Current treatment options for dogs with appendicular osteosarcoma - Veterinary Medicine
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Current treatment options for dogs with appendicular osteosarcoma
Your therapeutic choices for dogs with osteosarcoma in their limbs continue to expand. Deciding which option is best comes down to the site and extent of the tumor and the owner's preference.


VETERINARY MEDICINE


Cortical bone allograft implantation


FIGURE 1. A lateral radiograph of a dog distal forelimb after cortical bone allograft implantation for the treatment of a distal radial osteosarcoma. The proximal five cortical bone screws fasten the bone plate to the remaining radius. The six central bone screws are placed into the allograft. The five distal bone screws fasten the plate to the radial carpal bone and the third metacarpal bone. FIGURE 2A. Serial radiographs of a dog with a distal radial osteosarcoma undergoing bone transport osteogenesis to replace a subtotal radial defect with regenerate bone. The radiographs were obtained 14, 21, 28, and 35 days after surgery. Note the movement of the transport segment distally and the subsequent regenerate bone formation. The radius, ulna, and transport segment are secured within a circular external skeletal fixation frame. FIGURE 2B. A postoperative photograph and a corresponding radiograph of a forelimb undergoing bone transport osteogenesis.
The most common limb-sparing procedure used to treat distal radial osteosarcoma is cortical bone allograft implantation.16,17 In this procedure, a fresh-frozen (not preserved) cortical bone segment is cut to match the length of the excised tumor segment and affixed to the host bone with a bone plate and screws (Figure 1).17,26 Cortical bone allografts have been used in dogs with osteosarcoma affecting the distal radius, proximal humerus, ulna, and scapula; however, only those in the distal radius location have been widely successful.16

Dogs usually attempt to bear weight on the affected limb within 24 hours of surgery and gradually regain normal limb function within one or two months after surgery.11,16,17,26 Nontumor-related complications associated with cortical bone allograft limb-sparing procedures include infection, fracture of the host bone, rejection of the allograft, nonunion, or implant loosening or failure.16,28 Infection is the most common of these complications.16,28 About half the dogs undergoing cortical bone allograft implantation develop an infection at some point after surgery.16 Factors contributing to the high rate of infection include extensive surgical resection, use of a nonviable cortical bone allograft and large metallic implants, infusion of the allograft marrow cavity with bone cement to improve screw purchase, paucity of adjacent soft tissues to supply sufficient vasculature in the distal extremity, self-trauma, and the administration of adjunctive chemotherapy.16,28,29 Complete resolution of infection is extremely difficult because of bacteria residing in the allograft and in the implant-associated biofilm.16

Although 75% of infections can be treated with basic wound management, bandaging, and antibiotic therapy, the remaining 25% require additional surgery. Resolving the clinical signs related to the infection is sometimes achieved by removing the allograft or by implanting antibiotic-impregnated polymethyl methacrylate beads.30 For dogs that do not respond to these approaches, limb amputation may be the only option.16 It has been noted that dogs that develop infection at the surgical site have significantly longer survival times and higher local control rates than dogs that do not develop infections.16,31,32 The reason for this difference in survival and local tumor control is thought to have an immunologic basis.16 Although the effects of infection and the immune system are an area for future study, postoperative infection is not desirable because the quality of life for dogs with infected allografts is generally compromised by periods of pain, lameness, and drainage and the necessity for continual bandage changes and wound care. Amputation is elected in some dogs to resolve the adverse sequelae associated with infection.31

Pasteurized tumoral autografting

Pasteurized tumoral autografting involves the temporary removal (ostectomy) and pasteurization of the affected bone segment. The treated bone segment is then replaced as an orthotopic autograft and stabilized with a bone plate and screws.18,19 The pasteurization process requires placing the bone segment into a sealed container filled with sterile saline solution preheated to 149 F (65 C).19 The container is kept in a thermostat-controlled water bath and maintained at 149 F for 40 minutes.19 Pasteurization is advantageous in that all the cellular constituents of the excised bone segment are killed, but unlike autoclaving, which is pressurized and done at a higher temperature, important proteins, such as bone morphogenetic proteins, are not damaged.


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Source: VETERINARY MEDICINE,
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