Lachman Test

Anatomy and Physiology

The primary function of the ACL is to control anterior movement of the tibia and inhibit extreme ranges of tibial rotation. The ACL consists of 2 major bundles; the posterolateral bundle and the anteromedial bundle, which are named based on their tibial insertion. The bundles originate on the posteromedial side of the lateral femoral condyle and insert just anterior to the intercondylar tibial eminence. The Lachman test directly assesses the integrity of this anatomical relation.[2]

Indications

The clinician should ask about the timing of the injury, the mechanism, joint swelling, functional ability, joint instability, and associated injuries while performing an appropriate history and physical exam in a patient with a suspected ACL injury. Non-contact injuries most commonly cause ACL tears, and historical cues prompting an ACL evaluation include a sudden change of direction or awkward landing, causing the knee to "pop" or give way, resulting in knee pain, swelling or instability.

Contraindications

The current literature demonstrates safety in carrying out the test, following the correct procedure.

Equipment

The manual test (30 degrees stress physical examination) does not require any instrumentation to diagnose an anterior cruciate ligament injury. Remember that the test can be subject to errors, depending on the strength of the operator and the patient's posture. A study showed through an arthrometer that the average force to be applied with the Lachman test is about 80 N (Newton).

Preparation

Physical examination includes inspection, palpation, testing of mobility, strength, and stability, and performance of special tests of ACL integrity. One should always examine the unaffected knee for comparison as patients have a baseline increased laxity with Lachman testing that is not due to injury. It is often best to examine the patient immediately after the injury or at least within several hours for a suspected ACL injury to avoid evaluating a knee with significant swelling and hemarthrosis, which may lead to patient guarding and negatively impact testing accuracy.[3][4]

Technique or Treatment

The patient is positioned supine with their injured knee flexed to 20 to 30 degrees while also slightly externally rotating the injured leg to relax the iliotibial band.  The examiner then uses one hand to stabilize the distal femur while using the other hand to grasp the proximal tibia. Next, an anterior force is applied to the proximal tibia in an attempt to sublux the tibia forward while keeping the femur stabilized.[5]

The test is considered positive if there is excessive anterior translation of the proximal tibia greater than the uninjured side and also a lack of a firm endpoint. Endpoints are graded from “hard” to “soft,” and have been nominally classified as A (firm, hard endpoint) or B (absent, soft endpoint).[6] A hard endpoint is appreciated when there is an abrupt endpoint preventing further anterior translation of the tibia on the femur. A soft endpoint is regarded as a forward translation of the tibia without a distinct, firm, clear endpoint.[5]

A modified Lachman test involves placing the examiner’s knee below the patient’s posterior thigh of the affected leg to create a more stable anchor when performing the test. The prone Lachman test, which can be used to enhance patient comfort, is also a reliable evaluation technique that can be used to confirm the presence of an ACL tear but should not be used as the sole criterion to rule out the presence of the injury.[5][7]

Complications

The literature does not contain articles or case reports that highlight complications in the Lachman test procedure.

Clinical Significance

Interpretation

Tibial translation or movement of 5 mm or more than movement in the normal limb generally indicates a rupture of the ACL, and more than 2 mm of anterior translation of the affected knee compared to the unaffected knee is considered a positive test indicating ACL injury. Grading of ACL laxity is described as 1 through 3, which correlates to mild, moderate, and severe ACL injuries. Mild (grade I) is 0 to 5 mm, moderate is 6 to 10 mm (grade II), and severe is 11 to 15 mm (grade III) of anterior tibial translation compared to the uninjured side. The examiner should consider concomitant medial collateral ligament (MCL) and meniscal tears if there is greater than 11mm of translation.[6]

Correct technique is necessary for accurate test interpretation, as clinicians using proximal tibial placement were more likely to correctly interpret a Lachman test than those using a more distal tibial hand placement.[8]

Diagnosis

Diagnosis of an anterior cruciate ligament tear is definitively made by diagnostic imaging (MRI) or knee arthroscopy, but most often, the patient's history and physical presentation can reliably establish the diagnosis. Suggestive clinical findings of an ACL rupture include an acute knee effusion with positive Lachman, pivot shift, and/or anterior drawer tests.[4]

Test Accuracy

Lachman's test is generally regarded as the best test for assessing ACL integrity with a sensitivity of 87% and a specificity of 93%. The anterior drawer test has a sensitivity of 48% and a specificity of 93%. The pivot shift test has a sensitivity of 61% and a specificity of 97% and has the highest positive predictive value of the 3 tests.[5] Results have suggested that the pivot shift test has a lower sensitivity than the Lachman test because it is generally a harder test to perform in the acute setting due to patient guarding.[9]

Studies suggest performing both the Lachman and the pivot shift test to confirm an ACL rupture due to the high sensitivity of the Lachman and the high specificity of the pivot shift test. Also, a positive pivot shift test is the best for ruling in an ACL rupture, whereas a negative Lachman test is the best for ruling out an ACL rupture.[10][3]

Several factors can affect Lachman's test accuracy. If hemarthrosis is present, the increased intra-articular volume may cause pain on range of motion with extensive guarding and spasm of the hamstring muscle group. This may limit knee range motion and decrease the accuracy of Lachman test findings.[11] A retrospective study reported that Lachman test sensitivity might be improved with knee joint aspiration before the exam in patients with suspected hemarthrosis, which may limit exam accuracy.[12]

Additionally, false-positive Lachman tests can be associated with isolated posterior cruciate ligament injury and should be interpreted with caution in patients with suspected posterior cruciate ligament (PCL) injury diagnosed with either a positive posterior drawer sign or positive posterior sag sign.[13]

An orthopedic device called the KT-1000 knee ligament arthrometer can be used in diagnosis to provide an objective measurement of anterior-posterior tibial translation. The device is more widely used in clinical studies evaluating ACL injuries and less commonly used in clinical practice for ACL diagnosis because the physical examination is generally reliable.[14]

Enhancing Healthcare Team Outcomes

The Lachman test is widely regarded as the most useful test for diagnosing an acute ACL injury and should be used in conjunction with the pivot shift test and anterior drawer test for assessing ACL integrity. Prompt evaluation and diagnosis of ACL injuries by the interprofessional healthcare team are essential to expedite further management and rehabilitation. The team consists of primary care and emergency providers, sports medicine physician, orthopedists, and nurses. It is important to evaluate and consider other knee structures that often sustain an injury in conjunction with an ACL injury, as isolated ACL tears reportedly occur less than 10% of the time in acute knee injuries.[15] A clinician should also examine and test for medial and lateral collateral ligament, posterior cruciate ligament, and meniscal injuries in conjunction with the Lachman test for a suspected ACL injury. Appropriate positioning, technique, and interpretation of the Lachman test are essential for correctly diagnosing an ACL injury. If an ACL injury is detected, the patient is usually referred to an orthopedist. Orthopedic nurses assist in coordinating care, provide patient and family education, and communicate status to the orthopedist. [Level 5]

Nursing, Allied Health, and Interprofessional Team Interventions

A study reports that conducting the test in a multidisciplinary context could be detrimental to the accuracy of the test.[16] Probably, to take the test correctly, the doctor or the operator would have to do a manual training procedure (as for other manual tests).[17]

The test's accuracy is best under anesthesia.[18]