The ACL may tear, either partially or completely, as a result of a hard twist, sudden stop while running, jump landing or direct blow to the
knee. You may experience a loud, painful pop
when the ligament is first injured, followed by swelling of the knee. The pain and swelling of an ACL injury can last for several weeks. Short-term treatment can relieve the pain and inflammation, but it takes months for an ACL injury to heal completely.