Ligaments connect bones to bones. Tendons connect muscles to bones. The 4 main ligaments in the knee connect the thighbone (femur) to the shin bone (tibia).

The knee has 4 ligaments. They are:

• Anterior cruciate ligament (ACL)
• Posterior cruciate ligament (PCL)
• Medial collateral ligament (MCL)
• Lateral collateral ligament (LCL)

Your leg may also buckle when you try to stand on it. And you may have swelling and pain in the knee.

The ACL is often stretched or torn during a sudden twisting motion. This can happen when the feet stay planted one way, but the knees turn the other way. Skiing, basketball, and football are sports that have a higher risk for ACL injuries.

An ECG (electrocardiogram) is used to diagnose heart rhythm problems. But X-rays and MRI may be used to diagnose a knee injury. X-ray uses electromagnetic energy beams to make images of bones other internal body structures. MRI uses large magnets, radio waves, and a computer to make detailed images of organs and structures in the body.

Arthroscopy is commonly used to repair a torn ACL. In this procedure, the surgeon puts tiny surgical tools into the knee, along with the scope, through small incisions. Pictures sent to a video screen let the surgeon see and work inside the knee.

The ACL can be rebuilt with a tendon from around your knee. The material used to rebuild it is called a graft. Often a graft comes from the patellar tendon or the hamstring tendon.