An increasing number of female athletes are tearing their
anterior cruciate ligament (ACL) during sports participation. Most of these
tears are caused by noncontact injuries in sports, such as basketball,
soccer, gymnastics, and cheerleading, in the United States. In Europe,
participation in snow skiing and team handball results in up to eight times
more ACL injuries in women than in men.
What is the ACL?
The ACL is located in the center of the knee joint and connects the
femur (thigh bone) and the tibia (shin bone). Its primary purpose is to
provide stability to the knee. It prevents the tibia from moving too far
forward and from rotating too far inward under the femur.
How does the injury happen?
There are several ways noncontact ACL injuries occur, including stopping
quickly, cutting sharply, and landing and changing direction with both
feet planted. Most commonly in court sports, such as basketball, a pop
is felt. This pop also refers to the way the athlete lands with both feet
planted and out of control and feels a pop. It usually signals that the
ACL is torn completely.
The
gymnast in Figure 1 demonstrates this mechanism of injury as she tears
the ACL in her right knee during a floor exercise. Notice that her hip
is turned inward (internal rotation), her tibia is turned outward (external
rotation), her knee is bent about 30°, she is knock-kneed (genu valgum),
her foot is rolled inward, and her body is falling forward. This motion
causes a very quick whip-type action in the knee that tears the ACL.
As mentioned, in Europe more female than male skiers injure
their ACL. The mechanism of injury in skiers is different than in court
sport participants. When skiers injure the ACL, they are moving out of
control with the knee bent or extended. The uphill arm is back, the body
is off balance, the hips are lower than the knees, and the weight is placed
on the inside edge of the downhill ski. Dr. Robert Johnson describes this
mechanism of injury as the phantom foot ACL.
A knee joint with a torn ACL is abnormally loose, or lax.
Because of this severe laxity, the female athlete is actually at greater
risk for her knee giving way or pivoting without warning. The risk of other
serious, and possibly irrepairable, knee damage also increases.
Anatomic differences
Naturally,
women are built differently than men. These differences are evident when
examining the muscles and bones of their hips and legs. Compared with men
(Fig. 2), women have a wider pelvis (Fig. 3); their hips are more flexible
and have more rotation; their femur is tilted forward more at the top and
is angled more toward the knee; their lower leg is turned inward and angled
more toward the knee, but there are forces pushing outward; they have less
developed thigh muscles, making the knee more dependent on the ligaments
for stability; they have increased flexibility and hyperextension in their
joints; and they have a narrower notch in the femur where their smaller
anterior cruciate ligament is attached.
Why do these anatomic differences cause women to be more
prone than men to ACL injuries? Because the thigh muscles are lax, the
ACL must serve as the main stabilizer of the knee. However, the small ACL
often cannot handle the forces put on it during sports participation, so
it tears. Other contributing factors are associated with the sport and
with the physical make-up of a woman. Her position, coordination, skill,
talent, and coaching affect the way the female athlete uses her body and
can affect whether she is at increased risk for ACL injury. A poorly conditioned
or overweight body puts more pressure on the knee joint and puts the athlete
at greater risk for ACL injury. Hormonal levels at certain times during
the menstrual cycle and extremely low percentage body fat cause the ACL
to be more lax and, therefore, at increased risk for injury. Medical professionals
are continuing to do research to find the exact reason for this problem
in women and to find the best ways to prevent it.
In hopes of preventing ACL injury in female athletes,
some experts have suggested that basketball players and other court sport
participants try to land on two feet rather than jump stopping and try
to round off turns rather than cutting sharply.
The female athlete is very competitive and the mental
drive to be the best burns brightly within her. Upon returning to competition
after ACL reconstruction, a University of Tennessee female basketball player
stated that she would do anything to win a national championship including
tearing her ACL. Competitive female athletes need to take measures to prevent
ACL injuries. Finding ways to prevent ACL injuries will ensure longer,
more active athletic participation for women.
Mary Lloyd Ireland, M.D.
Lexington, Kentucky