Rotational Instability

For Medical Students

What It Tests

Rotational instability is the tibia rotating abnormally under the femur, rather than sliding forwards.

It is what a patient means when they say the knee gives way on a turn, and it is what the anterior cruciate and the anterolateral structures resist together. 3.7.7 covers rotational stability.

This page exists because the gap between what this chapter's tests measure and what the patient complains about is wider here than anywhere else on the site.

The translation tests are good and the rotational tests are either insensitive or unobtainable awake, so a knee can test well and still be rotationally unstable.

How It Is Performed

The pivot shift is the primary rotational test and is the one that reproduces the symptom. 4.10.6 covers it.

The Slocum test adds rotation to the anterior drawer and assesses the anteromedial and anterolateral structures. 4.14.2 covers it.

The dial test assesses external rotation at two flexion angles and separates an isolated posterolateral injury from a combined one. 4.13.5 covers it.

Dynamic assessment shows rotational control under load, which the static tests cannot. 4.10.8 covers it.

Perform all of them, record each with its angle, and accept that an awake examination may not settle the question. 4.1.8 covers the record.

What a Positive Means

A positive pivot shift indicates rotational instability and corresponds closely to the patient's complaint.

A high grade pivot shift suggests an anterolateral or lateral side injury alongside the cruciate rather than a worse cruciate injury. 4.14.3 covers the pattern.

External rotation increased at thirty degrees and not at ninety suggests an isolated posterolateral injury; increased at both suggests a combined one with the posterior cruciate. 4.13.4 covers the corner.

A normal translation examination with a convincing rotational history means the rotational component has not been demonstrated rather than that it is absent.

That last statement is the most important one on the page.

MRCS Level

What a Positive Means

The reasoning expected is that the anterior cruciate restrains rotation as well as translation, and does not do so alone.

The anterolateral structures contribute to rotational restraint, which is why a cruciate injury with a lateral component produces a larger pivot shift than a cruciate injury alone. 3.11 covers the anterolateral complex.

That is also why a reconstruction that controls translation can leave rotation uncontrolled, which is the mechanical basis for the lateral augmentation argument. 3.17.5 covers that argument and why it is unsettled.

The posterolateral structures restrain external rotation, so external rotation laxity points there rather than at the cruciate. 4.13.4 covers the assessment.

So rotational instability is a family of findings rather than one, and naming which plane and which angle is what makes a record useful.

How Good It Is

The examination's performance for rotation is the weakest part of the knee assessment, and that is the honest summary.

The pivot shift is specific and insensitive awake and is the best available test.

Guarding abolishes it, so the test that matters most is the one least likely to be obtainable in clinic. 4.10.6 covers the problem.

Under anaesthesia the rotational assessment becomes reliable, which is the main argument for performing one. 4.10.10 covers it.

Imaging does not assess rotational laxity, so there is no alternative instrument, and that is why this gap persists. No figures appear, under decision 023.

FRCS Level

How Good It Is

At decision level this gap produces the two commonest failures in anterior cruciate practice, and both are avoidable in principle.

The first is a reconstruction performed without the rotational state ever being assessed, so a residual rotational complaint afterwards cannot be dated or attributed.

The second is a residual rotational complaint attributed to a stretched graft when the lateral structures were never addressed. 4.10.12 covers revision assessment.

The practical response is to record the rotational assessment before every reconstruction, including recording that it could not be obtained, and to perform an examination under anaesthetic where the answer would change the operation.

Whether to add a lateral procedure on the strength of a high grade pivot shift is a genuine balance, and 3.17.5 sets out why it is the least settled in that chapter.

Where It Misleads

The commonest error is recording a negative awake pivot shift as rotational stability.

The second is leaving the rotational assessment blank, which is indistinguishable in a record from a normal result. 4.1.8 covers the distinction.

The third is testing anterior translation and concluding about stability, which conflates two different findings and is the error this whole page exists to name.

And attributing a rotational complaint after reconstruction to the graft without considering that the lateral structures were never assessed.

Fellowship Level

Where It Misleads

This page is the chapter's conclusion and it is worth stating plainly: the anterior cruciate examination is the best performing examination in the knee for the wrong variable.

It measures translation accurately, translation is not the complaint, and the test that measures the complaint is abolished by the patient being awake.

Almost every dissatisfied reconstruction in referred practice sits in that gap, either as an unaddressed rotational component or as an undocumented pre-operative rotational state.

The available responses are all partial: perform the pivot shift and accept its insensitivity, perform an examination under anaesthetic and accept its cost, and record the rotational assessment properly so the next clinician can date a complaint.

The honest teaching point is that this field's best examination has a known blind spot, that the blind spot is where its failures cluster, and that no current instrument closes it.

No figure here supports that claim, under decision 023.