Lachman Test | Special Test for ACL Tear

Lachman Test is used to assess the integrity of the anterior cruciate ligament (ACL) of the knee. It’s certain proof of anterior cruciate ligament insufficiency.

In his dissertation as early as 1875, the Greek physician George Noulis described the test of the cruciate ligaments in a nearly extended position of the knee, exactly the same test known today as the Lachman test, which was not described or so named until 1976.

See Also: Anterior cruciate ligament injury

How do you perform the Lachman’s test?

The examiner holds the patient’s knee between 15 and 30° of flexion. In this position in particular, the stabilizing function of the anterior cruciate ligament is essential in changing direction and braking.

Insufficiency of the anterior cruciate ligament is therefore particularly evident in this position of the joint as it approaches extension due to the occurrence of lateral subluxation of the proximal tibia (pivoting).

The tibia should be slightly externally rotated and the anterior tibial translation force (anterior drawer) should be applied from the posteromedial aspect.

Ensure that there are no tibial rotations while performing this test. This is to avoid action by secondary stabilizers and also that it is not posteriorly subluxated prior to initiation of the physical test (as occurs in a PCL-deficient knee). The joint position used during the Lachman test (15-30 degrees of flexion) alters the hamstring’s force vector, thereby reducing the possibility of a false-negative result.

In a heavier patient with bulky thighs, the patient can be examined prone by the side of the couch with the thigh supported on the couch. The knee is flexed 30°, and both hands are now used to hold the tibia, which is pushed anteriorly.

What does a positive Lachman Test mean?

The Lachman Test is positive if there is excessive anterior translation of the proximal tibia greater than the uninjured side and also a lack of a firm endpoint indicating an anterior cruciate ligament injury.

The end point of motion must be soft and gradual without a hard stop; any hard stop suggests a degree of stability of the anterior cruciate ligament:

• A hard end point within 3 mm suggests complete stability of the anterior cruciate,
• whereas one after 5 mm or more suggests relative stability of the anterior cruciate ligament, such as may be present following an earlier sprain.

Cruciate ligament injury should be suspected where the end point is soft or absent.

These discrepancies likely occur as there are a number of factors that can influence the results. These include:

1. An inability of the patient to relax;
2. The degree of knee flexion;
3. The size of the clinician’s hand (see below);
4. The stabilization (and thus relaxation) of the patient’s thigh (see below).

Lachman Test Modifications

1. Prone Lachman Test:

Prone Lachman Test is another special test for ACL injury.

The patient is prone. The examiner grasps the lateral aspect of the proximal tibia and immobilizes the patient’s leg in his or her own axilla. With the other hand, the examiner grasps the distal femur immediately proximal to the patella to immobilize the thigh. Then the examiner pushes the tibia anteriorly with respect to the femur.

Damage to the cruciate ligament is present where there is demonstrable mobility of the tibia relative to the femur. The motion must have a soft end point. Any hard end point suggests a certain stability of the anterior cruciate. Where this occurs within 3 mm , it suggests complete stability; where it only occurs after 5 mm , it suggests relative stability with previous elongation of the anterior cruciate.

Although the patient is relaxed in the prone position, it is not always easy to assess the quality of the end point:

• A hard end point and hemarthrosis suggest an acute partial tear;
• a hard end point without hemarthrosis suggests a suspected chronic partial tear, elongation, or excessive laxity.
• A soft end point and hemarthrosis suggest a complete tear; a soft end point without hemarthrosis suggests a chronic complete tear.

Where the end point is hard, a posterior cruciate lesion must be excluded by testing the spontaneous posterior drawer and applying the active tests.

A study on 52 patients referred from the emergency room of a hospital to orthopaedic surgery for definitive evaluation of a painful knee, the sensitivity and specificity of Prone Lachman Test was 70% and 80%, respectively.

2. Stable Lachman Test:

The patient is supine. The examiner places the patient’s thigh over his or her ow n thigh. This holds the patient’s leg in constant flexion that the patient cannot change. With the distal hand, the examiner pulls the tibia anteriorly while the other hand immobilizes the patient’s thigh on the examiner’s own thigh.

The classic Lachman test presents problem’s not only for examiners with small hands, simultaneously immobilizing the thigh and lower leg can also be difficult for any examiner with an obese or muscular patient. Using one’s ow n thigh as a “workbench” for examining the patient’s knee is an easy solution in such cases and one that allows examination even of obese or muscular patients.

The character of the end point (hard or soft) is easier to evaluate in this test.

3. No-Touch Lachman Test:

The patient is supine and grasps the thigh of the affected leg near the knee with both hands and slightly flexes the knee. The patient is then asked to raise the lower leg o the examining table while maintaining flexion in the knee. The examiner observes the position of the tibial tuberosity during this maneuver.

If the ligaments are intact, there will be no change in contour, or only a slight one as the tibial tuberosity moves slightly anteriorly. In an acute injury to the capsular ligaments involving the anterior cruciate and medial collateral ligaments, the examiner will observe a significant anterior displacement of the tibial tuberosity (subluxation of the joint).

This test often allows one to exclude complex injuries without having to touch the patient.

4. Active Lachman Test:

The examiner asks the supine patient to extend the leg in such a way as to lift the foot o the examining table. During this maneuver, the examiner keeps his or her eyes on the knee the better to discern the contours of the tibial tuberosity and patellar ligament. The examiner achieves slight passive flexion in the knee by passing one hand beneath the thigh of the patient’s affected leg and resting it on the contralateral knee. The effect of the quadriceps is increased by immobilizing the foot on the examining table.

Slight anterior migration of the tibial head will be observed where the anterior cruciate ligament is intact. In a cruciate tear, there will be a significant anterior migration compared with the contralateral side. This is because the anterior cruciate ligament no longer limits the displacement caused by contraction of the quadriceps.

This test should only be performed after excluding a posterior cruciate ligament injury, in which the tibia would spontaneously displace posteriorly.

There, too, contraction of the quadriceps will produce significant anterior displacement of the tibia and with it a false-positive active anterior drawer test. Contraction of the quadriceps can also cause meniscal impingement where loosening of the posterior attachment of the medial meniscus accompanies the insufficiency of the medial ligaments and anterior cruciate.

The active Lachman test differs from the traditional Lachman test in that the lower leg can easily be immobilized in various degrees of rotation and the stabilizing effect of the medial and lateral capsular ligaments can be assessed.

Generalized anterior instability (involving the anterior cruciate ligament and the medial, posteromedial, lateral, and posterolateral capsular ligaments) will produce significant active anterior tibial displacement in internal and neutral rotation and, especially, in external rotation.

Notes

A false-negative Lachman test may occur in these situations:

1. The femur is not properly stabilized.
2. Meniscus lesion or degenerative changes such as osteophytes on the intercondylar eminence block translation.
3. The tibia is medially rotated.
4. A significant hemarthrosis.
5. Protective hamstring spasm.
6. Tear of the posterior horn of the medial meniscus.

In a concurrent PCL injury, the knee can be posteriorly subluxated at the beginning of the test. This may result in a false positive pseudo Lachman test for the ACL. The error can be appreciated if the contralateral knee is examined first and compared to the injured knee. The normally palpable prominences of the anteromedial and lateral tibial plateau in the flexed-knee position are not felt if the knee is PCL deficient and there is posterior subluxation. An abnormal contour or sag may be evident at the proximal anterior tibia when viewed from a lateral position.

Accuracy

The accuracy and reliability of the anterior cruciate ligament test appears to vary. Katz et al. found that in the hands of an experienced clinician, accuracy of this test was:

• Sensitivity: 81.8 %
• Specificity: 96.8 %

The sensitivity and specificity of the Lachman test knee increases to 100% if the patient was anesthetized.

Lachman Test VS Anterior Drawer Test

The Lachman test has two advantages over the anterior drawer test in 90 degrees of knee flexion:

1. First, all parts of the anterior cruciate ligament are more or less equally taut.
2. Second, in acute lesions it is often impossible to position the knee in 90 degrees of flexion because of a hemarthrosis.

Advantages of Lachman’s test:

1. Highly specific for ACL rupture
2. Not hampered by posterior horn of meniscus
3. Not hampered by haemarthrosis
4. Less painful because the muscles are relaxed
5. Not hampered by sprained or partially ruptured medial collateral ligament
6. Performed in functional position of flexion of knee. Can be performed when there is a fracture close to knee.

In a study of patients with an ACL rupture, the Lachman test was positive in 80% of non-anesthetized patients and 100% of anesthetized patients. In comparison, the anterior drawer sign was positive in 9% of non-anesthetized patients and 52% of anesthetized patients.

Jonsson et al. compared both the Lachman and anterior drawer tests in 45 patients with an acute ACL injury and 62 patients with a chronic knee injury. Patients were tested while non-anesthetized and anesthetized, and the diagnosis was verified by arthroscopy. The Lachman test results for the acute injury group was 87% (conscious) and 100% (anesthetized). The anterior drawer test results were 33% and 98%, respectively. The chronic injury group scored a positive Lachman test in 97% (conscious) and 99% (anesthetized). The anterior drawer test was positive in 92% and 100%, respectively.

According to Larson, the Lachman test proved to be the most sensitive test for an ACL rupture. However, this article lacked statistical data to verify this assertion.

Another study that compared the two tests reported a sensitivity of 99% for the anterior cruciate ligament test and a sensitivity of 70% for the anterior drawer sign.

When examination findings include an apparently positive Lachman test or anterior drawer test, the knee must also be screened for PCL insufficiency. If the PCL is deficient, tests for ACL insufficiency may appear positive, since the tibia is relocated anteriorly from its posteriorly subluxed position on the femur.

Reference

1. Katz JW, Fingeroth RJ. The diagnostic accuracy of ruptures of the anterior cruciate ligament comparing the Lachman test, the anterior drawer sign, and the pivot shift test in acute and chronic knee injuries. Am J Sports Med. 1986 Jan-Feb;14(1):88-91. doi: 10.1177/036354658601400115. PMID: 3752353.
2. DeHaven KE. Arthroscopy in the diagnosis and management of the anterior cruciate ligament deficient knee. Clin Orthop Relat Res. 1983 Jan-Feb;(172):52-6. PMID: 6822005.
3. Jonsson T, Althoff B, Peterson L, Renström P. Clinical diagnosis of ruptures of the anterior cruciate ligament: a comparative study of the Lachman test and the anterior drawer sign. Am J Sports Med. 1982 Mar-Apr;10(2):100-2. doi: 10.1177/036354658201000207. PMID: 7081521.
4. Larson RL. Physical examination in the diagnosis of rotatory instability. Clin Orthop Relat Res. 1983 Jan-Feb;(172):38-44. PMID: 6822003.
5. Donaldson WF 3rd, Warren RF, Wickiewicz T. A comparison of acute anterior cruciate ligament examinations. Initial versus examination under anesthesia. Am J Sports Med. 1985 Jan-Feb;13(1):5-10. doi: 10.1177/036354658501300102. PMID: 3976980.
6. Donaldson WF 3rd, Warren RF, Wickiewicz T. A comparison of acute anterior cruciate ligament examinations. Initial versus examination under anesthesia. Am J Sports Med. 1985 Jan-Feb;13(1):5-10. doi: 10.1177/036354658501300102. PMID: 3976980.
7. Mulligan EP, Harwell JL, Robertson WJ. Reliability and diagnostic accuracy of the Lachman test performed in a prone position. J Orthop Sports Phys Ther. 2011;41(10):749-757.
8. NCBI – Skills in Rheumatology
9. Clinical Tests for the Musculoskeletal System, Third Edition book.
10. Mark Dutton, Pt . Dutton’s Orthopaedic Examination, Evaluation, And Intervention, 3rd Edition Book.