1. Issue 20
What’s NewZan educational service from Zimmer
The outcomes achieved with
standard femoral implants used in
total knee arthroplasty (TKA) are
satisfactory for most patients,
however there are significant reasons
for developing a gender specific knee
implant for women.
Standard implants can be a
contributing cause of post-operative
morbidity in women, said Dr Robert
E. Booth Jr, Clinical Professor of
Orthopaedic Surgery at the
University of Pennsylvania School
of Medicine, Philadelphia.
“Even though most women are
happy with their results after joint
replacement, some still have
residual pain in the front of the
knee…or say their artificial knee just
doesn’t feel or move the way their
own knee did when it was healthy,”
said Dr Robert Booth.
The problem is that while standard
implants are currently available in
variable sizes, they are based on the
combined average of male and
female anatomy that doesn’t take
into account shape-related
anatomical differences between
the genders, he said.
Standard implants are
currently available in
variable sizes, but are
based on the combined
average of women and
men’s anatomy that don’t
take into account shape-
related gender differences
These differences have been
reported in a number of studies1,2,3,4,5
but have been difficult to quantify
with a high degree of precision and
accuracy. As a result women
undergoing TKA have continued
to be treated simply as smaller
versions of men with regards to
implant selection, said Dr Booth.
The growing number of women
who require TKA has also led to
an increased demand for improved
outcomes. Women made up 58.1%
of primary TKA in 2004-5, the fastest
growing major joint replacement
in Australia (18.1% increase from
2002-3 to 2004-5), according to
Australian Joint Replacement
Registry data.6 This trend is set to
increase with the ageing population.
Research also shows that women are
three times less likely than men to
undergo arthroplasty although they
suffer from a higher prevalence of
arthritis, more severe symptoms and
greater disability.7
With an implant
“shaped to fit women’s anatomy”
there is an expectation that “far
more women will want to consider
knee replacement,” said Dr. Booth.
In addition, a better fitting implant
may require fewer intraoperative
adjustments to accommodate
anatomical differences, contributing
to reduced operating time.
In this issue
The need for a knee implant
designed specifically for women ..... 1
Best of both worlds - The Zimmer
Gender Solutions High-Flex Knee ....2
Three distinct differences
in shape .........................................2
(1) Modified Aspect Ratio – to better
fit the shape of a woman’s
trapezoidal distal femur............. 2 - 3
(2) Modified Anterior Flange –
reduced thickness to equal the
amount of bone removed and avoid
overstuffing ....................................4
(3) Lateralised Sulcus – to provide
more natural patella tracking for a
woman’s greater Q-angle ................4
The need for a knee implant
designed specifically
for women
Dr Robert E. Booth Jr. MD
Clinical Professor of Orthopaedic Surgery
at the University of Pennsylvania,
School of Medicine, Philadelphia

2. What’s NewZ Issue 0
“Knee implants have been
functioning very well for men
and women, but we want to meet
women’s unique needs by making
knee replacements that feel, fit
and function even better,”
said Dr Booth.
“The Gender Solutions Knee
is the best of both worlds. It’s
based on the NexGen®
Knee,
a highly successful implant with
great mechanics and ten years
of clinical success. Only the shape
is different, to make it feel more
natural,” he said.
The Gender Solutions Knee
is based on the NexGen®
Knee, a highly successful
implant with great
mechanics, only the shape
is different, to make it feel
more natural
Three distinct
differences in shape
The Gender Solutions High-Flex
Knee has the potential to achieve
substantial intraoperative and
post-operative benefits for TKA
patients by addressing three
distinct shape-related differences
of a woman’s knee.
(1) Decreased medial-lateral
(M/L) dimension reduces
implant overhang
Previous research has reported
differences in knee anatomy between
women and men.1,2,3,4,5
Poilvache et al conducted
measurements including trans-
epicondylar width and AP dimensions
before and after resection in their
1996 study of 54 female and 46 male
knees undergoing TKA.1
They found “a significant, although
small, difference…between males
and females in the ratio between the
transepicondylar width and the mean
height of the condyles…suggesting
that females had narrower femurs
than males. The difference was even
greater when subtracting the anterior
extent of the trochlea (anterior cuts)
from the height of the condyles.”1
In 2002 Chin et al conducted intra-
operative measurements of 100
female and 100 male femurs after
making the distal femoral cut. Their
data found that “for any given A/P
femoral dimension, women tend to
have a narrower M/L dimension than
men, independent of A/P height.”2
In 2003 Hitt et al also measured
the amount of M/L implant overhang
in both genders in addition to
confirming that the female femurs
were narrower. They observed that
the overhang was greater in females
regardless of the brand of implant.3
Despite the insights achieved by
these and other studies, the methods
used for the intra-operative
measurements, including calipers
and rulers, were limited by a lack
of precision and variability.
Zimmer®
Gender Solutions™
NexGen®
High-Flex Knee
Best of both worlds: The
Zimmer®
Gender Solutions™
NexGen®
High-Flex Knee

3. What’s NewZ Issue 0
Research conducted for Zimmer
by a team led by Mohamed Mahfouz,
Ph.D., director of Computational
Bioengineering at the University
of Tennessee, Knoxville, set
out to accurately quantify
these differences.
A continually growing knee bone
atlas based on more than 800 knees
and patellae was created for Zimmer
by Dr Mahfouz. Bone atlases have
been used in the past to create knee
replacements; however the data
were two-dimensional and
interpreted differently.
In contrast, Dr Mahfouz and co-
researchers utilised three-
dimensional computed tomography
(CT). Data was collected for the
femoral condyle dimensions to
create highly detailed virtual
blueprints of the knee as it looks
after resection when the bone is
ready for the implant.
Based on findings from this research
that was reported earlier this year,
a graph that plots the mid-box
medial-lateral (M/L) dimension
versus the overall anterior-posterior
(A/P) dimension confirms the
findings of the earlier research that
the average female knee had a
decreased M/L dimension compared
to men’s or ‘the male knee’ with the
same overall anterior-posterior
(A/P) dimension.8
The female knee has a
decreased M/L dimension
when compared to the male
knee anatomy.
A consequence of the narrower M/L
dimension is that female knees were
found to be more trapezoid-shaped,
whereas male knees were
characterized by a rectangle-shape.
Overhang is reduced at the
M/L interface leading to
potential intraoperative
and post-operative
benefits.
The decreased M/L dimension was
incorporated into the Zimmer®
Gender Solutions™
High-Flex Knee
design, with the aim of reducing
implant overhang, which has the
potential to achieve intraoperative
and post-operative benefits.
Overhang can press on or damage
surrounding soft tissues and may
possibly cause pain and reduced
function. Intraoperative adjustments
to compensate for the overhang are
often required.2
Overhang can occur because
a patient’s implant size is usually
selected based on the A/P
dimension, which is the key
to achieving normal knee kinematics
and maximizing the potential for
full flexion.
However standard non-gender
specific implant designs that provide
a good A/P fit are often too wide in
the M/L dimension leading to
overhang at the distal, anterior
and posterior M/L interfaces.1
Femoral condyle mid-box
medial-lateral (M/L) dimension versus
overall anterior-posterior (A/P) dimension
Difference in the distal femur shape:
Females (pink) compared to males (blue)
A/P
M/L Mid-Box
A/P
A standard implant may overhang at the distal,
anterior and posterior M/L interfaces compared
to the reduced or eliminated overhang of the
Gender Solutions High-Flex Knee
The new computational method devised by Zimmer for predetermining the contour of a resected
bone and fit of an implant that was used in the development of Gender Solutions High-Flex Knee

4. What’s NewZ Issue 0
() Reduced anterior flange
thickness decreases
implant protrusion
Research has shown that the female
knee has a less pronounced anterior
condyle compared to males due to
decreased bone thickness.2, 9
In the 1996 Poilvache et al study
cited earlier, measurements were
also taken of the resected thickness
of the anterior condyles. The average
lateral and medial condyle thickness
in males was statistically significantly
greater than for females.1
Zimmer data has confirmed the
gender difference in thickness –
0.8 mm less in females on the lateral
condyle and 1.3 mm less on the
medial condyle.9
In addition the M/L
dimension of the resected anterior
flange bone is narrower in women.9
The Gender Solutions High-Flex Knee
addresses the distinctive anterior
condyle differences by reducing the
anterior flange thickness as well
as narrowing the implant anteriorly
decreasing the M/L dimension
of the implant.
To compensate for reduced anterior
flange thickness, the anterior
condyles have been lowered and
the patella sulcus has been
recessed, while retaining the
NexGen®
patella articulation.
Reduced anterior flange
thickness of the implant
decrease anterior
protrusion of the joint
The advantage of the reduced
anterior flange thickness of the
Zimmer®
Gender Solutions™
High-Flex Knee implant is decreased
anterior protrusion of the joint,
which can reduce pain from
overstuffing the joint. In addition
to reducing bulkiness, patients may
experience improved function and
there may be less need for
intraoperative adjustments.
This is due, in part, to a reduction
in the stress on the patella ligament
as the knee moves into overstuffing
on angles. To compensate for this,
a surgeon’s only option (in the past)
was to translate the entire femoral
component inferiorly. This
intra-operative compromise
could result in either matching
of the femoral anterior cortex or
overstuffing the flexion gap. A knee
designed with a thinner anterior
flange demonstrates the need
for this compromise.
() Greater Q-angle reduces implant
patella maltracking
While patella maltracking remains
a concern for all patients following
TKA, it is a particular concern for
females due to their patellofemoral
joint biomechanics, which
predisposes them to pain associated
with patella malalignment and
quadriceps weakness.10
One of the main features of female
patellofemoral joint biomechanics
is a statistically significant higher
quadriceps femoral angle (Q-angle)
compared to men.11,12,13, 14
Aglietti et al found a 3º greater
Q-angle in the women compared
to males when measured with a
goniometer in supine in their 1983
study of 240 male and female
university-aged subjects.11
Gender Solutions
High-Flex
Femoral Implant
Traditional implant
The Gender Solutions High-Flex Knee
addresses the distinctive anterior
flange differences
Traditional implant Gender Solutions
High-Flex
Femoral Implant

5. What’s NewZ Issue 0
In 1990 Hsu et al measured the
Q-angle of 60 knees of subjects aged
25-40 years and 60 aged 41-60 years
using x-rays in standing, full weight-
bearing position. They found a 3.7º
difference in the women in the young
group and 2.7º in the older group.12
Two years later Woodland et al
measured the Q-angle of 269 male
and 257 female university-aged
subjects in supine and standing
using a goniometer and found it was
3.1º greater for the females in supine
and 3.4º in standing.13
Emulating the greater
Q-angle reduces
patella maltracking
The Zimmer®
Gender Solutions™
High-Flex Knee emulates the Q-angle
difference by increasing the patella
sulcus angle 3º laterally. The
potential benefit is reduced
patella maltracking and decreased
associated post-operative morbidity.
The early
Australian experience
The first orthopaedic surgeon in
Australia to use a Zimmer®
Gender
Solutions™
High-Flex Knee implant,
Dr Brett Courtenay, from the St
Vincent’s Clinic in Sydney, says the
improved fit was immediately clear
to see in the operating theatre.
“In many patients there is
considerable overhang of the
femoral component when the
correct sizes [of standard implants]
are used. This implant clearly
reduces this overhang without any
changes to the bone cuts. The
decision is made at the time of
using the trial implant,” he says.
“Having used the new implant I
would feel fairly confident that it
will allow me to use a more correct
sized prosthesis with my patients.”
Dr Courtenay says “in the past
when I was worried about overhang
I tended to slightly undersize which
is generally not a good thing to do
because it can lead to instability in
flexion and less efficient movement
of the prosthesis.”
In the past when I
was worried about
overhang I tended to
slightly undersize.
“The trouble is that if you put a
smaller prosthesis in it might feel
stable when the knee is extended
but it is not going to be as stable
when the knee is flexed.”
One of the key benefits offered by
the Gender Solutions™
High-Flex
Knee implant is increased variability.
“Previously we had one prosthesis
that was meant to fit all. Now
we’re going to have slimmer and
broader prostheses. I feel very
comfortable that this step is one
to address a problem that we have
had with sizes of prostheses,”
says Dr Courtenay.
“It allows me to use the correct
size according to the measurements
without the risk of an overhang,”
he says.
The Gender Solutions
High-Flex Knee allows
me to use the correct
size according to the
measurements without
the risk of an overhang.
Greater Q-angle of the Gender Solutions
High-Flex Knee

6. What’s NewZ Issue 0
“Time will tell how effective it will
be with regards to functional
outcome. But we’re coming from
a prosthesis that really has
demonstrated that it is very good
at returning bend to the knee.
The [Zimmer High-Flex Knee]
prosthesis, the basic one in its
design, is safe to 155 degrees. The
Gender Solutions is another step
in that process and very definitely
warrants encouragement.”
Additional sizes and
half sizes don’t address
the gender issue
Even though many standard implants
are provided in additional sizes or
half sizes, such as the Stryker
Triathlon implant, they do not
address the main gender issue,
which is the shape difference
between women and men.
Patient selection
The Zimmer®
Gender Solutions™
NexGen®
High-Flex Knee may
be suitable for:
Female patients requiring
a primary total knee
arthroplasty (TKA)
Some female patients
requiring revision total
knee arthroplasty (TKA),
to the extent that primary
TKA implants are currently
used by the surgeon for
revision TKA
A small proportion of male
patients with a narrower M/L
dimension for a given A/P
when compared to the rest
of the male population.
•
•
Zimmer systems
and techniques
The Zimmer®
Gender Solutions™
NexGen®
High-Flex Knee not only
retains all of the elements of
Zimmer’s clinically successful
NexGen® standard knee
system, but also provides the
added bonus of safely
accommodating up to
155 º of flexion for patients with
the desire and ability to achieve
overstuffing on.
In addition it is compatible with
other Zimmer surgical
techniques, including Minimally
Invasive Solutions™
procedures,
which typically offer smaller
scars, shorter hospitalization
and quicker rehabilitation
and recovery.
Femoral condyle mid-box medial-lateral
(M/L) dimension versus the overall
anterior-posterior (A/P) dimension of
standard implants and Gender Solutions
High-Flex Knee.
As seen on a graph that plots the
femoral condyle mid-box medial-
lateral (M/L) dimension versus
overall anterior-posterior (A/P)
dimension, standard implants still
tend to follow the same curve line,
which is based on the average of
both women and men, whereas the
Gender Solutions High-Flex Knee
stands out as having a decreased
M/L dimension.
In addition, standard implants do not
have the decreased anterior flange
thickness and greater Q-angle that
the Gender Solutions High-Flex Knee
implant exhibits.

7. What’s NewZ Issue 0
NOTES AND QUOTES
“We have known for years that there are differences between men and women.
And we’ve accommodated…that with our surgery technique. [But] as our
patients are becoming more active, wanting a better result, expecting more
for their total knee replacements I think we have to accommodate that by
having gender specific knees.”
Dr Richard A. Berger, Rush University Medical Center, Chicago
“If we think back twenty-five years ago, we had knees that weren’t even left
and right. Twenty-five years ago, we figured you had to have left and rights.
Twenty-five years later, we find out you have to have male and female…we’re
realizing that the size difference and the ratio of medial to lateral and anterior
to posterior [femoral condyle dimensions] are different for females.”
Dr Aaron A. Hoffman, University of Utah Medical Center, Salt Lake City
“I think if a surgeon questions whether or not if this is a real advance…he can
answer that question in the operating room as he puts a trial prosthesis on
and sees that it overhangs significantly and then puts the gender specific
prosthesis on and sees that it conforms accurately to the dimensions of that
particular knee. He’ll be instantly convinced that there is a place for this
particular prosthesis.”
Dr Kim C. Bertin, Utah Hip and Knee Center, Salt Lake City
The Zimmer®
Gender Solutions™
High-Flex Knee Advantage
A gender specific femoral implant design helps to meet the expectations
of female patients by providing a better anatomical fit leading to
potential benefits:
Reduced pain
Decreased feelings of bulkiness and overstuffing
Improved function and biomechanics, particularly patella tracking
Reduced need for intraoperative adjustments
•
•
•
•
REFERENCES
1. Poilvache PL, Insall JN, Scuderi GR, Font-
Rodriguez DE. Rotational landmarks and
sizing of the distal femur in total knee
arthroplasty. Clin Orthop Relat Res 1996
Oct;331:35-46.
2. Chin KR, Dalury DF, Zurakowski D, Scott
RD. Intraoperative measurements of male
and female distal femurs during primary
total knee arthroplasty. J Knee Surg 2002
Fall;15(4):213-7.
3. Hitt K, Shurman JR 2nd, Greene K, et al.
Anthropometric measurements of the
human knee: correlation to the sizing of
current knee arthroplasty systems. J Bone
Joint Surg Am, 2003;85-A Suppl 4:115-22.
4. Vaidya SV, Ranawat CS, Aroojis A, Laud
NS. Anthropometric measurements to
design total knee prostheses for the
Indian population. J Arthroplasty 2000
Jan;15(1):79-85.
5. Urabe K, Miura H, Kuwano T, et al.
Comparison between the shape of
resected femoral sections and femoral
prostheses used in total knee arthroplasty
in Japanese patients: simulation using
three-dimensional computed tomography.
J Knee Surg 2003 Jan;16(1):27-33.
6. Graves S, Davidson D, Ingerson L, et al.
Australian Orthopaedic Association
National Joint Replacement Registry
annual report. Adelaide: Australian
Orthopaedic Association, 2006.
7. Hawker GA, Wright JG, Coyte PC, et al.
Differences between men and women in
the rate of use of hip and knee
arthroplasty. N Engl J Med 2000 Apr
6;342(14):1016-22.
8. Mahfouz M, Booth R Jr, Argenson J, et al.
Analysis of variation of adult femora using
sex specific statistical atlases. Presented
at: Computer Methods in Biomechanics
and Biomedical Engineering
Conference; 2006
9. Data on file at Zimmer.
10. Csintalan RP, Schulz MM, Woo J, et al.
Gender differences in patellofemoral
joint biomechanics. Clin Orthop Relat Res
2002 Sep;(402):260-9.
11. Aglietti P, Insall JN, Cerulli G. Patella pain
and incongruence. I: Measurements of
incongruence. Clin Orthop Relat Res 1983
Jun;(176):217-24.
12. Hsu RW, Himeno S, Coventry MB, Chao
EY. Normal axial alignment of the lower
extremity and load-bearing distribution
at the knee. Clin Orthop Relat Res 1990
Jun;(255):215-27.
13. Woodland LH, Francis RS. Parameters
and comparisons of the quadriceps angle
of college-aged men and women in the
supine and standing positions. Am J
Sports Med 1992 Mar-Apr;20(2):208-11
14. Livingston LA. The quadriceps angle: a
review of the literature. J Orthop Sports
Phys Ther. 1998 Aug;28(2):105-9.

8. What’s NewZ Issue 0
The Zimmer® Gender Solutions™ High-Flex Knee
Total Knee Arthroplasty implant that emulates three distinct and scientifically
documented anatomical shape features of women’s knees
(1) Decreased mid-box medial-lateral (M/L) dimension versus overall A/P
dimension leads to an improved fit of the implant leading to reduced
overhang at the distal, anterior and posterior M/L interfaces →
() Reduced anterior flange thickness of the implant decreases
anterior protrusion →
() Greater Q-angle of the implant improves patella tracking →
A Special Thank You
On behalf of John Cooper, Vice President, Australia, New Zealand and India we
would like to thank our guests for celebrating the launch of the revolutionary
Gender Knee at the Zimmer ‘Art of the Knee’ Gala Dinner held 10th October at
the National Gallery of Australia.
For those people who were unable to attend the event, Professor Betty
Churcher introduced guests to the mysterious yet fascinating world of academic
art history. Guests experienced an informative and entertaining journey that
encompassed the representation of the human anatomy from the 10th century
Nordic tradition to present pieces produced by Australian contemporary
photographer Bill Henson. How artists depicted female nudes was not only
interesting but it was apparent that art and science can portray entirely
different facts about the human body.
To discuss the scientific attributes was international guest speaker Dr Robert
Booth, Chief of Orthopaedic Surgery, Pennsylvania Hospital, Philadelphia, USA.
Dr Booth was one of the key orthopaedic surgeons on the Zimmer® Gender
Solutions™
NexGen®
Knee Development Team. His presentation titled
‘The EVEolution’ of the TKA’ presented our learned audience with hard
clinical evidence that supported the design, development and manufacturing
of a femoral prosthesis shaped to fit the female anatomy.
The positive feedback that we have received from both orthopaedic surgeons
and partners alike has been overwhelming. Once again, we would like to thank
you for being a part of our very special evening.
Gender Solutions
High-Flex
Femoral Implant
on female bone
Traditional implant
overhangs female bone
Gender Solutions
High-Flex
Femoral Implant
Traditional
implant
(1)
()
()
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