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# Arcuate popliteal ligament

The arcuate popliteal ligament is a curved band that reinforces the back of the knee capsule on its outer side.

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## What it is

A curved band over the back of the knee capsule, outer side.

## What it does

Reinforces the back-outer corner of the joint.

## Key points

- Y-shaped thickening of the posterolateral capsule that arches over the popliteus tendon where it leaves the joint
- Grouped with the LCL, popliteus tendon and fabellofibular ligament as the arcuate complex (texts list its members differently)
- Avulsion of the fibular head apex, where these structures attach, is the arcuate sign of a posterolateral corner injury

## Key facts

**Attaches**
Apex of fibular head, arching over popliteus tendon to posterior capsule and posterior intercondylar area

**Function**
Reinforces posterolateral capsule; part of posterolateral corner

**Tight in**
Knee extension

## Relations

**Deep**
[Popliteus tendon](https://durgical.com/en/anatomy/tendon-of-popliteus/), which passes under its arch, and the posterior horn of the [lateral meniscus](https://durgical.com/en/anatomy/lateral-meniscus/)

**Behind**
[Lateral head of gastrocnemius](https://durgical.com/en/anatomy/lateral-head-of-gastrocnemius/)

**Below**
Apex (styloid process) of the fibular head

## How to find it

Not palpable: it lies under the lateral head of gastrocnemius at the back of the outer knee. Follow the biceps tendon down to the fibular head, whose apex anchors it; at surgery it is seen arching over the popliteus tendon once gastrocnemius is drawn aside.

## Examination

- Dial test: more than 10° of extra external rotation of the foot compared with the other side at 30° of flexion suggests a posterolateral corner injury; at both 30° and 90°, PCL injury as well
- External rotation recurvatum test: lifting both legs by the big toes, the injured knee falls into hyperextension, varus and external rotation; this suggests posterolateral corner injury, often with a cruciate tear

## On imaging

Rarely seen clearly on routine MRI; thin posterior coronal slices may show it over the [popliteus](https://durgical.com/en/anatomy/popliteus-muscle/). On an AP knee X-ray, a small elliptical flake beside the fibular head apex (arcuate sign) is the clue to its avulsion.

## Clinical notes

- Torn in posterolateral corner injuries; surgery usually rebuilds the LCL, popliteus tendon and [popliteofibular ligament](https://durgical.com/en/anatomy/popliteofibular-ligament/) rather than this ligament itself
- A posterolateral corner injury left untreated can cause a varus thrust when walking and lasting instability, which is harder to correct later

## Anatomical variants

- Inconstant: when a fabella is present the fabellofibular ligament tends to be well developed and the arcuate ligament small, and the reverse when it is absent

## Test yourself

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

## Which tendon does the arcuate popliteal ligament arch over?

The popliteus tendon, where it leaves the knee joint; the ligament is a Y-shaped thickening of the posterolateral capsule.

## What is the arcuate sign on a knee X-ray?

A small flake avulsed from the apex of the fibular head, marking a posterolateral corner injury.

## How does a fabella relate to the size of the arcuate popliteal ligament?

When a fabella is present the fabellofibular ligament is well developed and the arcuate ligament small; the reverse when it is absent.

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

## Its names

**Official Latin (TA2)**
ligamentum popliteum arcuatum TA2 1900

**Official Spanish (DeCS)**
Ligamento poplíteo arqueado

**English (TA2)**
Arcuate popliteal ligament

## Related

- [Femur](https://durgical.com/en/anatomy/femur/)
- [Fibula](https://durgical.com/en/anatomy/fibula/)
- [Tibia](https://durgical.com/en/anatomy/tibia/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Bony Pelvis and Lower Limb: Popliteal Region](https://www.ncbi.nlm.nih.gov/books/NBK532891/); [Anatomy, Bony Pelvis and Lower Limb, Knee](https://www.ncbi.nlm.nih.gov/books/NBK500017/); Anatomy of the Human Body (20th ed.): Surface Anatomy of the Lower Extremity (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.

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Representative model, for educational purposes only.

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