Clinique vétérinaire

du Dr Bardet

Open drainage and delayed autogenous cancellous bone grafting for treatment of chronic osteomyelitis in dogs and cats

Ten dogs and 1 cat with 12 chronically infected bones were treated surgically by means of saucerization, primary internal or external rigid fixation, and open irrigation drainage. After formation of a healthy granulation bed, autogenous cancellous bone grafting and skin closure were performed. Eleven of 12 bones healed 4 to 7 weeks (mean, 4.8 weeks) after treatment, without recurrence of infection. Eight of 12 chronically infected bones had a polymicrobial infection, with 2 to 6 bacterial species isolated. Gram-negative bacteria were isolated from 7 of the 12 bones, and anaerobic bacteria were isolated twice.

CHRONIC OSTEOMYELITIS, whether posttraumatic or postoperative, is a therapeutic challenge. Although chronic osteomyelitis is common in small animals, there is a paucity of information in the veterinary literature (1-10).

Treatment in human beings includes complete removal of infected and necrotic soft tissue and bone (11-18). In chronic osteomyelitis, the diseased bone suffers from chronic ischemia, and systemic antibiotic treatment may not be effective (12,16,17). In such cases, a variety of local treatments has been used with variable success. Continuous irrigation with an antimicrobial solution and closed suction drainage have been used successfully (11,13,16), but the patient's status must be monitored constantly. As an alternative to irrigation and suction drainage, gentamicin-polymethylmethacrylate beads provide a high local concentration of gentamicin, which promotes favorable conditions for bone healing (17,19). When the skin cannot be closed primarily (eg, in posttraumatic osteomyelitis), open drainage is the only alternative (11,12). As an adjunct to antibiotic therapy, hyperbaric oxygenation has been used successfully in the treatment of experimentally induced osteomyelitis (20).

Open drainage after saucerization and delayed internal fixation plus autogenous cancellous bone grafting for treatment of chronic osteomyelitis has been used successfully in man (15). The study reported here deals with a modification of this technique used in the treatment of chronic osteomyelitis in 10 dogs and 1 cat evaluated at The Ohio State University from 1980 to 1982.

Materials and Methods

Clinical details are presented in Table 1. The dogs were medium-size to large breeds (mean weight, 25.8 kg). The mean age at admission was 3.9 years, and the mean interval between time of fracture and time of treatment for chronic osteomyelitis was 13.2 weeks.

The 3 stages of the technique are illustrated in Figure 1. Before stage 1, the animal was maintained on a broad-spectrum antibiotic for at least 24 hours after specimens were taken from the fistulous tract(s) for aerobic and anaerobic cultures.

Fig 1 - Stages of treatment of chronic osteomyelitis (modified from Papineau et all (15).

Stage 1

Stage1 was performed following general anesthesia and aseptic preparation of the limb. A routine approach to the affected bone was used, after which the musculocutaneous fistulous tracts were excised, the sequestra were removed, and the endosteal or periosteal necrotic cortical bone was curetted. Removal of all necrotic diaphyseal cortical bone was considered mandatory. The remaining proximal and distal segments of the infected bone were fixed by various means (Table 1). The wound was left open and packed with surgical sponges containing a sulfonamide-urea solution (a). A light Robert Jones bandage was applied on the limb, and an Elizabethan collar was applied immediately after recovery and left on for the entire period of open drainage.

Table 1 - Chronic osteomyelitis in 10 dogs and 1 cat.

Stage 2

Stage-2 treatment commenced the day after surgery. The wound was irrigated 15 minutes twice a day with tap water. After irrigation the remaining clots were removed with sterile cotton-tipped swabs and the sulfonamide-urea sponges and the bandage were replaced. After 72 hours most of the necrotic soft tissue had been removed with the sponges and the drainage had decreased. Stage 2 ended when the granulation tissue appeared 4 to 12 days after the initial surgery.

Stage 3

When healthy pink granulation tissue covered the wound, stage 3 was initiated. At this time, a swab specimen was taken from the wound for bacterial culture. This stage required general anesthesia. The limb was clipped and prepared for aseptic surgery. The desiccated and necrotic tissues were removed, soft tissue structures were identified, and the inverted skin was slightly undermined to allow its closure. The cortical bone defect remaining after debridement was packed with an autogenous cancellous bone graft from the proximal end of the humerus. The wound was closed over Penrose tubing (b), using 2-0 coated polyglactin 910 (c) for the fascia and sub-cutaneous tissues, and 2-0 supramid (d) for the skin. The drain was removed from the wound after 2 days, and the wound was kept open and clean until the drainage stopped. When closure was not possible, vertical tension mattress sutures were applied on the skin edges to decrease the gap and cover the cancellous bone graft. The patients were treated orally with antibiotics for 4 to 6 weeks. Bone healing was evaluated by means of radiography at various intervals after surgery.

Results

In 11 of the 12 infected bones, results were satisfactory, with absence of signs of chronic osteomyelitis 4 months to 2 years after treatment. The fractures in 8 dogs and 1 cat were healed 4 to 7 weeks after the initial treatment (mean, 4.8 weeks). Dog 11 was admitted 2 months after treatment because of a recurring fistulous tract. Intravenous injection of 10 ml of a vital stain (e) revealed a 2-cm² area of necrotic cortical bone. The necrotic bone was removed surgically and the dog subsequently regained full use of the limb. Two dogs and 1 cat developed septic arthritis. Dog 2 had radiographic evidence of carpitis before surgery. Arthrodesis of the tarsocrural joint was performed in the remaining 2 animals with septic arthritis. In 8 of the bones, there was polymicrobial osteomyelitis, with 2 to 6 bacterial species isolated from each (Table 1). Staphylococcus aureus and Escherichia coli were the 2 most common pathogens.

Case examples

Dog 2- A year-old female German Shorthaired Pointer was admitted because of chronic osteomyelitis and nonunion of a fracture of the left radius and ulna. The fracture had been fixed with a radial intramedullary pin 4 weeks earlier. Since that time, the left front limb had become swollen and painful, and a fistulous tract had developed 1 week after the surgery.

The left front limb was swollen below the elbow, and 2 fistulous tracts were draining on the medial aspect of the limb. The fracture was unstable on palpation. Specimens were taken for bacterial culture. Radiography of the left front limb revealed severe soft tissue swelling and nonunion of the radius and ulna fractures, with exuberant periosteal new bone formation and sequestration of the radius and part of the ulna (Fig 2). The left carpus was swollen and painful in stress extension. Radiography of the antebrachiocarpal and middle carpal joints showed swelling of the periarticular soft tissues and loss of subchondral bone density, suggesting septic arthritis.

Fig 2 - Lateral radiograph of the left forelimb of dog 2, demonstrating radial sequestra (arrows), periosteal new bone formation, and soft tissue swelling. Ulnar sequestra are also seen.

Medical therapy was started the day before surgery (cephalexin, 20 mg/kg, TID, orally, and gentamicin, 2 mg/kg, TID, SC). At surgery, the radial and ulnar sequestra and the remaining necrotic bone were removed with rongeurs. A through-and-through Kirschner apparatus was applied. Both incisions were left open and treated as previously described. The cultures yielded 4 bacteria: E coli, Enterococcus sp, Streptococcus sp, and anaerobes, all sensitive to chloramphenicol. After 7 days of open drainage, an autogenous cancellous bone graft from the proximal end of the humerus was used to bridge the radial and the ulnar cortical bone defects. Soft tissue swelling prevented closure of the open wounds over the radius and ulna, and tension mattress sutures of 2-0 coated polyglactin 910 were used to close soft tissue over both cancellous bone grafts. Culture of specimens taken during surgery yielded a Pseudomonas sp and Corynebacterium sp in addition to the 4 bacteria previously isolated. Both wounds healed by second intention. The fracture was headed and the Kirschner fixation was removed at 5 weeks (Fig 3). The dog was walking with slight lameness. There was full weight bearing, with lameness only after strenuous exercise 10 weeks after the initial surgery. The dog had 90-degree range of motion, degenerative disease in the elbow, and radiographic signs of left carpitis. There was no evidence of infection after 9 months.

Fig 3 - Lateral radiograph of the left radius and ulna after removal of fixation apparatus at 5 weeks. The fractures are healed. There is a synostosis between the radius and the ulna.

Dog 6 - A 2-year-old female Brittany Spaniel was referred because of osteomyelitis. She had sustained a right femoral fracture a month earlier. After open reduction and internal fixation, using an intramedullary pin, she became febrile and the limb became extremely edematous while in a Thomas-Schroeder splint. The intramedullary pin had been removed because of persistent drainage above the greater trochanter. The dog was given tetracycline for 3 weeks. At the time of referral, she was not bearing weight on the right hindlimb. There was marked muscle atrophy and the range of motion in the right stifle was only 45 degrees. Routine hematology showed low PCV and RBC counts. Radiography of the right femur (Fig 4) revealed a comminuted and malaligned midshaft femoral fracture, with calcified callus formation around the fragments. There was osteolysis of some of the cortical sequestra entrapped in the callus, suggesting an active infection. Surgical intervention was indicated.

Fig 4 - Lateral radiograph of the right femur of dog 6, showing osteolysis of the sequestra, formation of a large callus, and healing in malunion of the proximal femur.

As a lateral approach to the femur was made, about 200 ml of purulent exudate was found between the vastus lateralis and the biceps femoris muscles. After obtaining swab specimens for bacterial culture, 3 necrotic cortical bone fragments were removed and a 9-hole plate for 3.5-mm cortical screws was applied to the lateral surface of the femur. The incision was packed open with surgical sponges and a sulfonamide-urea solution (a). After 5 days of open drainage and open irrigation, the bone defect (4.5 mm long) was packed with autogenous cancellous bone graft from the proximal end of the right humerus, and the wound was sutured over a drain. The culture yielded E coli and Proteus sp, both of which were sensitive to chloramphenicol. The dog was discharged 3 days later, with instructions to treat with chloramphenicol (500 mg, orally, TID) for 1 month. At 8 weeks after surgery, the fracture was healed (Fig 5 and 6). At 18 months after surgery, lameness was obvious only after strenuous exercise. The stifle had 70-degree range of motion.

Fig 5 - Lateral radiograph of the right femur 8 weeks after initial surgery. The soft tissue swelling and calcification in soft tissue have disappeared. The fracture gap is healed and the 2 fragments are incorporated into the femoral shaft. Notice the absence of periosteal new bone formation.
Fig 6 - Craniocaudal radiograph of the right femur 8 weeks after surgery. The fracture is healed.

a) Sulfasol Solution II; Fort Dodge Laboratories, Fort Dadge, Iowa.
b) Penrose Drain, Davol Inc, 100 Sockanosset RI. Cranston, RI.
c) Vicryl, Ethicon Inc, Somerville, NJ.
d) Braunamid, B. Braun, Melsonge AG, Germany.
e) Disulphine Blue, Imperial Chemical Industries Ltd, Pharmaceuticals Division, England.

Discussion

The rate of success for treatment of chronic osteomyelitis in man varies: 33% to 90% for continuous irrigation and suction drainage (11-13), 88% for the gentamicin-methylmethacrylate method (17), and 70% to 90% for open drainage and delayed autogenous cancellous bone grafting (15-22).

Most osteomyelitis in dogs results from open reduction and internal fixation of fractures (4-5). The pathophysiology of osteomyelitis following osteo-synthesis depends on the nature of the injury and the type of fixation (12). The pathogens in intramedullary nailing gain access to the surgical wound, follow the fracture line into the medullary cavity, and expand in the nail bed (12). A secondary intramedullary abscess can develop. The cortex may become necrotic on its endosteal and periosteal surfaces. With bone plate osteosynthesis, infection is usually caused by an infected hematoma over the plate. If early infection remains untreated, the infection spreads over the entire plate and surrounding hematoma (12). Pathogens may infect the intramedullary cavity or the cortex along screw holes or the fracture line, but the development of an extensive intramedullary abscess is extremely rare (12).

An unstable, devascularized cortical fragment is susceptible to sequestration. Bone necrosis appears to be the key to therapeutic problems associated with osteomyelitis (23). Microorganisms, if not removed with the sequestra, can repopulate affected tissues after the initial onset of infection. Acute osteomyelitis can be cured with antibiotics alone only if therapy is given before bone necrosis becomes extensive (24,25), whereas chronic osteomyelitis requires that all dead bone be surgically removed (4,5.7,8,11-17,19,21,22).

Radiography before surgery provides valuable information (10). The involved bone can be affected along a limited portion of its length (cases 1, 4, 5, 7, 9, 11) or along almost the entire length (cases 2, 3, 6, 8). There may be osteolysis (cases 3, 5, 8), little periosteal new bone formation (cases 1, 6, 7, 9), or a combination of osteolysis and much new bone formation (cases 2, 6). This radiologic classification is helpful in determining the amount of saucerization needed and the biologic activity of the infected bone. The persistence of necrotic bone in dog 11 explained the recurrence of the fistulous tract. When pathogens are of low virulence, it may be difficult to differentiate normal bleeding bone from necrotic bone. The use of vital staining is helpful (21). In general, all bone not covered by granulation tissue should be excised (15).

Infected bone can heal if there is rigid fixation (26). In 10 of these 11 animals, the initial fixation was replaced because of instability. In case 8, the Kirschner apparatus used after saucerization in a very osteoporotic radius was replaced after 3 weeks with a plate because of instability. The technique reported here is modified from that previously reported (15), by using fixation at stage 1 rather than at stage 3 of the procedure. This modification prevents destruction of the granulation tissue bed and trauma to the surrounding soft tissue during stage 3.

Drainage and irrigation decrease the virulence of infection (12). The spread of infection from its initial focus is stopped and the inflammation of the soft tissue regresses rapidly. The rapid decrease of inflammation observed in our study may have been secondary to a reduction of prostaglandin locally (27-31). Irrigation should be used in all cases of purulent drainage (12). The advantage of open irrigation and drainage is the elimination of large dead space cavities. Within such cavities, blood clots, serum, and tissue debris provide a medium for additional bacterial proliferation and the growth of fibrous tissue, which walls off the infection site (7). When the wound remains open, all the debris is drained, and healthy granulation tissue finally invades the bony defect and covers only the living bone (15). Visualization of the wound helps in assessing infection and the proper timing for delayed autogenous bone grafting.

A bright red granulation tissue bed begins to appear in open wounds from 3 to 6 days after injury (32). Granulation tissue did not appear until 12 days in cases 8 and 11; these animals were in poor physical condition at admission. The presence of healthy granulation tissue is a requirement for the initiation of stage 3 (Fig 1) of autogenous cancellous bone grafting. The surface cells of autologous cancellous bone grafts are able to survive if properly handled (33). They are important in the production of callus during the phase of early bone formation, which stabilizes the graft-host interface thus allowing early bony revascularization (33). In experimental osteotomy of the dog's ulna followed by autogenous cancellous bone grafting, microangiograms revealed florid vascularization of the entire graft area at 1 week (34). The rapid bone healing seen in our series (4.8 weeks) was thought to be the result of: (1) an excellent vascular supply from the granulation tissue and the regenerated medullary artery; (2) absence of exudate secondary to a septic process or a hematoma that would impair the diffusion of nutrients through plasmatic circulation; (3) mild tissue hyperoxia which enhances bacterial killing and increases resistance to infection; and (4) increased oxygen tension in affected tissues, which favors regeneration of bone by increasing both the synthesis of the collagenous matrix and mineralization (35).

Multiple bacterial species are uncommon in acute osteomyelitis but are commonly recovered from chronic bone infections (36). Staphylococcus aureus was the most common bacteria isolated by us, conforming to the experience of others (9). Gram-negative and anaerobic organisms were frequently isolated in those cases of polymicrobial infections (58% and 18%, respectively). The pathogenic significance of the species isolated in cases of polymicrobial osteomyelitis remains to be established, but anaerobic bacteria appear to play an important role in osteomyelitis (36,37). Repeated cultures are important when the clinical course is not satisfactory. The number of bacteria appears to increase with time when the wound is left open and drained (15). Changes in infecting flora may occur in polymicrobial osteomyelitis, and these changes may alter the selection of antimicrobial therapy and the outcome of the overall treatment.

The advantages of the technique described here are (1) simplicity of drainage, (2) minimal amount of instrumentation required for irrigation and drainage, (3) rapid bone healing which decreases the chances of implant breakdown and allows rapid return to function, and (4) high rate of success, with limited number of complications. However, further histologic and microangiographic investigations of this technique are needed to evaluate the physiologic basis of its success.

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