Pivot Shift Control

For Medical Students

The Principle

If one structure's loss allows a motion and another structure limits how far it goes, the two have different roles in the same event.

The first determines whether the event happens. The second determines its size.

Grading an event therefore tells you about the second structure once the first is known to be gone.

At the Knee

The pivot shift is a subluxation of the lateral tibia near extension followed by a reduction as the knee flexes. 3.7.9 covers the mechanics.

Losing the anterior cruciate is what allows the subluxation. 3.7.2 covers primary restraint.

The anterolateral structures limit how far the lateral tibia subluxates, so their state sets the grade. 2.11.5 covers the complex.

That is why a high grade pivot shift suggests anterolateral injury in addition to the cruciate, rather than a worse cruciate injury.

What Changes It

Anterolateral complex integrity, which sets the grade.

Lateral meniscus posterior horn status, which also restrains the subluxation. 3.6.5 covers meniscal load sharing.

Bony shape, since a convex lateral plateau and a steep slope allow more subluxation. 3.13 covers alignment.

Muscle guarding, which prevents the event in an awake patient.

Clinical Relevance

Grading the pivot shift is informative about what else is injured, which is why the grade is recorded. Section 4 covers the tests.

A high grade is one of the indications for adding a lateral procedure to a cruciate reconstruction. 3.11.7 covers the tenodesis.

A residual pivot shift after reconstruction suggests the anterolateral restraint was not restored. 3.11.8 covers the combined reconstruction.

The patient's symptom is this event, which is why abolishing it matters.

MRCS Level

The Principle

The pivot shift is a coupled motion, so its magnitude depends on every structure restraining either component. 3.2.9 covers coupling.

That makes the grade a composite measure rather than a test of one structure, which is both its clinical value and its measurement weakness.

Reading it as a composite is the way to use it: a high grade narrows the possibilities rather than naming a structure.

At the Knee

Conventional teaching grades the pivot shift one to three: a glide, a clunk, and a knee that subluxates and does not reduce.

Sectioning the anterolateral structures in a cruciate deficient knee increases the simulated pivot shift measurably, which is the quantitative basis for the grade's interpretation. 3.11.3 covers the structures.

Lateral meniscal posterior horn sectioning does the same, so a high grade can reflect meniscal rather than anterolateral injury. 6.35 covers ramp lesions as the medial equivalent.

Increased posterior tibial slope and a convex lateral plateau increase the subluxation for the same structural state. 3.13 covers alignment.

What Changes It

Anterolateral and lateral meniscal integrity.

Slope and lateral plateau morphology.

Guarding, which suppresses the event.

Examiner technique, which is a recognised source of variation.

How It Is Measured

Graded clinical examination is the standard and has modest inter observer reliability.

Instrumented measurement quantifies the reduction without an agreed threshold.

Robotic simulation applies a combined load and measures the coupled motion in cadavers.

Examination under anaesthetic is where the grade is most reliably obtained. 3.7.9 covers the test.

Clinical Relevance

Read a high grade as narrowing the possibilities rather than naming a structure.

Consider lateral meniscal injury as well as anterolateral injury in a high grade.

Measure slope where the grade exceeds what the injury explains.

Grade under anaesthetic where the grade will change the operation.

FRCS Level

At the Knee

Treat pivot shift control as the outcome a lateral procedure is added to achieve, and the grade as the indication. Conventional teaching supports augmentation in high grade rotatory laxity, revision, young pivoting athletes and generalised laxity. 3.11.7 covers the tenodesis.

The mechanical argument is apportionment: the cruciate graft restores its share and the anterolateral share is not restored by it. 3.7.2 covers primary restraint.

Residual pivot shift after reconstruction is associated with poorer outcome and graft failure, which is why abolishing it is the intraoperative aim. 3.7.9 covers the test.

What Changes It

Whether a lateral procedure was added.

Femoral tunnel position of the cruciate graft. 3.7.6 covers that bundle's territory.

Lateral meniscal repair.

Slope and plateau morphology, now partly modifiable.

How It Is Measured

Examination under anaesthetic before and after fixation is the practical check.

Instrumented pivot shift measures the effect in research cohorts.

Randomised trials of augmentation report reinjury rates, which is the outcome the mechanism predicts.

No threshold defines an acceptable residual shift.

Clinical Relevance

Check the pivot shift under anaesthetic after cruciate fixation.

Add a lateral procedure where the grade or the population indicates it.

Repair the lateral posterior horn, which also controls the subluxation.

Measure slope in a high grade shift, particularly before revision.