Cutting Instruments in Surgical Pathology Sampling

While sampling (cut in) does not necessarily require that a specimen be cut, as is often the case with biopsies, this is something which the vast majority of regular surgical pathology laboratories do. This very much artisan processing step when grossing requires appropriate instruments. This post discusses predominately personal experience that reflects specific conditions of local institution/s.

There are two kinds of cutting instruments: those for soft specimens and those for calcified specimens.  The choice of the in cutting instruments variants is less than during specimen immobilization. Moreover, some instruments, resembling tomato slicers, combine the tasks of cutting and immobilization. For example, suggested by MOPEC or more sophisticated by MILESTONE (ProCut).

The use of knives has been common for autopsies and large specimens. However the modern requirements for precise margins of resection and staging move the scale of choice towards blades due to their flexibility during section, their sharpness, and their disposability.

Nevertheless, knives will remain popular in the gross room, but they are shorter than old dissection knives, thinner, hopefully sharper made from high quality material.

It is unnecessary to describe all kinds of blades and knives offered by the manufacturers. Here we provide the principle of the choice of an appropriate knife or blade for the surgical pathology laboratory. Different types of disposable scalpels are not popular in surgical pathology (too expensive).

Blades are distinguishable by the standard numbers 10, 15, and 22.  Although 10 and 15 can be advantageous for very small biopsy specimens – such as ophthalmology surgery – the standard is 22 as it fits the standard handle. Handles used to be wooden, although are now made of plastic. While different kinds of metallic handles may look attractive, they are too thin. This is especially evident when needing to change blades, something which should be done often. In terms of the ideal handle, in my experience, it is pear-shaped handle that reliably fits the palm.

Device UniformPrototype 030

 

Blade changing is an issue deserving special attention because of safety considerations. In my opinion, while the devices for removal (Mopec’s, for instance) may look attractive, they are a waste because they are not reliable. They do not work with every type of handle, and the blade or handle can sometimes become stuck in the device.

I do not have an experience with BLADEX, Inc.  Safety Blade Exchanger. On the companies video, the handle is different than most used in the USA blade handles.

The safe way to remove the blade is by lifting the part that adheres to the handle with forceps, or even by thumb. This easily removes the blade. Really, I do not think that the safety blade exchangers are necessary. Such devices take precious space on the grossing table, but the blade is changed so often that additional device cannot substitute for attentive skilled work.

Photo with an arrow

Different kinds of blades starting with Double sided Grossing Blades and finishing with a regular Gillette like razor have limited used. First are cumbersome, proprietary, although some like them. The Gillette like razor blade is difficult to manage, brittle, in general unsafe. With some developed skills, it can be used in after ophthalmology surgery.

A grossing knife with two parallel blades intended to provide uniform thickness of the sample. However, this device is useful in autopsies sampling, but for every day work in surgical pathology with constant change of the processing mode and the type of specimen, this kind of knife is cumbersome.

Instruments for calcified specimens

There is a variety of instruments and a difference in opinions regarding them. The main perhaps question is in the attitude toward hand or mechanical sawing. I prefer hand sawing, using mechanical sawing in simple bone specimens. Bur even in a case of a femoral head with degenerative arthritis hand sawing is more manageable and more open to diagnostic revelations.

The table presents variants mechanical and hand saws offered by industry

Mechanical saws Hacksaws
Scroll saws; Exakt 312 Pathology Saw;Mar-Med Diamond Bone Band Saw;Dremel tool speed controlBuehler Isomet Low Speed ;Precision Sectioning Saw   metallurgical water cooling thin diamond-impregnated blade Variable SpeedJigsaw Bosch Finecut VS Power HandsawOscillating Stryker saws MOPEC’s SawBone double blade;MiniHack (Stanley);Metal hacksawHigh tension hacksaw (Stanley)Gigli wire saw

The main difference in the mechanical saws is in the blade.

Scroll saws ought to be avoided and abandoned in places where they are used. They are primitive, unreliable, and unsafe for a worker and laboratory environment.

Fragmdent of bone and soft tissue disseminated

Fragments of bone and soft tissue disseminated

Mechanical Saw

This was inside and outside the saw during cleaning

This was inside and outside the saw during cleaning

 

Diamond blade band saws are the current optimal instrument for mechanical saws. They differ by size and additional provisions for cleaning, cooling the blade, variants of speed. This addition changes everything about reliability of an efficient and precise bone cut.

The usability of other mechanical saws lies between the scroll saw and diamond blade saw. These alternatives have their defenders because they’re useful for limited goals, as determined by their practice. For example, Dr. Peters’ immobilization device with a Bosh FineCut saw.

Peter's vise saw

 

EXAKT 312 diamond band pathology saw is a variant of a diamond blade saws. It is over sized, but this circumstances opens an opportunity for a vertical metallic bar that is a definite advantage. It is unnoticed even in their video clip, but it makes the saw more reliable. This is exactly the technical implementation of the “third hand principle” that is discussed in many articles, including on this website (The “Third Hand” Immobilization Principle in Bone Gross Section). The metallic bar enhances reliability in precise cut.

The perennial dispute about preference for mechanical saws and hacksaws cannot be solved decisively. The usual, but correct, answer would be “it depends”.

The table presents the differences in use of mechanical and hand saws

Mechanical sawAdvantages HandsawAdvantages
Longitudinal sectionsBig specimensLess physically demanding More manageableMore options for immobilizationSmall specimensSaferEasier to clean

Mechanical sawing requires more skills to adjust to the speed of the blade, better immobilization, and more safety provisions. They require special place and requires greater cleaning arrangements.

My personal preference is for handsaws. They are universal, especially for complicated bone specimens. The MiniHackSaw is especially useful with fragile bone cutting (see Fragile Bones on the Grossing Table.)

KONICA MINOLTA DIGITAL CAMERA

My favorite saw

KONICA MINOLTA DIGITAL CAMERA

MiniHackSaw in action

In choice of a hack saw two factors should be taken into account:

1/ The amount of the blade’s teeth (the higher TPI (teeth per inch) the finer the cut.

2/ the saw’s weight (the lighter the saw, the gentler is the saw’s cut.)

KONICA MINOLTA DIGITAL CAMERA

The Stanley heavy Hacksaw is useful in a case when it is difficult to achieve secure immobilization in a fragile bone . The weight of the saw contributes to immobilization by friction and the sawing is precise.

This saw is especially useful for small bones or if a bone sample does not fit the processing cassette for many reasons (see Small Bones Cutting)

Cutting instrument’s choice depends very much on personal preferences. However, understanding of interaction of the instrument with the specimen is crucial. The specimen’s resistance to the cutting device ought to determine the choice of the cutting instrument.

More details in the comprehensive article in Annals of Diagnostic Pathology

 

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