As Tiger Woods and Mariano Rivera can tell you, anterior cruciate ligament (ACL) tears can prove to be a frequent and devastating injury among athletes, professional and amateur alike. An ACL tear takes about eight to 12 months to heal, and they’ve always been difficult to treat. Until recently, doctors were at a loss as to why patients kept complaining about instability in their knees after recovering from successful ACL-repair surgeries. Their knees would consistently fail the so-called pivot-shift test, used by physicians to evaluate sprains in the anterior and lateral parts of the knee. Now, a team of Flemish researchers has finally uncovered the problem: a previously unknown ligament in the knee.

These scientists were prompted to find the ligament after reading an article published in 1879 by Paul Segond, the namesake of the Segond knee fracture. The French surgeon described a “pearly, fibrous band” and hypothesized it was an additional ligament located on the anterior part of the human knee. Over a century later knee surgeons and an anatomist at the University of Leuven and Ghent University in Belgium set out to determine whether the flexible connective tissue that Segond discussed exists.

After investigating 41 unpaired knees from human cadavers the doctors found that all but one knee displayed the described ligament, now named the anterolateral ligament (ALL). The discovery, published in the October 2013 Journal of Anatomy, has given basic anatomy a fresh jolt. Co-author and anatomy professor Evie Vereecke hopes the study will encourage students to look to anatomy as an exciting science, where new features of the human body may be discovered, Vereecke says. The diagram of the right knee shows the joint’s important structures: the lateral femoral epicondyle (LFE), lateral collateral ligament (LCL), popliteofibular ligament (PFL), popliteus tendon (PT) and Gerdy’s tubercle (GT)

Other researchers, such as orthopedic surgeon Steven Claes, are currently trying to find a technique to repair that ligament. In the meantime they hope clinicians will take the ALL into consideration when making a diagnosis or planning reconstructive surgery.

- Julianne Chiaet