Varus OA

For Medical Students

What It Tests

A varus knee with medial compartment wear presents as medial joint line pain, a bow legged appearance that is worse standing, and often a visible lateral thrust on walking. 4.5.2 covers varus alignment.

The examination is deciding how large the deformity is, whether it corrects, and whether the lateral side has stretched. 4.3.10 covers the deformity.

It is the commonest pattern of knee wear, and the examination is mostly observation and alignment assessment rather than special tests.

How It Is Performed

Take the history: the medial pain, the duration, the walking distance and whether the leg shape has changed. 4.2.9 covers the onset.

Look at the patient standing from the front, with the feet together, because the deformity is a loaded finding. 4.3.3 covers standing alignment.

Watch the gait from the front, specifically for the knee moving laterally during stance, which is the lateral thrust. 4.4.6 covers the arthritic gait.

Palpate the medial joint line in flexion for tenderness and osteophyte. 4.6.4 covers joint line tenderness.

Assess the correctability by applying a valgus force with the knee near extension and recording how far the alignment improves. 4.12.1 covers valgus stress testing.

Assess the lateral collateral ligament, since a long standing varus knee stretches the lateral structures. 4.13.2 covers the lateral collateral assessment.

Measure the range, recording the fixed flexion separately, since varus knees commonly lose extension. 4.5.4 covers the flexion deformity.

What a Positive Means

Medial joint line tenderness with a standing varus deformity and a lateral thrust is the characteristic picture, and the thrust is the finding that matters most.

A deformity that corrects to neutral means the bone loss is limited and the lateral structures are not contracted, which widens the options. 4.3.10 covers the deformity.

A deformity that does not correct means contracture, bone loss, or both, and that narrows them.

Lateral laxity on top of a varus deformity means the lateral side has lengthened and the deformity is structural. 4.13.1 covers the varus stress test.

A thrust with a correctable deformity marks a knee that is dynamically unstable in the coronal plane, which accelerates the wear. 4.4.6 covers the arthritic gait.

MRCS Level

How It Is Performed

In a viva this is the varus knee station and the expected answer is observation standing, gait, correctability and lateral stability in that order.

The expected points are the standing alignment, the gait with the thrust named, the medial joint line, the correctability, the lateral ligament, the range and the hip.

Say that you would assess the alignment standing rather than supine, since the load is what produces the deformity. 4.3.3 covers standing alignment.

Say that you would look for a thrust during gait specifically, because it is easy to miss and it changes the urgency. 4.4.6 covers it.

Say that you would examine the hip and the ankle, since a varus knee changes the loading of both and either can be the symptomatic joint. 4.2.15 covers referred pain.

What a Positive Means

The reasoning expected is that medial wear lowers the medial side, the limb angulates into varus, the medial load rises further, and the cycle continues. 3.5.2 covers contact pressures.

A lateral thrust means the lateral soft tissues are no longer restraining the opening, so each step adds load to the medial side. 4.4.6 covers it.

Lateral lengthening makes the deformity structural, so correcting the bone alone leaves a lax lateral side. 4.13.1 covers the varus stress test.

A fixed flexion deficit in a varus knee usually comes from posterior osteophyte and capsular contracture together, so both have to be addressed. 4.5.4 covers it.

How Good It Is

The examination is reliable for the presence and the direction of the deformity and for the thrust, since all three are gross findings.

Its best contribution is the thrust and the correctability, neither of which appears on a static radiograph. 4.4.6 covers the arthritic gait.

It is imprecise about the magnitude of the deformity, which a long leg film measures and the examination estimates.

Long leg alignment films quantify the mechanical axis, so the examination supplies the dynamic and soft tissue findings and the film supplies the geometry. 4.1.6 covers that relationship.

No figures appear for any accuracy comparison on this page, under decision 023, and the comparison is the claim being made.

FRCS Level

How Good It Is

At decision level a varus knee is sorted by the magnitude of the deformity, its correctability, the state of the lateral compartment and the presence of a thrust, and the examination contributes to three of those four.

A young varus knee with medial pain, a correctable deformity, a full range and a normal lateral compartment is the load redistribution group, and the examination identifies it. 4.20.4 covers the osteotomy assessment.

A varus knee with a fixed deformity, lateral laxity or a lost range is not in that group, and again the examination is the discriminator. 4.3.10 covers the deformity.

A thrust changes the timing of the conversation rather than its content, since a dynamically unstable varus knee deteriorates faster. 4.4.6 covers it.

Lateral joint line tenderness in a varus knee is examined deliberately, because lateral involvement removes the compartment specific options. 4.6.4 covers the technique.

Where It Misleads

The commonest error is assessing the deformity supine, where a varus knee can look nearly normal. 4.3.3 covers standing alignment.

Correctability assessed with a strong valgus force overstates what is correctable, because a contracture stretches under enough load. 4.3.10 covers it.

A thrust can be missed if the patient is watched from the side rather than the front, and the finding is directional. 4.4.6 covers it.

Lateral laxity measured in extension in a knee with a fixed flexion deficit is unreliable, since the position alters what the ligament resists. 4.13.1 covers the varus stress test.

Varus can originate at the tibia, at the femur or at both, and the clinical examination does not localise it. 4.5.1 covers the mechanical axis.

Fellowship Level

Where It Misleads

At fellowship level the varus knee's examination has to separate four things that often coexist, and each can mask another.

Bone loss, capsular contracture, lateral lengthening and a dynamic thrust all contribute to the same appearance, and only the thrust and the correctability are directly observable. 4.4.6 covers the arthritic gait.

A knee that corrects fully and still thrusts is telling two different stories, and the thrust is the one that predicts progression.

Lateral laxity in a varus knee can be absolute or relative, since a shortened medial side makes a normal lateral side appear long, and the examination cannot separate those. 4.13.1 covers the varus stress test.

A coexisting cruciate deficiency changes the thrust's character and is easy to attribute to the deformity alone. 4.10.5 covers the anterior drawer test.

Torsional and rotational components of the deformity sit outside the coronal description entirely and are not captured by it. 4.19.7 covers torsional assessment.