0195-5616/92 $0.00
EXTERNAL SKELETAL FIXATION
+ .20
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION Joseph Harari, DVM, MS
In medical terminology, a complication is a secondary condition developing in the course of a primary disease.23 A complication appears unexpectedly and causes change in existing plans, methods, or attitudes. Complications associated with external skeletal fixation (ESF) can affect bone and soft tissue healing and often require change in treatment protocol. As with complications following other surgical techniques, complications of ESF occur as a consequence of failure in following basic guidelines and principles. Complications of ESF can be classified as pin tract infections, fixator problems, and impalement of neurovascular/muscular tissues (Table 1). The earliest description of ESF-related complications was by Parkhill, 21 who described in 1897 chronic drainage and infection in one patient and bone refractures in two patients treated with his adjustable, external bone clamp. PIN TRACT INFECTION
Pin tract sepsis is caused by necrosis and infection of soft and osseous tissues around the pin.13 Excessive pin motion directly contributes to the infection. Pin tract sepsis can be divided into major or minor conditions depending on the degrees of inflammation and patient discomfort, character of the drainage, and required treatment.13 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
99
100
HARARI
Table 1. CLASSIFICATION OF COMPLICATIONS ASSOCIATED WITH EXTERNAL SKELETAL FIXATION Pin tract infections Soft tissue sepsis Focal osteomyelitis Ring sequestrum Fixator problems • Premature pin loosening Unstable configuration Pressure necrosis of skin Tardy bone union Iatrogenic bone fracture Soft tissue impalement Neurovascular bundles Muscular tissue
Minor Pin Tract Infection
Minor drainage is characterized by a slight, sterile, serous drainage; minimal tissue inflammation; and little patient discomfort (Fig. 1).1, 13 It is considered a mild, normal consequence of transfixation, although controversy exists among surgeons regarding the need for treatment. Some clinicians prefer to allow this cutaneous drainage to form a sterile crust and possible barrier to infection,s, 10, 22 Other surgeons prefer to clean the pin sites daily with various solutions (soap and water, 2% hydrogen peroxide, 0.05% chlorhexidine, 0.1% betadine, sterile saline) to permit external drainage and avoid infection. 2 , 4, 13, 18 Major Pin Tract Infection
Major pin tract sepsis is caused by invasion of necrotic tissue by skin bacteria around the pin. It is characterized by persistent and excessive purulent drainage associated with soft tissue inflammation and patient discomfort (Fig. 2). In humans, Staphylococcus aureus, Pseudomonas aeruginosa, Proteus mirabilis, and Serratia marcescens are the most commonly isolated pathogens from pin tract infections.14 In dogs, Staphylococcus intermedius is the primary bacterial pathogen of skin, although polymicrobial infec~ tions occur in skin wounds. 15 In a retrospective review (unpublished data) of bacterial cultures from major pin tract drainages of dogs treated at the Washington State University Teaching Hospital (WSU-VMTH), the most commonly isolated bacteria were Staphylococcus intermedius, Corynebacterium pyogenes, and Pasteurella multocida. Focal osteomyelitis associated with pin tract sepsis has been described in dogs, although the clinical significance of the radiographic changes was questioned since lesions regressed without treatment in some patients,16 Radiographic changes included soft tissue swelling,
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION
101
Figure 1. Minor or normal pin-tract drainage characterized by formation of a serous crust. There is minimal soft-tissue irritation.
periosteal reaction, cortical lysis, and increased medullary density adjacent to the pin. Ring sequestrum secondary to pin tract osteomyelitis is an uncommon yet serious consequence of local infection. 17, 19 Radiographically the lesion is characterized by a zone of osteosclerosis, adjacent to the pin tract, surrounded by another zone of osteolysis. The sequestered bone may serve as a nidus for infection and refracture as a result of weakness. Generalized osteomyelitis associated with ESF has not been well documented, although a potential exists for spreading infection if percutaneous pins are passed through contaminated tissues. Pin tract infection can be minimized by reducing skin tension around the pin, avoiding thermal necrosis of bone during pin insertion, and limiting pin-bone and pin-skin motions. 1,3-5, 13 Skin tension can be reduced by enlarging pin entry and exit sites with incisions 1 to 2 cm in length. Alignment of fracture segments and overlying soft tissues and skin before pin insertion also reduces skin tension. Thermal
102
HARARI
Figure 2. Major pin-tract infection characterized by persistent drainage and soft-tissue inflammation.
necrosis of bone can be avoided by inserting pins with a hand or lowspeed (150 RPM) power drill. Predrilling with a bit smaller in diameter than the pin limits necrosis associated with forceful insertion and pin tract enlargement associated with wobbling during hand insertion. To eliminate pin-bone and pin-skin motions, some surgeons recommend placement of bandage material between skin and fixator, restriction of patient activity, and use of partially threaded pins engaged in the transcortex.1, 3, 13 Pin-bone motion will also be reduced if bone necrosis is avoided by proper pin insertion as previously described. Treatment of major pin tract sepsis includes daily cleansing of affected sites with an antiseptic solution to promote drainage of purulent materiaL!' 3, 4, 13 In addition, topical antistaphylococcal antibiotic ointment and bandages are placed at the pin site to reduce infection and pin-skin motion. Loose pins need to be removed and focal osteomyelitis/ring sequestrum treated by curettage of necrotic bone, cancellous bone grafting, and systemic antibiotics based on bacterial culture and antibiotic sensitivity assays.17 Aggressive therapy of these focal bone lesions should provide satisfactory clinical results. FIXATOR PROBLEMS
Problems with external fixators include premature (before fracture healing) pin loosening, unstable configurations, pressure necrosis of skin from overlying clamps and bar, tardy bone union, and iatrogenic bone fracture. 1, 3, 4, 10, 11
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION
103
Premature Pin Loosening
Premature pin loosening is characterized by an acute onset of lameness during an otherwise uneventful postoperative healing process. Osteolysis around pins and pin migration are visible in radiographs. Causes of premature pin loosening include thermal necrosis of bone and soft tissue during high-speed pin insertism; pin placement into osteopenic bone; increased diameter of pin tracts due to wobbling during hand insertion; placement of pins at an improper angle, into bone cracks or fissures, or too near a fracture line; use of improper pin size; and excessive patient activity during the postoperative period. 4 , 6, 13 Prevention of pin loosening can be accomplished by following basic guidelines during application of the fixator.1, 3, 6, 7, 10 These recommendations include low-speed (150 RPM) or hand drill insertions of trochar pointed pins into a smaller, predrilled hole; use of a drill sleeve to protect adjacent soft tissues; inserting pins 2 cm away from fractures or fissures; engaging near and far cortices during pin insertion; placing pins at an angle of 60 to 70 degrees to the long axis of the bone; using partially threaded pins engaged in the far cortex; and using pins whose diameter does not exceed 20% to 30% of the bone diameter. With endthreaded pins placement of the threaded-nonthreaded shaft junction in the medullary canal has also been recommended to reduce stress and prevent pin breakage or loosening. 20 Unstable Configuration
An unstable configuration can be associated with inadequate preoperative assessment of fracture repair and using a fixator beyond its capabilities. Stability of the external fixator can be improved by following guidelines for proper pin insertion (see earlier), placing the device on the tension side of the bone, spreading pins along the shaft of the bone, using a combination of threaded and smooth pins, and developing uniplanar or multi planar configurations with single clamps and several connecting bars. 1-3, 7-9 Supplemental fixation of fractures with interfragmentary screws, cerclage and Kirschner wires, and intramedullary pins can also improve bone stability and enhance healing. Pressure Necrosis of Skin
Pressure necrosis of skin occurs if pin clamps and bar are placed too close to the skin surface, thus providing insufficient space for postoperative tissue swelling. The condition may occur with fractures above the elbow and stifle joints involving heavily damaged muscles. Skin necrosis can be avoided by placing the pin clamps 1 to 2 cm away from the skin surface and using bandage dressings during the immediate postoperative period to reduce swelling. 2, 7, 13 Treatments for skin
104
HARARI
necrosis include clamp and bar adjustment away from the skin, hydrotherapy or physical therapy to reduce tissue swelling, and topical medication of affected sites. Tardy Bone Union
When used properly, external fixators are infrequently associated with nonunions. These cases are characterized by severe bone comminution, poor reduction of fragments, rigid fixation, and osseous defects.3, 13, 15 Delayed or absent healing can be avoided by accurate fracture reduction, cancellous bone grafting, and staged pin removal to load the bone. l , 13 Conversion of a type II or III external fixator to a type I by removal of the connecting bars and clamps decreases stress protection of bone and stimulates ossification. Staged disassembly can be performed at 2-week or monthly intervals during the healing process. With a type I unilateral fixator, moving the clamps and connecting bar(s) away from the limb will also reduce the stiffness of the configuration. 13
Iatrogenic Bone Fracture
Iatrogenic bone fracture can occur if transfixation pins are inserted into fissures, superficial cortical areas, and osteopenic bone. l , 4, 10, 13 Additionally, pin diameters should not exceed 20% to 30% of the bone diameter. I, 7 Prevention of iatrogenic bone fracture requires observance of pin insertion guidelines as previously described. Treatment requires removal and proper reinsertion of the pins or using alternate modes of fixation.
SOFT TISSUE IMPALEMENT Neurovascular Bundles
External fixator-related nerve or vessel injury is uncommon. Neurovascular bundles are usually pushed aside rather than being transfixed by percutaneous pins. 13 Knowledge of regional anatomy aids in proper pin placement through safe tissue "corridors" and reduces risk of neurovascular injury. Pin tract hemorrhage following pin placement in the proximal aspect of the tibia has been reported, although the source of the hemorrhage was not identified.16 At the WSU-VMTH, three dogs during the past 5 years (unpublished data) had profuse hemorrhage during repair of radial fractures with ESF (Fig. 3). The source of the bleeding was suspected pin trauma to the interosseous
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION
105
Figure 3. Swollen antebrachium caused by profuse hemorrhage during pin placement of an external skeletal fixator in a dog.
branches of the median artery (Fig. 4). Treatments included pin removal, temporary cancellation of surgery, and Robert Jones bandaging for 24 to 48 hours. Muscular Tissue Muscular impalement and injury from transfixation pins can occur if pins are placed through myotendinous structures. Clinical characteristics of tissue impalement include excessive pin tract drainage, muscular pain and discomfort, reduced physical activity, and decreased joint mobility. I, 4,13 Treatment of this condition involves pin removal, insertion at another site, or selection of an alternate mode of fixation. Quadriceps contracture has been described in a young dog with a femoral fracture treated with a type I biplanar splint. 12 A double bar uniplanar configuration is preferred in these cases to avoid pinning of the quadriceps muscles. 1, 12
.
SUMMARY Complications associated with ESF can deleteriously affect soft tissue and bone healing. Adherence to proper surgical techniques and guidelines will minimize development of ESF-related complications. The most common problems associated with ESF are pin tract infections, fixator problems, and soft tissue impalement. These complications can be avoided by using proper pin insertion techniques that reduce skin tension; pin-bone, pin-skin motion; and soft tissue trauma. In addition, proper selection of pins (size, threaded or smooth), fixator
106
HARARI
aroc,f, roJ- -
~
: :., ~Cofloterol ulnor
Pro);, colla teral ra dial, -
Oist coifateral rodioJ- - -
-Col/ateral "Inar,
cutoneous br.
Medion-
Common
i' l1t erosseous ~ ~
,.
N
~ Prox.
dorsal ,'nterosseous
Prox. collot rodlol, lot br: - - -
Po/ma r
loterosseous -
'A cC~SSO ( !j
interosseous
Pro x, collat. rodlol medbr: .
Rod io/- -
- - Ulnar
- - -Pol mar interosseous
Ro d fof, dorsa! br:'-- - Rodio/ ~ palmar br:
Figure 4. Arteries of the right antebrachium, medial aspect. (From Evans HE, Christansen GC (eds): Miller's Anatomy of the Dog, ed 2. Philadelphia, WB Saunders, 1979, p 703.)
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION
107
configuration, ancillary implants, and a cancellous bone graft further reduce the risk of complications and inadequate healing.
References 1. Aron DN: External skeletal fixation. Vet Med Rep 1:181, 1989 2. Aron DN, Toombs JP: Updated principles of external skeletal fixation. Comp Cont Ed Pract Vet 6:845, 1984 3. Aron DN, Toombs JP, Hollingsworth SC: Primary treatment of severe fractures by external skeletal fixation: Threaded pins compared with smooth pins. J Am Anim Hosp Assoc 22:659, 1986 4. Behrens F: General theory and principles of external fixation . Clin Orthop Rei Res 24:15, 1989 5. Boothe HW, Tangner CH: Clinical application of the Kirschner apparatus in long bone fractures. J Am Anim Hosp Assoc 19:679, 1983 6. Brinker WO, Flo GL: Principles and application of external skeletal fixation. Vet Clin North Am Small Anim Pract 5:197, 1975 7. Brinker WO, Piermattei DL, Flo GL (eds): Handbook of Small Animal Orthopedics and Fracture Treatment. Philadelphia, WB Saunders, 1990, p 20 8. Brinker WO, Vestraete MC, Soutas-Little RW: Stiffness studies on various configurations and types of external fixators . JAm Anim Hosp Assoc 21 :801, 1985 9. Egger EL: Static strength evaluation of six external skeletal configurations. Vet Surg 12:130, 1983 10. Egger EL: Introduction of external fixation. In Proceedings of the 55th Annual Meeting of the American Animal Hospital Association, Washington, DC, 1988, P 186 11. Egger EL, Greenwood KM: External skeletal fixation . InSlatter DL (ed): Textbook of Small Animal Surgery, ed 1. Philadelphia, WB Saunders, 1985, p 1972 12. Egger EL, Rigg DL, Blass CE: Type I biplanar configuration of external skeletal fixation. J Am Vet Med Assoc 187:262, 1985 13. Green SA: Complications of external skeletal fixation. Clin Orthop Rei Res 180:109, 1983 14. Green SA, Ripley MJ: Chronic osteomyelitis in pin tracks. J Bone Joint Surg [Am] 66:1092, 1984 15. Ihrke PJ: Integumentary infections. In Greene CE (ed): Infectious Diseases of the Dog and Cat, ed 1. Philadelphia, WB Saunders, 1990, p 72 16. Johnson AL, Kneller SK, Weigel RM: Radial and tibial fracture repair with external skeletal fixation . Vet Surg 18:367, 1989 17. Kantrowitz B, Smeak D, Vannini R: Radiographic appearance of ring sequestrum with pin tract osteomyelitis in the dog. J Am Anim Hosp Assoc 24:367, 1988 18. Mears DC (ed) : External Skeletal Fixation . Baltimore, Williams & Wilkins, 1983, p 182 19. Nguyen VD, London J, Cone RO: Ring sequestrum: Radiographic characteristics of skeletal fixation pin-tract osteomyelitis. Radiology 158:129, 1986 20. Palmer RH, Aaron DA: Ellis pin complications in seven dogs. Vet Surg 19:440, 1990 21. Parkhill C: A new apparatus for the fixation of bones after resection and in fractures with a tendency to displacement. Trans Am Surg Assoc 15:251, 1987 22. Pettit GD: Kirschner fixation splint. Kirschner Orthop Catalog 1:96, 1980 23. Webster's Ninth Collegiate Dictionary. Springfield, MA, Merriam Webster, 1983, p 269
Address reprint requests to Joseph Harari, DVM, MS Department of Veterinary Clinical Medicine and Surgery Washington State University College of Veterinary Medicine Pullman, WA 99164-6610
EXTERNAL SKELETAL FIXATION
+ .20
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION Joseph Harari, DVM, MS
In medical terminology, a complication is a secondary condition developing in the course of a primary disease.23 A complication appears unexpectedly and causes change in existing plans, methods, or attitudes. Complications associated with external skeletal fixation (ESF) can affect bone and soft tissue healing and often require change in treatment protocol. As with complications following other surgical techniques, complications of ESF occur as a consequence of failure in following basic guidelines and principles. Complications of ESF can be classified as pin tract infections, fixator problems, and impalement of neurovascular/muscular tissues (Table 1). The earliest description of ESF-related complications was by Parkhill, 21 who described in 1897 chronic drainage and infection in one patient and bone refractures in two patients treated with his adjustable, external bone clamp. PIN TRACT INFECTION
Pin tract sepsis is caused by necrosis and infection of soft and osseous tissues around the pin.13 Excessive pin motion directly contributes to the infection. Pin tract sepsis can be divided into major or minor conditions depending on the degrees of inflammation and patient discomfort, character of the drainage, and required treatment.13 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
99
100
HARARI
Table 1. CLASSIFICATION OF COMPLICATIONS ASSOCIATED WITH EXTERNAL SKELETAL FIXATION Pin tract infections Soft tissue sepsis Focal osteomyelitis Ring sequestrum Fixator problems • Premature pin loosening Unstable configuration Pressure necrosis of skin Tardy bone union Iatrogenic bone fracture Soft tissue impalement Neurovascular bundles Muscular tissue
Minor Pin Tract Infection
Minor drainage is characterized by a slight, sterile, serous drainage; minimal tissue inflammation; and little patient discomfort (Fig. 1).1, 13 It is considered a mild, normal consequence of transfixation, although controversy exists among surgeons regarding the need for treatment. Some clinicians prefer to allow this cutaneous drainage to form a sterile crust and possible barrier to infection,s, 10, 22 Other surgeons prefer to clean the pin sites daily with various solutions (soap and water, 2% hydrogen peroxide, 0.05% chlorhexidine, 0.1% betadine, sterile saline) to permit external drainage and avoid infection. 2 , 4, 13, 18 Major Pin Tract Infection
Major pin tract sepsis is caused by invasion of necrotic tissue by skin bacteria around the pin. It is characterized by persistent and excessive purulent drainage associated with soft tissue inflammation and patient discomfort (Fig. 2). In humans, Staphylococcus aureus, Pseudomonas aeruginosa, Proteus mirabilis, and Serratia marcescens are the most commonly isolated pathogens from pin tract infections.14 In dogs, Staphylococcus intermedius is the primary bacterial pathogen of skin, although polymicrobial infec~ tions occur in skin wounds. 15 In a retrospective review (unpublished data) of bacterial cultures from major pin tract drainages of dogs treated at the Washington State University Teaching Hospital (WSU-VMTH), the most commonly isolated bacteria were Staphylococcus intermedius, Corynebacterium pyogenes, and Pasteurella multocida. Focal osteomyelitis associated with pin tract sepsis has been described in dogs, although the clinical significance of the radiographic changes was questioned since lesions regressed without treatment in some patients,16 Radiographic changes included soft tissue swelling,
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION
101
Figure 1. Minor or normal pin-tract drainage characterized by formation of a serous crust. There is minimal soft-tissue irritation.
periosteal reaction, cortical lysis, and increased medullary density adjacent to the pin. Ring sequestrum secondary to pin tract osteomyelitis is an uncommon yet serious consequence of local infection. 17, 19 Radiographically the lesion is characterized by a zone of osteosclerosis, adjacent to the pin tract, surrounded by another zone of osteolysis. The sequestered bone may serve as a nidus for infection and refracture as a result of weakness. Generalized osteomyelitis associated with ESF has not been well documented, although a potential exists for spreading infection if percutaneous pins are passed through contaminated tissues. Pin tract infection can be minimized by reducing skin tension around the pin, avoiding thermal necrosis of bone during pin insertion, and limiting pin-bone and pin-skin motions. 1,3-5, 13 Skin tension can be reduced by enlarging pin entry and exit sites with incisions 1 to 2 cm in length. Alignment of fracture segments and overlying soft tissues and skin before pin insertion also reduces skin tension. Thermal
102
HARARI
Figure 2. Major pin-tract infection characterized by persistent drainage and soft-tissue inflammation.
necrosis of bone can be avoided by inserting pins with a hand or lowspeed (150 RPM) power drill. Predrilling with a bit smaller in diameter than the pin limits necrosis associated with forceful insertion and pin tract enlargement associated with wobbling during hand insertion. To eliminate pin-bone and pin-skin motions, some surgeons recommend placement of bandage material between skin and fixator, restriction of patient activity, and use of partially threaded pins engaged in the transcortex.1, 3, 13 Pin-bone motion will also be reduced if bone necrosis is avoided by proper pin insertion as previously described. Treatment of major pin tract sepsis includes daily cleansing of affected sites with an antiseptic solution to promote drainage of purulent materiaL!' 3, 4, 13 In addition, topical antistaphylococcal antibiotic ointment and bandages are placed at the pin site to reduce infection and pin-skin motion. Loose pins need to be removed and focal osteomyelitis/ring sequestrum treated by curettage of necrotic bone, cancellous bone grafting, and systemic antibiotics based on bacterial culture and antibiotic sensitivity assays.17 Aggressive therapy of these focal bone lesions should provide satisfactory clinical results. FIXATOR PROBLEMS
Problems with external fixators include premature (before fracture healing) pin loosening, unstable configurations, pressure necrosis of skin from overlying clamps and bar, tardy bone union, and iatrogenic bone fracture. 1, 3, 4, 10, 11
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION
103
Premature Pin Loosening
Premature pin loosening is characterized by an acute onset of lameness during an otherwise uneventful postoperative healing process. Osteolysis around pins and pin migration are visible in radiographs. Causes of premature pin loosening include thermal necrosis of bone and soft tissue during high-speed pin insertism; pin placement into osteopenic bone; increased diameter of pin tracts due to wobbling during hand insertion; placement of pins at an improper angle, into bone cracks or fissures, or too near a fracture line; use of improper pin size; and excessive patient activity during the postoperative period. 4 , 6, 13 Prevention of pin loosening can be accomplished by following basic guidelines during application of the fixator.1, 3, 6, 7, 10 These recommendations include low-speed (150 RPM) or hand drill insertions of trochar pointed pins into a smaller, predrilled hole; use of a drill sleeve to protect adjacent soft tissues; inserting pins 2 cm away from fractures or fissures; engaging near and far cortices during pin insertion; placing pins at an angle of 60 to 70 degrees to the long axis of the bone; using partially threaded pins engaged in the far cortex; and using pins whose diameter does not exceed 20% to 30% of the bone diameter. With endthreaded pins placement of the threaded-nonthreaded shaft junction in the medullary canal has also been recommended to reduce stress and prevent pin breakage or loosening. 20 Unstable Configuration
An unstable configuration can be associated with inadequate preoperative assessment of fracture repair and using a fixator beyond its capabilities. Stability of the external fixator can be improved by following guidelines for proper pin insertion (see earlier), placing the device on the tension side of the bone, spreading pins along the shaft of the bone, using a combination of threaded and smooth pins, and developing uniplanar or multi planar configurations with single clamps and several connecting bars. 1-3, 7-9 Supplemental fixation of fractures with interfragmentary screws, cerclage and Kirschner wires, and intramedullary pins can also improve bone stability and enhance healing. Pressure Necrosis of Skin
Pressure necrosis of skin occurs if pin clamps and bar are placed too close to the skin surface, thus providing insufficient space for postoperative tissue swelling. The condition may occur with fractures above the elbow and stifle joints involving heavily damaged muscles. Skin necrosis can be avoided by placing the pin clamps 1 to 2 cm away from the skin surface and using bandage dressings during the immediate postoperative period to reduce swelling. 2, 7, 13 Treatments for skin
104
HARARI
necrosis include clamp and bar adjustment away from the skin, hydrotherapy or physical therapy to reduce tissue swelling, and topical medication of affected sites. Tardy Bone Union
When used properly, external fixators are infrequently associated with nonunions. These cases are characterized by severe bone comminution, poor reduction of fragments, rigid fixation, and osseous defects.3, 13, 15 Delayed or absent healing can be avoided by accurate fracture reduction, cancellous bone grafting, and staged pin removal to load the bone. l , 13 Conversion of a type II or III external fixator to a type I by removal of the connecting bars and clamps decreases stress protection of bone and stimulates ossification. Staged disassembly can be performed at 2-week or monthly intervals during the healing process. With a type I unilateral fixator, moving the clamps and connecting bar(s) away from the limb will also reduce the stiffness of the configuration. 13
Iatrogenic Bone Fracture
Iatrogenic bone fracture can occur if transfixation pins are inserted into fissures, superficial cortical areas, and osteopenic bone. l , 4, 10, 13 Additionally, pin diameters should not exceed 20% to 30% of the bone diameter. I, 7 Prevention of iatrogenic bone fracture requires observance of pin insertion guidelines as previously described. Treatment requires removal and proper reinsertion of the pins or using alternate modes of fixation.
SOFT TISSUE IMPALEMENT Neurovascular Bundles
External fixator-related nerve or vessel injury is uncommon. Neurovascular bundles are usually pushed aside rather than being transfixed by percutaneous pins. 13 Knowledge of regional anatomy aids in proper pin placement through safe tissue "corridors" and reduces risk of neurovascular injury. Pin tract hemorrhage following pin placement in the proximal aspect of the tibia has been reported, although the source of the hemorrhage was not identified.16 At the WSU-VMTH, three dogs during the past 5 years (unpublished data) had profuse hemorrhage during repair of radial fractures with ESF (Fig. 3). The source of the bleeding was suspected pin trauma to the interosseous
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION
105
Figure 3. Swollen antebrachium caused by profuse hemorrhage during pin placement of an external skeletal fixator in a dog.
branches of the median artery (Fig. 4). Treatments included pin removal, temporary cancellation of surgery, and Robert Jones bandaging for 24 to 48 hours. Muscular Tissue Muscular impalement and injury from transfixation pins can occur if pins are placed through myotendinous structures. Clinical characteristics of tissue impalement include excessive pin tract drainage, muscular pain and discomfort, reduced physical activity, and decreased joint mobility. I, 4,13 Treatment of this condition involves pin removal, insertion at another site, or selection of an alternate mode of fixation. Quadriceps contracture has been described in a young dog with a femoral fracture treated with a type I biplanar splint. 12 A double bar uniplanar configuration is preferred in these cases to avoid pinning of the quadriceps muscles. 1, 12
.
SUMMARY Complications associated with ESF can deleteriously affect soft tissue and bone healing. Adherence to proper surgical techniques and guidelines will minimize development of ESF-related complications. The most common problems associated with ESF are pin tract infections, fixator problems, and soft tissue impalement. These complications can be avoided by using proper pin insertion techniques that reduce skin tension; pin-bone, pin-skin motion; and soft tissue trauma. In addition, proper selection of pins (size, threaded or smooth), fixator
106
HARARI
aroc,f, roJ- -
~
: :., ~Cofloterol ulnor
Pro);, colla teral ra dial, -
Oist coifateral rodioJ- - -
-Col/ateral "Inar,
cutoneous br.
Medion-
Common
i' l1t erosseous ~ ~
,.
N
~ Prox.
dorsal ,'nterosseous
Prox. collot rodlol, lot br: - - -
Po/ma r
loterosseous -
'A cC~SSO ( !j
interosseous
Pro x, collat. rodlol medbr: .
Rod io/- -
- - Ulnar
- - -Pol mar interosseous
Ro d fof, dorsa! br:'-- - Rodio/ ~ palmar br:
Figure 4. Arteries of the right antebrachium, medial aspect. (From Evans HE, Christansen GC (eds): Miller's Anatomy of the Dog, ed 2. Philadelphia, WB Saunders, 1979, p 703.)
COMPLICATIONS OF EXTERNAL SKELETAL FIXATION
107
configuration, ancillary implants, and a cancellous bone graft further reduce the risk of complications and inadequate healing.
References 1. Aron DN: External skeletal fixation. Vet Med Rep 1:181, 1989 2. Aron DN, Toombs JP: Updated principles of external skeletal fixation. Comp Cont Ed Pract Vet 6:845, 1984 3. Aron DN, Toombs JP, Hollingsworth SC: Primary treatment of severe fractures by external skeletal fixation: Threaded pins compared with smooth pins. J Am Anim Hosp Assoc 22:659, 1986 4. Behrens F: General theory and principles of external fixation . Clin Orthop Rei Res 24:15, 1989 5. Boothe HW, Tangner CH: Clinical application of the Kirschner apparatus in long bone fractures. J Am Anim Hosp Assoc 19:679, 1983 6. Brinker WO, Flo GL: Principles and application of external skeletal fixation. Vet Clin North Am Small Anim Pract 5:197, 1975 7. Brinker WO, Piermattei DL, Flo GL (eds): Handbook of Small Animal Orthopedics and Fracture Treatment. Philadelphia, WB Saunders, 1990, p 20 8. Brinker WO, Vestraete MC, Soutas-Little RW: Stiffness studies on various configurations and types of external fixators . JAm Anim Hosp Assoc 21 :801, 1985 9. Egger EL: Static strength evaluation of six external skeletal configurations. Vet Surg 12:130, 1983 10. Egger EL: Introduction of external fixation. In Proceedings of the 55th Annual Meeting of the American Animal Hospital Association, Washington, DC, 1988, P 186 11. Egger EL, Greenwood KM: External skeletal fixation . InSlatter DL (ed): Textbook of Small Animal Surgery, ed 1. Philadelphia, WB Saunders, 1985, p 1972 12. Egger EL, Rigg DL, Blass CE: Type I biplanar configuration of external skeletal fixation. J Am Vet Med Assoc 187:262, 1985 13. Green SA: Complications of external skeletal fixation. Clin Orthop Rei Res 180:109, 1983 14. Green SA, Ripley MJ: Chronic osteomyelitis in pin tracks. J Bone Joint Surg [Am] 66:1092, 1984 15. Ihrke PJ: Integumentary infections. In Greene CE (ed): Infectious Diseases of the Dog and Cat, ed 1. Philadelphia, WB Saunders, 1990, p 72 16. Johnson AL, Kneller SK, Weigel RM: Radial and tibial fracture repair with external skeletal fixation . Vet Surg 18:367, 1989 17. Kantrowitz B, Smeak D, Vannini R: Radiographic appearance of ring sequestrum with pin tract osteomyelitis in the dog. J Am Anim Hosp Assoc 24:367, 1988 18. Mears DC (ed) : External Skeletal Fixation . Baltimore, Williams & Wilkins, 1983, p 182 19. Nguyen VD, London J, Cone RO: Ring sequestrum: Radiographic characteristics of skeletal fixation pin-tract osteomyelitis. Radiology 158:129, 1986 20. Palmer RH, Aaron DA: Ellis pin complications in seven dogs. Vet Surg 19:440, 1990 21. Parkhill C: A new apparatus for the fixation of bones after resection and in fractures with a tendency to displacement. Trans Am Surg Assoc 15:251, 1987 22. Pettit GD: Kirschner fixation splint. Kirschner Orthop Catalog 1:96, 1980 23. Webster's Ninth Collegiate Dictionary. Springfield, MA, Merriam Webster, 1983, p 269
Address reprint requests to Joseph Harari, DVM, MS Department of Veterinary Clinical Medicine and Surgery Washington State University College of Veterinary Medicine Pullman, WA 99164-6610
