The anterior cruciate ligament restricts the tibia from sliding in front of the knee.
When you tear this ligament there are several symptoms that will almost always accompany this injury.
Pop or Snap Sound When Injury Occurs One of the most common ways to tell if you have injured your ACL is from the injury itself.
If when you injured your knee you felt a snap or pop and then collapsed it is possible you have torn your ACL.
Swelling ACL injuries especially tears are often accompanied by significant swelling in the knee shortly after the injury.
This is not always the case, from my personal experience both times I tore my ACL there was minimal swelling, however most people experience a lot of swelling.
Knee Instability After you have injured your ACL you will likely notice knee instability this is due to your ACL no longer supporting and stabilizing your knee.
If you are not in to much pain immediately after the injury you will likely notice the "funny" feeling you have walking where your knee no longer feels stable.
Loose Knee Similar to the instability issue above, a common way to determine if you have an ACL injury is by testing your knees looseness.
To do this sit in a chair with your leg relaxed and foot flat on the ground.
Keeping your leg relaxed push place one hand on top of your injured knee and with the other push on the back of your calf.
If both knees feel the same than you may not have injured your ACL.
However, if you feel like the injured knee is loose and there is nothing stopping you from pushing the back of your calf forward than you could have an ACL injury.
Clicking/Popping While Walking The final symptom of an ACL injury is clicking/popping while walking.
Now this isn't actually a symptom of an acl injury it is a symptom of meniscus damage which can often accompany an ACL injury.
This symptom by itself is not enough to say you have an ACL injury but if you have this symptom along with the 4 above than you have likely injured your ACL and meniscus.
How to fix and ACL injury? Surgery is often the recommended choice of recovery for an ACL tear.
The recovery process for ACL surgery can be long and time consuming but there are advanced recovery techniques that can greatly reduce the recovery time.
ACL Surgery Recovery Experience and Timeline