Valgus Alignment

For Medical Students

The Principle

The same lever argument applies on the other side. A load passing outside a joint loads the outer part of it.

But two sides of a joint are rarely built the same, so the same geometry does not produce the same result.

A smaller surface carrying a larger share wears faster than a larger surface carrying the same share.

At the Knee

Valgus means the knee points inwards and the leg looks knock kneed. The mechanical axis passes outside the knee centre. 3.13.1 covers the axis.

The lateral compartment then carries a larger share than usual. 3.5.3 covers load distribution.

The lateral side of the knee has a smaller, more convex surface and a more mobile meniscus than the medial side. 2.2.2 covers the plateau.

The medial soft tissue is stretched in a valgus knee, which is the opposite pattern to varus. 3.9.1 covers valgus stability.

What Changes It

Bone shape, which is the usual reason.

Lateral cartilage loss, which lets that side collapse further.

Previous lateral meniscus surgery, which removes a load spreader from the smaller compartment. 3.5.5 covers meniscal loss.

A fracture healed in valgus, particularly of the lateral tibial plateau.

Clinical Relevance

Lateral compartment wear is less common than medial, but valgus knees are harder to manage when it happens. 6.74 covers the condition.

The medial soft tissue stretches over time in a valgus knee, which adds instability to the wear.

Correction is less predictable than on the medial side, partly for that reason. 3.13.9 covers osteotomy.

4.5.3 covers how it is assessed clinically.

MRCS Level

The Principle

Geometrically valgus is varus reflected. Clinically it is not, because the compartments differ in area, in congruence, in meniscal mobility and in soft tissue.

Load share is only half the story. The same share on a smaller contact area is a higher pressure. 3.5.1 covers contact areas.

So a symmetrical geometric statement produces an asymmetrical clinical one.

At the Knee

Valgus reduces the external adduction moment and raises the abduction moment, which loads the lateral compartment. 3.4.6 covers external moments.

The lateral plateau is smaller and convex while the medial is larger and concave, so lateral contact pressure rises faster for a given share. 3.5.1 covers it.

The lateral meniscus is more mobile and contributes more of its compartment's load spreading, which makes its loss more consequential there. 3.5.5 covers that.

Chronic valgus stretches the medial collateral complex, producing a combined deformity and laxity problem. 3.9.1 covers the restraints.

Valgus deformity is more often femoral in origin than tibial, which changes where a correction belongs. 3.13.6 covers localisation.

What Changes It

Distal femoral morphology, which is the commonest site of the deformity.

Lateral cartilage and bone loss, which is the intra-articular component.

Previous lateral meniscectomy, which raises lateral pressure independently. 3.5.9 covers it.

Medial soft tissue competence, which decides how much of the measured deformity is correctable.

Inflammatory arthropathy, which produces valgus more often than mechanical wear does. 6.79 covers it.

How It Is Measured

Hip knee ankle angle on a standing long leg film, as for varus. 5.3.2 covers the technique.

Joint orientation angles, which identify the femoral predominance. 3.13.6 covers them.

Stress radiography, which separates the medial laxity component from the bony deformity.

Gait analysis for the abduction moment, which is less studied than its adduction counterpart. 3.16.7 covers motion capture.

The lateral compartment has less published pressure data than the medial, so figures there are weaker.

Clinical Relevance

Localise a valgus deformity before correcting it, since it is more often femoral. 3.13.6 covers it.

Assess medial soft tissue competence, because chronic valgus produces laxity as well as deformity.

Expect lateral compartment pressure to rise faster than the load share does, because the surface is smaller. 3.5.1 covers it.

Consider inflammatory causes in a valgus knee, which is a different pathway from mechanical wear. 6.79 covers it.

FRCS Level

At the Knee

The asymmetry between varus and valgus is the useful teaching point, and it has four sources: compartment area, congruence, meniscal contribution and soft tissue behaviour.

Because the lateral compartment is smaller and convex, a correction that equalises load share does not equalise pressure, which is one reason lateral results are less predictable. 3.5.1 covers the areas.

The medial soft tissue laxity that accompanies chronic valgus means a bony correction can leave a knee that is aligned and unstable. 3.9.1 covers the restraints.

Distal femoral osteotomy is the usual correction site, which is a different operation with a different complication profile from a proximal tibial one. 7.70 covers it.

Conventional teaching treats valgus correction as having a narrower indication than varus correction, and the evidence base is correspondingly thinner. 6.154 covers the controversies.

What Changes It

The site of the deformity, femoral or tibial, which decides the operation. 3.13.6 covers it.

Medial laxity, which is both a consequence of the deformity and a limit on correcting it.

Lateral meniscal status, which changes the compartment's tolerance independently of alignment. 3.5.9 covers it.

The underlying disease process, since inflammatory and mechanical valgus behave differently. 6.79 covers it.

Patellofemoral consequences, because changing coronal alignment moves the extensor vector too. 3.12.11 covers that.

How It Is Measured

Standing long leg radiography and joint orientation angles, which together localise the deformity.

Stress views, which quantify the medial laxity that will not be corrected by bone.

Magnetic resonance imaging for lateral meniscal and cartilage status, which modifies the prognosis. 5.11 covers cartilage imaging.

Gait analysis, which has far less valgus data than varus data in the literature.

The thinner evidence base is itself a finding: most of what is quoted about alignment and load comes from varus knees.

Clinical Relevance

Localise the deformity and correct at its site, which in valgus is usually the femur. 7.70 covers the operation.

Quantify medial laxity before correction, because an aligned unstable knee is a poor result.

Expect lateral pressure to fall less than load share suggests, and counsel accordingly.

State that most alignment and load data comes from varus knees when applying it here.

Weigh the patient's age, physiology, comorbidities, knee demand, psychological state and their own ideas, concerns and expectations, since the indication here is narrower and the evidence thinner than for varus.