Modular joint prosthesis stabilization and augmentation system

A modular joint prosthesis system includes an articulation component having a bone engaging surface and an opposed articulation surface. Fixation peg members and/or augmentation components are selectively attachable to the bone engaging surface of the articulation component. The articulation component may be a cruciate sacrificing femoral component of a knee prosthesis.

BACKGROUND OF THE INVENTION 
The invention relates to joint prostheses having enhanced stability and 
modularity. 
Joint arthroplasty is a well known surgical procedure by which a diseased 
and/or damaged natural joint is replaced by a prosthetic joint. Joint 
arthroplasty is commonly performed for knees, hips, elbows, and other 
joints. The health and condition of the joint to be replaced dictate the 
type of prosthesis that can suitably be used to replace the natural joint. 
For example, knee prostheses, and particularly femoral components of knee 
prostheses, are available in different designs to meet the needs of 
varying patient conditions. 
Some femoral components for knee joint prostheses are known as cruciate 
retaining femoral components since they are useful as a prosthesis 
component where a patient's cruciate ligaments are not sacrificed during a 
knee arthroplasty procedure. This type of femoral component typically has 
fixation pegs integrally mated upon the medial and lateral distal flats of 
the superior surface of the prosthesis to stabilize the prosthesis upon 
mounting to the femur. The cruciate ligaments also contribute to the 
stability of the artificial knee joint. 
Another type of femoral component for a knee joint prosthesis is known as a 
cruciating sacrificing femoral component. This type of prosthesis 
component is useful where the patient's cruciate ligaments are 
non-functional or must be removed in the course of a knee arthroplasty 
procedure. Cruciate sacrificing femoral components typically have an 
intercondylar notch formed on a superior, bone engaging surface of the 
femoral component. This structure is in the form of a box, having 
substantially vertical medial, lateral, anterior and posterior walls, and 
a substantially horizontal superior wall. The intercondylar notch is 
mounted within the patient's femur to stabilize the prosthesis. Typically, 
an aperture is formed in the superior wall of the intercondylar notch and 
it is useful to mate a femoral stem to the femoral component. The femoral 
stem helps to anchor the femoral component to a patient's femur, and to 
contribute stability to the artificial joint. 
Femoral component fixation in cruciate substituting total knee replacement 
surgery is sometimes achieved through cement attachment of the femoral 
component to the prepared femur while stability is imparted to the femoral 
component by the intercondylar notch, femoral chamfer cuts, and the 
optional attachment of femoral stems or rods. It is sometimes possible for 
cruciate substituting femoral components to loosen and thus contribute to 
the need for total knee replacement surgery and enhanced stabilization of 
the prosthesis. 
In some instances, due to disease or trauma, insufficient healthy bony mass 
exists at the distal end of a bone (e.g., the femur) to which a joint 
prosthesis is to be secured. In arthroplasty procedures, it is often 
necessary to remove additional portions of bone (e.g., the femur) in an 
asymmetrical manner, to ensure sufficient anchoring and proper fit for a 
prosthesis. In the example of knee joint arthroplasty, it is sometimes 
necessary to augment the superior portion of the femoral component 
prosthesis to add additional thickness to the prosthesis to compensate for 
any removed bony tissue. The femoral component can be augmented by adding 
augmenting blocks of appropriate shapes and sizes to the superior surface 
thereof. Various types of augmentation blocks are known to those having 
ordinary skill in the art. An exemplary augmentation system is disclosed 
in U.S. Pat. No. 4,936,847 (Manginelli). 
The stability of cruciate substituting femoral components can be reduced 
with the installation of augmentation components, some of which can 
approach the height of the intercondylar notch. Since these prostheses 
rely largely on the intercondylar notch for secure engagement within the 
femur, any relative decrease in the height of the intercondylar notch 
above the medial and lateral distal flats can decrease the stability of 
the femoral component. 
Many existing knee prosthesis designs do not offer the ability to 
selectively enhance prosthesis stability of the femoral component. 
Prosthesis stability can be a problem of particular concern in revision 
cruciate substituting femoral components that require augmentation 
systems. It would thus be desirable to offer improved joint prostheses 
components which offer surgeons increased versatility to achieve 
prosthesis stability. 
SUMMARY OF THE INVENTION 
The present invention relates to modular joint prostheses that offer 
surgeons enhanced versatility to achieve prosthesis component stability. 
In particular, the prosthesis system of the invention enables surgeons to 
selectively add fixation stabilizing members and/or augmentation 
components. While the invention is applicable to a variety of joint 
prosthesis components in which stabilization is important and augmentation 
is sometimes necessary, the invention is described herein with respect to 
femoral components of knee prostheses. 
The invention comprises a modular joint prosthesis that includes an 
articulation component, such as a femoral component of a knee prosthesis, 
having a first, bone-engaging surface and a second, articulation surface. 
At least one securement cavity is formed in the first surface, and most 
preferably a securement cavity is formed on each of the medial and lateral 
distal flats of the femoral component. The system also includes at least 
one elongate fixation peg member, each of which is selectively mateable to 
the securement cavity in the first surface to provide enhanced prothesis 
stability. The fixation pegs each have distal and proximal ends and 
include an axial bore which may include internal fixation structures such 
as internal threads. The system also includes a collet member for each 
fixation peg, and each collet member has two or more expandable elements 
that are able to selectively engage the sidewalls of one of the securement 
cavities. A bore preferably extends through the collet, and at least a 
proximal portion of the bore may include fixation structures such as 
internal threads. One or more expansion pins are also provided and each 
has a distal end that is able to expand the collet and a proximal end 
which may include a structure, such as external threads, which facilitates 
mating within the bores of the fixation peg member and the collet member. 
In use, the fixation peg is positioned over a securement cavity and the 
expansion element of the collet is disposed within the cavity. The 
expansion pin is then inserted within the collet and the fixation peg to 
positively engage the peg and to expand the expandable elements of the 
collet such that they engage the walls of the cavity to secure the peg to 
the prosthesis. 
One or more augmentation blocks, of desired shapes and sizes, may be 
provided to fit between the first surface of the femoral component and the 
fixation pegs such that the augmentation block and the fixation pegs are 
together selectively affixed to the articulation component. This system is 
particularly useful with cruciate substituting femoral components of knee 
joint prosthesis to provide added prosthesis stability. 
In one embodiment the collet members are separate from the fixation pegs 
and the expansion pins engage both the collet and the fixation peg. In 
another embodiment the collet members are integral with and are formed on 
a distal end of the fixation pegs.

DETAILED DESCRIPTION OF THE INVENTION 
The invention provides a joint prosthesis system 10 that offers enhanced 
intraoperative versatility and modularity to improve femoral component 
fixation and stability. The invention is particularly applicable to 
cruciate substituting femoral components. For illustrative purposes, the 
present invention is described with reference to an anticipated use with a 
femoral component of a knee joint prosthesis. It is understood, however, 
that the invention can be adapted for use with a variety of joint 
prostheses. A particular advantage of the present invention, which lends 
itself to use with various types of joint prostheses, is the ease with 
which fixation elements and augmentation pieces can be secured to a 
prosthesis. 
As noted above, and as illustrated in FIGS. 1 through 6, the invention is 
particularly applicable to use with cruciate substituting femoral 
components. FIG. 1 illustrates the prosthesis system 10 of the invention 
in which a cruciate substituting femoral component 12 has an intercondylar 
notch 13, anterior and posterior portions 14, 16 and condyles 18, 20. Each 
condyle includes an inferior articulation surface 22 and an opposed 
superior bone engaging surface 24. FIGS. 2A and 2B illustrate that the 
lateral distal flat 30 includes a securement cavity 32, and a similar 
cavity (not shown) is formed in the medial distal flat 28. Fixation pegs 
26 are selectively mounted within securement cavities 32 upon the medial 
and lateral distal flats 28, 30 of superior surface 24, on opposite sides 
of intercondylar notch 13. 
As illustrated in FIGS. 2A through 4, the system includes modular, 
selectively mountable fixation pegs 26. The fixation pegs 26 are 
substantially elongate members having a peg body 33 with proximal and 
distal ends 34, 36. Preferably, a bore 52 extends between the proximal and 
distal ends of the fixation peg. Further, an expansion collet 38 is 
integral with and is disposed distally of the distal end 36 of peg body 
33. The system also includes a supply of expansion pins 40 having a 
proximal end 42, including external threads 44, and a distal, collet 
expanding end 46. Although the illustrated expansion pins include external 
threads, it is understood that alternative surface features may exist on 
the expansion pins, instead of threads, to permit positive engagement with 
the bore 52 of the fixation peg 26. 
As noted above, the modularity of the fixation pegs is an important feature 
of the invention. Since fixation pegs need not be installed on all 
cruciate sacrificing femoral components, the modularity offered by this 
invention gives the surgeon the option to attach fixation pegs to a 
prosthesis to be implanted. 
Fixation pegs can be selectively mounted upon a prosthesis by simply 
placing the expansion collet end 38 of peg 26 within one of the securement 
cavities. Thereafter, set screw 40 is inserted within the proximal end 34 
of the fixation peg and into bore 52. In an embodiment in which a threaded 
expansion pin is utilized, the expansion pin is advanced within the bore 
and external threads on the screw mate with complementary threads in the 
bore. Further advancement of the expansion pin causes the distal end of 
the expansion pin to expand collet 38 so that the collet interferingly 
engages the walls of cavity 32 to secure the fixation peg to the 
prosthesis. 
The overall length of the fixation pegs can vary depending upon the 
anatomical requirements of a patient, the dimensions of prostheses 
components, and whether the peg is to be used with or without any 
augmentation block. Generally, the overall length of the peg can be from 2 
to 60 millimeters, and more preferably from about 10 to 50 millimeters. 
The length of the collet end 38 of peg 26 should be such that it is 
slightly less than the depth of cavity 32, allowing distal base 48 of peg 
26 to rest on superior surface 24 of the femoral component. The length of 
the collet is generally about 2 mm to 20 mm. Further, the fixation peg 
preferably decreases in diameter from distal end 36 to proximal end 34. 
The diameter at base 48 is about 4 mm to 10 mm, while the diameter at 
proximal end 34 is about 2 mm to 8 mm. External surface features 50, such 
as axial grooves, axial ribs, annular grooves or annular ribs, can be 
formed in the external surface of the peg to enhance fixation of the 
prosthesis within bone. 
FIG. 5A is a bottom view of fixation pin 26, illustrating the expansion 
collet 38. The collet 38 is preferably slotted, with two perpendicular 
slots 35 formed therein that separate the collet into four substantially 
triangular shaped wedges 37. Although not illustrated, an interior portion 
of collet 38 is angled inwardly to enable the internal geometry of the 
collet to cooperate with the distal end 46 of expansion pin 40 to cause 
wedges 37 to expand and to separate from one another when the distal end 
of the expansion pin is forced into engagement with the corresponding 
internal surfaces of the wedges. 
It is understood that it is not necessary that the collet have two slots 
disposed therein to form four substantially triangular wedges 37. It will 
be readily apparent to one having ordinary skill in the art that the 
collet may have one or more slots disposed therein. 
FIG. 5B is a sectional view of peg 26, showing a bore 52 that extends the 
length of the body 33 of peg 26. Bore 52 preferably includes internal 
threads 54 that are able to mate with complementary external threads 44 of 
expansion pin 40. Although bore 52 includes threads 54 in an illustrated 
embodiment, it is understood that other structures may be formed within 
bore 52 to facilitate engagement with complementary external structures on 
expansion pin 40. 
Expansion pins 40 are of a length sufficient to enable them to fit within 
peg 26 to the extent necessary to expand collet 38. The expansion pin 
includes a proximal end 42, having external threads 44 that are mateable 
with internal threads 54 of bore 52, and a distal end 46. The proximal end 
of the expansion pin may include a structure or mechanism, such as a hex 
head 45, that cooperates with an installation tool to enable it to be 
advanced into bore 52. Distal end 46 preferably has a geometry that will 
cause expansion of the distal stem of the collet. The distal end 46 of pin 
40 can include a radius tip 56, a dogged end (not shown) or similar 
geometries. 
Although the expansion pins 40 are described as being threaded members that 
threadingly engages internal threads 54 within bore 52, it is understood 
that other fixation structures and techniques may be utilized to maintain 
the expansion pins within the bore 52 and to expand collet 38. As noted 
above, internal structures may be formed within bore 52 that accommodate 
complementary surface features on expansion pin 40 to enable mechanical 
engagement of the components. 
In another embodiment, illustrated in FIGS. 3 and 4, the modular system 10 
of the invention may also include an augmentation block 58 that is secured 
on superior surface 24 of femoral component 12, between the femoral 
component 12 and the fixation peg 26. Augmentation blocks of various 
designs are well known in the art and are commonly used to facilitate 
proper seating of prosthesis components within a patient when insufficient 
bony mass exists in certain areas of the patient's bone upon which the 
prosthesis is to be mounted. 
The augmentation block 58 illustrated in FIGS. 3, 4 and 6 is adapted to 
mount on the superior surface 24, on either the medial or lateral distal 
flats 28, 30 of a femoral component 12 of an artificial knee joint. Block 
58 may be adapted for use in either left or right side knee prostheses. An 
augmenting block suitable for a left side prosthesis can mount upon either 
the medial or lateral inferior condylar surfaces, and an augmenting block 
suitable for a right side prosthesis can mount upon either the medial or 
lateral inferior condylar surfaces of the prosthesis. As illustrated, 
block 58 has a first (distal) surface 60 and a second (proximal) surface 
62 and an aperture 61 extending between these surfaces. A recessed area 63 
may surround the aperture 61. The area of the proximal surface 62 
preferable is greater than the area of the distal surface 60 in order for 
the block to conform to the geometry of the inner condylar surface of a 
knee joint femoral component. 
Augmenting block 58 has two opposed, canted surfaces 64, 66 that can be 
either posterior or anterior surfaces, depending upon whether the 
augmentation block is mounted on the medial or lateral side, or on a left 
or right side prosthesis. Preferably, surfaces 64, 66 are canted as such 
that each surface slopes inwardly from the proximal surface 62 to the 
distal surface 60 as shown in FIGS. 4 and 6. The angle of the canted 
surfaces 64, 66 can vary as will be appreciated by those having ordinary 
skill in the art. Preferably, the angle of surfaces 64, 66 corresponds to 
the angle of the anterior and posterior chamfers 68, 70 of the femoral 
component to enable proper seating of the augmenting block 58 within a 
femoral component. 
Augmenting block 58 further includes surfaces 72, 74 which correspond to 
either medial or lateral facing surfaces, depending upon whether the 
augmentation block 58 is used on the lateral or medial side of a 
prosthesis, or in a left or right side prosthesis. Side surfaces 72, 74 
preferably are substantially vertical and extend at a right angle to the 
plane of the proximal or distal surfaces 62, 60. 
As illustrated in FIG. 3 augmentation block 58 is adapted to mount on a 
prosthesis component, such as the medial or lateral distal flats 28, 30, 
such that the distal surface 60 of block 58 contacts the superior surface 
24 of femoral component 12. The distal end of expansion collet 38 of 
fixation peg 26 preferably extends through aperture 61 and beyond the 
distal surface 60 of block 58 by a distance sufficient to enable collet 38 
to fit within a securement cavity 32 disposed in a surface of the femoral 
component to be augmented. The frictional and/or mechanical engagement of 
the collet with cavity 32 enables the augmentation system to be secured to 
an appropriate surface of the femoral component. The distance by which 
distal stem extends beyond the distal surface of the block can vary 
depending upon the requirements of a given application. Typically, this 
distance is about 0.155 to 0.175 inch and most preferably about 0.165 
inch. One of ordinary skill in the art will appreciate that the length of 
the distal stem should not be so great that its distal end contacts the 
bottom of cavity 32. 
As noted above, an expansion pin 40 controls the expansion (and, 
optionally, the contraction) of the distal stem of collet 58. In one 
embodiment, where the expansion pin is a threaded screw, tightening of the 
screw expands the distal stem of the collet, while loosening screw enables 
a once expanded collet to contract. When collet 38 is in a non-expanded 
condition there is little or no frictional and/or mechanical engagement 
between collet 38 and securement cavity 32; the augmentation block can be 
freely removed and inserted into securement cavity 32 in this condition. 
Conversely, when the collet 38 is in the expanded condition, as shown in 
FIG. 3, sufficient frictional and/or mechanical engagement exists between 
the collet 38 and the walls of the securement cavity 32 to enable the 
augmentation block and the fixation peg to be held firmly on the 
prosthesis component. 
As noted above, the invention described above can be used with or without 
augmentation blocks. Further, because the fixation pegs are not 
permanently installed upon the prosthesis, they can be selectively affixed 
to the prosthesis at the option of the surgeon. 
The dimensions of the various components of system 10 can vary. It is 
important, however, that the relative dimensions of the components be such 
that collet 38, in the non-expanded condition shown in FIG. 2B, be able to 
fit within the securement cavity (and, where applicable through 
augmentation block aperture 61) without excess friction or interference. 
Upon expansion of the collet, as shown in FIG. 2A, the outer walls of 
wedges 37 should firmly engage the inner walls of securement cavity 32 to 
prevent dislodgement or movement of the fixation peg. The preferred 
tensile attachment force of the collet to the prosthesis should be in the 
range of about 50 to 500 kg. The dimensions of these components will vary 
depending upon the requirements of a given application, and one of 
ordinary skill in the art can readily determine the appropriate relative 
dimensions. Generally, the diameter of the collet in the non-expanded 
condition is approximately 0.240 to 0.260 inch, and preferably it is about 
0.250 inch. The diameter of the collet in the expanded condition 
preferably is about 0.010 to 0.020 inch greater than the diameter in the 
non-expanded condition. The diameter of the securement cavity 32 is 
sufficient to yield a secure interference fit between the collet and the 
cavity when the collet is expanded. Preferably, the cavity has a diameter 
of about 0.26 inch .+-. 0.10 inch. The depth of the mounting cavity can 
vary, as will be understood by those of ordinary skill in the art, but 
preferably the depth is about 0.18 to 0.26 inch. As noted above, the 
collet 38 should not engage the bottom wall of cavity 32. 
Another embodiment, illustrated in FIGS. 7 through 11, provides an 
alternative fixation technique for the modular prosthesis system 100 of 
the invention. In this embodiment, the collet is not integral with the 
fixation peg, but the same modular fixation options exist. That is, 
fixation pegs can be mounted directly upon the superior surface of a joint 
prothesis, without an augmentation block, or an augmentation block can be 
disposed between the fixation peg and the prosthesis. 
FIG. 7 illustrates a cruciate substituting femoral component 102 that 
includes an intercondylar notch 104, an inferior surface 106 having 
condyles 108, 110 and a superior bone engaging surface 112 having lateral 
and medial distal flats. For purposes of illustration, the prosthesis 
depicted in FIG. 7 is assumed to be a left knee femoral component having 
anterior 118 and posterior 120 surfaces. Further, FIG. 7 illustrates an 
augmentation block 122 and fixation peg 124 mounted on lateral distal flat 
116. It is understood that the fixation peg 124 can be mounted directly 
upon the medial or lateral distal flats without an augmentation block. 
FIGS. 8A through 11 illustrate the various components of system 100. These 
components include fixation pegs 124, one or more optional augmentation 
blocks 122, one or more collets 126 and one or more expansion pins 128. 
Further, as noted above with respect to FIGS. 1 through 6, the femoral 
component 102 includes at least one securement cavity 130. Preferably, one 
securement cavity is mounted on each of the medial and lateral distal 
flats of the femoral component. 
Fixation peg 124 is an elongate member having proximal and distal ends 132, 
134. The distal end 134 of the peg includes a base 136 which surrounds an 
opening 138 of an internal bore 140 which extends within the peg. Internal 
threads 141 or other internal fixation structures (not shown) preferably 
are present within the bore and may extend the entire length of the bore 
or, alternatively, threads be present only in selected regions of the 
bore. Although the proximal end 132 of peg 126 is shown to include a 
closed top 142, the top may alternatively be open. The base 136 abuts the 
proximal surface 144 of augmentation block 122. Alternatively, if no 
augmentation block is used, base 136 will abut the superior surface 112 of 
femoral component 102. 
Fixation peg 124 is of a construction similar to that described above with 
respect to FIGS. 1 through 6, except that it does not include an integral 
distal collet. Fixation peg 124 thus may include external surface features 
146 and may have a larger diameter at distal end 134 than at proximal end 
132. 
As shown in FIGS. 9 and 11, expansion pin 128 is an elongate member that 
has distal 148 and proximal 150 ends. The expansion pin is intended to 
expand collet 128, by action of its distal end 148, while its proximal end 
150 engages both a proximal end 152 of the collet and the fixation peg. 
Although various structures can enable the expansion pin to expand the 
collet and to engage the collet and the fixation peg, a preferred 
embodiment is described below. 
The proximal end 150 of the expansion pin 128 preferably includes external 
threads 154. Preferably, the threads 154 extend over a distance of about 2 
to 20 mm. The distal end 148 of the collet is non-threaded and preferably 
has a diameter that is slightly less than the diameter of proximal end 
150. The distal tip 153 of expansion pin 128 has a geometry that will 
cause expansion of the collet, such as a radius tip point 155, a dogged 
end (not shown), or similar geometries. Preferably, the head 151 of the 
expansion pin 128 is a hex head. 
Collet 126 has a proximal end of 152, including collar 156 and a distal, 
collet expanding end 158. The collar 156 can mount within a recessed area 
surrounding cavity 130. Alternatively, if an augmentation block 122 is 
used, the collar 156 will be seated in a recessed area 159 surrounding 
aperture 160 on a proximal surface 144 of block 122. The collar 156 and 
the recessed area can be of virtually any corresponding shapes including, 
for example, circular and D-shaped. A D-shaped collar, which includes a 
flat end 169, or another irregularly shaped collar, can be useful to 
prevent any unwanted rotation of the collet within the securement cavity 
130 or aperture 160. 
As illustrated in FIG. 10C, collet 126 preferably includes internal threads 
164 within proximal region 152. These threads are complementary to threads 
154 of expansion pin 128 such that a lower (distal) portion of threads 154 
mate with threads 164 to maintain the expansion pin in a desired position 
with the collet. The distal end of the collet is preferably slotted and is 
of a structure as described above for collet 38 illustrated in FIGS. 1 
through 6. 
As noted above, FIGS. 7 through 9 illustrate an augmentation block 122 used 
with system 100. It is understood that the use of augmentation block 122 
is optional. If the augmentation block 122 is not to be used, the fixation 
peg 124 is mounted directly to the superior surface 112 of femoral 
component 102. 
The dimensions of the various components described above can vary depending 
upon the size and type of prostheses which they are used. One of ordinary 
skill in the art can readily determine the appropriate dimensions. 
System 100 can be utilized as follows. If a surgeon determines that it is 
desirable to mount fixation pegs 124 upon prosthesis 102, set screw 128 is 
advanced within collet, without expanding the collet, until threads 154 
and 164 mate. The collet is then positioned within securement cavity 130 
and the set screw is tightened until the collet expands to the extent that 
it maintains good purchase upon the inner walls of the securement cavity 
130. The torque needed to effect such expansion generally is about 20 to 
40 inch-pounds, and more preferably about 30 inch-pounds. Thereafter, the 
fixation peg is threaded upon expansion pin 128 such that threads 154 mate 
with internal threads 141 of fixation peg 124. Preferably the length of 
the external threads 154 that remain exposed once the expansion pin is 
deployed to expand the collet is about 6 to 12 mm. A similar procedure is 
utilized for an embodiment in which an augmentation block 122 is to be 
used. In such embodiment collet 126 may be predisposed within aperture 160 
of augmentation block 122. Once the augmentation block is properly 
positioned on femoral component 102, expansion pin 128 is advanced within 
the collet causing the collet to expand and to secure the augmentation 
block to the femoral component. Next, the fixation peg can be threaded 
upon the proximal end of the expansion pin. 
The illustrated embodiments of system 100 include internal threads within 
the collet 126 and fixation peg 124, and external threads on expansion pin 
128. It is understood that other structures can be used, instead of 
threads, to facilitate joinder of the set screw to both the collet and the 
fixation peg. 
The prostheses components of the invention can be made from a variety of 
biocompatible materials having high strength, durability and resistance to 
wear debris. Examples of such materials include metal alloys such as a 
cobalt chromium alloys, titanium alloys, stainless steel, ceramics and 
other materials, including polymers, that are well known for use in the 
manufacture of implantable bone prostheses. A preferred material for the 
prostheses components is a cobalt chromium alloy such as ASTM F-75. 
The collet components preferably are made from a malleable metal or metal 
alloy to reduce the risk of tensile failure as a result of collet 
expansion. Where such materials are used to form a threaded component, the 
materials should be able to deform (but not fail) when subjected to a 
torque of about 20 to 65 in-lbs, and more preferably about 25-35 in-lbs. A 
preferred material is a wrought cobalt chromium alloy such as ASTM F-90. 
The set screw preferably is made from a metal or metal alloy that has a 
higher modulus and a greater hardness than does the collet. Such 
properties ensure that the collet (and not the expansion pin) will deform 
when subjected to torque and/or axial load. A preferred material from 
which the expansion pin can be manufactured is wrought cobalt chromium 
alloy such as ASTM F-1537 (formerly known as ASTM F-799). 
The tensile securement values of the fixation pegs and/or augmentation 
blocks to the femoral components preferably are in the range of about 50 
to 500 kg. This secure fit ensures that the performance of the prosthesis 
component is not compromised. Moreover, the modular fixation peg and 
augmentation system of the invention can be easily attached within a 
femoral component of a knee joint prosthesis. 
The foregoing description of the illustrative embodiment of the invention 
is presented to indicate the range of constructions to which the invention 
applies. Variations in the physical architecture and dimensions of the 
invention will be apparent to those having ordinary skill in the art based 
upon the disclosure herein, and such variations are considered to be 
within the scope of the invention in which patient rights are asserted, as 
set forth in the claims appended hereto. All publications and references 
cited herein are expressly incorporated herein by reference in their 
entirety.