One of the most common injuries of the knee is an anterior cruciate Ligament (ACL) sprain or tear. It has been reported that there are approximately 200,000 ACL injuries a year in the United States. These injuries may occur when participating in sports such as skiing, basketball, football, and soccer. They often happen specifically when changing directions or abruptly stopping or jumping. The ACL connects the femur to the tibia and stabilizes the knee. It functions to keep the knee from extending beyond the normal range of motion and over rotating.
The most common indication of ACL injury is a popping sound and immediate swelling around the knee cap. Physical and joint examination including an X-ray are used to diagnose an ACL injury. Diagnosis of an ACL tear is made by knowing your symptoms, medical history, performing a physical examination of the knee, and performing other diagnostic tests such as X-rays, MRI scans, stress tests of the ligament, and arthroscopy.
ACL injuries are classified in three categories
- Grade 1—Trauma to the ligament is relatively minor. Some of the fibers are stretched. This is a sprain
- Grade 2—Trauma to the ligament is more severe. Some of the fibers are torn. This is called a "partial tear"
- Grade 3—This is the most severe ACL injury. The fibers of the ligament are completely torn. It is referred to as a "complete tear".
Some patients recover from ACL injuries with rest, modification of activities and rehabilitation. Others require surgery. Surgery is often recommended for patients who have active lifestyles.
If the overall stability of the knee is intact, your doctor may recommend nonsurgical methods. Non-surgical treatment consists of rest, ice, compression, and elevation (RICE protocol); all of which assist in controlling pain and swelling. Physical therapy may be recommended to improve knee motion and strength. A knee brace may be needed to help immobilize your knee.
Athletes involved in pivoting sports will most likely require surgery to safely return to sports. The usual surgery for an ACL tear is an ACL reconstruction which tightens your knee and restores its stability. Surgery to reconstruct an ACL is done with an arthroscope using small incisions. Your doctor will replace the torn ligament with a tissue graft that can be obtained from your knee (patellar tendon) or possibly a cadaver allograft. Following ACL reconstruction, physical therapy helps to resume a wider range of activities.