A tiny mechanical “wrist” could give needlescopic surgery a new degree of dexterity.
Needlescopic surgery, which uses surgical instruments shrunk to the diameter of a sewing needle, is the ultimate form of minimally invasive surgery. The needle-sized incisions it requires are so small that they can be sealed with surgical tape and usually heal without leaving a scar.
Although it’s been around since the 1990s, the technique, which is also called mini- or micro-laparoscopy, is so difficult that only a handful of surgeons around the world use it regularly. In addition, it has largely been limited to scraping away diseased tissue with sharp-edged rings called curettes or burning it away with tiny lasers or heated wires.
Now, a research team headed by Robert Webster, associate professor of mechanical engineering at Vanderbilt University, has developed a surgical robot with steerable needles equipped with wrists that are less than 1/16th of an inch (2 mm) thick.
The new device is designed to provide needlescopic tools with a degree of dexterity that they have previously lacked. Not only will this allow surgeon-operators to perform a number of procedures such as precise resections and suturing that haven’t been possible before, but it will also allow the use of needles in places that have been beyond their reach, such as the nose, throat, ears, and brain.
“The smaller you can make surgical instruments the better ... as long as you can maintain an adequate degree of dexterity,” says S. Duke Herrell, professor of urological surgery, who is consulting on the project. “In my experience, the smaller the instruments, the less postoperative pain patients experience and the faster they recover.”
Minimally Invasive Surgery
That has certainly been the case with traditional minimally invasive surgery (MIS), which has become increasingly common in recent years. This method, which involves operating with instruments inserted through incisions that range from 3/8th to 3/16th of an inch (10 mm to 5 mm), generally causes patients less pain, less tissue damage, less scarring, and shorter recovery periods.
The effort to adapt robotic technology to MIS has been dominated by Intuitive Surgical’s da Vinci Surgical System, a robotic surgical system designed specifically for the minimally invasive approach. Depending on the type of surgery, it requires incisions that are 1/3 of an inch (8 mm) or 3/16th of an inch (5 mm).
“Although it works very well for abdominal surgery, the da Vinci uses a wire-and-pulley system that is extremely difficult to miniaturize any further, so it won’t work in smaller spaces like the head and neck,” says Webster.
For the past six years, Webster and his colleagues have been developing a surgical robot that uses “steerable needles.” This is a system of telescoping tubes that are made out of nitinol, a “memory metal” that retains it shape. Each tube has a different intrinsic curvature. By precisely rotating, extending, and retracting the tubes, an operator can steer the tip in different directions, allowing it to follow a curving path through the body.
This design allows the needles to operate in areas of the body that neither manual endoscopic instruments, which are straight rods equipped with a variety of end effectors, nor the da Vinci robot can reach. However, its usefulness was limited by the fact that the needles didn’t have a wrist.
Building a Smaller Wrist
“Adding the wrists to the steerable needles greatly expands the system’s usefulness,” Herrell says. “There are a myriad of potential applications in some really exciting areas such as endoscopic neurosurgery, operating within small lumens such as the ear, bronchus, urethra, etc. This would allow us to do surgeries that at present require much larger incisions and may even enable us to perform operations that are not feasible at present.”
