Knee Orthopaedic Test: Slocum's Test

The Slocum Test is a modified anterior drawer-style test used to assess anteromedial or anterolateral rotatory knee instability by changing tibial rotation. A positive finding may include increased anterior translation or rotational laxity compared with the other side. Diagnostic accuracy evidence for the exact test is limited, so it should be interpreted with ACL, collateral, meniscal and functional findings.

Introduction

Rotatory knee instability can involve complex interactions between cruciate ligaments, collateral structures, menisci, capsule and bony alignment. The Slocum Test attempts to add a rotational bias to anterior drawer-style testing.

Modern rotatory knee instability literature emphasises that rotational instability is complex and requires assessment beyond a single manual test.  

Quick Summary

Test name: Slocum Test
Purpose: Assess anteromedial or anterolateral rotatory knee instability
Body region: Knee
Commonly associated presentation: Rotatory instability, ACL involvement, capsular or collateral contribution
Positive finding: Increased anterior translation or rotational asymmetry compared with the other side
Negative finding: No meaningful side-to-side translation or rotational difference
Best used with: Lachman, anterior drawer, pivot shift, varus/valgus stress tests, meniscal tests and functional testing
Key limitation: Exact-test diagnostic accuracy evidence is limited

What Is the Slocum Test?

The Slocum Test is a modification of anterior drawer testing where tibial rotation is added to bias different rotational structures. Internal or external tibial rotation changes the stress placed through the knee and may help assess anterolateral or anteromedial rotatory instability.

The test is less commonly used than Lachman, anterior drawer or pivot shift testing.

Why It Is Used

The test is used when rotatory knee instability is suspected and additional information beyond straight anterior tibial translation may be useful.

What It Assesses

The test assesses anterior tibial translation with rotational bias.

It does not identify a single injured structure, confirm ACL injury, quantify rotational instability precisely or replace broader ligament assessment.

Who It Is Useful For

This test may be useful for clients with giving-way symptoms, suspected ACL involvement, suspected capsular or collateral contribution, or rotational instability complaints.

It may not be suitable with acute high pain, swelling, guarding, suspected fracture or inability to tolerate the testing position.

When to Use This Test

Use the test when the clinical picture suggests rotatory knee instability and the client can tolerate controlled manual testing.

When Not to Use or When to Be Cautious

Use caution with acute trauma, suspected fracture, significant swelling, locked knee, neurovascular symptoms or strong guarding.

Equipment Required

Treatment table
Pain scale
Measurz for recording
Optional comparison side notes
Optional referral notes

Step-by-Step Protocol / Practice

Setup

Position the client supine or side-lying depending on the version used.

Client position

For the anterior drawer-style version, flex the knee to approximately 90 degrees.

Examiner position

Position yourself to stabilise the foot and control tibial rotation.

Hand placement

Place both hands around the proximal tibia.

Stabilisation

Stabilise the foot and maintain the selected tibial rotation position.

Movement or force direction

Apply an anterior drawer force with the tibia internally or externally rotated.

Instructions

Ask the client to relax and report pain, apprehension or familiar instability.

Positive finding

A positive finding is increased anterior translation, rotational asymmetry, soft end-feel or familiar instability compared with the opposite side.

Negative finding

A negative finding is no meaningful side-to-side difference in translation, rotation or symptoms.

Stopping criteria

Stop if pain escalates, guarding prevents assessment or instability appears unsafe.

Safety notes

Use controlled force. Record tibial rotation direction clearly.

Positive and Negative Test Interpretation

A positive Slocum Test may increase suspicion of rotatory knee instability when increased translation or asymmetry matches the client’s history and other ligament findings.

A negative test may reduce suspicion of marked rotatory laxity under the tested setup, but it does not exclude ACL or capsular involvement.

Interpretation is stronger when combined with Lachman, anterior drawer, pivot shift, varus/valgus stress testing, meniscal tests and functional tasks.

Sensitivity, Specificity and Diagnostic Accuracy

High-quality diagnostic accuracy evidence for the exact Slocum Test is limited. Clinical education sources note that the Slocum Test has not been included widely in diagnostic accuracy studies, making its clinical value less certain than better-studied ACL tests.  

Recent rotatory knee instability literature supports the need for comprehensive assessment because rotational instability involves multiple structures and cannot be reduced to a single test result.  

Because robust sensitivity, specificity and likelihood ratio values are not established for the exact test, values should not be invented.

Reliability and Validity

Reliability depends on knee angle, tibial rotation position, force applied, client relaxation and examiner experience.

Validity is limited as a stand-alone test. The result is most useful when it aligns with other ligament and functional findings.

Common Errors and Limitations

Common errors include failing to record tibial rotation direction, not comparing sides, allowing hamstring guarding, applying inconsistent force and interpreting vague pain as instability.

Limitations include limited exact-test evidence, examiner subjectivity and overlap with other ligament findings.

Practical Applications

Use the Slocum Test as an additional rotational knee assessment when straight-plane tests do not fully explain symptoms or instability.

How to Record This in Measurz

Record test name, side tested, position used, tibial rotation direction, result as positive, negative, unclear or unable to test, translation amount, end-feel, pain score, symptom location, apprehension, comparison side, confidence in result, stopping reason and related findings.

Related Tests / Internal Links

Anterior Drawer Test of the Knee
Lachman Test
Pivot Shift Test
Lever Sign Test
Posterior Drawer Test
Varus Stress Test
Valgus Stress Test

FAQs

What does the Slocum Test assess?

It assesses anterior tibial translation with a rotational bias.

What is a positive Slocum Test?

A positive finding may include increased anterior translation, rotational asymmetry or familiar instability compared with the other side.

Does the Slocum Test confirm ACL injury?

No. It supports assessment reasoning but does not confirm a condition on its own.

Why record tibial rotation direction?

Internal and external rotation bias different structures, so the direction affects interpretation.

Are diagnostic accuracy values available?

High-quality exact-test diagnostic accuracy evidence is limited.

Key Takeaways

The Slocum Test is a modified anterior drawer-style rotatory knee test.
Tibial rotation direction must be recorded.
A positive finding may suggest rotational asymmetry but is not diagnostic.
Exact diagnostic accuracy evidence is limited.
Use Measurz to track position, rotation, symptoms and related findings.

References

Hughes, J. D., Rauer, T., Gibbs, C. M., & Musahl, V. (2019). Diagnosis and treatment of rotatory knee instability. Journal of Experimental Orthopaedics, 6, 48.

Huang, W., et al. (2022). The diagnostic accuracy of clinical tests for anterior cruciate ligament injury: A systematic review and meta-analysis. Knee Surgery, Sports Traumatology, Arthroscopy, 30, 3285–3295.