Needle-sized mechanical wrist gives surgery a new angle

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A tiny mechanical wrist can make surgical incisions the diameter of a sewing needle and then bend inside your body by as much as 90 degrees, opening new doors in needlescopic surgery(Credit: MED Lab, Vanderbilt University)

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Some of the most difficult types of surgery just got easier and more versatile. A team of engineers and doctors at Vanderbilt University has developed a tiny mechanical wrist that can be used for millimeter-sized incisions and sutures that allow new kinds of operations and less-invasive ways of conducting existing procedures. The wrist is flexible enough that its end can be steered to allow needles to reach inside the nose, throat, ears, urethra, and brain.

Many larger surgical tools with flexible ends already exist, with designs that range from 2.4 to 15 mm (0.1 to 0.6 in) in diameter, but none come close to the 1.16 mm (0.05 in) of this new wrist.

While the mechanical wrist is expected to be useful in many different kinds of precise, small-scale surgery, the researchers believe it will be particularly handy in needlescopic surgery (also known as micro-laparoscopy). This involves making incisions so tiny that they can be sealed with surgical tape and leave no scar behind. Like laparoscopy, but on a smaller scale, it is accomplished using tiny surgical instruments that are fed through narrow tubes into the incision, with a similarly tiny camera providing visual guidance. It's minimally-invasive surgery taken to the extreme.

Surgeon Duke Herrell (pictured) noted that the smaller endoscopic instruments such as this new mechanical wrist are, the better(Credit: John Russell/Vanderbilt)

Armed with the flexible mechanical wrist, surgeons will soon be able to conduct operations on this scale through natural orifices such as the nose and throat and through the sharp corners encountered in other areas such as the ankle and middle ear.

To start with, the researchers plan to test the wrist in transnasal surgery. This kind of surgery normally involves cutting a big hole in a patient's skull or face so that tumors can be removed from the pituitary gland and skull base. It can also be done through the nasal cavity with an endoscope (a thin tube with a camera attached), but the procedure is extremely difficult. The mechanical wrist, they hope, will make this less-invasive alternative – and many other kinds of operations – less difficult, which will have the knock-on benefit that most patients will suffer less post-operative pain and recover faster.

"We think once we give this tool to surgeons, they will find all kinds of applications we haven't thought of," said research team lead Robert Webster.

The wrist is made from a rigid tube of a material called nitinol, which is a metal alloy of nickel and titanium that can be moulded at a set curvature. To design the tool, the researchers first tried to combine lots of small pieces, but at one point they realized they could instead take a nitinol tube and cut four or five holes in it to allow it to bend dynamically by as much as 90 degrees. They also found that a wire attached to the tip could be used to control this bending – if you remove tension from the wire, the wrist springs back into a straight position, and if you gradually increase or decrease tension, you can precisely control how it bends.

Vanderbilt University applied for a provisional patent on the design in May, and the software interface that allows surgeons to control the mechanical wrist should be completed by the end of August. It then needs to go through FDA approval, which could take four or five years.

The video below that explains how the mechanical wrist works.

A paper describing the research was presented in May at the International Conference on Robotics and Automation in Seattle.

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