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injury during the pre-ovulatory phase of the
menstrual cycle compared with the post-ovu-
latory phase [7]. It remains unclear how hor-
mones associated with the menstrual cycle
modulate injury risk, or whether hormones
act on structures other then the ACL.
Hormones could be affecting changes at a
neuromuscular level. Testosterone is not
being studied – are we missing a potential
protective effect?
The criticism of current hormonal research
is that one or two measurements may not be
enough to capture the unique and changing
female physiology. Normative standards are
not well defined. Most studies have very
small numbers which are unlikely to capture
hormonal variability, and most studies have
very large standard deviation bars.
Although the relationship of hormonal
influence and musculoskeletal injury, in par-
ticular ACL injury, has inconclusive data, it
continues to be an area of continued research
interest.
ANATOMIC RISK FACTORS
The most studied anatomic risk factor in
regards to ACL injuries is the role of the
intercondylar notch. Current data suggests
that the increased rate of ACL tears in
patients with narrower notches is a manifes-
tation of a smaller ACL [4]. However, the
question of whether the smaller ACL is
appropriate for that person’s size/strength of
the individual or whether it is due to a gen-
der, hormonal, or training sequence conti-
nues to confuse this area.
An anatomic factor that has more recently
been hypothesized as potentially playing a
role in ACL injury is the slope of the tibia.
Henri Dejour
et al.
[2] were the first to note
that tibial translation was in part a function of
the tibial slope. More recent studies suggest
that those patients with an ACL rupture com-
pared to controls have a greater lateral tibial
slope and a lower medial tibial slope, perhaps
increasing rotation of the knee as well.
We accept that changing the slope was a the-
rapeutic option for ACL insufficiency in the
canine species [8]. This has not been tho-
roughly studied in humans.
It is possible that there is an anatomic equa-
tion that involves rotational variation of the
knee, limb alignment, intracondylar notch
size, and tibial slope that combine to create
a strong anatomic risk factor for ACL injury.
Anatomic risk factors may not be easy to cor-
rect; however, they are important to unders-
tand if we are going to identify who is at
increased risk of suffering an ACL injury.
NEUROMUSCULAR RISK
FACTORS
Females who developed an increased knee
abduction moment (“dynamic” knee valgus)
during impact from landing have an increa-
sed risk of ACL injury. Female athletes have
muscle activation patterns in which the qua-
driceps predominate and decreased knee
stiffness appears to occur [7].
Research shows that programs that strengthen
posterior limb musculature (in particular
hamstring strength), improve rotational
control of the limb underneath the pelvis,
engage knee and hip flexion with jump lan-
dings, and improve balance are all favorable
to ACL injury reduction in females [3, 4, 5 6].
It is likely that the increased risk of ACL inju-
ries in females will come down to a multi-
factorial variable. We know from the
Uhorchak study looking at West Point cadets
[9] that several risk factors combine to have
a 100% correlation with ACL injury (small
femoral notch + generalized joint laxity + (in
females only) – high BMI and knee laxity as
evidenced by KT-1000). There is likely a risk
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