An anterior cruciate ligament, or ACL, injury is a tear in one of the
ligaments that joins the upper leg bone with the lower
leg bone. The ACL keeps the knee stable. See a picture of the
knee and the ACL.
Injuries range from mild, such as a small tear, to
severe, such as when the ligament tears completely or when the ligament and
part of the bone separate from the rest of the bone.
treatment, the injured ACL is less able to control knee movement, and the bones
are more likely to rub against each other. This is called chronic ACL
deficiency. The abnormal bone movement can also damage the tissue (cartilage) that covers
the ends of the bones and can trap and tear the pads (menisci) that
cushion the knee joints. This damage can lead to
Sometimes other knee
ligaments or parts of the knee are also injured. This includes cartilage such
as the menisci, or bones in the knee joint, which can be
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