Age and Gender Related Differences in Femoral Neck

Age and Gender Related Differences in Femoral Neck - Shaft Angles
+1Rickels, T; 2Kreuzer, S; 3Lovell, T; 4Nogler, M; 5Puri, L
+1Stryker Orthopaedics, Mahwah, NJ, 2Memorial Bone and Joint Clinic, Houston, TX, 3Providence Physician Services, Spokane, WA,
4
University of Innsbruck, Innsbruck, AT, 5Northwestern Memorial Hospital, Chicago, IL
[email protected]
MATERIALS AND METHODS:
All FNS angle measurements were taken from a virtual bone database
which is made up from more than 600 patient’s CT scanned femurs [3].
This database includes corresponding patient data for age, race, gender,
weight and height. All patient data that was collected for this study was
automatically output into an Excel table for further analysis. Any patient
data that was found to be missing age and/or gender related data was
excluded from this study. After excluding patients with missing age and
gender data, 518 patients remained. Patients were then divided into
groups to look at both male and female populations under 50 years old
and over 50 years old.
RESULTS:
Out of the 518 patients in this study, 117 patients were under 50 years
old and 401 patients were over 50 years old. There were 235 females
and 283 males. For the under 50 age group, males accounted for 55 of
the patients and females accounted for 62 of the patients. For the over 50
age group, males accounted for 228 of the patients and females
accounted for 173 of the patients.
FNS Angle vs. Age and Gender
FNS Angle vs. Age
130
127.0
125
122.5
120
115
110
FNS Angle (Deg)
FNS Angle (Deg)
130
Males
Females
125
120
115
110
Under 50
Over 50
Figure 1: FNS Angle vs. Age
Under 50
Over 50
Figure 2: FNS Angle vs.
Age and Gender
Figure 1 shows the average FNS angle for the two age groups. The
average FNS angle for patients under 50 was 127.0 degrees. The average
FNS angle for patients over 50 was 122.5 degrees. Individual t-tests
confirmed that a statistically significant difference of 4.5 +/- 0.6 degrees
exists between these two groups average FNS angles (p<0.001). Figure 2
shows the same data from figure 1 broken down by both age and gender.
Both of the female group’s average FNS angles were higher than the
male FNS angles. A statistically significant difference (p<.001) was
observed between the males and females in the Over 50 group. A
significant difference could not be detected between the average FNS
angles in the Under 50 groups of males and females.
Figure 3 shows a scatter plot that was used to display all of the FNS
angles and corresponding patient ages that were collected and analyzed
in this study. In this plot, red points indicate female FNS angles and blue
points indicate male FNS angles. All of the points to the
Femoral Neck - Shaft Angle vs. Age
145
140
FNS Angle (Degrees)
INTRODUCTION:
Femoral neck – shaft (FNS) angles, also known as caput-collumdiaphyseal (CCD) angles, have been measured in past studies to help
understand how much variation exists within the human population [1].
Orthopaedic manufacturers have been using data from various studies
like these for decades to help develop new hip stem designs with a
variety of neck angles that can be utilized to help restore the anatomic
center of the hip. To date, very little research has been done to look for
age related differences in adult humans FNS angles.
Tillman and Tondury [2] suggested that FNS angles start out at
approximately 150 degrees during fetal development and decrease to
approximately 125 degrees by the time of skeletal maturity. After
reaching skeletal maturity, it is believed that this angle continues to
decrease although no data was supplied to backup this statement.
The aim of this study was to compare young and old adult patient’s
FNS angles and determine if a statistically significant difference exists
between both age groups. Additional focus will be given to look at male
and female groups within each age category to see if age related changes
affect the two gender groups differently.
135
130
125
120
115
Males Under 50
110
Females Under 50
Females Over 50
105
Males Over 50
100
10
20
30
40
50
60
70
80
90
100
Age (Years)
Figure 3: FNS Angle vs. Age
left side of the 50 year mark were displayed in solid colors to help
distinguish the two age groups. Age and gender specific trend lines were
also used in this graph to show how the average FNS values change with
time.
CONCLUSION:
The lower FNS values observed in the Over 50 age group indicate
that femoral geometry does change significantly with age in skeletally
mature adults. Assuming that the neck length of the femur remains the
same, a decrease in the FNS angle should result in a higher femoral head
offset value. With this thought in mind, the femoral head offset data
from the same groups of patients was analyzed to determine the validity
of this assumption. The results from this follow-up study confirmed that
the average femoral head offset values do increase with patient age
while the average FNS angles are decreasing with age.
The trend lines that were displayed in figure 3 indicate that the FNS
angles are decreasing at a higher rate in the Over 50 populations of male
and females. This change in the rate of decline for FNS angles may be a
result of decreasing bone density. It was hypothesized early on in the
development of this study that older female’s FNS angles may be
decreasing at a faster rate than males of the same age due to the risk of
post-menopausal osteoporosis [4]. No evidence in this analysis appears
to support this theory about older women’s FNS angles.
The information from this study will be helpful for designing the next
generation of femoral hip stem designs for total hip replacement.
Currently, the majority of femoral hip stems that are produced for the
orthopedic market are monolithic with fixed neck/shaft angles. In order
to accommodate patients with a variety of FNS angles, multiple
neck/shaft angles have been developed for each monolithic hip stem
design which increases inventory significantly for manufacturers. The
utilization of a hip stem with a modular neck design may be more
effective for addressing the variety of FNS angles that exist in patient’s
femurs which have been shown in this study to be changing with age.
__________________________________________________________
1
Yoshioka Y, Siu D, Cooke TD. (1987). The anatomy and functional
axes of the femur. J Bone Joint Surg Am, 69(6), 873-880.
2
Tillmann B & Töndury G. (1998). Band I: Bewegungsapparat: (p467).
New York: Georg Thieme Verlag Stuttgart
3
Wuestemann T, Bastian A, Schmidt W, Cedermark C, Rothman R,
Parvizi J. “A novel technique for studying proximal femoral bone
morphology for hip implant design”. Orthopaedic Research Society
Poster. New Orleans, LA, 2010.
4
Cranney A, Jamal SA, Tsang JF, Josse RG, Leslie WD. (2007). Low
bone mineral density and fracture burden in postmenopausal women.
CMAJ, 177 (6), 575–80.
Poster No. 2279 • ORS 2011 Annual Meeting

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