Emergency Craniotomy instruments

Instruments for head trauma operations include those used to set up the surgical environment (power, sterile field, visual and physical access), as well as those used to operate within it.

Magnification

While magnification has become steadily more important in almost all areas of neurosurgery -- indispensable in cerebrovascular -- most of the maneuvers in a head trauma operation are performed on objects on a scale of several millimeters to a few centimeters. Operating microscopes (typically 5 to 6 times magnification) are useful when operating on objects a few millimeters in diameter and are therefore not necessary for the vast majority of head trauma operations.

Loupes are magnifying objectives mounted on a standard pair of glasses allowing the surgeon to see a magnified (albeit constricted) field. The 2 to 3 times magnification of loupes is adequate for most head trauma operations.

FIGURE: Loupes

With even optimal illumination and magnification and organization of his field, the surgeon is still incapacitated by obscuring blood, cloudy irrigation fluid, or other debris. Efficient intracranial surgery requires keeping the operative field clear of physical and visual obstacles by diligent irrigation, attentive aspiration, and meticulous hemostasis.

Irrigation and aspiration are complimentary aspects of surgical field maintenance. The irrigating-aspirating assistant must concentrate on following the movements of the surgeon's hands visually and with irrigant and suction. Areas of surgical interest are most safely addressed at the time of maximal cleanliness: immediately after they have been washed clean and aspirated dry.

Irrigant should be squirted onto the field under enough pressure to displace blood, but if the bulb is squeezed too hard and fluid issues under too much pressure, fluid from the bulb will be reflected back against the stream because it cannot dissipate fast enough, with the consequence that a splashing of mixed blood-irrigant fluid ends up in the surgeon's face and widely scattered across the field. Better control of the stream from the irrigation fluid bulb is achieved by manipulating it with the dominant hand.

The primarily aqueous solution used for surgical irrigation not only dilutes the blood but pushes it ahead of the irrigant stream. This washing force is greatest at the tip of a irrigation bulb where the irrigant fluid pressure is maximal.

Suction

Blood accumulates with irrigation fluid in dependent portions of the field as it escapes and is washed from lacerated vessels. The bloody fluid then interferes with the working of the electrocautery devices used to stop further bleeding from the openings in the vessels. To this is added the problem of blood's opacity, so that even in small quantities as even a thin layer, it obscures the surgical field.

Suction is a maintenance activity, keeping the operative field clear of debris, blood, or smoke that can obstruct visualization. Whenever possible the suction attachment should be held in the non-dominant hand.

Surgical field suction instrumentation attaches to the same suction cannisters which provide suction for anesthesia. Distally non-sterile, proximally sterile tubing connects the suction device to the distal end of the metal suction handle and tip. The proximal end of the metal sucker connects to the suction tubing.

Suction tube (suctiontube.gif)

There are/is a bend in the instrument (between its handle and shaft) such that the thumb can be flexed to occlude or open an air inflow opening in the handle. The working end comes in various lengths with a range of tip aperture diameters depending on the space available for sucking and the material to be sucked. The amount of suction at the instrument tip is regulated by a hole in the instrument's handle that can be occluded to decrease or increase the amount of suction through the opening at the end through which fluid is drawn into the tube.

The angle that the tube makes once distal to the thumb controlled portion is another important feature of sucker design. This angle determines the site of suction and the trajectory of the tube into that site with respect to the surgeon's hand. The angle of the sucker tip tube varies to allow the surgeon to hold his hand in a different posture with respect to the operative field. The tube lengths can also be varied.

Another design variable is the length of the suction tip. Usually the standard 6 or 7 cm tip is adequate, but occasionally in a deep space or where it is desirable to hold the hand further away from the wound, a longer tube can be utilized.

The size of the aperture will also determine the area within the operative field over which suction can be applied by approximating the aperture to the tissue to be aspirated. The appropriate aperture size for the suction tube will depends on the area within which one is working. Manipulation within deep crevasses and narrow holes may necessitate the use of smaller aperture suction tubes.

The size of the hole in the thumb piece determines how fine is the surgeon's control of the amount of air that is sucked in distally versus through the thumb piece. More suction force will arrive distally if the thumb hole is covered.

The shape of the aspiration force regulating hole is also an important variable in the determining the sucking output at the tip. The aperture of the thumb piece with a round hole is occluded by rolling the thumb to progressively cover more of the round hole. A side aperture the patency of which can be varied by the position of the surgeon's thumb regulates the amount of suction generated through the suction tip. A tear-shaped hole (as on the "Fukushima" sucker) allows the surgeon to regulate with his thumb the inward suction force at the aperture with more precision and accuracy.

The sucker tip is a metal cylinder with a rectangular end. Advancing the sucker with downward pressure onto the pial surface is no different than applying a towel to this delicate surface. The fine vessels that overlay the pial surface are similarly dug into and cut. Pial bleeding, from vessels too small to be visualized and efficiently coagulated can be very difficult to control with tamponade or bipolar cautery.

Aspiration of fluid in the wound, if done properly keeps the field clear, but if done improperly, can be traumatic to the tissue from which fluid is being aspirated. The suction tips through which fluids are sucked out of the field are at their tips uniformly harder and more rigid than the tissues from above which they work. As long as the contact between the sucker tip and the tissue is indirect, through the column of aspirating pressure tissue, whether pia, arachnoid, or brain parenchyma itself, will not be traumatized.

Touching the sucker tip to the tissue produces both percussive and lacerating forces that cause unsightly and unruly hemorrhage at and below the cortical surface. The sucker tip is a metal cylinder with a rectangular end. Advancing the sucker with downward pressure onto the pial surface is no different than applying a trowel to this delicate surface. The fine vessels that overlay the pial surface are similarly dug into and cut. Pial bleeding, from vessels too small to be visualized and efficiently coagulated, can unnecessarily complicate the operation virtually from its outset. When sucking a thin layer of blood from a soft tissue surface keep the sucker tip slightly off the surface to avoid trauma to the pial surface.

If the tip is placed onto the surface of the clot such that no air is allowed to enter the suction device the effect can be like a vacuum cleaner trying to suck in a piece of paper laid flat over the end of its suction hose. The most effective way to aspirate fluid is with the tip of the sucker at an acute angle, a millimeter or so from the surface.

When properly held the instrument handle end rests against the base of the fingers, upper palm and the thumb is extended. The handle should be positioned with respect to the hand such that on flexion of the distal most interphalangeal joint the distal pad of the thumb fully occludes the sucker side hole. Keeping the handle against the hand by adduction of the proximal thumb, flexion and extension of the distal phalanx allow the surgeon to adjust how much air flows past it through the air hole and the force of suction at the tip.

Aerodynamics are such that maximum suction force does not occur at the aperture of the suction tip but rather at a distance from it. Clot can be more effectively aspirated by holding the tip just above rather than on the clot. If the tip is placed onto the surface of the clot such that no air is allowed to enter the suction device the effect can be like that of trying to suck a piece of paper placed over the cylindrical aperture of a vacuum cleaner. Placing the suction tip in fluid results in some aspiration, but in general the most effective way to aspirate fluid is with the tip of the sucker at a acute angle, a millimeter or so from the surface.

Wiping with a gauze pad is an alternative to suction for removing fluids from the operative field but has the disadvantage that it is very traumatic to friable tissues such as pia, arachnoid, and small blood vessels.

Whenever possible the suction attachment should be held in the non-dominant hand. Suction is as maintenance activity, keeping the operative field clear of debris, blood, or smoke that can obstruct visualization. Such activity should be subordinated to the more important manipulations of dissection, resection, or tissue manipulation.

If the tip is placed onto the surface of the clot such that no air is allowed to enter the suction device the effect can be like that of trying to suck a piece of paper layed over the cylindrical aperture of a vacuum cleaner. Placing the suction tip in fluid results in some aspiration, but in general the most effective way to aspirate fluid is with the tip of the sucker at a acute angle, a millimeter or so from the surface.

The sucker tip is a metal cylinder with as rectangular end. Advancing the sucker with downward pressure onto the pial surface is no different than applying a towel to this delicate surface. The fine vessels that overlay the pial surface are similarly dug into and cut. Pial bleeding, from vessels too small to be visualized and efficiently coagulated can unnecessarily complicate the operation virtually from its outset. The proximal end connects to the suction tubing. There are/is a bend in the instrument such that the thumb can be flexed to occlude or open an air inflow opening in the handle. The working end comes in various lengths with a range of tip aperture diameters depending on the space available for sucking and the material to be sucked. Position the hand as if to scoop something with the thumb extended. Bring the hand around the instrument such that the handle end rests against the base of the fingers, upper palm with the thumb still extended. Position handle with respect to the hand such that on flexion the distal pad of the thumb can fully occlude the side hole. Keeping the handle against the hand by adduction of the proximal thumb, flex and extend the distal phalanx to adjust how much air flows past it through the air hole.

A suction device moved to and fro over the clot can injure the brain surface because the depth of the interface between the bottom of the clot and the pial surface cannot be ascertained until it is inadvertently encountered, at which point damage to the pial surface may already have been done. For this reason it is advisable to combine suction moved to and fro with gentle irrigation to try to develop a plane between the clot and the pial surface and lift the clot away from the pial surface. Once a patch of pial surface has been identified, irrigate this off and place a cottonnoid patty on the surface of the brain to protect it from further suction trauma. Now the depth of the clot can be gauged and suction can be applied more vigorously and rapidly. Irrigation can be used to lift the clot from the surface of the brain.

c.3 Hemostasis

Hemostasis is essential when a clear view of small structures in dependent portions of a surgical field. In neurotrauma surgery the dual aspects of hemostasis are prevention and control of bleeding accomplished by a combination of: positioning, tamponade, electrocautery, and deposition of clot promoters.

Maintenance of a clean surgical field free of accumulations of bloody dirty fluid requires that these be removed at least as fast as they are produced. Prevention of, or decreasing the rate of, hemorrhage improves the chances that suction and irrigation will be adequate to keep the field clear.

Uncontrolled bleeding can occur following a deliberate or inadvertent surgical maneuver. Arteries have thick walls that can tolerate application of clips and ligatures without rupturing. The walls of veins are much thinner and more fragile and therefore compression control of bleeding from these structures is more problematic with other means often preferred and more effective.

The techniques used for prevention and control of intraoperative bleeding include: 1. mechanical tissue compression (tamponade), 2. Blood pressure control, 3. promotion of intra- and perivascular coagulation, and

d) Hemodynamic

        Blood under pressure dilates vessels (and their lumina) and pushes its way out through defects in vessel walls. Reducing blood pressure is an effective way of reducing bleeding from transected and lacerated vessels.

Reduction of blood pressure can be achieved by simply raising the head and torso portions of the operating table such that the level of the patient's head is higher than that of his heart. This not only forces arterial blood to flow upwards but also facilitates the downward flow of venous blood.

    e) Mechanical

        Mechanical control of bleeding includes tamponade and application of clips and clamps.

    e.1 Clips and clamps

Scalp clips are used to prevent arterial bleeding from incisions too long for sufficient tension generation along the incision line to close small vessels of the skin and deeper layers. Different designs and materials notwithstanding, the common principle of all scalp clips is application of continuous pressure from above (skin surface) and below (subgaleal) the scalp edge

FIGURE: Scalp clip
compressing bleeding
scalp layers

Although there are different types of clips used in neurosurgery, the principal of the scalp clips is to apply force to the scalp through the spring action built into the clip explicitly as a spring or implicit in its composition of pliable plastic.

Because the clips compress larger arterial vessels they can be used to stop bleeding distal (along the direction of arterial blood flow). The extended range of distal arterial hemostasis obviates the need to apply them in tandem along the incision. Since each clip controls bleeding locally along the segment on which it was applied the number required for hemostasis increases with the length of the incision.

A variety of clips and clip appliers are available. Because the time spent in placing clips around the scalp is only 5 to 10 minutes during most craniotomies decreasing this by half will not significantly reduce the total surgical time and does not justify the purchase of disposable appliers that may save time but jam frequently and are less dependable than the "old fashioned" scalp clip appliers. The fully manual scalp clip appliers are easy to use, and fast. They give the surgeon better control of over the exact placement (depth and pressure) of the scalp clip blades which is most important for effective hemostasis.

Hemostatic clamps with interlocking teeth maintain squeezing pressure on layers of scalp or other tissue that is bleeding after being cut.

Dandy clamps are a curved variation on the straight hemostat.

Dandy clamps should be placed in succession approximately 1 cm apart along the cut scalp edge with the tips grabbing the galea and the instrument hanging down, reflecting back the scalp and mechanically tamponading vessels at the scalp edge. The handles of every five or so successive Dandy clamps are bundled with a rubber band in order that they not flop around too much.

FIGURE: Dandy application technique (Dandyclampapplication.gif)

Dandys are particularly useful when a flap is being created not only as hemostats but also pulling downward.

Vascular clips can be used on transected sinuses or larger vessels. In general arteries are sutured, veins clipped. Aneurysm clips may be used for traumatic aneurysms, particularly to reconstitute across a site of vessel wall weakening or rupture.

e.2 Tamponade

Yet another method from removal of blood and cloudy fluid from the field are to soak it up in pledgets that can be removed from the field after they have absorbed to their capacity, being then replace by fresh, clean, and dry ones. Because of their resemblance to cotton, these pledgets are called "cottonoid". They come in two shapes: squares and ribbons.

The working principle of the cottonoid pledgets is that they are made with a porous absorptive material that adsorbs irrigant fluid and blood. They can be placed atraumatically on brain tissue and protect the pial surface from carelessly wielded sucker tips.

The cottonoids are a non-suction-dependent technique alternative to that of wiping blood from soft tissue surfaces with a heavy gauze pad. Blood can be effectively sucked from a delicate tissue surface through the thickness of the interstices-abundant cottonoid, thereby enabling indirect aspiration of fluid or blood from the surface of the brain.

Most patties are flexible but have enough rigidity such that they apply force over a fairly wide area when pushed on focally. They are thus excellent hemostatic agents for tamponade of surface bleeding. Cottonoid patties can of course also be used in conjunction with (usually on top of) hemostasis-promoting materials such as Surgi-Cel or Gelfoam which allows the cottonoids to promote hemostasis by small vessel pressure occlusion while the coagulum promoting factors in Surgicel and Gelfoam were beginning their work.

The interstitial volume per surface area of a cottonoid is enormous. A relatively thin, unobtrusive cottonoid placed along a slow ooze of blood from the potential epidural space between the dura and the periosteum, will quietly soak up large volumes of the ooze which eventually overflows. The cottonoids buy the surgeon time to identify sites of bleeding. However, sooner or later the cottonoids must be aspirated or changed for dry or moist ones with vacant pores.

To the patties are attached strings which can be used to identify their presence deep within a wound or hole when the strip itself cannot be visualized. The strips are also usually provided with an embedded small radio opaque filament which can easily be detected on a plain X-ray in the event that the count is inaccurate and there is a suspicion or possibility that a strip has been left in the patient. There is of course no way to detect the amputated portion of the pattie rejected previously because it had no attached radioopaque tag. Cutting up of cottonoids should be done as far from the operative field as possible to minimize the risk that radiographically non-detectable fragments end up left in people's heads.

The surgeon should learn the approximate rather than precise dimensions of cottonoids. There are four basic cottonoid configurations: small and large, squares and ribbons. The small squares (about the width of a finger tip) are good for applying focused pressure at their center, These cottonoids are for putting pressure over small isolated bleeding foci. A larger size, two or three finger breadths square, will provide reasonably good hemostasis over a like extent of tissue surface.

The cottonoid is picked up by the working end of a forceps instrument without teeth. Teeth will hook into the fibers of the pledget and make it difficult to detach the cottonoid from the forceps working end. The forceps grasp the most superficial layer of the cottonoid. A this layer partially separates it allows the larger bulk of the cottonoid to remain spread out flat for easier application to similar flat broad surfaces.

Surgicel is bacteriostatic dehydrated cellulose that dissolves within 2 weeks of placement in the body. Bleeding stops upon application of surgicel because blood cells and larger particles form a coagulum within the interstices of the cellulose, converting the piece of surgicel into an impermeable, relatively heavy, patch.

FIGURE: Surgicel (surgicel.gif)

   e.3 Ligation

Ligation of vessels is done much less often in head trauma than other kinds of surgery largely because actively bleeding large arteries free along enough of their length for clip placement are rarely encountered. The only intracranial venous structures occasionally but with utmost selectivity ligated are the dural sinuses. As noted elsewhere, only the anterior third of he sagittal sinus is safely ligated. Dural sinuses are ligated with non-absorbable suture, such as 2-0 prolene.

    e.4 Cautery

Coagulated blood plugging a vessel will stop bleeding as can as externally applied pressure. Intravascular coagulation can be promoted by application of heat (cautery) which will denature proteins causing them to form a mesh. Two types of electrocautery coagulation are currently available for obtaining hemostasis in the head trauma operative field these differ not only in the physics underlying their design but also in their effects on tissue, and their indications for use

FIGURE: Monopolar and bipolar electrocautery devices (monopolarbipolar.gif)

The heat delivered from mono- and bi-polar are different in their properties of intensity, focality, and dispersion through biologic tissue. The current arc between the two poles of the bipolar is focused to a small area. The maximum temperature is several hundred degrees, celsius. Because of physical implications of its sinusoidal transmission wave, bipolar heat does not disperse widely through contiguous biologic tissue. The bipolar is turned on by depressing a pedal which produces an all-or-none, on-or-off response at the coagulating tips. The bipolar is not for indiscriminate coagulation but rather for vessels that can be identified and touched directly.

The energy from the monopolar radiates from a long source with a broad or pointed working end. The heat disperses widely through tissue. The monopolar blade delivers both pressure and heat to biologic tissue. Tissue desiccated by the latter tear with less of the former.

Electrocautery devices work unpredictably, poorly, or not at all, in an aqueous medium so irrigation fluid should be sprayed judiciously onto the field.. The basin that holds the irrigation fluid is separate from others to keep the fluid, which forms a layer through which the surgeon must look clean and clear.

    f) Clot promotion

        Clot formation at sites of bleeding from vessels can block these and stop further hemorrhage. Surgicel is a clot formation promoting material that allows platelets and aggregates of thrombin and particulate blood elements to cling and form a coagulum that can act as a patch.

Other clot promoters include collagen derivatives which act like thrombin forming a protein scaffolding that acts to stop further bleeding.

	Prevention	Control
Clips and clamps	asd	asd
Ligation	asd	asd
Hemodynamic	asd	asd
Cautery	asd	asd
Tamponade	asd	asd
Clot promotion	asd	asd

b) Head support and positioning

Patient head support and positioning options include the donust head and horseshoe headrests which support the head with stabilization by gravity.

b.1 Donut

The "donut" is a solenoid, a circular tube, into the "hole" of which the patient's head is set when gravity and the contact between the head and the inner aspect of the tube are sufficient to hold the head throughout the course of the operation. The donut will not hold the head against vigorous forces applied laterally or tangentially to the head, but works well when the head will be pushed on from above. That the head is "held" only by gravity and a few centimeters of donut rim predisposes it to displacement when force is tangentially applied.

The head on a donut can be rotated axially through almost 180 degrees giving access thereby to most of the frontotemporoparietal regions where the vast majority of surgical traumatic intracranial hematomas are encountered. Intraoperative rotation of the head without external fixation is possible by simple lifting of the head off the donut with a gentle turn to the left or right (provided that the entire area has been preoperatively scrubbed and sterilely draped).

b.2 Horseshoe

The horseshoe is a padded semicircular device that supports the head at three points of contact: 1. the forehead and 2. and 3. the malar eminences. The sides of the horseshoe can be adjusted such that the face (and head) sit deeper below within the device and in there better resist laterally applied forces than the donut.

The horseshoe gives the same degrees of rotational mobility as the donut but in addition allows for adjusting the level of the head with respect to the trunk but has the advantage that it attaches rigidly to the bed through an articulated metal arm allowing adjustment of the height of the head with respect to the rest of the body.

Soft tissue

Instruments are used in tissue to divide, separate, retract, manipulate, and approximate soft tissue during craniotomies.

1.1. Division

Division across a soft tissue tissue layer is distinguished from division within a tissue layer conceptually, physically, and by the surgical instruments required. Tissue is most resilient, at molecular (collagen), microscopic (cellular), and gross (fascia) levels, across its constituent layers. Layers of tissues head trauma operations for which appropriate instruments of division must be selected, are skin, fascia, dura, and pia. Between these layers are "planes" frequently fluid-filled or frequently "potential" meaning that they exist only after the normally apposed layers above and below them have been separated with blunt instruments or even fingers sometimes with only minimal force.

Cold metallic blades divide the strong bonds within tissue by crushing and cutting. Single blades attached to handles are knives. Double blades that approximate across a fulcrum are scissors. The former are better for a layer that is approached from above, the latter for a layer approached from the side.

Downward dissection is easier and faster with larger than smaller blades. Larger blades are thus used for rapid, deep cuts, as of the skin, whereas smaller blades cut shallow but afford the surgeon much better control in terms of the line of incision and depth of cut, desirable through a relatively thin layer of fascia just below which lies well vascularized muscle. A layer as thin and friable as the pia must be divided by the most delicate of blades whether single as a knife, or double as a scissors.

The cut of the respective blades is different. The wider the blade the wider the incision. The 10 blade is the heaviest with the largest diameter making it best for cutting skin. The 15 blade, with a smaller radius of curvature cuts thin layers such as the dura. The 11 blade has a triangular shape ideal for puncturing tissue layers, as of the dura for ventricular catheter insertion.

The #10 blade works well on the thicker skin in adults whereas in small babies the smaller #15 blade is sufficient for both penetration and cutting. The disadvantage of the #15 blade in adults is that the depth of the skin incision will be less, requiring more passes with the knife to go through the skin.

Different handle sizes and shapes are available for use with the different sizes and shapes of knives. A long thin handle is appropriate for use with the long pointed #11 blade used for puncturing tissue, as for example the dura when opening this membrane during a ventricular catheter placement procedure. A broader, heavier blade is used with the broader, curved #10 blade, for longer, deeper incisions such as that of the skin for a craniotomy. The smaller #15 blade can be placed on a broader, shorter handle or a long, fine handle. This blade is appropriate for use for making small soft tissue incisions in limited spaces.

Scissors can be used either to divide or separate tissue. They are not good for cutting skin because they macerate skin edges and do not cut straight. Larger scissors, such as the Metzenbaum, are good for dividing thicker tissue layers such as temporalis fascia. Smaller scissors, such as the Jameison are good for cutting dura.

TABLE Scissors features and indications

Scissor	Figure	Shape	Indication
Suture		sdf	sdf
Metzembaum		sdf	sdf
Jameison	(jameisonscissor.gif)	sdf	sdf
Tenotomy	(tenotomyscissor.gif)	sdf	sdf
Mayo		sdf	sdf

The electric monopolar cautery cuts through a tissue layer breaking the bonds through it with heat energy. Hot blades divide by burning their way through along an incision line. Beyond the intense cutting heat is a region of coagulation which is relatively inert with respect to inward migration of fibrocytes necessary for granulation and restoration of the bonds that will hold the skin edges reapproximated upon healing. The long term consequence of a hot knife cut through the outer layer of the skin is a scar that could have been avoided simply by cutting with a metal knife instead.

1.2. Separation

Separation within a soft tissue layer should be as atraumatic as possible. Separating soft tissue along clefts within it or from other tissues should preserve as much tissue as possible. Soft tissue held apart during the procedure can be restored to its original location during closure.

The tissue layers defined by dissection can be of the same composition, the same in terms of properties of softness or hardness (but not of the same composition), and similarly soft or hard but of different composition.

Muscle must be separated along clefts or divided against the direction of its fibers to create the scalp flap. This division can be accomplished without blood loss if done along existing fascial planes, with minimal blood loss if done along the direction of muscle fibers, and with potentially significant loss if done at any angle but parallel to the fibers.

FIGURE Separators (separators.gif)

Different instruments are used to divide muscle depending on whether fascial planes are present or absent. Muscle is not adherent to its enveloping fascia. Simple finger dissection is usually enough to create a plane between them. When fascial is present it defines a bloodless plane between muscles. If this plane can be entered and identified with a scissors, muscles can be bluntly separated by an advancing finger without much blood loss.

In the absence of fascia, creation of a plane is more difficult. Selection of an instrument for muscle division also depends on whether such division is parallel or oblique to the orientation of the muscle fibers. Absence of fascial planes in muscle requires using a hot knife which will coagulate small muscle vessels as it divides the tissue.

Muscle is most easily divided in the same direction as its fibers, usually with a dissector and scissors. Scissors can be used to cut as they are advanced into a tissue layer but also to separate when pushed into the substance of the muscle and opened creating thereby a plane parallel to the fibers. The shorter Metzenbaum scissors are good for dissection of more superficial tissue layers. Deeper, a longer variation of the Metzenbaum, is ideal.

Separation of muscle oblique to the direction of the fibers causes bleeding which is difficult to stop because it is from small vessels that cannot be identified and individually coagulated. The hot knife is preferred to the metal knife or scissors for cross fiber muscle dissection, coagulating as it descends, thin layer by layer through the tissue.

Separation of galea and pericranium is easy because of the presence of an intervening layer of loose areolar tissue. This tissue is translucent, almost like a film. Blunt dissection with a finger suffices to separate the layers with a loop or army-navy retractor (see discussion of hand-held retractors below) assisting by pulling the scalp back along the advancing plane.

Another interface at which two soft tissues are separated is that between an intracranial hematoma and dura or pia. Brain spoons and spatulas mechanically lift coagulated blood off thick surfaces such as the dura but are not appropriate on the pial surface. A vigorous wash from the irrigation bulb can dislodge clot from the pial surface if it is not too thick. Semisolid acute blood frequently is not susceptible to aspiration with any of the suction tip orifice diameters available.

Hematoma and brain parenchyma are two soft tissues that must be separated if one is to be removed and the other left behind. The interface between brain parenchyma and hematoma differs from that between hematoma and pia in that there is less of a potential plane between the latter and former. A plane can be created between coagulum and brain tissue by gentle insinuation and forward pressure of a cottonoid patty.

The Woodson dural separator (Illustration: Separators and dissectors) is probably the most useful and versatile of the instruments used to separate the dura from overlying bone in spine surgery. However, in the intracranial procedures, the #3 Penfield is more often used. The Penfield has a curved tongue-type shape at the working end and comes to a thin termination.

Because pericranium is densely adherent to the underlying bone, its separation from the skull requires an instrument with a sharp leading edge such as a Cobb or periosteal elevator. The Cobb has a flat, broad, rounded end that comes to an edge sharp enough that it can be used to reflect periosteum from bone. The joker periosteal elevator is also good for narrower dissection of pericranium from cranial surface.

Muscle is directly adherent to bone over the extent of its origin. The temporalis muscle is directly adherent to the frontal and temporal bones from which it originates. The occipital musculature orginates from the posterior and suboccipital portion of the skull where it is similarly directly adherent to the bone. At this interface a Cobb is used to put the muscle fibres on stretch ahead of an advancing hot knife. With each sweep of the hot knife, approximately ? cm of bone is uncovered. Increasing the space between successive swathes leaves clumps of muscle protruding from the bone surface where they can potentially obstruct an advancing craniotome blade.

The Cobb (also used for elevating periosteum from underlying bone) is the principal instrument for elevation of the bone flap from the underlying dura (the elevation techniques are identical; the soft tissues elevated differ in thickness and consistency, and the first is done from the outer, while the second from the inner surface of the cranium).

TABLE Layers requiring separation during trauma craniotomy

Retraction

Once a layer of tissue has been divided or separated it must be held separate in order for the surgeon to proceed to the next level of dissection. Instruments that hold divided or separated tissue apart can be hand-held or self-retaining. Tissue retractors vary not only in the means for maintaining them in place but also in the depth to which tissue can be separated and over what length. Tissue retraction instruments are designed to be strong enough to pull back tissue but unobtrusive in terms of the operative field.

FIGURE Malleable ribbon retractors (malleableribbonretractors.gif)

Metallic malleable ribbon retractors will, with force bend to virtually any curvature. They are important in operations for head trauma as a means to protect the dura and underlying brain when making holes through the bone with the drill bit. They are also useful for retracting brain tissue relatively atraumatically. They come in different widths, which enables distribution of the retracting force to narrow or broader patches of brain tissue depending on location and exposure.

FIGURE Cushing loop retractor (Cushingloopretractor.gif)

The "loop" of the Cushing loop retractor is large enough to hold not only the entire scalp thickness as well as reflected temporalis muscle.

Because the self-retaining retractor puts the scalp tissue on stretch, it closes down many of the small vessels which bleed from the edge of a scalp incision. Bleeding from straight line and "lazy S" incisions of up to 10 cm can be controlled by strategic placement of self-retaining retractors which when opened stretch the scalp tissue narrowing to close openings in vessels that crossed the incision line before transection by the knife.

The disadvantages of self-retaining retractors for incision hemostasis is that they provide adequate stretch of tissue only over a relatively limited incision length and that the extent to which the tissues can be spread is limited by the length of the retractor arms which is itself limited by the dimensions of the surgical and operative fields.

The Weitlaner is a self-retaining retractor with a slight curve to its arms. It is relatively small but can easily be manipulated. The longer the arms the more difficult is insertion and removal because the instrument becomes disproportionate with respect to the surgeon's hands. When working in a deeper wound, the curved so-called "cerebellar" retractor achieves a good degree of wound opening. While the handle and proximal portion of the arms lie relatively flat on the skin surface.

The Ghelpi has a tapered end that is curved so that it hooks the tissue with a hook that is much less bulky than the pronged end of the other self retaining retractors. The Ghelpi arms are also bent so that the proximal end of the instrument lies relatively low profile on the surface of the pt.

Cerebellar retractors are a modification of the Weitlaner. Their working end is offset at an angle from the handle. Cerebellar retractors are used for deep retraction without lengthening of the retractor prongs, while maintaining a low profile of the handle with respect to the skin surface.

Manipulation

Tissues are grabbed and manipulated by a variety of instruments including forceps and clamps. Forceps are hinged at the handle with tips for grabbing either with teeth or without. Forceps variables include length and weight of the instrument, whether or not bayoneted, with or without teeth, indications for use, potential damage to tissue. Forceps grab tissue of various compositions and thicknesses and therefore must themselves be of different sizes.

FIGURE Forceps (Russian/Swedish, Geralds, Adson, Bayonnet)

The Mayo-Russian and Swedish forceps are large with thick end that can take hold of larger, bulkier segments of the scalp. They are used to position the scalp for application of hemostatic clips.

The rat tooth and Geralds with teeth are forceps that differ not so much in the size or shape of their biting elements as in their length and bulk. Geralds are long, slender forceps that securely grasp tissue at a distance from the surgeon's hands, frequently in holes. They are more delicate and therefore for use with thinner tissue than that manipulated with rat tooth forceps. Geralds without teeth also reach objects at a distance from the fingers, but do so without interlocking grasping. Adson tissue forceps are broad at the portion of the instrument where the finger pressure is applied but the tips are fine, thin and with teeth. The distance from the finger pressure and the tips is short. The Adsons thus provide great control for fine finger movements, as is desirable when trying to put sutures into the skin, positioning the edge to receive an incoming needle.

Bayonet forceps drop the hand below the surgeon's line of sight to the tips and thus facilitate work within holes where vision above the instrument is limited. This instrument configuration has been adapted to bipolar electrocautery in the Malis device.

TABLE: Forceps

Approximation

Tissue can be approximated from the surface or at one or several of its deep layers. At the surface (skin) tissue approximation can be done with sutures, wires, staples, or tape. Deeper tissue is approximated with sutures.

Sutures vary in size depending on the amount of stress they are designed to tolerate without breaking or coming undone at the knot. The other variable for sutures is whether or not they dissolve over time.

Sutures vary also by the way that they are attached to the distal needle shaft. There are three main ways that suture is attached to the needle: 1. through a loop, like a standard sewing needle 2. Securely attached directly to the end of the needle, and 3. Attached enough only to drag through the skin and soft tissues but readily detached with even a gentle but firm pull by the surgeon.

The caliber of the needle shaft is proportional to the size of the tip at the needle point. The shape of the needle tip can be tapered at the end to make a more circular hole. The denser the tissue, the more resistance it presents to penetration by a tapered needle. "Cutting" tips on needles advance more readily through resistant tissue because of their blade-like shape which allows them to cut through, rather than puncture and dilate, tissue.

Needles are differentiated by how (and if) they are attached to sutures, the shape of the needle, the width of the needle and whether the needle cuts or tapers, but most important, the indications for their use.

The appropriate needle holder to use with a given needle must provide a good working distance between the surgeon's hand and the point of application of the needle, and have a tip which holds the size needle firmly. Holding the needle is a function of the tightness with which the tips approximate and the closeness of the bumps on the flat surface of the needle holder point.

Needles get bent when they are forced through or against thick or hard tissue. If the bend is minimal the surgeon can usually keep sewing through tissue. If more significant he may need to try to bend it back to its original configuration. If too badly bent best is to ask for a new needle and discard the deformed one.

TABLE Suture and needle features and indications

2. Bone

Bone is perforated and/or cut in the course of any intracranial trauma surgery.

Irrigation accomplishes two purposes in the setting of drilling bone. First, it cools down the bone. This is important in terms of the mechanics of bone cutting: the bits cuts more effectively through cooler bone and in the absence of bone dust that can clog its rotations.

Perforation

Bur holes

Holding and manipulating the perforator and craniotome require the coordinated action of the forearms as well as the hands because of the greater force that must be applied to hard tissue. The perforator is held perpendicular to the outer table.

FIGURE: Perforator perpendicular to outer table (perfornatorperpendicularbone.gif)

Irrigation accomplishes two purposes in the setting of drilling bone. First, it cools down the bone. This is important in terms of the mechanics of bone cutting….the bits cut more effectively through cooler bone.

Drill

Drilling small diameter holes in bone is most conveniently done with a power drill with a small diameter bit.

Bone can be perforated by a surgeon muscle- or external power-driven instrument. Power for turning the perforator bit is either electricity or pressurized gas. Any instrument for perforating bone must have an effective catch mechanism to prevent plunging into the brain. In spite of the fact that power is faster and just as safe, there are definite indications for using manual bone perforation. Another difference between perforators is how they handle bone dust.

Holding and manipulating the perforator and craniotome require the coordinated action of the forearms as well as the hands because of the greater force that must be applied to hard tissue.

As the burr hole bit descends through the bone, that it displaces is lifted by the rotation of the spiral cutting bit, to the bone surface. This bone dust must be constantly irrigated away or it will obstruct the surgeon's view of the moving bit.

It is important that there be some mechanism whereby power driven instruments in general, and bone perforators in particular, stop automatically when there is no more material to be drilled or cut, because the next layer of tissue may be too delicate to sustain the trauma of an inadvertent.

Assembly of power perforators is no small technical challenge. Three or four attachments must be arranged from proximal to distal from the working end of the instrument.

2.2. Cutting

Cutting of bone can be done either manually or with a power-assisted instrument. What makes the instrument go is either gas under pressure or electrical current. The options for cutting differ depending on the saw, as do the risks. The power craniotome is a blade that rotates at high speed chipping tiny pieces of bone so rapidly that it seems to be cutting. The cut through the bone is not does not break the bonds between the edges cut but rather forms a trough between them.

FIGURE Craniotome blade and footplate (craniotomebladefootplate.gif)

Each tooth of the saw takes a small chip out at each encounter with bone. The cumulative effect of the line of teeth cutting along the same line is that line created in the bone through which the instrument passes.

FIGURE: Position and movement of hands in craniotome manipulation (craniotomemanipulation)

Manual bone cutting is done with the Gigli saw which is an instrument made of a twisted wire which when grabbed at both ends and held taut and then moved forth and back chips a trough through bone. The wire is advanced in the space between the dura and the overlying bone using a special instrument which makes this tunnel relatively atraumatically to the dura. To the end of this instrument is attached the wire. Thus when the instrument is pulled out at the other end of the tunnel the sawing wire is in place. Handles are then attached to the ends of the saw and it is pulled up at the same time that it is pulled to and fro and a sawing action results.

The Gigli saw advantage is that because the sawing wire is placed only after the dura has been separated from the bone, sawing through the bone can be done without trauma to the underlying dura. The Gigli saw disadvantage is that each segment that it saws between two burr holes must be straight and thus to make a curved craniotomy required more burr holes and more Gigli saw cuts. In addition, the Gigli saw probably takes more time than a power driven craniotomy saw.

The choice for bone cutting instruments is between manual and power. Power-driven craniotomies are faster, hand saws are less traumatic (to the underlying dura which the craniotome has an unfortunate tendency to tear). Craniotomies must be assembled from several small parts that contract and expand fitting together successively less well with every trip to the autoclave.

FIGURE: Craniotome parts (craniotomeparts.gif)

2.3. Shaping

Curettes look like miniature ice-cream scoops with sharp edges (Illustration: Curette). They are useful for removing thin edges of bone, such as that left behind on the dura by the perforator at the bottom of a burr hole.

Rongeurs are instruments for biting bone. They cut by applying a force to a sharp edge against the surface of the bone. The size and shape of the piece of bone bitten off as well as of the remnant portion is determined by the size and shape of the biting edge of the rongeur. All rongeurs have a handle where compressive forces can be exerted as well as a sharp working end which makes contact with bone. They differ in the size and shape of the bite as well as the mechanism which powers it.

The Adson cranial rongeur for example removes relatively large, smooth-edged bone pieces due to the ovoid configuration of its biting portion. The biting end of the Adson rongeur is in line with the axis of the instrument and therefore perpendicular to the line of action of applied force from the surgeon's hand. Therefore the force of biting is in the same orientation as the force of the surgeon's grasping.

The Leksell curved rongeur has a double action feature which enables generation of a large amount of force at the long arms of the instrument which is translated through the double action portion into a significant force across relatively short distance between short biting arms.

The Kerrison ronguer (or "punch") with a biting mechanism at the end of a long beak-like working end, is useful for refining the bone work from a standard craniotomy when small bites are desirable. Sometimes the rongeurs are a bit unwieldy and much torque can be generated across the end in biting off bone suboccipitally for a posterior fossa craniectomy, a punch can be used to gradually approach the transverse and sigmoid sinuses.

The principle types of rongeurs available and necessary during head trauma operations are those where the cutting force of the rongeur is parallel to the force being applied by squeezing the hand or squeezing the instrument or is at an angle to this force. Selection of a rongeur depends on the distance across which the force to cut the bone must be applied and the angle of accessibility to the bone to be cut. Rongeur selection also depends on how much bone is to be cut with each applied force. In tight spaces where control of the amount of potential trauma is desirable or where a cosmetic deformity should be avoided, one may select a Kerrison rongeur.

TABLE Rongeuers features and indications

Ronguer Figure Shape Indication

Leksell

sdf sdf

Adson

sdf sdf

Kerrison (Kerrison.gif) sdf sdf

2.4. Securing

Bone can be secured with heavy suture, wire, or screw fixed burr hole covers. Wire (or even non-absorbable suture such as "0"-silk) can be passed through holes drilled on either side of the bone flap and tied to fix them together. The wire needs to be strong enough to hold the bone securely and to resist impacts the patient is likely to sustain once up and about, but must also be fine enough that the surgeon can maneuver it two ends into a knot. Special wire cutters are also required… even the heaviest surgical scissors will be ruined cutting wires.

Small burr hole covers fixed to the skull with screws work well and do not take much time to place but do not hold the craniotomy bone flap in better than a like number of wires or sutures combined with the granulation tissue that forms around and along the bone incision and contributes to fixation. While convenient and time saving (about 5 minutes per wire, 3 minutes per suture, 1 minute per burr hole cover) the screw-cover combination is a luxury item in head trauma or any other intracranial surgery.