Valgus Motion

For Medical Students

The Principle

Valgus motion is coronal angulation that opens the medial side of the joint and closes the lateral side.

As with varus, a distinction holds throughout: valgus alignment is where the limb sits, valgus motion is how far the joint opens under a force.

Most knees have a few degrees of valgus alignment normally, which is why the word describes a normal state as well as an abnormal one.

At the Knee

Conventional teaching gives physiological valgus alignment as about 5 to 7 degrees, with women on average slightly higher than men.

The superficial medial collateral ligament is the primary restraint to valgus motion, with the deep collateral, the posteromedial corner and the cruciates secondary. 2.9.1 covers it.

Testing at 20 to 30 degrees of flexion isolates the collateral ligament, because the secondary restraints contribute less there.

Opening in full extension means the posteromedial corner has gone as well, which 2.9.4 covers.

What Changes It

Flexion angle, deciding which restraints are loaded.

Alignment, with a valgus limb loading the lateral compartment and the medial soft tissues.

Injury, with the medial collateral the most commonly injured ligament at the knee.

Healing. Unlike the cruciates, this ligament usually heals, so medial laxity often resolves without surgery. 2.9.1 covers why.

Clinical Relevance

Valgus laxity at 20 to 30 degrees alone suggests the medial collateral ligament. Laxity in full extension as well suggests the posteromedial corner and a cruciate. 4.12 covers the examination.

Because the ligament heals, the question in a medial injury is usually the position it heals in rather than whether it heals.

Valgus alignment increases patellofemoral load as well as lateral compartment load, which is why it appears in two different clinical conversations.

MRCS Level

The Principle

The medial and lateral sides are not mirror images, despite the symmetry of the motions.

The medial side heals and the lateral side does less well, because of the vascularity difference 2.10.1 describes. That asymmetry decides treatment more than the mechanics do.

The medial side also has a dynamic component through semimembranosus and the pes, which 2.9.6 covers, and the lateral has one through biceps femoris.

At the Knee

The superficial collateral carries the large majority of valgus restraint at 25 degrees of flexion, with the posteromedial corner taking an increasing share towards extension. 3.9.1 carries the apportionment.

Conventional teaching grades medial injury by the opening at 30 degrees: a few millimetres for grade one and two, and a complete loss of endpoint for grade three.

The anterior cruciate is a secondary restraint to valgus, which is why a complete medial injury and a cruciate injury often occur together.

The distal and proximal divisions of the collateral restrain rotation as well as valgus, so a medial injury can present rotationally. 2.9.1 covers it.

What Changes It

Flexion angle and injury pattern, as throughout.

Healing, which changes the finding over weeks in a way no other knee ligament does.

Bracing, which changes the position the ligament heals in and is therefore a mechanical intervention rather than a comfort measure.

How It Is Measured

Valgus stress testing at 0 and 30 degrees, graded by opening and endpoint.

Stress radiography gives a number and is used where the grade matters, for example before a cruciate reconstruction.

Serial examination matters here more than elsewhere, because the finding changes as the ligament heals.

Clinical Relevance

Test at both angles and record both, since the pair separates the collateral from the corner.

Re-examine a medial injury after a few weeks, because the ligament heals and the early finding is not the final one.

Examine the anterior cruciate in any complete medial injury.

Treat bracing as a mechanical intervention aimed at healing position, and explain it that way.

FRCS Level

At the Knee

Treat medial laxity as a question about length rather than continuity. The tissue is usually present and usually healed; what matters is whether it healed short enough to restrain.

The posteromedial corner carries the extension restraint and the collateral the flexion restraint, a reciprocal pair like the cruciate bundles. 2.9.4 covers it.

Valgus alignment loads the lateral compartment and the patellofemoral joint together, so a valgus knee presents in two ways.

What Changes It

Time, uniquely among the ligament injuries at this joint. A medial injury reassessed at six weeks is a different problem from the same injury on the day.

Alignment, which decides whether a reconstruction is loaded or protected.

Associated cruciate injury, which changes both the mechanics and the rehabilitation that the medial side needs to heal in a good position.

How It Is Measured

Stress radiography is the quantitative method and the one that settles a grade three from a grade two when the decision matters.

Examination under anaesthetic removes guarding and is the measurement that most closely reflects the structural state.

Sectioning study figures describe the acute cut ligament and not the chronically lengthened one, which is the state most patients present in.

Clinical Relevance

Delay the decision in an isolated medial injury where the anatomy says healing is likely, and re-examine rather than operating on the first finding.

Assess alignment before reconstructing chronic medial laxity, since a valgus limb protects a medial reconstruction and a varus one does not.

Consider shortening rather than only reattaching in a chronic injury, because the problem is length.

Avoid reading continuity on imaging as competence.