LCL Injuries

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Student MRCS FRCS Fellow

For Medical Students

What It Shows

The lateral collateral ligament runs from the lateral femoral epicondyle to the fibular head and resists varus. 2.10.1 covers the LCL.

It appears on coronal images as a thin cord separate from the capsule, crossing the joint to the fibula. 5.5.9 covers the ligaments.

It matters because it is the most reliably visualised of the lateral structures, which makes its injury the signal to look at the rest. 2.10.4 covers the posterolateral corner.

How It Is Acquired

Assess it on coronal images through the fibular head. 5.5.9 covers the ligaments.

Follow it across slices to both attachments. 2.10.1 covers the LCL.

Assess the fibular head for avulsion at the attachment. 2.3.2 covers the attachments.

Assess the other lateral structures in the same read. 5.10.3 covers PLC injuries.

Assess the cruciates, since combined injury is the usual pattern. 5.7.3 covers complete tears.

What Normal Looks Like

A thin continuous low signal cord from the epicondyle to the fibular head. 2.10.1 covers the LCL.

Separation from the capsule along its course. 5.5.9 covers the ligaments.

An intact fibular head with no marrow change. 5.13.1 covers bone marrow oedema.

A normal popliteus tendon running deep to it. 2.10.2 covers the popliteus tendon.

What Abnormal Looks Like

Discontinuity, or a wavy lax contour. 5.5.9 covers the ligaments.

Avulsion from the fibular head, sometimes carrying a bone fragment. 2.3.2 covers the attachments.

Avulsion from the femoral epicondyle. 2.10.1 covers the LCL.

Marrow change at either attachment. 5.13.1 covers bone marrow oedema.

Injury of the other lateral structures alongside it. 5.10.3 covers PLC injuries.

Key Learning Points

The ligament runs epicondyle to fibular head and resists varus.
It is the most reliably seen lateral structure.
Its injury should start a search rather than end one.
An avulsion can carry a bone fragment.
An isolated injury here is uncommon.

MRCS Level

How It Is Acquired

In a viva the expected answer treats the finding as the start of a search.

The expected points are the coronal images, both attachments, the fibular head, the other lateral structures, and the cruciates.

Say that an isolated injury is uncommon. 5.10.3 covers PLC injuries.

Say that the clinical grade comes from the varus examination. 4.13.1 covers the varus stress test.

Say that the fibular head is part of the ligament's assessment. 2.3.2 covers the attachments.

What Abnormal Looks Like

The reasoning expected is that the ligament is one of several structures resisting varus and rotation, so damage to it means the force exceeded what that group tolerates. 3.10.1 covers the varus stability.

Varus laxity at full extension is a clinical measurement with no imaging equivalent. 4.13.2 covers the LCL assessment.

A fibular avulsion is a ligament injury carrying bone, so the report should name the ligament. 5.3.15 covers Segond fractures.

Chronic injury appears thickened or absent rather than oedematous, so the interval changes the appearance. 5.5.9 covers the ligaments.

How Good It Is

Magnetic resonance imaging is a reliable test of this ligament and tells you nothing about the knee's varus stability.

Its best contribution is the continuity, the site and the fibular attachment. 2.10.1 covers the LCL.

It is limited because stability is clinical, because an isolated finding here is rarely the whole injury, and because the chronic appearance misleads. 4.13.1 covers the varus stress test.

No figures appear for accuracy on this page, under decision 028, and no laxity values or grading thresholds appear either: those are clinical grades with published definitions and this environment cannot check them.

Key Learning Points

The ligament is one of several varus restraints.
Varus laxity at extension has no imaging equivalent.
An avulsion is a ligament injury carrying bone.
The interval changes the appearance.
An isolated finding is rarely the whole injury.

FRCS Level

How Good It Is

At decision level the question is whether this is an isolated injury or part of a corner injury. 2.10.4 covers the posterolateral corner.

An isolated injury with varus laxity only at extension is managed differently from a corner injury. 4.13.2 covers the LCL assessment.

A fibular styloid avulsion implies the deeper structures. 5.10.4 covers the popliteofibular ligament.

A cruciate injury alongside changes the operation entirely. 3.10.9 covers the combined PCL and PLC injury.

Alignment belongs in the plan for a chronic lateral injury. 5.3.6 covers the long leg alignment films.

Where It Misleads

The commonest error is reporting this ligament and stopping. 5.10.3 covers PLC injuries.

The ligament is confused with the biceps tendon on coronal images. 2.10.5 covers the biceps femoris.

A chronic absent ligament is reported as normal because no oedema is present. 5.5.9 covers the ligaments.

A fibular avulsion is reported as a fracture without naming the attachment. 2.3.2 covers the attachments.

Laxity is inferred from the appearance. 4.13.1 covers the varus stress test.

Key Learning Points

Reporting the ligament and stopping is the error.
The biceps tendon is mistaken for it.
A chronic absent ligament reads as normal.
An avulsion should name the attachment.
Laxity cannot be inferred from the appearance.

Fellowship Level

Where It Misleads

At fellowship level the lateral side arrives reported as a sprain of this ligament and the referral is about rotation. 3.10.2 covers the external rotation stability.

The structures that carry rotation are deeper and smaller, and their absence from the report carries no information. 5.10.4 covers the popliteofibular ligament.

A chronic lateral injury with varus alignment loads the reconstruction before it is made. 5.17.4 covers the osteotomy.

An examination under anaesthesia answers what the scan cannot and is recorded in a different vocabulary. 4.13.5 covers the dial test.

Ultrasound can assess this ligament dynamically and is operator dependent. 5.4.10 covers the LCL.

The useful report gives the continuity, the site, the fibular head, every other lateral structure, and the cruciates. 5.20.1 covers structured reporting.

Key Learning Points

The rotational structures are deeper and smaller.
Their absence from a report carries no information.
Varus alignment loads a lateral reconstruction.
The examination and the scan use different vocabularies.
The report should list every lateral structure.

Explore Further

Where this topic came from and where it goes next in the spiral.

References

No reference list is attached to this draft. Evidence verification has not run, because source retrieval was unavailable at generation time. Under the Operations Handbook a missing reference is acceptable and an invented one is a critical failure, so nothing has been cited and no citation marker appears in the text. This page carries no diagnostic accuracy figure, which is decision 028 rather than an omission: the comparative standing of the modalities is standard teaching and a specific sensitivity written from memory is the same class of claim as an invented citation, so ACC-001 refuses the number and the page states the comparison. A reviewer with the literature can add the figures into How Good It Is without restructuring the page. Any measurement here, including a sequence parameter, an angle or a millimetre, is written from standard teaching, has not been checked, and is registered under decision 006 in pipeline/config/figures with a verification state of UNVERIFIED_FROM_MEMORY.

Safety. KneeSchool is educational and does not give individual medical advice. Seek urgent assessment for a knee that cannot bear weight after an injury, a hot swollen knee with a fever, or new numbness, weakness or coldness in the leg or foot.