The ACL is the ligament that connects the femur (thigh bone) and
tibia (shin bone) inside the knee joint. Ligaments are tough,
non-stretchable fibers that hold bones together. The ACL, along
with the posterior cruciate ligament (PCL), medial collateral
ligament (MCL), and menisci (cartilages), helps keep the knee
stable and helps protect the knee from shifting, rotating, and
hyperextending during running, jumping, or landing. ACL tears
can occur from forceful contact to the front or outer part of
the knee or from the knee twisting or hyperextending. An ACL
tear is usually associated with sudden knee pain and a sense of
the knee giving way. Commonly, those with an ACL tear feel a
“pop” in the knee when they are injured. Swelling often occurs
within 24 hours. While there may be pain, restricted motion, and
a feeling of looseness in the knee, some individuals with ACL
tears will have only minor pain, swelling, or limitation of
weight-bearing activity. Some athletes with an ACL tear may be
able to walk or run eve