Fracture Complications

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Posttraumatic Osteomyelitis Terry D. Braden, DVM, MS*

DEFINITION There is some confusion in the literature regarding osteomyelitis because the terms acute osteomyelitis, chronic osteomyelitis, posttraumatic osteomyelitis, hematogenous osteomyelitis, and wound infection often are used interchangeably. Acute and chronic osteomyelitis are merely different durations of the same disease. The term acute osteomyelitis is often used mistakenly when wound infection is meant. Dorland's Medical Dictionary11 defines osteomyelitis as inflammation of bone caused by a pyogenic organism. Posttraumatic osteomyelitis is an infection (inflammation) of the bone after trauma or surgery to the bone. Posttraumatic osteomyelitis tends to remain localized to the bone or bones traumatized and is not a systemic condition. There is intermittent localized swelling and drainage from the infected bone. Mortality due to posttraumatic osteomyelitis is low. Hematogenous osteomyelitis also is an infection of the bone, but it is not associated with trauma or surgery. The source of the organism is infection elsewhere in the body. Unlike posttraumatic osteomyelitis, hematogenous osteomyelitis is a systemic disease. The animals often have signs of systemic illness, such as fever and anorexia. Hematogenous osteomyelitis occurs more commonly in humans, rabbits, and neonate horses than in other animals. The mortality of hematogenous osteomyelitis is high. Wound infection is an infection of the soft tissue and does not involve the bone. Because wound infection is also caused by trauma or surgery, results in localized swelling and drainage, and can progress to posttraumatic osteomyelitis if not adequately treated, wound infection is often mistakenly referred to as acute osteomyelitis. Like posttraumatic osteomyelitis, the mortality is low in wound infections. Occasionally, the patient can become systemically ill with clinical signs of significant swelling, fever, and anorexia. More often, however, wound infections cause local signs of slight to moderate swelling, local heat, drainage, and tenderness. This condition *Diplomate, American College of Veterinary Surgeons; Professor and Head of Orthopedics, Veterinary Clinical Center, Michigan State University College of Veterinary Medicine, East Lansing, Michigan Veterinary Clinics of North America: Small Animal Practice-Val. 21, No. 4, July lfl9l

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must be distinguished from posttraumatic osteomyelitis so that specific treatment can be rendered.

BIOGRAPHICS It has been found that posttraumatic osteomyelitis is not an age-specific disease; its range of prevalence followed the age distribution curve of the normal canine population (Fig. 1). 10 A scan of the breeds involved in the cases of this study (Table 1) does not indicate any breed predisposition for the disease. The incidence of osteomyelitis appears to parallel the distribution of breeds as seen in the hospital populations in which the study was conducted. The three breeds found most often in that study (German Shepherds, Labradors, and Great Danes) are very popular in the author's area of the United States. The study found that posttraumatic osteomyelitis was almost twice as prevalent in male dogs (43 of 67 cases = 64%) as it was in female dogs (24 of 67 cases = 36% ). 10 A similar gender distribution is found for fractu~es in dogs (62% males and 38o/o females). 3 This is also the situation in humans. 1 Men are more likely to suffer trauma and consequently to develop posttraumatic osteomyelitis. The appendicular skeleton, long bones of the dog, is involved in osteomyelitis more often than the axial skeleton (Fig. 2). The long bones also are fractured more often than the bones of the axial skeleton. 3 This is most likely due to the relatively greater soft-tissue protection of the axial skeleton compared with the appendicular skeleton. Also, the longer bones are more susceptible to torque and fracture more easily.

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2-6 6-12 months

1-2

2-4

4-7 7-10 10-15 years

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Figure l. Age distribution in 67 dogs with osteomyelitis (From Caywood DD: Osteomyelitis in the dog: A review of67 cases. JAm Vet Med Assoc 172:943, 1978; with permission. )

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POSTTRAUMATIC OSTEOMYELITIS

Table l. Breed Distribution in 67 Dogs with Osteomyelitis Afghan Airedale Beagle Bluetick Coonhound Borzoi Brittany Bulldog Collie Dalmatian English Setter German Shepherd German Shorthair Pointer

2 2 2 1 1 1 1 2 1 1 12 2

Golden Hetriever Great Dane Irish Setter Irish Wolfhound Labrador Mixed Breeds Poodle Samoved Saint .Bernard Shetland Sheepdog Springer Spaniel Staffordshire

l 6

3 3 8 5 2 1 4 2 2

With the exception of posttraumatic osteomyelitis of the feet (metacarpals, metatarsals, and phalanges) almost all cases involved just one bone. 10 The bones of the feet appear to be involved with a higher rate of osteomyelitis than is explained by the rate of fractures alone. 3 This may be because injury to the metacarpal and metatarsal bones and phalanges involves not only fractures but also penetration injuries. These penetration injuries can lead to soft tissue infection and thus to osteomyelitis. On the other hand, the bony pelvis appears to be relatively uninvolved with osteomyelitis both in comparison to other bones, and to the incidence of pelvic fractures. 4 · 8 This is most likely attributable to the large muscle mass on all sides of the pelvis. This muscle mass protects the pelvis in two fashions. The muscles act as shock absorbers, helping to prevent penetration of the skin, which would contaminate the wound and potentially lead to

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Figure 2. Location of 77 lesions in 67 dogs with osteomyelitis (From Caywood DD: Osteomyelitis in the dog: A review of 67 cases. J Am Vet Med Assoc 172:943, 1978; with permission.)

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Table 2. Bacterial Organisms Isolated from 67 Dogs with Osteomyelitis

Aerobacter Corynebacterium Escherichia coli Micrococcus Nocardia Pasteurella Proteus Staphylococcus Streptococcus

NO.

%

2 2 14 4 2 5 10 50 20

2 2 13 4 2 5 9 45 18

109

100

osteomyelitis. The pelvic musculature also helps to immobilize fractured bone, preventing the fracture ends from penetrating the skin and becoming infected. The relevance of open fractures is far less in the pelvis than in the long bones. 3 The extremely rich blood supply of the pelvic musculature may improve the chances of eliminating contamination before it develops to infection, and it may improve the delivery of systemic antimicrobials to the site. The most common bacterium isolated from dogs with osteomyelitis is Staphylococcus spp. 10 Streptococcus spp are the second most common (Table 2). Most often (53%), only one bacterial pathogen is cultured from the osteomyelitic wound. Two organisms were involved about one third of the time (31% ), and three organisms were isolated from 15% of the cases. Rarely, four organisms are identified on culture. 10 These data (multiple organisms) may be misleading because at the time that the cases were being studied, 10 it was more common to examine cultures from the draining tract. Today, it is known that culturing draining tracts can result in identifYing organisms from the environment as well as organisms causing the infection. Currently, cultures from the deep wound, next to the bone, are recommended. The author suspects that this diagnostic change will increase the percentage of single organisms cultured. The draining tract is cultured today only as a last resort (if surgery or needle aspiration is impossible), based on the theory that the information of the organisms of the draining tract is better than nothing.

PATHOGENESIS Studies identifying the source of the pathogen infecting the bone in both humans and animals have shown that poor surgical technique is the leading source of infection. The most common source of bacteria leading to osteomyelitis was poor surgical technique in 58% of the cases. 10 Studies at Tulane University have shown an infection rate of closed fractures managed conservatively to be 0.4% compared with those managed with open reduction and internal fixation, which was l. 7%, a fourfold increase attributable to surgical technique. The same study at Tulane found that the infection

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rate for fractures fixed with open reduction and internal fixation was 2.4% if the fracture was closed and 2. 9% if the fracture was open. Again, the most significant factor in the cause of infection is the surgical technique. The other source of the infection is the open wound. Comparison of the figures of surgical technique source versus open wound source from the two studies just mentioned shows a four or five times greater probability that the surgical technique was the cause. The importance of surgical technique cannot be over emphasized and is discussed later in the Prevention section of this article. Research over a 6-year period on posttraumatic osteomyelitis has led to the following basic understanding of the pathogenesis of posttraumatic osteomyelitis (Fig. 3). s.- 7 As the figure shows, there are three components necessary for the creation of posttraumatic osteomyelitis: an infected wound, avascular bone, and a favorable milieu. If any one of the three components is missing, osteomyelitis is unlikely. The author's experience in attempting to create posttraumatic osteomyelitis experimentally confirms this. Injecting greater than lOS colony-forming units (CFU s) of Staphylococcus au reus into a normal tibia through a drill hole resulted in 0% posttraumatic osteomyelitis. When the milieu was made more favorable by traumatizing the medullary canal with a wire attached to a high-speed drill and making the same injection into the medullary canal, posttraumatic osteomyelitis developed in approximately 50% of the dogs; however, within 4 weeks, 95% of those dogs were spontaneously cured. Only when the author created a favorable milieu, injected greater than 105 CFUs, and created a sequestrum, was a usable model of posttraumatic osteomyelitis successfully created. 5 Using all three ingredients resulted in a model of posttraumatic osteomyelitis in 90% of the dogs. The first component is an infected wound. The infected wound is a result of a contaminated wound given enough bacteria to start reproducing (>lOS CFUs) and sufficient time (lag phase). All traumatic orthopedic wounds can be considered contaminated. The National Research Council of the National Academy of Sciences has placed traumatic wounds of more than 4 hours duration in the dirty wound category. This is the worst of the four categories (clean, clean-contaminated, contaminated, and dirty). 16 The source of the contamination has been described; however, the key to this problem is not the existence of contamination but the extent of contamination. Elek and Conen 12 demonstrated that six million Staphylococci had to be injected intradermally to produce a pustule. If fewer Staphylococci were injected, the body's defenses handled the invasion, and no pustule formed. When more than 105 CFUs were injected, after some time (lag phase = 6 hours), the bacteria start multiplying, resulting in an infected wound (Fig. 4). The author defines a contaminated wound as a wound in which bacteria are present, whereas an infected wound has bacteria present that are multiplying at a logarithmic rate. The second ingredient in creating posttraumatic osteomyelitis is avascular bone. Avascular bone is devoid of blood supply; thus, it is segregated from the body's humoral defenses and from systemic antibiotics. Avascular bone forms a wonderful haven for bacteria. The third ingredient is a favorable milieu. Most bacteria need an

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Surgical Technique

Contaminated Wound
10' organisms/gm tissue)

~ Post-traumatic ~OSTEOMYELITIS

Avascular Bone

~ (3) Favorable Mil leu - Hematoma - Necrotic Tissue

Figure 3. Schema of the pathogenesis of posttraumatic osteomyelitis.

acceptable environment to exist. To multiply, however, they need a favorable environment. In the wound, the most favorable environment is stagnant blood (hematoma), closely followed by necrotic soft tissue. Bacteria can easily derive their needed nutrients from one or both of these tissues.

PREVENTION

Treating posttraumatic osteomyelitis can be extremely difficult, can involve surgery, is far less than 100% successful, and is very costly in time, money, and emotion. Therefore, prevention is of utmost importance in this disease. Consequently, this is the most important section of this article. As discussed previously, in examining the pathogenesis schema (Fig. 3), it can be seen that there are three major components needed to produce posttraumatic osteomyelitis-infected wound, avascular bone, and favorable milieu. If one of those components can be prevented from being present in the wound, there is a possibility that posttraumatic osteomyelitis will not develop. If two of these ingredients are prevented, there is a good chance that osteomyelitis will not occur. And if all three components can be prevented, there is no chance of a resultant osteomyelitis. Prevention of the Infected Wound Preventing an infected wound from occurring can be accomplished by keeping the number of bacteria below 105 organisms (CFUs) per gram of tissue. Remember, it is impossible to have a traumatic wound completely free of all bacteria at the end of surgery; therefore, traumatic orthopedic wounds should be considered contaminated. Contamination is present at closing because of the nature of these wounds, that is, trauma to the soft tissues, fracture of bones, rupture of vessels, long duration of surgery, large wound openings, and invasive procedures. This is the reason that the National Research Council of the National Academy of Sciences has designated a traumatic wound of more than 4 hours duration as a dirty wound. 16

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Number of Organisms In Wound

10

- - L a g Phase - - L - Contaminated ___J Wound

L_

Hours

Infected ___J Wound

Figure 4. Graph of the number of organisms in an open wound and the time of the contaminated (lag) phase and the infected phase.

Although contamination of most orthopedic wounds is inevitable, infected wounds are not. With proper open wound management (if open from the trauma) and good surgical technique, the bacteria count can be kept far below the level needed to lead to infection (> 105 CFUs/g tissue). From the schema (Fig. 3), it can be seen that there are two areas that will affect the amount of contamination in the wound-surgical technique and the open wound management. Surgical Technique. The surgeon develops good surgical technique by spending time and effort, on a daily basis, practicing the following basic surgical principles:

1. 2. 3. 4. 5. 6.

Aseptic surgery Accurate and sharp incision Fastidious hemostasis Approach via intermuscular planes Gentle handling of soft tissues Anatomic closure

These six areas need meticulous devotion to detail if the surgeon wishes to advance his or her surgical technique from average to the level of good. Aseptic Surgery. In the veterinary arena, aseptic surgery entails the following: Surgical room free of insects and dust Broad area of the body clipped of hair Surgical scrub of the skin Double drape Sterilized instruments Sterile suture material Cap and mask Personal scrub Gloves and gown

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Surgical room free of insects and dust means complete cleaning of the room (surgical table, floor, top of the surgical lights, I. V. stands, shelves, top of x-ray viewer) on a daily basis. It also entails developing some means of preventing flies from entering the room and an immediate disposal plan when one does enter. Broad area of the body clipped of hair: this is one of the areas that is most often neglected in veterinary practice, partly because it takes more time to clip a wide area and partly because most owners wish (and some even request) no or minimal clipping. Remember, it is impossible to cleanse skin with hair on it. Therefore, clip an area slightly wider than you think you will need. Surgical scrub of the skin: The entire area that has been clipped needs to be surgically scrubbed. It is commonly accepted that five scrubs of the clipped area will reduce the flora of the skin to a low enough level to not lead to an infected wound (provided the rest of the surgical technique is good). It is important that these five scrubs be considered the minimal amount. It should be remembered that their purpose is to reduce the bacterial flora of the skin. If the skin is dirty or greasy, the number of scrubs needs to be increased to the number of scrubs needed to get to a clean-looking skin plus the five final scrubs. The product used in scrubbing the skin is far less important than the area scrubbed and the number of scrubs. The scrub product needs to help physically remove dirt, grease, and bacteria, kill bacteria, lubricate the skin to minimize the abrasion from the scrub, and leave a residue to inhibit the repopulation of bacteria. The most commonly used product is a povidone iodine scrub followed by a povidone iodine solution sprayed or painted on at the end of the scrub procedure. This is a very good system; however, any product that fulfills the above listed requirements of a scrub is acceptable. Double drape: This area of aseptic technique is another problem area within veterinary practice. It is unfortunate because the time and cost is minimal compared with the cost of treating osteomyelitis. One of th~ drapes should cover both the animal and the table down to the knee level of the surgeon. Otherwise, as the body or limb of the patient is maneuvered during surgery, short drapes creep up and expose the contaminated table, which contaminates the gown, which, in turn, contaminates the gloves and then the wound. This large drape should be the first one. The second drape should cover the entire surgical field, and this drape, if not both, should be impermeable to fluids. This prevents contaminated fluids from the body or table from soaking through the drape. Also, the impermeable drape prevents blood and lavage fluids from the wound from soaking the drape. A drape that is soaked through is no longer a barrier between the contaminated area and the surgical field. Sterilized instruments: All surgical instruments need to be steamsterilized or ethylene oxide-sterilized. The length of time and concentration of gas and degree of heat vary from sterilizer to sterilizer. Manufacturers' representatives give specific instructions on using the equipment to ensure the packs and instruments are sterile. Sterilized check strips should be placed in each surgical pack to monitor that the equipment is functioning properly. The use of unsterile instruments, cold solutions for sterilization

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of instruments, and multiple case use of the same surgical pack is not aseptic surgery. Sterile suture material: It almost goes without saying that anything left in the wound should be sterile. Suture cassettes often become contaminated before they are empty, and thus should not be used in sterile surgery. It is good surgical technique to use individual packets of sterile suture. The kind and type of suture is a matter of personal preference and does not affect surgical technique. Cap and mask: The surgeon and all people entering the surgery room should wear a cap and mask. These items should be kept close to the surgery room door so they are convenient for all personnel to don them. Personal scrub: The purpose for the scrubbing of the hands and arms up to and including the elbows is to remove all dirt and bacteria from the skin. Once a year, each surgeon should check his or her scrub technique by placing all five fingers into the agar of a sterile petri dish after a routine scrub. This check also should be done by surgical assistants. It is best if this is a surprise check initiated by the technician unbeknownst to all scrubbing in. The product that is used in the scrub is not important as long as it can be delivered by a foot bulb or some other method whereby the hands are not repeatedly contaminated during the scrub. The time of the scrub traditionally is 10 minutes. This is a good time to use initially. If your mechanical movements are adequately fast and the finger cultures are negative; this time can be reduced one minute at a time. With rapid mechanical scrub and a good scrub soap, some surgeons have reduced their scrub time to 5 minutes and still record negative finger cult\lres. Another commonly practiced philosophy for surgeons is to scrub for 10 minutes on the first scrub of the day, 7 minutes for the second scrub, and 5 minutes for each successive scrub. An important word to note in this paragraph is scrub. It is important to scrub, not wash, the hands. It takes a brush, not a sponge or hand manipulation, to get the dirt and bacteria out of the pores, skin folds, junction of skin and nail, and beneath the nails. All rings must be removed before scrubbing. If there is some skin injury that prevents the scrub by a brush, a sponge is allowable but should be followed by double gloving in surgery. Gloves and gown: To perform sterile surgery, both gloves and gowns are needed. Both should be sterile, either from the manufacturer (disposable) or steam-sterilized if reusable (gowns). The gloves should be used once and discarded. Several studies have shown that gloves used in orthopedic surgery that were visibly intact had punctures in greater than 50% of the gloves tested. These studies have caused some orthopedic surgeons to use double gloving routinely or use cotton gloves over the latex gloves when handling bones, pins, drill bits, or any sharp objects. The surgeon and all assistants should at least be cognizant of their gloves, change them immediately upon puncture, and dispose of them after each use. It is important that the surgeon's perspiration does not soak through the front of the gown and on the forearms. These areas are considered to be part of the surgical field. Most disposable gowns are made of a treated or coated paper product that is impermeable to perspiration. If these disposable gowns are to be cleaned and resterilized, they must remain

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impermeable to perspiration or be discarded. Like drapes, if the gown is soaked through, it is no longer a barrier between the contaminated area and the sterile area. The goal of aseptic surgery is to keep the number of bacteria in the wound at closure below 105 CFUs. Each time there is a break in any of these points of aseptic technique, the number of bacteria goes up. The surgeon with good surgical technique practices all of the described techniques and the number of bacteria in the closing wound is routinely below the infection level. Accurate and Sharp Incision. The skin incision should be placed immediately over the desired anatomic structure or over an intermuscular plane for approach to deeper structures. This accurate placement of the incision is important because then subcutaneous dissection is eliminated. Subcutaneous dissection is a waste of time and results in dead space at closure. This dead space is a possible area for a hematoma or seroma to develop. Fastidious Hemostasis. Fastidious care given to hemostasis has several benefits for the surgeon which translate to good surgical technique. First, with control of bleeding, the deeper tissues (bone, cartilage, ligaments, and tendons) are visualized better and easier. This allows the procedure to be accomplished quicker despite the added time spent controlling hemorrhage. A second benefit is that if hemorrhage is controlled, there is less of a chance that a hematoma will be left in the wound or develop in the wound after closure. Blood in the wound is a perfect medium for bacteria. Lastly, if the surgeon maintains hemostasis, he or she also maintains complete psychologic control of the surgery. On the other hand, once hemorrhage gets out of control, the drapes, along with the gloves and gowns, become bloody. After allowing this break in aseptic technique, it seems that a second break occurs even more easily, then a third, and so forth. This permissive philosophy (frustration) always results in poor surgical technique. Approach Via Intermuscular Planes. When operating on deep tissues such as bones or joints, it is important to approach them through intermuscular planes. The surgeon must avoid cutting muscle at all cost. The goal of orthopedic surgeons in both bone and joint surgery is early return to full function. Intact and atraumatized muscles are necessary for this goal to be a reality. If the approach to the desired structure cannot be done strictly through intermuscular planes, subperiosteal elevation of muscle off bone is preferred to cutting muscle. The periosteum will rapidly reattach to the bone when the muscle fascia is sutured back in place. A tenotomy or osteotomy also is preferred to cutting muscle for an approach. Tendons can be sutured and osteotomies fixed so that the muscles can function relatively soon after surgery. Avoid cutting muscle at all cost. Gentle Handling of Soft Tissues. It is important to respect the soft tissues and handle them gently. This is best accomplished with the philosophy of gentle but firm. This philosophy is attained by the use of retractors, either manual (Senn, Meyerding, Army, Israel, etc.) or selfretaining (Weitlaner, Gelpi, Balfour, Finochietto, etc.) (these retractors are manufactured by Scanlan Instruments, Englewood, CO). The routine use of retractors is less traumatic to muscle than the use of hands, spreads less contamination and blood, and allows better visibility. The use of fingers or

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hands for routine retracting of soft tis~ues and muscles is not good surgical technique. Anatomic Closure. Each layer of tissue that was incised should be sutured closed independently of other layers. This practice allows these layers (tendons, fascia, and muscles) to glide independently. This gliding function of the tissues is important for our overall goal of early return to full function. Open Wound Management. The second source of bacteria to the wound is from an open wound (a wound that has been opened traumatically). With proper management of the open wound, the bacterial level in the wound after surgery will be below the level that leads to an infection. Open (traumatic) wounds can be classified into five different types: 1. 2. 3. 4. 5.

Hemorrhaging wound Body cavity wound Cleanly lacerated wound Heavily traumatized wound Infected wound

The hemorrhaging wound and the body cavity wound are not discussed in this article, because they would be articles in their own right. Cleanly Lacerated Wounds . .A cleanly lacerated wound is defined as a wound that has neat and sharp edges; involves only skin, subcutaneous tissue or fat; is not grossly contaminated; and is not infected. The plan for treatment should be to prepare and close these wounds. Specifically, this involves filling the wound with a sterile gauze impregnated with sterile petroleum jelly, sterile water-based jelly, or antibiotic ointment. This gauze keeps the clipped hair from getting in the wound. The area around the wound is clipped and scrubbed as previously discussed. Next, the gauze is removed from the wound, the wound is surgically scrubbed once, and the wound is flushed. Flushing the wound should involve at least a liter of lactated Ringer's (LR) solution for small wounds and more for larger wounds. The flush should be administered by a syringe or bulb syringe, slowly poured from the bottle or bag, or run in via an open I. V. tube. It should not be administered via a high-pressure system such as a Water Pik (Ft. Collins, CO). With a high-pressure system, the wound may look better immediately after flushing, but too many bacteria are forced into deep areas of the wound and infection is more likely than with the gravity feed or low-pressure systems mentioned above. Suction can be used to remove the fluid from the wound, or it can be allowed to spill over the wound edge into a sink, drain, or absorbent pad (disposable diaper). Lactated Ringer's solution is preferred over saline because cells can live in LR and not in saline solution. During the flushing and debridement steps of open wound management, it is best to kill as few cells as possible. The debridement of these cleanly lacerated wounds generally is a short procedure in that there is not very much, if any, hair, sticks, or other foreign material that needs to be removed. Also, there usually is not much necrotic tissue that needs to be removed. Closure of the wound follows the flushing and debridement. The suture material is a matter of surgeon's preference. The subcutaneous tissue layer and the skin should be closed. The wound should be protected by a bandage for several days. The bandage

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should be changed at 3 to 5 days and removed with the sutures at 10 to 14 days. Heavily Traumatized Wounds. A heavily traumatized wound is defined as a wound that has severe damage to the skin, subcutaneous tissue, or fat; is grossly contaminated; or visibly involves damaged bones, joints, tendons, or ligaments. The plan for these types of wounds is to prepare and treat as an open wound. The preparation of these wounds is the same as described for the cleanly lacerated wounds; that is, protecting the wound with a sterile impregnated gauze, clipping, scrubbing, and flushing. The debridement step needs to be more extensive in these wounds because by definition, there are foreign material and dead tissue in the wound. This foreign material needs to be physically removed during the debridement. After the debridement, a LR-soaked sterile gauze should be placed over the wound; this gauze should be held in place with gauze wrapped around the leg or body, a layer of cotton should be applied, then another layer of gauze to hold the cotton in place, and, lastly, a layer of tape. This bandage should be changed daily until there are minimal amounts of exudate in the bandage and the bandage's smell is not offensive. At this time, the bandage is changed every 2 days until the exudate and smell are minimal, and then changed every 3 days. When the 3-day bandage contains minimal amounts of exudate and is not offensive to smell, the wound can be closed. It is only at this time that the wound should be surgically closed. Far too many heavily traumatized wounds are closed too early and become infected wounds. By treating the wound with the open wound management discussed here, the body is allowed to heal the wound from inside to the outside. The body can expel foreign material, exudate, and dead tissue into the bandage. The foreign material is then removed as the bandage is changed. The gauze attaches to the superficial layers of tissue, and when

Figure 5. Heavily traumatized open wound. The soft tissues are severely damaged and inflamed. The bone has been exteriorized for several days.

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Figure 6. Lateral radiograph of a comminuted fractured tibia that has been classified as a heavily traumatized open wound because of the damage to the soft tissues. Same case as Figure 5.

the gauze is removed, it takes these layers with it (micro-debridement). In this process, bacteria are physically removed during the bandage changes or removed by the body's defenses; there are not any of the areas for bacteria to hide or multiply in that would be present if the wound is closed. After the wound has cleansed itself (with the help of the debridement and micro-debridement), granulation tissue begins to be laid down. This granulation tissue is a sign that the wound can now be surgically closed. If the wound has been classified as a heavily traumatized wound because the soft tissues have been severely traumatized, this procedure should be followed even if there are concomitant orthopedic problems. Extensive orthopedic surgery at the time of initial wound management will more readily lead to an infected wound or significant skin slough. The bones or joints can be stabilized with a form of coaptation splint incorporated in the bandage or an external fixator (Figs. 5-7). The time at which the wound starts to form granulation tissue or the 3-day bandage is clean is the time for definitive orthopedic reconstruction. If the wound has been classified as a heavily traumatized wound solely because of the injuries to the bone, joint, or ligaments and the soft-tissue injuries are minimal (Figs. 8 and 9), the surgeon has anothe r option. In this case, the wound may be debrided as discussed earlier, then the

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Figure 7. Postoperative lateral and anterior-posterior radiographs of the fractured tibia case shown in Figures 5 and 6. A four-pin/one-bar external fixator has been applied after closed reduction.

orthopedic procedure can be performed. The surgical pack, gloves, and gown should be changed after the debridement. If possible, the skin incision should be away from the open wound to minimize the spread of any contamination (Figs. 10 and 11). A third option for treatment of heavily traumatized wounds with orthopedic trauma but minimal soft-tissue trauma is to treat the open wound as described, bandage, and delay the surgery until a full surgical team arrives or until referral can be made if necessary. Infected Wounds. An infected wound is defined as a wound that has bacteria present that are multiplying. Generally, the wound is extremely

Figure 8. Heavily traumatized open wound involving a fractured tibia, with minimal damage to the soft tissues.

Figure 9. Anterior-posterior and lateral radiographs of a comminuted tibial fracture with an open wound classified as heavily traumatized because of the damage to the bone. Same case as Figure 8.

Figure 10. Surgical approach to the fractured tibia shown in Figures 8 and 9. Notice the skin incision has been placed anterior to the open wound.

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Figure ll. Anterior-posterior and lateral radiographs taken immediately postoperatively. Same case as shown in Figures 8, 9, and 10.

inflamed, and an exudate is present. These wounds need to be treated with open wound management until the infection is brought under control. Definitive bone and joint surgery should not be performed regardless of the condition of the soft tissues until the infection has been treated successfully. Open wound management of these wounds should follow the earlier description until the debridement step. At this point, when debriding the deepest area of the wound, a culture of the tissues should be taken for microbiologic identification of the causative bacteria and to determine antibiotic sensitivity. After debridement and flushing, the infected wound should be filled with povidone-iodine solution soaked sponges and then bandaged with the wound gauze, cotton, and tape described earlier. A dilute solution of povidine-iodine (0.1 %-1%) has been found to be more bactericidal than full-strength (10%) solution. 2 During the daily bandage changes, the Betadine-soaked sponges are removed and discarded and replaced (less one sponge each day). On day 6, no Betadine-soaked sponges are placed in the wound. Povidone-iodine is a good antiseptic and readily kills bacteria in a wound , but it is cytotoxic when used at high dosages and for long periods . 17 No deleterious effect to wound healing has been noticed if the povidone-iodine therapy is limited to 5 days or fewer and a 0.1% to 1% solution is used. During this time, the animal should also be initially

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treated with a broad-spectrum systemic antibiotic followed by the definitive antibiotic as indicated by the microbiologic sensitivity analyses. When the infection is under control as evidenced by some granulation tissue in the wound or the 3-day bandage test, the orthopedic procedure can be performed. Until that time, the fracture or unstable joint should be stabilized with a coaptation splint or external fixator. The two secrets of proper open wound management is to treat the contaminated or infected wound first, and then know when to perform the definitive orthopedic procedure. When should open wound management be initiated? Remembering that the goal of open wound management is to minimize the number of bacteria in the wound, the closer to the trauma that management is started, the better. If conditions are ideal for bacteria, the lag phase (time between the trauma that opens the wound and introduces the bacteria and the point at which the bacteria start to multiply) may be as short as 6 hours (see Fig. 4). Therefore, treat all open wounds as an emergency; that is, treat as early in the lag phase as possible. This classification system of open wounds involves a description of the tissue condition of the open wound. There is also another classification system of open wounds with fractures that should be discussed. It involves the cause of the open wound. Specifically, first-degree open fracture is caused by the sharp fractured bone-end puncturing the skin at the time of trauma or at the time of flight after trauma (see Figs. 8 and 9). A seconddegree open fracture is caused by an external object breaking the skin and then breaking the bone (bullet or bumper). A third-degree open fracture has the same cause as the second degree but with massive soft-tissue damage. 9 On studies using this system of classification, it was found that second-degree open fractures are twice as likely to become infected as firstdegree fractures. Three-degree open fractures were twice as likely to become infected as second-degree fractures. Therefore, the more severe the degree of open fracture, the more crucial are early and proper open wound management. Prevention of the Infected Sequestrum

The second component needed to create posttraumatic osteomyelitis is avascular bone. There is always some avascular bone involved with all fractures. Histopathologic tissue sections of fracture ends show a certain amount of bone with empty lacunae (dead bone) associated with each fracture end. These few millimeters of dead bone are thought to be a result of loss of vacularization and are referred to as the "die back" area. Although these few millimeters of bone are dead, the orthopedic surgeon should treat all major bone fragments as alive and should not debride them. They are essential to anatomic reduction and stable fixation. If the fragment of bone in the wound is large and has soft-tissue attachment, these large fragments should be involved in the reduction and fixation process. The soft-tissue attachments should be preserved. Those fragments with soft-tissue attachments generally remain alive (except for the die-back edges). If the bone in the wound is a large fragment and has no soft-tissue

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attachments, it should be part of the reduction and fixation process even though it is avascular and presumably dead. Research has shown that with stable fixation, these large, avascular fragments actually revascularize and become living bone. These large avascular fragments are very important in the alignment, reduction, and fixation of the fracture repair. If the repair is stable, it is believed that neovascularization of the fracture site leads to revascularization of the fragment. The revascularization uses the existing Volkmann's and Haversian canals. Osteoblasts recolonize in the empty lacunae, and new bone is laid down. Thus, this dead bone is mechanically important to the stability of the overall fracture repair and also is important in protecting the biologic process of revascularization. Therefore, this dead bone is housing a living process that will slowly replace the dead bone. This process is called creeping substitution and is in essence an accelerated version of the remodeling process of bone whereby osteoclasts remove bone, osteoblasts move in and mature to osteocytes, and the osteocytes lay down new bone. This process occurs with any dead bone, but the advantage here with large fragments that are stable is that this creeping substitution can take place from thousands of points within the bone. Dead bone that does not revascularize is replaced from the ends or sides only. This takes much longer. If the bone in the wound is a small fragment (small is defined as too small to accept a screw, Kirschner wire, or cerclage wire), the wound was traumatically open, and there was serious contamination or infection, these small fragments should be discarded. If there is a significant fracture gap left because of the debridement of those small fragments of cortical bone, it should be filled in with autogenous cancellous bone. Unlike avascular cortical bone, cancellous bone will not become an infected sequestrum. If there is no traumatically open wound, or if the open wound has minimal contamination, no infection, and no massive soft-tissue damage, these small fragments of avascular cortical bone should be left in the wound as close to the fracture gap as possible. In conclusion, the management of these avascular cortical bone fragments is a compromise between removing them and avoiding all possibility of an infected sequestrum forming, or leaving them for a more stable fracture repair or earlier bridging callus. Prevention of a Favorable Bacteria Milieu The third component of posttraumatic osteomyelitis is a favorable bacteria milieu. Bacteria do not only exist but multiply in a milieu that contains blood or necrotic tissue. Therefore, if the hematoma and dead tissue is eliminated from the wound, a favorable milieu is eliminated. Eliminating the hematoma involves religiously practicing the surgical principle of hemostasis. Whether by ligation or electrocautery, all bleeding from vessels must be stopped. The wound should be visualized layer by layer and examined for bleeding vessels upon closure. The second type of tissue that bacteria can hide in, exist in, and multiply in is necrotic tissue. Therefore, any tissue that is necrotic from the trauma should be removed upon closing (if it was not removed during the surgical procedure). Also, care must be taken to treat the soft tissues

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of the wound delicately so as not to cause any necrosis during the surgery procedure. As mentioned earlier, this involves firm but gentle retraction of the soft tissues. In addition, dehydration of the soft tissue can cause necrosis. These-tissues, that is, fat, muscle, and fascia, will dehydrate, dry out, and die when exposed to room air and surgical lights. To prevent this from occurring, the wound should be lavaged routinely throughout the procedure (approximately every 5 minutes). Upon closing, after each layer is sutured, the wound should be lavaged thoroughly to bathe the tissues and to remove any small blood clots. Thus, upon closure, there are no bleeding vessels, no blood clots, and no dead fat, fascia, or muscle. To summarize, posttraumatic osteomyelitis can be prevented by keeping the wound from becoming infected, preventing avascular bone from becoming an infected sequestrum, and preventing the wound from becoming a favorable milieu for bacteria.

DIAGNOSIS

A diagnosis of posttraumatic osteomyelitis may be made by evaluating six different parameters: drainage, soft-tissue swelling, periosteal reaction, serial radiographs, microbiology, and histopathology. Drainage is not a normal sequela to surgery; therefore, its presence indicates there is a problem (wound infection or osteomyelitis). The reverse is not always true, however, that is, no drainage does not rule out osteomyelitis. Typically, an osteomyelitis lesion produces exudate that builds up in the wound. Finally, with pressure from the buildup of exudate and time to channelize to the exterior, the drainage starts. Some cases of osteomyelitis continue to drain. Others, however, drain for a few days; then the body's healing process seals over the draining tract until the pressure of the exudate builds up again. Therefore, if drainage is present it can easily be picked up on physical examination. If drainage is not present, however, it may be found in the historical examination in most cases of posttraumatic osteomyelitis. Drainage is the most common presenting complaint by the owner. Soft-tissue swelling is a parameter that cannot be used for the first 4 weeks after trauma or surgery because swelling is to be expected after trauma or surgery. After 4 weeks, however, the swelling from surgery or trauma should be gone. Therefore, if soft-tissue swelling is present longer than 4 weeks after surgery or trauma, osteomyelitis is a possible diagnosis. Swelling generally is not present if the lesion is draining. If the body has sealed over the draining tract, however, the exudate starts to accumulate, which causes greater and greater swelling to occur until the drainage starts again. Periosteal reaction is bony proliferation from the periosteum in response to the stimulation of the periosteum by the infection. Not all cases of osteomyelitis have this bony proliferation. The more mild cases of osteomyelitis tend to be proliferative and the severe cases tend to be lytic. When periosteal reaction is present in osteomyelitis, it is easily palpable in lesions below the elbow and stifle. Even if soft-tissue swelling is present,

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the difference of the two tissues is discernible upon palpation. Periosteal reaction is a hard enlargement of the area (Fig. 12). Above the elbow and stifle, it is difficult to evaluate this parameter because of the musculature. Serial radiology is an extremely useful noninvasive parameter but is not definitively diagnostic in and of itself. The sensitivity of radiology in the diagnosis of posttraumatic osteomyelitis (the ability to demonstrate positive lesions in diseased cases) was 62.5% in a study conducted by boardcertified radiologists. 7 The specificity of radiology in the diagnosis of posttraumatic osteomyelitis (the ability of demonstrating negative findings in subjects free of the disease) was 57.1 %. 7 The typical radiographic signs of osteomyelitis are soft-tissue swelling, irregular periosteal reactions, cortical lysis, and increased medullary density (Figs. 13 and 14). 17 These radiographic signs correlate well with histopathologic changes seen in osteomyelitic bone (Figs. 15 and 16). 18 Most of these radiographic signs also are present in bone healing; therefore, diagnosing posttraumatic osteomyelitis after a fracture and surgical repair by radiology alone is difficult. The longer the period after surgery and trauma, the more likely that positive radiographic signs indicate osteomyelitis and rule out secondary bone healing. Although not highly definitive, radiology can be supportive. When added to other diagnostic parameters, the diagnosis of posttraumatic osteomyelitis can be made. A radiograph is a picture taken at one instance in time. Serial radiographs are several pictures separated by time. Usually, a period of 2 to 4 weeks between radiographs is recommended for evaluating bony changes. With serial radiographs, it is easier to interpret what is happening than with a single time frame . With secondary bone healing, external callus should build up in response to the instability, eventually bridge the fracture gap, and then begin to regress after clinical union. If this regression of the

Figure 12. Posterior-anterior photograph of a tibial region of a leg with osteomyelitis showing marked periosteal reaction.

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external callus does not occur, osteomyelitis is a strong possibility on the tentative diagnosis list. Microbiology is the most definitive parameter in diagnosing osteomyelitis. But even a positive culture is not 100% definitive of osteomyelitis. Two possibilities must be considered: osteomyelitis and wound infection. To differentiate bone infection from wound infection, radiology and microbiology are used. If there is a positive microbiology culture and the radiographic bone lesions discussed earlier, it is safe to diagnose osteomyelitis. If there is a positive microbiology culture and no radiographic bone lesions, then the diagnosis is wound infection. Histopathology can be useful in the diagnosis of osteomyelitis and can be defined as the morphologic identification of bacteria in the periosteal reactive tissue, bone, or medullary canal. Upon histopathologic examination of bone tissue with osteomyelitis, marked myeloid hyperplasia (active marrow) is evident. However, active marrow alone cannot be considered evidence of osteomyelitis, because hyperplasia of the marrow cells is also present in several other situations such as bone healing, haematopoiesis, and noninfectious inflammatory conditions of the bone. Using the above definition for histopathology, the sensitivity (demonstrated positive findings in disease state) in the diagnosis of posttraumatic osteomyelitis was 33.3%. 7 The specificity (demonstrated negative findings in disease free state) of histopathology was 86.3%. 7 Clinically, the clinician or practitioner does not often use histopathology in the diagnosis of osteomyelitis because it is invasive, it leaves the bone weaker, and its sensitivity is low. However, during the course of wound management (debridement) or fracture management of cases that may have osteomyelitis, a small piece of avascular bone (sequestrum) usually can be found and submitted for histopathologic interpretation. With the low sensitivity, a negative result does not eliminate osteomyelitis. However, with the high specificity, a positive histopathologic finding can confirm a diagnosis of the disease. From this discussion, it should be evident that posttraumatic osteomyelitis cannot be confirmed by one positive test. A diagnosis of posttraumatic osteomyelitis takes the professional training of the clinician or practitioner to put the history (trauma, surgery, drainage, lameness), together with the physical examination (soft-tissue swelling, periosteal reaction, drainage, lameness) and the radiographic and microbiologic findings (and possibly histopathology). During the author's research on osteomyelitis, several other parameters were measured and recorded that were not very much help in diagnosing or monitoring treatment of osteomyelitis. They are clinical function (use or nonuse of the leg), local tissue temperature, rectal temperature, pain (upon palpation), complete blood count (CBC), serum calcium, serum phosphorus, serum glucose, blood urea nitrogen (BUN), uric acid, serum cholesterol, total protein, serum albumin, total bilirubin, alkaline phosphatase, and aspartate transferase (formerly called serum glutamic oxalacetic transaminase, SCOT). These parameters are of little significance in diagnosing (or monitoring the treatment of) posttraumatic osteomyelitis because they are systemic measurements, and this disease is a local disease. It is important

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to realize this fact for three reasons. First, not running useless tests m1mmizes the veterinarian's time and effort. Second, it minimizes the client's cost. And third, it maximizes research dollars. Therefore, if posttraumatic osteomyelitis is on the top of the tentative diagnosis list, concentrate on the six parameters mentioned earlier in this section: drainage, softtissue swelling, periosteal reaction, serial radiographs, microbiology, and histopathology. TREATMENT The treatment of posttraumatic osteomyelitis involves two areas: improvement of the environment and proper antibiotic therapy. Improving the environment involves removing pus, removing necrotic tissue, removing dead bone, removing implants, removing foreign bodies, and open wound therapy for 5 days. In examining this list of things to be done in improving the environment as part of the treatment of posttraumatic osteomyelitis, it becomes obvious that surgery is needed. It is not until it is realized that posttraumatic osteomyelitis is a surgical disease that any respectable success rate in the treatment of this disease is obtained.

F igure 13. Posterior-anterior radiograph of a hume rus with osteomyelitis. The arrows outline an infected sequestrum.

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With this realization, a surgical exploration should be performed with the goal to remove whatever is in the wound that should not be there. This may be bacteria and pus or excessive amounts of necrotic soft tissue, but most often it is dead bone that has become an infected sequestrum (Fig. 13) or a foreign body (Figs. 14 and 17). Occasionally, it is the orthopedic implants (Figs. 18 and 19). Deciding the area to explore surgically generally is not a problem in posttraumatic osteomyelitis. It is almost always the area of the fracture or the area of previous surgery. The surgery should involve a full preparation (as discussed earlier) and an aseptic approach. Although this is an infected wound, introducing new numbers or kinds of bacteria must be avoided. During the approach, hemostasis should be practiced, and debride me nt of any necrotic soft tissue should be performed. Any fistulous tract tissue should also be debrided at this time . Once the wound is entirely opened, a swab of the deep wound should be performed, microbiologic culturing should be done for aerobes and anaerobes, and antibiotic sensitivity should be determined. Next, copious amounts (1 to 5 L) of LR should be used to lavage the wound. This should be delivered via a low-pressure or gravityfed system. The lavage should be removed via suction system. Proper debridement and lavage should remove a significant amount of the bacteria, most of the pus, and most of the necrotic tissue from the wound.

. Figure 14. Lateral radiograph of a humerus with osteomyelitis that had been draining for 1 ye~r. The p eriosteal reaction has proliferated around a foreign body (see Figure 17).

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Figure 15. Cross-section of a tibia with osteomyelitis showing the bony changes that are seen radiographically such as cortical lysis. periosteal bone proliferation, and medullary bone proliferation.

Figure 16. Cross section of a normal tibia and fibula. Compare with Figure 15.

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Figure 17. Two surgical sponges that were acting as foreign bodies in the osteomyelitis case shown in Figure 14. A small cerclage wire was present and also was removed.

During or after the debridement and lavage steps, an exploratory examination of the wound is performed to identify and remove dead bone (Fig. 13). An infected sequestrum usually can be identified by the fact that it usually is not attached to other tissues such as other bone, callus, or soft tissue. The body has been attempting to wall it off, so it generally is loose. Also, the infected sequestrum tends to be a yellowish-white, whereas living bone is almost always white, pink-white, or bluish-white. The edges of an infected sequestrum often look like they have been chewed on by a mouse and show several "gnaw marks," especially in chronic cases. It is rare to explore a wound of a case of osteomyelitis and find an infected sequestrum smaller than 0.5 em. Most likely this is because the body's phagocytic defense system can remove the small sequestrum. Usually, the infected sequestrums are 0.5 to 3 em in length (Fig. 13). However, there is no maximum size (Figs. 20 and 21). Foreign bodies found in posttraumatic osteomyelitis wounds can be anything, but most often are surgical sponges (Figs. 14 and 17) or wooden twigs and occasionally Penrose drains, grasses, dirt, gravel, or stones. Needless to say, they should be removed. If implants (cerclage wire, Kirschner wire, intramedullary pins, Jonas Pins (Fig. 18), screws, and plates) are loose, they are not serving their original function and should be removed because they prevent or hinder the body's defense system reaching the areas stressed by instability. There are small areas around implants that new vessels cannot grow into and remove or kill bacteria. In veterinary orthopedics, it is common that prosthetics are implanted as replacements for joints. These occasionally become infected (Fig. 19), and they then

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Figure 18. Lateral radiograph of a tibia with osteomyelitis in which a Jonas pin was implanted 3 years previous to the start of drainage . Notice the irregular periosteal reactions, cortical lysis, and the increased medullary density.

Figure 19. Lateral radiograph of the pelvis and femurs of a dog that has had two total hip replacements performed . They have become infected, the bone is osteomyelitic, and the implants are acting as foreign bodies. Notice the large dark space between the cortex and the cement implant.

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Figure 20. Largest sequestrum from a dog ever seen by this author. Approximately 9 em in length from a tibia.

Figure 21. Lateral radiograph of a tibia of a dog with osteomyelitis. The large infected sequestrum of Figure 20 is present. During the 6 months since the trauma, the body has bridged this proximal tibia section with new bone.

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should be removed whether they are loose or not. With the prosthesis present, the infection cannot be successfully treated. There is one situation that may be present in posttraumatic osteomyelitis in which the implants should not be removed. If the infection is low grade, there is a fracture that has not healed yet, and the implants are still stable, they should be left in until clinical union. Bone will continue to heal slowly but definitively in the face of a low-grade osteomyelitis. Lowgrade osteomyelitis is differentiated from moderate and severe cases by the clinical signs and radiographs. Generally, there is a small amount of drainage, but there is not a much soft-tissue swelling or periosteal reaction present on palpation. Generally, the radiographic lesions are very slight with minimal proliferation of bone and very little to no osteolysis. After the exploratory surgery, the wound should be managed open. Five Betadine solution-soaked sponges should be placed in the wound. This bandage is changed daily and one fewer sponge placed in the wound each day. Generally, by day 6, the wound can be surgically closed. Only about 90% to 95% of the length of the wound is closed. The lowest area is left open for exudate to escape into the bandage. Penrose drains are foreign bodies and should not be used in these wounds. At this time, the bandage can be changed every 3 days until the wound is closed by second intention. The surgical management portion of the treatment of posttraumatic osteomyelitis has been discussed before the medical management portion because it is far more important. A significant success rate can be achieved by use of the surgical management plan alone. A very poor success rate is achieved with the medical management of posttraumatic osteomyelitis alone. Together, the surgical and medical management can lead to a success rate approaching 90%. Unfortunately, for the patient's health and owner's pocketbook, it is a common practice to use medical management alone. Medical management as part of the treatment of posttraumatic osteomyelitis refers to proper antibiotic therapy. A sample of the tissue or tissue fluid must be taken from the deep wound during the exploration of the wound. This sample should be microbiologically cultured for aerobes and anaerobes to determine which bacterium is causing the infection. An antibiotic sensitivity analysis should be performed on any bacteria that grow on culture to determine which definitive antibiotic should be used. It is of very little value, and it is sometimes misleading, to culture the draining tract. Often, contaminants from the environment are cultured, not the true causative bacteria. Also, the patient should not receive any antibiotics for at least 7 days before the surgical exploration. Once the definitive antibiotic has been identified, it should be used properly; that is, maximum recommended dose given as often as recommended via the recommended route for 28 days unless the label contraindicates long-term administration. Twenty eight days has been shown to be more effective than shorter treatment regimes when treating posttraumatic osteomyelitis. 5 Generally, there is a 2- to 5-day period between harvesting a deep tissue sample and receiving the sensitivity results of microbiology. During this period, the use of an empirical antibiotic is recommended. This should be started during the exploratory surgery immediately after the microbiol-

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ogy samples are taken. It is best to use an antibiotic that has been shown to be effective in osteomyelitic bone, such as clindamycin, given twice a day at 11 mg/kg (5 mg/lb). 5 If the causative bacterium is sensitive to clindamycin, treatment can be continued for a total of 28 days . If the bacterium cultured is not sensitive to clindamycin, the definitive antibiotic should be administered. Most clinicians and practitioners who have treated cases of osteomyelitis have found themselves less than pleased with the results of an antibiotic that was sensitive to the causative bacteria in vitro. There may be several reasons for these results; for example, the environment (wound) is not cleaned totally or the real causative bacterium is not identified. Another reason is the formation of a glycocalyx in vivo, but not in vitro. The glycocalyx is a sticky slime produced by the bacteria that acts as a biofilm and protects the microorganism from antibiotic treatment and other unfavorable environmental surroundings (Figs. 22 and 23). 14 The bacterial

F igure 22. Electron micrograph of Bacteroides thetaiotaomicron. The glycocalyx envelopes each cell in an integral relation to each capsule and is at least 200 nm in thickness. (From Lambe DW: The morphological stabilization of the glycocalyx of 23 strains of 5 Bacteroides species using specific antisera. Can J Microbial 30:814, 1984; with permission.)

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glycocalyx consists of exopolysaccharides that contain 95% to 98% water. 15 It may be an integral part of the bacterial capsule via a network of extensive fibrous exopolysaccharide matrices (Fig. 22) or just a slime layer around the capsule (Fig. 23). Generally, in the ideal environment of a culture dish, the bacteria do not produce a glycocalyx, and the sensitivity results reflect the antibiotic effect on the bacteria only, whereas in the osteomyelitic wound, the environment may not be as ideal as the culture dish, and the bacteria may produce an extensive glycocalyx. 13 In the wound (body), the antibiotic must be able to penetrate the glycocalyx and attack the bacteria. For this reason, some antibiotics may work better than others in the body although the in vitro sensitivity tests were the same. When treating

F igure 23. Enlargement of Staphylococci spp, surrounded by a massive amount of glycocalyx slime . (From Lambe DW: Bacterial adherence and glycocalyx formation in osteomyelitis experimentally induced with Staphylococcus aureus. Infect lmmun 43:827, 1984; with permission .)

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osteomyelitis, an antibiotic that penetrates bone and the glycocalyx should be used. Therefore, use an antibiotic that is recommended on the sensitivity test with which you have had previous clinical success or one that has been scientifically shown to be effective in treatment of infected bone. 6

REFERENCES l. Allgower M, Durig M, Wolff G: Infection and Trauma. Surg Clin North Am 60:2, 1980 2. Berkelman RL, Bolland BW, Anderson RL: Increased bactericidal activity of dilute preparations of povidone-iodine solution. J Clin Microbial 15:635-639, 1982 3. Braden TD: Fracture Documentation. In Proceedings of the 14th Annual Conference of the Veterinary Orthopedic Society, 1987 4. Braden TD, Prieur WD: New plate for acetabular fractures. Technique of application and long-term follow-up evaluation. JAm Vet Med Assoc 188:10, 1986 5. Braden TD, Johnson CA, Gabel CL, et a!: Posologic evaluation of clindamycin, using a canine model of post-traumatic osteomyelitis. Am J Vet Res 48:7, 1987 6. Braden TD, Johnson CA, Wakenell P, et a!: Efficacy of clindamycin in the treatment of Staphylococcus aureus osteomyelitis in dogs. JAm Vet Med Assoc 192:12, 1988 7. Braden TD, Tvedten HW, Mostosky UV, et a!: The sensitivity and specificity of radiology and histopathology in the diagnosis of post-traumatic osteomyelitis. Vet Comp Ortho Trauma 3:98, 1989 8. Brinker WO: Canine Surgery. Wheaton, IL, American Veterinary Publications, 1965, p 744-847 9. Brinker WO, Piermattei DL, Flo GL: Handbook of Small Animal Orthopedics and Fracture Treatment. Philadelphia, WB Saunders, 1990, p 50 10. Caywood DD, Wallace LV, Braden TD: Osteomyelitis in the dog: A review of 67 cases. JAm Vet Med Assoc 172:943-946, 1978 ll. Dorland WAN: The American Illustrated Medical Dictionary. Philadelphia, WB Saunders Co, 1951, p 1060 12. Elek SD, Conen PE: The virulence of Staphylococcus pyogenes for man; a study of the problems of wound infection. Br J Exp Pathol 38:573, 1957 13. Cristina AG, Oga M, Webb LX, eta!: Adherent bacterial colonization in the pathogenesis of osteomyelitis. Science 228:990-993, 1985 14. Lambe DW, Costerton JW: The Role of Glycocalyx in Osteomyelitis: Current Hospital Topics. Kalamazoo, Michigan, The Upjohn Company, 1985 15. Lambe DW, Mayberry-Carson KJ, Ferguson KP, et a!: Morphological stabilization of the glycocalyces of 23 strains of five Bacteroides species using specific antisera. Can J Microbial 30:809-819, 1984 16. National Academy of Sciences-National Research Council. Division of Medical Sciences, Ad Hoc Committee of the Committee on Trauma: Postoperative wound infections: The influence of ultraviolet irradiation of the operating room and various other factors. Ann Surg 160:1, 1964 17. Tvedten HW, Till GO: Effect of povidone, povidone-iodine, and iodide on locomotion (in vitro) ofneutrophils from people, rats, dogs, and rabbits. Am J Vet Res 46:1797, 1985 18. Walker MA, Lewis RE, Kneller SK, et a!: Radiographic signs of bone infection in small animals. JAm Vet Med Assoc 166:908, 1975

Address reprint requests to Terry D. Braden, DVM, MS Veterinary Clinical Center Michigan State University College of Veterinary Medicine East Lansing, MI 48824