1094–9194/02 $15.00 .00
SMALL EXOTIC MAMMAL ORTHOPEDICS Peter J. Helmer, DVM, and Teresa L. Lightfoot, DVM, Diplomate ABVP-Avian
Many factors contribute to the selection of the most appropriate fracture-ﬁxation technique, including the anatomic location and classiﬁcation of fracture type, animal age, any concurrent disease conditions, and owner and animal compliance. Most small mammal fractures are traumatic in origin, with the animals having fallen from a height or having been dropped, stepped on, sat on, crushed by furniture, caught in doors, or attacked by more aggressive pets. The ensuing fracture may be obvious, but it is important to examine the whole animal to determine the full extent of its injuries. A rapid physical assessment should be performed to ensure the existence of a patent airway, to provide hemostasis if necessary, and to prevent circulatory collapse. Depending on the severity of the trauma, therapeutic measures such as intravenous or intraosseous ﬂuids may be required to prevent or treat shock. Corticosteroids should be used with caution in rabbits and rodents.20 Once the animal is stable, a thorough physical examination should be performed including the identiﬁcation of any soft tissue damage or neurological deﬁcits. When orthopedic problems (fractures) are obvious or are the reason that the owner presented their pet to the hospital, it is advisable to acknowledge this injury to the owner and to explain the necessity of stabilizing the animal before addressing the fractured bone. Communication is vital in these situations so that the owner does not perceive that his or her primary concerns are being overlooked or ignored. The physical examination, signalment, and history provide neces-
From the Avian and Animal Hospital of Bardmoor, Inc., Largo, Florida VETERINARY CLINICS OF NORTH AMERICA: EXOTIC ANIMAL PRACTICE VOLUME 5 • NUMBER 1 • JANUARY 2002
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sary information for an initial assessment. Important factors such as the age of the animal, nutritional status, and previous or concurrent diseases must be considered. Because the history is likely to be limited by the owner’s initial observation of the problem, it may not necessarily coincide with the occurrence of the trauma. With smaller exotic mammals in which little daily interaction occurs, the fracture can be days to weeks old, and more serious issues such as dehydration, malnutrition, and infection may require the practitioner’s attention. Traumatic fractures often have associated neurologic and vascular injuries that must be identiﬁed. If feasible (assuming sufﬁcient animal size and stability and owner acceptance), a minimal series of laboratory tests, including a complete blood count and serum chemistries, aids in the identiﬁcation of concurrent diseases. Generally, survey whole-body radiography is not recognized as an ideal academic technique; however, before restraining the animal and isolating and radiographically examining the obviously affected bones, obtaining a survey ﬁlm (which is relatively nonstressful) may reveal signiﬁcant abnormalities. The detection of a diaphragmatic hernia, vertebral fracture or luxation, free peritoneal ﬂuid, pneumothorax, or other signiﬁcant pathology on a survey radiograph may alter the prognosis or indicated therapy signiﬁcantly. With a stable animal, taking a minimum of two radiographic views of the fracture site is recommended. Assessment of these radiographs identiﬁes the type and location of the fracture and any soft tissue swelling and potential underlying bony pathology (e.g., osteomyelitis, metabolic bone disease [particularly common in the sugar glider, Petaurus breviceps, and the Virginia opossum, Didelphis species], hypovitaminosis C [in the guinea pig, Cavia porcellus], or neoplasia [common in both African hedgehogs, Atelerix albiventris, and black-tailed prairie dogs, Cyonomys ludovicianus]). Pathologic fractures caused by these conditions often are managed in a different manner than those caused by primary traumatic fractures. Orthopedic injuries are divided into three classes based on the urgency of repair:3 1. Fractures with the potential to cause injury to the central nervous system (e.g., vertebral or depressed skull fractures) or fractures that involve multiple ribs and cause respiratory compromise (or ﬂail chest) 2. Luxations, intra-articular fractures, and physeal fractures 3. Closed long-bone-shaft fractures, nonarticular pelvic fractures, scapular fractures, metacarpal fractures, and metatarsal fractures. Class 1 fractures require immediate ﬁxation, whereas the repair of class 2 and 3 fractures can be delayed up to several days if necessary. The temporary management of class 2 and 3 fractures distal to the elbow or stiﬂe often is accomplished with external support (e.g., a Robert–Jones bandage), which decreases soft tissue damage, prevents bone fragments from penetrating the skin and becoming an open fracture, and increases animal comfort. Class 2 and 3 fractures proximal to the elbow or stiﬂe
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are managed with a Spica splint, adhesive binding (taping) to the body wall, or a cage rest. An excellent review of bandaging and splinting methods was published recently.25 Analgesia and sedation often are indicated, and current recommended drug dosages are available.12, 20 In small prey species, the prevention of catecholamine release by the administration of analgesics and sedatives is not only humane but also may be life saving. Despite the increased success and survival rates noted during the past decade with the advent of analgesic use and the advancements in surgical techniques, there is still a signiﬁcant percentage of failure with exotic pet fracture repair. In addition to the effects of catecholamine release, the reasons for surgical failure include obsessive chewing by many of these species, having thin cortices in their long bones, and possessing a limited amount of the soft tissue that surrounds and protects the distal long bones. Before any orthopedic procedure, the animal’s owner should be informed that, despite excellent surgical care, a nonunion may occur and that amputation as a salvage procedure is a possibility. Open fractures must be managed immediately to prevent further soft tissue injury and contamination. Because of the small amount of soft tissue that covers the limbs of these animals and the often-traumatic nature of their injuries, open fractures are not uncommon. It is easy to overlook a skin laceration through which the bone has passed if the bone subsequently has reduced to a location under the skin. With complete oblique or transverse fractures of the distal long bones, the animal must be examined carefully to rule out an open fracture. Open fractures are classiﬁed into three grades3: 1. A small external wound that has been caused by bone penetration to the outside 2. A skin wound that has resulted from external trauma and is contiguous with the fracture 3. A severe open wound with high degree of comminution and soft tissue and skin damage has occurred All open wounds have the potential to be contaminated. Infection of the wound depends on the viability of the bone and soft tissues, the bacterial load present, and the efﬁcacy of the animal’s body defense mechanisms. The treatment of these wounds should include: Immediate application of a sterile dressing Assessment of neurologic and vascular status, especially of tissues distal to the wound Minimal manipulation of the wound (probing before deﬁnitive de´bridement increases the risk of nosocomial infections) Broad-spectrum antibiotic therapy with a drug that achieves therapeutic concentrations in bone and soft tissues (e.g., cephalosporins) Radiography Deﬁnitive surgical de´bridement requires anesthesia that may be local, regional, or general depending on the general status of the animal.
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Sterile jelly should be applied to the wound before clipping to prevent hair contamination. A full surgical preparation should be performed. Copious lavage is accomplished with a 35-mL syringe and 18-gauge needle using sterile isotonic saline with or without 0.05% chlorhexidine. The initial de´bridement should consist of sharp dissection to remove obviously devitalized tissues. Gloves and instruments then should be changed, and the area should be prepared again before ﬁnal de´bridement. Culture and sensitivity samples should be taken after de´bridement because causative agents of wound infections are correlated with those present after cleaning. Bone fragments without soft tissue attachment should be removed to avoid sequestrum formation, with fragments that maintain soft tissue attachment being retained (whether they are incorporated into the ﬁxation or not). Generally, casts and splints are not recommended for ﬁxation of open fractures because wound care is difﬁcult. Class 3 wounds generally are left open so that the soft tissue may heal by second intention. External skeletal ﬁxators are an excellent option for orthopedic restoration in this type of fracture, because pins are placed away from the fracture line and soft tissue damage, thereby preserving the blood supply and leaving the wounds accessible for treatment. The goals of fracture repair are an early return to function, the prevention of fracture disease (i.e., a combination of joint stiffness, capsular ﬁbrosis, and muscular disuse atrophy), anatomical reduction, stable ﬁxation (i.e., neutralization of rotation, shearing, and bending forces while maintaining fragment apposition), and preservation of blood supply. The normal afferent blood supply to bone is derived from three sources: the nutrient artery of the diaphysis, the metaphyseal vessels, and the periosteal arterioles. Most of the cortical supply is derived from the medullary vessels and the centrifugal ﬂow from the medulla to the cortex. The periosteal vessels supply the outer third of the cortex. After a fracture, the disruption of the medullary supply results in a temporary shift to an extraosseously derived, centripetal supply to the callus. The medullary supply is reestablished a few weeks after stable ﬁxation.9 Many methods of fracture ﬁxation exist. The best method for each situation is based on the type, location, and age of the fracture; the size and age of the animal; the number of bones or limbs involved; the behavior of the animal; owner compliance; the expected postoperative performance level; cost; the practitioner’s surgical expertise; and equipment availability. EXTERNAL COAPTATION Indications for casts and splints as deﬁnitive ﬁxation devices include the ﬁxation of closed fractures distal to the elbow or stiﬂe, the ability to perform closed reduction with at least 50% contact between proximal and distal fragment ends, the stability of bones within the cast, and the expectation of rapid healing in certain cases (e.g., fractures in young
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animals, greenstick fractures, radial or tibial fractures with intact ulna or ﬁbula).28 The joints above and below the fracture must be immobilized. The cast or splint should be applied for the shortest time possible to achieve healing but also to minimize fracture disease. Usually, general anesthesia is required for effective cast placement, and radiographs are made after placement to ensure alignment.18, 26, 28 Although rabbits and rodents tend to chew on casts and splints, a number of casting materials (e.g., Orthoplast, Johnson & Johnson, New Brunswick, NJ; Caraform, Carapace, Inc, Tulsa, OK; Hexcelite, AOA, A Division of Kirschner Medical, Timonium, MD) have been used successfully. INTRAMEDULLARY PINS Intramedullary (IM) pins are popular and useful ﬁxation devices. Advantages of these pins include relatively low cost, short operative time, decreased bone exposure, and ease of placement. Only bending forces, however, are neutralized; IM pins have little effect on rotational or shearing forces. Additionally, placing these pins through a joint to achieve correct fracture alignment may cause arthritis or more pronounced joint pathology, and large pins can interfere with medullary blood supply. A pin diameter that is 60% to 70% of the medullary canal diameter is recommended.9, 26 In small animals, hypodermic needles work well. The biomechanical shortcomings of IM pins may be overcome with the concurrent use of supplemental ﬁxation devices (e.g., multiple IM pins [stack pinning], cerclage wire, external skeletal ﬁxation [ESF]). Combining external coaptation with IM pin ﬁxation is not advised, with the following exceptions: 1) ﬁxation of metacarpal or metatarsal bone fractures, and 2) severely comminuted fractures in larger-breed rabbits in which the fractured bone is large enough to accommodate an IM pin and the bone fragments require either a cast or ESF to maintain rotational stability. The added weight of the coaptation can restrict the use of the limb and also may act as a fulcrum at the fracture site that could impede healing. CERCLAGE WIRING Cerclage wires are used as ancillary ﬁxation with IM pins, ESF, or bone plates. The fundamental principles of their use include the following: 9, 26 • Use should be restricted to long oblique fractures (those in which the length of the fracture line is at least twice the diameter of the bone) or when preventing longitudinal ﬁssure propagation. • A minimum of two wires should be placed no closer than 5 mm to the fracture line and at least 1 cm apart.
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• Only monoﬁlament stainless steel wire should be used. The size varies with each situation. • All wires must be applied tightly. Properly placed wires do not disturb blood ﬂow to the healing fracture. Loose wires disrupt periosteal capillary networks, devascularizing the underlying bone and slowing periosteal callus formation. Wires should be checked for tightness after the placement of all ﬁxation devices and replaced if any motion is detected. • Removal is not necessary. No signiﬁcant stress-shielding effect has been documented, and the wires eventually become incorporated into the callus. BONE PLATING A review of the use of bone plates is beyond the scope of this article, so the reader is directed to several other excellent sources.9, 26 The use of bone plates in small exotic mammal fracture ﬁxation is limited. Several factors contribute to this lack of use, including the small size of the plates and screws required, the thin bone cortices (especially in rabbits and chinchillas), the disruption of periosteal blood supply that can cause cortical osteopenia, a signiﬁcant increase in the risk of wound infection when plates or screws are present,13, 16 and the technical expertise required. The source for small plates of suitable size for the long bones of these animals is often through a human pediatric orthopedic supplier. The advantages of bone plating include counteracting the bending, shearing, and rotational forces and maintaining good fragment apposition. Generally, there is an early return to function and little postoperative care. Extensive research has been conducted into the use of bone plates for the ﬁxation of tibial osteotomies in rabbits as a model for human injury. The results have revealed the stress-shielding effects of rigid metal plates on the bone. In brief, the metal plate absorbs the normal biomechanical loads on the bone, which is protected from responding to normal physiologic stimuli. Studies have demonstrated that plating resulted in 1) more rapid healing of fractures when compared with ESF and full-limb casts, and 2) less limb angulation than with full-limb casts. Plated bones, however, rapidly decreased in strength after 6 weeks of application and retained only 50% of their strength 12 weeks after application if the plates had been left on.19, 31, 32 Bone plating usually results in primary bone healing (also known as direct or osteonal reconstruction healing). The stability provided by plates usually allows the direct growth of blood vessels across the defect and direct bone remodeling. Periosteal callus is not associated with this type of healing.15 In one large study, plated rabbit tibial osteotomies were healed by intermediate callus formation (or indirect healing) in which periosteal and intramedullary calluses bridged the fragment gap to
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provide stability. This difference was attributed to the large bending stresses on rabbit tibiae during sitting and hopping.32 A comparison study that used plates of varying stiffness concluded that callus size is inversely proportional to plate rigidity and that, with sufﬁcient rigidity and bony contact, primary healing in rabbit tibiae does occur.30 Primary healing of plated tibial osteotomies was reported in another study in which biomechanical bone properties were normal 6 weeks after plating; however, a signiﬁcant reduction in bone strength was present at 12 weeks.34 A comparison of neutral and compression plates demonstrated no signiﬁcant difference in speed or quality of repair; however, both methods resulted in signiﬁcant loss of bone strength.14 The results of these studies indicate that, for uncomplicated tibial osteotomies, plate removal at 6 weeks after surgery was optimal.34 In the clinical setting in which comminution and vascular damage exist, the postoperative interval is longer and should be based on radiographic changes. This comminution and neovascularization along with periosteal reaction that often occur in nonsurgically induced fractures may make plate removal difﬁcult or impossible. The compliance of owners also can be a deterrent to plate removal because they may decline to return to the hospital when their pet is ambulating normally 6 weeks after surgery. The evaluation of radiographic changes during the healing period has demonstrated excellent prediction of the time of bony union. The fracture may be considered healed when the striation of bone texture across the fracture gap is longitudinal in orientation and when the density of the fracture area approaches that of the surrounding bone.22
EXTERNAL SKELETAL FIXATION External skeletal ﬁxation (ESF) has many applications in the fractures of small exotic mammals. Laboratory research1, 2, 6, 8, 21, 33 and occasional case reports7, 24 have yielded a large amount of information. The advantages of ESF include the elimination of bending, rotational, and shearing forces; the maintenance of fracture apposition; minimal damage to soft tissue and vasculature; avoidance of fracture site implants; accessibility of wounds for soft tissue wound management; relatively low cost; and ease of application. Premature pin loosening, damage to the ﬁxator, and pin-tract infections are potential complications of ESF. There are many designs of ESF devices, and the reader is directed to the excellent reviews in other sources for more in-depth coverage.9, 26 Regardless of the type of ESF used, adherence to the following basic principles is necessary: • Threaded pins increase pin contact with bone, thus increasing ﬁxator stiffness and decreasing premature pin loosening. • Fixation stiffness is proportional to the diameter of the pins; however, the use of large pins may result in iatrogenic fractures. A pin
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• • •
diameter that is 20% of the bone diameter has been recommended. In small animals, hypodermic needles may be used. Direct-power pin insertion is preferred to hand insertion, because pins tend to wobble during hand insertion and may create larger holes and result in premature pin loosening. Drill speed should be less the 150 rpm to avoid thermal necrosis of the bone that surrounds the holes. Nonthreaded pins should be placed at divergent angles (⬃70 to the bone’s long axis) to avoid premature loosening. Ideally, two is the minimum number of pins in any fragment. Increasing the number of pins per fragment increases the area of the pin–bone interface and decreases bone resorption around the pins, thus decreasing the premature loosening of pins. No biomechanical advantage is gained by placing more than four pins per fragment. Place pins as close as practical (i.e., one half of the bone diameter) to the bone ends to increase stiffness. Pins must penetrate both cortices. Perioperative antibiotics are indicated to minimize pin-tract infections.
Fractures treated with ESF heal via secondary periosteal callus formation. Examinations of tibial osteotomies in rabbits have demonstrated that ESF devices are stiff enough to provide adequate ﬁxation and are elastic enough to minimize stress shielding. Unilateral ESF ﬁxation resulted in only a 7% loss in bone mineral content at 6 weeks after surgery.2 In a direct-comparison study of tibial-osteotomy healing with ESF or full-limb cast in rabbits, the animals with ESF healed more rapidly (i.e., complete ossiﬁcation in ESF animals occurred at 6 weeks compared with a still-immature callus in casted animals at 10 weeks). Histologically, the study demonstrated that casted limbs develop a greater hematoma at the fracture site because of more fragment movement. Ossiﬁcation cannot begin until hematoma resorption is complete. Medullary ossiﬁcation began at week 1 in ESF treated rabbits compared with week 3 in casted-limb rabbits.8 The timing of ﬁxation removal varies based on many factors and should be dictated by radiographic changes. Bone strength was greater in osteotomized tibiae when ﬁxators were removed at 4 weeks after surgery compared with their removal at 12 weeks; however, there was a signiﬁcant risk of limb angulation in the former group.33 In the same study, all osteotomies had healed radiographically at 6 weeks after surgery and no signiﬁcant stress protection was detected at that time.33 In a case report of ESF ﬁxation of a comminuted tibial fracture, the removal of the ﬁxator 6 weeks after surgery supports this experimental data in a clinical setting.24 The importance of fragment apposition has been demonstrated. Three groups of rabbits with the ESF ﬁxation of tibial osteotomies were
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compared. One group had ﬁxation placed to maintain a 0.3-mm gap between fragments, a second group had fragments maintained in apposition, and a third group had fragment ends compressed. Animals with fragment ends apposed or compressed demonstrated cortical bone union at 6 weeks after surgery compared with a ﬁbrous delayed union at 10 weeks in animals in which the fracture gap had been maintained.6 The percutaneous injection of autogenous bone marrow has been shown to improve defect healing in rabbits. Radial osteotomies were created surgically, with the ulna remaining intact. One cubic centimeter of bone marrow that had been aspirated from the femur was injected into the defect. No ancillary ﬁxation methods were used. Radii with grafted marrow demonstrated increases in callus volume, breaking load, and tensile strength. Marrow-treated radii also demonstrated earlier and greater stability that resulted in earlier healing.23 Recent studies on rabbits and dogs have shown preliminary success with increased bone stability and decreased healing time when a cancellous autogenous graft is combined with hyaluronic acid.5 Adjustable metal connecting bars generally are used in dog- and cat-ﬁxation devices. Because of their weight and size, however, these devices often are impractical for use in small animals. Methylmethacrylate (MMA) is an excellent substitute that is easily molded to whatever shape is needed and has a strength comparable with that of metal rods of the same size. The authors have had success placing the ﬁxation pins, reducing the fracture by palpation, and then embedding the pin ends in styrofoam as a temporary connecting bar. Styrofoam not only is rigid enough to maintain the reduction temporarily but also allows easy repositioning if the reduction is not radiographically sufﬁcient. When reduction is adequate, one side of the styrofoam is removed (assuming a type II ﬁxator). The other side maintains fragment reduction while the MMA is applied. Several techniques have been described for MMA application. Straws or intravenous tubing may be placed over the ends of the pins to connect them, after which the MMA is injected inside the tubing. Excellent results also have been achieved with ESF putty (Jorgensen Laboratories, Loveland, Colorado), which comes in a sausage-like cylinder and is mixed by kneading. The fumes are much less overwhelming than with other preparations, and the product is ﬁrm enough to mold over the pins without any tubing. Bending the ends of the pins increases the stability of the MMA. Regardless of the type of connecting bar used, the distance between the limb and the connecting bar should be minimized to increase biomechanical stiffness and to decrease the overall apparatus size. The space left must be sufﬁcient to accommodate postoperative soft tissue swelling and to protect the tissue from the exothermic curing of the MMA. Postoperative care is minimal. Nonadherent pads should be placed around the skin punctures and a light pressure bandage usually is applied for the ﬁrst 24 hours. A small amount of seepage is normal. Afterward, a light bandage should be applied around the ﬁxator to maintain cleanliness and to prevent it from getting caught on the cage.
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The ﬁxator should be checked again within 1 week of being placed; loose pins usually require removal. Continued seepage from the pin holes is an indication for radiography to rule out osteomyelitis. A rigid ESF may beneﬁt from a process known as dynamization, which is designed to reload the fractured bone gradually and to enhance callus hypertrophy and remodeling. Dynamization is accomplished by removing the connecting bar on one side of a type II ﬁxator or removing alternating pins of a type I design. Callus formation should be underway before attempting this procedure. Exercise restriction is recommended for 4 weeks after removal of the ﬁxator to prevent refracture. RADIOGRAPHIC EVALUATION OF FRACTURE FIXATION Regardless of the ﬁxation type, immediate postoperative radiographs always are indicated, as they are periodically throughout the healing process. The mnemonic AAAA is often used to critique the repair26: Alignment: The evaluation of angular and torsion deformity compared with normal Apposition: The anatomical proximity of fracture fragments Apparatus: The evaluation of ﬁxator placement and whether there is evidence of loosening or bending of the ﬁxator Activity: The evaluation of the amount of callus formation, signs of infection such as lysis, and new periosteal bone formation COMPLICATIONS OF FRACTURE REPAIR Adhering to the principles of orthopedic ﬁxation maximizes the chances of a successful outcome; however, complications (e.g., delayed union, nonunion, osteomyelitis) do arise and must be managed. The union of a fracture is termed delayed if it has not healed in the usual healing time necessary for the particular fracture type. This timeframe varies greatly depending on the type of fracture, type of ﬁxation used, age of the animal, and so forth. A nonunion is a fracture in which 1) all evidence of osteogenic activity has ceased, 2) movement is present at the fracture site, and 3) union is no longer present at the fracture site.25 Contributing factors to these conditions include the following: Inadequate immobilization Inadequate fragment reduction (i.e., a gap left between fragments) Impairment of blood supply either from the initial trauma or from surgery Infection (soft tissue or bone) Loss of bone fragments from surgery or trauma
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Less common factors include old age, high-dose corticosteroid treatment, and metabolic abnormalities (e.g., nutritional secondary hyperparathyroidism).35 Radiography is indicated for the further diagnosis of these conditions. In cases of inadequate fragment stability, additional ﬁxation devices can be applied. Infection or nonunions usually require more invasive surgical de´bridement and treatment. The diagnosis and treatment of delayed unions and nonunions are well described elsewhere.17, 25 Osteomyelitis is deﬁned as the inﬂammation of bone and the marrow contents. The causal agent usually is bacterial, with occasional fungal and rare parasitic or viral causes. Prophylactic antibiotic therapy should be considered in clean orthopedic procedures with foreign material implantation. Therapy should be initiated before the skin is incised to ensure therapeutic drug levels in the tissue at the time of surgery. Timing depends on the pharmacokinetics of the chosen drug. The most common contaminates of clean orthopedic procedures are Staphylococcus species. Cefazolin, a bactericidal antibiotic, has excellent activity against organisms and provides therapeutic levels in bone and soft tissue when given intravenously 20 minutes before surgery.27, 29 The penicillins are less effective because they penetrate bone poorly and have poor activity against Staphylococcus epidermitis.29 First-generation cephalosporins and penicillins must be used with caution in rabbits and rodents because of the risk of dysbiosis; however, few problems are encountered when these agents are given parenterally. After open fracture repair, signs of acute osteomyelitis may manifest within 3 to 5 days and include pain, redness, local edema, pyrexia, and an inability to bear weight on the affected limb. Radiographs are indicated to evaluate the repair site for proliferation of new bone, lysis around the implants, and gas in soft tissues. Sequestra usually are not visible until several months after surgery. Fine-needle aspirates of the area and swabs of any draining tracts should be submitted for aerobic and anaerobic cultures; multi-agent causes are not uncommon. Pasteurella species should be considered in rabbit infections. Aggressive, early therapy is essential. Implants should be evaluated, and those that do not provide rigid stability should be removed. Broad-spectrum antibiotic therapy should be instituted and later modiﬁed based on culture and sensitivity results. This therapy should continue for at least 4 weeks.27 Surgical de´bridement, lavage, and drainage of the wound are indicated. Because rabbit abscesses tend to be caseous, traditional drainage techniques usually are ineffective. In these cases, suspicious tissue should be removed and the wound should be managed as an open wound. Human studies have found third-generation cephalosporins (e.g., cefotaxime, ceftazidime) to be effective when administered parenterally in the treatment of osteomyelitis caused by sensitive agents. Oral ciproﬂoxacin has low toxicity, a long half-life, excellent bone penetration, and broad-spectrum activity against gram-positive and -negative bacteria. Oral ciproﬂoxacin therapy is as effective as parenteral therapy in humans who have osteomyelitis that is caused by a wide variety of
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pathogens.11 Oral enroﬂoxacin therapy is well tolerated in rabbits and rodents; when anaerobic bacteria are not involved in the osteomyelitis, ﬂuoroquinolones should be considered as a treatment option for sensitive bacteria.
AMPUTATION Indications for limb amputation are severe trauma, ischemic necrosis, intractable orthopedic infection, severe disability caused by arthritis, paralysis, congenital deformity, and neoplasias.35 Small exotic mammals adapt to amputation well, including the hind limb in larger rabbits. The idea of an animal existing as an amputee has very negative emotional connotations for some owners; thus, practitioners have found it helpful to maintain (until adopted) a three-legged animal as a hospital pet to demonstrate the quality of life that can be achieved without the anthropomorphic stigma of amputation. Amputation techniques are similar to those in other small mammals and are well described.35 Amputation should be performed through normal tissue and proximal to the diseased tissue. The creation of a long dangling stump should be avoided. In amputations of the front limb, removing the scapula is faster and easier to perform than disarticulating the shoulder joint. Although the chest wall is more susceptible to trauma, this is rarely a consideration in small mammals. Amputation of the hind limb at the mid-femoral level leaves a functional stump and is easier than hip disarticulation; the musculature here provides adequate soft tissue for closure. Amputation should be performed through the bone instead of through a joint, because transected bones atrophy and soft tissue coverage is maintained more easily. The thin cortices of rabbits should be cut using gigli wire or a power saw to avoid shattering. Seromas can be avoided though the use of gentle tissue handling, effective hemostasis, closure of fascial planes, elimination of dead space, and avoidance of extensive subcutaneous dissection. The main principles of fracture repair in canines and felines are readily applicable to small exotic mammals. Identifying and addressing the factors that contribute to successful repair maximizes the potential for an acceptable outcome.
References 1. Aalto K, Holmstrom T, Karaharju E, et al: Fracture repair during external ﬁxation: Torsion tests of rabbit osteotomies. Acta Orthop Scand 58:66–70, 1987 2. Adolphson P, Jonsson U, Dalen N, et al: Stress protection by external ﬁxation of the rabbit tibia. Acta Orthop Scand 61:324–326, 1990 3. Anson LW: Emergency management of fractures. In Slatter D (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders, 1993, pp 1603–1610 4. Arens S, Schlegel U, Printzen G, et al: Inﬂuence of materials for ﬁxation implants on
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5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.
local infection: An experimental study of steel versus titanium DCP in rabbits. J Bone Joint Surg (Br) 78B:647–651, 1996 Brekke JH, Toth JM: Principles of tissue engineering applied to programmable osteogenesis. J Biomed Mater Res 43:380–398, 1998 Brueton RN, Brookes M, Heatley FW: The vascular repair of an experimental osteotomy held in an external ﬁxator. Clin Orthop 257:286–304, 1990 Conn M: Tibial fracture in a guinea pig. Exotic DVM 2.5:5–6, 2000 Court-Brown CM: The effect of external skeletal ﬁxation on bone healing and bone blood supply: An experimental study. Clin Orthop 201:278–289, 1985 De Young DJ, Probst CW: Methods of internal fracture ﬁxation: General principles. In Slatter D (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders, 1993, pp 1610–1640 DeCamp CE: External coaptation. In Slatter D (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders, 1993, pp 1661–1676 Flecknell PA: Analgesia of small mammals. Vet Clin North Am Exot Anim Pract 4:47–56, 2001 Gentry LO: Antibiotic therapy for osteomyelitis. Infect Dis Clin North Am. 4:485–498, 1990 Grewe SR, Stephens BO, Perlino C, et al: Inﬂuence of internal ﬁxation on wound infections. J Trauma 27:1051–1053, 1987 Holmstrom T, Paavolainen P, Slatis P, et al: Effect of compression on fracture healing: Plate ﬁxation studied in rabbits. Acta Orthop Scand 57:368–372, 1986 Hulse D, Hyman B: Fracture biology and biomechanics. In Slatter D (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders, 1993, pp 1595–1603 Johansson A, Lindgren JU, Nord CE, et al: Local plate infections in the rabbit. Injury Int J Care Injured 30:587–590, 1999 Kaderly RE: Delayed union, nonunion, and malunion. In Slatter D (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders, 1993, pp 1676–1685 Kapatkin A: Orthopedics in small mammals. In Hillyer EV, Quesenberry KE (eds): Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. Philadelphia, WB Saunders, 1997, pp 346–357 Laftman P, Sigurdsson F, Stromberg L: Recovery of diaphyseal bone strength after rigid internal plate ﬁxation: An experimental study in the rabbit. Acta Orthop Scand 51:215–222, 1980 Mason DE: Anesthesia, analgesia, and sedation for small mammals. In Hillyer EV, Quesenberry KE (eds): Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. Philadelphia, WB Saunders, 1997, pp 378–391 Ouzounian TJ, Kabo JM, Grogan TJ, et al: The effects of pressurization on fracture swelling and joint stiffness in the rabbit hind limb. Clin Orthop 210:254–256 Paavolainen P, Karaharju E, Slatis P, et al: Radiographic evaluation of fracture healing after rigid plate ﬁxation: Experiments in the rabbit. Acta Radiologica Diagnosis 22:697– 702, 1981 Paley D, Young MC, Wiley AM, et al: Percutaneous bone marrow grafting of fractures and bony defects: An experimental study in rabbits. Clin Orthop 208:300–312, 1986 Pead MJ, Carmichael S: Treatment of a severely comminuted fracture in a rabbit using a Kirschner-Ehmer apparatus. J Small Animal Pract 30:579–582, 1989 Piermattei DL, Flo GL: Delayed union and nonunion. In Brinker, Piermattei, and Flo’s Handbook of Small Animal Orthopedics and Fracture Repair. Philadelphia, WB Saunders, 1997, pp 154–162 Piermattei DL, Flo GL: Fractures: Classiﬁcation, diagnosis and treatment. In Brinker, Piermattei, and Flo’s Handbook of Small Animal Orthopedics and Fracture Repair. Philadelphia, WB Saunders, 1997, pp 124–146 Piermattei DL, Flo GL: Treatment of acute and chronic bone infections. In Brinker, Piermattei, and Flo’s Handbook of Small Animal Orthopedics and Fracture Repair. Philadelphia, WB Saunders, 1997, pp 163–169 Simpson AM, Radlinsky M, Beale BS: Bandaging in dogs and cats: External coaptation. Compend Contin Educ Pract Vet 23:157–164, 2001
HELMER & LIGHTFOOT
29. Smith MM: Orthopedic infections. In Slatter D (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders, 1993, pp 1685–1694 30. Terjesen T, Johnson E: Effects of ﬁxation stiffness on fracture healing: External ﬁxation of tibial osteotomy in the rabbit. Acta Orthop Scand 57:146–148, 1986 31. Terjesen T, Svenningsen S: The effects of function and ﬁxation stiffness on experimental bone healing. Acta Orthop Scand 59:712–715, 1988 32. Terjesen T: Bone healing after metal plate ﬁxation and external ﬁxation of the osteotomized rabbit tibia. Acta Orthop Scand 55:69–77, 1984 33. Terjesen T: Healing of rabbit tibial fractures using external ﬁxation: Effects of removal of the ﬁxation device. Acta Orthop Scand 55:192–196, 1984 34. Terjesen T: Plate ﬁxation of tibial fractures in the rabbit: Correlation of bone strength with duration of ﬁxation. Acta Orthop Scand 55:452–456, 1984 35. Waters RV, Gamradt SC, Asnis P, et al: Systemic corticosteroids inhibit bone healing in a rabbit ulnar osteotomy model. Acta Orthop Scand 71:316–321, 2000 36. Weigel JP: Amputations. In Slatter D (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders, 1993, pp 1901–1910 Address reprints requests to Peter J. Helmer, DVM Avian and Animal Hospital of Bardmoor, Inc. 11405 Starkey Road Largo, FL 33773