Supine Assessment

For Medical Students

What It Tests

The supine position is where the knee is relaxed, unloaded and accessible, which is what every manual test needs.

That is also its limitation. An unloaded knee is not the knee the patient complains about, so the supine examination grades structures and the standing and walking assessments grade the problem. 4.3.2 covers gait observation.

Before any test is performed, the supine position itself produces findings: the resting position of each knee, the contour of the thigh, and whether the two limbs lie the same way. 4.3.9 covers muscle wasting.

How It Is Performed

Lay the patient flat with both legs straight, exposed from the groin to the ankle, and with nothing under the knees.

Stand at the foot of the couch and look along both limbs, comparing their resting rotation and whether either knee rests in flexion. 4.5.4 covers flexion deformity.

Look from each side in turn at knee level, comparing the profile of the two knees. 4.11.1 covers the sign this view produces.

Look at the contour of the quadriceps and compare the two thighs at the same distance above the joint line.

Note the position of each foot, because an externally rotated limb at rest suggests a hip problem or a corner injury rather than a knee one. 4.5.6 covers rotational alignment.

Only then begin the palpation and the tests. 4.6.1 covers systematic palpation.

What a Positive Means

A knee resting in flexion when the other lies straight indicates a flexion deformity, an effusion, or pain avoided by flexion. 4.8.2 covers the effusion.

A loss of the normal tibial step off on one side, seen in profile, is a posterior sag and is read before anything is touched. 4.11.1 covers it.

An externally rotated resting foot points away from the knee and towards the hip or the corner, and examining the hip answers it. 4.1.4 covers the structured approach.

Visible quadriceps wasting indicates a knee that has been used less, which is a duration finding rather than a diagnosis. 4.3.9 covers it.

A knee lying in hyperextension raises the posterolateral corner, particularly when it is asymmetrical. 4.13.7 covers the recurvatum test.

MRCS Level

How It Is Performed

In a viva the expected answer treats the supine position as the start of the examination rather than as the examination, and says what has already been observed before reaching it.

The expected points are the flat couch with nothing under the knees, the full exposure, the view along the limbs, the profile view at knee level, the thigh contour, and the resting foot position.

Say that you would ensure the patient is actually relaxed, because every ligament test is affected by guarding and the supine examination is where guarding does the most damage. 4.14.6 covers the setting that removes it.

Say that you would examine the uninjured knee first, which establishes the normal and relaxes the patient. 4.1.2 covers the principle.

Say that you would place the hip in a neutral position, since a rotated hip rotates the tibia and changes the collateral tests. 4.12.1 covers valgus stress testing.

What a Positive Means

The reasoning expected is that the resting position of a joint reflects the balance of the structures crossing it, so a resting abnormality is a structural statement made without applying any force. 4.11.1 covers the clearest example.

An effusion holds the knee in slight flexion because that is the position of greatest capsular volume, which is why an effused knee rests flexed and resists full extension. 4.8.1 covers normal fluid physiology.

Relaxation matters because muscle is a dynamic restraint, and a guarding patient reduces every translational and rotational finding in the same direction. 4.11.3 covers the test built on that.

The supine position also removes the load, so alignment findings disappear and have to be obtained standing. 4.5.1 covers the mechanical axis.

How Good It Is

The supine examination is where almost every reproducible finding in Section 4 is obtained, and its reliability is the reliability of those tests rather than of the position.

Its systematic weakness is that it is unloaded, so it reads structures and not function, and this section has repeated that division on every page.

Its practical weakness is guarding, which reduces findings rather than inventing them, so the supine examination fails towards false reassurance. 4.13.4 covers the assessment that suffers most.

It is also the position in which the inspection findings are most often skipped, because the examiner's hands are already moving towards the first test.

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 supine examination supplies the grades, and the grades inform the technique more often than they decide the operation.

Where the supine findings and the loaded findings disagree, the plan follows the loaded ones and the technique follows the supine ones, and that division has appeared in every chapter of this section. 4.11.5 covers the loaded side.

The supine inspection specifically contributes two decisions: a resting flexion deformity changes what a reconstruction can achieve, and a posterior sag establishes a diagnosis before any test. 4.7.7 covers contractures.

In the acute knee the supine examination is unreliable, and recognising that early is what leads to the examination under anaesthesia that the plan is actually built on. 4.11.7 covers that sequence.

Documenting the resting position is worth more at the second visit than any single grade, because a change in the resting position is unambiguous. 4.1.8 covers the record.

Where It Misleads

The commonest error is starting the examination here, which discards the standing and walking assessments.

The second is examining with a pillow under the knees, which hides a flexion deformity and a posterior sag at once.

The third is examining a guarding patient and recording the result as a normal examination.

The fourth is examining through partial exposure, where the thigh contour and the resting rotation cannot be compared.

The fifth is treating the supine grades as the whole assessment, which is the error this section was arranged to prevent.

Fellowship Level

Where It Misleads

In referred practice the supine examination has usually been done and usually done in isolation, and the referral's answer is often in the parts that were not.

A patient with normal supine findings and a disabling complaint has either a loaded problem, a rotational problem the supine tests under read, or a problem that is not the knee. All three are separated by moving the examination rather than repeating it. 4.11.5 covers the loaded assessment.

A patient whose supine examination is abnormal and who walks and works without difficulty is the commonest reason an operation should not be offered, and saying so clearly is the consultation. 4.11.6 covers that argument.

In a multiply operated knee the resting position is the most reliable finding left, because scar alters endpoints and previous surgery alters tracks, and where the tibia sits at rest is still where it sits. 4.2.30 covers previous surgery.

A pillow or a wedge left under the knee is the commonest reason a posterior sag is missed in a hospital bed, which matters in the acute multiligament knee where the finding is urgent. 4.11.7 covers that assessment.

In medicolegal work the recorded resting position at the time of injury is more useful than a recorded grade, for the same reason: it is harder to perform badly and harder to dispute. 4.23.7 covers that setting.