The knee is a joint that is often susceptible to injury. In recent years, there has been a significant increase in ACL (anterior cruciate ligament) injuries. Injuries to the intra-articular ligament of the knee can be very serious and it usually occurs during physical activity. Why are knee injuries so common? The knee joint is particularly vulnerable to injury. The knee joint is located between the two longest bones and the weight of the entire body is transferred to the foot through the knee joint. The knee is also more susceptible to injury because its stability decreases as the knee flexes. The meniscus and ligaments provide little effective support when the knee is bent. What is the structure inside the knee joint and where is the ACL located? The knee joint contains bone, ligaments, tendons, cartilage, nerves, and blood vessels. A fibrous joint capsule formed by collagen fibers surrounds the joint and the end of each bone, providing stability to the knee joint. What are the signs and symptoms of an ACL injury? 1. “Thump” – Many patients, but not all, will hear or feel a “thump” when the ACL tears. 2, immediate swelling – indicates bleeding at the injured ligament. 3, pain – most patients feel pain when the ACL is injured. 4. Instability – Patients often describe a feeling of interlocking or unstable knee joints.