Back in 1879, French surgeon Paul Segond noticed a “pearly, resistant, fibrous band” in the knee. This particularly ligament (a kind of tough tissue that hold bones together) was mostly forgotten until the 1970s, and then was mentioned only rarely, its form and purpose hazy. Deciding to clear up “the mystery surrounding this enigmatic structure,” surgeons in Belgium finally investigated and properly identified the perplexing ligament in 2013.
They found that the band—now called the anterolateral ligament or ALL—lies on the front of the knee, connecting the thighbone and shinbone, and is distinct from the four other ligaments that help stabilize the joint. The ALL might help protect the knee as we twist and change direction.
Some people have trouble recovering from a torn anterior cruciate ligament (ACL), an injury that often befalls athletes in sports that involve a lot of pivoting, like soccer or football. The surgeons who described the ALL suspect that this is because this fifth, poorly-understood knee ligament is often injured in tandem with the ACL. When patients don't respond well to treatment, it could be that their ALL is still torn.