Ligament Structure Prevents Giraffes' Legs from Collapsing

Specialized ligament structure prevents Giraffe's spindly legs from collapsing under the weight of the animal, a new study has found.

Giraffes are not just tall, but are incredibly heavy. But, unlike other massive animals, giraffes have relatively thin legs.

Researchers at the Royal Veterinary College (RVC) of London have found that a groove in giraffes' leg bones protect a supportive ligament. The unique bone design helps the legs support the animals' weight despite being under enormous mechanical stress.

The team explained that the bones in giraffe that are equivalent to a human's metatarsal bone (in the foot) and metacarpal bone (in the hand) are twice as long.

"Giraffes are heavy animals (around 1000 kg), but have unusually skinny limb bones for an animal of this size" explained lead investigator Christ Basu, a PhD student in the Structure & Motion Lab. "This means their leg bones are under high levels of mechanical stress."

For the study, researchers analyzed limbs obtained from EU zoos. The limbs belonged to giraffes that had died due to natural causes in captivity or had been euthanized. The bones were fixed in a rigid frame and researchers applied forces of up to 2500 Newtons or about 250 kilograms. The force simulated the weight of the animal on each limb. The team found that the limbs didn't buckle under the force and could withstand even greater weight, according to a news release.

According to the researchers, suspensory ligament is not a muscle, but an elastic tissue. The ligaments can't generate force and offers only passive support. The giraffes, thus, use less muscle to stand and so are able to reduce muscle fatigue.

The team hopes that the research could explain how giraffes went from being short antelopes to the long-necked animals.

"I'd like to link modern giraffes with fossil specimens to illustrate the process of evolution" Basu said in a news release. "We hypothesise that the suspensory ligament has allowed giraffes to reach large sizes that they otherwise would not have been able to achieve".

The research can even advance robotic design, Basu told BBC.