Successful treatment of a radioulnar synostosis in a Mississippi kite (Ictinia mississippiensis).
Article Type: Report
Subject: Wings (Animal) (Abnormalities)
Ulna (Abnormalities)
Bones (Abnormalities)
Bones (Diagnosis)
Bones (Care and treatment)
Authors: Beaufrere, Hugues
Ammersbach, Melanie
Nevarez, Javier
Heggem, Brittany
Tully, Thomas N., Jr.
Pub Date: 06/01/2012
Publication: Name: Journal of Avian Medicine and Surgery Publisher: Association of Avian Veterinarians Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2012 Association of Avian Veterinarians ISSN: 1082-6742
Issue: Date: June, 2012 Source Volume: 26 Source Issue: 2
Geographic: Geographic Scope: Canada Geographic Code: 1CANA Canada
Accession Number: 298292706
Full Text: Abstract: A Mississippi kite (Ictinia mississippiensis) was presented to the Wildlife Hospital of Louisiana, School of Veterinary Medicine, Louisiana State University, for an inability to fly and was subsequently diagnosed with a minimally displaced, closed, simple, short oblique, diaphyseal fracture of the distal third of the right ulna. A figure-8 bandage was initially applied to the wing to stabilize the fracture. Over a 5-week period, the kite developed progressive reduction in wing extension, and serial radiographs revealed a bridging callus at the ulnar fracture site, as well as development of a radioulnar synostosis. To restore wing function and extension, surgical excision of the bony union between the radius and the ulna was performed, after which a polypropylene mesh implant was interposed between the 2 bones. Within 2 weeks after the surgical procedure, the kite had recovered normal wing extension and was able to fly without noticeable impairment. The bird was released 2 weeks after surgery. This case illustrates a common complication of external coaptation used as sole means of managing fractures of the avian ulna, radius, or both, which results from lack of interosseous soft tissue in the antebrachial area. On the basis of the successful outcome in this case, surgical excision of the interdiaphyseal callus and interposition of a polypropylene mesh could be a viable option for management of posttraumatic radioulnar synostosis in birds of prey.

Key words: ulnar fracture, synostosis, orthopedics, birds of prey, avian, Mississippi kite, Ictinia mtsstsstpptensts

Clinical Report

An adult free-ranging Mississippi kite (Ictinia mississippiensis) was found near a road unable to fly and was brought to the Wildlife Hospital of Louisiana, School of Veterinary Medicine, Louisiana State University (Baton Rouge, LA, USA), for assessment and rehabilitation. A right wing droop was noted before restraining the bird. The bird weighed 250 g and had good body condition (body condition score 3.5/5) but was approximately 5% dehydrated. Soft tissue swelling and a hematoma, with red coloration indicating recent trauma, were noted on the right wing where a closed distal diaphyseal ulnar fracture was palpated. Extension of the affected wing was considered normal for this species. A fundic examination revealed no abnormalities.

A figure-8 bandage was applied to stabilize the injured wing. Blood was collected and submitted for a blood smear and measurement of packed cell volume and total solids. Initial treatment consisted of meloxicam (0.5 mg/kg IM; Metacam, Boehringer Ingelheim, St Joseph, MO, USA), fluid administration (30 mL/kg SC; Normosol-R, Abbott Laboratories, Chicago, IL, USA), and force-feeding small pieces of mice. Values for packed cell volume, total solids, and white blood cell count estimated from the blood smear were all within normal reference ranges for Accipitridae, and no blood parasites were observed.

The day after initial presentation, the kite was anesthetized by face mask induction with isoflurane in oxygen, intubated, and maintained with isoflurane. Ventrodorsal and lateral whole-body radiographs and an anteroposterior projection of the right wing were obtained. Recovery from anesthesia was uneventful. Radiographs revealed a minimally displaced, closed, simple, short oblique, diaphyseal fracture of the distal third of the ulna with minimal soft tissue swelling (Fig 1A).

[FIGURE 1 OMITTED]

On the basis of the nature of the ulnar fracture, as well as the integrity of the radius, the decision was made to manage the fracture conservatively with a figure-8 bandage. Treatment with meloxicam, fluid administration, and hand-feeding, using small pieces of mice, mealworms, and crickets according to the bird's daily energy requirements, were continued until the kite started eating on its own 3 days later. The bandage was changed weekly, and physical therapy, consisting of 15 minutes of passive range of motion of the right wing, was performed at each examination. Fracture healing was monitored with radiographs at 3 and 5 weeks after initial presentation (Fig 1B and C, respectively). Radiographs at 3 weeks revealed endosteal and periosteal callus formation with loss of sharp margins of the fracture fragments and progressive disappearance of the fracture line. A periosteal bony callus on the radius appears to connect with the ulnar callus adjacent to the fracture site (Fig lB). At 5 weeks, radiographs demonstrated increased opacification of the callus and presence of bony bridging between the ulnar fragments and between the ulnar fracture site and the radius, which was also palpable (Fig 1C). These findings were consistent with a radioulnar synostosis. Progressive reduction of wing extension was noted over the 5-week period, with carpal extension eventually decreased by approximately 30% and overall wing extension moderately reduced.

Because of the decreased wing extension and associated function attributed to the radioulnar synostosis, surgical separation of the radius and ulna with interposition of a polypropylene mesh was elected. The kite was anesthetized as previously described and maintained with 2% 3% isoflurane throughout the surgical procedure. The end-tidal C[O.sub.2], heart rate, and core body temperature and an electrocardiogram were assessed by using a wireless veterinary monitor (PC-Vet Gard+, Vmed Technology, Mill Creek, WA, USA). The bird's body temperature was maintained by using a conductive fabric warming blanket (Hot Dog Warmer, Augustine Biomedical, Eden Prairie, MN, USA). Butorphanol was administered preoperatively (1 mg/kg IM; Torbugesic, Fort Dodge Animal Health, Fort Dodge, IA, USA), and a brachial plexus nerve block was performed by injecting lidocaine (1 mg/kg) as previously described. (1) Fluids were delivered subcutaneously (50 mL/kg; Normosol), and cefazolin sodium (100 mg/kg IM; Novopharm, Schaumburg, IL, USA) was administered 30 minutes before the skin was incised and at completion of the surgery approximately 80 minutes later. The prophylactic antimicrobial protocol used perioperatively in this case was adapted from current recommendations in orthopedic surgery in small animals, humans, and raptors with dose and frequency modified according to the pharmacokinetic disposition of cephalosporins in avian species (administration every 2 half-lives). (2-8)

Feathers on the dorsal wing, with the exception of the secondary flight feathers, were plucked, and the area was surgically prepared. A 3-cm skin incision was made over the distal half of the dorsal antebrachium by using Harrison bipolar forceps and a radiosurgical unit (Surgitron dual frequency, Ellman International, Oceanside, NY, USA). The bony callus and extensor metacarpi ulnaris m. were readily visible. A small Lempert rongeur and straight-edge periosteal elevator were used to remove the majority of interosseous fibrous callus from the interosseous space, taking care not to damage either the extensor metacarpi ulnaris m. overlying the callus or the tendon of the metacarpi radialis m. dorsal to the radius (Fig 2A). After removing the majority of the synostosis, a 3-cm length of polypropylene mesh (Prolene; Ethicon, San Angelo, TX, USA) was folded longitudinally in 2 layers and interposed between the radius and ulna. The ventral portion of the mesh was wrapped around the ulnar fracture site (Fig 2B). The skin incision was closed with the use of 5-0 polydiaxonone (PDS, Ethicon) in a simple continuous pattern. The total surgery time was 45 minutes. Because a stable callus was present at the ulnar fracture site, the wing was left unbandaged to permit motion between the radius and the ulna. Postoperative radiographs confirmed the decreased amount of bony callus between the radius and ulna (Fig 3A). Treatment for postoperative analgesia was continued with butorphanol (1 mg/kg q4h x 8 hours) and meloxicam (0.5 mg/kg q12h x 7 days). Additionally, amoxicillin/clavulanate (125 mg/kg PO q 12h x 10 days; Clavamox, Pfizer Animal Health, Exton, PA, USA) was administered to help prevent postoperative infection at the site of the polypropylene mesh implant.

The bird recovered uneventfully, and a physical therapy protocol was implemented by using passive range of motion exercise and extension/ flexion of the wing for 15 minutes once daily for 1 week as previously described. (5) During the 48 hours after surgery, the bird progressively recovered normal wing extension. One week after surgery, the kite was transferred to an outside aviary measuring 20 m x 10 m x 2.5 m. The bird's wing position and attitude appeared normal during the postoperative period. In the outside enclosure, the bird was encouraged to fly the complete length of the aviary 1-2 times daily for 20-30 minutes. By 4 days after transfer to the outside aviary, the bird had gradually regained flight capability with apparently normal flight aptitudes. The complexity of aerial maneuvers, turning abilities, and endurance during exercises were evaluated to assess flight aptitudes. (9) Food items, including pieces of mice and insects, were placed twice daily on perches at either side of the enclosure.

A radiograph of the right wing performed 2 weeks after surgery demonstrated continued bone remodeling and no evidence of recurrent synostosis formation (Fig 3B). Two days after this final radiographic evaluation was completed, the bird's flight was considered normal for the species. The bird was exhibiting excellent flight capabilities and endurance. Flight reconditioning had been undertaken during mid-September, which was near the end of the fall migration period for Mississippi kites. (10) Not releasing the bird during the migration period would have required keeping it for a full season until the following migration period, thus exceeding federal regulations stating that state birds must not be maintained in rehabilitation for more than 180 days without a formal request to the US Fish and Wildlife Services. In our experience, the fractious nature of this species in captivity was not suitable for long-term housing. Other factors affecting the timing of release were space constraints, feeding costs, and labor involved in longterm housing of the bird. After examining these considerations, the decision was made to release the bird. During release, the bird did not show any noticeable flight impairment. Long-term follow-up with radio tracking was not performed.

[FIGURE 2 OMITTED]

Discussion

In this report, we document the successful surgical treatment of a posttraumatic radioulnar synostosis in a Mississippi kite by excision of the bony union and interposition of a polypropylene mesh between the radius and ulna. The case progression emphasizes the advisability of considering surgical fixation of ulnar fractures, particularly when the distal aspect of the bone is involved. It is generally accepted that most ulnar and radial fractures should be surgically stabilized in free-ranging birds to avoid the formation of radioulnar synostosis and provide a more predictable outcome for restoration of flight capabilities. (5) For minimally displaced fractures of the ulna when the radius is intact, external coaptation with a figure-8 bandage could be a less complex and less costly method of management entailing minimal iatrogenic trauma to the soft tissue. (11-15) An intact radius can share the load of forces on the wing and act as an internal splint. However, complications such as muscle atrophy, joint ankylosis, tendon contraction, bone shortening, malunion, and patagial constriction are commonly encountered with wing bandaging. (13) Some of these complications can be overcome with physical therapy. Recommended surgical techniques used to repair ulnar fractures include the use of an intramedullary pin-external skeletal flxator tie-in or a type I external skeletal fixator. (5) Because of the relative mobility of the radius, external coaptation alone is not recommended for the management of radial fractures, which are best stabilized with an intramedullary pin. (5,14,16) When both the radius and ulna are fractured, stabilization of both bones is recommended to prevent synostosis formation. (5)

[FIGURE 3 OMITTED]

Radioulnar synostosis can occur both as a postoperative complication or when external coaptation is used as the sole form of stabilization. (5,14,15-17,18) Synostosis between the radius and ulna appears to occur most commonly with fractures involving the distal third of the radial or ulnar diaphysis, particularly when 1 fragment is displaced toward the adjacent bone, where the presence of soft tissue and the distance between the bones are minimal. (5) With the kite in this case report, the uncomplicated and minimally displaced nature of the fracture, in addition to time and monetary constraints, suggested conservative management of the fracture, but this approach subsequently led to formation of a radioulnar synostosis.

In birds, the radius and ulna articulate with each other in a drawing parallel mechanism, which enables passive coordination of the elbow and the wrist as well as synchronization of wing flexion and extension; it might also function to automate circumduction motions of the wing during flapping flight. (19,20) The radius is a relatively mobile bone that has the ability to shift back and forth along the length of the ulna. Prevention of this motion will restrict wing extension and impair the normal wingbeat cycle. (16) A radioulnar synostosis in birds mechanically obstructs mobility of the radius along the ulna and, consequently, prevents flight.

Although surgical treatment of radioulnar synostosis has been performed in birds, the procedure is still considered anecdotal and, to our knowledge, has not been reported in the peer-reviewed literature. The synostosis is typically excised with rongeurs or an air drill, and a fat pad, usually harvested from the subcutaneous fat overlying the coelom, is placed between the radius and ulna to prevent reformation of a bony bridge (P. Redig, written communication, 2010). (18) In this case, the availability and ease of placing and shaping a synthetic biocompatible implant (polypropylene mesh) was preferable. The mesh yielded satisfactory results with apparently minimal discomfort and full return to wing function. Radial ostectomy has also been reported as a treatment for radioulnar synostosis. (21) However, because of the importance of the radius in avian wing support and biomechanics, ostectomy cannot be recommended for wild birds for which release is the goal and chances for long-term survival in a noncaptive environment must be optimized.

In humans, highly comminuted and open fractures appear more likely to develop posttraumatic radioulnar synostosis. (22-25) The recommended surgical treatment is excision of the synostosis and interposition of biological or synthetic materials in the interosseous space. (22,25) Interpositional materials can include fat, muscle, fascia, silicone, cellophane, polyethylene, or bone wax. (22,26) In 1 case series, synthetic materials (silicone) provided better results than biologic materials, which might have contributed to the generation of scar tissue. (26,27) In another study, various results were obtained by tissue excision alone, and interposition of a fat graft did not yield any significant advantage. (28) Interposition of vascularized muscle or adipofascial

grafts has also been effective. (25,27,29.30) Currently in human surgery, fascia, fat, and muscle are preferred over nonbiological materials for placement between the radius and ulna. (22,30) There are no reports regarding the use of polypropylene mesh as an interpositional material in people. Whether the various surgical methods used in humans can be effectively extrapolated to repair of the avian wing is difficult to determine considering the difference in biomechanics between the wing and human forearm. In humans, as with birds, postoperative physical therapy is generally recommended after synostosis surgery. (22) More frequent physical therapy during the initial management of this kite could have prevented the development of a radioulnar synostosis, but the concern was that frequent motion of the bone fragments might delay bone healing.

There are no general recommendations for evaluation of long-term complications or a defined time span during which complications may arise. However, the tissue tolerance and biocompatibility of polypropylene mesh are considered acceptable. (31-33) In humans, complications include foreign body inflammatory response and infections involving the implant. (31,32,34) No short-term complications, including inflammation, were noted at the bird's surgical site 2 weeks postoperatively. Long-term infections involving the mesh were considered unlikely, and because of the lack of significant muscle groups in the area, we felt that potential fibrosis of the interosseous area would not impair muscles and wing biomechanics.

In birds, the availability of potential tissues for interposition of vascular graft is limited in the distal wing, which primarily includes tendons of the carpal flexor and extensor muscles. Interposition of biological materials excised from a distant site appears to provide good results but necessitates additional incisions and tissue excision, which might not be practical in smaller species. Alternatively, the use of synthetic materials such as a polypropylene mesh, silicone, or bone wax could prove to be both practical and effective in the management of posttraumatic radioulnar synostosis in birds of prey.

Acknowledgments: We thank Martine Angel for her invaluable help during the rehabilitation process and follow-up of this kite.

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Hugues Beaufrere, Dr Med Vet, Dipl ECZM (Avian), M61anie Ammersbach, DVM, Javier Nevarez, DVM, PhD, Brittany Heggem, DVM, and Thomas N. Tully Jr, DVM, MS, Dipl ABVP (Avian), Dipl ECZM (Avian)

From the Wildlife Hospital of Louisiana, Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA (Beaufrere, Nevarez, Heggem, Tully); and the Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario N1G 2W1, Canada (Ammersbach).
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