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Knee Ligament Injuries
 | The knee joint is stabilized
primarily by four very strong ligaments. Three of them, the anterior cruciate
ligament, the posterior cruciate ligament, and the medial collateral ligament,
connect the end of the femur (thigh bone) to the top of the tibia (shin
bone). The lateral collateral ligament actually connects the end of the femur
to the top of the fibula, which is a much smaller bone in the shin. The
fibula and tibia are connected to each other by very strong bindings, so the
effect of the lateral collateral ligament is to control the motion between the
femur and tibia, just like the other three ligaments that connect these bones
directly to each other. |
| The medial collateral
ligament (MCL) is located outside of the joint space and on the inner aspect
of the knee. Likewise, the lateral collateral ligament (LCL) is located
outside of the joint and on the outer aspect of the knee. The two cruciate
ligaments are located in the center of the knee joint itself. These cross
each other, hence the name “cruciate.” The insertion of these ligaments onto
the tibia is such that the anterior cruciate ligament (ACL) inserts on the
anterior (front) aspect of the top of the tibia and the posterior
cruciate ligament (PCL) inserts on the posterior (back) aspect of the top
of the tibia. |
| The end of the femur
being round and the top of the tibia being relatively flat, there is very
little intrinsic stability imparted by the bony architecture. Rather,
the stability of the knee is fundamentally dependent upon the ligamentous
structures. Disruption of these ligaments can lead to instability of the knee
joint. The degree of instability depends on the number of ligaments that have
been injured and their capacity to heal. The medial collateral ligament and
the lateral collateral ligament do have significant capacity to heal after
injury. Therefore, isolated injuries to these ligaments can often be
treated by bracing and activity modification and rehabilitation. Once the
ligaments have healed, normal activity can be resumed. In contrast, the
cruciate ligaments, being inside the joint, have very poor capacity to heal.
Restoring function of torn cruciate ligaments therefore requires surgical
intervention. |
| Posterior cruciate
ligament (PCL) injury is generally well tolerated by the knee. With
appropriate rehabilitation, people can typically return to activity after an
isolated posterior cruciate ligament injury. In fact, an estimated 2% of NFL
players are playing on knees without posterior cruciate ligaments. A strong
quadriceps muscles is thought to be able to take over some of the duties of
the posterior cruciate ligament and thereby compensate for its absence or
incompetence. As a
result, most isolated PCL injuries can be successfully treated without
surgery. In some severe cases, however, the PCL does require reconstruction to
decrease severe laxity. |
| In contrast to the PCL, anterior
cruciate ligament (ACL) deficiency is less well compensated for by
rehabilitation. Although one can restore motion and strength to the knee, the
instability that results from ACL-deficiency limits one’s ability to do
cutting, pivoting, twisting, and jumping-type activities. Straight-ahead
activities like jogging or bicycling are unaffected. However, sports such as
basketball, soccer, or football are usually not possible for patients with
ACL-deficient knees. An analogy can be made of a four-wheel vehicle vs. a
three-wheel vehicle. A four-wheel vehicle can take corners a lot faster than
a three-wheel vehicle due to the inherent stability provided by four wheels.
However, on a straight track, both vehicles may perform similarly. |
| The ACL has such a
poor ability to heal, that even surgical repair has not been very successful.
In order to restore it’s function, we must reconstruct it. This means
replacing the torn ligament with tissue to act as a new ligament. Many
synthetic grafts have been tried and have uniformly met with failure.
However, a high degree of success has been achieved by the use of tendons to
act as the new anterior cruciate ligament. Traditionally, a portion of
the patellar tendon (which connects the kneecap to the tibia) is used. The
central third of this tendon is taken along with a small piece of the kneecap
and a small piece of the tibia. This is then put through drill holes in
the top of the tibia and the end of the femur to take the place of the torn
anterior cruciate ligament. More recently, techniques have been
developed to take a couple of the small hamstring tendons from the medical
(inside) aspect of the knee to act as a new ACL. Also, tendinous tissue
from organ donors has also been used to reconstruct the ACL. All three
methods have a high degree of success and each one has advantages and
disadvantages. Discussing these options with a surgeon skilled in all
these various techniques is the best way of deciding which graft source
is the best choice for your knee. |
| Arthroscopic picture of a normal ACL: |
| Acute ACL Tear: |
| Same knee after ACL Reconstruction: |
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