Slocum Test

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Student MRCS FRCS Fellow

For Medical Students

What It Tests

The Slocum test is the anterior drawer performed with the tibia rotated, and it is designed to separate rotational instability from straight anterior translation.

The anterior drawer with the tibia in neutral rotation reads translation. Rotating the tibia presents one side of the joint forwards, so the drawer then reads that side's restraint. 4.10.5 covers the neutral test.

Turning the foot outwards tests the medial side; turning it inwards tests the lateral side. 3.9.7 covers the medial pattern.

How It Is Performed

Position the patient supine with the knee flexed to about ninety degrees and the foot flat on the couch, as for an anterior drawer.

Rotate the foot externally by about fifteen degrees and sit on it to hold it there.

Draw the tibia forwards and watch the medial tibial plateau, noting whether it rotates forwards more than the other knee does.

Return the foot to neutral, draw again, and compare.

Then rotate the foot internally by about thirty degrees, hold it, and draw forwards again, this time watching the lateral plateau.

What a Positive Means

More anterior movement of the medial plateau in external rotation than in neutral indicates anteromedial rotatory instability. 4.14.4 covers that pattern.

More anterior movement of the lateral plateau in internal rotation than in neutral indicates anterolateral rotatory instability, although the pivot shift reads that pattern better. 4.14.1 covers the pivot shift.

Reduced translation in internal rotation is the normal finding, because internal rotation tightens the posterior structures, so an increase there is the abnormality.

A knee with increased translation in neutral and no change with rotation has an anterior cruciate injury without a rotational component. 4.10.5 covers that.

Key Learning Points

The anterior drawer with the tibia rotated, designed to separate rotation from translation.
External rotation presents the medial side forwards; internal rotation presents the lateral side.
The finding is the difference from the neutral drawer, not the rotated reading alone.
Reduced translation in internal rotation is normal, so an increase there is the abnormality.
Increased translation in neutral with no change on rotation is a cruciate injury without a rotational component.

MRCS Level

How It Is Performed

In a viva this is the test to name when asked how you would separate rotatory from straight instability at ninety degrees, and the neutral comparison is the mark.

The expected points are the ninety degree position, the amount of rotation in each direction, holding the foot, watching the plateau rather than the tubercle, and the neutral comparison.

Say that the medial side is tested in external rotation and the lateral side in internal rotation, because candidates reverse this.

Say that the test is historically important and is now largely superseded by the pivot shift for the lateral side, which is a reasonable thing to say rather than a criticism of the question. 4.14.1 covers the pivot shift.

Say that you would record the findings rather than the label, since the classification of rotatory instability is contested. 4.1.8 covers the record.

What a Positive Means

The reasoning expected is that rotating the tibia alters which structures lie in the path of an anterior force, so the drawer in rotation reads a different restraint from the drawer in neutral. 3.9.2 covers rotational stability.

External rotation slackens the medial structures and presents the medial plateau anteriorly, so the posteromedial corner is what limits that movement. 3.9.5 covers the posterior oblique ligament.

Internal rotation tightens the posteromedial structures and the posterior cruciate's contribution, which is why translation normally decreases.

The anterior cruciate is required for either pattern in most descriptions, because it resists the anterior component, so a rotatory instability is usually a combined diagnosis. 3.9.10 covers the combination.

How Good It Is

The Slocum test is more reproducible than the pivot shift and less informative, which is an unusual combination and explains its position.

Its medial half remains useful, because no other test at ninety degrees reads the posteromedial corner. 4.12.6 covers that assessment.

Its lateral half has been superseded by the pivot shift, which loads the same structures in a way that reproduces the patient's complaint. 4.14.1 covers it.

It is performable in a knee that tolerates ninety degrees of flexion and fails in the acute guarding knee, in the direction of a false negative.

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

Key Learning Points

More reproducible than the pivot shift and less informative.
The medial half remains useful, because nothing else at ninety degrees reads the posteromedial corner.
The lateral half has been superseded by the pivot shift.
External rotation slackens the medial structures and presents the medial plateau forwards.
Internal rotation normally reduces translation, so an increase is the abnormality.

FRCS Level

How Good It Is

At decision level the test contributes to the medial decision and almost nothing to the lateral one.

An increased anteromedial pattern in a knee listed for an anterior cruciate reconstruction is a reason to assess the posteromedial corner before operating, and that is the test's practical use. 4.12.5 covers the corner.

It does not grade and it does not quantify, so where a decision turns on severity the examination under anaesthesia and the stress radiographs carry it. 4.14.6 covers the former.

It has no role in following a reconstruction, because the rotational finding after surgery is read better by the pivot shift and the dial test. 4.13.5 covers the dial test.

The historical value of the test is worth knowing for a different reason: the classification of rotatory instability it belongs to shaped how these injuries are still described, and letters still use its language. 4.14.5 covers those patterns.

Where It Misleads

The commonest error is performing it without the neutral drawer, which removes the comparison the test depends on.

The second is reversing the directions and testing the medial side in internal rotation.

The third is reading the whole tibia translating as a rotation.

The fourth is over rotating the foot, which locks the joint and prevents the movement the test is looking for.

The fifth is reporting a classification label without the findings, which is hard for the next clinician to use.

Key Learning Points

The test contributes to the medial decision and almost nothing to the lateral one.
An anteromedial pattern before a cruciate reconstruction is a reason to assess the corner.
It does not grade, so severity decisions rest on anaesthesia and stress radiographs.
Over rotating the foot locks the joint and prevents the movement being tested.
Its language still appears in letters, which is a reason to know it.

Fellowship Level

Where It Misleads

In referred practice this test appears mainly as a phrase in an old letter, and interpreting the letter is most of its remaining use.

A recorded anteromedial pattern before a cruciate reconstruction that later failed is worth taking seriously, because it suggests the medial corner was identified and not addressed. 4.12.8 covers that assessment.

A recorded anterolateral pattern means less, because the pivot shift grade from the same era, if it exists, is the better record of the same thing. 4.14.1 covers it.

The test is unreliable in a knee with a previous meniscectomy, where the posterior horn no longer blocks the movement and the translation is larger for reasons unrelated to the ligaments. 4.9.10 covers meniscal deficiency.

In a hypermobile patient every version of the test is abnormal and the comparison with the other knee is the only interpretable part. 4.23.3 covers those patients.

In medicolegal work the test's contested classification makes it weak evidence, and the findings recorded without the label are worth more than the label. 4.23.7 covers that setting.

Key Learning Points

Its main remaining use is interpreting old letters.
A recorded anteromedial pattern before a failed reconstruction suggests the corner was identified and not addressed.
A recorded anterolateral pattern means less, because the pivot shift grade is the better record.
After a meniscectomy the translation is larger for reasons unrelated to the ligaments.
The findings recorded without the label are worth more than the label.

Explore Further

Where this topic came from and where it goes next in the spiral.

References

No reference list is attached to this draft. Evidence verification has not run, because source retrieval was unavailable at generation time. Under the Operations Handbook a missing reference is acceptable and an invented one is a critical failure, so nothing has been cited and no citation marker appears in the text. This page carries no diagnostic accuracy figure, which is decision 023 rather than an omission. The comparative standing of these tests is standard teaching and a specific sensitivity written from memory is the same class of claim as an invented citation, so ACC-001 refuses the number and the page states the comparison. A reviewer with the literature can add the figures into How Good It Is without restructuring the page, and chapter 3.17 lists the studies the figures would come from. Any measurement here, including a flexion angle, is written from standard teaching, has not been checked, and is registered under decision 006 in pipeline/config/figures with a verification state of UNVERIFIED_FROM_MEMORY.

Safety. KneeSchool is educational and does not give individual medical advice. Seek urgent assessment for a knee that cannot bear weight after an injury, a hot swollen knee with a fever, or new numbness, weakness or coldness in the leg or foot.