Participation in sports has grown exponentially in the United States. The
advent of Title IX in 1972 nearly doubled the number of athletes in our
country’s high schools and colleges in the last four decades, and
athletics has become more accessible to all people in general. With the
increase in sports participation, there has also been a rise in anterior
cruciate ligament (ACL) tears. The majority of these occur in the 15-45
year old demographic. In the United States, there are 100,000-250,000
ACL tears annually, making it one of the most common sports injuries.
An overview of the topic helps one to understand how the injury occurs,
how it is treated and how to take precautions against it.
The knee joint is formed by the articulation of three bones: the thighbone
(femur), the shinbone (tibia), and the kneecap (patella). These surfaces
are covered with cartilage that allows them to smoothly move over each
other. Between the tibia and the femur are two C-shaped structures called
meniscus that help to distribute the stress on the joint when walking
or running. There are four main ligaments of the knee. On the inside of
the knee is the medial collateral ligament (MCL), and on the outside of
the knee is the lateral collateral ligament or (LCL). These ligaments
give the knee side-to-side stability. In the middle of your knee are two
cruciate ligaments. Cruciate means to cross and these ligaments form an
“X” in the middle of the knee. The anterior cruciate ligament
sits in the front of the knee and travels diagonally from tibia to femur.
It prevents the tibia from sliding out in the front of the femur and gives
the knee rotational stability. The posterior cruciate ligament (PCL) sits
in the back of the knee and prevents the tibia from sliding behind the femur.
Mechanism of injury
High-risk sports for an ACL injury include soccer, football, basketball,
volleyball and skiing. The ACL can be injured in many ways. Approximately
70 percent of ACL injuries are non-contact injuries. The injury usually
occurs during a sudden change in direction with a planted foot (pivoting
and cutting). Other mechanisms of injury to the ACL can be from a sudden
stop, landing from a jump incorrectly or direct contact, such as a football
tackle. In all of these scenarios, the injury is sustained when the tibia
(shinbone) violently moves forward in front of the femur, thereby tearing
the ACL. Several studies have shown that female athletes are two to eight
times more likely to rupture their ACL than male athletes. There is no
definitive reason as to why, however, it is proposed that this is due
to differences in physical conditioning, neuromuscular control, muscle
strength, lower extremity alignment, ligamentous laxity and even the effects
of estrogen on ligament properties.
Signs and symptoms
The typical scenario in an ACL injury is that the athlete will hear or
feel a “pop” in the knee, directly followed by a feeling of
instability. The ACL has a robust blood supply and commonly there will
be immediate swelling of the knee, along with loss of motion and discomfort
while walking. If other injuries exist, there can also be tenderness along
the joint line.
At your first doctor’s visit following an ACL injury, a physician
will discuss your medical history, including the mechanism of injury,
and perform a physical examination of the affected knee. This will allow
the doctor to assess all structures of the knee and compare to the uninjured
knee. Most ligamentous injuries can be diagnosed during the physical examination
unless the patient has significant swelling that will limit a proper exam.
Also at this visit, X-rays will be taken to evaluate for any fractures.
Once a physician has a presumptive diagnosis for an ACL tear, an MRI is
ordered. Though an MRI is not required to make the diagnosis, it produces
better images of the soft tissues and cartilage of the knee to look for
concomitant injuries such as meniscus tears, cartilage injuries and other
Non-operative treatment for ACL tears is only recommended for elderly patients
or those with low activity levels. Operative treatment is the recommendation
for other patients, especially those involved in moderate to high activity
levels. To adequately restore the knee stability, the ACL has to be reconstructed
because direct repair has poor results. This reconstruction requires the
use of a tissue graft. The graft can be obtained from a couple of sources:
either tissue harvested from the patient (autograft) or tissue from a
cadaver graft (allograft) can be used. There are advantages and disadvantages
to both types of grafts. Recent studies have shown a high recurrent ACL
tear rate in athletes less than 25 who had their ACLs reconstructed with
cadaver graft (allograft). Therefore, it is recommended to use the athlete’s
tissue as the graft source when the patient is less than 25 years old.
For older patients with this type of injury, the decision about the graft
source can be made on a case-by-case basis.
Rehabilitation is an integral part of treatment before and after ACL tears.
Before surgery, therapy is important to decrease swelling and return the
athlete to pre-injury range of motion. This decreases the risk for knee
stiffness and scar formation. After surgery, physical therapy first focuses
on returning motion to the joint, followed by activation of the surrounding
muscles with a strengthening program while allowing the new ligament to
heal. The protocol for ACL rehab gradually increases stress across the
ligament. The final phase is individualized to the athlete’s sport
for functional return. The entire rehabilitation process can easily last
for 9-12 months. Early return without proper functional return of strength
of the operative leg greatly increases the risk for recurrent ACL tear
or tear of the opposite ACL, making rehab vital for the best outcome.
Prevention programs have been developed to decrease the incidence of ACL
injuries. These programs are especially important in female athletes,
focusing on neuromuscular training to encourage better lower extremity
control. FIFA began a program in 2003 that now has international implementation
at all levels of soccer. It is known as the FIFA 11+ and it is a comprehensive
warm up program to reduce injuries in male and female soccer players.
In a study out of Norway, teams that performed the FIFA 11+ twice a week
had a 30-50 percent reduction in injuries. Any program that strengthens
the muscles in the knee can help prevent an ACL injury. Focus on exercises
that strengthen the muscles around the knee such as squats, lunges, burpees,
On the horizon
There has been extensive research and early trials utilizing a scaffold
to allow for healing of an athlete’s native ACL. This new technique,
called Bridge Enhanced ACL Repair (BEAR™), utilizes a sponge injected
with the patient’s blood that is sutured to the native ACL to promote
healing. Early clinical trials have been very promising.
If you enjoyed the information provided in this blog, keep a look out for
ACL Part II: Rehab and Return to Play!