Sitting Assessment

For Medical Students

What It Tests

Sitting with the knees flexed over the edge of the couch loads the patellofemoral joint and lets the examiner watch the patella move through a range, which no other position does as easily.

It also allows a comparison of the two knees in the same position without the couch supporting either limb, so a resting difference is visible. 4.3.5 covers the supine position.

The sitting position is where the extensor mechanism declares itself: the patella's track, the tubercle's position, and whether the patient can hold the knee straight. 4.7.8 covers extension lag.

How It Is Performed

Sit the patient on the edge of the couch with both knees flexed to about ninety degrees and the feet hanging free.

Look at the two knees from the front and compare the patellae: their height, their position relative to the midline, and whether one sits higher than the other.

Ask the patient to straighten the knee slowly and watch the patella's path, noting whether it deviates laterally near full extension.

Ask them to hold the knee straight against gravity and note whether they can, and whether the knee drops. 4.7.1 covers active motion.

Look at the tibial tubercles and at the line from the tubercle to the patella, and note any obvious rotation of the limb. 4.5.6 covers rotational alignment.

What a Positive Means

A patella that deviates laterally as the knee approaches extension suggests a tracking abnormality, and it is easier to see sitting than lying. 2.4.4 covers patellar tracking.

A patella sitting higher than the other side suggests a high riding patella, a previous tendon injury, or an effusion lifting it. 4.6.5 covers patellar tenderness.

An inability to hold the knee straight against gravity indicates an extensor mechanism problem, which includes quadriceps weakness, a tendon rupture and inhibition from pain or an effusion. 4.8.2 covers the clinical significance of an effusion.

A knee that rests in flexion when the other is straight, with the patient sitting, suggests a flexion deformity rather than a positional difference. 4.5.4 covers it.

Wasting of the quadriceps is more visible sitting than lying, because the muscle is at a different length and the contour is easier to compare. 4.3.9 covers muscle wasting.

MRCS Level

How It Is Performed

In a viva the sitting assessment is worth doing without being asked, because it is quick and because the patellofemoral findings do not appear in any other position.

The expected points are both knees at the same flexion angle, the comparison of the patellae, the active extension watching the track, holding against gravity, and the tubercles.

Say that you would watch the last part of extension in particular, because that is where the patella leaves the trochlear groove and where a tracking abnormality shows. 2.4.4 covers tracking.

Say that you would assess the quadriceps bulk here as well as supine, since the contour is clearer with the muscle under tension.

Say that you would ask the patient to perform the movement rather than moving the knee yourself, since this is an active assessment and the passive version is a different measurement. 4.7.2 covers passive motion.

What a Positive Means

The reasoning expected is that the patella enters the trochlear groove in early flexion and is least constrained near extension, so a tracking abnormality is most visible at the end of the extension arc. 2.4.3 covers patellar biomechanics.

Holding the knee extended against gravity requires the extensor mechanism to be continuous and the quadriceps to be able to generate the force, so failure localises to one of those. 4.7.8 covers extension lag.

An effusion inhibits the quadriceps, which is why an effused knee can fail this test with an intact extensor mechanism and recover when the effusion settles. 4.8.2 covers it.

Sitting also unloads the joint relative to standing, so a finding present standing and absent sitting is load dependent and belongs to the alignment assessment. 4.5.7 covers dynamic alignment.

How Good It Is

The sitting assessment is the most efficient part of the inspection, because it produces patellofemoral information no other position gives for the same effort.

It is better for tracking than any passive manoeuvre, since tracking is an active phenomenon.

It is poor at grading anything. The findings are present or absent rather than measured, and the measurement happens elsewhere.

It is unreliable in a patient who cannot sit unsupported or whose body habitus hides the contours, and the standing and supine assessments then carry more weight. 4.23.4 covers those patients.

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 the sitting assessment contributes to the patellofemoral decision and almost nothing to the ligament decisions, which is a narrow but real contribution.

An extension lag in a knee listed for a ligament reconstruction changes the timing, because reconstructing a knee that cannot actively reach extension produces a stiff result. 4.7.7 covers contractures.

A tracking abnormality found here in a patient whose complaint is instability raises whether the instability is patellar rather than ligamentous, and that is a different operation entirely. 4.2.2 covers instability as a symptom.

A high riding patella in a patient with anterior knee pain and a posterior cruciate deficient knee is a consequence of the deficiency rather than an independent problem. 4.11.6 covers that knee.

Beyond those, the sitting assessment is a screen, and treating it as more than that over reads it.

Where It Misleads

The commonest error is not sitting the patient up, which is a choice made by examining supine only.

The second is reading a lateral deviation as a diagnosis rather than as a finding, since a visible deviation occurs in people with no complaint.

The third is reading an extension lag as a mechanical block, which it is not. 4.7.8 covers that distinction.

The fourth is comparing knees at different flexion angles, which makes the patellar heights incomparable.

The fifth is attributing quadriceps failure to weakness when it is inhibition from an effusion, which resolves and does not need treating as weakness. 4.8.2 covers it.

Fellowship Level

Where It Misleads

In referred practice the sitting assessment is where a patellofemoral problem masquerading as something else is caught.

The commonest case is a patient referred with a meniscal complaint whose pain is anterior, whose patella tracks badly, and whose sitting examination has never been performed. 4.2.1 covers pain.

A patient with a posterior cruciate deficient knee and anterior pain has patellofemoral loading as a consequence of the deficiency, and the sitting examination is where the two findings are seen together. 4.11.6 covers that knee.

An extension lag that persists after a technically sound reconstruction is the finding most predictive of a dissatisfied patient, and it is usually recorded once and not followed. 4.7.10 covers post-operative range.

In a multiply operated knee the patellar height and track are altered by previous surgery, so the comparison with the other side is no longer a comparison with normal and the operation notes are needed. 4.2.30 covers previous surgery.

A patient who cannot hold the knee straight and has no effusion and normal quadriceps bulk needs a neurological explanation sought rather than a knee one, and that is a different examination. 4.23.6 covers complex cases.