The knee is a joint that provides the basic functions for lower-extremity activities, essential for going up or down stairs, running, and squatting among other things. It is the joint with the highest rate of injury in athletic populations, however it also affects the majority of the population in a degenerative way, causing pain and limited function.

Knee injuries tend to involve one or more of the following structures:

  • Meniscus: a type of cushion that distributes weight between the surfaces of the femur and tibia.
  • Ligaments: responsible for providing stability in different directions, such as the anterior cruciate ligament, which is most frequently is torn. However there is also the posterior cruciate ligament, medial collateral ligament, lateral collateral ligament, and the ligament complex of the posterolateral corner.
  • Cartilage: a layer that reduces the friction between surfaces and prevents bone on bone contact.
  • Muscles: a large quantity of muscles is inserted around the knee, with different functions. These include the knee flexors, extenders, and others with indirect functions that stabilize the joint.


These are the quintessential injuries in many sports caused by running, changing directions, pivoting, or jumps. They occur frequently and if not treated may have consequences and complications.

It’s important to know that not all knee injuries require surgery. The type of injury can be determined, as well as the correct way of treating it, through its symptoms and the tests performed.

Anterior Cruciate Ligament (ACL)

The most common injury in young patients, an ACL tear is brought about by excessive rotational movement of the femur, which causes the ligament to tear and, characteristically, leads to a joint effusion (swelling of the knee) as well as a sensation of instability in the knee (a feeling akin to abnormal knee movements).

In some cases these injuries are accompanied by other injuries like a torn meniscus, cartilage damage, or bone injuries.

When broken this ligament cannot reattach naturally to the site from which it was torn, which is why it is necessary to replace the ACL surgically.

Currently, these procedures can be done arthroscopically (minimally invasive surgery) and manages to reestablish stability using the existing tendon or from a cadaver; both work adequately, however the type of grafting will depend on the patient, including the patient’s preference.

The current surgery is much better than its previous iterations and technological advances allow us to rebuild to the precise needs of each patient. However, the complexity of the injury depends largely on other injuries provoked by the ACL tear.


Posterior Cruciate Ligament

The much more complex knee injury, the posterior cruciate ligament provides stability for the posterior knee, such that it prevents the tibia from shifting backwards abnormally. The equilibrium between the anterior and the posterior cruciate ligaments hold the tibia centered with respect to the femur. This is indispensable in activities like walking, running, and jumping.

This ligament typically tears after falling on the knee or accidents that involve blunt trauma to the shins. In some cases, if the tear isn’t complete or only a small percentage of the fibers are injured, treatment may not be surgical. However when the tear creates instability, it must be repaired arthroscopically.

This tear is more complex than an ACL tear and its prognosis will depend on how much repair can be done, but undergoing rehabilitation is also very important.


Collateral Ligaments

When the inner or outer part of the knee appears to be affected, this usually involves either the medial collateral ligament or the lateral collateral ligament. If they are only slightly injured, a conservative treatment of rest is the best option. However if there is a high-energy mechanism that puts stability at risk, a reconstructed ligament is required. This is generally associated with high-energy or complex knee injuries.


Meniscus Tear

The knee has two structures called menisci, one in the inner part of the knee and one on the outer (image). These structures distribute weight along the surface of the knee, absorbing the impact from walking, running, or jumping. However, these structures often are injured from extreme knee movements and sometimes are accompanied by other injuries like an ACL tear.

Meniscus tears usually appear suddenly after an abrupt movement with pain, and sometimes with a feeling that the knee has locked. Joint effusions are commonly experienced as well.

There are distinct types of injuries and range from simple ones that only require rest and physical therapy to complex injuries that require an arthroscopic repair if possible, or if not due to heavy damage, removal of a piece of the injured meniscus.


Cartilage Injury

Sometimes cartilage may be damaged due to trauma or from injuries to other structures like ligaments. Cartilage may peel away and create a mechanical block in the knee, meaning that a fragment of the cartilage becomes “stuck” between the bones, creating intense pain, swelling, and limited mobility in certain activities.

This type of injury has a large number of clinical presentations, resulting in slight symptoms or completely incapacitating the patient.

The most common injuries in patients 30-40 years of age are usually sports-related wear and tear, and its normal manifestation is moderate, with continuous pain when performing daily activities. The patellofemoral joint is most commonly affected.


Posterolateral Corner Injury

This injury is normally very serious and is a high-energy injury, from car accidents, or motorcycle or skiing injuries. In these cases, various components of the knee ligaments are torn and destabilize the knee on its rotational plane, often accompanied by anterior o posterior cruciate ligament tears, or even a traumatic dislocation of the knee.

These are complex injuries, in their diagnosis and their treatment; they at times require a double surgery, in that the first surgery reconstructs part of the injury and the rest of the injury is treated during the second.

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