Examination Under Anaesthesia

For Medical Students

What It Tests

Examination under anaesthesia is the same set of tests performed on a patient who is fully relaxed, and relaxation is what most of the rotational tests need.

A guarding patient prevents the subluxation the pivot shift depends on, so the awake test fails towards a false negative. Under anaesthesia it does not. 4.14.1 covers the pivot shift.

The anterior cruciate chapter describes the general setting. What this page covers is the rotational examination specifically, which is the part that most depends on relaxation. 4.10.10 covers the general case.

How It Is Performed

Examine both knees, always, and examine the uninjured one first so the normal is established before the abnormal is interpreted.

Perform the pivot shift on both sides and grade it, since the grade rather than the presence is the finding. 4.14.1 covers the grading.

Perform the dial test at thirty and ninety degrees on both sides. 4.13.5 covers it.

Perform the Lachman test, the posterior drawer with the tibia reduced, and valgus and varus stress at two angles each. 4.11.2 covers the drawer.

Record the findings in the operation note as numbers and grades rather than as positive or negative, because this record is the one that will be read years later. 4.1.8 covers that argument.

What a Positive Means

A pivot shift grade that is larger than the awake grade is the usual finding, and it is the real grade.

An asymmetric dial difference established here is more reliable than an awake one, because the awake version fails in a guarding patient. 4.13.5 covers it.

A reverse pivot shift found here is less reliable than awake, because the rate of positive results in normal knees rises with relaxation. 4.11.4 covers that test.

Findings that appear only under anaesthesia are real laxity. Whether they matter to the patient is a separate question the examination cannot answer, which is this section's recurring division. 4.11.5 covers the functional side.

MRCS Level

How It Is Performed

In a viva this is the answer to how you would grade a pivot shift reliably, and saying so directly is better than describing a better awake technique.

The expected points are both knees, the uninjured side first, the graded pivot shift, the dial test at two angles, the translation tests, and the recorded grades.

Say that you would examine before the tourniquet is inflated and before any arthroscopy, because both alter the findings.

Say that you would record the examination in the operation note as the primary record, since it is more reliable than the clinic examination that preceded it.

Say that a finding present under anaesthesia and absent awake is still a real finding, and that the decision to act on it is a separate judgement. 4.11.5 covers that judgement.

What a Positive Means

The reasoning expected is that muscle activity is a dynamic restraint, so removing it removes a restraint the awake examination cannot separate from the ligaments. 3.11.4 covers pivot shift control.

The hamstrings resist anterior translation and the quadriceps resists posterior translation, so guarding reduces the Lachman test, the pivot shift and the posterior drawer in the same direction. 4.11.3 covers the test built on the quadriceps.

The dial test is affected the same way, which is why a normal awake dial test in a painful knee is an absent test rather than a negative one. 4.13.5 covers it.

The reverse pivot shift moves the other way, because the relaxation that reveals a true positive also produces false ones. 4.11.4 covers it.

How Good It Is

Examination under anaesthesia is the most reliable clinical assessment of rotational laxity available, and it is the reference the awake tests are judged against.

Its weakness is access rather than accuracy. It requires an anaesthetic, so it cannot be used to decide whether to operate unless the operation is already planned.

That constraint shapes practice. It is used to settle a plan at the start of a listed operation, and to establish laxity in a knee too painful to examine, and it is not a clinic investigation. 4.11.7 covers the acute setting.

It is also the one examination whose record routinely survives, because it goes into an operation note rather than a clinic letter. 4.1.8 covers the record.

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 this examination is where the plan for a rotationally unstable knee is finalised, and in multiligament surgery it is where the plan is made at all.

A pivot shift graded here is the clinical basis for adding a lateral extra-articular procedure, and grading it awake is not good enough for that decision in a borderline case. 4.14.3 covers the pattern.

A dial test established here decides whether a corner is reconstructed alongside a cruciate, and in the acute knee there is no other way to establish it. 4.13.4 covers the corner assessment.

In the acute multiligament knee it is part of the assessment rather than part of the operation, and arranging it early is what allows acute repair within its window. 4.11.7 covers the sequence.

In a revision it is worth arranging deliberately, because the question is usually whether the graft is incompetent or the knee was never rotationally controlled, and that is an anaesthetised examination. 4.10.12 covers revision assessment.

Where It Misleads

The commonest error is examining only the injured knee, which removes the comparison in the one setting where it is easiest to obtain.

The second is examining after arthroscopy or after the tourniquet, both of which change the findings.

The third is recording positive or negative, which wastes the most reliable examination the patient will ever have.

The fourth is treating a finding present only under anaesthesia as an indication by itself, when whether it matters is a functional question. 4.11.5 covers it.

The fifth is relying on a reverse pivot shift found here, which is the one test anaesthesia makes worse. 4.11.4 covers it.

Fellowship Level

Where It Misleads

In referred practice the anaesthetised examination from the first operation is often the single most useful document in the file, and its absence is the commonest reason a revision has to start from guesswork.

A recorded grade zero pivot shift at the end of the first reconstruction, with a high grade shift now, establishes that something changed rather than that the knee was never controlled. That distinction decides the revision. 4.14.3 covers the pattern.

No recorded examination means the distinction cannot be made from the notes, and the present anaesthetised examination has to carry it alone.

An examination performed after the tourniquet or after a long arthroscopy reads differently, and a grade recorded in those circumstances is worth discounting rather than trusting.

In a multiply operated knee the examination is constrained by previous surgery and the comparison with the other knee is no longer a comparison with normal, so the findings are read against the operation notes. 4.2.30 covers previous surgery.

In medicolegal work this is the strongest examination evidence that exists about a knee, and a careless entry in an operation note carries more weight than a careful clinic letter. That is an argument for recording it properly rather than for recording less. 4.23.7 covers that setting.