ACL Injury


An ACL injury is the tearing of the anterior cruciate ligament, a tough, rope-like tissue that helps keep the knee stable. An ACL injury usually occurs during sports in which there are sudden stops with one foot planted, while the athlete pivots and changes directions. The sports in which the most ACL injuries occur are basketball, soccer, tennis and volleyball.

Symptoms and Diagnosis

When the ACL is injured, a “pop” might be heard or felt. Pain is perceived outside the knee and in back of the knee. The knee swells immediately; the faster and greater the swelling, the more severe is the injury. Often some other structure or structures which form the knee are also injured. Pain is immediate and may be so severe that it prohibits weight-bearing and walking. The pain and swelling limit movement of the knee.

Diagnosis is based on the medical history and physical examination. How the injury occurred, symptoms at the time it occurred, history of other joint injuries or problems, and medical history in general are all relevant. The knee is checked for stability, strength, range of motion, swelling and tenderness. With a severe injury, the surrounding muscles may be so tense and the swelling so great that it interferes or prohibits the physical exam. An X-ray may be performed but does not show ligament tissue. It will show any injury to bone. An imaging study, called an MRI, can show tears of ligaments or cartilage (soft tissues). If MRI is not available, a CT scan may be performed, but shows less detail than an MRI.


An ACL injury can occur if the leg is straightened beyond the normal limits (hyper-extension), if the knee is twisted or is bent at the sides. Landing after a jump, (common to basketball), stepping off a curb, into a hole, or missing a step when walking downstairs are common mechanisms of injury. A contact injury, in which the knee is struck from the side, as in clipping, can cause an ACL injury.

Women are more vulnerable to ACL injury than are men participating in the same sport. Women have front thigh muscles (quadriceps) disproportionately stronger than muscles at the back of the thigh (hamstrings). The hamstrings prevent the tibia from moving too far forward during activities, but landing from a jump can increase stress on a woman’s ACL, with hamstrings strength insufficient to protect the ligament from excessive stretch. Estrogen can have a softening effect on tough ligament tissue, a benefit when giving birth, but possibly detrimental to the strength of some ligaments. Continue reading for Prevention and Treatment Information . . .

Pages: 1 2