- Email: [email protected]
Treatment of Post-traumatic Osteomyelitis
Orthopedic Salvage Procedures
0195--5616/87 $0.00 + .20
Treatment of Post-traumatic Osteomyelitis
Robert B. Parker, D.V.M.*
Osteomyelitis and its treatment date back to the recovery of a 500,000year-old human fossil, a femur of a Java man, that showed evidence of a fracture complicated by osteomyelitis. In his text on post-traumatic osteomyelitis, Burri6 recounted the early history of osteomyelitis treatment. In the first century AD, the Roman physician Celsus described bone debridement in the treatment of chronic osteomyelitis. In 1266, Theoderich recommended dry wound treatment and suggested the use of wine compresses for topical treatment and alcoholic beverages for general wound healing. After Lister's discovery ofbacteria, Franz Konig, in 1873, described local treatment of "putrid osteomyelitis" with antiseptic solutions delivered by closed-suction irrigation. Even today, osteomyelitis is often refractory to therapy. Hippocrates once said of open fractures and osteomyelitis: "One should especially avoid such cases if one has a reasonable excuse, for the risks are great and the rewards are few. "37 Today' s knowledge of surgical treatment and pharmacology has not invalidated this statement. Osteomyelitis is defined as an inflammation of the bone, cortex, and/or periosteum. Most commonly, the clinician thinks of bacterial osteomyelitis; however, fungi, parasites, and viruses can also produce the disease. Bacterial inoculation of bone by itself will not produce disease. 27 Experimental evidence has shown the importance of concomitant loss of blood supply. 22. 3o ROUTES OF CONTAMINATION Infective organisms can reach bone by either hematogenous or direct routes. Although hematogenous osteomyelitis is fairly common in man, it is rarely seen in small animal orthopedic surgery. 24 Direct contamination *Diplomate, American College of Veterinary Surgeons; Associate Professor and Chief, Small Animal Surgery, Department of Surgical Sciences, University of Florida College of Veterinary Medicine, Gainesville, Florida
Veterinary Clinics of North America: Small Animal Practice-Val. 17, No.4, July 1987
841
842
ROBERT
B.
PARKER
can occur after open reduction of a closed fracture, as a consequence of an open fracture, or by contiguous spread from surrounding soft tissue infection. If properly treated, the majority of open fractures should heal without developing osteomyelitis. In a study of 67 cases of osteomyelitis, only 10 per cent were initially presented as open fractures. 7 The principles of open fracture management have been reviewed. 25 The majority of cases of osteomyelitis occur after open reduction and internal fixation. Surgical trauma and bacterial inoculation of the surgical wound are major reasons for this occurrence. Sterile, atraumatic surgical technique with rigid internal fixation and judicious antibiotic prophylaxis are the keys to successful fracture management. It is far easier to prevent osteomyelitis than to treat it. Pathophysiology
Post-traumatic osteomyelitis has been divided into acute and chronic phases; however, there are no sharp delineations, and one phase may slowly progress into another. The initial inflammatory response following bacterial inoculation is the same for bone as for any other tissue. Hyperemia, increased vascular permeability, and an influx of polymorphonuclear cells, serum, antibodies, and complement occur locally. Bacteria destroy many of the white cells, liberating potent proteolytic enzymes. 1• 28 The resulting necrotic tissue and bacteria become a focus of suppuration. The direction in which the inflammation will progress is determined by bacterial virulence, local environment, and the host immune response. If the body is unable to control the infection, more exudation and bone destruction occur. As pressure builds within the marrow, the inflammatory exudate penetrates into cortical bone through the Volkmann and haversian systems. 11 This exudate leads to collapse of small vessels in the nonexpansile vascular channels of bone, with resultant bone infarction. As cortical bone destruction proceeds, the infection eventually breaks out into the subperiosteal space. This development causes periosteal elevation and further compromise of cortical blood supply, especially in young animals. Because of compromised medullary and periosteal blood supply, a segment of cortex may become devoid of its blood supply (infarction) and form a sequestrum. The sequestrum can become completely separated from living cortical bone. The body attempts to isolate the fragment by surrounding it with fibrous tissue and an involucrum of bone. The involucrum walls off the sequestrum and infection but also acts as a barrier that is impervious to penetration of antibodies and antibiotics. Therefore, the sequestrum becomes a nidus for infection and a constant source of relapsing chronic osteomyelitis. 1• 11 • 28 When bacterial contamination occurs after an open fracture reduction or an open fracture, the basic pathophysiologic events are similar. The condition of the host is frequently a factor promoting development of osteomyelitis. Systemically, the patient may be suffering from shock and immunosuppression. Locally, the energy released from the bone causes damage and vascular compromise to both bone and soft tissues. Periosteum is frequently stripped, leaving bone fragments detached from their blood
TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
843
supply. Surrounding soft tissues can become ischemic or eventually necrotic. Metallic implants entrap bacteria and cause varying degrees of bone circulation impairment. This is especially true when the implants do not provide rigid fixation or are improperly applied and lose.
CLINICAL MANIFESTATIONS Osteomyelitis can present in a number of forms, and the clinical signs and management for each can be very different. Acute hematogenous osteomyelitis is seen more frequently in the juvenile human being than in puppies and kittens. 11• 24 This condition occurs most commonly at the metaphysis of long bones where the metaphyseal vessels (branches of the nutrient artery) turn back on themselves at the growth plate and form venous sinusoids. Blood-borne bacteria tend to settle in these areas of sluggish blood flow. 11 Spread of infection from contiguous areas or from a puncture wound can produce a localized osteomyelitis that is commonly present within the first week after injury (or trauma). Local tissue pain, swelling, and occasional drainage are common clinical signs. Osteomyelitis following open reduction of open or closed fractures presents in two forms: acute or chronic. Acute osteomyelitis generally occurs within 2 weeks following open reduction. Chronic osteomyelitis is usually an extension of acute osteomyelitis and is also often associated with previous open-fracture reduction and internal fixation. If loose metallic implants are present, an infected delayed union or nonunion may be an additional complication. Unfortunately, this form of osteomyelitis is fairly common in veterinary practice and can be a difficult problem for the veterinary orthopedic surgeon. The surgeon's goal is to achieve bony union and resolve the infection.
DIAGNOSIS History and Physical Examination A history of open reduction and internal fixation usually accompanies cases of chronic osteomyelitis. Frequently, a surgical error had occurred, and rigid fixation was not achieved at the initial operation. The clinical signs vary somewhat with the stage of osteomyelitis present. Fever, malaise, depression, leukocytosis, swelling, and lameness are common clinical signs with acute osteomyelitis or an acute exacerbation of chronic osteomyelitis. Purulent drainage may exit either from the surgical incision or from a fistulous tract. Pain, lameness, muscle atrophy, and draining sinuses are often observed with chronic osteomyelitis. Radiology Radiographic signs of osteomyelitis include both local bone destruction and new bone formation. 8 Areas of cortical bone lysis, irregular periosteal
844
R OBERT
B.
PARKER
Figure l. A , Preoperative radiograph of a radial/ulnar fracture treated 5 weeks previously with intramedullary pins. Draining tracts and instability were present. Radiographic changes include: irregular callus formation away from the fracture site, irregular mottling of the distal portion of the proximal fragment, medullary sclerosis, and a dense cortical fragment involving the cranial radius, which probably represents a sequestrum . B, Postoperative removal of the intramedullary pins, sequestrectomy, cancellous bone graft application, and stabilization with a type I full Kirschne r apparatus. C, Follow-up at 12 weeks showing fracture healing.
new bone, and increased bone density (sclerosis) are seen with osteomyelitis (Figs. lA and 2C); however , similar signs are seen with other orthopedic diseases, and differentiation can be difficult. Primary bone tumors and aseptic motion at a fracture site may produce similar radiographic signs at various stages; thus, correlation with other clinical data will help the clinician establish the correct diagnosis. Periosteal new bone production with malignant bone neoplasia may appear somewhat laminated due to repeated elevations of the periosteum during alternating periods of rapid and slow growth. 26 Aseptic motion at a fracture site and loose implants also
TREATM E N T OF PosT-TRAUMATIC 0STE0~1YELITIS
845
Figure 2. Late ral (A) and craniocaudal (B) postope rative radiographs of repair of a comminuted midshaft tibial fracture. C, Follow-up at 3 weeks with marked irregular bony callus and periosteal prolife ration along the entire tibia. Marked soft tissue swelling is also evident.
cause lucency and periosteal proliferation, especially near active fissure lines. Contrary to irregular bone resorption in response to infection, resorption secondary to instability is usually sharply outlined and limited to the zone of movement of the loose implant. 6 The classic radiographic signs of osteomyelitis include formation of sequestrum and involucrum. The sequestrum form s when a fragment of cortical bone fails to resorb. Having lost its blood supply, the sequestrum retains its original density, in contrast to the surrounding bone, which becomes lytic in appearance (Figs. 3A and B and 4A). During the early stages of osteomyelitis, soft tissue swelling and loss of demarcation between fascial and muscular planes may be demonstrated. Prominent osteolytic and productive changes may not appear for 10 to 14 days. Bacteriology From 46 to 74 per cent of aerobic bacterial isolates from osteomyelitis cases in dogs are Staphylococcus spp. 2• 7• 17• 3 1 Escherichia coli, betahemolytic Streptococcus spp., Proteus spp, and Pseudomonas spp. have all been reported to be common pathogens. Polymicrobial isolations are common, being reported in 3.5 to 66 per cent of the cases. Resistant strains of Pseudomonas, Proteus, and Klebsiella are common in hospitals and may
846
ROBERT
B.
PARKER
Figure 3. Lateral (A) and craniocaudal (B) radiographs of a dog whose distal femur fracture had been treated 8 weeks previously with an intramedullary pin. Two draining tracts were present. Radiographic signs included a marked periosteal callus with a large sequestered cortical segment. Lateral (C) and craniocaudal (D) radiographs following sequestrectomy, bone plating, drainage, and cancellous bone grafting. Lateral (E) and craniocaudal (F) follow-up at 9 months illustrating fracture healing.
cause nosocomial infections. These infections have proved very difficult to treat with conventional antibacterial therapy. Anaerobic bacteria may play an important role in the pathogenesis of osteomyelitis.35 From 19 specimens submitted from proven osteomyelitis cases, 74 per cent yielded anaerobic bacteria in pure culture or mixed with aerobic or facultative anaerobic bacteria. Bacteroides spp. and Peptostreptococcus spp. were most frequently isolated. This study points out the importance of proper anaerobic culture techniques when obtaining microbiologic samples. Anaerobic infections should be suspected when the following conditions are present: (1) a foul odor, (2) a sequestrum, (3) chronic osteomyelitis, (4) osteomyelitis from a bite wound, (5) osteomyelitis resulting from a surgical repair or open fracture, (6) Gram's stain revealing multiple bacteria having different morphologic characteristics, or (7) failure
TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
847
Figure 4. A , Late ral radiograph of a femur from a dog with a 1-year history of draining tracts and lameness following intramedullary repair of a midshaft femur fracture. Bony remodeling and a large radiolucent defect filled with sequestra are present. B, Craniocaudal view following debridement, drainage, and sequestrectomy.
to grow aerobic bacteria, especially when bacteria were seen on a Gram's stain. Obtaining appropriate samples is an important aspect of the microbiologic evaluation. As a gene ral rule, specimens should not be obtained from draining tracts. In a study on human patients, only 44 per cent of sinustract cultures contained the operative pathogen. 19 The study concluded that, unless Staphylococcus was isolated from a sinus tract, the predictive value of such a sample was very low. Therefore, to obtain the most precise microbiologic result, the surgeon should submit samples directly from the infected site . Sequestra, bone presumed to be infected, and soft tissue adjacent to suspected bony infection are preferred samples. 35 Because anaerobic bacteria are frequently destroyed by exposure to air for 30 minutes and most veterinary hospitals do not have the capability to culture anaerobic bacteria, the use of anaerobic culturettes is recommended. 28 TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
The following situations are common in clinical veterinary practice. Examples of the pathogenesis of acute and chronic infections and treatment methods are described.
848
ROBERT
B.
PARKER
Hematoma Formation After Internal Fixation Despite meticulous surgical technique with attention to hemostasis and obliteration of dead space, hematomas can form following open reduction. Such formation should not be taken lightly or assumed to be "just a seroma." In one report in human beings, 20 per cent of aseptically aspirated hematoma samples grew bacteria. 6 Treatment should be initiated because (1) a contaminated hematoma may become infected, and (2) the hematoma may dissect through the incision and create a route for contamination and infection. Prompt treatment is particularly important in areas such as the medial tibia, where implants are commonly placed subcutaneously. After aseptic skin preparation, small hematomas may be evacuated under local anesthesia with a needle and syringe. The needle should be inserted away from the incision, and the aspirated fluid should be examined cytologically and cultured. 6 • 11 The limb should be wrapped in a light bandage following hematoma evacuation to prevent further hemorrhaging and fluid accumulation. Large hematomas usually require open drainage in the operating room, utilizing strict aseptic technique. 6 • 11 The original wound is opened wide enough to allow gentle evacuation of the hematoma. One should avoid squeezing the skin and soft tissue. Bleeding vessels are occluded by electrocautery or fine ligature, and dead space is carefully closed. The use of closed-suction drainage should be considered; however, the potential for ascending contamination around the tubing exists. A pressure bandage is an effective adjunctive measure, preventing recurrence of the hematoma. Acute Infection After Internal Fixation Heat, pain, swelling, and purulent drainage from an incision are the signs of acute osteomyelitis after internal fixation. Early and aggressive treatment can limit the extent of or even eliminate the infection (Fig. 2A to C). Basic therapeutic principles include (1) antimicrobial culture and sensitivity determination, (2) wound debridement, (3) voluminous lavage, (4) fracture stabilization, (5) adequate drainage, and (6) appropriate antimicrobial therapy. Samples for culture are obtained by needle aspiration or during debridement, and a broad-spectrum parenteral antibiotic is administered. The choice of antibiotics depends on the specific microorganisms predominant in the hospital environment. Our current recommendation is ampicillin (22 to 44 mg per kg, three times a day, orally) and gentamicin (2 mg per kg, three times a day, subcutaneously). Cephalexin (20 mg per kg, three times a day, orally) can be substituted for ampicillin. This empirical treatment is begun without delay and is modified, depending on final culture and sensitivity results. With the patient under general anesthesia in the operating room, the wound is opened. After obtaining samples for aerobic and anaerobic culture, a systematic evaluation of the fracture site and wound is made. The debridement should remove both necrotic tissue and unnecessary foreign material, but should not damage the soft tissues. 6 Copious lavage during debridement is extremely important. The type of lavage fluid is probably
TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
849
not as important as its volume. It is not uncommon to use up to 10 L of lavage fluid. Irrigation solutions provide mechanical removal and dilution of bacteria, and may provide direct bactericidal effects. Suggested solutions include normal saline, dilute povidone iodine solution (1:10 dilution of stock), or chlorhexidine (1:10 dilution of stock). 14 The bactericidal effects of povidine iodine are due to the formation of reactive ions, hydrolysis, and bacterial-protein complex formation. If an antibiotic is added to the lavage solution, the total daily parenteral dose should not be exceeded. Antibiotics are absorbed from the lavaged wound and add to serum levels of antibiotic already present. This is especially significant with antibiotics like the aminoglycosides that have a lower margin of safety. The amount of antibiotic absorbed from this type of wound would not be comparable with intraperitoneallavage and, therefore, total amount of antibiotic may be less critical. Assessment of fracture stability is extremely important during the procedure. The stability of the fracture is determined by rotating and bending the limb while simultaneously checking for motion at the fracture site. If any motion is detected, additional stabilization is necessary. Loose implants should be removed and more secure fixation applied. Frequently, the addition of a Kirschner-Ehmer apparatus will provide the necessary stabilization. Any loose bone fragments should be either removed or restabilized. Fragments are best stabilized by compression, using either heavy full-cerclage wire, hemicerclage wire, or lag screws. 11 If major fragments are removed, the use of a cancellous bone graft should be considered at this point or as a delayed procedure. After debridement and stabilization, the wound may either be closed over drains or allowed to heal by second intention. Wounds that are heavily contaminated or can only be closed under tension should be left open. Although closed-suction irrigation is commonly recommended for human patients, personal experience with this method in animals has been frustrating. Animals often interfere with the system, even when it is covered with protective bandages. Also, the drain tubes become easily obstructed and lose effectiveness. More effective drainage is usually provided by open drainage. Wet to dry dressings are initially applied and are changed one or two times per day. During dressing changes, the wound is irrigated with an appropriate lavage solution that may be delivered with a high-pressure pulsatile lavage system. This treatment continues until healthy granulation tissue covers the wound. At that time, one can make the decision to allow the wound to heal completely by second intention or to close the wound surgically. Chronic Infection After Internal Fixation Chronic osteomyelitis is difficult to treat. 1• 2 • B--9 , 11 • 14• 24 • 28 • 38 The hallmark of chronic osteomyelitis is infected, dead bone within a compromised soft tissue and bony envelope. The coexistence of infected, nonviable tissues and an ineffective host response lead to chronicity, Because dead bone is frequently isolated from the systemic circulation and acts as a nidus for relapsing infection, surgical intervention is necessary. Thorough debridement, adequate drainage, obliteration of dead space, wound protection, and specific antibiotic therapy are the goals of successful treatment.
850
RoBERT
II
Ill
B.
PARKER
Figure 5. Illustration of the University of Texas Medical Branch staging system of osteomyelitis. (From Cierny G, Medar JT: Adult chronic osteomyelitis. Orthopedics 7:1557-1564, 1984; with permission.)
IV
In an attempt ,to provide a common classification scheme for chronic osteomyelitis, Cierny proposed the following anatomic staging system (Fig. 5). 9 Class I chronic osteomyelitis is primarily intramedullary and may result hematogenously or from intramedullary pinning. Class II involves a portion of the cortex only. This form is common after a deep puncture or bite wound. Class III is well marginated by reactive or healthy bone and usually involves both medullary and periosteal surfaces. This type is commonly seen in small animals. Class IV is a diffuse, through-and-through osteomyelitis with intercalary instability. It is also common and requires intense treatment. Four major factors influence the pathogenesis and treatment of chronic osteomyelitis: (l) the degree of bone necrosis, (2) the condition of the host, (3) the site and extent of the involvement, and (4) delayed or nonunion fractures. In addition, septic nonunions are commonly present. Nonunions are often associated with metallic implants at the fracture site. Debridement The debridement procedure should be carefully planned and executed. Preoperative radiographs should be closely examined for potential areas of dead, sequestered bone and evaluated for evidence of fracture instability. In addition, a fistulogram might prove helpful in defining the limits and extent of the process. 11 Fistulography is done using a soluble organic iodide contrast material, such as Renografin-76, delivered through a Foley catheter. Although a fistulogram may provide information about the cause and
TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
851
Figure 6. A and B, Sequestrum removed from the patient in Figure 3.
extent of the disease process, it is important to realize that the extent of involved tissue usually exceeds that seen on the radiograph. 10 The debridement, including the skin incision, is performed with the final reconstruction in mind. 9 Alternate or multiple approaches to the bone may be necessary because of multiple areas of bony involve ment or the presence of large draining wounds. Generally, it is best to try to avoid the draining wound and achieve primary wound closure; however, in areas such as the medial tibia, "en bloc" excision of affected tissue is necessary.6 After debridement, these wounds may be allowed to heal by second intention, or they may be covered by a local or distant skin flap . The key to successful debridement is the removal of all necrotic bone and soft tissue. Abnormal soft tissue surrounding an area of chronic osteomyelitis usually is in the form of a fibrous capsule that may extend to the outside by way of fistulous tracts. The sinuses and infected soft tissue must be carefully excised from healthy tissue. Avascular bone is generally distinguished by its loss of integrity and yellowish color (Fig. 6A and B).28 To help delineate avascular tissue, a 1 per cent solution of methylene blue dye can be injected into the draining tract 12 to 24 hours prior to surgery. 11· 24• 28 The dye stains avascular tissue, whereas vascular tissue is able to remove the dye and is not stained. The dye is excreted by hepatic and renal mechanisms. The opposite effect is achieved by disulphine blue dye that is administered intravenously 1 hour prior to surgery. This dye stains vascular tissue blue, whereas an avascular bone fragment would appear white . 28 The removal of dead bone and sequestra is the most important step in the control and treatment of chronic osteomyelitis. 1 · 2 • 6 • 8 • 9 • 11• 24 • 28 • 31 All sclerotic bone is removed with rongeurs or a high-speed bone burr (Fig.
852
ROBERT
B.
PARKER
4A and B). The medullary canal is opened, and all avascular cancellous bone is removed with a curette. The area is constantly checked for avascular cortical fragments that could represent unrecognized sequestra. The remaining cortical and cancellous bone must bleed uniformly (the "paprika sign"). 9 The resulting bony defect often resembles a saucer; hence, the term "saucerization" is ascribed to this procedure. Intraoperative specimens are obtained for both aerobic and anaerobic cultures. The need for copious lavage cannot be overemphasized. Bone Stability After extensive bone debridement, the structural integrity of the bone may be compromised. An excellent method to provide additional stability is the use of the Kirschner-Ehmer apparatus. A four-pin type I (half pin) or type II (full pin) configuration will provide additional stability without causing vascular disruption to the soft tissues at the affected site. Septic delayed and nonunion fractures after an attempt at open fracture reduction and internal fixation are common types of chronic osteomyelitis. The initial goal in treating these conditions is bony union; therefore, metal implants should not be removed if they provide absolute rigid, stable fixation. Although total elimination of the infection may not result until implant removal, bone union is the first priority. If union has not been achieved, or if existing fixation does not provide stability, additional stabilization is necessary. In general, bone plating is preferred for this situation (Fig. 3C to F); however, consideration should be given to Kirschner-Ehmer fixation, especially the type II (full pin) and type III (threedimensional) configurations. Because of the possibility of spread through the medullary canal, these techniques are preferred over intramedullary fixation. 11 · 24 Drainage and Management of Dead Space The best way to achieve drainage is to leave the wound open and cover it with protective bandages that are changed every day. This is a popular method in human orthopedics. 29 A recent report by Bardet and colleagues cited successful treatment of osteomyelitis using a modification of the Papineau open cancellous technique in dogs. 2 Initially, debridement and internal fixation are performed as previously described as the first treatment stage. The wound is left open and packed with sponges soaked in a sulfonamide-urea solution. The sponges obliterate dead space and facilitate exudate removal. The second stage begins the day after surgery and involves twice-daily irrigations with tap water. After the irrigation, the sponges are replaced, and a protective bandage is applied. This stage concludes when a layer of healthy granulation tissue lines the defect. This development usually occurs in 4 to 12 days. The final stage involves a second surgical procedure to pack the defect with autogenous cancellous bone graft and to perform a delayed primary wound closure. Bacterial cultures are taken initially and at wound closure, and appropriate antibiotics
TREATMENT oF PosT-TRAUMATIC OsTEOMYELITIS
853
are administered. The results of this treatment were excellent, with 11 of 12 wounds healed within 4 to 7 weeks without recurrence of infection. 2 Caywood has described a semiclosed packing technique in which, after debridement, the cavity is filled with povidone iodine-impregnated umbilical tape and the wound is closed primarily, with the tape end exiting through a small stab incision. 8 The tape, which initially obliterates dead space, is removed in 10 to 14 days. A second procedure is performed in approximately 30 days, when cancellous bone graft is added to the defect. Closed suction and irrigation have also been recommended as a means of mechanical debridement, local treatment, and drainage from areas of chronic osteomyelitis. The Snyder Hemovac and the Jackson-Pratt suction systems have been recommended. 1· 11 • 24 With these systems, an afferent delivery tube delivers irrigation fluid across the infected site, and an efferent suction-tubing system evacuates the fluid under negative pressure. A vacuum is created mechanically by the collection reservoir. To be effective, the irrigation solution should fill the cavity before being removed by the suction drain; therefore, the afferent tube should be placed as deeply as possible, whereas the efferent tube should be in a more superficial position. 6 Fluid selection follows the same guidelines as previously mentioned. Because local antibiotic solutions have been shown to cause cancellous bone graft death, the simultaneous use of bone grafts and suction irrigation should probably be avoided. Secondary grafting after drain removal should be considered. Premature drain removal by the patient and clogged tubes tend to be recurrent problems. Constant infusion and suction may help delay occlusion; however, 24-hour monitoring would be necessary. Ideally, the suction-irrigation tubes are left in place until all dead space is eliminated. The elimination can be evaluated by infusing contrast material into the irrigation tube and taking a radiograph. In the human medical literature, the use of local, transferred muscle flaps has been shown to be beneficial in eliminating residual bony dead space, improving local vascularity, and delivering parenterally administered antibiotics. 13 These techniques have not been described in the veterinary literature; however, their future use should be considered. Antibiotic Therapy Unless the patient is seriously ill or compromised, antibiotic therapy may be delayed until cultures and sensitivities have returned. Many laboratories are now reporting quantitative bacterial sensitivity in the form of minimum inhibitory concentration (MIC), which is the lowest concentration of the antibiotic required to inhibit bacterial growth. By knowing expected (or actual) serum and tissue concentrations for a particular antibiotic, a rational selection can be made. The selected drug should be capable of a tissue concentration that reaches or exceeds the MIC. Bone is the same as any tissue, and an antibiotic that achieves satisfactory tissue levels will penetrate vascularized bone and soft tissue. The statement that a particular antibiotic "penetrates bone" many not be totally valid. Unfortunately, specific guidelines concerning treatment duration can-
854
ROBERT
B.
PARKER
not be made. The duration is generally for a prolonged period (months) and is probably best monitored by the clinical response. RECENT ADVANCES IN THE TREATMENT OF OSTEOMYELITIS Polymethylmethacrylate (PMMA) bone cement, to which water-soluble antibiotics have been added in powder form prior to polymerization, was used initially as a prophylactic measure to prevent infection following total joint replacement. 32 Considerable research has shown that antibiotics will elude from the hardened cement and achieve a beneficial local effect. 16 Various antibiotic-PMMA combinations have been studied in vitro. 3 This knowledge has prompted surgeons to employ antibiotic-PMMA beads as a form of local treatment for osteomyelitis. The beads are fashioned prior to polymerization and allowed to harden around a stainless-steel wire. The beads are implanted after debridement and are usually removed in approximately 2 weeks. 16 Although this technique is being used clinically, major clinical trials need to be performed. Plaster of paris impregnated with antibiotics has been proposed as another type of antimicrobial delivery system. 18 The plaster is replaced by bone and, therefore, need not be removed. This technique is still in the early, investigative stage. Highly concentrated fibrinogen that has been coagulated by a thrombin solution and calcium ions into fibrin has been used as a biologic tissue adhesive. Recently, various in vitro, in vivo, and clinical studies have been performed with a fibrin-antibiotic complex. 5 The complex acts as a physiologic vehicle for the antibiotic, and it can be applied either with or without mixed cancellous bone graft. In 69 human patients with chronic osteomyelitis, 59 had no recurrence following this treatment. Local antibiotic therapy by venous perfusion has also been described as a method of achieving very high local antibiotic concentration. 12 This technique probably is not feasible in veterinary medicine and is still considered experimental. Hyperbaric oxygen, 20 electric stimulation, 36 silver electrolysis, 4 and white cell, 23 osteoblast, 15 and thymus suppressor21 inhibition have all been described as forms of osteomyelitis therapy. REFERENCES l. Aron DN: Pathogenesis, diagnosis, and management of osteomyelitis in small animals.
Compend Contin Ed Pract Vet 1:824-830, 1979 2. Bardet JF, Hohn RB, Basinger R: Open drainage and delayed autogenous cancellous bone grafting for treatment of chronic osteomyelitis in dogs and cats. J Am Vet Med Assoc 183:312-317, 1983 3. Bayston R, Milner RDG: The sustained release of antimicrobial drugs from bone cement. J Bone Joint Surg 64B:460--466, 1982 4. Becker RO, Spadaro JA: Treatment of orthopedic infections with electrically generated silver ions. J Bone Joint Surg 60A:871-876, 1978
TREATMENT OF PosT-TRAUMATIC OSTEOMYELITIS
855
5. Braun A, Gussbacher A, Heine WD, et a!: Fibrin-antibiotic complex: Laboratory investigation and clinical results. In Uhthoff HK (ed): Current Concepts of Infections in Orthopedic Surgery. Berlin, Springer-Verlag, 1985 6. Burri C: Post-traumatic osteomyelitis. Bern, Hans Huber Publishers, 1975 7. Caywood DD, Wallace LJ, Braden TD: Osteomyelitis in the dog: A review of 67 cases. J Am Vet Med Assoc 172:943-946, 1978 8. Caywood DD: Osteomyelitis. Vet Clin North Am [Small Anim Pract] 13(1):43-53, 1983 9. Cierny G, Mader JT: Adult chronic osteomyelitis. Orthopedics 7:1557-1564, 1984 10. Clawson DK, Stevenson JK: Treatment of chronic osteomyelitis. Surg Obstet Gynecol 120:59-65, 1965 11. Daly WR: Orthopedic infections. In Slatter DH (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders Co, 1985 12. Finsterbusch A: Venous perfusion of the limb with antibiotics for osteomyelitis and other chronic infections. J Bone Joint Surg 54A:1227-1234, 1972 13. Fitzgerald RH, Ruttle RE, Arnold PC, et a!: Local muscle flaps in the treatment of chronic osteomyelitis. J Bone Joint Surg 67A:175-185, 1985 14. Harari J: Osteomyelitis. JAm Vet Med Assoc 184:101-102, 1984 15. Haynes DW, Morrissy RT: Systemic cell changes in osteomyelitis. Poster exhibit #A-7. 48th Annual Meeting of the American Academy of Orthopedic Surgeons, Las Vegas, Nevada, 1981 16. Hedstrom S: Antibiotic containing bone cement beads in the treatment of deep muscle and skeletal infections. Acta Orthop Scand 51:863-869, 1980 17. Hirsh DC, Smith TM: Osteomyelitis in the dog: Microorganisms isolated and susceptibility to antimicrobial agents. J Small Anim Pract 19:679-687, 1978 18. Mackey D, Varlet A, Debeaumont D: Antibiotic loaded plaster of paris pellets: An in vitro study of a possible method of local antibiotic therapy in bone infections. Clin Orthop 167:263-268, 1982 19. Mackowiak PA, Jones SR, Smith JW: Diagnostic value of sinus-tract cultures in chronic osteomyelitis. J Am Med Assoc 236:2772-2775, 1978 20. Mader JT, Brown GH, Guckian JC, eta!: A mechanism for the amelioration by hyperbaric oxygen of experimental staphylococcal osteomyelitis in rabbits. J Infect Dis 142:915-922, 1980 21. Munster AM, Winchurch RA: Manipulation of the immune response following thermal injury. In The Immune Consequences of Thermal Injury. Baltimore, Williams & Wilkins, 1981 22. Norden CW: Experimental osteomyelitis. I. A description of the model. J Infect Dis 122:410--418, 1970 23. Ninneman JL: Immune depression in burn and trauma patients: The role of circulating suppressors. In Traumatic Injury Infection and Other Immunologic Sequelae. Baltimore, University Park Press, 1983 24. Nunamaker DM: Osteomyelitis. In Newton CD, Nunamaker DM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott Co, 1985 25. Parker RB, Waldron DW: The initial treatment of open fractures. Vet Clin North Am [Small Anim Pract] 10(3):707-716, 1980 26. Roberts RW: Radiographic examination of the musculoskeletal system. Vet Clin North Am [Small Anim Pract] 13(1):19-42, 1983 27. Robertson DE: Acute hematogenous osteomyelitis. J Bone Joint Surg 9-B:S-15, 1927 28. Rudd RG: A rational approach to the diagnosis and treatment of osteomyelitis. Compend Contin Ed Pract Vet 8:225-232, 1986 29. Sanders M, Albright JA: Autogenous bone grafting in clinical osteomyelitis and septic nonunion (the Papineau technique). Orthopedics 7:1608-1612, 1984 30. Scheman L, Janota M, Lewin P: The production of experimental osteomyelitis. J Am Med Assoc 117:1525--1529, 1941 31. Smith CW, Schiller AG, Smith AG, et al: Osteomyelitis in the dog: A retrospective study. J Am Anim Hosp Assoc 14:589-592, 1978 32. Wahlig H, Dingeldein E, Bergmann R, et a!: The release of gentamicin from polymethylmethacrylate beads. J Bone Joint Surg 60B:270-282, 1978 33. Wahlig H, Dingeldein E, Buchholz HW, et a!: Pharmacokinetic study of gentamicinloaded cement in total hip replacements. J Bone Joint Surg 66B:175-182, 1984
856
ROBERT
B.
PARKER
34. Walker MW, Lewis RE, Kneller SK, et a!: Radiographic signs of bone infection in small animals. JAm Vet Med Assoc 166:908-910, 1975 35. Walker RD, Richardson DC, Bryant MJ, et a!: Anaerobic bacteria associated with osteomyelitis in animals. JAm Vet Med Assoc 182:814-816, 1983 36. Watkins R, Patzakis MJ, Moore TM, eta!: Treatment of infected nonunions of the tibia. Paper #213. 50th Annual Meeting of the American Academy of Orthopedic Surgeons, Anaheim, California, 1983 37. Weiland AJ, Moore JR, Daniel RK: The efficacy of free tissue transfer in the treatment of osteomyelitis. J Bone Joint Surg 66-A:181-193, 1984 38. Wingfield WE: Surgical treatment of chronic osteomyelitis in dogs. J Am Anim Hosp Assoc 11:568-569, 1975 Department of Surgical Sciences College of Veterinary Medicine University of Florida Gainesville, Florida 32610
0195--5616/87 $0.00 + .20
Treatment of Post-traumatic Osteomyelitis
Robert B. Parker, D.V.M.*
Osteomyelitis and its treatment date back to the recovery of a 500,000year-old human fossil, a femur of a Java man, that showed evidence of a fracture complicated by osteomyelitis. In his text on post-traumatic osteomyelitis, Burri6 recounted the early history of osteomyelitis treatment. In the first century AD, the Roman physician Celsus described bone debridement in the treatment of chronic osteomyelitis. In 1266, Theoderich recommended dry wound treatment and suggested the use of wine compresses for topical treatment and alcoholic beverages for general wound healing. After Lister's discovery ofbacteria, Franz Konig, in 1873, described local treatment of "putrid osteomyelitis" with antiseptic solutions delivered by closed-suction irrigation. Even today, osteomyelitis is often refractory to therapy. Hippocrates once said of open fractures and osteomyelitis: "One should especially avoid such cases if one has a reasonable excuse, for the risks are great and the rewards are few. "37 Today' s knowledge of surgical treatment and pharmacology has not invalidated this statement. Osteomyelitis is defined as an inflammation of the bone, cortex, and/or periosteum. Most commonly, the clinician thinks of bacterial osteomyelitis; however, fungi, parasites, and viruses can also produce the disease. Bacterial inoculation of bone by itself will not produce disease. 27 Experimental evidence has shown the importance of concomitant loss of blood supply. 22. 3o ROUTES OF CONTAMINATION Infective organisms can reach bone by either hematogenous or direct routes. Although hematogenous osteomyelitis is fairly common in man, it is rarely seen in small animal orthopedic surgery. 24 Direct contamination *Diplomate, American College of Veterinary Surgeons; Associate Professor and Chief, Small Animal Surgery, Department of Surgical Sciences, University of Florida College of Veterinary Medicine, Gainesville, Florida
Veterinary Clinics of North America: Small Animal Practice-Val. 17, No.4, July 1987
841
842
ROBERT
B.
PARKER
can occur after open reduction of a closed fracture, as a consequence of an open fracture, or by contiguous spread from surrounding soft tissue infection. If properly treated, the majority of open fractures should heal without developing osteomyelitis. In a study of 67 cases of osteomyelitis, only 10 per cent were initially presented as open fractures. 7 The principles of open fracture management have been reviewed. 25 The majority of cases of osteomyelitis occur after open reduction and internal fixation. Surgical trauma and bacterial inoculation of the surgical wound are major reasons for this occurrence. Sterile, atraumatic surgical technique with rigid internal fixation and judicious antibiotic prophylaxis are the keys to successful fracture management. It is far easier to prevent osteomyelitis than to treat it. Pathophysiology
Post-traumatic osteomyelitis has been divided into acute and chronic phases; however, there are no sharp delineations, and one phase may slowly progress into another. The initial inflammatory response following bacterial inoculation is the same for bone as for any other tissue. Hyperemia, increased vascular permeability, and an influx of polymorphonuclear cells, serum, antibodies, and complement occur locally. Bacteria destroy many of the white cells, liberating potent proteolytic enzymes. 1• 28 The resulting necrotic tissue and bacteria become a focus of suppuration. The direction in which the inflammation will progress is determined by bacterial virulence, local environment, and the host immune response. If the body is unable to control the infection, more exudation and bone destruction occur. As pressure builds within the marrow, the inflammatory exudate penetrates into cortical bone through the Volkmann and haversian systems. 11 This exudate leads to collapse of small vessels in the nonexpansile vascular channels of bone, with resultant bone infarction. As cortical bone destruction proceeds, the infection eventually breaks out into the subperiosteal space. This development causes periosteal elevation and further compromise of cortical blood supply, especially in young animals. Because of compromised medullary and periosteal blood supply, a segment of cortex may become devoid of its blood supply (infarction) and form a sequestrum. The sequestrum can become completely separated from living cortical bone. The body attempts to isolate the fragment by surrounding it with fibrous tissue and an involucrum of bone. The involucrum walls off the sequestrum and infection but also acts as a barrier that is impervious to penetration of antibodies and antibiotics. Therefore, the sequestrum becomes a nidus for infection and a constant source of relapsing chronic osteomyelitis. 1• 11 • 28 When bacterial contamination occurs after an open fracture reduction or an open fracture, the basic pathophysiologic events are similar. The condition of the host is frequently a factor promoting development of osteomyelitis. Systemically, the patient may be suffering from shock and immunosuppression. Locally, the energy released from the bone causes damage and vascular compromise to both bone and soft tissues. Periosteum is frequently stripped, leaving bone fragments detached from their blood
TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
843
supply. Surrounding soft tissues can become ischemic or eventually necrotic. Metallic implants entrap bacteria and cause varying degrees of bone circulation impairment. This is especially true when the implants do not provide rigid fixation or are improperly applied and lose.
CLINICAL MANIFESTATIONS Osteomyelitis can present in a number of forms, and the clinical signs and management for each can be very different. Acute hematogenous osteomyelitis is seen more frequently in the juvenile human being than in puppies and kittens. 11• 24 This condition occurs most commonly at the metaphysis of long bones where the metaphyseal vessels (branches of the nutrient artery) turn back on themselves at the growth plate and form venous sinusoids. Blood-borne bacteria tend to settle in these areas of sluggish blood flow. 11 Spread of infection from contiguous areas or from a puncture wound can produce a localized osteomyelitis that is commonly present within the first week after injury (or trauma). Local tissue pain, swelling, and occasional drainage are common clinical signs. Osteomyelitis following open reduction of open or closed fractures presents in two forms: acute or chronic. Acute osteomyelitis generally occurs within 2 weeks following open reduction. Chronic osteomyelitis is usually an extension of acute osteomyelitis and is also often associated with previous open-fracture reduction and internal fixation. If loose metallic implants are present, an infected delayed union or nonunion may be an additional complication. Unfortunately, this form of osteomyelitis is fairly common in veterinary practice and can be a difficult problem for the veterinary orthopedic surgeon. The surgeon's goal is to achieve bony union and resolve the infection.
DIAGNOSIS History and Physical Examination A history of open reduction and internal fixation usually accompanies cases of chronic osteomyelitis. Frequently, a surgical error had occurred, and rigid fixation was not achieved at the initial operation. The clinical signs vary somewhat with the stage of osteomyelitis present. Fever, malaise, depression, leukocytosis, swelling, and lameness are common clinical signs with acute osteomyelitis or an acute exacerbation of chronic osteomyelitis. Purulent drainage may exit either from the surgical incision or from a fistulous tract. Pain, lameness, muscle atrophy, and draining sinuses are often observed with chronic osteomyelitis. Radiology Radiographic signs of osteomyelitis include both local bone destruction and new bone formation. 8 Areas of cortical bone lysis, irregular periosteal
844
R OBERT
B.
PARKER
Figure l. A , Preoperative radiograph of a radial/ulnar fracture treated 5 weeks previously with intramedullary pins. Draining tracts and instability were present. Radiographic changes include: irregular callus formation away from the fracture site, irregular mottling of the distal portion of the proximal fragment, medullary sclerosis, and a dense cortical fragment involving the cranial radius, which probably represents a sequestrum . B, Postoperative removal of the intramedullary pins, sequestrectomy, cancellous bone graft application, and stabilization with a type I full Kirschne r apparatus. C, Follow-up at 12 weeks showing fracture healing.
new bone, and increased bone density (sclerosis) are seen with osteomyelitis (Figs. lA and 2C); however , similar signs are seen with other orthopedic diseases, and differentiation can be difficult. Primary bone tumors and aseptic motion at a fracture site may produce similar radiographic signs at various stages; thus, correlation with other clinical data will help the clinician establish the correct diagnosis. Periosteal new bone production with malignant bone neoplasia may appear somewhat laminated due to repeated elevations of the periosteum during alternating periods of rapid and slow growth. 26 Aseptic motion at a fracture site and loose implants also
TREATM E N T OF PosT-TRAUMATIC 0STE0~1YELITIS
845
Figure 2. Late ral (A) and craniocaudal (B) postope rative radiographs of repair of a comminuted midshaft tibial fracture. C, Follow-up at 3 weeks with marked irregular bony callus and periosteal prolife ration along the entire tibia. Marked soft tissue swelling is also evident.
cause lucency and periosteal proliferation, especially near active fissure lines. Contrary to irregular bone resorption in response to infection, resorption secondary to instability is usually sharply outlined and limited to the zone of movement of the loose implant. 6 The classic radiographic signs of osteomyelitis include formation of sequestrum and involucrum. The sequestrum form s when a fragment of cortical bone fails to resorb. Having lost its blood supply, the sequestrum retains its original density, in contrast to the surrounding bone, which becomes lytic in appearance (Figs. 3A and B and 4A). During the early stages of osteomyelitis, soft tissue swelling and loss of demarcation between fascial and muscular planes may be demonstrated. Prominent osteolytic and productive changes may not appear for 10 to 14 days. Bacteriology From 46 to 74 per cent of aerobic bacterial isolates from osteomyelitis cases in dogs are Staphylococcus spp. 2• 7• 17• 3 1 Escherichia coli, betahemolytic Streptococcus spp., Proteus spp, and Pseudomonas spp. have all been reported to be common pathogens. Polymicrobial isolations are common, being reported in 3.5 to 66 per cent of the cases. Resistant strains of Pseudomonas, Proteus, and Klebsiella are common in hospitals and may
846
ROBERT
B.
PARKER
Figure 3. Lateral (A) and craniocaudal (B) radiographs of a dog whose distal femur fracture had been treated 8 weeks previously with an intramedullary pin. Two draining tracts were present. Radiographic signs included a marked periosteal callus with a large sequestered cortical segment. Lateral (C) and craniocaudal (D) radiographs following sequestrectomy, bone plating, drainage, and cancellous bone grafting. Lateral (E) and craniocaudal (F) follow-up at 9 months illustrating fracture healing.
cause nosocomial infections. These infections have proved very difficult to treat with conventional antibacterial therapy. Anaerobic bacteria may play an important role in the pathogenesis of osteomyelitis.35 From 19 specimens submitted from proven osteomyelitis cases, 74 per cent yielded anaerobic bacteria in pure culture or mixed with aerobic or facultative anaerobic bacteria. Bacteroides spp. and Peptostreptococcus spp. were most frequently isolated. This study points out the importance of proper anaerobic culture techniques when obtaining microbiologic samples. Anaerobic infections should be suspected when the following conditions are present: (1) a foul odor, (2) a sequestrum, (3) chronic osteomyelitis, (4) osteomyelitis from a bite wound, (5) osteomyelitis resulting from a surgical repair or open fracture, (6) Gram's stain revealing multiple bacteria having different morphologic characteristics, or (7) failure
TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
847
Figure 4. A , Late ral radiograph of a femur from a dog with a 1-year history of draining tracts and lameness following intramedullary repair of a midshaft femur fracture. Bony remodeling and a large radiolucent defect filled with sequestra are present. B, Craniocaudal view following debridement, drainage, and sequestrectomy.
to grow aerobic bacteria, especially when bacteria were seen on a Gram's stain. Obtaining appropriate samples is an important aspect of the microbiologic evaluation. As a gene ral rule, specimens should not be obtained from draining tracts. In a study on human patients, only 44 per cent of sinustract cultures contained the operative pathogen. 19 The study concluded that, unless Staphylococcus was isolated from a sinus tract, the predictive value of such a sample was very low. Therefore, to obtain the most precise microbiologic result, the surgeon should submit samples directly from the infected site . Sequestra, bone presumed to be infected, and soft tissue adjacent to suspected bony infection are preferred samples. 35 Because anaerobic bacteria are frequently destroyed by exposure to air for 30 minutes and most veterinary hospitals do not have the capability to culture anaerobic bacteria, the use of anaerobic culturettes is recommended. 28 TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
The following situations are common in clinical veterinary practice. Examples of the pathogenesis of acute and chronic infections and treatment methods are described.
848
ROBERT
B.
PARKER
Hematoma Formation After Internal Fixation Despite meticulous surgical technique with attention to hemostasis and obliteration of dead space, hematomas can form following open reduction. Such formation should not be taken lightly or assumed to be "just a seroma." In one report in human beings, 20 per cent of aseptically aspirated hematoma samples grew bacteria. 6 Treatment should be initiated because (1) a contaminated hematoma may become infected, and (2) the hematoma may dissect through the incision and create a route for contamination and infection. Prompt treatment is particularly important in areas such as the medial tibia, where implants are commonly placed subcutaneously. After aseptic skin preparation, small hematomas may be evacuated under local anesthesia with a needle and syringe. The needle should be inserted away from the incision, and the aspirated fluid should be examined cytologically and cultured. 6 • 11 The limb should be wrapped in a light bandage following hematoma evacuation to prevent further hemorrhaging and fluid accumulation. Large hematomas usually require open drainage in the operating room, utilizing strict aseptic technique. 6 • 11 The original wound is opened wide enough to allow gentle evacuation of the hematoma. One should avoid squeezing the skin and soft tissue. Bleeding vessels are occluded by electrocautery or fine ligature, and dead space is carefully closed. The use of closed-suction drainage should be considered; however, the potential for ascending contamination around the tubing exists. A pressure bandage is an effective adjunctive measure, preventing recurrence of the hematoma. Acute Infection After Internal Fixation Heat, pain, swelling, and purulent drainage from an incision are the signs of acute osteomyelitis after internal fixation. Early and aggressive treatment can limit the extent of or even eliminate the infection (Fig. 2A to C). Basic therapeutic principles include (1) antimicrobial culture and sensitivity determination, (2) wound debridement, (3) voluminous lavage, (4) fracture stabilization, (5) adequate drainage, and (6) appropriate antimicrobial therapy. Samples for culture are obtained by needle aspiration or during debridement, and a broad-spectrum parenteral antibiotic is administered. The choice of antibiotics depends on the specific microorganisms predominant in the hospital environment. Our current recommendation is ampicillin (22 to 44 mg per kg, three times a day, orally) and gentamicin (2 mg per kg, three times a day, subcutaneously). Cephalexin (20 mg per kg, three times a day, orally) can be substituted for ampicillin. This empirical treatment is begun without delay and is modified, depending on final culture and sensitivity results. With the patient under general anesthesia in the operating room, the wound is opened. After obtaining samples for aerobic and anaerobic culture, a systematic evaluation of the fracture site and wound is made. The debridement should remove both necrotic tissue and unnecessary foreign material, but should not damage the soft tissues. 6 Copious lavage during debridement is extremely important. The type of lavage fluid is probably
TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
849
not as important as its volume. It is not uncommon to use up to 10 L of lavage fluid. Irrigation solutions provide mechanical removal and dilution of bacteria, and may provide direct bactericidal effects. Suggested solutions include normal saline, dilute povidone iodine solution (1:10 dilution of stock), or chlorhexidine (1:10 dilution of stock). 14 The bactericidal effects of povidine iodine are due to the formation of reactive ions, hydrolysis, and bacterial-protein complex formation. If an antibiotic is added to the lavage solution, the total daily parenteral dose should not be exceeded. Antibiotics are absorbed from the lavaged wound and add to serum levels of antibiotic already present. This is especially significant with antibiotics like the aminoglycosides that have a lower margin of safety. The amount of antibiotic absorbed from this type of wound would not be comparable with intraperitoneallavage and, therefore, total amount of antibiotic may be less critical. Assessment of fracture stability is extremely important during the procedure. The stability of the fracture is determined by rotating and bending the limb while simultaneously checking for motion at the fracture site. If any motion is detected, additional stabilization is necessary. Loose implants should be removed and more secure fixation applied. Frequently, the addition of a Kirschner-Ehmer apparatus will provide the necessary stabilization. Any loose bone fragments should be either removed or restabilized. Fragments are best stabilized by compression, using either heavy full-cerclage wire, hemicerclage wire, or lag screws. 11 If major fragments are removed, the use of a cancellous bone graft should be considered at this point or as a delayed procedure. After debridement and stabilization, the wound may either be closed over drains or allowed to heal by second intention. Wounds that are heavily contaminated or can only be closed under tension should be left open. Although closed-suction irrigation is commonly recommended for human patients, personal experience with this method in animals has been frustrating. Animals often interfere with the system, even when it is covered with protective bandages. Also, the drain tubes become easily obstructed and lose effectiveness. More effective drainage is usually provided by open drainage. Wet to dry dressings are initially applied and are changed one or two times per day. During dressing changes, the wound is irrigated with an appropriate lavage solution that may be delivered with a high-pressure pulsatile lavage system. This treatment continues until healthy granulation tissue covers the wound. At that time, one can make the decision to allow the wound to heal completely by second intention or to close the wound surgically. Chronic Infection After Internal Fixation Chronic osteomyelitis is difficult to treat. 1• 2 • B--9 , 11 • 14• 24 • 28 • 38 The hallmark of chronic osteomyelitis is infected, dead bone within a compromised soft tissue and bony envelope. The coexistence of infected, nonviable tissues and an ineffective host response lead to chronicity, Because dead bone is frequently isolated from the systemic circulation and acts as a nidus for relapsing infection, surgical intervention is necessary. Thorough debridement, adequate drainage, obliteration of dead space, wound protection, and specific antibiotic therapy are the goals of successful treatment.
850
RoBERT
II
Ill
B.
PARKER
Figure 5. Illustration of the University of Texas Medical Branch staging system of osteomyelitis. (From Cierny G, Medar JT: Adult chronic osteomyelitis. Orthopedics 7:1557-1564, 1984; with permission.)
IV
In an attempt ,to provide a common classification scheme for chronic osteomyelitis, Cierny proposed the following anatomic staging system (Fig. 5). 9 Class I chronic osteomyelitis is primarily intramedullary and may result hematogenously or from intramedullary pinning. Class II involves a portion of the cortex only. This form is common after a deep puncture or bite wound. Class III is well marginated by reactive or healthy bone and usually involves both medullary and periosteal surfaces. This type is commonly seen in small animals. Class IV is a diffuse, through-and-through osteomyelitis with intercalary instability. It is also common and requires intense treatment. Four major factors influence the pathogenesis and treatment of chronic osteomyelitis: (l) the degree of bone necrosis, (2) the condition of the host, (3) the site and extent of the involvement, and (4) delayed or nonunion fractures. In addition, septic nonunions are commonly present. Nonunions are often associated with metallic implants at the fracture site. Debridement The debridement procedure should be carefully planned and executed. Preoperative radiographs should be closely examined for potential areas of dead, sequestered bone and evaluated for evidence of fracture instability. In addition, a fistulogram might prove helpful in defining the limits and extent of the process. 11 Fistulography is done using a soluble organic iodide contrast material, such as Renografin-76, delivered through a Foley catheter. Although a fistulogram may provide information about the cause and
TREATMENT OF POST-TRAUMATIC OSTEOMYELITIS
851
Figure 6. A and B, Sequestrum removed from the patient in Figure 3.
extent of the disease process, it is important to realize that the extent of involved tissue usually exceeds that seen on the radiograph. 10 The debridement, including the skin incision, is performed with the final reconstruction in mind. 9 Alternate or multiple approaches to the bone may be necessary because of multiple areas of bony involve ment or the presence of large draining wounds. Generally, it is best to try to avoid the draining wound and achieve primary wound closure; however, in areas such as the medial tibia, "en bloc" excision of affected tissue is necessary.6 After debridement, these wounds may be allowed to heal by second intention, or they may be covered by a local or distant skin flap . The key to successful debridement is the removal of all necrotic bone and soft tissue. Abnormal soft tissue surrounding an area of chronic osteomyelitis usually is in the form of a fibrous capsule that may extend to the outside by way of fistulous tracts. The sinuses and infected soft tissue must be carefully excised from healthy tissue. Avascular bone is generally distinguished by its loss of integrity and yellowish color (Fig. 6A and B).28 To help delineate avascular tissue, a 1 per cent solution of methylene blue dye can be injected into the draining tract 12 to 24 hours prior to surgery. 11· 24• 28 The dye stains avascular tissue, whereas vascular tissue is able to remove the dye and is not stained. The dye is excreted by hepatic and renal mechanisms. The opposite effect is achieved by disulphine blue dye that is administered intravenously 1 hour prior to surgery. This dye stains vascular tissue blue, whereas an avascular bone fragment would appear white . 28 The removal of dead bone and sequestra is the most important step in the control and treatment of chronic osteomyelitis. 1 · 2 • 6 • 8 • 9 • 11• 24 • 28 • 31 All sclerotic bone is removed with rongeurs or a high-speed bone burr (Fig.
852
ROBERT
B.
PARKER
4A and B). The medullary canal is opened, and all avascular cancellous bone is removed with a curette. The area is constantly checked for avascular cortical fragments that could represent unrecognized sequestra. The remaining cortical and cancellous bone must bleed uniformly (the "paprika sign"). 9 The resulting bony defect often resembles a saucer; hence, the term "saucerization" is ascribed to this procedure. Intraoperative specimens are obtained for both aerobic and anaerobic cultures. The need for copious lavage cannot be overemphasized. Bone Stability After extensive bone debridement, the structural integrity of the bone may be compromised. An excellent method to provide additional stability is the use of the Kirschner-Ehmer apparatus. A four-pin type I (half pin) or type II (full pin) configuration will provide additional stability without causing vascular disruption to the soft tissues at the affected site. Septic delayed and nonunion fractures after an attempt at open fracture reduction and internal fixation are common types of chronic osteomyelitis. The initial goal in treating these conditions is bony union; therefore, metal implants should not be removed if they provide absolute rigid, stable fixation. Although total elimination of the infection may not result until implant removal, bone union is the first priority. If union has not been achieved, or if existing fixation does not provide stability, additional stabilization is necessary. In general, bone plating is preferred for this situation (Fig. 3C to F); however, consideration should be given to Kirschner-Ehmer fixation, especially the type II (full pin) and type III (threedimensional) configurations. Because of the possibility of spread through the medullary canal, these techniques are preferred over intramedullary fixation. 11 · 24 Drainage and Management of Dead Space The best way to achieve drainage is to leave the wound open and cover it with protective bandages that are changed every day. This is a popular method in human orthopedics. 29 A recent report by Bardet and colleagues cited successful treatment of osteomyelitis using a modification of the Papineau open cancellous technique in dogs. 2 Initially, debridement and internal fixation are performed as previously described as the first treatment stage. The wound is left open and packed with sponges soaked in a sulfonamide-urea solution. The sponges obliterate dead space and facilitate exudate removal. The second stage begins the day after surgery and involves twice-daily irrigations with tap water. After the irrigation, the sponges are replaced, and a protective bandage is applied. This stage concludes when a layer of healthy granulation tissue lines the defect. This development usually occurs in 4 to 12 days. The final stage involves a second surgical procedure to pack the defect with autogenous cancellous bone graft and to perform a delayed primary wound closure. Bacterial cultures are taken initially and at wound closure, and appropriate antibiotics
TREATMENT oF PosT-TRAUMATIC OsTEOMYELITIS
853
are administered. The results of this treatment were excellent, with 11 of 12 wounds healed within 4 to 7 weeks without recurrence of infection. 2 Caywood has described a semiclosed packing technique in which, after debridement, the cavity is filled with povidone iodine-impregnated umbilical tape and the wound is closed primarily, with the tape end exiting through a small stab incision. 8 The tape, which initially obliterates dead space, is removed in 10 to 14 days. A second procedure is performed in approximately 30 days, when cancellous bone graft is added to the defect. Closed suction and irrigation have also been recommended as a means of mechanical debridement, local treatment, and drainage from areas of chronic osteomyelitis. The Snyder Hemovac and the Jackson-Pratt suction systems have been recommended. 1· 11 • 24 With these systems, an afferent delivery tube delivers irrigation fluid across the infected site, and an efferent suction-tubing system evacuates the fluid under negative pressure. A vacuum is created mechanically by the collection reservoir. To be effective, the irrigation solution should fill the cavity before being removed by the suction drain; therefore, the afferent tube should be placed as deeply as possible, whereas the efferent tube should be in a more superficial position. 6 Fluid selection follows the same guidelines as previously mentioned. Because local antibiotic solutions have been shown to cause cancellous bone graft death, the simultaneous use of bone grafts and suction irrigation should probably be avoided. Secondary grafting after drain removal should be considered. Premature drain removal by the patient and clogged tubes tend to be recurrent problems. Constant infusion and suction may help delay occlusion; however, 24-hour monitoring would be necessary. Ideally, the suction-irrigation tubes are left in place until all dead space is eliminated. The elimination can be evaluated by infusing contrast material into the irrigation tube and taking a radiograph. In the human medical literature, the use of local, transferred muscle flaps has been shown to be beneficial in eliminating residual bony dead space, improving local vascularity, and delivering parenterally administered antibiotics. 13 These techniques have not been described in the veterinary literature; however, their future use should be considered. Antibiotic Therapy Unless the patient is seriously ill or compromised, antibiotic therapy may be delayed until cultures and sensitivities have returned. Many laboratories are now reporting quantitative bacterial sensitivity in the form of minimum inhibitory concentration (MIC), which is the lowest concentration of the antibiotic required to inhibit bacterial growth. By knowing expected (or actual) serum and tissue concentrations for a particular antibiotic, a rational selection can be made. The selected drug should be capable of a tissue concentration that reaches or exceeds the MIC. Bone is the same as any tissue, and an antibiotic that achieves satisfactory tissue levels will penetrate vascularized bone and soft tissue. The statement that a particular antibiotic "penetrates bone" many not be totally valid. Unfortunately, specific guidelines concerning treatment duration can-
854
ROBERT
B.
PARKER
not be made. The duration is generally for a prolonged period (months) and is probably best monitored by the clinical response. RECENT ADVANCES IN THE TREATMENT OF OSTEOMYELITIS Polymethylmethacrylate (PMMA) bone cement, to which water-soluble antibiotics have been added in powder form prior to polymerization, was used initially as a prophylactic measure to prevent infection following total joint replacement. 32 Considerable research has shown that antibiotics will elude from the hardened cement and achieve a beneficial local effect. 16 Various antibiotic-PMMA combinations have been studied in vitro. 3 This knowledge has prompted surgeons to employ antibiotic-PMMA beads as a form of local treatment for osteomyelitis. The beads are fashioned prior to polymerization and allowed to harden around a stainless-steel wire. The beads are implanted after debridement and are usually removed in approximately 2 weeks. 16 Although this technique is being used clinically, major clinical trials need to be performed. Plaster of paris impregnated with antibiotics has been proposed as another type of antimicrobial delivery system. 18 The plaster is replaced by bone and, therefore, need not be removed. This technique is still in the early, investigative stage. Highly concentrated fibrinogen that has been coagulated by a thrombin solution and calcium ions into fibrin has been used as a biologic tissue adhesive. Recently, various in vitro, in vivo, and clinical studies have been performed with a fibrin-antibiotic complex. 5 The complex acts as a physiologic vehicle for the antibiotic, and it can be applied either with or without mixed cancellous bone graft. In 69 human patients with chronic osteomyelitis, 59 had no recurrence following this treatment. Local antibiotic therapy by venous perfusion has also been described as a method of achieving very high local antibiotic concentration. 12 This technique probably is not feasible in veterinary medicine and is still considered experimental. Hyperbaric oxygen, 20 electric stimulation, 36 silver electrolysis, 4 and white cell, 23 osteoblast, 15 and thymus suppressor21 inhibition have all been described as forms of osteomyelitis therapy. REFERENCES l. Aron DN: Pathogenesis, diagnosis, and management of osteomyelitis in small animals.
Compend Contin Ed Pract Vet 1:824-830, 1979 2. Bardet JF, Hohn RB, Basinger R: Open drainage and delayed autogenous cancellous bone grafting for treatment of chronic osteomyelitis in dogs and cats. J Am Vet Med Assoc 183:312-317, 1983 3. Bayston R, Milner RDG: The sustained release of antimicrobial drugs from bone cement. J Bone Joint Surg 64B:460--466, 1982 4. Becker RO, Spadaro JA: Treatment of orthopedic infections with electrically generated silver ions. J Bone Joint Surg 60A:871-876, 1978
TREATMENT OF PosT-TRAUMATIC OSTEOMYELITIS
855
5. Braun A, Gussbacher A, Heine WD, et a!: Fibrin-antibiotic complex: Laboratory investigation and clinical results. In Uhthoff HK (ed): Current Concepts of Infections in Orthopedic Surgery. Berlin, Springer-Verlag, 1985 6. Burri C: Post-traumatic osteomyelitis. Bern, Hans Huber Publishers, 1975 7. Caywood DD, Wallace LJ, Braden TD: Osteomyelitis in the dog: A review of 67 cases. J Am Vet Med Assoc 172:943-946, 1978 8. Caywood DD: Osteomyelitis. Vet Clin North Am [Small Anim Pract] 13(1):43-53, 1983 9. Cierny G, Mader JT: Adult chronic osteomyelitis. Orthopedics 7:1557-1564, 1984 10. Clawson DK, Stevenson JK: Treatment of chronic osteomyelitis. Surg Obstet Gynecol 120:59-65, 1965 11. Daly WR: Orthopedic infections. In Slatter DH (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders Co, 1985 12. Finsterbusch A: Venous perfusion of the limb with antibiotics for osteomyelitis and other chronic infections. J Bone Joint Surg 54A:1227-1234, 1972 13. Fitzgerald RH, Ruttle RE, Arnold PC, et a!: Local muscle flaps in the treatment of chronic osteomyelitis. J Bone Joint Surg 67A:175-185, 1985 14. Harari J: Osteomyelitis. JAm Vet Med Assoc 184:101-102, 1984 15. Haynes DW, Morrissy RT: Systemic cell changes in osteomyelitis. Poster exhibit #A-7. 48th Annual Meeting of the American Academy of Orthopedic Surgeons, Las Vegas, Nevada, 1981 16. Hedstrom S: Antibiotic containing bone cement beads in the treatment of deep muscle and skeletal infections. Acta Orthop Scand 51:863-869, 1980 17. Hirsh DC, Smith TM: Osteomyelitis in the dog: Microorganisms isolated and susceptibility to antimicrobial agents. J Small Anim Pract 19:679-687, 1978 18. Mackey D, Varlet A, Debeaumont D: Antibiotic loaded plaster of paris pellets: An in vitro study of a possible method of local antibiotic therapy in bone infections. Clin Orthop 167:263-268, 1982 19. Mackowiak PA, Jones SR, Smith JW: Diagnostic value of sinus-tract cultures in chronic osteomyelitis. J Am Med Assoc 236:2772-2775, 1978 20. Mader JT, Brown GH, Guckian JC, eta!: A mechanism for the amelioration by hyperbaric oxygen of experimental staphylococcal osteomyelitis in rabbits. J Infect Dis 142:915-922, 1980 21. Munster AM, Winchurch RA: Manipulation of the immune response following thermal injury. In The Immune Consequences of Thermal Injury. Baltimore, Williams & Wilkins, 1981 22. Norden CW: Experimental osteomyelitis. I. A description of the model. J Infect Dis 122:410--418, 1970 23. Ninneman JL: Immune depression in burn and trauma patients: The role of circulating suppressors. In Traumatic Injury Infection and Other Immunologic Sequelae. Baltimore, University Park Press, 1983 24. Nunamaker DM: Osteomyelitis. In Newton CD, Nunamaker DM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott Co, 1985 25. Parker RB, Waldron DW: The initial treatment of open fractures. Vet Clin North Am [Small Anim Pract] 10(3):707-716, 1980 26. Roberts RW: Radiographic examination of the musculoskeletal system. Vet Clin North Am [Small Anim Pract] 13(1):19-42, 1983 27. Robertson DE: Acute hematogenous osteomyelitis. J Bone Joint Surg 9-B:S-15, 1927 28. Rudd RG: A rational approach to the diagnosis and treatment of osteomyelitis. Compend Contin Ed Pract Vet 8:225-232, 1986 29. Sanders M, Albright JA: Autogenous bone grafting in clinical osteomyelitis and septic nonunion (the Papineau technique). Orthopedics 7:1608-1612, 1984 30. Scheman L, Janota M, Lewin P: The production of experimental osteomyelitis. J Am Med Assoc 117:1525--1529, 1941 31. Smith CW, Schiller AG, Smith AG, et al: Osteomyelitis in the dog: A retrospective study. J Am Anim Hosp Assoc 14:589-592, 1978 32. Wahlig H, Dingeldein E, Bergmann R, et a!: The release of gentamicin from polymethylmethacrylate beads. J Bone Joint Surg 60B:270-282, 1978 33. Wahlig H, Dingeldein E, Buchholz HW, et a!: Pharmacokinetic study of gentamicinloaded cement in total hip replacements. J Bone Joint Surg 66B:175-182, 1984
856
ROBERT
B.
PARKER
34. Walker MW, Lewis RE, Kneller SK, et a!: Radiographic signs of bone infection in small animals. JAm Vet Med Assoc 166:908-910, 1975 35. Walker RD, Richardson DC, Bryant MJ, et a!: Anaerobic bacteria associated with osteomyelitis in animals. JAm Vet Med Assoc 182:814-816, 1983 36. Watkins R, Patzakis MJ, Moore TM, eta!: Treatment of infected nonunions of the tibia. Paper #213. 50th Annual Meeting of the American Academy of Orthopedic Surgeons, Anaheim, California, 1983 37. Weiland AJ, Moore JR, Daniel RK: The efficacy of free tissue transfer in the treatment of osteomyelitis. J Bone Joint Surg 66-A:181-193, 1984 38. Wingfield WE: Surgical treatment of chronic osteomyelitis in dogs. J Am Anim Hosp Assoc 11:568-569, 1975 Department of Surgical Sciences College of Veterinary Medicine University of Florida Gainesville, Florida 32610