EXTERNAL SKELETAL FIXATION
0195-5616/92 $0.00
+ .20
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION' FRACTURES WITH EXTERNAL SKELETAL FIXATION James D. Lincoln, DVM, MS
External skeletal fixation (ESF) is an ideal fixation method for treating open diaphyseal fractures and fractures in which union has been delayed or not occurred. Rigid fixation can be achieved with minimal invasion of soft tissues and disruption of blood supply. Because the fixation pins can be placed proximal and distal to the wound of an open fracture, the wound is left accessible for treatment. Once the wound and fracture are stable, the ESF device can be removed without affecting soft tissues or causing discomfort to the patient. When treating delayed union or nonunion fractures, variable amounts of stability can be achieved. As union occurs, rigidity can be decreased, allowing restoration of bone stiffness and function. 6 OPEN FRACTURES Preliminary Management
When an injured dog or cat with an open fracture is presented, immediate concern must be directed at assessing the animal's general condition. Depending on the cause of the open fracture, other injuries From the Department of Veterinary Clinical Medicine and Surgery, Washington State University College of Veterinary Medicine, Pullman, Washington.
VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22' NUMBER 1 • JANUARY 1992
195
196
LINCOLN
may be present. Further wound contamination and hemorrhage can be controlled by placing a clean compression bandage over the wound at the scene of the accident or on arrival at a veterinary emergency care facility. Avoid allowing exposed bone to retract into and contaminate soft tissues. Manipulation of the fracture or probing of the wound before treatment in surgery is unnecessary. Both result in further damage to soft tissues and contamination. 10, 11 Once attention can be directed to definitive treatment of the wound and fracture, the wound should be decontaminated and the damaged area prepared for surgery. Type I open fractures, in which the bone has penetrated the skin, may be the most difficult to recognize since the wound may be quite small and not visible. If such a situation is suspected, hair should be clipped from the area over and surrounding the fracture and the skin carefully examined for evidence of a break. Wounds not discovered result in a missed diagnosis, improper treatment, and infection. 10 Types II and III open fractures are much easier to recognize because
Figure 1. A type II open fracture of the tibia caused by a gunshot.
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
197
of more extensive disruption or loss of soft tissue (Fig. 1). Open fractures caused by trauma are classified as contaminated or infected. A wound is generally considered contaminated if the time since injury has been short (less than 4 to 6 hours) and tissues have been damaged and inoculated with microorganisms that have not yet begun growing in the wound. A wound is considered infected if enough time (more than 6 hours) has passed to allow microorganisms to begin growing ·in the wound. An infected wound is characterized by pain, inflammation, and purulent exudate. The degree of contamination depends on the length of time since injury and the animal's environment. The type of trauma, the amount of traumatized tissue, availability of blood supply, time since injury, degree of contamination, and pathogenicity of bacteria determine when a wound becomes infected. IS Wounds open longer than 6 hours should be considered infected.1O Great care must be taken to avoid further contamination of the wound while the wound is being assessed and treatment started . Radiographs of the fractured bone should be taken once the animal is stabilized and before surgical qebridement and management of the fracture. Radiographic views in two planes, including the joint above and below the fracture, are necessary to assess bone damage fully. Sedation or anesthesia may be required for restraint and proper positioning. Previously placed bandages should not be disturbed during radiography and should be left in place until cleansing and debridement of the wound can be done under aseptic conditions.
Initial Treatment
Aseptic technique, including use of caps, masks, and gloves, must be used when removing bandages and examining the wound. Often organisms cultured from open wounds can be traced to the care center rather than the scene of the injury.1O Selection of antibiotics is based on the type of bacteria expected in the wound, such as Streptococcus spp., Staphylococcus spp., and Escherichia coli. A first-generation cephal()sporin such as cefazolin is an excellent choice because of its resistance to betalactamase inactivation, half-life of 90 to 180 minutes, and good tissue penetration. IS Pasteurella spp. may be found in bite wounds for which penicillin G would be an appropriate choice. 8 Further guidance for choosing an antibiotic can be obtained from a Gram stain revealing the dominant bacterial population in the wound. If gram-negative bacteria are present, an aminoglycoside antibiotic such as gentamicin should be included as part of the antibiotic therapy.4 Intravenous antibiotic therapy is started after culturing the wound, ideally within the first 3 hours after injury before bacteria have begun to multiply or are protected in an organizing hematoma. IS
198
LINCOLN
Definitive Treatment
With the animal heavily sedated or anesthetized, treatment of the wound is performed in three phases: cleansing of the wound, stabilization of the fracture, and definitive treatment of the wound. Cleaning the wound must not be delayed. A common mistake made when transferring animals with open fractures to a referral center is to cover the injury instead of thorougli decontamination. Delay in cleaning the wound produces an infected rather than a less complicated contaminated wound. With the bandage removed, the open wound is covered with sterile water-soluble lubricating gel (K-Y Jelly, Johnson and Johnson, New Brunswick, NJ) or moistened sterile gauze sponges. Hair surrounding the wound is clipped with a no. 40 clipper blade and vacuumed or washed away with warm water. Disinfectants such as 0.05% chlorhexidine can be used. Alcohol or detergents commonly used in scrub solutions cause tissue devitalization and must not come in contact with the wound. A plastic drape is used to isolate the wound area and allow drainage of fluids from the field. Vigorous and copious irrigation of the wound with sterile isotonic saline removes the watersoluble lubricating gel and rinses the wound. Devitalized tissue tends to turn grayish-white with irrigation and is removed by sharp dissection. Disruption of viable soft tissue is avoided. Sharp dissection must be carefully performed to avoid important structures such as nerves or vessels. Thorough irrigation of the wound with sterile isotonic saline will aid in removal of debris and reduce the bacterial population of types II and III wounds. A type I fracture should be opened and evaluated. Irrigation, debridement, and culturing of the wound are indicated. Failure to treat and reducing the fracture in a closed manner can cause an infected fracture. Exposed bone is thoroughly irrigated and wiped clean with sterile moist gauze sponges. Ligation with minimal amounts of monofilament polydioxanone suture (Ethicon, Sommerville, NJ) is used to control hemorrhage . Several sessions may be required for complete debridement and sterilization of the wound. The wound is kept covered with a sterile bandage between treatments . With completion of each session of debridement and cleansing, a culture should be obtained to evaluate the types of bacteria remaining in the wound. Effectiveness of antibiotic therapy and sterility of the wound are determined from the results of culture and sensitivity testing and provide guidance for antibiotic therapy. IS With the wound and exposed bone decontaminated, attention is turned to fracture fixation. Stabilization of the fracture can be performed any time after wound decontamination and debridement. Immediate fixation alleviates pain and discomfort, which reduces stress and may improve the ability of the animal to control infection locally and systemically. With the fracture stabilized, further disruption of the injured area is avoided and the early stages of wound healing, including revascularization, can begin. Revascularization reduces the likelihood of a persistent infection. 10
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
199
If fixation must be delayed, the injured limb should be covered with a sterile dressing and immobilized. For injuries at or below the stifle or elbow joints, a Robert Jones bandage is an ideal method of immobilization. Careful observance of principles and techniques of application of ESF will minimize complications associated with the reduction and stabilization of open fractures. Configuration of the external fixation device is determined by the type and locafion of the fracture(s) . A single fracture involving the diaphysis of the bone will present few problems related to stabilization. Because an open fracture is potentially infected, methods of fixation that tend to spread infection are avoided. Intramedullary pinning may be useful in restoring axial alignment as an adjunct to ESF. Insertion of an intramedullary pin, however, may expose the entire medullary canal to infection.
Application of External Skeletal Fixators
ESF is especially suited for severely comminuted fractures of the tibia and radius. Bone fragments in the fractured area often have soft tissue attachments and a tenuous blood supply if left in place. Fixation pins are applied as far distal and proximal as possible. Following reduction, connecting rods are applied to these pins and alignment is restored. Perfect reduction of fracture fragments is not necessary. Restoration of function of a fractured bone is the primary goal. As long as the joints on either end of the bone are in alignment and function normally, the shape of the healing bone is not a major concern. As stated by Wolff's law, once healing and function return, the bone will remodel along lines of stress and gradually regain its original shape. Therefore, concern should be focused on joint alignment and normal tension and compression relationships across joints. A high incidence of angular limb deformity associated with stabilization of comminuted fractures with ESF has been reported .9 The purpose of the external fixator is to transfer loads from the proximal end of the fractured bone to the external fixator and back to the distal fragment while keeping the fracture fragments stable. The fixation pins and the pattern in which they are arranged must be of adequate strength to allow functional use of the limb, while the fracture fragments remain undisturbed. Generally fractures of the radius and tibia are reduced using a type II configuration (Fig. 2). As many pins as necessary to achieve stability are added while avoiding the fracture site. With rigid fixation, however, periosteal callus will not form and the united fracture will not be as strong as it would be if callus developed. 5 When the distal or proximal fragment is very short, creative placement of fixation pins is required. Emphasis is placed on avoidance of joint surfaces, vessels, nerves, and major muscle masses while
200
LINCOLN
Figure 2. Stabilization of a fracture of the radius using a type II fixator with half and full pins.
placing the pin through the largest transverse diameter of a fragment. Transarticular stabilization may be useful for reducing the load placed on the fixation pin in the small fragment while allowing the small fragment to be stabilized (Fig. 3).16 If bone fragments are missing, a decision must be made to compress the ends of the remaining bone and accept the resulting loss of length or to maintain length and place an autogenous cancellous bone graft in the defect. Up to 20% femoral length has been removed without causing loss of limb function. 7 Clinically acceptable loss of length of other bones has not been reported. Generally, a dog or cat can compensate by increasing the standing angle of the joints of the shortened limb or decreasing the standing angle of the joints of the opposite limb. If autogenous cancellous bone grafting is selected, the technique is usually performed after initial wound healing and reduction of infection. 2 Because the fracture site is potentially infected, the cancellous bone harvest must be performed as a separate procedure to prevent contamination of the donor site. Cortical bone grafts are not recommended primarily because they require long-term rigid fixation but also because they may act as a continued nidus for infection. 12 Large fragments devoid of a blood supply must be rigidly fixed to vascularized bone to reduce the incidence of nonunion and sequestra-
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
201
Figure 3. A, A fracture of the proximal end of the radius and ulna caused by a gunshot, stabilized using transarticular fixation. B, Appearance of the injured area at time of removal of the fixator 8 weeks later. Range of motion was reduced but functional.
202
LINCOLN
tion. Interfragmentary compression by lag screw fixation or cerclage wiring, full or hemicerclage, are appropriate techniques. When using cerclage wiring techniques, specific principles must be followed to avoid 100sening. 3 Rigid fixation of vascularized fragments is not critical. Manipulation of such fragments may disrupt remaining blood supply and cause subsequent loss of viability. By moving larger fragments into alignment, smaller fragments may also be drawn into alignment. Union will occur as the result of secondary bone li.ealing. Following fracture fixation, primary wound closure is performed if the wound is less than 4 to 6 hours old, there is little necrotic tissue or dead space, and good vascularity along with minimal skin tension exists. If dead space or necrosis is present, drainage may be necessary. When drains are used in a wound, the principles of their use must be applied to keep the wound from becoming infected as the result of the presence of the drain. 15 Debrided and sterile wounds that cannot be closed are covered with sterile, moist gauze sponges and cotton roll. Delayed wound closure is performed once the wound is sterile, or it can be allowed to heal by second intention. Skin grafting techniques, when healthy granulation tissue is present, are used to complete wound coverage. 15 As union and stability of the fracture progress, the rigidity of the ESF can be gradually reduced. Often activity of the animal will cause loosening of the fixation pins and the splint. Decreasing rigidity of the splint increases forces across the fracture and may result in increased stiffness across the fracture. 9 Clinical union can be determined by releasing the connecting rods and testing the fracture by gently attempting to bend the bone at the fracture site. If motion is detected or a painful response evoked, the device should be replaced and the limb protected until clinical union is achieved. Once the ESF device is removed, the limb should be protected by restricting the animal's activity or by placing a light support wrap on the limb until adequate bone strength is achieved.
DELAYED UNION AND NONUNION
Use of ESF in treatment of a delayed union or nonunion fracture has the same advantages as treatment of an open fracture. Delayed union can be defined as a fracture that has not healed in the expected time. Fractures in which union does not occur are classified as nonunions. The most common causes of delayed union or nonunion are motion at the fracture site, fracture gap, interposed soft tissue, and poor blood supply. Infection, osteopenia, poor nutrition, or radiation are other causes. 1 When delayed union or nonunion is identified, the cause must be determined to apply effective treatment. Often delayed union will respond by simply improving stability. If infection and drainage are associated with a sequestrum, the dead bone must be removed before treatment of the unstable fracture.
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
203
Radius and Ulna Fractures in Toy Breeds
Radius and ulnar fractures of toy breed dogs stabilized with external coaptation, splints, or casts often result in delayed union or nonunion. If there is any motion at the fracture site causing pain or discomfort, the dog will refuse to use the limb. Decreased use of the limb results in decreased vascularity, which delays union. 13 Healing can be achieved with application of ESF. In dogs weighing less than 5 kg, K-wires (0.045" or 0.062") can be substituted for small fixation pins. The K-wires are applied in a type II configuration and fastened to small connecting rods using small single clamps. Methyl methacrylate rods applied to the pin ends have also been used. Once polymerized, the rigid methyl methacrylate stabilizes the fracture via the fixation pins (Fig. 4A). Methyl methacrylate cannot be adjusted, however, if pin loosening occurs. This may lead to pain, lameness, and failure of the fracture to heal as the result of disuse (Fig. 4B). To avoid this problem, the small single fixation clamps and small connecting rods are used and readily applied to K-wires of all sizes. The use of clamps rather than acrylic bars allows adjustment of the splint and maintenance of stability (Fig. 5). Nonunions
Nonunion fractures are classified as vascular or avascular pseudarthrosis based on radiographic appearance. Vascular nonunion is
Figure 4. A, Delayed union of the radius of a Yorkshire Terrier stabilized with methyl
methacrylate attached to the fixation pins. Illustration continued on following page
204
LINCOLN
Figure 4 (Continued). B, Appearance of the radius after removal of the implants. Note the lack of ossification at the fracture site and large defects created in the radius because the splint could not be adjusted and kept tight.
characterized by callus formation at the fracture site with a radiolucent line through the fracture site. Closed fixation with a type II fixator under compression is often adequate (Fig. 6). Alternatively the fracture site may be opened, fibrous connective tissue removed from the fracture site, and autogenous cancellous bone implanted to improve the potential of bone union. 12. 13 Atrophic or avascular nonunion fractures are characterized by a lack of adequate blood supply for healing. The bone ends tend to be sclerotic, and the medullary cavity is closed. Treatment consists of debriding the bone ends and opening the marrow cavity. Removal of sclerotic bone may result in loss of limb length. Autogenous cancellous bone is placed in the fracture site, and rigid fixation, preferably with compression, must be achieved for union to occur. 1 Pain-free function is essential when treating small dogs since they will not use the limb if pain is present. Active use of the limb increases overall vascularity, which in turn promotes healing. The animal's owner can also help by massaging the limb and providing passive motion for the joints of the limb.
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
205
Figure 5. Bilateral fractures of the radius and ulna of a Chihuahua stabilized using small external fixation clamps attached to K·wire fixation pins.
Limb-Lengthening Procedures
Methods of bone lengthening, currently being applied to lengthen limbs of humans, can be applied to veterinary patients. The Ilizarov method of limb lengthening l4 can be adapted but would require excellent owner compliance. Basically the fracture is compressed for a short period of time, usually 7 days, then distracted at the rate of 1 mm per day until adequate length is gained. Obviously the external fixation apparatus used in this method is more complex than clamps, fixation pins, and connecting rods. As the fractured bone regains stability, rigidity of the external fixation splint should be gradually reduced by removing the pins nearest the fracture site. Once adequat~ stiffness, as determined by loosening the splint and testing for clinical union, occurs, the external fixator is removed. The healing bone should be protected with a bandage or by restricting patient activity as strength is regained. The final decision to remove protection and restrictions is based on radiographic evidence of adequate healing and clinical judgment.
206
LINCOLN
Figure 6. A, Hypertrophic nonunion of 1 year's duration. B, Stabilization of the hypertrophic nonunion with type II fixation; clinical union was established 13 weeks later.
SUMMARY
ESF is useful in treatment of open fractures and delayed union and nonunion fractures. The fixation pins can be placed away from the fracture site to avoid disruption of blood supply. The appliance is well tolerated and inexpensive, and many of the parts can be reused. Adjustment of the splint is possible to permit correction of stabilization for optimal results. Gradual reduction of frame rigidity improves the quality of healing by increasing the stress on the bone. As stiffness of the healing fracture increases, return of limb function occurs. Early fixator removal reduces patient morbidity and permits a return to normal activity.
References 1. Aron ON: Delayed union and nonunion. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery, ed 2. Philadelphia, Lea & Febiger, 1990, pp 895-901
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
207
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. Brinker WO, Piermattei DL, Flo GL: Cerclage or hemicerclage wire. In Handbook of Small Animal Orthopedics and Fracture Treatment, ed 2. Philadelphia, WB Saunders, 1990, pp 32-34 4. Brown SA: Treatment of gram-negative infections. Vet Clin North Am Small Anim Pract 18:1141-1165, 1988 5. Chao EYS, Aro HT, Lewallen DG, Kelly PJ: The effec.,t of rigidity on fracture healing in external fixation. Clin Orthop ReI Res 241:24-35, 1989 6. Egger EL: Advantages of external fixation . Vet Med Proc 1:263-266, 1989 7. Franczuszki 0, Chalman JA, Butler HC, DeBowes RM, Leipold H: Postoperative effects of experimental femoral shortening in the mature dog. J Am Anim Hosp Assoc 23:429-437, 1987 8. Greene CE, Lockwood R, Goldstein EJC: Dog and cat bite infections. In Greene CE (ed): Infectious Diseases of the Dog and Cat. Philadelphia, WB Saunders, 1990, pp 614-618 9. Johnson AL, Kneller SK: Radial and tibial fracture repair with external skeletal fixation . Effects of fracture type, reduction, and complications on healing. Vet Surg 18:367-372, 1989 10. Nunamaker OM: Treatment of open fractures in small animals. Comp Cont Ed Pract Vet 1:66-75, 1979 11. Nunamaker OM: Management of the open fracture. In Newton CD, Nunamaker OM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, pp 481-485 12. Nunamaker OM, Rhinelander FW: Bone grafting. In Newton CD, Nunamaker OM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, pp 519-526 13. Nunamaker OM, Rhinelander FW, Heppenstall RB: Delayed union, and malunion. In Newton CD, Nunamaker OM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, pp 511-518 14. Schwartsman V, Choi SH, Schwartsman R: Tibial non unions: Treatment tactics with the Ilizarov Method. Orthop Clin North Am 21:639-653, 1990 15. Swaim SF, Henderson RA: Wound Management. In Small Animal Wound Management. Philadelphia, Lea & Febiger, 1990, pp 9-33 16. Toombs JP, Aron ON, Basinger RR: Angled connecting bars for transarticular application of Kirschner-Ehmer external fixation splints. J Am Anim Hosp Assoc 25:213-216, 1989
Address reprint requests to James D. Lincoln, DVM, MS Department of Veterinary Clinical Medicine and Surgery Washington State University College of Veterinary Medicine Pullman, WA 99164-6610
0195-5616/92 $0.00
+ .20
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION' FRACTURES WITH EXTERNAL SKELETAL FIXATION James D. Lincoln, DVM, MS
External skeletal fixation (ESF) is an ideal fixation method for treating open diaphyseal fractures and fractures in which union has been delayed or not occurred. Rigid fixation can be achieved with minimal invasion of soft tissues and disruption of blood supply. Because the fixation pins can be placed proximal and distal to the wound of an open fracture, the wound is left accessible for treatment. Once the wound and fracture are stable, the ESF device can be removed without affecting soft tissues or causing discomfort to the patient. When treating delayed union or nonunion fractures, variable amounts of stability can be achieved. As union occurs, rigidity can be decreased, allowing restoration of bone stiffness and function. 6 OPEN FRACTURES Preliminary Management
When an injured dog or cat with an open fracture is presented, immediate concern must be directed at assessing the animal's general condition. Depending on the cause of the open fracture, other injuries From the Department of Veterinary Clinical Medicine and Surgery, Washington State University College of Veterinary Medicine, Pullman, Washington.
VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22' NUMBER 1 • JANUARY 1992
195
196
LINCOLN
may be present. Further wound contamination and hemorrhage can be controlled by placing a clean compression bandage over the wound at the scene of the accident or on arrival at a veterinary emergency care facility. Avoid allowing exposed bone to retract into and contaminate soft tissues. Manipulation of the fracture or probing of the wound before treatment in surgery is unnecessary. Both result in further damage to soft tissues and contamination. 10, 11 Once attention can be directed to definitive treatment of the wound and fracture, the wound should be decontaminated and the damaged area prepared for surgery. Type I open fractures, in which the bone has penetrated the skin, may be the most difficult to recognize since the wound may be quite small and not visible. If such a situation is suspected, hair should be clipped from the area over and surrounding the fracture and the skin carefully examined for evidence of a break. Wounds not discovered result in a missed diagnosis, improper treatment, and infection. 10 Types II and III open fractures are much easier to recognize because
Figure 1. A type II open fracture of the tibia caused by a gunshot.
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
197
of more extensive disruption or loss of soft tissue (Fig. 1). Open fractures caused by trauma are classified as contaminated or infected. A wound is generally considered contaminated if the time since injury has been short (less than 4 to 6 hours) and tissues have been damaged and inoculated with microorganisms that have not yet begun growing in the wound. A wound is considered infected if enough time (more than 6 hours) has passed to allow microorganisms to begin growing ·in the wound. An infected wound is characterized by pain, inflammation, and purulent exudate. The degree of contamination depends on the length of time since injury and the animal's environment. The type of trauma, the amount of traumatized tissue, availability of blood supply, time since injury, degree of contamination, and pathogenicity of bacteria determine when a wound becomes infected. IS Wounds open longer than 6 hours should be considered infected.1O Great care must be taken to avoid further contamination of the wound while the wound is being assessed and treatment started . Radiographs of the fractured bone should be taken once the animal is stabilized and before surgical qebridement and management of the fracture. Radiographic views in two planes, including the joint above and below the fracture, are necessary to assess bone damage fully. Sedation or anesthesia may be required for restraint and proper positioning. Previously placed bandages should not be disturbed during radiography and should be left in place until cleansing and debridement of the wound can be done under aseptic conditions.
Initial Treatment
Aseptic technique, including use of caps, masks, and gloves, must be used when removing bandages and examining the wound. Often organisms cultured from open wounds can be traced to the care center rather than the scene of the injury.1O Selection of antibiotics is based on the type of bacteria expected in the wound, such as Streptococcus spp., Staphylococcus spp., and Escherichia coli. A first-generation cephal()sporin such as cefazolin is an excellent choice because of its resistance to betalactamase inactivation, half-life of 90 to 180 minutes, and good tissue penetration. IS Pasteurella spp. may be found in bite wounds for which penicillin G would be an appropriate choice. 8 Further guidance for choosing an antibiotic can be obtained from a Gram stain revealing the dominant bacterial population in the wound. If gram-negative bacteria are present, an aminoglycoside antibiotic such as gentamicin should be included as part of the antibiotic therapy.4 Intravenous antibiotic therapy is started after culturing the wound, ideally within the first 3 hours after injury before bacteria have begun to multiply or are protected in an organizing hematoma. IS
198
LINCOLN
Definitive Treatment
With the animal heavily sedated or anesthetized, treatment of the wound is performed in three phases: cleansing of the wound, stabilization of the fracture, and definitive treatment of the wound. Cleaning the wound must not be delayed. A common mistake made when transferring animals with open fractures to a referral center is to cover the injury instead of thorougli decontamination. Delay in cleaning the wound produces an infected rather than a less complicated contaminated wound. With the bandage removed, the open wound is covered with sterile water-soluble lubricating gel (K-Y Jelly, Johnson and Johnson, New Brunswick, NJ) or moistened sterile gauze sponges. Hair surrounding the wound is clipped with a no. 40 clipper blade and vacuumed or washed away with warm water. Disinfectants such as 0.05% chlorhexidine can be used. Alcohol or detergents commonly used in scrub solutions cause tissue devitalization and must not come in contact with the wound. A plastic drape is used to isolate the wound area and allow drainage of fluids from the field. Vigorous and copious irrigation of the wound with sterile isotonic saline removes the watersoluble lubricating gel and rinses the wound. Devitalized tissue tends to turn grayish-white with irrigation and is removed by sharp dissection. Disruption of viable soft tissue is avoided. Sharp dissection must be carefully performed to avoid important structures such as nerves or vessels. Thorough irrigation of the wound with sterile isotonic saline will aid in removal of debris and reduce the bacterial population of types II and III wounds. A type I fracture should be opened and evaluated. Irrigation, debridement, and culturing of the wound are indicated. Failure to treat and reducing the fracture in a closed manner can cause an infected fracture. Exposed bone is thoroughly irrigated and wiped clean with sterile moist gauze sponges. Ligation with minimal amounts of monofilament polydioxanone suture (Ethicon, Sommerville, NJ) is used to control hemorrhage . Several sessions may be required for complete debridement and sterilization of the wound. The wound is kept covered with a sterile bandage between treatments . With completion of each session of debridement and cleansing, a culture should be obtained to evaluate the types of bacteria remaining in the wound. Effectiveness of antibiotic therapy and sterility of the wound are determined from the results of culture and sensitivity testing and provide guidance for antibiotic therapy. IS With the wound and exposed bone decontaminated, attention is turned to fracture fixation. Stabilization of the fracture can be performed any time after wound decontamination and debridement. Immediate fixation alleviates pain and discomfort, which reduces stress and may improve the ability of the animal to control infection locally and systemically. With the fracture stabilized, further disruption of the injured area is avoided and the early stages of wound healing, including revascularization, can begin. Revascularization reduces the likelihood of a persistent infection. 10
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
199
If fixation must be delayed, the injured limb should be covered with a sterile dressing and immobilized. For injuries at or below the stifle or elbow joints, a Robert Jones bandage is an ideal method of immobilization. Careful observance of principles and techniques of application of ESF will minimize complications associated with the reduction and stabilization of open fractures. Configuration of the external fixation device is determined by the type and locafion of the fracture(s) . A single fracture involving the diaphysis of the bone will present few problems related to stabilization. Because an open fracture is potentially infected, methods of fixation that tend to spread infection are avoided. Intramedullary pinning may be useful in restoring axial alignment as an adjunct to ESF. Insertion of an intramedullary pin, however, may expose the entire medullary canal to infection.
Application of External Skeletal Fixators
ESF is especially suited for severely comminuted fractures of the tibia and radius. Bone fragments in the fractured area often have soft tissue attachments and a tenuous blood supply if left in place. Fixation pins are applied as far distal and proximal as possible. Following reduction, connecting rods are applied to these pins and alignment is restored. Perfect reduction of fracture fragments is not necessary. Restoration of function of a fractured bone is the primary goal. As long as the joints on either end of the bone are in alignment and function normally, the shape of the healing bone is not a major concern. As stated by Wolff's law, once healing and function return, the bone will remodel along lines of stress and gradually regain its original shape. Therefore, concern should be focused on joint alignment and normal tension and compression relationships across joints. A high incidence of angular limb deformity associated with stabilization of comminuted fractures with ESF has been reported .9 The purpose of the external fixator is to transfer loads from the proximal end of the fractured bone to the external fixator and back to the distal fragment while keeping the fracture fragments stable. The fixation pins and the pattern in which they are arranged must be of adequate strength to allow functional use of the limb, while the fracture fragments remain undisturbed. Generally fractures of the radius and tibia are reduced using a type II configuration (Fig. 2). As many pins as necessary to achieve stability are added while avoiding the fracture site. With rigid fixation, however, periosteal callus will not form and the united fracture will not be as strong as it would be if callus developed. 5 When the distal or proximal fragment is very short, creative placement of fixation pins is required. Emphasis is placed on avoidance of joint surfaces, vessels, nerves, and major muscle masses while
200
LINCOLN
Figure 2. Stabilization of a fracture of the radius using a type II fixator with half and full pins.
placing the pin through the largest transverse diameter of a fragment. Transarticular stabilization may be useful for reducing the load placed on the fixation pin in the small fragment while allowing the small fragment to be stabilized (Fig. 3).16 If bone fragments are missing, a decision must be made to compress the ends of the remaining bone and accept the resulting loss of length or to maintain length and place an autogenous cancellous bone graft in the defect. Up to 20% femoral length has been removed without causing loss of limb function. 7 Clinically acceptable loss of length of other bones has not been reported. Generally, a dog or cat can compensate by increasing the standing angle of the joints of the shortened limb or decreasing the standing angle of the joints of the opposite limb. If autogenous cancellous bone grafting is selected, the technique is usually performed after initial wound healing and reduction of infection. 2 Because the fracture site is potentially infected, the cancellous bone harvest must be performed as a separate procedure to prevent contamination of the donor site. Cortical bone grafts are not recommended primarily because they require long-term rigid fixation but also because they may act as a continued nidus for infection. 12 Large fragments devoid of a blood supply must be rigidly fixed to vascularized bone to reduce the incidence of nonunion and sequestra-
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
201
Figure 3. A, A fracture of the proximal end of the radius and ulna caused by a gunshot, stabilized using transarticular fixation. B, Appearance of the injured area at time of removal of the fixator 8 weeks later. Range of motion was reduced but functional.
202
LINCOLN
tion. Interfragmentary compression by lag screw fixation or cerclage wiring, full or hemicerclage, are appropriate techniques. When using cerclage wiring techniques, specific principles must be followed to avoid 100sening. 3 Rigid fixation of vascularized fragments is not critical. Manipulation of such fragments may disrupt remaining blood supply and cause subsequent loss of viability. By moving larger fragments into alignment, smaller fragments may also be drawn into alignment. Union will occur as the result of secondary bone li.ealing. Following fracture fixation, primary wound closure is performed if the wound is less than 4 to 6 hours old, there is little necrotic tissue or dead space, and good vascularity along with minimal skin tension exists. If dead space or necrosis is present, drainage may be necessary. When drains are used in a wound, the principles of their use must be applied to keep the wound from becoming infected as the result of the presence of the drain. 15 Debrided and sterile wounds that cannot be closed are covered with sterile, moist gauze sponges and cotton roll. Delayed wound closure is performed once the wound is sterile, or it can be allowed to heal by second intention. Skin grafting techniques, when healthy granulation tissue is present, are used to complete wound coverage. 15 As union and stability of the fracture progress, the rigidity of the ESF can be gradually reduced. Often activity of the animal will cause loosening of the fixation pins and the splint. Decreasing rigidity of the splint increases forces across the fracture and may result in increased stiffness across the fracture. 9 Clinical union can be determined by releasing the connecting rods and testing the fracture by gently attempting to bend the bone at the fracture site. If motion is detected or a painful response evoked, the device should be replaced and the limb protected until clinical union is achieved. Once the ESF device is removed, the limb should be protected by restricting the animal's activity or by placing a light support wrap on the limb until adequate bone strength is achieved.
DELAYED UNION AND NONUNION
Use of ESF in treatment of a delayed union or nonunion fracture has the same advantages as treatment of an open fracture. Delayed union can be defined as a fracture that has not healed in the expected time. Fractures in which union does not occur are classified as nonunions. The most common causes of delayed union or nonunion are motion at the fracture site, fracture gap, interposed soft tissue, and poor blood supply. Infection, osteopenia, poor nutrition, or radiation are other causes. 1 When delayed union or nonunion is identified, the cause must be determined to apply effective treatment. Often delayed union will respond by simply improving stability. If infection and drainage are associated with a sequestrum, the dead bone must be removed before treatment of the unstable fracture.
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
203
Radius and Ulna Fractures in Toy Breeds
Radius and ulnar fractures of toy breed dogs stabilized with external coaptation, splints, or casts often result in delayed union or nonunion. If there is any motion at the fracture site causing pain or discomfort, the dog will refuse to use the limb. Decreased use of the limb results in decreased vascularity, which delays union. 13 Healing can be achieved with application of ESF. In dogs weighing less than 5 kg, K-wires (0.045" or 0.062") can be substituted for small fixation pins. The K-wires are applied in a type II configuration and fastened to small connecting rods using small single clamps. Methyl methacrylate rods applied to the pin ends have also been used. Once polymerized, the rigid methyl methacrylate stabilizes the fracture via the fixation pins (Fig. 4A). Methyl methacrylate cannot be adjusted, however, if pin loosening occurs. This may lead to pain, lameness, and failure of the fracture to heal as the result of disuse (Fig. 4B). To avoid this problem, the small single fixation clamps and small connecting rods are used and readily applied to K-wires of all sizes. The use of clamps rather than acrylic bars allows adjustment of the splint and maintenance of stability (Fig. 5). Nonunions
Nonunion fractures are classified as vascular or avascular pseudarthrosis based on radiographic appearance. Vascular nonunion is
Figure 4. A, Delayed union of the radius of a Yorkshire Terrier stabilized with methyl
methacrylate attached to the fixation pins. Illustration continued on following page
204
LINCOLN
Figure 4 (Continued). B, Appearance of the radius after removal of the implants. Note the lack of ossification at the fracture site and large defects created in the radius because the splint could not be adjusted and kept tight.
characterized by callus formation at the fracture site with a radiolucent line through the fracture site. Closed fixation with a type II fixator under compression is often adequate (Fig. 6). Alternatively the fracture site may be opened, fibrous connective tissue removed from the fracture site, and autogenous cancellous bone implanted to improve the potential of bone union. 12. 13 Atrophic or avascular nonunion fractures are characterized by a lack of adequate blood supply for healing. The bone ends tend to be sclerotic, and the medullary cavity is closed. Treatment consists of debriding the bone ends and opening the marrow cavity. Removal of sclerotic bone may result in loss of limb length. Autogenous cancellous bone is placed in the fracture site, and rigid fixation, preferably with compression, must be achieved for union to occur. 1 Pain-free function is essential when treating small dogs since they will not use the limb if pain is present. Active use of the limb increases overall vascularity, which in turn promotes healing. The animal's owner can also help by massaging the limb and providing passive motion for the joints of the limb.
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
205
Figure 5. Bilateral fractures of the radius and ulna of a Chihuahua stabilized using small external fixation clamps attached to K·wire fixation pins.
Limb-Lengthening Procedures
Methods of bone lengthening, currently being applied to lengthen limbs of humans, can be applied to veterinary patients. The Ilizarov method of limb lengthening l4 can be adapted but would require excellent owner compliance. Basically the fracture is compressed for a short period of time, usually 7 days, then distracted at the rate of 1 mm per day until adequate length is gained. Obviously the external fixation apparatus used in this method is more complex than clamps, fixation pins, and connecting rods. As the fractured bone regains stability, rigidity of the external fixation splint should be gradually reduced by removing the pins nearest the fracture site. Once adequat~ stiffness, as determined by loosening the splint and testing for clinical union, occurs, the external fixator is removed. The healing bone should be protected with a bandage or by restricting patient activity as strength is regained. The final decision to remove protection and restrictions is based on radiographic evidence of adequate healing and clinical judgment.
206
LINCOLN
Figure 6. A, Hypertrophic nonunion of 1 year's duration. B, Stabilization of the hypertrophic nonunion with type II fixation; clinical union was established 13 weeks later.
SUMMARY
ESF is useful in treatment of open fractures and delayed union and nonunion fractures. The fixation pins can be placed away from the fracture site to avoid disruption of blood supply. The appliance is well tolerated and inexpensive, and many of the parts can be reused. Adjustment of the splint is possible to permit correction of stabilization for optimal results. Gradual reduction of frame rigidity improves the quality of healing by increasing the stress on the bone. As stiffness of the healing fracture increases, return of limb function occurs. Early fixator removal reduces patient morbidity and permits a return to normal activity.
References 1. Aron ON: Delayed union and nonunion. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery, ed 2. Philadelphia, Lea & Febiger, 1990, pp 895-901
TREATMENT OF OPEN, DELAYED UNION, AND NONUNION FRACTURES
207
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. Brinker WO, Piermattei DL, Flo GL: Cerclage or hemicerclage wire. In Handbook of Small Animal Orthopedics and Fracture Treatment, ed 2. Philadelphia, WB Saunders, 1990, pp 32-34 4. Brown SA: Treatment of gram-negative infections. Vet Clin North Am Small Anim Pract 18:1141-1165, 1988 5. Chao EYS, Aro HT, Lewallen DG, Kelly PJ: The effec.,t of rigidity on fracture healing in external fixation. Clin Orthop ReI Res 241:24-35, 1989 6. Egger EL: Advantages of external fixation . Vet Med Proc 1:263-266, 1989 7. Franczuszki 0, Chalman JA, Butler HC, DeBowes RM, Leipold H: Postoperative effects of experimental femoral shortening in the mature dog. J Am Anim Hosp Assoc 23:429-437, 1987 8. Greene CE, Lockwood R, Goldstein EJC: Dog and cat bite infections. In Greene CE (ed): Infectious Diseases of the Dog and Cat. Philadelphia, WB Saunders, 1990, pp 614-618 9. Johnson AL, Kneller SK: Radial and tibial fracture repair with external skeletal fixation . Effects of fracture type, reduction, and complications on healing. Vet Surg 18:367-372, 1989 10. Nunamaker OM: Treatment of open fractures in small animals. Comp Cont Ed Pract Vet 1:66-75, 1979 11. Nunamaker OM: Management of the open fracture. In Newton CD, Nunamaker OM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, pp 481-485 12. Nunamaker OM, Rhinelander FW: Bone grafting. In Newton CD, Nunamaker OM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, pp 519-526 13. Nunamaker OM, Rhinelander FW, Heppenstall RB: Delayed union, and malunion. In Newton CD, Nunamaker OM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, pp 511-518 14. Schwartsman V, Choi SH, Schwartsman R: Tibial non unions: Treatment tactics with the Ilizarov Method. Orthop Clin North Am 21:639-653, 1990 15. Swaim SF, Henderson RA: Wound Management. In Small Animal Wound Management. Philadelphia, Lea & Febiger, 1990, pp 9-33 16. Toombs JP, Aron ON, Basinger RR: Angled connecting bars for transarticular application of Kirschner-Ehmer external fixation splints. J Am Anim Hosp Assoc 25:213-216, 1989
Address reprint requests to James D. Lincoln, DVM, MS Department of Veterinary Clinical Medicine and Surgery Washington State University College of Veterinary Medicine Pullman, WA 99164-6610
