There are four ligaments that give you stability to the knee: the MCL on the inside part of the knee; the LCL on the outside part of the knee; and the ACL and PCL, which cross deep inside the knee itself. Injuries to the MCL and LCL can usually heal with bracing followed by a rehab program. Injuries to the ACL or PCL usually do not have the ability to heal themselves and may require surgical reconstruction.
When injuring an ACL, it is also very common to injure one of the C-shaped shock absorbers known as the meniscus or you end up with a bone bruise on the outside part of your knee. In addition to examining your knee, your doctor likely will order an MRI scan, which is usually accurate in establishing the extent of the injuries to the ligaments and knee meniscal cartilage.
If an ACL tear is present, usually this will be treated first with a rehabilitation program to get the swelling down, restore the range of motion, and strengthen the knee prior to determining whether surgery is necessary. An accurate diagnosis is essential, so please get to your doctor quickly.