What is the Lachman test?
The Lachman test is done to check for a forward cruciate ligament (ACL) injury or tear. The ACL connects two of the three bones that make up the knee joint:
- Patella or kneecap
- The femur or thigh bone
- Warm or shin
When the anterior cruciate ligament is torn or injured, you may not be able to fully use or move your knee joint. Anterior cruciate ligament tears and injuries are common in athletes, especially soccer, basketball, and baseball players, who use their legs to run, kick, or tackle other players.
The Lachman test consists of a few simple steps. It is careful a reliable way to diagnose an ACL injury and choose what treatment is best for your injury.
Let’s take an earlier look at how the test works, how it’s used to diagnose conditions related to your ACL, and what happens next based on your results.
How accurate is this Lachman test?
Many studies have shown that the Lachman test is very accurate in diagnosing ACL injuries, especially when used in conjunction with an ADT or other diagnostic tool.
A 1986 study of 85 persons tested under anesthesia with knee injuries found that this test had a success rate of nearly 77.7 percent in helping diagnose ACL injuries that occurred less than two weeks before they occurred.
However, there is some subjectivity. A 2015 study, a trusted source, found that two doctors who tested the same patient agreed 91 percent of the time. This means that there is some margin of error among physicians as to whether they interpret the results correctly.
A 2013 study, which observed 653 people with ACL tears, found that the Lachman test had a 93.5 percent achievement rate, just 1 percent less accurate than the ADT. The 2015 study, Trusted Source, observed a similar success rate of around 93 percent.
The formation of scar tissue in the ACL can result in a false positive. This makes the leg appear as if it is limited to the normal range of motion when in reality it is just scar tissue holding it back.
Lastly, Trusted Source studies have found that being under general anesthesia makes it more likely that your doctor will make an accurate diagnosis.
How is the Lachman test performed?
With the patient lying down and relaxed, the inspector bends the knee slightly (about 20 to 30 degrees). The examiner then stabilizes the thigh as he pulls the shin forward. Holding the leg in a slight external (outward) rotation will help to relax the IT band.
The test puts pressure on the ACL. Both the volume of movement (displacement) of the shinbone and the feel of the endpoint of movement (how solid the tendon feels) provide information about the ACL.
Purpose of Lachman test
The Lachman test is an inert accessory knee motion test performed to identify the integrity of the anterior cruciate ligament (ACL). The test is designed to evaluate single and sagittal plane instability.
Lay the patient supine on the bed. Place the patient’s knee in about 20-30 degrees of flexion. According to the Bates Physical Exam Guide, the leg should also be turned externally slightly. The examiner should place one hand behindhand the tibia and the other on the patient’s thigh. The examiner’s thumb must be on the tibial tuberosity. When dragging the tibia anteriorly, an intact ACL should prevent forward translational gesture of the tibia at the femur (“firm end feel”).
Anterior translation of the tibia associated with a final soft or mushy sensation indicates a positive test. More than approximately 2 mm of anterior conversion compared to the unaffected knee suggests an ACL tear (“soft touch at the end”), as does 10 mm of total anterior conversion. An instrument called “KT-1000” can be used to determine the greatness of the undertaking in millimeters.
Performing the Lachman test
The patient should be relaxed for this test, especially the limb being examined. The examiner places the examined leg in approximately 20 degrees of flexion, placing the examiner’s knee under the patient’s thigh. Use one hand to steady the distal femur near the joint line on the anterior side, while palpating the joint line. Place the scan of the other hand on the anterior side of the tibia and the fingers grasping the posterior side of the tibia near the joint line.
Apply rapid forces directed posterior to anterior across the tibia. There should be a firm final feel. A positive test is an excessive movement or lack of a firm final feel. An alternative method is to hold the femur and tibia without the examiner’s knee under the patient’s thigh. The correct joint angle must be used for this test because a position closer to full extension naturally has a less anterior translation of the tibia and can result in a false endpoint.
Importance of the Lachman test
The anterior cruciate ligament is stabilized against the anterior translation of the tibia in the femur, due to insertion on the anterior tibial plateau and posteriorly on the medial side of the lateral femoral condyle (Neumann 534). The force practical by the examiner stresses the ligament and is a better test for evaluating ACL integrity in acute wounds compared to the anterior drawer test for several reasons. The 20-degree knee flexion position is a less painful position than the 90 degrees required for the anterior drawer test; therefore, there is less chance of protective hamstring spasms.
Also, at 20 degrees of flexion, the ACL is maximally harassed and can be more accurately assessed, because other tissues do not boundary anterior translation of the. It should be noted that patients with a PCL tear may test positive on the Lachman test. In the initial location of the Lachman test, the tibia will rest further posterior than usual due to the absence of the LCP, increasing the excursion during the test (Manske, 2006). This means that the integrity of the PCL must be evaluated before analyzing the integrity of the ACL. Often with ACL injuries, other tissues and structures can also be injured. One of the most important findings recently has been bone contusions with ACL injuries. Look for research on the topic to be published soon.