“During the physical exam, your doctor will check your knee for swelling and tenderness — comparing your injured knee to your uninjured knee. He or she also may move your knee into a variety of positions to assess range of motion and overall function of the joint. The physician will often perform the Lachman's test to see if the ACL is intact. If the ACL is torn, the examiner will feel increased forward (upward or anterior) movement of the tibia in relation to the femur (especially when compared to the normal leg) and a soft, mushy endpoint (because the ACL is torn) when this movement ends.”

• “X-rays. X-rays may be needed to rule out a bone fracture. However, X-rays can't visualize soft tissues, such as ligaments and tendons.
• Magnetic resonance imaging (MRI). An MRI uses radio waves and a strong magnetic field to create images of both hard and soft tissues in your body. An MRI can show the extent of an ACL injury and signs of damage to other tissues in the knee.
• Ultrasound. Using sound waves to visualize internal structures, ultrasound may be used to check for injuries in the ligaments, tendons and muscles of the knee”.

“Your doctor may recommend surgery if:

• You're an athlete and want to continue in your sport, especially if the sport involves jumping, cutting or pivoting
• More than one ligament or the cartilage in your knee is injured
• You're young and active
• The injury is causing your knee to buckle during everyday activities

During ACL reconstruction, the surgeon removes the damaged ligament and replaces it with a segment of tendon — tissue similar to a ligament that connects muscle to bone. This replacement tissue is called a graft. Your surgeon will use a piece of tendon from another part of your knee or a tendon from a deceased donor. The graft will serve as scaffolding on which new ligament tissue can grow.

After surgery you'll resume another course of rehabilitative therapy. Successful ACL reconstruction paired with rigorous rehabilitation can usually restore stability and function to your knee. Athletes often can return to their sports after eight to 12

REF https://orthoinfo.aaos.org/en/treatment/acl-injury-does-it-require-surgery/

Ref: Google images