External Rotation Recurvatum Test

For Medical Students

What It Tests

The external rotation recurvatum test looks for the knee falling into hyperextension with the tibia rotating externally when the leg is lifted by the foot.

The posterolateral corner resists hyperextension and external rotation, so its loss allows both to happen at once under nothing more than the weight of the limb. 3.10.6 covers the corner.

It is the lateral equivalent of the posterior sag sign in one respect: gravity supplies the force and the examiner only has to look. 4.11.1 covers that parallel.

How It Is Performed

Lay the patient supine with both legs straight and relaxed, and stand at the foot of the couch.

Lift each leg in turn by the great toe, or by the toes, allowing the knee to hang.

Watch the knee rather than the foot, and look for the knee dropping into hyperextension and the tibia rotating externally.

Compare the two sides in the same way, with the same grip and the same lift.

Note the amount of hyperextension and whether the tibial tubercle rotates laterally, because the rotation is the part that distinguishes this from simple hyperextension.

What a Positive Means

Hyperextension with external rotation of the tibia on the affected side indicates a posterolateral corner injury.

Hyperextension alone, symmetrical on both sides, is physiological and not a finding. 4.23.3 covers hypermobile patients.

A positive test usually indicates a substantial corner injury rather than a subtle one, so it is specific and insensitive.

A positive test in a knee with an anterior cruciate rupture suggests the two are combined, and that combination makes the pivot shift larger and the reconstruction more demanding. 4.14.1 covers the pivot shift.

The test does not grade the injury and does not localise within the corner, so it prompts the full corner assessment rather than replacing it. 4.13.4 covers that sequence.

MRCS Level

How It Is Performed

In a viva this test is a good thing to mention and a poor thing to lead with, and knowing that order is part of the answer.

The expected points are the supine relaxed position, lifting by the great toe, watching the knee, the external rotation of the tibia, and the comparison.

Say that you would look at the standing alignment as well, because a knee that hyperextends lying often has a recurvatum deformity standing, and the two findings belong together. 4.11.5 covers dynamic assessment.

Say that you would perform the dial test, which is the assessment the corner diagnosis rests on. 4.13.5 covers it.

Say that a positive test raises the question of a common peroneal nerve injury, as any corner finding does. 4.11.7 covers that sequence.

What a Positive Means

The reasoning expected is that the posterolateral structures tighten in extension, so they are the restraint to hyperextension, and their loss lets the knee pass into it. 3.10.6 covers the corner.

The same structures resist external rotation, which is why the two movements appear together rather than separately. 3.10.2 covers external rotation stability.

The cruciates contribute to resisting hyperextension, so a positive test in a knee with a cruciate injury is a larger injury than a positive test alone.

A knee with a positive test and an increased dial difference at thirty degrees only has an isolated corner injury, and the dial test is what says so. 4.13.5 covers the pattern.

How Good It Is

The test is the most specific corner finding and the least sensitive, which makes it a useful confirmation and a poor screen.

A clearly positive asymmetric result is close to diagnostic of a corner injury. A negative result excludes almost nothing.

It is more reproducible than the reverse pivot shift and less informative than the dial test, so it sits between the two in the assessment. 4.13.5 covers the dial test.

It is readable in the acute knee, which most corner tests are not, because it does not require flexion or a tolerated force. That makes it the corner test most likely to be positive in an emergency department. 4.13.4 covers the full assessment.

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 this test contributes a severity impression rather than a decision, and it contributes it early.

A positive test in an acute knee is often the first indication that the lateral side is substantially injured, at a point where the dial test cannot be performed because of pain. That is the test's real value.

It also contributes to the question of whether a knee was dislocated, since gross recurvatum with external rotation belongs to a high energy injury. 4.11.7 covers that assessment.

Where a recurvatum deformity is present standing, the decision moves towards alignment and bony correction alongside any soft tissue work, and that is a different operation from a corner reconstruction.

In the chronic knee a recurvatum that has developed over years indicates progressive stretching of the corner, and that trajectory is an argument for reconstruction that a single reading is not.

Where It Misleads

The commonest error is reading symmetrical hyperextension as a positive test.

The second is lifting by the ankle rather than the toe, which supports the tibia and prevents the rotation the test is looking for.

The third is reading the hyperextension and not the rotation, which turns a corner test into a hypermobility observation.

The fourth is relying on a negative result, which is uninformative.

The fifth is finding it positive and not performing the dial test, since the operation is planned from the dial test rather than from this. 4.13.5 covers it.

Fellowship Level

Where It Misleads

In referred practice a positive test is usually found in a knee that has had a corner reconstruction, and it means the reconstruction has stretched.

That finding is more useful than the dial test for the specific question of whether a corner reconstruction has failed over time, because it is easy to reproduce identically at successive visits. 4.13.4 covers the assessment.

A recurvatum deformity that was present before the operation and persists after it is usually a bony problem that was not addressed, and the soft tissue reconstruction was never going to hold it.

In a knee with hyperextension from a previous tibial osteotomy the test is abnormal for a reason unrelated to the corner, and the operation note is what distinguishes them.

A patient with genu recurvatum from a childhood growth disturbance has a bilateral finding that is not ligamentous, and the examination of the other knee settles it in one movement. 4.23.3 covers the comparison.

In medicolegal work a recorded positive test at the time of injury is useful evidence of a corner injury, because the test is hard to produce in a normal knee and easy to describe accurately. 4.23.7 covers that setting.