New Ligament Found in Human Knee

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New Ligament Found in Human Knee
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The anterolateral ligament (ALL), a new ligament identified in the human knee.

Humans have been studying their own bodies for centuries, piecing together what all the parts are and how they work and interact, but apparently one tiny piece in the human knee has gone undiscovered until now.

Belgian researchers have for the first time described a new ligament in the human knee, termed the anterolateral ligament (ALL).

The researchers conducted in-depth examinations of 41 cadaver knees, and found the new ligament in all but one of them. A French surgeon first postulated its existence in 1879, but it hadn't been proven and fully described until now, said Dr. Steven Claes, an orthopedic surgeon and study co-author at the University of Leuven, Belgium. [The 7 Biggest Mysteries of the Human Body]

"The anatomy we describe is the first precise characterization with pictures and so on, and differs in crucial points from the rather vague descriptions from the past," Claes told LiveScience. "The uniqueness about our work is not only the fact that we identified this enigmatic structure for once and for all, but we are also the first to identify its function." The researchers presented their new work this March at the American Academy of Orthopaedic Surgeons meeting in Chicago. 

Occasionally when people injure their anterior cruciate ligament (ACL), they suffer what is called "pivot shift," where the knee gives way when it is moved a certain way. A new study published in the October issue of the Journal of Anatomy suggests this "pivot shift" may be caused by an injury to the ALL, which helps to control the rotation of the tibia, one of the two bones in the lower leg, he said.

One type of "pivot shift" occurs hand in hand with a lesion to the ALL, Claes said. "If the lesion would be overlooked or untreated, this might be the cause of persistent instability after traditional ACL surgery in highly instable cases," he added.

Why wasn't it found before? Claes said he didn't know, though it could be due to poor dissection techniques, or degradation of the ligament in older cadavers

This isn't the first time a new human body part has been discovered recently. Scientists reported in June they had found a new eye layer, named Dua's layer after its discoverer, that sits at the back of the cornea, or the sensitive, transparent tissue at the very front of the human eye that helps to focus incoming light.

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