Orthopedic surgery in small mammals (Proceedings)
Fractures in small mammals generally involve the femur, tibia, and occasionally the humerus. These fractures are usually the result of being dropped or getting the leg caught in a wire cage floor. The patient usually presents acutely with minimal metabolic changes. The patient is treated for metabolic compromise or shock as needed. If the patient is very stressed, it should be placed in a warm (75-80o F), dark, quiet location and allowed to recover from shock prior to addressing the fracture.
Most fractures of the femur and humerus in small mammals are not open making the routine use of therapeutic antibiotics inappropriate. Perioperative antibiotic therapy is recommended with intravenous administration perioperative and every 90 min. during the surgery. Fractures of the distal extremity are more often open because there is little soft tissue coverage. The area surrounding the wound is clipped, cleaned, and dressed until the patient can safely be anesthetized for definitive treatment. If the patient is stable, under anesthesia any necrotic soft tissue and bone is debrided. The bone is replaced under the skin, the limb bandaged, and broad-spectrum antibiotic therapy initiated pending culture results. Cultures are obtained at the time of surgery. Care must be taken when selecting an antibiotic for use in rabbits and rodents.
Analgesia is especially important in small mammals because many are prey species and do not tolerate stress well. Buprenorphine (0.05-0.5 mg/kg SQ q 6-12 hr; 0.01-0.04 mg/kg in ferrets), butorphanol (0.1-0.4 mg/kg SQ q 4 hr) are useful for providing analgesia.Preoperative laboratory evaluation should include a hematocrit, total serum solids, glucose, and urea evaluation. If the hematocrit is less than 20% surgery should be delayed or a blood transfusion should be considered. An increased urea may be an indication of dehydration or renal disease. The hematocrit and total solids are useful in determining which. Normal serum glucose in small mammals is 75-150 gm/dl. Hypoglycemic patients benefit from the addition of dextrose to their fluid regimen. Insulinoma should be considered in ferrets that are hypoglycemic.
The principles of fracture management in small mammals are similar to those established for larger mammals and include rigid stabilization and anatomic alignment with minimal disturbance of callus formation and soft tissue dissection. The inherent problems in working with rabbit and rodent bones are the small size and the thin, brittle cortices. Any apparatus used must be well tolerated by the patient and it is best to provide early return to function to prevent fracture disease. Practical considerations in fracture management include the cost of the materials, ease of application, availability of equipment, and the surgeon's level of expertise with various fixation devices.
Compression, rotation, bending, and shear forces are exerted on the fracture and must be neutralized to promote fracture healing. Comminuted fractures are susceptible to compression, rotation, bending, and shear forces. Any fracture fixation should neutralize the inherent forces acting on the fracture to prevent motion at the fracture site. The more forces that must be neutralized by the fixation, the higher the incidence of complications and failure.