extend. As before, the entire 
undersurface 9' of the tray portion 13' is covered with porous bony 
ingrowth material 35' which, as before, enhances the fixation of the 
prosthesis to the proximal tibia. 
The tray portion 15' includes a top surface 41' including the concavities 
47' and 49' and the rib-like portion 51'. 
All of the structure described above regarding the embodiment of FIGS. 5-8 
is substantially identical to the corresponding structure in the 
embodiment of figures 1-4. Where the embodiment of FIGS. 5-8 differs from 
the embodiment of FIGS. 1-4, is in the interface between the tray portion 
13' and the articular insert portion 15'. As seen in FIGS. 5-8, the upper 
surface 61 of the tray portion 13' is completely flat except for the 
presence of a dovetail-type protrusion 63 centrally located thereon. In a 
corresponding way, the lower surface 65 of the articular insert portion 
15' is completely flat except for a dovetail-type recess 67 formed therein 
and designed to slidably receive, in assembly, 
the dovetail protrusion 63 of the tray portion 13'. Thus, with the 
interface between the tray portion 13' and the articular insert portion 
15' being flat, the two components may be assembled together by sliding 
the articular insert portion recess 67 over the tray portion 13' dovetail 
protrusion 63 so as to snugly assemble the components together. 
With reference to FIGS. 5 and 6, it is seen that the fasteners 33' 
preferably but not necessarily extend through the domical contours 29' in 
directions substantially radially emanating from the respective center of 
curvature of the respective contours 29', as is the case in the embodiment 
of FIGS. 1-4. As may be seen with reference to FIGS. 7 and 8, since the 
surface 61 is flat and does not include recesses such as those which are 
designated by the reference numeral 25 in FIG. 2, it is seen that the 
starting points of the respective holes 27' are closely adjacent one 
another as opposed to the spacing of the holes best seen in FIGS. 2 and 3. 
Since the surface 61 must be devoid of any protruding objects so as to 
enable the articular insert portion to be slid thereover, in assembly, the 
starting point for the holes 27' may be located in a slightly recessed 
chamber designated by the reference numeral 69 in FIG. 8 so as to ensure 
that the flatness of the surface 61 will not be compromised. 
The materials from which the tray portion 13' may be manufactured are the 
same as those which were described hereabove with reference to the tray 
portion 13'. With regard to the articular insert portions 15 and 15', in 
the preferred embodiments, these structures are made of a strong, 
low-friction, bio-compatible material such as plastic. A preferred plastic 
for use in manufacturing the portions 15 and 15' comprises polyethylene. 
With reference now to FIG. 9, a further embodiment of the present invention 
is designated by the reference numeral 1" and is seen to include an 
articular insert portion 15" which may, if desired, be made in accordance 
with the teachings of either of the embodiments of FIGS. 1-4 or 5-8. 
Further, the embodiment of FIG. 9 includes a tray portion 13" which may, 
if desired, interface with the articular insert portion 15" in the manner 
taught by either of the embodiments of FIGS. 1-4 or 5-8. The device 1" 
differs from the embodiments of FIGS. 1-4 and 5-8 in the specific shape of 
the domical contours 29" thereof. In the embodiment of FIG. 9, the domical 
contours 29' are formed of an elliptical configuration formed by rotating 
a curved line corresponding to the surface of an ellipse about its axis of 
rotation. Thus, it may be seen that the contours 29" of the embodiment of 
FIG. 9 are slightly flatter and more laterally elongated than is the case 
in the embodiments of FIGS. 1-4 and 5-8. As stated hereinabove, any curved 
domical contour surface is considered to form a part of the present 
invention. Thus, in theory, any domical surface which may be created 
through the rotation of a curved line about its axis of rotation would be 
considered to be included in the teachings of the present invention. Such 
a requirement is necessary because the recesses 9 and 11 which must be 
formed in the proximal tibia (FIG. 2) must be made within the purview of 
the present invention through the use of a reaming device including a 
rotary cutting head. Thus, any rotary cutting head which may have a 
cutting surface thereof defined by the rotation of a curved line about its 
axis of rotation may be utilized to form the appropriate recesses 9 and 11 
into which the domical contours of the inventive tray portion 13' or 13", 
may be inserted. 
When a surgeon is deciding which domical contour should be used in 
installing the prosthesis of the present invention on the proximal tibia, 
several factors must be taken into account. As the degree of convexity is 
decreased, less surface area of engagement exists and thus the fixation 
will have a lessened chance of success. On the other hand, the larger the 
degree of convexity, the greater amount of bone which must be removed from 
the proximal tibia so as to facilitate installation. Thus, the surgeon 
must strike a balance between increasing the area of fixation while 
limiting the amount of bone removal. In the present invention, it has been 
found that the optimal extent of protrusion of the domical contours is 
from 3 to 6 millimeters from the undersurface of the tray portion. Keeping 
the extent of protrusion at a particular fixed level, the surface area of 
the domical contour may be increased by increasing the radius of curvature 
of surface thereof. Thus, in each particular case, the surgeon may study 
the proximal tibia to determine the appropriate radius of curvature which 
should be employed in the domical contours for optimum fixation and 
installation. 
If desired, depending upon the particular characteristics of the proximal 
tibia, the surgeon may elect to utilize a prosthesis having domical 
contours of differing heights and/or radii of curvature. Thus, a 
particular prosthesis may include two domical contours, for example, 
having different extents of protrusion but with differing radii of 
curvature so that each domical contour displaces the same volume of bone 
tissue. On the other hand, the surgeon may choose to utilize a tray 
portion having domical contours of equal height but of differing radii of 
curvature so that the domical contours displace differing volumes of bone 
tissue. Such options are always available to the surgeon depending upon 
the particular configuration and shape of each proximal tibia. 
Additionally, truncated domical contours may be utilized where indicated. 
Reference is now made to FIGS. 10 and 11 wherein a template 80 is depicted 
which may be utilized by the surgeon to locate the areas on the proximal 
tibia where bone tissue is to be removed so as to create domical recesses 
which are to receive the domical contours of the undersurface of the tray 
portion of the improved prosthesis. As shown in FIG. 10, the template 80 
includes a periphery 81 designed to substantially match the periphery of 
the proximal tibia as best seen in FIG. 2. Within the top surface 83 of 
the template, a plurality of openings 85 are formed therethrough. As best 
seen with reference to FIG. 11, the openings 85 are characterized by 
including a portion 87 of enlarged diameter, a portion 89 of reduced 
diameter and a shoulder 91 therebetween and connecting the portions 87 and 
89. The shoulder is provided for a purpose to be described hereinafter. 
With reference to FIG. 10, the template 80 also includes a plurality of 
small holes 93 formed therethrough. The holes 93 are provided so as to 
enable the surgeon to utilize a plurality of pins (not shown) to fixate 
the template 80 in a secure position on the upper surface of the resected 
proximal tibia so as to facilitate the reaming operation without fear that 
the template 80 will move during the process. The shoulders 91 are 
provided so as to interact with peripheral surfaces formed on the reaming 
head so as to limit the extent of penetration of the reaming head into the 
tibial surface as will be described in greater detail hereinafter. 
Reference is now made to FIGS. 12 and 13 wherein a reaming device generally 
designated by the reference numeral 100 and designed to be utilized in 
installing the inventive prosthesis is shown. With reference first to FIG. 
12, the template 80 is seen installed over the proximal tibia and a 
reaming device 100 is seen entering one of the holes 85 in the template 80 
to ream a concave surface in the proximal tibia. As seen in FIG. 12, the 
drive shaft 101 of the reaming device 100 is at an angle to the axis 103 
of rotation of the reamer head generally designated by the reference 
numeral 105 in FIG. 13. 
As seen in FIG. 13, the reamer head 105 includes a drive shaft 107 having a 
pinion gear 109 attached to its proximal end. A housing 110 is provided 
having an opening 111 therethrough through which the shaft 107 extends and 
the opening 111 also comprises a bearing for supporting the shaft 107 for 
rotation perpendicular to the direction of elongation of the opening 111. 
Within the housing 110 is a further pinion gear 113 which is connected at 
the distal end of the drive shaft 101 and which has depending therefrom a 
guide shaft 115 having a distal end inserted into an opening (not shown) 
in a wall of the housing 110 so as to enable the gear 113 to be rotated in 
a controlled manner. 
With further reference to FIG. 13, it is seen that the reamer head 105 
includes a plurality of cutting protrusions 117 thereon which facilitate 
the removal of bone tissue from the proximal tibia. As further seen in 
FIG. 13, at the proximal end of the reamer head 105, an annular protrusion 
119 is formed. The protrusion 119 has a circular periphery and is designed 
to be of slightly smaller diameter than the diameter of the opening 87 of 
the template so that the surface 119 may enter the template opening 87, 
but the surface 119 is slightly larger in diameter than the inner diameter 
of the shoulder 91 so that interengagement of the protrusion 119 and the 
shoulder 91 limits the axial extent to which the reamer device 105 may be 
inserted into the proximal tibia tissue. The largest diameter of the 
cutting surface of the reamer device 105 is just below the protruding 
surface 119 and this cutting surface is designed to be slightly smaller in 
diameter than the diameter of the opening 89 of the template 80 so that 
the cutting surface may be extended completely through the opening 89 to 
facilitate cutting of the bone tissue of the proximal tibia. 
As stated above, in the preferred embodiment of the present invention, it 
is preferred that the angle between the axis of rotation 103 of the reamer 
device 105 and the axis of rotation of the drive shaft 101 be between 
45.degree. and 90.degree.. This angle range is chosen because with the 
reamer head 105 so angled with respect to the drive shaft 101, the surgeon 
may most easily insert the device 100 into an incision and utilize it in 
removing the appropriate bone tissue. It is stressed in this regard that 
the particular angle chosen is chosen depending upon the particular 
circumstances of the particular surgery and in some cases with the knee 
flexed so that the femur and tibia lie at substantially right angles to 
one another, the drive shaft 101 may be disposed in axial alignment with 
the axis 103 of rotation of the reamer 105. If desired, instead of the 
gears 109 and 113, a flexible coupling may be utilized which enables the 
angle of rotation between the reamer 105 and the drive shaft 101 to be 
infinitely varied. 
With the prosthesis 1, template 80 and reamer device 100 having been 
described, the method of installation of the inventive prosthesis 1 will 
not be described. 
Firstly, the proximal tibia is resected in a manner well known to those 
skilled in the art so as to provide a flat proximal surface of proper 
orientation to the tibial shaft. Thence, the template 80 is placed over 
this flat proximal tibial surface and is secured thereto through the use 
of pins (not shown). Thereafter, the reamer device 100 is inserted into 
the incision and the cutting head thereof is inserted sequentially through 
the respective holes 85 in the template 80 so as to facilitate the removal 
of bone tissue from the proximal tibia. Interaction of the annular 
protrusion 119 of the reamer head 105 with one of the shoulders 91 of the 
respective openings 85 in the template 80 will indicate to the surgeon 
that the maximum extent of penetration of the reamer head 105 has been 
accomplished Thereafter, the reamer head is inserted into all subsequent 
openings 85 sequentially so as to complete the creation of the domical 
recesses in the proximal tibia. 
Thereafter, the tray portion 13, 13', 13", of the prosthesis 1 is placed 
over the resected and reamed proximal tibial surface and attached thereto, 
preferably through the use of the screws 27, 27', 27". Thereafter, the 
articular insert portion in installed over the tray portion through 
whatever means is included in the particular embodiment used, whether 
screw-type fasteners, dovetail-type fasteners or the like. Then, the 
surgery is completed through those techniques known to those skilled in 
the art including the closing of the appropriate incision or incisions. 
Thus, an invention has been described in terms of the improved prosthesis 
and in terms of the improved template and reamer device which are utilized 
in its installation. Various changes, modifications, alterations and the 
like may be contemplated by those skilled in the art without departing 
from the intended spirit and scope of the present invention. Accordingly, 
it is intended that the present invention only be limited by the terms of 
the appended claims.