Varus Stress Test

For Medical Students

What It Tests

Varus stress testing measures how far the lateral side of the knee opens when the joint is pushed into varus, and it tests the lateral restraints.

The principal structure is the lateral collateral ligament, which is a discrete cord rather than a sheet and can often be felt. 3.10.3 covers its function.

As on the medial side, the test is performed at thirty degrees and in full extension, because different structures share the restraint at the two angles. 3.10.1 covers varus stability.

The difference from the medial side is what the result means. The lateral structures heal poorly, so a grade here is more likely to be permanent. 3.10.6 covers the corner.

How It Is Performed

Lay the patient supine with the leg relaxed and the knee straight.

Hold the ankle in one hand and place the other along the medial side of the knee as the fulcrum, with your fingers over the lateral joint line.

Apply a varus force through the ankle and feel the lateral joint line open under your fingers.

Record the opening and the endpoint, then repeat with the knee flexed to thirty degrees.

Compare both angles with the other knee, and control rotation of the limb, because an internally rotated leg opens laterally without any ligament being torn.

What a Positive Means

Increased lateral opening with a soft endpoint indicates deficient lateral restraints at the angle tested.

Opening at thirty degrees with a firm endpoint in extension points at the lateral collateral ligament in relative isolation. 4.13.2 covers that assessment.

Opening in full extension as well indicates that more than the collateral is torn, and in practice that means the posterolateral corner or a cruciate. 4.13.4 covers the corner.

Any varus laxity should prompt a specific search for the posterolateral corner and for a common peroneal nerve injury, because both travel with it. 4.11.7 covers that sequence.

A patient who stands with a varus thrust and has varus laxity has a problem that will not be solved by a ligament operation alone, because the limb loads the lateral side with every step. 4.11.5 covers dynamic assessment.

MRCS Level

How It Is Performed

In a viva the expected points are the two angles, the fulcrum, the fingers on the joint line, controlled rotation, the endpoint, and the comparison.

Say that you would examine the common peroneal nerve, because that is the single point most candidates omit and the one with the most consequence. 4.11.7 covers the sequence.

Say that you would palpate the ligament in the figure of four position, where it stands out as a cord and can be followed from the femoral epicondyle to the fibular head. 4.13.2 covers it.

Say that you would assess alignment standing, since varus alignment and varus laxity are different things that often coexist and have to be separated.

Say that you would perform the dial test, because external rotation is the plane the lateral structures resist most and varus is the plane they resist least. 4.13.5 covers it.

What a Positive Means

The reasoning expected is that the lateral collateral ligament is the principal varus restraint through mid flexion, and that the corner structures contribute more in extension and in rotation. 3.10.1 covers varus stability.

The popliteus and the popliteofibular ligament resist external rotation more than varus, which is why a corner injury can give a near normal varus test and a grossly abnormal dial test. 3.10.5 covers the popliteofibular ligament.

The cruciates contribute to varus restraint in extension, so opening there makes a cruciate injury likely and makes the diagnosis a combined one. 3.10.9 covers the combination with the posterior cruciate.

A varus test that is normal does not exclude a corner injury, and that is the single most important thing to know about this test. 4.13.4 covers the assessment that does.

How Good It Is

The varus test is as reproducible as the valgus test and considerably less informative, because the structures that matter most on this side are not the ones it reads.

It grades the collateral ligament well. It is close to blind to the popliteus complex, which is the part of the corner whose loss changes the operation.

Its weakness is therefore a false reassurance rather than a false alarm, and that is the dangerous direction for a test to fail in.

It is reliable in the acute knee, which matters because the acute corner injury is the one most often missed. 4.13.8 covers combined injuries.

No figures appear for any of these comparisons, under decision 023, and the comparison is the claim being made.

FRCS Level

How Good It Is

At decision level a varus grade is a reason to look harder rather than a decision in itself.

A clear varus laxity with a soft endpoint is almost never an isolated collateral injury, so the grade's main value is as the finding that triggers the full corner assessment and the stress radiographs. 4.13.4 covers it.

Where the grade does decide something is in a chronic knee with varus alignment, where the question is whether the laxity or the alignment is the problem, and the answer determines whether the operation is an osteotomy or a reconstruction.

In a combined posterior cruciate and corner injury the varus grade contributes to the staging decision, because a grossly lax lateral side changes what can be done in one sitting. 3.10.9 covers the combination.

Stress radiographs in varus are the reference for comparing over time and are worth obtaining in any knee where a reconstruction is being considered.

Where It Misleads

The commonest error is reading a normal varus test as a normal lateral side, which is how corner injuries are missed.

The second is testing one angle.

The third is an internally rotated limb.

The fourth is treating varus laxity as a ligament problem in a varus aligned knee, where the alignment is loading the lateral side and a soft tissue reconstruction will stretch. 4.11.5 covers the dynamic assessment.

The fifth is finding varus laxity and not examining the nerve, which is the omission with the longest consequences for the patient.

Fellowship Level

Where It Misleads

In referred practice the varus test is usually normal in the knees that are referred, which is precisely why they were referred late.

A patient with a posterior cruciate reconstruction that stretched, a normal varus test and an abnormal dial test has the explanation, and the varus test contributed nothing to finding it. 4.13.5 covers the dial test.

A chronically varus knee with lateral laxity and medial compartment wear is an alignment problem whose ligament finding is a consequence rather than a cause, and the sequence of treatment follows from that.

In a knee with a previous lateral reconstruction the varus test can be firm while rotation remains abnormal, because the reconstruction restored the plane it was designed for and not the other one. 3.10.8 covers reconstruction biomechanics.

A partially recovered common peroneal nerve palsy changes the gait and the dynamic examination permanently, and the varus thrust it produces is not ligamentous. 4.11.5 covers that distinction.

In the multiligament knee the varus grade is usually recorded and usually not the finding the plan turns on, which is worth knowing when reading somebody else's assessment. 4.11.7 covers that sequence.