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MPFL

Page 5.4.11 · Ultrasound of the Knee · imaging page

The medial patellofemoral ligament, thin and superficial, which suits ultrasound and rarely changes the plan.

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.

MPFL

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For Medical Students

What It Shows

The medial patellofemoral ligament runs from the medial femur to the medial patellar border and restrains lateral patellar translation. 2.12.2 covers the MPFL anatomy.

It is a thin superficial structure within easy reach of a high frequency probe. 5.2.7 covers the frequency selection.

It matters because it is the structure that fails in a patellar dislocation, and its femoral attachment is where failure most often occurs. 5.12.5 covers MPFL injury.

How It Is Acquired

Scan transversely across the medial patellar border and follow the ligament towards the femur. 2.12.2 covers the MPFL anatomy.

Identify the femoral attachment specifically, which is the commonest site of failure. 5.12.5 covers MPFL injury.

Keep the beam perpendicular, because the ligament is thin and anisotropic. 5.2.10 covers anisotropy.

Look at the adjacent retinaculum, which contributes to the same restraint. 2.12.4 covers the retinacula.

Apply a gentle lateral glide while scanning where the question is restraint. 5.4.14 covers patellar tracking.

What Normal Looks Like

A thin bright band running from the medial patella towards the femur. 2.12.2 covers the MPFL anatomy.

A clean femoral attachment without fluid. 5.12.5 covers MPFL injury.

An intact adjacent retinaculum. 2.12.4 covers the retinacula.

No excessive lateral patellar translation on a gentle glide. 5.4.14 covers patellar tracking.

What Abnormal Looks Like

Thickening or discontinuity of the band. 5.12.5 covers MPFL injury.

Fluid or disruption at the femoral attachment. 5.12.5 covers MPFL injury.

An avulsed fragment from the medial patellar border. 5.3.14 covers avulsion injuries.

Excessive lateral translation on a gentle glide, with the ligament not restraining. 5.4.14 covers patellar tracking.

Key Learning Points

  • The ligament restrains lateral patellar translation.
  • It is thin and superficial, within reach of a high frequency probe.
  • The femoral attachment is the commonest site of failure.
  • The adjacent retinaculum contributes to the same restraint.
  • A gentle lateral glide tests restraint during scanning.

MRCS Level

How It Is Acquired

In a viva this is the structure to name when asked what fails in a first patellar dislocation.

The expected points are the transverse approach, the femoral attachment, the perpendicular beam, the retinaculum, and the dynamic glide.

Say that the femoral attachment is where failure usually occurs. 5.12.5 covers MPFL injury.

Say that the decision in instability rests on the bony measurements rather than on this ligament. 5.16.4 covers the tuberosity to groove measurement.

Say that a magnetic resonance study gives the ligament and the bony anatomy together. 5.12.1 covers trochlear dysplasia.

What Abnormal Looks Like

The reasoning expected is that the ligament is the main passive restraint to lateral translation near extension, so its failure is what allows a dislocation rather than being a consequence of one. 3.12.5 covers the MPFL function.

The femoral attachment is where the strain concentrates, which is why it is the usual failure site. 2.12.2 covers the MPFL anatomy.

The ligament's state does not by itself determine treatment, because recurrence risk is driven by the bony anatomy the ultrasound cannot measure. 5.12.1 covers trochlear dysplasia.

That makes this a structure ultrasound images well and a question it does not answer. 5.16.4 covers the tuberosity to groove measurement.

How Good It Is

Ultrasound shows this ligament clearly and contributes little to the instability decision.

Its best contribution is confirming an acute femoral sided disruption, which is a structural finding available quickly. 5.12.5 covers MPFL injury.

It is limited because the operative decision depends on trochlear shape, patellar height and tuberosity position, none of which it measures. 5.16.4 covers the tuberosity to groove measurement.

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

Key Learning Points

  • The ligament is the main passive restraint to lateral translation near extension.
  • Its failure allows a dislocation rather than following one.
  • Strain concentrates at the femoral attachment.
  • Recurrence risk is driven by bony anatomy ultrasound cannot measure.
  • Imaged well, and the question is answered elsewhere.

FRCS Level

How Good It Is

At decision level this ligament's state is one input among several and not the decisive one.

An acute femoral sided disruption confirms the mechanism, which is useful in a first dislocation where the history is unclear. 5.12.5 covers MPFL injury.

The recurrence decision rests on trochlear dysplasia, patellar height and tuberosity position, which need cross sectional imaging. 5.12.1 covers trochlear dysplasia.

A medial patellar avulsion fragment is a direct finding that can be fixed. 5.3.14 covers avulsion injuries.

A dynamic glide examination adds a functional observation that no static study gives, and it is not a measurement. 5.4.14 covers patellar tracking.

Where It Misleads

The commonest error is treating the ligament's appearance as the instability assessment. 5.16.4 covers the tuberosity to groove measurement.

Anisotropy in the thin band is read as disruption. 5.2.10 covers anisotropy.

The retinaculum is confused with the ligament. 2.12.4 covers the retinacula.

A chronic appearance after a previous dislocation is read as an acute injury. 5.12.5 covers MPFL injury.

A dynamic glide impression is reported as a measurement. 5.4.14 covers patellar tracking.

Key Learning Points

  • The ligament's appearance is treated as the instability assessment.
  • Anisotropy in the thin band is read as disruption.
  • The retinaculum is confused with the ligament.
  • A chronic appearance is read as an acute injury.
  • A glide impression is reported as a measurement.

Fellowship Level

Where It Misleads

At fellowship level this is a structure ultrasound sees well in a condition whose decisions are made from bone.

Patellar instability surgery is planned from trochlear morphology, patellar height and tuberosity position, all measured on cross sectional imaging, so the ligament's appearance rarely alters the plan. 5.16.4 covers the tuberosity to groove measurement.

The ligament is also commonly abnormal after a previous dislocation without current symptoms, so an abnormal appearance carries little weight in the chronic setting. 5.12.5 covers MPFL injury.

Dynamic patellar assessment is the question the clinic actually has, and ultrasound can observe it without quantifying it, which is the same gap the skyline view left. 5.4.14 covers patellar tracking.

Dynamic magnetic resonance imaging quantifies tracking and is not routine, so the most relevant measurement remains unavailable in both modalities. 5.18.6 covers dynamic magnetic resonance imaging.

The honest position is that this page describes a structure well and that the decision lives in chapter 5.16. 5.1.3 covers choosing the correct investigation.

Key Learning Points

  • Instability surgery is planned from bony measurements.
  • The ligament is commonly abnormal after a previous dislocation.
  • Dynamic assessment can be observed without being quantified.
  • Dynamic magnetic resonance imaging quantifies tracking and is not routine.
  • The structure is described here and the decision lives elsewhere.

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.