GENDER DIFFERENCES IN THE HISTOLOGY OF THE HUMAN ANTERIOR CRUCIATE LIGAMENT
+*Meaney Murray, M; *Dawson, C; *Kocolas, I; *Spector, M
+*Brigham and Women's Hospital, Boston, MA. Orthopaedic Research Laboratory, 75 Francis St, Boston, MA 02115, 617 732-6702, Fax: 617 732-6705,
[email protected]
Cells/mm2
Figure 1: The influence of gender on cell
density of the human ACL (mean +/- SEM)
1200
1000
800
600
400
200
0
Female (n=27)
Male (n=14)
0 mm
1 mm
2 mm
4 mm
6 mm
Distance from the Femoral Region
Age had a significant effect on cell number density with dramatic
differences seen in ligaments retrieved from patients under 65 years old (n=7
for women, n = 5 for men) than those obtained from patients over 65(n=20 for
women and n = 9 for men) (Fig 2). This difference was more prominent in
women than in men (two-factor ANOVA, p < 0.0001 for age and p < 0.0004
for gender with powers of 99 and 96%). The decrease in cell density was not
affected by ERT (Fisher’s post-hoc PLSD, p > 0.85).
Two-factor ANOVA demonstrated no significant effect of gender on
blood vessel density (p > 0.11); however, location was found to significantly
affect this parameter (p < 0.002). Post-hoc testing revealed significant
differences between the blood vessel density adjacent to the femoral insertion
and that at 4 and 6 mm from the femoral insertion ( p < 0.001 and p < 0.0001).
Cells/mm2
Figure 2: The influence of gender on the cell
density of the human ACL (mean+/-SEM)
1200
1000
800
600
400
200
0
Women
Men
<65
65 to 74
>74
Patient Age (Years)
The expression of SMA was significantly effected by gender, but not by
patient age (Figure 3; two-factor ANOVA, p <0.008 and p>0.90 respectively).
Figure 3: The influence of age and gender on
% SMA positive cells (mean +/-SEM)
% SMA positive cells
INTRODUCTION: Women engaged in intercollegiate sports have a higher
risk of anterior cruciate ligament (ACL) injury than their male counterparts
(1). Proposed reasons for this discrepancy include differences in how men
and women take off and land in a jump, hormonal differences, differences in
training techniques and anatomical differences. This study was performed to
determine if there are any histological differences between the ACL in women
and men. Ligaments from two groups of women, those on and off estrogen
replacement therapy, were also examined to determine if exogenous estrogen
had any significant effect on the measured parameters.
METHODS: Intact ACLs were obtained from 41 patients undergoing total
knee arthroplasty. Fourteen ligaments were obtained from men (mean age 68),
nine from postmenopausal women on estrogen replacement therapy (ERT;
mean age 66), and eighteen from postmenopausal women not on estrogen
replacement therapy (mean age 70). All ligaments were fixed in formalin,
embedded in paraffin, and 7 µm sections microtomed. Hematoxylin and eosin
staining and immunohistochemistry for the α-smooth muscle actin (SMA)
isoform were performed. Sections taken adjacent to the femoral insertion of
the ligament and at 1, 2, 4 and 6 mm from the insertion site were analyzed
histomorphometrically. At each location, 0.1mm2 areas were analyzed for
total cell number and the percentage of cells staining positive for SMA. The
number of blood vessels at each site was counted and divided by the width of
the section at that point to yield a “blood vessel density.” RESULTS: Twofactor ANOVA revealed a significant effect of both gender and location on
cell number density (Fig 1; p<0.002 and p<0.0001, powers of 92 and 99%).
Post-hoc testing revealed a significant difference between the cell density
adjacent to the femoral insertion of the ligament and the density in the
remainder of the ligament (p<0.05). The cell density of the ACL was higher
in women than in men at all sites (Fisher’s post-hoc PLSD, p < 0.0009), with
a 40% difference seen adjacent to the femoral insertion. There was no
statistically significant difference in cell density between those women on
ERT and those not on ERT (Fisher’s post hoc PLSD, p > 0.85).
16
14
12
10
8
6
4
2
0
Women
Men
<65
65 to 74
>74
Patient Age (years)
DISCUSSION/CONCLUSIONS: The histology of the ACL is different in
men and women – the female ACL is more cellular than that of the male ACL,
and this difference is not altered by exogenous estrogen in postmenopausal
women. These specimens were, however, obtained from patients older than
the population that typically presents with ACL rupture and from patients with
degenerative joint changes necessitating arthroplasty. That differences in cell
number density were present in the younger decades of the population studied
here, compels the need to investigate specimens from younger individuals free
of joint disease, albeit difficult to obtain. A difference in cell number density
could possibly result in a higher propensity of the ligament to failure, as the
cells may act as defects in the tissue and thus result in decreased mechanical
strength. In this regard, further work is needed to characterize the extracellular
matrix organization and structural properties.
The marked gender difference in the percentage of SMA-expressing
cells in the ACLs from individuals <65 years old is of uncertain meaning. It
may signal other phenotypic differences between male and female ACLs and
warrants additional investigation.
In studying ligaments obtained from post-menopausal women and agematched male controls, this work was able to demonstrate a marked decrease
in cellularity of the ligament in women over 65 years - an effect that was seen
in both women taking ERT and those not. This suggests that the
musculoskeletal changes after menopause may occur in ligaments as well as
bone, and may not be altered by estrogen replacement.
REFERENCE: 1. Arendt, E. and Dick, R., Amer J Sports Med, 23(6), 1995.
Poster Session - ACL - Hall E
47th Annual Meeting, Orthopaedic Research Society, February 25 - 28, 2001, San Francisco, California
0789