Ostriches Have Double Kneecaps and Here’s What That Means for Prosthetics

Posted by TF Oren

The ostrich is the only animal in the world with a double kneecap.

Exactly why this is so, and what purpose the unique structure serves for the flightless birds, however, are still unknown.

According to PhD student Sophie Regnault of the Royal Veterinary College in London, learning more about this singular feature of the ostrich could have applications in prosthesis design, veterinary surgery, and robotics.

According to Regnault, the ostrich’s upper kneecap looks very similar to kneecaps found in many other species. It’s the fixed, bony lower kneecap, which resembles the point of an elbow, that’s so puzzling.

“As far as we know, this double kneecap is unique to ostriches, with no evidence found even in extinct giant birds,” says Regnault.

This image is a combination of X-ray video and the team’s 3D reconstruction of the ostrich’s double kneecap. Photo by Sophie Regnault via Science Daily

In order to study the double kneecap, Regnault and her team did a series of studies on a real ostrich leg. These studies included CT scans, and a technique called ‘X-ray reconstruction of moving morphology’ (XROMM).

The team used the information from the scans to build a 3D model of the leg, and then moved the leg around in order to animate the CT bone models. This provided the team with information about how both kneecaps move in 3D space.

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Based on the information this yielded, the researchers believe that the double kneecap is actually disadvantageous to the mechanical efficacy of the knee extensor muscles from the thigh bone.

The effect that the structure has on the ostrich’s ability to run remains in question, but Regnault and her team suspect it “might mean ostriches are able to extend their knees relatively faster than they would with one kneecap.”

ostrich runs

Regnault’s research has shed some light on the how – the mechanics of the ostrich’s double kneecap – but the why still remains a mystery.

“It might help to protect the tendon of these heavy fast-running birds, but there are other potential roles that we haven’t yet explored,” says Regnault.

What do you think of this wacky bird’s unusual anatomy? Let us know in the comments section!

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Ostriches Have Double Kneecaps and Here’s What That Means for Prosthetics