A new knee ligament discovered?

It’s all over the media—a new knee ligament discovered by researchers in Belgium. 

Dr. Steven Claes and Dr. Johan Bellemans’ press release states that they “discovered a previously unknown ligament in the human knee. This ligament appears to play an important role in patients with anterior cruciate ligament (ACL) tears.” 

This new ligament, which they call the anterolateral ligament, was found in 40 of 41 cadaveric knees during dissection. They postulate its importance in stability of the knee in both ACL injuries and knee replacements. The researchers go on to state in their press release that “Subsequent research shows that pivot shift, the giving way of the knee in patients with an ACL tear, is caused by an injury in the ALL (anterolateral) ligament.”

As the paper indicates, there is a structure that goes from the lateral femoral epicondyle to the anterolateral tibia. The authors carefully noted that a number of previous authors have identified such a structure. The initial identification was made by Dr. Segond in 1879 when he noted a “pearly resistant fibrous band which showed extreme amounts of tension during forced internal rotation.”

As we have known for decades, this band is attached to the Segond fracture which is indicative of an ACL injury. The authors of the present article acknowledged that not much was made in terms of description of the structure until Dr. Houston described it in better detail in 1976. In fact, at that time Dr. Houston described the mid third lateral capsular ligament which he also noted played an important role in anterolateral instability of the knee. 

Anterolateral instability is a key finding in ACL insufficiency. Furthermore, a number of other authors have described similar ligaments. Dr. Vincent in 2012 described a similar ligament but noted a different origin.  A paper published in 2007 by Vieira et al. actually named the structure the anterolateral ligament. 

The press release on this paper made it sound like these authors’ findings represented a brand new discovery of a ligament that was never previously noted. These authors simply better characterized the ligament and better described it. In fact, this ligamentous structure was known and recognized as an important structure and responsible for the Segond fracture that was noted to be associated with ACL injury since 1879. 

There have been numerous published papers on the ligament, called the lateral capsular ligament, going back as far as 1976. The authors correctly concluded in their research paper that this is the first study to provide detailed anatomical description of the anterolateral ligament—but they did not conclude that this was a "new ligament" as the press release and the news media would lead you to believe.

Their press release states “The research questions current medical thinking about serious ACL injuries and could signal a breakthrough in the treatment of patients with serious ACL injuries” and that “Subsequent research shows that pivot shift, the giving way of the knee in patients with an ACL tear, is caused by an injury in the ALL ligament.” 

To date, there is no study supporting their theory that the ALL ligament itself plays a specific role in rotational stability of the knee any more than the lateral and posterolateral ligamentous structures are already known to do.   It is no surprise to any of us who work in this area and deal with these anatomic structures on a regular basis to find that this ligament has again been identified as an actual structure with these authors very precisely characterizing it.

What is most important to realize is that this is not a brand-new concept or brand-new ligament but rather a very nice description of the structure that was and has been noted to be present in the literature dating back many years. 

But regarding it being a potential breakthrough in treating ACL injuries, the authors are making a great leap because no scientific evidence yet exists in support of reconstruction of this ligament for anterolateral rotatory instability as seen with ACL injury.