And Removal Of Bone Specimens

Routine preparation of gross and microscopic bone specimens can be carried out only on a limited scale. However, portions of rib with costochondral junction, sternum, vertebral body, or iliac crest, and sternoclavicular joint should be removed and permanently saved in every autopsy. Specimens suggested for study in cases of metabolic or other systemic bone and joint diseases are indicated below. The site of a circumscribed neo-plastic or inflammatory bone lesion can be determined from clinical or roentgenological examination. Circumscribed oste-olytic processes in the ribs or in the calvarium can often be identified by viewing these specimens against a bright light.

Specimens consisting of both bone and soft tissue may be difficult to prepare for satisfactory preservation. The best method is to freeze the fixed specimen and to cut the solidly frozen tissue with a band saw. The sliced specimen is placed in a tank of alcohol. The layer, on the cut surface, of frozen fat and sawdust is removed with a brush or will float off spontaneously. The alcohol treatment will also restore the color in specimens fixed in Kaiserling I solution (1) (see Chapter 14).

SAWING Handsaws and chisels have become obsolete and at present, only two types of saws are in general use.

Oscillating Saws The Stryker autopsy saw (Stryker Corporation, 420 Alcott Street, Kalamazoo, MI) still is the most popular tool in this class. The blade of this saw cuts bone by high-speed oscillation. Blades of various shapes with round cutting edges can be attached to the arbor, depending on the size and location of the bone specimen to be removed. One of the largest blades (#1105) is used for the anterior removal of the spinal column (see Chapter 6). Temporal bones are removed with a trephine (Schuknecht temporal trephine, Stryker Corporation). According to the specifications, this trephine cuts about 4.5 cm deep and removes a specimen about 3.7 cm in diameter.

The Lipshaw autopsy saw (saw no. 450; Lipshaw Manufacturing Company, 7446 Central Ave., Detroit, MI) differs from the S tryker saw because its motor is not in the handpiece but separated from the instrument by a cable. Lipshaw blades also can be used with the Stryker saw; these blades generally are less expensive.

A disadvantage of oscillating saws is the production of bone dust, both in the air and in the structures of the cut surface. Inhalation should be prevented by wearing a face shield or hood and by removing the calvarium inside a plastic bag (2,3) (see Chapters 16 and 6, respectively). After use of oscillating or other saws, bone dust on the cut surface can in part be brushed off, but histologic sections must be from deep within the block to avoid the dust particles. Use of cold saline during sawing will wash away some bone dust and will also prevent heating of bone.

All oscillating saws become hot after prolonged use. Occasional greasing of the moving parts is advisable.

Band Saws This type of saw is ideal if one wishes to prepare even section through large bones such as the femur or the spinal column. Band saws also are preferred for cutting small specimens into thin slices for histologic preparations. Unfortunately, they are difficult to clean and hazardous to operate. Because of the increased concerns related to infection control, we no longer use a band saw on fresh specimens.

PREPARATION OF HISTOLOGIC SPECIMENS To achieve optimal fixation with minimal exposure to decalcifying agents, bone specimens for histologic study should not be thicker than 3 mm. However, bone dust from sawing machines may have been ground into all levels of such a specimen, so that somewhat thicker sections may be required. Thin sections are easier to prepare with a band saw, which also grinds less bone dust into the section than does an oscillating saw. For the hazards of band saws, see previous paragraph. Brushing and flushing of the cut surfaces with saline and submerging the specimen in alcohol help to remove superficial bone dust. Excellent results can also be achieved by freezing the specimens in water and then sawing them in a solid block of ice until pieces of the desired shape and thickness are obtained. The plane of the saw sections will usually be perpendicular to articular, periosteal, or other surfaces. Buffered neutral formalin (Chapter 14) is a recommended fixative. Additional fixing in 20% formalin may be indicated, particularly for large specimens.

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