33 Special Tests. One Sheet
All major ortho special tests across 6 body regions — shoulder, knee, hip, spine, elbow, wrist. One printable PDF for clinical placement.
| Also known as | Lachman’s test |
| Structure tested | Anterior cruciate ligament (ACL) |
| Patient position | Supine, knee flexed 20–30° |
| Positive sign | Soft or mushy endpoint with excessive anterior tibial translation |
| Sensitivity | ~85% (Benjaminse et al., 2006) |
| Specificity | ~94% (Benjaminse et al., 2006) |
What Is the Lachman Test?
The Lachman test is the most widely used clinical test for assessing anterior cruciate ligament (ACL) integrity. It tests one-plane anterior stability of the tibia relative to the femur and is considered the most sensitive clinical test for ACL rupture, particularly in the acute phase following injury.
The test is performed with the knee in 20–30° of flexion — a position that reduces hamstring tension and allows more reliable assessment of ACL restraint than tests performed at 90° flexion. It was popularized by Torg et al. (1976) based on a technique developed by John Lachman.
Anatomy: The Anterior Cruciate Ligament
The ACL is an intra-articular, extra-synovial ligament that runs from the posteromedial aspect of the lateral femoral condyle to the anterior intercondylar area of the tibia. It has two functional bundles — the anteromedial (AM) bundle and the posterolateral (PL) bundle — which together provide translational and rotational stability through the range of motion.
The ACL is the primary restraint to anterior tibial translation. It also contributes to rotational stability, which is why combined tests (Lachman + Pivot Shift) improve overall diagnostic accuracy.
Involved Structures
- Anterior cruciate ligament (ACL) — primary structure tested
- Posterior cruciate ligament (PCL) — provides posterior check against excessive translation
- Arcuate-popliteus complex — secondary stabilizer
How to Perform the Lachman Test
Starting Position
Position the patient supine with the knee to be tested flexed to approximately 20–30°. This angle is important: less than 20° may recruit the posterior capsule as a secondary stabilizer; more than 30° begins to engage the hamstrings, which can mask ACL deficiency.
Stabilize the distal femur with one hand, gripping firmly just above the joint line. Grasp the proximal tibia with your other hand just below the joint line, with your thumb on the tibial tuberosity.
Test Movement
With the femur stabilized, apply a firm, smooth anterior force to the proximal tibia. Assess both the amount of anterior tibial displacement and the quality of the endpoint when translation stops. Always test both knees and compare side to side — asymmetry of 3mm or more is considered clinically significant.
Modified Lachman (Prone Position)
When femoral stabilization is difficult — typically in patients with large thighs or when examiner hand size is a limiting factor — a prone modification can be used. The patient lies prone with the knee flexed over the edge of the table. The examiner applies an anteriorly directed force to the posterior proximal tibia. This reduces grip demands and can improve reliability in larger patients.
Positive Sign and Interpretation
A positive Lachman test is indicated by a soft or mushy endpoint during anterior tibial translation. This reflects the absence of the normal abrupt halt provided by an intact ACL. Secondary structures eventually limit movement, but the endpoint lacks the firm quality of a healthy ligament.
A firm or hard endpoint indicates an intact ACL halting anterior translation abruptly. Note that a firm endpoint does not rule out a partial ACL tear — partial tears can produce near-normal endpoint quality with only slightly increased translation.
Grading Tibial Translation
| Grade | Translation | Interpretation |
|---|---|---|
| 1+ | 3–5 mm | Mild laxity — partial tear possible; endpoint quality is key |
| 2+ | 6–10 mm | Moderate laxity — significant ACL disruption likely |
| 3+ | >10 mm | Severe laxity — complete ACL tear likely |
Endpoint quality is generally considered more diagnostically important than translation amount alone. A soft endpoint at any grade raises concern for ACL disruption.
Sensitivity and Specificity
| Metric | Value |
|---|---|
| Sensitivity | ~85% (range 63–100% across studies) |
| Specificity | ~94% (range 89–99% across studies) |
| Positive likelihood ratio (LR+) | ~10.2 |
| Negative likelihood ratio (LR−) | ~0.14 |
Values from Benjaminse et al. (2006), based on a systematic review and meta-analysis of 28 studies in the Journal of Orthopaedic and Sports Physical Therapy.
A positive LR of ~10 represents a large, clinically meaningful shift in post-test probability. A positive Lachman in the right clinical context substantially increases the likelihood of ACL rupture. A negative LR of ~0.14 means a negative test moderately reduces that probability but does not rule it out.
Lachman vs. Anterior Drawer Test
The Anterior Drawer test is performed at 90° of knee flexion; the Lachman is performed at 20–30°. That difference matters clinically:
- At 90° flexion, the hamstrings are under tension and can act as secondary ACL stabilizers, splinting the tibia and masking anterior laxity — particularly acutely, when guarding is high.
- At 20–30° flexion, hamstring tension is reduced, allowing more reliable assessment of isolated ACL restraint.
The Lachman is generally more sensitive than the Anterior Drawer, especially in the acute setting. The Anterior Drawer remains useful and widely taught, but the Lachman is the preferred test when ACL integrity is the primary question.
Clinical Considerations
- Acute injuries: The Lachman is more reliable acutely than the Anterior Drawer. Swelling and guarding affect both tests, but the lower flexion angle reduces the hamstring-splinting effect.
- Examiner experience: Grading translation and endpoint quality requires practice. Distinguishing a firm partial-tear endpoint from a true intact endpoint is a learned skill.
- Compare bilaterally: Some patients have constitutional ligamentous laxity. Always compare to the uninvolved side before calling a result positive.
- Don’t use it in isolation: Combine with the Pivot Shift test and clinical history for the most accurate assessment. Positive Lachman + positive Pivot Shift carries very high specificity for ACL rupture.
- Partial tears: A partial ACL tear may produce normal or near-normal translation with a firm endpoint. When a partial tear is suspected, MRI is essential.
Related Knee Tests
- Anterior Drawer Test — ACL integrity assessed at 90° flexion
- Pivot Shift Test — Rotational instability; combines with Lachman for high specificity
- Posterior Drawer Test — PCL integrity
- McMurray Test — Meniscal pathology
Frequently Asked Questions
What does a soft endpoint on the Lachman test mean?
A soft or mushy endpoint means the ACL is not providing its normal abrupt check to anterior tibial translation. Secondary structures eventually arrest movement, but the endpoint lacks the firm quality of an intact ligament. This finding indicates ACL disruption — either partial or complete.
Is the Lachman test the most accurate clinical test for ACL tears?
Among individual tests, the Lachman has the best combination of sensitivity (~85%) and specificity (~94%) for ACL rupture. The Pivot Shift test has higher specificity but lower sensitivity and is more technically demanding. Using both tests together improves diagnostic accuracy further.
Why is the knee positioned at 20–30° for the Lachman test?
This position minimizes hamstring tension. At 90° flexion, the hamstrings can limit anterior tibial translation and reduce test sensitivity — especially acutely, when patients guard more. The Lachman position largely removes this confounding factor.
References
- Benjaminse A, Gokeler A, van der Schans CP. Clinical diagnosis of an anterior cruciate ligament rupture: a meta-analysis. J Orthop Sports Phys Ther. 2006;36(5):267–288.
- Torg JS, Conrad W, Kalen V. Clinical diagnosis of anterior cruciate ligament instability in the athlete. Am J Sports Med. 1976;4(2):84–93.
- Magee DJ. Orthopedic Physical Assessment. 6th ed. Elsevier; 2014.
Video Demonstration
video source: University of Wisconsin – Department of Family Medicine
>> Return to the list of Common Tests in Orthopaedic Examination of the Knee