MPFL Assessment

For Medical Students

What It Tests

The medial patellofemoral ligament runs from the medial femoral epicondyle to the medial border of the patella, and it is the principal restraint to lateral patellar displacement in the first part of flexion. 2.12.2 covers its anatomy.

Assessing it means establishing whether the lateral glide is increased near extension and whether the patient recognises the direction of displacement. 4.15.4 covers the glide.

No test isolates the ligament. The assessment is the glide with the apprehension test and the tenderness over its course, read together. 4.15.3 covers the apprehension test.

How It Is Performed

Lay the patient supine with the knee extended and the quadriceps relaxed.

Palpate along the ligament's course, from the medial femoral epicondyle to the medial patellar border, noting tenderness and its position. 4.6.5 covers patellar tenderness.

Assess the lateral glide in quadrants, at full extension and at thirty degrees. 4.15.4 covers the grading.

Perform the apprehension test, watching the patient rather than the patella. 4.15.3 covers it.

Assess the tracking actively in sitting, since a deficient ligament contributes to a lateral deviation near extension. 4.15.1 covers tracking.

What a Positive Means

An increased lateral glide near extension with apprehension indicates a deficient medial patellofemoral ligament.

Tenderness along its course after a dislocation indicates an acute injury to it, and the position of the tenderness suggests where it tore. 4.2.22 covers the dislocation event.

An increased glide with no apprehension and no episodes indicates laxity rather than instability, and in a hypermobile patient it is a normal variant. 4.23.3 covers those patients.

A deficient ligament with trochlear dysplasia is a combined problem, and the bony abnormality is usually the dominant one. 4.15.8 covers dysplasia.

A normal glide in a patient with recurrent dislocations raises the question of whether the instability is patellar at all, or whether the examination is being performed with the quadriceps contracted. 4.15.4 covers that trap.

MRCS Level

How It Is Performed

In a viva the expected answer says the ligament cannot be isolated and then gives the three findings that together assess it.

The expected points are the palpation along its course, the glide at two angles, the apprehension test, and the active tracking.

Say that its contribution is greatest in the first part of flexion and falls as the trochlea engages, which is why the glide is tested at two angles. 3.12.5 covers its function.

Say that you would assess the bony factors, because a reconstruction into a dysplastic knee with patella alta has a worse result and that is the decision the examination feeds. 4.15.8 covers dysplasia.

Say that you would record the glide in quadrants and the apprehension in the patient's words. 4.1.8 covers the record.

What a Positive Means

The reasoning expected is that the ligament provides most of the soft tissue restraint to lateral displacement in the first part of flexion, and almost none beyond that, where the trochlea takes over. 3.12.5 covers its function.

That division is why a deficient ligament produces instability near extension specifically, which matches the arc in which patients describe the patella going. 3.12.8 covers patellar instability.

The ligament tears when the patella dislocates laterally, which is why the medial tenderness is the characteristic acute finding and why its position indicates the site of the tear. 2.12.6 covers the surgical anatomy.

Where the trochlea is dysplastic the ligament is carrying restraint over a wider arc than it was designed for, which is the mechanical argument for addressing the bone. 3.12.4 covers trochlear function.

How Good It Is

The assessment is reliable for establishing lateral laxity and cannot confirm the ligament specifically, which is an anatomical limit rather than a technical one.

Magnetic resonance imaging identifies the ligament and the site of its tear, and this is a clear case where imaging adds a diagnosis the examination suspects. 4.1.6 covers that relationship.

The apprehension test contributes the specificity and the glide contributes the measurement, and neither alone is enough. 4.15.3 covers the first.

The examination remains the better guide to whether the laxity matters, which is the division this whole section keeps describing. 4.15.4 covers the measurement.

No figures appear for any accuracy comparison on this page, under decision 023, and the comparison is the claim being made.

FRCS Level

How Good It Is

At decision level the assessment contributes to whether a reconstruction is offered and, with the imaging, to whether it is offered alone.

A deficient ligament with recurrent dislocations, a normal trochlea and a normal patellar height is the group in which a reconstruction alone has the best case. 4.15.8 covers the factors that weaken it.

A deficient ligament with dysplasia, patella alta or marked malrotation is the group in which a reconstruction alone most often fails, and the examination plus the imaging identifies it. 4.5.6 covers rotational alignment.

An acutely torn ligament after a first dislocation is a different decision, and the number of episodes and the presence of an osteochondral fragment weigh more than the ligament itself. 4.2.22 covers the event.

After reconstruction the glide is the measure of whether the graft holds, and an over tight graft presents as medial pain and stiffness. 4.20.6 covers that assessment.

Where It Misleads

The commonest error is assessing the glide with the quadriceps contracted.

The second is treating increased laxity as instability in a patient with no apprehension and no episodes.

The third is attributing instability to the ligament without assessing the bony factors.

The fourth is reading medial tenderness months after a dislocation as an acute finding.

The fifth is reconstructing the ligament in a knee whose dominant problem is the trochlea. 4.15.8 covers it.

Fellowship Level

Where It Misleads

In referred practice this assessment is usually being performed on a knee that has already had a reconstruction, and the question is which way it has failed.

A patient with an increased lateral glide and recurrent instability after a reconstruction has a stretched or failed graft, and the bony factors need re-examining before another soft tissue attempt. 4.15.8 covers them.

A patient with a reduced glide in both directions, medial facet pain and stiffness is over constrained, which is the complication most often attributed to something else. 4.6.5 covers patellar tenderness.

A patient with a technically sound reconstruction, a stable patella and persisting apprehension has a confidence problem rather than a mechanical one, and further surgery worsens it. 4.22.6 covers the score for that question.

In a hypermobile patient a graft tensioned to the contralateral glide reproduces the laxity, so the target has to be chosen deliberately and recorded. 4.23.3 covers those patients.

In medicolegal work the recorded medial tenderness at the time of a dislocation is useful evidence that one occurred, and it is one of the few findings here that carries weight. 4.23.7 covers that setting.