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Medial Knee

Page 5.4.2 · Ultrasound of the Knee · imaging page

The medial structures in layers, which ultrasound separates better than it is usually credited for.

Pipeline status. Editorial draft. Evidence verification did not run. Not consultant reviewed. Not for clinical use.

The same topic at 4 depths

Each tier deepens the one below it and never repeats it. Choose the level you want.

Medial Knee

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For Medical Students

What It Shows

The medial side holds the superficial and deep collateral layers, the meniscocapsular junction and the medial tendons. 2.9.1 covers the superficial collateral anatomy.

Those layers are shallow and stacked, so a high frequency probe separates them. 5.2.7 covers the frequency selection.

It matters because the layered structure is what grading a medial injury depends on, and ultrasound shows the layers directly. 5.9.3 covers deep medial collateral injuries.

How It Is Acquired

Scan in the coronal plane along the collateral fibres, from femur to tibia. 2.9.1 covers the superficial collateral anatomy.

Identify the superficial layer, the deep layer and the meniscus between them, which is the sequence to recognise. 2.9.2 covers the deep collateral anatomy.

Apply gentle valgus while scanning where laxity is the question, which is a dynamic examination. 5.4.15 covers dynamic instability.

Keep the beam perpendicular, since the collateral is parallel fibred and anisotropic. 5.2.10 covers anisotropy.

Scan the posteromedial corner separately, which is a different structure group. 2.9.4 covers the posteromedial corner.

What Normal Looks Like

A thin bright superficial collateral band running femur to tibia. 2.9.1 covers the superficial collateral anatomy.

A deep layer attaching to the meniscus, separated from the superficial band. 2.9.2 covers the deep collateral anatomy.

A meniscal body appearing as a homogeneous triangle at the periphery. 5.6.1 covers the normal meniscus.

No fluid between the layers. 5.5.12 covers the bursa.

What Abnormal Looks Like

Thickening and loss of the collateral band's fibrillar pattern. 5.9.2 covers medial collateral sprains.

Fluid between the superficial and deep layers, indicating a deep injury. 5.9.3 covers deep medial collateral injuries.

A discontinuity in the band, indicating a complete tear. 5.9.2 covers medial collateral sprains.

Separation at the meniscocapsular junction, which is visible from this approach. 5.6.10 covers ramp lesions.

Key Learning Points

  • The medial side is layered and ultrasound separates the layers.
  • Superficial band, deep layer and meniscus are the sequence to recognise.
  • Valgus applied during scanning makes the examination dynamic.
  • The collateral is parallel fibred, so anisotropy applies.
  • The posteromedial corner is a separate structure group.

MRCS Level

How It Is Acquired

In a viva this is the region to name when asked where ultrasound can grade a ligament injury.

The expected points are the coronal plane, the layer sequence, the dynamic valgus, the perpendicular beam, and the posteromedial corner.

Say that the layer involved is what grades a medial injury. 5.9.3 covers deep medial collateral injuries.

Say that the dynamic examination is the part no static study offers. 5.4.15 covers dynamic instability.

Say that a magnetic resonance study assesses the rest of the knee at the same time. 5.5.1 covers the standard protocol.

What Abnormal Looks Like

The reasoning expected is that the superficial and deep layers restrain differently, so the layer that failed determines the laxity pattern and therefore the grade. 2.9.2 covers the deep collateral anatomy.

Fluid between the layers indicates the deep layer has separated, which is the distinction that changes the injury's significance. 5.9.3 covers deep medial collateral injuries.

Applying valgus while watching shows whether the structure restrains, which is a functional observation rather than a structural one. 4.12.1 covers valgus stress testing.

The meniscocapsular junction is visible here, which makes ultrasound one of the few ways to look at it directly without arthroscopy. 5.6.10 covers ramp lesions.

How Good It Is

Ultrasound of the medial knee grades a collateral injury well and leaves the rest of the knee unexamined.

Its best contribution is the layer by layer assessment combined with a dynamic valgus examination. 5.9.3 covers deep medial collateral injuries.

It is limited because a medial injury rarely occurs alone, and the associated cruciate and meniscal injuries are out of reach. 5.7.4 covers the acute cruciate injury.

No figures appear for accuracy on this page, under decision 028, and no laxity or thickness measurements appear either: those are published quantities and this environment cannot check them.

Key Learning Points

  • The superficial and deep layers restrain differently.
  • The layer that failed determines the laxity pattern and the grade.
  • Fluid between the layers indicates deep separation.
  • Valgus during scanning is a functional observation.
  • A medial injury rarely occurs alone and the rest is out of reach.

FRCS Level

How Good It Is

At decision level a medial ultrasound answers a focused question and should not be the only study after a significant injury.

An isolated collateral injury in a knee with a normal cruciate examination is the case where ultrasound is sufficient. 4.12.1 covers valgus stress testing.

A deep layer injury or a posteromedial corner injury changes whether the injury is managed non-operatively. 5.9.5 covers posteromedial corner injuries.

A dynamic examination under valgus contributes where the static grade is equivocal. 5.4.15 covers dynamic instability.

Any suspicion of a combined injury makes magnetic resonance imaging the study, because the cruciate and meniscus decide the plan. 5.7.4 covers the acute cruciate injury.

Where It Misleads

The commonest error is accepting an isolated medial diagnosis without assessing the cruciate. 5.7.4 covers the acute cruciate injury.

Anisotropy in the collateral is read as a sprain. 5.2.10 covers anisotropy.

Fluid between layers is missed because only the superficial band was followed. 5.9.3 covers deep medial collateral injuries.

The posteromedial corner is not examined. 5.9.5 covers posteromedial corner injuries.

A collateral scanned without tension is reported as lax. 5.4.15 covers dynamic instability.

Key Learning Points

  • An isolated medial diagnosis is accepted without a cruciate assessment.
  • Anisotropy is read as a sprain.
  • Fluid between layers is missed by following only the superficial band.
  • The posteromedial corner goes unexamined.
  • An untensioned collateral is reported as lax.

Fellowship Level

Where It Misleads

At fellowship level the medial knee is where ultrasound's unique dynamic capability meets its inability to see the rest of the joint.

Grading a collateral injury by layer is genuinely better done here than on a static magnetic resonance study, and the injury almost never occurs in isolation, so the better tool answers the smaller part of the question. 5.9.3 covers deep medial collateral injuries.

The meniscocapsular junction is visible from this approach, which matters because that lesion is the one magnetic resonance imaging detects least reliably, and nobody has established whether ultrasound does better. 5.6.10 covers ramp lesions.

Dynamic valgus assessment has no agreed protocol or measurement, so it is a qualitative impression recorded as a finding. 5.4.15 covers dynamic instability.

Stress ultrasound has been proposed as a way to quantify laxity and remains outside routine practice, which leaves the quantitative question to the examination. 4.12.1 covers valgus stress testing.

The defensible use is a focused medial question in a knee whose cruciate and meniscus have already been accounted for. 5.1.3 covers choosing the correct investigation.

Key Learning Points

  • Layer grading is better here than on a static study.
  • The injury rarely occurs in isolation, so the better tool answers less.
  • The meniscocapsular junction is visible and the comparison is unstudied.
  • Dynamic valgus assessment has no agreed protocol or measurement.
  • Use it for a focused question in an otherwise accounted for knee.

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.

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