Joints and ligaments · Lower limb
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 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, which passes under its arch, and the posterior horn of the lateral meniscus
- Behind
- 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. 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 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.
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
Sources: Terminologia Anatomica (TA2); Anatomy, Bony Pelvis and Lower Limb: Popliteal Region; Anatomy, Bony Pelvis and Lower Limb, Knee; 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.
