The Anatomy and Biomechanics of the Lateral collateral ligament

What is Lateral Collateral Ligament (LCL)? Where is the LCL located?

The lateral collateral ligament (LCL) is also known as fibular collateral ligament. The Lateral collateral ligament is a thin cord-like band of connective tissue located on the outside (lateral) of the knee joint. It provides varus stability to the knee joint.

What is Varus stress in the knee? 

Varus stress in the knee is the forces coming from medial to lateral side (inside to outside). Therefore, LCL provides support against these varus stresses.

Lateral compartment of the knee 

The lateral compartment of the knee plays an essential role in stabilizing the knee joint. Lateral knee structures include a complex arrangement of tendons, ligaments, and muscles. These lateral knee structures act as a primary restraint (provides support) against varus stresses, internal and external rotation, and anterior and posterior translation of the tibia.

Lateral Collateral Ligament (LCL) Anatomy

The lateral collateral ligament (LCL) originates from the lateral femoral epicondyle. It travels distally (downwards) and finally attaches to the fibula’s head, where it also joins with the biceps femoris tendon to form the conjoined tendon.

LCL attachment points

The LCL has two attachment points, one on the femur (proximal) and another on the tibia (distal).

LCL Origin 

The proximal portion of the lateral collateral ligament attaches to the lateral epicondyle of the femur, then it travels distally (downwards).


LCL insertion

After travelling distally downwards, LCL finally inserts or attaches on the fibula’s head, where it also joins with the biceps femoris tendon to form the conjoined tendon. 

lateral collateral ligament joins with the biceps femoris

Unlike the medial collateral ligament, LCL is a separate ligament. As in MCL, the deep MCL is a thickening of the joint capsule, but LCL is not thickening of the joint capsule. As it is independent throughout much of its length and therefore regarded as an extracapsular ligament.

Biomechanical function of Lateral collateral ligament

Lateral collateral ligament (LCL) prevents the varus stresses (forces coming from medial to lateral side). As a study conducted by Grood and colleagues, they concluded that –

At 5 degrees of knee flexion or near full extension – LCL contributes to 55% of the support against the varus stresses.

At 25° of knee flexion – LCL contributes to 69% of the support against the varus stresses.

Even though the fibular or lateral collateral ligament (LCL) primary function is to prevent or resist the varus stresses, along with that LCL orientation allows the it to avoid excessive lateral rotation of the tibia.

Mechanism of injury

Lateral compartment injuries are less common than medial compartment knee injuries, as they are more disabling. Therefore, the LCL injuries are comparatively low (6 to 8%) compared to the other knee injuries. LCL injuries are often associated with other knee ligament injuries. Some common causes includes –

  • An excessive varus force that exceeds the strength of the LCL.
  • A direct blow to the inner aspect (inner side) of the knee or posterior lateral corner of the knee.

Some common symptoms 

The patient may complain of superficial swelling laterally, he may or may not have trouble weight-bearing, he may suffer instability, where the knee wants to buckle outward.

Assessment –


The examiner will palpate on the lateral side and will look for

  • Lateral swelling.
  • Tenderness on palpation over the LCL.
  • Examiner will try to palpate the LCL, but if there is a complete rupture, he may not palpate the LCL.

Position of the Patient – Ask your patient to cross your legs with the ankle resting on the opposite knee (90° knee flexion, hip abduction and external rotation).

In this position, LCL is easier to isolate as the iliotibial band relaxes. The ligament is located posteriorly and laterally along the joint line. There would happen three possible cases after performing the palpation –

If the LCL is intact or uninjured- The examiner will be able to palpate the thin cord-like band structure on the lateral side of the knee joint. 

If there is a partial tear – The examiner may feel some amount of tenderness over the LCL.

When there is a Complete tear – The examiner may not be able to palpate the LCL.

Special Tests –

Varus Stress Test


A particular test named Varus (adduction) stress test is used to assess the integrity or stability of the LCL.


  • To perform the test, the patient should lied down in a relaxed supine position. Grab on to the lower leg with one hand just above the ankle joint.
  • Now, fixate or stabilize the medial side of the femur with the other hand. Now apply lateral rotation in the knee joint.
  • After that, apply a passive abduction force in the knee joint. This abduction force will put stress on the lateral collateral ligament.
  • Now perform the same test in 30 degrees of flexion. When conducting the valgus stress test, look for excessive gapping on the lateral side of the knee joint. Here is the video demonstrating the Valgus stress test.


An excessive gapping or knee adduction greater than usual at the lateral side indicates a positive varus stress test. And a positive varus stress test is an indication of the LCL tear.

Reliability and validity

This test is performed in two positions, one at 0 degrees of flexion and the other at 30 degrees of flexion.

If the varus stress test is positive at 0° and negative at 30° – It indicates that only LCL is torn.

If the varus stress test is positive at both 0° and 30° – It indicates LCL tear along with the cruciate ligament involvement (ACL OR PCL).

Releated Article

Medial collateral Ligament – Anatomy and the Biomechanics

Posterior Cruciate Ligament – Anatomy and Biomechanics

Anterior Cruciate Ligament – Anatomy And the Biomechanics

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