Who Needs a True 200 μm Core Fiber? December 21 2015
I find myself addressing this question with customers on an almost weekly basis, so I thought I would blog about it since many of you likely have the same questions:
OK, I admit it; I added the second half of the question to sing the praises of InnovaQuartz versus the competition one more time…. As to why a 200 μm core fiber has utility, the answer is simple enough:
True 200 μm fibers are more flexible that fibers that are simply called 200 μm, but are actually significantly larger. Most “200 μm fibers” are actually 273 μm. And to confuse matters even more, the core diameter is really not an important dimension to the surgeon; the cladding diameter determines fiber flexibility and the buffer diameter determines occlusion to irrigation flow.
Note on 272 versus 273: Only the cladding diameter can be measured on-line when making fiber so the core is calculated based upon the cladding to core diameter ratio CCDR. A “272” fiber is made to a target 300 μm and has a 1.1 CCDR so the core diameter is 300 cladding / 1.1 CCDR = 272.72727272… I don’t know about you, but I was taught to round up in these cases.
The cladding diameter of a “272 μm” fiber, as noted in the note above, is 300 μm. The cladding diameter of a 200 μm fiber is 240 μm or 20% smaller so it is 20% more flexible as well.
Flexible ureteroscopes are wondrous instruments but they’re not without their limitations. Deflection is usually provided by several wires, attached to a control lever and running down the length of the endoscope. The amount of force that can be communicated by these control wires is limited, typically by a clutch system incorporated within the control lever to prevent snapping the wires.
Multiple studies have been done to measure scope deflection while loaded with optical fibers and other instruments for both new scopes and used scopes and have used scopes made by just about all of the companies in the business. These studies have shown that “272 μm” fibers restrict scope deflection to about 240° of the empty 270° in new scopes where true 200 μm fibers permit full scope deflection, even in used scopes with stretched scope wires or work clutches.
If you need full deflection from your scope, you need a 200 μm fiber.
Why don't others offer a true 200? They would if they could, but they can't figure it out.