Introduction
The Lachman test comes under the physical examination procedure to check for the integrity of the anterior cruciate ligament in an anterior cruciate ligament (ACL) injury case. This test is used to identify the anterior translation movement of the tibial bone concerning the thigh bone. This test is the other variant of the anterior drawer test. Studies have shown that the Lachman test is more effective in diagnosing acute anterior cruciate ligament tears when compared to the pivot shift test and anterior drawer test. John Lachman, an orthopedic surgeon from Philadelphia, invented this technique.
What Is the Anatomy and Physiology of the Anterior Cruciate Ligament?
The primary function of the anterior cruciate ligament is to connect three major bones from the joint of the knee, namely:
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Patella (kneecap).
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Femur (thigh bone).
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Tibia (shin bone).
It consists of two bundles, namely the posterolateral bundle and the anteromedial bundle. These bundles are named based on the tibial insertion. These posterolateral and anteromedial bundles originate from the posteromedial area of the lateral femoral condyle and insert into the anterior area of intercondylar tibial eminence.
What Are the Indications for the Lachman Test?
The Lachman test is most commonly performed to diagnose anterior cruciate ligament (ACL) injury. Anterior cruciate ligament injuries usually cause tears that happen due to violent or repetitive movements of the ligament over time. Non-contact injuries to the anterior cruciate ligament happen due to sudden or awkward landing, which causes the knee to pop, resulting in intense pain, swelling, instability, and movement restriction.
What Are the Procedures That Should Be Done Before the Lachman Test?
The physical examination procedure to diagnose the anterior cruciate ligament injury includes inspection, palpation, testing of strength, stability, and mobility, and performance of the Lachman test. The doctors will always do examinations for the uninjured leg to identify the baseline laxity of the knee. It is important to perform these examinations immediately after the injury or within a few hours before the hemarthrosis and swelling to avoid a negative impact on accuracy.
What Is the Technique of the Lachman Test?
The steps doctors instruct and perform during the Lachman test include:
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This technique, while performed manually, does not require any equipment. But to overcome the errors caused by the changes in the examiner's strength and the patient's posture, studies show that using an arthrometer with a force of about 80 N (Newton) is beneficial.
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The patient should lie down on their back with their leg straight out, and muscles relaxed, especially the hamstring muscles.
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Then the doctor will bend the knee slowly and gently to a 20 to 30-degree angle. The doctors may also rotate the patient's leg to make the knee point outward.
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The doctor will place one hand on the lower thigh and the other hand on the lower leg below the bent leg.
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Then the doctor will firmly pull the patient's lower leg forward by keeping their thigh stable with the help of their other hand.
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This test is said to be positive if there is an excessive translation of the proximal tibia than the uninjured side.
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The modification in the Lachman test involves the placement of the doctor's hand below the patient's posterior thigh of the injured leg to create excessive stability.
How Is an Anterior Cruciate Ligament (ACL) Injury Diagnosed?
Along with medical history, physical examination, which includes the Lachman test, anterior cruciate ligament injury is also diagnosed using MRI (magnetic resonance imaging) and knee arthroscopy. The clinical findings include rupture of the anterior cruciate ligament (ACL), acute knee effusion with positive Lachman test, anterior drawer test, and pivot shift test.
What Is the Grading for the Lachman Test?
The two major criteria used to assign a grade in the Lachman test for diagnosing anterior cruciate ligament injury include
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Endpoint - The endpoint is used to reference the shin bone and knee movement during the rest. The anterior cruciate ligament keeps the shin bone and knee with a certain limited range of motion. If these two parts move more than normal, it indicates the anterior cruciate ligament injury. It may also help the doctors to identify whether surrounding tissue also injures and causes improper stabilization of the joint.
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Laxity - The laxity is used for the reference of the firm feel of the anterior cruciate ligament when moved within the normal range of motion during the test. If the anterior cruciate ligament doesn't respond with a hard endpoint when it reaches the normal range of motion, it indicates torn or injury in the ligament.
By observing both legs with the above criteria the doctors may grade the injured leg, which includes:
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Normal - There will be no injury to the leg when compared to the opposite leg.
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Mild (Grade 1) - The injured leg may move two to five millimeters more than the normal range of motion in comparison with the uninjured leg.
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Moderate (Grade 2) - The injured leg may move 5 to 10 mm more than the normal range of motion in comparison with the uninjured leg.
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Severe (Grade 3) - The injured leg may move 10 to 15 mm more than the normal range of motion in comparison with the uninjured leg.
Some doctors may use a KT-1000 arthrometer to get accurate readings.
Conclusion
Anterior cruciate ligament (ACL) injury is painful and limits the knee movements or sometimes the full movement of the leg. Anterior ligament injuries can be diagnosed using the Lachman test and several other tests to confirm and proceed with further treatments. Proper diagnosis and treatment can correct the injury or tear along with the RICE (Rice, Ice, Compression, and Elevation) principle, physical therapy, and knee braces. An anterior cruciate ligament injury may also require ligament restoration surgery and post-surgical care. All these diagnostic methods and treatment modalities may help a person recover from anterior cruciate ligament injuries. Reaching out to healthcare professionals may be beneficial.
