Self-diagnosing an ACL tear injury is not an easy task. For a correct diagnosis, you need to be aware of all the symptoms and signs, perform an examination. You will need to know which is the most common mechanism of an ACL tear injury. That is a sudden deceleration, jumping or cutting action. An ACL tear injury can also occur after a direct impact on the knee, which usually happens in contact sports like football, basketball, and hockey.
A correct diagnosis is important so the patient and physician can determine the best course of action. In case of partial ACL tear injuries, conservative treatment might be an option while surgery for an ACL tear injury is the best choice for complete ACL tear.
Knowing The Symptoms Of An ACL Tear Injury
Most patients will feel or hear a popping sound right after an ACL tear injury. A sensation of the knee giving way is also very common. The pain is sharp and disabling so the injured person will not be able to run or walk without severe pain.
In case of a complete ACL tear injury, the swelling will start immediately after the injury and within a few hours, the knee will be full of blood. 
If you take a look at your knee, there will be no sharp edge between the patella and the rest of the knee joint. Instead, the area surrounding the patella will be distended. The presence of blood in the knee will distend the knee joint capsule and limit the motions in the knee, especially flexion. The patient might also have pain while trying to flex the knee.
Patellar Ballottement Test
The best test to check whether you have swelling inside the knee joint is the patellar ballottement test. To self-perform this test, you will have to sit with the injured leg extended. Then grab the lower pole of the patella with the thumb and index finger of one hand and stabilize it while applying pressure on top of the patella towards the knee joint with the thumb of another hand. Under normal circumstances, the patella will move just for around 1 cm, while in case of swelling the patella will move a lot more.
A combination of a popping sound, giving way and swelling of the knee joint is a strong predictor of a possible ACL tear injury .
To be sure that you suffered an ACL tear injury, there are a number of orthopedic tests which can be used to diagnose the ACL tear injury. If you want to self-diagnose your injury, then you might have a problem with some of these tests because of the mechanism of performing them. You will have to adapt and modify tests while trying to do them by yourself.
Modification Of The Anterior Drawer Test
You can sit with your leg extended. Now flex the knee to 90 degrees of flexion and hold the foot on the bed. You can place something on the dorsum of your foot to keep it in position. Place your hands around the upper part of your lower leg, just below the knee joint and push it anteriorly. Now rotate the foot inward and repeat the process. At the end, rotate the foot outward and repeat the process again. If your lower leg moves more than 8 mm, then there is a chance that you have an ACL tear injury.
Modification Of The Lachman Test
You can sit and place your leg on pillows under the thigh and lower leg so that the knee is in slight flexion. Place one hand on the thigh to prevent movements. Now place the other hand on the back side of the knee and push it anteriorly. If the lower leg moves anteriorly there is a chance that you have an ACL tear injury.
Modification Of The Pivot Shift Test
Sit on the bed with fully extended leg and rotate the leg inwards as much as you can. Now place one hand on the outer side of the lower leg and the other hand on the inner side of the knee joint and apply pressure pushing it outward. Flex the knee at the same time while applying pressure. The test is positive if you feel pain or discomfort while moving the lower leg.
If you heard a popping sound, your knee is swollen and you can’t bear weight after the injury, there is a high chance of an ACL tear injury. Even where signs, symptoms and positive orthopedic tests indicate an ACL injury, MRI remains the gold standard for imaging of injuries of structures within the knee joint . In some cases, diagnostic arthroscopy is the only way to diagnose an ACL tear injury .