According to the National Heart, Lung, and Blood Institute, more than half a million heart surgeries are performed every year. Add to that number another hundred thousand lung surgeries, and the need for better tools quickly becomes apparent. Because of the antiquated design of thoracic retractors being used today and the number of surgeries being performed, the incidents of rib fractures has continued to increase.
Crenshaw and Pell recognized that there had been little research pertaining to the forces generated by rib spreaders in the past, and brought together a team to measure the effects and produce the technology to greatly reduce damage. Bones can flex quite a bit before breaking, often due to the rate at which the spreader moves -- a sudden bend like that delivered by a hand-cranked thoracic retractor can cause a rib to snap. Bone fibers need a little time to adjust.
By placing sensors in the Assuage rib spreader, it's easier to detect whether fibers begin to break down. This information is then fed back into the tool so that it responds instantly to tissue events. This closed-loop feedback to the motor must have a high degree of precision and be completely reliable to be used inside medical devices.
Maxon provides a complete line of motors and motor controls for the medical market including its EC brushless series, which is particularly suited for use in medical devices.
Physcient designed a prototype rib spreader around a motor manufactured by Maxon. One of the more important specifications for the motor was the lack of cogging that often occurs at very low speeds. The rib spreader has to be able to move smoothly without jerking motions that can cause undue damage to the patient. DC brushless motors easily operate from a battery, and an onboard controller and sensor system helps to maintain a controlled spreading process. In order to handle the high forces necessary, Physcient selected high-torque motors.
"The motors we use from Maxon not only have to handle the greatest retraction forces ever measured in the medical industry, they also have to be precise in order to reduce damage to ligaments and soft tissues," Pell said.
We've seen huge advances in medical technology over the past decade. This is another example. Medical technology has become a very exciting are of development. This new technology for helping with chest surgery is good to see.
Nice idea for adding closed loop feedback on the motor as an added measure to protect against unnecessary spreading force. Good example of innovative thinking on an existing product.
Since ribs are still being spread, probably about the same distance, my guess is that a similar amount of force is being applied.
So while the new system tool is possibly much easier to control, and certainly much more modern in fuctionality, the actual benefit has not been made clear to me. The ribs are still being spread by force, and that force is still about the same, and now a device that does not have intrinsic force feedback is provided. A hand driven jack mechanism provides instant feedback through the feel to the operator, while this system evidently provides a display of the force. Different for sure, but I don't know how much better, since the mechanism of advantages was not explained, I don't think.
The real difference is that the software is controlling how much force is placed on the ribs rather than the surgeon. So, do you believe that the machine has a better feel for what's happening to the patient or the surgeon? One could argue that the machine is more objective or that the surgeon knows his patient and procedure better. The medical devices I was involved with were designed to perform a particular way, but the surgeon was always allowed to override the "standard settings", our belief being that the surgeon, much like a pilot, is always in command.
It may be that the software can spread the ribs more gently, or something like that. My feeling is that there are a few details not mentioned in the writeup, although it is at least possible that simply having a different form factor was the large benefit. On some rare occasions the shape of a tool is more important than the actual function of that tool. Not very often, but occasionally.
Sophisticated algorithms help improve closed loop feedback systems along with computer modeling can definitely improve motor motion needed for this medical application tool. Great article on medical robotics!
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