Patellar Apprehension Test

For Medical Students

What It Tests

The patellar apprehension test displaces the patella laterally and looks for the patient's apprehension: a reflex guarding, a grab at the examiner's hand, or a statement that this is how it feels when it goes.

It is the only test in this section whose positive finding is a behaviour rather than a laxity, and that is both its strength and its weakness. 4.2.2 covers instability as a symptom.

What it establishes is that the patient recognises the direction of their instability, which is more specific for patellar instability than any measurement of patellar mobility. 4.15.4 covers the measurement.

How It Is Performed

Lay the patient supine with the knee extended and the quadriceps relaxed, and explain what you are about to do.

Place both thumbs on the medial border of the patella and displace it gently laterally.

Watch the patient's face and the quadriceps, and stop as soon as apprehension appears.

Flex the knee gently while maintaining the lateral pressure, since apprehension often appears in the first part of flexion as the patella is carried towards the groove.

Record what the patient did and said, rather than recording the test as positive. 4.1.8 covers the record.

What a Positive Means

Apprehension, guarding, or the patient stopping you indicates that the lateral displacement reproduces their symptom, which supports patellar instability.

A patient who says this is exactly how it feels when the knee goes has given the most useful version of the finding.

Discomfort without apprehension is not a positive test, and recording it as one converts a painful knee into an unstable one. 4.15.9 covers patellofemoral pain.

A negative test in a patient with documented dislocations does not exclude instability, because apprehension depends on the patient's confidence as much as on the anatomy. 4.2.22 covers the dislocation event.

Apprehension on medial displacement is unusual and suggests a previous reconstruction that is over constrained or a medial instability. 4.20.6 covers that assessment.

MRCS Level

How It Is Performed

In a viva this test rewards a candidate who explains it to the patient first and who stops at apprehension rather than pushing through it.

The expected points are the relaxed extended knee, the explanation, the thumbs on the medial border, watching the patient rather than the patella, and the gentle flexion.

Say that you would stop at apprehension, both because continuing is unkind and because the finding is already obtained.

Say that you would record the patient's words, since the specific statement is worth more than the label. 4.1.8 covers the record.

Say that you would perform the glide and tilt tests separately, because those measure the restraints and this one reads the symptom. 4.15.4 covers the glide.

What a Positive Means

The reasoning expected is that the medial patellofemoral ligament is the principal restraint to lateral patellar displacement near extension, so displacing the patella laterally loads it and reproduces the mechanism of dislocation. 2.12.2 covers the ligament.

Apprehension is a protective response to that mechanism being reproduced, which is why the finding is specific to instability rather than to pain. 3.12.8 covers patellar instability.

The response often appears in early flexion rather than in full extension, because that is where the patella is being carried across the lateral trochlear facet. 3.12.4 covers trochlear function.

A patient with a deficient ligament and an intact confidence can have a lax patella and no apprehension, which is why the test and the glide measure different things. 4.15.4 covers it.

How Good It Is

The apprehension test is the most specific clinical test for patellar instability, because the response is hard to produce in a patient who has never dislocated.

It is moderately sensitive and depends on the patient, so a negative result in a guarded or stoical patient is uninformative rather than reassuring.

It is more useful than any measurement of patellar mobility for the question of whether the instability is patellar, which is the question most often at stake. 4.15.4 covers the measurements.

It cannot grade the instability, which the number of episodes and the imaging do between them. 4.1.6 covers that relationship.

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 apprehension contributes to whether an instability complaint is patellar, and that is a diagnosis rather than a grade.

A patient with apprehension, a history of dislocation and a maltracking patella has patellar instability, and the operative decision rests on the imaging and the number of episodes rather than on this test. 4.15.2 covers the sign.

A patient with a complaint of giving way, no apprehension and a normal patellar examination is describing something else, and the cruciate and rotational assessments are where it will be found. 4.14.3 covers one of them.

A patient with apprehension and no documented dislocation has a subluxation pattern, which is a real diagnosis and a harder operative decision.

After surgery the loss of apprehension is a meaningful outcome and is more closely related to the patient's experience than any laxity measurement. 4.20.6 covers that assessment.

Where It Misleads

The commonest error is recording discomfort as apprehension.

The second is pushing through apprehension, which hurts the patient and adds nothing.

The third is reading a negative test as excluding instability.

The fourth is performing it without explaining it, which produces guarding that is not apprehension.

The fifth is recording the label rather than what the patient did and said.

Fellowship Level

Where It Misleads

In referred practice the apprehension test separates the two groups who present with patellar complaints and need opposite treatments.

A patient with apprehension and recurrent dislocations has a structural problem, and the assessment moves to the imaging and the bony factors. 4.15.8 covers dysplasia.

A patient with anterior pain, no apprehension and a normal glide has a load problem, and operating on the patella makes it worse. 4.15.9 covers patellofemoral pain.

A patient who remains apprehensive after a successful reconstruction, with a stable patella on examination, has a confidence problem, and that responds to rehabilitation rather than to revision. 4.22.6 covers the score built for that question.

A patient with apprehension on medial displacement after a reconstruction is over constrained, which is under recognised and is the complication most often attributed to something else. 4.20.6 covers the assessment.

In medicolegal work the recorded apprehension response is weak evidence, since it is a behaviour, and the recorded dislocation history is what carries an opinion. 4.23.7 covers that setting.