Method of sizing a femoral canal using a modular femoral trial hip replacement system

A multi-piece trial femoral component kit for use in sizing a femoral cavity prior to implantation of a prosthetic femoral implant. The trial femoral component kit has at least two distal trial components of different size and two proximal trial components of different size and mating elements which allow the proximal and distal components to be releasably coupled to form a femoral trial prosthesis. The distal trial component combines with the proximal trial component to form the stem of the femoral trial prosthesis, the joint of the two components located in the circumferential area between the gluteal tuberosity and about 2" below the pectineal line of the femur when the femoral trial is inserted within the femur. The distal and proximal components may further include means for selectively combining the proximal and distal components to form a femoral trial prosthesis that corresponds to an available prosthetic femoral implant. The dimensions of the distal and proximal components may be undersized when compared to the corresponding regions of the prosthetic femoral implant.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an orthopedic trial femoral component for use in 
determining the correct prosthetic femoral component for implantation from 
a group of prosthetic femoral components. More particularly, this 
invention relates to a two-piece trial component to be used as a guide for 
the surgeon in selecting the proper sized prosthetic femoral component. 
2. Description of the Prior Art 
Orthopedic surgery to replace a femur head and neck with a prosthetic 
component or to replace a previously implanted femoral prosthetic device 
is a complex operation requiring a relatively lengthy surgery. There has 
been a need to shorten and simplify this procedure while simultaneously 
providing the best fit between the prepared femoral canal and the 
prosthetic implant. This is especially true since many of the patients 
requiring such surgery are elderly or multi-trauma patients who require a 
series of operations and the longer the patient is under anesthesia, the 
greater the risk. 
To determine the appropriate femoral implant size, the surgeon takes and 
examines X-rays of the femur. He then uses a trial component as a guide in 
preparing the femur to receive the chosen prosthesis. The surgeon attempts 
to select a trial implant which fits so that his final implant will 
likewise fit. 
In the past, surgeons have used a series of one-piece trial prostheses 
which were identical in size to corresponding prosthetic implants. These 
prosthetic femoral implants came in discrete sizes which had been 
determined to cover the widest range of patients that surgeons were likely 
to encounter. 
The surgeon would prepare the femoral canal by rasping and/or reaming and 
through guesswork, he would determine if the one-piece femoral trial 
prosthesis fit. Difficulties were encountered with a one-piece femoral 
trial-prosthesis because the proximal body of the trial prosthesis blocked 
the view of the medullary canal and this made it difficult to determine 
the correct one-piece prosthesis. The surgeon, upon implementation, often 
found that either his preparation of the femur was incorrect or the 
geometry of the prepared femur did not allow for the preliminarily chosen 
femoral implant to be used. Often it was extremely difficult to discern 
whether the problem or obstruction was located distally around the stem or 
proximally around the body portion of the trial prosthesis. 
Manufacturers compensated for these difficulties by providing a series of 
femoral prosthetic implants with identical stem lengths but different 
neck/body sizes or vice versa. The surgeon also was provided with a series 
of one-piece trial prostheses with multiple stem and body sizes. The 
surgeon then used trial and error methods to determine the best fitting 
trial prosthesis from the different trial prostheses. 
To overcome this position, modular two-piece trial prostheses were 
developed such as disclosed in U.S. Pat. No. 5,100,407. The disclosed 
modular trial system provides a two-piece trial component kit with a 
plurality of interchangeable heads and stems. This two-piece trial 
prosthesis separates the head and neck region of the trial prosthesis from 
the stem portion to provide the surgeon with a cross-sectional view of the 
bone where the surgeon cuts the femur. With this two-piece trial system, 
the stem and proximal body components of the femoral trial prosthesis are 
fitted separately so that the surgeon can address each fit independently 
and more easily. 
The two-piece trial prosthesis of U.S. Pat. No. 5,100,407 is particularly 
adapted for resection cases where the surgeon must remove the head and 
neck of the femur in order to replace it with a femoral implant. The 
surgeon prepares a bone bed for the proximal body component of the 
two-piece trial prosthesis by using the trial proximal component as a 
guide for the necessary proximal cut of the femur and/or to check the 
accuracy of his rough cut. 
The surgeon then moves onto fitting the distal trial stem component by 
first inserting various trial stem sizes to see which fits the patient 
best. The surgeon can quickly access the stem fit because there is no 
proximal head and body to block his view so he can clearly see the stem 
within the femoral canal. In the one-piece system, it would not be 
possible to view the distal fit because the integral head/body would 
obstruct the surgeon's view. 
In the described two-piece trial system, the trial prosthesis is composed 
of a stem component and a body component, thus the distal and proximal fit 
of the stem within the femoral canal is addressed by use of a single trial 
component. Therefore, it is not always possible to size the stem of the 
prosthesis both distally and proximally within the femoral canal. In 
revision cases, where a previous femoral implant is being replaced and the 
epiphysis of the femur is gone, it becomes increasingly important to fit 
the femoral canal with the implant along its entire length. Thus, there 
has been a need in the art for a trial prosthesis which adequately address 
the aforementioned difficulties and drawbacks of existing devices. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a two-piece trial 
femoral prosthesis to be used as a guide in determining the correct 
prosthetic femoral implant for implantation into a femur from a group of 
prosthetic femoral implants. 
It is also an object of the present invention to provide a two-piece trial 
femoral prosthesis that allows the proximal and distal fit of the femoral 
canal to be accurately and independently performed. 
It is a further object of the present invention to provide a two-piece 
femoral trial prosthesis that addresses proximal and distal fill of the 
femoral canal of the femur with different components so that the surgeon 
can select the correct prosthetic femoral implant for implantation 
into-the femur from a group of prosthetic femoral implants. 
It is an object of the invention to provide a two-piece femoral trial 
prosthesis that separates the stem of the trial prosthesis into two 
separate components so that maximum interference between the implant along 
the length of the femoral canal can be achieved. 
It is an object of the invention to provide a method of addressing both 
proximal and distal fill of the femoral canal by the use of combinable 
proximal and distal trial components having an area of intersection when 
inserted into the femur that corresponds to the metaphysis. 
These and other objects are provided by the present invention which 
includes a multi-piece trial femoral component kit for use in sizing a 
femoral cavity prior to implantation of a prosthetic femoral implant. The 
trial component kit includes a number of different distal components and a 
number of different proximal components which are combinable to form 
numerous different-sized femoral trial prostheses. The distal and proximal 
trial components are coupled to produce a trial femoral prosthesis which 
can be used as a guide for correctly sizing the cavity within the femur 
for a prosthetic femoral implant. 
Each distal portion and proximal component includes a mating element to 
couple the two pieces together. The combination of the distal trial 
component and proximal trial component together form the stem of a modular 
trial femoral prosthesis. The two components of the modular trial 
prosthesis couple in the stem of the trial prosthesis corresponding to the 
circumferential area on the femur between the gluteal tuberosity and about 
two (2) inches below the pectineal line, i.e., between the soft spongy 
bone of the epiphysis and the hard cortical bone of the metaphysis. The 
mating elements are configured so that the two-piece trial femoral 
prosthesis can be held together to form a one-piece unit but can be 
selectively separated so that more than one proximal component can be 
coupled to each distal component or vice versa. 
The present invention uses a variety of proximal stem geometries that are 
independent of the various distal stem geometries. With this unique 
separation of the stem of the trial prosthesis, and the various distal and 
proximal stem geometries available, proximal and distal fit of the femoral 
canal can be evaluated independently, i.e., the distal stem portion 
separate from the proximal stem portion, so that an implant can be 
selected that captures maximum interference along the length of the 
femoral canal. 
Each mating element can be provided with a key or keyway shaped to allow 
selected proximal components to be coupled to selected distal components 
to ensure that the surgeon can only form a two-piece trial prosthesis 
which corresponds to an actual prosthetic femoral implant. 
The femoral trial prosthesis may be undersized so that minimal resistance 
of the trial within the prepared femur will ensure a proper fit of the 
femoral implant. The distal trial component may have a diameter that is 
approximately 0.75 mm smaller than the corresponding portion of the actual 
implant while the proximal trial component may have a diameter that is 
approximately 1.0 mm smaller than the diameter of the corresponding 
portion of the actual implant. 
These and other objects and advantages of the present invention will become 
apparent from the following description of the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1 and 2, there is shown the two-piece trial femoral 
prosthesis of the present invention generally denoted as 10. Trial femoral 
prosthesis 10 is composed of a distal trial component 12 coupled to a 
proximal trial component 14. Distal trial component 12 has a distal 
portion 22 that is received in the prepared femoral canal 140 (see FIG. 8) 
and a proximal portion 24 that couples with the distal portion 26 of the 
proximal trial component 14. A proximal portion 28 of the proximal trial 
component 14 includes a flange or collar 21 that butts against and rests 
on the bone where the surgeon resected the femur, a trunion 20 which is 
used to mount a spherical ball (not shown) and an opening 30 (shown in 
FIG. 7) to receive a trial positioner handle 25. 
The trial femoral prosthesis 10 represents the combination of a distal 
trial component 12 and a proximal trial component 14 which may be formed 
from a multi-piece trial femoral component kit 16. Referring to FIG. 3, 
the multi-piece trial femoral component kit 16 may include, for example, a 
number of different distal trial components 12', 12", 12'", and a number 
of different proximal trial components 14', 14". These can be combined to 
form numerous different-sized femoral trial prostheses 10. 
The distal trial components may vary, for example, in diameter, length and 
geometry. FIG. 5 shows a cross-section 112 of distal component 12 with a 
diameter 23. It being understood that the cross-sectional shape shown in 
FIG. 5 is representative and that various cross-sectional shapes are 
possible. The distal trial components, for instance, may vary from 12.5 mm 
to 21.5 mm in 1.5 mm diameter increments, may be 180 mm or 250 mm in 
length and may be bowed or straight in configuration. The bowed distal 
trial components can be assembled to create a right or left trial 
prosthesis. Referring to FIG. 3, there is illustrated distal trial 
component 12', 12", which are both straight and of the same length but 
vary in diameter. Distal trial component 12'", is bowed and is longer than 
either distal components 12', or 12". 
The proximal trial components 14', 14", vary proximally in neck length of 
the femur, collar width as well as proximal calcar area geometry. The neck 
length of the femur is varied by changing the length of the trunion 20 
while the collar width refers to changes in the size of the lip created by 
collar 21. The proximal calcar area refers to the proximal stem 19 on 
proximal component 14 which begins at a location just below the collar 21 
and extends to the distal end 27 of the proximal component 14. The 
proximal calcar area of the different proximal components 14 vary in 
cross-sectional area and length. 
FIG. 6 shows a cross-section 114 of proximal component 14 with a diameter 
25. It is to be understood that the term diameter as used herein is used 
to refer to the width of both circular and non-circular cross-sections of 
distal and proximal components 12, 14 and is illustrated in FIGS. 5 and 6 
as 23, and 25, 25'. It again being understood that the cross-sectional 
area shown in FIG. 6 is for illustrative purposes and that various 
cross-sectional shapes of the proximal stem 19 are possible. 
The length of the proximal components 14 are varied with the proximal 
calcar geometry so that the proximal components 14 extend to roughly the 
same area when inserted within the prepared femoral canal 140. In this 
manner, a proximal component 14 with a larger cross-sectional site at a 
point just distal to the collar 21 will have a longer length so that the 
distal end 27 of the proximal component 14 will extend deep enough into 
the patient's prepared femoral canal 140. Representative lengths of the 
proximal stem 19 are approximately 40-50 mm. Multiple other variations in 
proximal component 14 will be apparent to persons of ordinary skill in the 
art. 
The contents of a preferred trial kit of the present invention include 
eighteen (18) total pieces with seven (7) straight distal trial components 
of 180 mm in length, seven (7) bowed distal trial components of 250 mm in 
length and three (3) proximal trial components. These eighteen (18) 
components allow the surgeon to construct forty-two (42) combinations of 
monolithical femoral implants. The distal trial components 12 vary from 
about 12.5 mm to about 21.5 mm in diameter, preferably in about 1.5 mm 
increments. Proximally the trial components 14 vary in neck length of the 
femur, collar width as well as proximal calcar area geometry. Of course, 
these combinations can be multiplied by adding different distal and/or 
proximal trial components. 
When the trial femoral prosthesis 10 of the present invention is fitted 
within the femur, the joint 32 between the distal and proximal trial 
components 12, 14 is located in the metaphysis 52 of the femur 40 (see 
FIG. 4) or more specifically the circumferential area 54 between the 
gluteal tuberosity 46 and about two inches (2") below the pectineal line 
48. The area of intersection is the area between the soft spongy bone of 
the epiphysis 50 and the hard cortical bone of the metaphysis 52 or an 
area approximately half-way into the metaphysis 52 of the femur. 
The combination of the distal trial component 12 with the proximal trial 
component 14 together form the stem 18 of the trial femoral prosthesis 10. 
In other words, the stem 18 of the trial femoral prosthesis 10 is composed 
of two separate pieces. In particular, the stem 18 of the trial prosthesis 
10 is formed by the combination of the proximal stem 19 of the proximal 
trial component 14 with the distal trial component 12. In this manner, the 
stem 18 of the trial prosthesis 10 which is inserted into the femoral 
canal of the femur 40 can be independently and separately sized both 
distally and proximally by the distal and proximal trial femoral 
components 12, 14. 
By having different-sized and geometrically-shaped distal and proximal 
trial components 12, 14 available, and by independently selecting 
different proximal and distal components 12, 14 to form the stem 18 of the 
trial prosthesis 10, the surgeon can choose the best size monolithical 
femoral implant that will maximize distal-to-proximal interference of the 
medullary canal. The ability to maximize the fit of the stem of the 
femoral implant within the femoral canal is particularly important in 
revision surgical procedures where a previous femoral implant is to be 
replaced and the epiphysis 50 of the femur 40 has been removed. 
The femoral trial prosthesis 10 may be undersized when compared to the 
prosthetic femoral implant so that minimal resistance upon fitting the 
trial prosthesis 10 will ensure that the femoral implant will make contact 
with the bone. Accordingly, the cross-sections of the distal and the 
proximal trial components 12, 14 in the trial kit 16 must be undersized 
when compared to the respective distal and proximal regions of the implant 
to which the distal and trial components correspond. The distal trial 
component 12 may have a diameter 23 that is approximately 0.5 to 1.25 mm, 
and preferably 0.75 mm, smaller than the corresponding diameter of the 
implant and the proximal trial component 14 may have a diameter 25 that is 
approximately 0.5 to 1.25 mm, and preferably 1.0 mm, smaller than the 
corresponding diameter of the actual femoral implant. It is to be 
understood that the distal and proximal components 12, 14 can be 
undersized by varying amounts, i.e., 0.5 to 1.25 mm, along their 
respective lengths. 
At distal end 27 of proximal trial component 14 is a male element 34 which 
is adapted to be inserted within a corresponding opening 36 (not shown) in 
the proximal end 24 of distal femoral component 12. The male element 34 
and opening 36 are preferably a square-drive socket combination and 
preferably of 3/8" size, although other socket configurations are equally 
useful. In the square drive combination, as shown in FIG. 7, the male 
element 34 is provided with a spring 38 and detent ball 39 designed to 
selectively, releasably and repeatably couple distal trial component 12 to 
proximal trial component 14. The ball 39 is depressed as male element 34 
is slid within corresponding opening 36 and then springs out, locking the 
components together, upon reaching a predetermined point. The spring 38 is 
sized so that a predetermined amount of hand pressure tending to separate 
proximal trial component 14 from distal trial component 12 depresses the 
ball 39 and allows the two-piece trial prosthesis to be uncoupled. It is 
understood that the respective male element 34 and opening 36 may be 
reversed or any other coupling mechanism may be utilized that allows the 
distal trial component 12 and proximal trial component 14 to be 
selectively, releasably, and repeatably connected. 
Because implant manufacturers only supply a discrete number of femoral 
implants, it is necessary to ensure that the surgeon only chooses a 
proximal and distal component 12, 14 that couple to form a trial 
prosthesis 10 that corresponds to an actual implantable prosthesis. 
In order to achieve this, the male element 34 or opening 36 may be provided 
with a key or keyway (not shown) sized to allow selected distal components 
12 to be coupled to selected proximal components 14 so that only a 
two-piece trial prosthesis 10 can be formed that corresponds to an 
available femoral implant. A different way of preforming this same 
function is to provide a label 60 on the proximal trial component 14 which 
provides a list of the different distal components 12 that will couple 
with that proximal trial component 14 to form a trial prosthesis 10 which 
corresponds to an available femoral implant. Using the label method 
requires the surgeon to check that the combination of distal and proximal 
components 12, 14 used correspond to an available femoral implant. 
The process of utilizing the trial component kit 16 of the present 
invention will now be described. Initially, the surgeon is supplied with a 
series of proximal trial components 14', 14", etc., from the kit 16, one 
corresponding in size to each size stem/body portion of an implantable 
prosthesis. Likewise, the surgeon is supplied with a group of distal trial 
components 12', 12", 12'", etc., from the kit 16, one corresponding in 
size to each distal stem portion provided on an implantable prosthesis. 
With the modular trials of the present invention, the surgeon can begin 
the procedure with attention to either proximal or distal fit. 
In the case of revision surgery, the failed femoral prosthesis and cement 
should first be removed. Thereafter, and in the case of rejecting the 
femur, the surgeon then prepares for the osteotomy. The appropriate broach 
is laid against the femur at the point where the medial aspect of the 
broach lies slightly distal to the most distal medial bone loss. The 
osteotomy can be marked off the broach with methylene blue. The surgeon 
makes the osteotomy in line with the angle of the broach. The broach can 
be used as a cutting surface. 
In most revision cases, the surgeon can very clearly access the distal 
femoral canal. If, however, the technique used to implant the previous 
femoral component did not open the medial aspect of the greater trochanter 
42 (see FIG. 4), the surgeon should precede distal reaming by opening this 
area of the proximal bone. The surgeon should have straight-line access to 
the distal femoral canal. 
The surgeon can now prepare the distal femoral canal for the distal trial 
component 12. The femoral canal should be enlarged by reaming to accept 
one of the available distal stem components 12. Reaming should extend into 
the femoral canal to a point distal to the full length of the anticipated 
implant. It is expected that in most cases involving the 250 mm length 
stem and in some cases involving the 180 mm length version, the distal 
canal will require at least about 1 mm of over-reaming. 
At any time during the reaming process, the surgeon may insert the distal 
trial component 12 into the reamed canal to check the implant's ultimate 
fit. For these purposes trial handle positioner 25 is provided, which 
releasably attaches to the distal stem trial component 12. Referring to 
FIG. 5, a male mating element 134 which has the same configuration as male 
element 34 of proximal trial component 14 attaches to the distal trial 
component 12 in the same manner as mating element 34 of the proximal trial 
component 14. 
The distal stem trial component 12 is undersized, preferably by 
approximately 0.75 mm in diameter as compared to the corresponding portion 
of the actual implant. Therefore, the distal trial component 12 trial 
should seat in the canal without much resistance. A distal trial component 
12 that does encounter resistance indicates a tight fit of the implant 
within the femoral canal. 
Referring to FIG. 6, a retrieval hook 70 is provided to retrieve the distal 
stem trial component 12 and pull it out 0f the femur 40 in the unlikely 
event that the distal trial component 12 slips down the femoral canal. 
When distal stem preparation is complete, the surgeon can focus on 
proximal bone preparation. 
The proximal region of the revision femur usually experiences far more 
unpredictable bone loss than does the distal canal. Therefore, before 
beginning proximal bone preparation, the proximal trial component 14 is 
inserted in order to access the potential fit of the trial. The same trial 
handle positioner 25 that is used with the distal stem component 12 is 
used with the proximal trial component 14. Trial handle positioner 25 fits 
within opening 30 in order to couple with proximal trial component 14. 
Mating element 134 of the trial handle positioner 25 couples with the 
proximal component 14 in opening 30 in the same manner as mating element 
34 couples with opening 36 in the distal trial component 12. 
Regardless of whether or not the modular proximal trial component 14 is 
used before proximal bone preparation, both midshaft reamers and broaches 
should be used to prepare the proximal area of the femur 40. Seating of 
proximal trial component 14 should be attempted periodically throughout 
bone preparation. The proximal trial component 14 is undersized 
approximately 1.0 mm compared to the dimensions in the corresponding 
region of the implant. The proximal trial component 14 therefore should 
offer little resistance. 
The surgeon who has completed distal stem preparation should ensure that 
the chosen proximal trial component 14 couples with the distal trial 
component 12 already reamed and fitted to form a trial femoral prosthesis 
10 that corresponds to an available implant and vice versa for the surgeon 
who prepares the proximal portion of the femur first. 
The modular trial components 12, 14 can be assembled to perform the final 
trial reduction. The surgeon places the trial prosthesis 10 in the femur 
40 and if the trial prosthesis 10 seats with minimum resistance, the 
corresponding implant will make proper contact with the bone upon 
implantation. The trial handle positioner 25 can be inserted into the 
proximal trial component 14 to make manipulation of the trial prosthesis 
10 easier. If the modular trial components 12, 14 were used during bone 
preparation, it is unlikely that any difficulties will occur while 
inserting the trial prosthesis 10. If any resistance is experienced as the 
trial prosthesis. 10 is inserted, the surgeon should redo the broaching 
and reaming steps of the bone preparation. Plastic heads are placed on the 
trunion 20 to complete the trial reduction. The surgeon may even desire to 
take interoperative X-rays to judge the fit and alignment of the trial 
prosthesis. The modular trial prosthesis 10 is removed upon verifying the 
fit and the corresponding one-piece implant is implanted within the femur 
using known techniques. 
While the present invention has been described in its essentials, and by 
illustrative examples, those skilled in the art can appreciate that many 
changes and modifications may be made without departing from the spirit 
and scope of the present invention.