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Anterior Cruciate Ligament (ACL) Injury

The Anterior Cruciate Ligament (ACL) connects the front top of the tibia (the lower leg bone) to the rear bottom of the femur (the thigh bone). Athletes are often diagnosed with this common sports knee injury. 

Causes and Risk Factors

  • High impact collision or direct contact
  • Stopping suddenly or rapid directional change
  • Slowing down while running
  • Landing from a jump incorrectly
  • Several studies have shown that female athletes have a higher incidence of ACL injury than male athletes in certain sports, possibly due to pelvic or lower leg alignment


  • A “popping” noise and feeling of knee “giving out”
  • Pain with swelling
  • Loss of full range of motion
  • Tenderness along the joint line
  • Difficulty and discomfort while walking

Diagnosis and Treatment

Diagnosis usually involves a physical examination from an orthopedic surgeon, although sometimes imaging tests such as an x-ray or MRI scan help the doctor confirm diagnosis. Nonsurgical treatment can include bracing or physical therapy, but a torn ACL will not repair itself. Surgical treatment usually involves arthroscopy, where a tiny camera is inserted in the knee through a small incision and connected to a video monitor in the operating room. Your surgeon uses the camera to repair the damaged ACL with tissue from another part of your body, typically a tendon from your knee or hamstring, or from a cadaver. There are risks and benefits to each kind of replacement tissue. ACL reconstruction is usually very successful and rehabilitation includes physical therapy. The patient may return to sports when there is no longer pain or swelling, when full knee range of motion has been achieved, and when muscle strength, endurance and functional use of the leg have been fully restored, typically 4-6 months.