[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Lower limb](https://durgical.com/en/anatomy/region/lower-limb/) › LCL

[Joints and ligaments](https://durgical.com/en/anatomy/system/joints-and-ligaments/) · [Lower limb](https://durgical.com/en/anatomy/region/lower-limb/)

# LCL

The lateral collateral ligament (LCL) is a cord on the outer side of the knee, from [femur](https://durgical.com/en/anatomy/femur/) to [fibula](https://durgical.com/en/anatomy/fibula/); it keeps the knee from bending outward.

Official name: Fibular collateral ligament

[See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=lower_limb&select=lcl&side=r)

Opens in the Durgical app, no sign-up needed.

## What it is

A cord-like band on the outer side of the knee, from the femur to the head of the fibula.

## What it does

Keeps the knee from bending outward.

## Key points

- Varus stress at 30° isolates the LCL; opening also in full extension points to cruciate and posterolateral corner damage
- Main static stabilizers of the posterolateral corner: LCL, popliteus tendon and [popliteofibular ligament](https://durgical.com/en/anatomy/popliteofibular-ligament/)
- Isolated LCL tears are uncommon; most come with a posterolateral corner or cruciate injury
- The common fibular nerve winds round the fibular neck just below its insertion and can be injured with it

## Key facts

**Attaches**
Lateral epicondyle of femur to lateral surface of fibular head; separate from capsule and lateral meniscus

**Function**
Resists varus stress; limits external rotation of [tibia](https://durgical.com/en/anatomy/tibia/); part of posterolateral corner

**Tight in**
Knee extension; varus stress

## Relations

**Superficial**
[Biceps femoris tendon](https://durgical.com/en/anatomy/tendon-of-biceps-femoris/), which splits around the LCL as both insert on the fibular head

**Deep**
[Popliteus tendon](https://durgical.com/en/anatomy/tendon-of-popliteus/), passing between it and the [lateral meniscus](https://durgical.com/en/anatomy/lateral-meniscus/); the inferior lateral genicular artery runs between it and the capsule

**Behind**
[Common fibular nerve](https://durgical.com/en/anatomy/common-fibular-nerve/), behind the biceps tendon, heading for the fibular neck

**In front**
[IT band](https://durgical.com/en/anatomy/iliotibial-tract/) (iliotibial band) ending on Gerdy tubercle, and the anterolateral capsule

## How to find it

Seated with the leg crossed in a figure-of-four (ankle resting on the opposite knee), the ligament stands out as a firm, pencil-thick cord between the lateral femoral epicondyle and the fibular head, just in front of the biceps tendon.

## Examination

- Varus stress at 30°: lateral opening compared with the other knee means an LCL tear
- Varus stress at 0°: opening in full extension adds posterolateral corner and often cruciate injury
- Dial test: over 10° more external rotation than the other side at 30° points to the posterolateral corner
- External rotation recurvatum test: lifted by the big toes, the injured knee falls into hyperextension, varus and external rotation (posterolateral corner, often with a cruciate)

## On imaging

MRI: a thin dark band from the lateral epicondyle to the fibular head, seen across several posterior coronal slices because it runs obliquely. On X-ray, a small avulsion of the fibular head apex (arcuate sign) marks a posterolateral corner injury.

## Common problems

- Less often injured alone; usually from a blow to the inner side of the knee.
- Often part of an injury to the back-outer corner of the knee.

## How it is diagnosed

An exam test that gently pushes the knee outward (varus stress test). MRI.

## Treatment

- Mild injuries: brace and physical therapy.
- Severe or combined injuries: surgical repair or reconstruction.

## Clinical notes

- An unrecognised posterolateral corner injury is a classic cause of ACL or PCL graft failure
- Foot drop after a varus knee injury suggests common fibular nerve damage; ankle dorsiflexion and sensation on the dorsum of the foot are checked
- Anatomic posterolateral corner reconstruction rebuilds the LCL, popliteus tendon and popliteofibular ligament with grafts passed through the fibular head and lateral femur

## Test yourself

Think of the answer, then tap the question to see it.

## What are the attachments of the lateral collateral ligament (LCL)?

Lateral epicondyle of the femur to the lateral surface of the fibular head; it is separate from the capsule and the lateral meniscus.

## At what knee position does varus stress isolate the LCL?

At 30° of flexion. Opening also in full extension points to cruciate and posterolateral corner damage.

## What are the main static stabilizers of the posterolateral corner of the knee?

The LCL, the popliteus tendon and the popliteofibular ligament.

## What does foot drop after a varus knee injury with an LCL tear suggest?

Common fibular nerve damage: the nerve winds round the fibular neck just below the LCL insertion.

## Where is the LCL felt on examination?

In the figure-of-four position, as a firm, pencil-thick cord between the lateral femoral epicondyle and the fibular head, in front of the biceps tendon.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/fibular-collateral-ligament/)

Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
ligamentum collaterale fibulare TA2 1895

**Official Spanish (DeCS)**
Ligamento colateral fibular (peroneo) DeCS D017885

**English (TA2)**
Fibular collateral ligament

**Also called**
lateral collateral ligament of knee

## Related

- [Biceps femoris tendon](https://durgical.com/en/anatomy/tendon-of-biceps-femoris/)
- [Popliteus tendon](https://durgical.com/en/anatomy/tendon-of-popliteus/)
- [Popliteofibular ligament](https://durgical.com/en/anatomy/popliteofibular-ligament/)
- [IT band](https://durgical.com/en/anatomy/iliotibial-tract/)
- [Anterolateral ligament (ALL)](https://durgical.com/en/anatomy/anterolateral-ligament-of-knee/)
- [Femur](https://durgical.com/en/anatomy/femur/)
- [Fibula](https://durgical.com/en/anatomy/fibula/)

Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=31553); [Anatomy, Bony Pelvis and Lower Limb, Knee](https://www.ncbi.nlm.nih.gov/books/NBK500017/).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/anatomy/fibular-collateral-ligament/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/fibular-collateral-ligament/