Fibular collateral ligament

At a glance

English

Fibular collateral ligament

Latin (TA2)

Ligamentum collaterale fibulare

System

Ligament

Region

Lower limb

Side

Paired, left and right

About the fibular collateral ligament

The fibular (lateral) collateral ligament is the main ligament of the lateral knee and a key part of its posterolateral corner. Unlike the flat medial collateral ligament, it is a rounded, pencil-like cord that stands clear of the joint. It runs obliquely downwards and backwards from the femur's lateral epicondyle to the outer surface of the fibular head, in front of its apex.

It is separate from the capsule and from the lateral meniscus, and this freedom makes it more flexible than its medial partner and less often injured. The popliteus tendon arises from a groove immediately beneath the ligament's origin and passes deep to the ligament, between it and the meniscus. The inferior lateral genicular nerve and vessels also run deep to it. The biceps femoris tendon overlies most of its outer face, which splits around the lower end of the ligament as both reach the fibular head.

The medial and lateral collateral ligaments both tighten as the knee straightens and loosen as it bends, because the curvature of the femoral condyles brings their attachments closer together in flexion. Together they hold the knee steady in the side-to-side plane. The fibular collateral ligament resists varus force, the push that opens the outer side of the joint, and it helps to limit external rotation of the tibia.

Injury follows a varus stress, as from a blow to the inner side of the knee, or a hyperextension twist, and it usually occurs with damage to other knee ligaments. Pain on the outer knee, swelling, bruising and a feeling of giving way are typical, and the varus stress test reveals laxity. The common fibular nerve winds round the neck of the fibula just below, so it may be stretched in the same injury, causing foot drop or tingling. Isolated low-grade sprains settle with rest and rehabilitation; complete or combined tears may need repair or reconstruction.

Attachments and function

Attaches from

The femoral lateral epicondyle, just above the popliteus groove.

Attaches to

The lateral surface of the head of the fibula, in front of its apex, between the two parts of the biceps femoris tendon.

Function

Resists varus force on the knee and limits external rotation of the tibia; taut in extension, slack in flexion.

Nerve supply

Articular branches of the common fibular nerve.

Blood supply

The superior and inferior lateral genicular arteries.