The anterior cruciate ligament is one of a pair of cruciate ligaments (the other being the posterior cruciate ligament) in the human knee. They are also called cruciform ligaments as they are arranged in a crossed formation. Tearing of this ligament can occur whilst stopping or changing direction suddenly so often occurs as a sports injury. An MRI scan or X-ray is used to determine the severity of the tear. The ligament is corrected by either stitching it back together or grafting new tissue onto it and this procedure is performed by a knee surgeon within the field of orthopaedic surgery.