Frequently Asked Questions

The lateral collateral ligament (LCL), also called the fibular collateral ligament (FCL), is the main structure on the lateral, or outside, portion of the knee to prevent the knee from gapping open. The term fibular collateral ligament (FCL) is more anatomically correct, but this ligament is more commonly referred to as lateral collateral ligament (LCL). In clinical terms, this is noted as varus gapping. It is a thin, round, stout ligament, which courses from the femur down to the lateral aspect of the fibular head.

An LCL injury can occur with sudden stops and starts, a blow to the inside of their knee, or a contact or noncontact hyperextension injury. Sometimes a LCL tear of the knee can go undiagnosed for a few weeks before an athlete notices problems with instability.

Symptoms of an LCL Injury (FCL Injury)

  • Mild swelling and pain – no obvious deep swelling within the knee
  • Difficulty stopping and cutting
  • Instability of the knee shifting side-to-side

Many athletes note that they cannot stop and cut towards the side where they have the LCL tear, due to a feeling of instability of the knee shifting side-to-side. Unfortunately, due to the unstable nature of the lateral compartment of the knee with two convex surfaces opposing each other, grade III lateral collateral ligament tears usually do not heal, and can lead to further instability.

The diagnosis of an LCL tear is made through a combination of physical examination and radiographic techniques. In most circumstances, the athletes will complain of a feeling of side-to-side instability and have varus gapping on the physical exam. Varus stress x-rays are very useful to determine the amount of gapping to determine if it is a complete or partial tear and are highly recommended to be performed. Studies have reported that greater than 2.7 millimeters of side-to-side gapping is consistent with a complete tear of the lateral (fibular) collateral ligament and a reconstruction should be considered.

Treatment for LCL Tear (FCL Tear)

In the acute situation, a reconstruction of the lateral collateral ligament is recommended using a hamstrings autograft or allograft. We utilize an anatomic technique that was developed and validated in our biomechanical research lab. This technique has also been validated in patient outcome studies. In patients with a chronic injury, it is important to assess their overall alignment. If they are in varus alignment, there is a very high risk that the LCL reconstruction would stretch out if the varus alignment was not concurrently fixed. Thus, a concurrent proximal tibial opening wedge osteotomy with a combined LCL reconstruction would be indicated.


The outcomes of lateral collateral ligament reconstructions are excellent. Patients who follow the rehabilitation program and who demonstrate excellent return of stability on varus stress X-rays can usually return to full function within 5-7 months after surgery.

Related Studies

  • Fibular Collateral Ligament Biceps Femoris Bursa Anatomic Study
  • Biomechanical Analysis of an Isolated Fibular Collateral Ligament (FCL)
  • Varus Stress Radiographs
  • Posterolateral Attachments of the Knee
  • Assessment of Healing of Grade III Posterolateral Corner Injuries
  • Prospective MRI Study of Incidence of PLC and Multiligaments