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All You Need to Know about Knee Ligaments

The knee is a complicated joint that is one of the most overworked parts of the body. It is the largest joint in the body, essential for movement and prone to injury.  The knee is a hinge joint that bears weight and allows for mobility. The knee comprises bones, ligaments, tendons, and meniscus.

Knee ligaments hold the knee joint together and support it by connecting the bones and cartilage. They are made of stiff, elastic connective tissue. Ligaments are tight, fibrous structures that connect bones to other bones. They are strong like ropes, preventing excessive motion and encouraging stability.

Knee ligaments are thick tissue strands consisting of collagenous fibers that link the upper and lower leg bones. There are four main knee joint ligaments. Their primary purpose is to limit knee mobility to maintain joint stability.

Knee Ligament Diagram

One of the most important components of knee stability and control is the knee ligaments.  Ligaments of the knee are thick fibrous bands that act like cords to give support and movement control.

knee ligaments

The knee ligaments link the tibia and femur (thigh and shin bones). They work together to control the movement of the knee to keep it stable and avoid injury.

In the knee, there are four distinct ligaments:

  1. The Medial Collateral Ligament (MCL) is a ligament that runs down the inside of the knee.
  2. The Lateral Collateral Ligament (LCL) is a ligament that runs along the outside of the knee.
  3. The Anterior Cruciate Ligament (ACL) is a ligament that runs across the center of the knee.
  4. The Posterior Cruciate Ligament (PCL) is a ligament that also runs across the center of the knee.

Types of Knee Ligaments

There are two major ligaments of the knee which are collateral knee ligaments and cruciate knee ligaments;

Collateral Knee Ligament

The collateral knee ligaments are found on the sides of the knee joint. The tibia and femur bones are held together by them, which provides sideways stability. The medial (MCL) and lateral (LCL) collateral ligaments are the two types of collateral ligaments (LCL).

Medial Collateral Ligament (MCL): On the medial (inside) side of the knee, the MCL is located. It is a broad, flat ligament that connects the tibia and femur. It is around 10 cm long. The MCL protects the leg from external stresses (valgus forces).

Lateral Collateral Ligament (LCL): The LCL connects the femur with the fibula on the outer side of the knee. It deflects forces coming from the inside of the knee (varus forces). The lateral collateral ligament is shorter than the medial collateral ligament. Hence, it is less likely to be injured.

knee ligaments

Cruciate Knee Ligament

The cruciates are the most vital knee ligaments for maintaining knee stability. These ligaments are attached to the femur and tibia deep into the center of the joint. They resemble the St Andrews Cross (x) as they cross over each other, hence the name cruciate.

The cruciate knee ligaments are as thick as a pencil but very strong, with a ‘breaking strain’ of around 60 kg. The cruciate ligaments' function is to control the knee joint from moving forward and backward. They also help with proprioception, or the body's capacity to sense where it is and make little adjustments to stay balanced.

The cruciate ligament is 2 cm long, and any pressure that stretches it beyond 1.7 mm tears it completely. The anterior (ACL) and posterior (PCL) cruciate ligaments are the two types of cruciate ligaments.

Anterior Cruciate Ligament (ACL): The ACL is a ligament that runs across the center of the knee joint. It connects the tibia and femur in the front and back, respectively. The ACL is the major structure for proprioception. This is because it prevents the tibia from sliding forward too much in relation to the femur.

Posterior Cruciate Ligament (PCL): The PCL connects the back of the tibia to the front of the femur and lies deep in the knee joint. The PCL is 3/5 the length of the ACL, but it is twice as strong. The PCL prevents the tibia from moving too far away from the femur.

Injuries to Knee Ligaments

The knee joint can become unstable if the ligaments get injured. A sports injury is a common reason for ligament damage. 

Knee movement is restricted owing to a damaged ligament. As a result, the leg is unable to turn, twist, or pivot. If various medical treatments fail to heal a torn ligament, surgery may be an option.

Collateral Knee Ligament Injury

Injury to the medial collateral ligament (MCL) is more common than injury to the lateral collateral ligament (LCL). A hit to the outer side of the knee causes stretch and tear injuries to the collateral ligaments. This can be caused, for example, when playing football or hockey.

A collateral ligament injury makes the knee pop and buckle. This triggers pain and swelling. The signs and symptoms of collateral ligament damage can be mistaken for other illnesses/medical disorders. For a diagnosis, always seek medical advice.

knee ligaments

Cruciate Knee Ligament Injury

One of the most commonly injured ligaments is the anterior cruciate ligament (ACL). During a quick sudden twisting movement, the ACL is usually stretched and/or torn. That is when the feet remain planted one way, the knees turn the other way, and the ACL gets injured. ACL injuries are more common when involved in activities like skiing, basketball, and football.

A knee ligament that often tears is the posterior cruciate ligament (PCL). The PCL injury is usually caused by a sudden, direct impact. For example, during a football tackle or in a vehicle accident.

Cruciate ligament damage does not always result in pain. Instead, a popping sound could be heard as the injury happens. This is followed by the leg buckling as the person attempts to stand on it, and swelling. However, each person may experience different symptoms

The symptoms of a cruciate ligament injury can be confused with those of other disorders or illnesses. Always seek medical advice before making any decisions.

Treatment for Knee Injury

Following are some examples of early medical treatment for a knee ligament injury:

  • Rest
  • Application of an ice pack (to reduce swelling within some time of the injury)
  • Compression (from an elastic brace or bandage)
  • Elevation
  • Pain-Killers

The following procedures can be used to treat a torn knee ligament:

  • Exercising to build muscle
  • Knee brace for protection (for use during exercise)
  • Limitations on activity

Knee ligament repair is a procedure for treating a complete tear of a knee ligament that causes knee instability. Normal tasks that require twisting or turning at the knee could be impossible for those with torn knee ligaments. It is possible that the knee could buckle or give away Ligament repair surgery can be an effective treatment if medicinal treatments are ineffective.

The ligament is replaced with a segment of a healthy tendon during surgery to repair a damaged knee ligament.  To bind the knee joint together, a tendon from the hamstring or kneecap is grafted into place. The tendon graft might be from the patient (autograft) or a donor organ (allograft).


Ligaments of the knee are thick, elastic bands of connective tissues that encircle a joint, providing support and limiting movement. The femur (thighbone) and tibia (shinbone) are connected in the knee via ligaments.

There are 4 major ligaments in the knee, which are Anterior cruciate ligament (ACL), Medial collateral ligament (MCL), Posterior cruciate ligament (PCL), and Lateral collateral ligament (LCL).

The knee joint may become unstable if ligaments are injured. A sports injury is a common cause of ligament damage. Knee ligament repair is a procedure for treating a complete tear of a knee ligament that causes knee instability.

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