Successful Management of Open, Contaminated Metacarpal Fractures in an Adult Snowy Owl (Bubo scandiacus) With a Minimal Type II External Skeletal Fixator.
Key words: fractures, metacarpal, osteomyelitis; external skeletal fixator, type II ESF, avian, snowy owl, Bubo scandiacus
An adult male (based on morphological criteria) (1) snowy owl (Bubo scandiacus) was found down in December and unable to fly in a rural area of western New York State. At admission, the bird was bright, alert, and responsive, but in poor body condition (body condition score, 1/5) and weighing 940 g. Severe dehydration was noted as indicated by a prolonged upper eyelid tent. A reduced direct pupillary light response was present in the right eye. A chronic (estimated greater than 1 week) open wound was apparent in the area of the right metacarpus surrounded by caseous debris. An open (compound) transverse fracture of the major metacarpal bone was visible and the fracture ends appeared necrotic. A severe feather louse infestation was present.
Basic laboratory workup, including a fecal, complete blood count (CBC), plasma biochemisty and lead testing, was performed. A zinc sulfate fecal flotation and direct smear revealed no parasites or ova. A blood sample (1 mL) was collected from the right jugular vein and analyzed within 1 hour in a VetScan analyzer (Avian/ Reptilian Profile Plus; Abaxis North America, Union City, CA, USA) and a point-of-care lead analyzer (LeadCare II; Magellan Diagnostics, North Billerica, MA, USA). White blood cell (WBC) count was analyzed using a modified Unopette system (Avian Leukopet; VetLab Supply, Palmetto Bay, FL, USA). The packed cell volume (PCV) demonstrated a mild anemia at 34% (reference interval, 37%-60%). (2) Red blood cells (RBCs) displayed mild polychromasia (<5%) with a few spherocytes and rubricytes present. Moderate-to-severe percentages of toxic heterophils and reactive lymphocytes were present. Hyperuricemia (28.2 mg/dL; reference interval, 5.1-24.2 mg/dL), hypoproteinemia (1.6 g/dL; reference interval, 2.94.8 g/dL), hypoalbuminemia (1.0 g/dL; reference interval, 2.0-3.9 g/dL), and hyponatremia (143 mmol/L; reference interval, 148-164 mmol/L) were present on the plasma biochemical profile. (3) All other values were within normal reference intervals. Blood lead levels were insignificant (<3.3 [micro]g/ dL).
The bird was premedicated with butorphanol (1 mg/kg IM; Torbugesic, Fort Dodge Animal Health, Fort Dodge, IA, USA) and anesthetized with isoflurane (l%-5% induction, 3% maintenance) in 100% oxygen via facemask for a ventrodorsal whole-body radiograph and a ventrodorsal radiograph of the right wing. Radiographs demonstrated no significant findings on the whole-body view, but a ventrodorsal wing film showed a moderately displaced, mid-diaphyseal, transverse fracture of the right major and minor metacarpal bones (Fig 1). Approximately 1 cm of the fracture ends of the major metacarpal bone had increased medullary opacity. While under anesthesia, the fracture site was gently cleansed with 0.05% Chlorhexidine solution (Nolvasan; Fort Dodge Animal Health), rinsed with sterile saline, bandaged with saline-moistened sterile gauze, and stabilized with a figure-of-8 bandage. Subcutaneous fluids (50 mL/kg; Plasma-lyte A; Abbott Laboratories, North Chicago, IL, USA), enrofloxacin (15 mg/kg in SC fluid pocket; Enrofloxacin 2.27%), and meloxicam (0.3 mg/kg IM) were administered. Carbaryl flea powder was applied to the skin and feathers. The rehabilitator was advised of the poor prognosis but chose to pursue further treatment with initial medical stabilization of the bird and surgical stabilization of the wing 2 days later. The rehabilitator was to administer fluids (40 mL/kg SC q 12h; Plasma-lyte A), meloxicam (0.5 mg/kg PO q12h), enrofloxacin (15 mg/kg PO q24h), itraconazole (10 mg/kg PO q24h; Sporonox; Janssen Pharmaceutica, Beerse, Belgium), and tube feeding (20 mL/kg PO q12h; Carnivore Care; Oxbow Animal Health, Murdock, NE, USA) until surgery.
Two days later, the bird was premedicated and anesthetized as described previously. He was intubated with a 3.5-mm uncuffed endotracheal tube and maintained on anesthesia with 3% isoflurane in oxygen. A 22-gauge hypodermic needle was placed as an intraosseous catheter in the left distal ulna through which fluids (10 mL/kg per hour; Plasma-lyte A) were administered via intermittent bolus during the procedure. Feathers were plucked around the wound on the ventral and dorsal surfaces of the distal wing (Fig 2). The fracture site on the ventral surface of the wing (2 X 2 cm) was disinfected with 0.05% Chlorhexidine solution, gently debrided, and flushed with sterile saline (Fig 3). The skin was incised proximally and distally to the fracture site and necrotic edges of skin tissue were dissected from the wound. The skin was undermined carefully from the subcutaneous tissues. Necrotic and devitalized tissues were debrided and the area was flushed copiously with sterile saline. The distal major metacarpal fragment appeared to be devitalized due to approximately 2 mm of discoloration adjacent to the fracture site. Bone rongeurs were used to remove 1 to 2 mm of bone from the fragment at the fracture site. Clotted blood and necrotic debris were removed from the medullary canal with a scalpel and hemostats and flushed clean with sterile saline. Fracture segments were realigned and the major metacarpal bone was stabilized with a minimal type II ESF (Fig 4). After realignment, a 0.62 mm Interface Positive Profile ESF Half-pin (Imex Veterinary, Inc., Longview, TX, USA) was placed into the proximal fragment and a 0.62 mm half pin into the distal condyle of the distal fragment from dorsal to ventral. Plastic corrugated tubing 6 mm in diameter was placed over the dorsal ends of both pins and acrylic (Acrylx ESF Acrylic; Imex) was inserted into the tubing. The acrylic was allowed to cure for 12 minutes per manufacturer's instructions while holding the bone fragments in place. The proximal and distal portions of skin were closed with 4-0 polypropylene suture (Prolene; Ethicon US, Somerville, NJ, USA) using Ford interlocking and simple interrupted patterns. The central portion of the wound (approximately 1.5 X 1.5 cm) was unable to be closed due to lack of skin coverage. A 0.45 mm half pin (Imex) was placed into the proximal fragment distal to the 0.62 mm half pin from ventral to dorsal at an approximately 30[degrees] angle to the bone. An additional 0.45 mm half pin was placed similarly into the distal fragment proximal to the 0.62 mm half pin. Plastic tubing 6 mm in diameter was placed over the ventral end of all four pins and acrylic was inserted into the tubing and allowed to cure (Fig 5a). The pins were trimmed even with the plastic tubing and elastic tape (Elastikon; Johnson & Johnson, Skillman, NJ, USA) was placed over the sharp edges (Fig 5b).
Low level laser therapy (15.0 Joules; Companion Therapy Laser, Newark, DE, USA) was administered over the fracture site for 1 minute with a power of 60 watts and a distance of 1 cm with a defocusing hand piece. Transparent dressing (Tegaderm; 3M Health Care Ltd, Loughborough, Leicestershire, UK) was placed over the suture line and open wound. The owl remained stable throughout the anesthetic event but recovered slowly. Due to the length of the procedure and visualization of proper fracture alignment during surgery, postoperative radiographs were not performed. Upon release to the rehabilitator, meloxicam, enrofloxacin, and itraconazole were continued. Clindamycin (50 mg/kg PO q12h) was added into the regimen to enhance spectrum of coverage and due to the poor condition of the bone, the necrotic debris removed from the medullary cavity, and observed gross contamination of the wound.
The transparent dressing was removed and replaced, and the wound was debrided using local anesthesia with 2% lidocaine (1 mg/kg topically) and flushed with 0.05% Chlorhexidine solution and saline twice weekly until granulation tissue was present over the exposed bone (approximately day 22 postoperatively). Sutures were removed 8 days after surgery. Vitamin B complex with vitamin C (0.1 mL/kg PO q24h; Liquid B-12; Now Foods, Bloomingdale, IL, USA) was added at 4 days postoperatively to help with anemia and overall immunity. (4) At 2 weeks postoperatively, a blood sample was obtained for a PCV and plasma biochemistry. PCV of 44% was within normal reference intervals (37%-60%). (2) Repeat plasma biochemical profile revealed no abnormalities. The skin had closed over the wound at approximately day 25 postoperatively and ventrodorsal (Fig 6a) and caudocranial radiographs of the right wing were performed using butorphanol and isoflurane anesthesia as described previously. Appropriate periosteal callus formation was present and rechecks were changed to once weekly. The rehabilitator moved the owl into a 5 X 5 m flight cage at day 29 postoperatively to encourage wing use and exercise. At day 42 postoperatively, butorphanol and isoflurane anesthesia were administered as described previously. Ventrodorsal and caudocranial radiographs (Fig 6b) revealed periosteal callus formation at the fracture site with no obvious signs of osteomyelitis and the ESF device was removed. Antibiotics were discontinued and meloxicam was reduced to once daily for 1 more week as the bird was becoming very confrontational. Itraconazole was continued until release. The owl was placed into a 12 x 25 m flight barn at day 50 postoperatively to encourage longer flight. A final recheck exam at day 56 showed excellent range of motion with a large stable callus present over the fracture site and a weight of 1360 g. The owl was released 6 days later, 2 months postoperatively, and exhibited sustained flight.
Approximately 7 weeks later, a photograph of the owl in flight seemed to show blood under the affected wing. It was trapped by the New York Department of Environmental Conservation and presented for examination. At hospital admission, the bird was bright, alert, and responsive, but again in poor body condition (body condition score, 2/5) at a weight of 1050 g. Mild dehydration (<5%) was noted as indicated by a slightly prolonged upper eyelid tent. The right wing had a small 2X2 mm abrasion covered in a crust and a bony callus palpated at the previous fracture location. No blood was visible on the wing. Ventrodorsal (Fig 7) and caudocranial radiographs of the right wing revealed a stable periosteal callus at the fracture site with no obvious signs of osteomyelitis. A synostosis was present between the major and minor metacarpals. A PCV of 39% was within normal limits (reference interval, 37%-60%). (2) Subcutaneous fluids (20 mL/kg; Plasma-lyte A) were administered once and antifungal medications were reinstated for 2 weeks. Three days later, the owl had gained 100 g of body weight, and ventrodorsal and right lateral full body radiographs were performed under isoflurane anesthesia as described previously with no significant findings. After over-summering in a larger 10 X 50 m flight cage, the owl was released the following November, 11 months after surgical stabilization at a weight of 1750 g. At the time of this writing, the owl has been observed to be doing well 1 month after release.
The snowy owl is one of the largest owls in the world and the largest by weight in North America. Snowy owls have unusually high wing-loading that is more typical of hawks and falcons and the opposite of light, buoyant owls, such as the barn owl (Tyto alba). (5) Fractures of avian metacarpals can be managed conservatively with external coaptation or surgically with placement of tie-in fixator (TIF) devices, intramedullary (IM) pinning, or external skeletal fixation (ESF) devices.
The avian manus has been vastly adapted for flight. The carpometacarpus, a fusion of the central and distal carpal and the metacarpal bones, forms a rigid platform for the attachment of the primary flight feathers. (6) The major and minor metacarpal bones are fused proximally and distally forming an intermetacarpal space. (7) Fractures of the major metacarpal bone are challenging to manage in avian species. These fractures require more attention to careful assessment and selection of a proper fixation device for maximal healing than any other bone in the avian skeleton. (8) Often, both metacarpal bones are fractured. The prognosis is improved if the minor metacarpal bone is intact. (8) The carpometacarpus has few soft tissue structures and a limited blood supply which impedes healing. Damage to the vascular supply may occur and the wing tip could be lost since the superficial ulnar artery is the single artery located between the major and minor metacarpal bones. (7) The majority of these fractures are high-energy from flying into a fence, power line, or projectile. The high-energy impact results in these fractures presenting as open and/or comminuted. (8) Success rates with surgical or nonsurgical intervention are substantially reduced compared to those of other long bones in the avian skeleton. (8)
Several methods of fixation have been suggested with varying success. Closed, easily reduced fractures of the metacarpus are managed with coaptation using a reinforced splint (curved-edge splint) and figure-of-8 bandage, especially if the minor metacarpal bone is intact or the fracture is too proximal for fixation hardware. (8) The wing must be splinted for approximately 3 weeks, increasing the potential for immobilization-related complications. (8) Procedures for applying curved-edge splints are described in the literature. (9) A recent case report found that metacarpal fractures (3 open, 12 closed) in free-living raptors can be managed successfully with external coaptation with the median time bandaged being 21 days. (10) The author found that 14 of 15 metacarpal fracture cases were released to the wild with only 1 case resulting in nonunion. (10)
Simple metacarpal fractures, comminuted metacarpal fractures, or those with extensive soft tissue damage or fracture displacement can be managed with external fixation. (8) The fixator must bear the entire load during healing as metacarpal fractures are often highly unstable. (8) A TIF that includes an IM pin and ESF device is an option for metacarpal fractures but recent literature suggests that TIF devices have been less successful than other fixation modes. (8) IM pins alone may be the least desirable choice due to potential injury associated with implantation of the pin and are not recommended without further stabilization. (8) A recent case report detailed a successfully repaired compound, comminuted metacarpal fracture in a black kite (Milvus migrans) using an IM pin and coaptation. (11)
External skeletal fixator devices are recommended for fractures that are highly comminuted with soft tissue damage or are displaced. Using an ESF device allows for 2 pins placed above and below the fracture, providing more load sharing. Type I ESF devices incorporate pins through both cortices of the bone which are exteriorized and attached to a connecting bar on one side of the limb (unilateral). Type II ESF devices differ in that the pins are exteriorized and attached to connecting bars on two sides of the limb (bilateral). (12) It is recommended that metacarpal fractures repaired with type I ESF devices be coapted to the body to prevent dislodgement of the fixator if the patient flaps its wing forcefully. (8) In contrast, type II ESF devices ensure less risk of pin loosening or pull out without coaptation since pins are exteriorized with connecting bars on both sides of the limb. Type II devices are divided into maximal, where all pins are connected to both connecting bars, and minimal, where some pins are connected to both bars and others are connected only to one. (12) All ESF devices have potential complications, including pin loosening and migration, reaction to the fixation devices, and development of osteomyelitis or sequestrum. (13)
Dorsal and ventral approaches to the carpometacarpus have been described, but approach will likely depend on whether an open wound is present. Currently, a ventral approach is recommended due to the primary feather insertions on the dorsal surface of the metacarpus. A dorsal approach may compromise a bird's soaring and gliding ability. (14) A ventral approach is described in great detail elsewhere. (7,14)
We estimated the injury to have occurred 1 to 2 weeks before initial presentation due to the poor condition of the owl and the appearance of the wound. This fracture was considered a type 3 due to extensive soft tissue damage including tendons. If this had been a closed fracture, an IM pin could have been placed retrograde to align the major metacarpal pieces. However, an IM pin would have likely been a nidus for infection and caused delayed healing or nonunion. Instead, 2 ESF pins and a dorsal connecting bar were used to approximate the fracture. Then the 2 additional pins and ventral connecting bar were added for additional fracture stability creating a minimal type II ESF device. Since we used a type II ESF device in this bird, coaptation did not seem necessary. This also minimized the need for hands-on physical therapy and range of motion exercises for this high stress bird. The bird was gradually placed in larger enclosures to perform auto-physiotherapy.
Ideally, a culture should have been performed on this bird before initiating of antibiotic therapy. A broad-spectrum antibiotic for skin and bone (enrofloxacin) and the antibiotic of choice for bone (clindamycin) were chosen empirically. These antibiotics synergize for mixed gram-positive and gram-negative infections. Nonsteroidal anti-inflammatory drugs, such as meloxicam, are contraindicated in patients with dehydration. This owl's pain was considered significant enough to warrant the risk to the kidneys along with aggressive fluid therapy provided by the rehabilitator. Alternatively, opioids, such as butorphanol or tramadol, could have been administered repeatedly. Prophylactic antifungal therapy was initiated since northern owl species are considered particularly high-risk to aspergillosis in captivity. (13) Hyperuricemia was likely caused by severe dehydration in this case since repeat bloodwork demonstrated a normal value. Emaciation was the likely cause for the initial hypoproteinemia, hypoalbuminemia, and hyponatremia as these also were normal on repeat bloodwork. Concern for instability of the catheter during the procedure led to placement of an intraosseous catheter versus an intravenous catheter.
Orthogonal radiographs usually are required to properly describe a fracture. A single view was elected in this case because the fracture displacement was visible on physical exam. Postoperative radiographs also generally are recommended after orthopedic surgery. Since the fracture was visible throughout the procedure and proper alignment was readily apparent, these were not performed. The radiograph taken on day 25 postoperatively showed the proximal pin in the distal fragment not penetrating the ventral cortex. This pin was palpated as it exited the cortex at operation and likely migrated postoperatively. Radiographs from day 42 postoperatively demonstrated increased opacification of the medullary cavity. This was attributed to bone metabolism; however, resolving concurrent osteomyelitis could not be ruled out. The synostosis present between the major and minor metacarpals in the radiograph after recapture did not seem to impede flight in this snowy owl.
The owl's capture and initial release were highly publicized, since snowy owls are uncommon enough that photographers and birders flock to see them. For this reason, many avian-related organizations recommend minimizing disturbances of sensitive species, such as owls. (15,16) The owl's location was repeatedly published on social media websites and was reported to have been driven from his roosting area by photographers and birders. This may have led to him staying in the area after he should have been migrating north. Another possibility is that he was released prematurely. He was initially released based on his sustained flight, good body condition, and to coincide with migration. Perhaps the owl needed more time to rehabilitate to flight after convalescence. The owl was rehabilitated over the summer in a larger flight enclosure and released again in November to coincide with the arrival of other snowy owls in the northern states.
To our knowledge, this is the first use of a type II ESF device on the major metacarpal bone of a bird. This case would suggest that type II ESF devices could be considered for other cases of metacarpal fractures in raptors. Hopefully, the merits and disadvantages of this method can be studied further and documented with future cases and research. The successful outcome of this bird was due to an extremely dedicated rehabilitator who brought the bird back for frequent recheck appointments and provided excellent daily care and observation. Keeping the open wound properly dressed with frequent bandage changes was an important part of management of this case. Finally, an early return to wing use was key to this bird returning to flight.
Acknowledgments: We thank Marianne Hites at Messinger Woods Wildlife Care and Education Center in Holland, NY, for being instrumental in this bird's return to the wild, Scott Weidensaul (Project SNOWstorm. www.projectsnowstorm.org) for consultation, Tony Martyn, LVT and the staff at Specialized Care for Avian and Exotic Pets, and Sam Wicker, DVM, for help editing several versions of this paper.
Richard R. Burdeaux, Jr, DVM, and Laura Wade, DVM, Dipl ABVP (Avian)
From Specialized Care for Avian and Exotic Pets, 10882 Main Street. Clarence, New York 14031, USA.
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Caption: Figure 1. Ventrodorsal radiograph demonstrates moderately displaced fractures of the major and minor metacarpals of the right wing of a snowy owl. Increased medullary opacity also is visible at the fracture site.
Caption: Figure 2. Preoperative photograph of the open wound on the ventral surface of the right wing in the snowy owl described in Figure 1 after plucking. Caseous debris and necrotic bone are visible.
Caption: Figure 3. Photograph of wound of the snowy owl described in Figure 1 after debridement and lavage.
Caption: Figure 4. Placement of minimal type II ESF in the major metacarpal bone fracture in the snowy owl described in Figure 1. Insertion of 0.62 mm positive profile half-pins (a) and application of plastic tubing and acrylic to align and stabilize the fracture (b). Insertion of 0.44 mm positive profile half-pins (c) and application of plastic tubing and acrylic (d) to further stabilize the fracture. Note: fracture gap greatly exaggerated for diagram (fragments were placed adjacent to each other during actual surgery).
Caption: Figure 5. Intraoperative photograph of the anesthetized owl described in Figure 1 with the completed ESF device (a) before trimming pin ends. Note ball bandages on feet for human protection, (b) Elastic tape was applied to cover the sharp pin tips exiting the acrylic tubing.
Caption: Figure 6. (a) Caudocranial radiograph of the owl described in Figure 1 at day 25 postoperatively. Periosteal callus is visible at the fracture site. Note: Proximal pin in distal fragment did not appear to have penetrated the ventral cortex but was palpated as such during surgery, (b) Day 42 postoperatively. Periosteal callus is visible spanning the fracture. There is increased medullary opacity consistent with increased metabolic activity.
Caption: Figure 7. Ventrodorsal radiograph of the owl described in Figure 1 after recapture demonstrating a stable periosteal callus. A synostosis is seen between the major and minor metacarpals at the fracture site.
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|Title Annotation:||Clinical Report|
|Author:||Burdeaux, Richard R., Jr.; Wade, Laura|
|Publication:||Journal of Avian Medicine and Surgery|
|Date:||Sep 1, 2018|
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