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Force Feedback / Haptics in surgical robotics

What are haptics - definition

A dry definition of haptics is: “the use of technology that stimulates the senses of touch and motion, especially to reproduce in remote operation or computer simulation the sensations that would be felt by a user interacting directly with physical objects.”

In basic terms is touch and feel, and the interaction of physical objects. So in open surgery with the hands of the surgeon in direct contact with the organs they can feel things like:

The force they are applying to pull the organ

How heavy it is

How soft or hard it is

How elastic it is

How rough it is, or how smooth it isHow hot it is

Does it have a pulse

Etc etc

These are critical sensations that help greatly when performing surgery.

It may not be obvious at first, but as we can see from this list, there are different kinds of haptics at play here. Some of the sensations here are based on forces (Kinesthetic sensation) while others are based on touch and feel (Tactile sensation).

Both critical inputs to the surgeon, but both quite different. And we need to think of that for later when we decide what do we want to apply to surgical robotics.

Surgeons rely upon the haptics in coordination with visual cues to get a full understanding of the situation in open surgery.

Haptics in surgery

For this post, it’s important to understand what happens to both visual cues and haptics when you move from say; open surgery to laparoscopic surgery.

We all know that in most laparoscopy we move from 3D highest vision (our eyes) to 2D and often lower acuity imaging; often with with false lighting, poor colour rendition and lower resolution. But generally we can still see the surgical field well.

We also all know that the surgeon now operates via long laparoscopic instruments - directly holding them and interacting with the tissue through a trocar / cannula / port. So already some things are changing with the haptics when we move from open direct tissue contact to laparoscopic contact with tissue via laparoscopic instruments.

Between the hands of the surgeon and the tissue is a 30cm long instrument that is operated by ring handles; all through a fixed pivot point. So some of the tactile sensation is immediately lost. But also some of the force feedback information becomes distorted by the mechanical actuators - levers - pivots - springs etc that sit between the surgeon and the tissue.

One simple example is that it is almost impossible to tell if tissue is hot or cold via laparoscopic instruments. That is a loss of tactile sensation.

If something is rough or smooth becomes an interpretation of how the instrument feels as you rub it across the surface - not the direct touch of a fingertip on that surface.

The same is with palpation. Where the interpretation of the force resistance to the instrument determines how the user decides if the tissue is hard or soft.

However - despite some of these differences - there is still a major degree of haptic feedback that comes to the surgeon - and the fact they can no longer determine if the tissue is hot or cold may have little impact on the clinical outcome. But it does take some time to be able to fully interpret the haptic sensations and collate them to the tissue effect. It’s not quite the same as open surgery - but not a million miles away.

Now that all changes when we move to tele-operated robotic systems. There is a console with controllers for the surgeon, and a bedside unit with an instrument holding that instrument and moving it. Between the two is a wire and a computer. So now the surgeon is 100% disconnected from any type of haptic feedback from the robot. They cannot feel the sensations at all from the tissues.

That for some people is a massive barrier to being able to make the leap to the robot (more later.) They need to retain some haptic sensations to be able to operate.

Now the surgeon still has the visual clues and muscle memory from open and lap surgery. The brain is pretty good at stitching together the visual clues and making an interpretation of what is happening with force. As a simple example - if I showed you a video of someone stretching an elastic (rubber) band in their hands - your brain would automatically start to understand that there are forces at play - even though you are not touching it - stretching it yourself. And experience would tell you if they were stretching it way too much.

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