ACL Injury Symptoms & Diagnosis

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Lachmans test for acl injuryAn ACL injury is usually caused by a sudden twisting of the knee whilst the foot is planted on the ground, or a direct impact or trauma to the knee, often on the outside of the joint.

The following is for information purposes only. We advise seeking professional advice if you suspect an anterior cruciate ligament injury.


Symptoms include sudden pain in the knee joint at the time of injury, sometimes with an audible pop or crack. The athlete may have a feeling of instability and rapid swelling may occur from bleeding within the joint which will feel warm to touch.

Often an athlete will seek professional advice at a clinic the next day or two after injury. By that time there will be considerable swelling making it very difficult to diagnose exactly what is wrong with the knee. After a few days when the swelling has gone down it will be easier to examine the knee joint.

There will be restricted range of movement with particular difficulty straightening the leg. Tenderness or pain may be felt all around the knee joint and there will be positive signs in the anterior drawer test and Lachman's test.


Two tests which are used to assess the knee to determine if there has been damage to the anterior cruciate ligament, the anterior draw test and Lachman's test.

Anterior draw test

LachmansWith the patient laying on their back with the injured knee bent to 90 degrees and the foot flat on the table. The practitioner may stabilize the foot by sitting on it.The practitioner will grasp the upper Tibia (shin bone) with both hands. They will then attempt to pull the Tibia forwards, towards them. A positive result is if the Tibia moves excessively forwards.The injured knee should always be compared to the healthy knee for 'normal' movement.

Lachman's test

The patient lies on their back with the knee flexed between 15 and 30 degrees. The practitioner grips the outside of the lower femur or thigh bone with the upper hand and the inside of the upper Tibia with the lower hand. The femur is stabilised with the upper hand as the lower hand applies an anterior force on the tibia. A positive result is found if the tibia moves excessively forward compared to the healthy knee.

As well as the tests described above, the practitioner may also test the range of motion at the joint, the strength of the surrounding muscles, and test for associated injuries such as meniscus tears.


An MRI scan can confirm the diagnosis and an X-ray can eliminate an avulsion fracture where the ligament pulls a piece of bone away.

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