UNIVERSIDAD CATÓLICA DE LA SANTÍSIMA CONCEPCIÓN
4.- PROCEDIMIENTOS DE MATRÍCULA a) Matrícula Presencial
If reduction is satisfactory, most patients will respond to stable fixation of any type. Compression at the fracture site (e.g., with a compression plate) is especially effica- cious. Callus should be disturbed as little as possible when applying fixation, even to the point of contouring the plate to accommodate the callus. Type II and III exter- nal fixators can also be employed, especially in the radius/ulna and the tibia. These fixators are the best choice if the nonunion is infected. Type I external fixators com- bined with intramedullary (IM) pins can be applied in some situations (Figure 4-6).
A B C
E D
FIGURE 4-6. Moderately hypertrophic nonunion of a supracondylar fracture in a small Yorkshire terrier immobilized by use of an improperly placed intramedullary (IM) pin. There was rotation at the fracture site. A, Radiographic appearance at 3 months. Clinically, the area was very painful, and the animal refused to use the leg. B and C, A lateral open approach was used, and an IM pin and unilateral external fixator (1/1 pin) were applied for stabilization. The external fixator was removed in 6 weeks because there was sufficient callus to stabilize against rotation. D and E, Clinical union was present at 3 months, and the IM pin was removed. The animal regained a full range of movement and function.
4—Delayed Union and Nonunion 175 If reduction is unsatisfactory, the callus must be divided at the fracture site. Some
callus may need to be resected to achieve bone-to-bone contact and to open the medullary canal with an IM pin, allowing speedy reestablishment of the medullary blood supply. Appropriate fixation is then applied. Bone grafting is not needed, although pieces of resected callus can be packed around the fracture site.
Nonviable Nonunion
An open approach is made to allow reflection of the covering of thickened perios- teum with a periosteal elevator or osteotome and removal of the fibrous soft tissue between the bone ends. Sclerosed bone is removed from the bone ends with rongeurs until bleeding is observed from the periosteum and endosteum; however, excessive bone length should not be sacrificed to achieve this. Additionally, a suit- able diameter of Steinmann pin or a twist drill is used to open the medullary canal. The space between the reflected periosteum and bone is packed with cancellous bone chips, and stable fixation is applied (e.g., bone plate, external fixator, or IM and external fixator) (Figure 4-7; see also Figure 4-3, B, C, and D). Healing is slow, and the fixation will need to remain in place for a prolonged period (4-6 months). Some of the more indolent conditions may necessitate grafting procedures a second or third time.
Future Treatment Possibilities
Bone morphogenetic proteins (BMPs) function to induce transformation of undif- ferentiated mesenchymal cells into chondroblasts and osteoblasts and have been shown to induce new bone formation in vivo and in vitro.4BMPs have been isolated
from a variety of mammalian tissues and are on the verge of becoming commer- cially available through recombinant DNA technology in quantities sufficient for
A B C
FIGURE 4-7. Nonunion of a fracture of the femur. The extremely comminuted fracture was originally fixed by use of a plate; however, the fracture site deficits were not filled with bone graft. At 15 months, when the animal returned for plate removal, it was favoring the leg. A, Radiograph of femur after plate removal, lateral view. B, After reflection of the modified periosteum in the fracture site area, an intramedullary (IM) pin and a unilateral external fixator (1/1 pin) were applied for fixation, lateral view. A bone graft was applied in the frac- ture area. C, Clinical union at 41/2 months, lateral view. Demineralized bone such as this responds faster if subjected to stresses; therefore the IM pin and external fixator were chosen for stabilization.
clinical application. Potential applications include use as alternatives to bone grafts, promoters of osteointegration of implants, and treatment of nonadaptive bone disease such as stress fractures. Thus, BMPs would appear to have value in the treat- ment of delayed union and nonunion fractures, but their role in this area remains to be defined through clinical trials.
Microsurgical technique has allowed the use of autogenous free vascular bone grafts as treatment for nonunion fractures in dogs. The distal ulna and the medial tibial cortex have been described as potential donor sites, with external fixators used for graft stabilization. Successful experimental vascular bone transplantation also has been described.5-7Microvascular anastomosis of a bone graft blood supply
has a demonstrated experimental advantage over avascular grafts in a bacteria- contaminated graft site.7 Avascular bone becomes an infected sequestrum in the
presence of bacteria, whereas vascularized autogenous bone (see Figure 3-4) quickly incorporates with local bone and hypertrophies to accept a load during weight bearing.5-7
Bone transport osteogenesis, with the use of circular-frame external fixators, has been described as a possible treatment for large segmental defects, as seen with nonunion fractures.8-10A circular-frame external fixator is applied to the bone, and
an osteotomy is performed distant to the nonunion site. Serial distraction is used to transport autogenous bone slowly across the bone defect until the defect is closed and the fracture has healed. New bone forms in the distracting osteotomy site and rapidly remodels into lamellar bone. The transported bone provides vascularized autogenous bone at the site of the poor healing environment of the nonunion gap. Use of this technique has been very limited for nonunion fractures in animals, and further clinical and scientific studies are needed to define its use in veterinary orthopedics.
References
1. Hohn RB, Rosen H: Delayed union. In Brinker WO, Hohn RB, Prieur WD, editors: Manual of inter-
nal fixation in small animals, Berlin, 1984, Springer-Verlag, pp 241-254.
2. Brinker WO: Fractures. In Canine surgery, ed 2 (Archibald, editor), Santa Barbara, Calif, 1974, American Veterinary Publications, pp 949-1048.
3. Weber BG, Cech D: Pseudoarthrosis: pathology, biomechanics, therapy, results, Bern, 1976, Hans Huber Medical Publisher.
4. Kirker-Head CA: Recombinant bone morphogenetic proteins: novel substances for enhancing bone healing, Vet Surg 24:408-419, 1995.
5. Szentimrey D, Fowler D: The anatomic basis of a free vascularized bone graft based on the canine distal ulna, Vet Surg 23:529-533, 1994.
6. Szentimrey D, Fowler D, Johnston G, et al: Transplantation of the canine distal ulna as a free vascularized bone graft, Vet Surg 24:215-225, 1995.
7. Bebchuck TN, Degner DA, Walshaw R, et al: Evaluation of a free vascularized medial tibial bone graft in dogs, Vet Surg 29:128-144, 2000.
8. Lesser AS: Segmental bone transport for the treatment of bone defects, J Am Anim Hosp Assoc 30:322-330, 1994.
9. Stallings JT, Lewis DD, Welch JT, et al: An introduction to distraction osteogenesis and the principles of the Ilizarov method, Vet Comp Orthop Traumatol 11:59-67, 1998.
10. Tommasini Degna M, Ehrhart N, Feretti A, et al: Bone transport osteogenesis for limb salvage,
Osteitis or osteomyelitis is defined as a bone inflammation involving the haversian spaces, Volkmann canals, and generally the medullary cavity and periosteum. Bone infection is usually associated with open fractures, bone surgery (especially involv- ing metallic implants), and systemic illness. Bite wounds are common causes of osteomyelitis in the lower limbs, mandible, and maxilla in dogs and the coccygeal vertebrae in cats.
Acute infection is characterized by a supportive history, localized pain, swelling, erythema, and elevation of body temperature (≥103° F [39.5° C]). In most early cases, radiological signs are not evident. Persistent fever is the most reliable early sign of infection. Postsurgical osteomyelitis signs are usually evident 48 to 72 hours after surgery, but during this period it is difficult to distinguish between incipient osteomyelitis and deep wound infection. Wound disruption and drainage takes several days to develop.
Chronic infection is characterized by a supportive history; draining sinus tracts (±); muscle atrophy, fibrosis, and contracture; variable lameness; and positive radio- graphic changes. These changes may include cortical resorption and thinning; osteoporosis; periosteal new bone formation that may be smooth, expansile, or spiculated1; formation of sequestra and involucra; sclerosis; and soft tissue swelling
(Figure 5-1). A sequestrum is a piece of dead bone that has become separated from normal bone during the process of necrosis and is surrounded by a pool of infected exudate. Because it has not undergone any resorptive process and is not vascularized, its radiographic density is high, giving the appearance of a very white piece of bone that has very sharp and ragged edges. Most sequestra are found within the medullary cavity or beneath a bone plate. An involucrum is a covering or sheath of new bone formation and fibrous tissue covering a sequestrum.
Most often, osteomyelitis implies bacterial infection; however, fungi or viruses can also infect bone and marrow. Staphylococci cause 50% to 60% of bone infec- tions in dogs,1 and historically the organism most frequently reported has been
Staphylococcus aureus; however, one report indicates that Staphylococcus inter- medius is more common.2The significance here is that most of these were resistant
to penicillin because of β-lactamase production. Other common organisms include Streptococcus, Escherichia coli, Proteus, Klebsiella, Pseudomonas, and Pasteurella when bite wounds are present. The importance of anaerobes, especially in bite wound osteomyelitis, has been emphasized by Muir and Johnson,3 who reported a
64% incidence of anaerobic bacteria isolated from such cases. Such isolates include Actinomyces, Clostridium, Peptostreptococcus, Bacteroides, and Fusobacterium.
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