The anterior cruciate ligament (ACL) is one of the four ligaments that make up the knee joint. It is prone to injury in many sports that put stress on the knee, which can tear the ligament. ACL injuries are usually accompanied by swelling and instability in the knee. ACL tears are more likely to occur in women and people over 40 due to wear and tear on ligaments.
Tears in the ACL are most common during high impact sports in which the knee could be hyperextended or over-rotated. ACL tears often require extensive rehab and knee surgery to repair the ligament.