Bones in the Surgical Pathology Grossing Room

 

Bones are cumbersome and sometimes physically challenging objects in the surgical pathology grossing room. The lack of ability to do bones is often the cause of the processing “misbehavior.” There are some technical details that can make the bone cutting procedures easier and more accessible even to people with minimal physical dexterity.

These remarks reflect my personal experience at the grossing table in surgical pathology. They do not intend to substitute for the grossing manuals, but are an attempt to advise how to best execute the manuals’ recommendation.

The technical aspect of bone cutting is rarely mentioned in surgical pathology manuals. Some manuals are inaccurate by presenting unrealistic illustrations. For example, a very popular Surgical Pathology Dissection: an Illustrated Guide by Hruban  & others shows a cut (dangerous, by the way) of a femoral head, like a wooden board. The goal is to get the most representative section for histology.

A proper bone cut depends on three main conditions: first, firm support, second, an appropriate saw and third, preliminary orientation. The most difficult of these is the secure support of the specimen.

IMMOBILIZATION

Although it is understood that the bone should not move while it is being cut, it not easy to establish a firm grasp of the specimen without compromising convenience as well as an appropriate surface for cutting.

Many devices are used to ensure appropriate immobilization of the specimen, starting with a vice and ending with a variety of contrivances that are offered by manufacturers. Each of them can serve satisfactory in some occasions, but they lack the flexibility for working with diverse bony specimens.

The devices provided by the industry are either flat or round, but bones are, with some exceptions, neither strictly round, nor absolutely flat. These devices also have a second disadvantage as a metallic surface that is undesirable because it prevents from getting a complete section of bone especially with attached soft tissue. Some devices, for example MOPEC’s, make a blind cut, but the section that is intended for histology should be the most representative. Finally, they are bulky and cannot be placed on the grossing station table close to the exhaust and the sink. Even, a relatively small Shandon’s parallel hacksaw measures 44 x 25 x 11 cm. The difficulties of an appropriate cleaning of these devices should also be taken in the consideration.

A variety of self- constructed wooden cutting boards with carved surfaces have been used in research and clinical laboratories. Wood is the most appropriate material for bone cutting support devices.

For many ears, I have used a modified The Davidson Marking System wood holding tray. This stand has various hollow spaces that can be adjusted to different bone surfaces. The pegs sometimes help to navigate the saw as well as serving as additional support.  The significant advantage of this wooden bone- cutting device is that it can be used on the standard grossing station table. It is easy to clean in the sink and convenient for disinfection. Numerous cuts, like a warrior’s scars, reflect its frequent use.

(See BONE SUPPORT GADGET in the link Instruments & Gadgets).

Although a wooden support device is the most appropriate for every day practice, there are situations when it is reasonable to use plastic. For example, I use a Styrofoam box or lid for a longitudinal cut of a femur with attached soft tissue. Some urethane foam plates surround the specimen for a relative immobilization. Even a packaging pressed thick cardboard box (every laboratory has abundant of them) can be used for immobilization in a case of an unusual configuration of a bone specimen.

(See HARD-PRESSED PACKING CARTON GADGETS in the link Instruments & Gadgets).

There are occasions when a bone cut is made on an amputated leg or an arm. Good support is essential, otherwise the sliding and twisting specimen is difficult and dangerous to cut.

I have used a large (32 oz) plastic bucket with semicircle cuts to put the limb in them. The bucket is filled with water for more stability. This simple gadget makes the bone cut, besides other advantages for soft tissue and vessel dissection, effective and safe.

(See SUPPORT FOR AMPUTATED EXTREMITIES in the link Instruments & Gadgets).

The second condition for firm immobilization is an appropriate forceps. The best for this purpose is a Russian Tissue Forceps (203.2 mm) available from MOPEC that grasps all surfaces of the bone. Its firm but flexible grasp allows the user to change both the direction and the angle of the cut, especially in complicated cases involving both tumor and bone. Some gadgets like a meatball maker work in a case of a standard femoral head, but there is no real substitute for a forceps with a toothed dip for a firm hold on the bone during cutting.

A vise remains a reliable tool for bone immobilization. The vise with a vacuum base that is attached to the metal surface of the grossing table is indispensable when it comes to complicated bones like mandible.

SAW

No one can dispute the importance of an appropriate cutting instrument. Obviously, different bones and situation require different kinds of saws.

The Stryker-like oscillatory saw is indispensable in doing autopsies, but it can also used in surgical pathology grossing room, especially if it is necessary to cut a long tubular      bone or a femur head. However, this type of saw has some negative features that are important in surgical pathology. First, the high speed of the oscillating blade requires a more precise approach to of the initial cut. Second, the boney tissue is easily overheated, and sometimes even burned at the site of the cut. Third, the saw generates abundant undesirable bone dust (only diamond saws like the Bueler Isomet Low Speed Saw do not introduce bone dust into the specimen). Fourth, the standard blade cannot be used if the bone is more than   23 mm thick. Actually, an oral surgeon’s Stryker type saws are more preferable in surgical pathology. In general, the Stryker saw requires more training and skills for appropriate use.

The band saw can be used for large and/or dense bones, especially if it is necessary to obtain a longitudinal cut of a slab of bone tumor (for instance, to evaluate tumor necrosis in chemotherapy). However, the space-occupying commercial band saw is more crude, creates more dust, takes more bone material while cutting, soils the room, and more dangerous to personnel (Modern Surgical Pathology, 2003 by Weidner and others even placed a photograph of a band saw injury). I would not recommend it for a standard surgical pathology grossing room, unless it serves a special investigative purpose.

I have read some positive statements regarding band saws, including Mar-Med Band Saw, but my personal experience do not confirms them. Band saws require a reliable immobilization of the bone to make mechanical cutting more efficient for every day use.

The regular handsaw is the best option in most surgical pathology cases. A preferable blade length is 10 “ (the 32T is better for fine cutting, the 14T works faster).  This saw is suitable for a variety of bones beginning with femoral heads and ending with facial bones. It can be used easily on the grossing station table. This saw is easy to clean. The blade is inexpensive and it can be changed frequently.

The fret saw, like the Precision Hacksaw (TOOL SHOP) with a 6” blade is very useful if a fine cut must be made, especially if soft tissue or tumor tissue is attached to the bone. This saw is most useful in cutting maxillary bones, ribs and other fragile bone structures. When there is a small bone or a specific area of interest, the loss of bone material during cutting should be kept in mind. In these situations the thin blade of a fret saw is very valuable. Sometimes, I begin with a Stryker saw and finish with a fret saw, for example, in mandibles with an attached tumor. A fret saw is very useful in larynx with ossification of cartilages.

The low speed diamond saw (Buehler Ltd.) is very useful in cutting a bone with metallic mesh inside that occurs in complicated bone fractures.

There are other useful instruments for handling bones in surgical pathology, for example, curved rib shears, hammers and chisels, but the saw remains the primary instrument.

Using a knife/blade with a hammer, as occurs not so rare, should be discouraged as ineffective and unsafe.

PRELIMINARY ORIENTATION

This part of the bone cutting procedure includes not only decisions regarding pathology issues, but also the correct approach to the area of initial cut to maintain anatomical and pathological relationship. All soft tissue incisions should be made before, precisely at the areas of intended bone cuts. The bone cut should be made through the soft tissue/tumor incision while holding the bone down on the wooden support board. The soft tissue should be taken out quite wide directly at the thickness of the saw’s blade otherwise the soft tissue will be stripped off from the bone by the saw’s movement and the bone will be almost denuded at the places of interest that compromise the diagnostic outcome. This is important when it is long longitudinal cut of the bone, for example in a femur or tibia with a sarcoma diagnosis. This is also important when a rib is cut with adherent soft tissue, due to the fragility of a rib.

Another part of orientation is the determination of the appropriate sequence of cutting to keep parts of the bone available for forceps support otherwise a good section is not possible. The direction of cuts is the main point of the preliminary orientation. Of course, the golden rule of surgical pathology, to make all cuttings in one direction should be honored. Usually, the cut should be made as much possible perpendicularly crossing the longitudinal approach, although there are numerous exceptions. The rib could be mentioned as one of them, if a multiple myeloma is suspected.

SECTION. Of course, the section should fit a standard histology cassette, but it is better if it is at least 1 mm from the borders, otherwise it does not fit the standard embedding mold that is slightly smaller than the cassette. During embedding the section should be easy to orient. Sometimes bones are difficult to cut and it is easier if the microtome knife strikes the periosteum or important structures longitudinately.

The section should be around 2-3 mm thick. Lester’s Manual of Surgical Pathology (2001, page 118) recommends 0.5 cm, but it is wrong because even the depth of the standard histology cassette is less than 5 mm. However, a thin bone fragment (less than1 mm) has a tendency to pop out during microtome cutting. The trimming before cutting uneven surface should also be kept in mind.

The bone dust is undesirable product of bone cutting because the debris is pressed into the bone surface. It is a good idea to rinse the section under running water using a soft brush immediately after cutting.

Some well-known rules that often are not followed.

FIXATION. A common mistake occurs when the entire fresh bone is placed in fixative with the assumption that the bone should be completely fixed before cutting. In reality, even overnight fixation of the entire bone is insufficient, because the fixative penetrates very slowly through the periosteum. The bone should be cut before fixation. However, if soft tissue, especially a tumor is attached to the bone, the initial fixation should precede the bone cut. Then the cut section should be fixed again.

DECALCIFICATION. The sole goal of decalcification is to make the bone suitable for cutting on the microtome. Undecalcified bones are examined for the diagnosis of metabolic bone disease that rarely occurs in clinical practice.

Before discussing the technical details, it is necessary to write in bold:

DO NOT put a bone for decalcification BEFORE cutting and fixation. Everyone agrees but not so many follow. Failure in decalcification can affect all previous efforts by defects in nuclear staining. While decalcification solutions differ in recipe, all of them contain a mineral acid that, in contact with unfixed tissue (soft tissue, bone marrow, etc.) leads to some kind of colliquative necrosis.

 

 

Only fragile maxillary and ethmoidofrontal bones with already diagnosed tumor can be mentioned as an exception when it is better to put the specimen after fixation for decalcification that enables precise cuts with a knife to determine the margin’s involvement. I believe that only very fragile parts of the specimen might be exempt from initial cutting when the appropriate technique is applied.

 First, the section must be completely fixed. Mixtures of formaldehyde and formic acid can provide simultaneous fixation and decalcification, but they are rarely used in practice due to prolonged procedure.

Second, keeping the section too long in decal solution is much worse than under decalcification. Over decalcification is a very common mistake. Under decalcification can be corrected by some measures (the histothechnicians have some methods, like surface decalcification on block).  Over decalcification is often irreparable.

The acid solutions require monitoring the end point of decalcification. The specimens with combination of bone and soft tissue require especially careful decalcification. The end point of decalcification can be tested by the flexibility of the section. Some histotechnicians determine sufficient decalcification   if a fingernail leaves an indentation in the bone section.

Third, the section should be rinsed with running water after decalcification for 10 –15 minutes. Although SurgiPath do not recommend rinsing, it is wrong because hydrochloric acid contaminates the histology tissue processor.

SAFETY. Bones are the most hazardous material in a grossing room due to the dust while cutting and the possible trauma by the instruments or bone fragments. This means that in addition to the universal safety precautions, there should be applied some specific rules.

It is unrealistic to recommend the dust collection devices like the Mopec’s  DCD.

Even in autopsy room they are not used, unfortunately. The Autopsy Bone Saw Extraction System (Surgipath) is inconvenient in surgical pathology grossing room.

Each bone cutting should be done on a grossing station table where some kind of exhaust and running water in the sink is available. Two pair of gloves and a shield mask is obligatory especially if a Striker type saw is used.

A rib is handled differently from a mandible with teeth. The appropriate technique and reliable tools are main conditions for successful bones processing in surgical pathology grossing room.

This  article summarizes the general approach to bone grossing in surgical pathology. More details are presented  in posts at the links “Grossing Techniques” and “Equipment, Instruments, Gadgets”, as well as in my article  Dimenstein IB: Bone grossing techniques: helpful hints and procedures. Annals of Diagnostic Pathology 2008; 12:191-198.

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