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Distraction osteogenesis correction of mandibular ramis fracture malunion in a juvenile mute swan (Cygnus olor).

Abstract: A juvenile mute swan (Cygnus olor) was presented with right lateral deviation of the mandible. Radiographs demonstrated a healed fracture of the right mandibular ramis, which had compromised osteogenesis. A corrective osteotomy was performed and an osteogenic distractor was inserted over the lateral aspect of the right mandible. Dental acrylic implants were fixed to the rhinotheca to correct rotational alignment. A pharyngostomy tube was placed to facilitate administration of nutrition and medication. Postoperative images confirmed correct alignment of the mandible in relation to the maxilla. Implants were removed and postoperative complications were not reported. This is the first report of an osteogenic distractor used to correct mandibular deviation in an avian species. Distraction osteogenesis should be considered as a valid surgical option in juvenile or adult avian patients with pathologic bone shortening.

Key words: fracture, misaligned ossification, distraction osteogenesis, orthopedics, mandible, rhinotheca, avian, mute swan, Cygnus olor

Clinical Report

A wild juvenile mute swan (Cygnus olor) was presented to a wildlife rescue organization because of beak deformity, dysphagia, and poor body condition (Fig 1). The bird was notably smaller than its siblings, and it seemed unable to feed properly by itself. Radiographs were taken by the veterinarian at the wildlife rescue center within 24 hours of admission and confirmed mandibular malalignment (Fig 2). The right mandibular rami demonstrated some loss of bone density at the level of the palatine bone; the initial fracture was speculated to be on both the os prearticulare (prearticular bone) and the os supra-angulare (supra-angular bone). (1)

On physical examination, the bird was otherwise bright and alert, the mucous membranes were pink and moist, no skin tent was observed, and all vital parameters were within normal limits. The cygnet had a body condition score of 2.5/5 (based on the general muscle mass) (2) and weighed 3.5 kg. Results of hematologic testing were within reference intervals for the species. Results of plasma biochemical analysis revealed slightly high concentrations of creatine kinase (1642 U/L; reference interval. 1239 [+ or -] 173 U/L), (3) aspartate aminotransferase (165 U/L; reference interval, 116 [+ or -] 8 U/L), (3) and lactate dehydrogenase (972 U/L; reference interval, 688 [+ or -] 37 U/L), (4) compatible with muscle injury due to anorexia. The result of serologic testing for Chlamydia species was negative.

The bird was hospitalized and treated with meloxicam (0.5 mg/kg PO q24h) and assisted feeding (30 mL PO q4h; mixture of 4 parts of water, 3 parts of Emeraid Omnivore Care, and 2 parts of Emeraid Herbivore Care [Emeraid Critical Care Nutrition, Lafeber Company, Cornell, IL, USA]). While treatment options were considered, the swan was also given Hartmann's solution (Aquapharm 11, Animalcare Limited, Dunnington, York, UK) at maintenance rate (50 mL/kg per 24 hours SC), as it was not drinking during hospitalization.

After 12 hours of supportive treatment, butorphanol was administered (1 mg/kg IM q4h) in preparation for surgical repair. To minimize potential complications such as aspiration pneumonia from regurgitation, assisted feeding was stopped 4 hours before surgery. To induce anesthesia, a combination of ketamine (3 mg/kg) with medetomidine (150 [micro]g/kg; Domitor, 0.1% solution, Elanco Animal Health, Basingstoke, Hampshire, UK) was administered intravenously through a 22-gauge catheter in the left medial tarsal vein. The bird was intubated with a 6.5-mm uncuffed endotracheal tube and maintained on 2.0%-2.5% isoflurane in oxygen with intermittent manual positive-pressure ventilation. Fluid therapy (10 mL/kg per hour; Hartmann's solution) was administered during surgery.

[FIGURE 1 OMITTED]

The beak and right side of the face were aseptically prepared. A skin incision was made at the level of the distal third of the right mandible, and subcutaneous tissue and muscle were retracted and the right mandibular bone was exposed. A transverse osteotomy was performed by using an oscillating saw at the distal third of the right mandibular rami immediately adjacent to the primary healed fracture site. Two smooth 0.9-mm Steinmann pins were placed in the right mandible on either side of the osteotomy. The pins were passed through a lightweight constructed distractor and reinforced in position with a methyl methacrylate-based fast-curing resin (Technovit 6091, Heraeus Kulzer GmbH. Wehrheim, Germany).

[FIGURE 2 OMITTED]

Commercial osteogenic distractor options were considered, but a handmade device was selected. The device used consisted of a 4-mm-diameter threaded stainless steel connecting rod, fitted into 2 1-mL syringes in the place of the plunger. Two nuts were previously placed on the rod, and each was located at the flanged end of each syringe, allowing the further distraction by rotating the nuts in opposite directions (Fig 3). The rod was screwed into the syringes manually and required no extra support. The pins were passed through the body of the syringes that were then filled with the fast-curing resin (Fig 4).

[FIGURE 3 OMITTED]

The initial plan also included the placing a transfrontal sinus pin linked to the end of the rhinotheca with an elastic band to correct rhinothecal alignment. However, the pin was unstable. As an alternative, a hard, chairside reliner dental acrylic shell (Kooliner, GC America, Alsip, IL, USA) was placed over the rhinotheca to apply pressure toward correct rotational alignment (Fig 5). The rhinotheca was manually rotated and the acrylic shell applied; the beak was maintained in the position approximately 10 minutes, until the acrylic shell achieved its final consistency and strength.

A pharyngostomy tube was placed in the proximal cervical esophagus immediately after surgery while the patient was still under general anesthesia. This allowed assisted feeding in the postoperative period while the surgical device was in place. Tape was applied around the feeding tube at the level of the skin wound, and it was then sutured to the skin with 4 simple interrupted sutures. Postoperative radiographs confirmed the correct positioning of the pins and the distractor device. The patient recovered from anesthesia uneventfully and was discharged to the rescue organization with oral meloxicam and amoxicillin-clavulanic acid (125 mg/kg PO q12h), together with assisted feeding. Staff at the wildlife rescue center were instructed to distract bone ends starting the day after surgery at a rate of 1 mm per day, comprising 0.5 mm every 12 hours, by rotating one of the nuts 180[degrees] clockwise daily (alternating the nut to be rotated).

Seven days after surgery, the juvenile swan was rechecked and had gained approximately 10% of its initial body weight (3.5 kg). No signs of infection around the pin insertion were noted.

Two weeks after surgery, the mandible and the rhinotheca were in correct physiologic position and the bird was able to eat normally. The swan was anesthetized by following the same protocol as previously described for the initial surgery, and radiographs revealed the presence of a callus at the osteotomy site, with no sign of inflammation, infection, or adverse reaction (Fig 6). Therefore, all the surgical implants were removed (Fig 7).

Three weeks after implant removal, wildlife center staff reported recurrence of malalignment. On examination, the malalignment was confirmed and the bird was admitted again at the referral hospital. The next day, a second general anesthesia was performed and the surgical procedure was repeated. At this time, 3 intramedullary pins (1.2 mm) were placed in the proximal side and 4 pins (0.9 mm) were placed in the distal side of the osteotomy site. A second handmade osteogenic distractor was placed by following the same procedure as previously. No dental acrylic shell, pins, or implants were placed in the rhinotheca or the frontal sinus, as the positioning of the rhinotheca was considered correct. On recovery, the patient was discharged and the staff at the wildlife rescue center were instructed to distract the bone ends at a rate of 0.3 mm per day, starting the next day.

At 21 days after the second surgery, the patient was assessed radiographically. Radiographs revealed some pin loosening but correct healing with minimal callus, and the mandible was stable. The external fixator was removed. A week later, the feeding tube was removed after confirming the bird was able to eat without any problems and maintain its body condition.

The final position achieved presented a deviation to the right side (Fig 8) but this did not compromise normal prehension and swallowing of food. The juvenile swan was maintained in the wildlife rehabilitation facilities for a month with no recurrence or complications. It was finally released to the original location where it had been found.

[FIGURE 4 OMITTED]

Discussion

To our knowledge, this is the first reported clinical case of distraction osteogenesis in the rostrum mandibulare of an avian species. The avian skull remains remarkably uniform throughout all bird groups. (5) The mandible consists of 6 pairs of bones that are more or less fused together. (6) Each ramus of the mandible consists of the os supra-angulare (dorsal supra-angular bone), os angulare (ventral angular bone), os articulare (osterior articular bone), os spleniale (splenial bone), os prearticulare (prearticular bone), and os dentale (dentary bone) (Fig 9).

The rostrum mandibulare (lower mandible, jaw or bill) is actively involved in prokinesis, a particular type of cranial kinesis seen in fowl and psittacine species. Depression of the mandible rotates the quadrate bones rostrally and pushes the pterygoid bone, palatine bones, and jugal arches forward, having as a result the rostrum maxillare (upper mandible, jaw, or bill) swinging forward and upward at the craniofacial hinge where the bone is thin and flexible. (7)

The rhamphotheca is the keratin layer covering the beak (8) (Fig 4) and comprises the upper bill (rhinotheca), and the lower bill (gnathotheca) keratin layers. The rhamphothecal growth is determined by diet, age, disease, and species, and it has been speculated that pathologic processes directly altering the structure of the bill or influencing keratin metabolism can also affect rhamphothecal growth. (9) Before any corrective surgery on the beak is attempted in any avian species, (9) clinicians should always assess whether or not growth plates are closed; however, the clinical assessment may be challenging. In this swan, the rhamphotheca appeared normal despite the initial trauma, indicating that the germinal tissue was likely undamaged. Appropriate nutrition was provided, and the patient was monitored during healing process.

[FIGURE 5 OMITTED]

Although no clear percentage or prevalence has been determined, fractures of the mandible in the lower beak in psittacine birds, passerine birds, and raptors, and of the upper or lower beaks (mandible and premaxilla) in long-billed birds (such as cranes, herons, and ibises) are common injuries. (10) Beak injuries are also commonly seen in wild Anseriform birds, mainly as a result of predator attacks and strangulation with fishing lines." In waterfowl, such as ducks, geese, and swans, the beak is thin and soft (12,13); this may lead to a higher fracture rate consequent to traumatic incidents compared with other species.

A malocclusion or misalignment of the mandible impairs normal beak function, compromising the ability to ingest food normally. In this case, the pathogenic consequence was impaired ingestion. If this was not restored, euthanasia would have been the alternate outcome. Treatment options discussed included corrective osteotomy and repair of the defect with bone grafting. However, because of the more invasive surgery involved with an autologous bone graft and the cost of synthetic bone matrix, this was not considered a good treatment option. Subsequently, we elected to use an osteogenic distractor and considered the short period of treatment-related stress was justified if a positive outcome was achieved, particularly because swans have an expected life span of over 25 years in the wild. (14) Preening ability did not seem to be affected despite the beak misalignment. Feather quality was considered normal since the time of first admission, and after full access to water, feathers seemed to maintain normal appearance and waterproof characteristics.

[FIGURE 6 OMITTED]

Distraction osteogenesis is a surgical process used to reconstruct skeletal deformities and lengthen bones. (15) The technique was popularized in the 1940s by Gavrill Ilizarov, and it was first reported in veterinary medicine in the 1980s. (16) An osteotomy is performed to divide the bone into 2 fragments, then the bone ends are gradually moved apart during the distraction phase, allowing new bone to fill in the gap. When the desired or possible length is reached, the consolidation phase starts: the bone is allowed to finish healing. Distraction osteogenesis has the benefit of simultaneously increasing bone length and the volume of surrounding soft tissues. (15)

In reported cases in birds, the technique has been used successfully in fracture repair of the tibiotarsus of a yellow-napped Amazon parrot (Amazona ochrocephala auropalliata), (17) a peregrine falcon (Falco peregrinus), (18) and a great horned owl (Bubo virginianus). (18) In the first case, distraction osteogenesis was used successfully after failed attempts to repair a tibiotarsal fracture. In the falcon, distraction osteogenesis was used after a significant leg shortening developed subsequent to an otherwise successful repair of a tibiotarsal fracture. The great-horned owl was presented with a partially healed fracture with a significant shortening of one leg. A case of bilateral mandibular fracture in a juvenile mute swan has been described (19); it was managed successfully with a unilateral, uniplanar external skeletal fixator applied on both sides of the jaw, with 2 pins in either side of the fracture. In our case, the juvenile mute swan was presented after an old fracture that was suspected to have affected the growth of the right mandible, leading to a beak deviation.

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

Distraction osteogenesis is a useful technique to correct severe mandibular brachygnathia in pediatric human patients. (20) In a study done with rabbits as a human model, mandibular lengthening by distraction osteogenesis proved possible, providing that particular anatomy (type of bone and shape) is considered and that data extrapolated from tubular bones is analyzed carefully. (21) Because of the lack of reports on distraction osteogenesis in the avian mandible, reports in other species were considered in this case, as well as the few reports of this technique in avian species.

[FIGURE 9 OMITTED]

In horses, this technique has been used to correct congenital deviation of the nasal septum (22) and congenital brachygnathia. (23) A successful case of mandibular lengthening in a juvenile camel (Camelus bactrianus) has also been reported. (24)

The Ilizarov technique is also used to correct long-bone defects after surgical removal of bone neoplasia in human patients, allowing limb preservation and optimizing function. (25) It has also been used successfully in dogs. (26)

Numerous factors influence the final outcome of osteogenic distraction, including materials used, with latency, rate of distraction, rhythm of distraction, and consolidation being the major considerations. (17) In this swan, a handmade device was used, composed of a threaded stainless steel connecting rod, fitted into 2 1-mL syringes in place of the plunger. It was necessary to use a lightweight device because of the type of patient and the location of the fracture. Commercial options were considered, but a handmade device was selected by preference due to the heavy weight of commercial options. The initial plan also included placing a transfrontal sinus pin linked to the end of the rhinotheca with an elastic band to correct rhinothecal alignment. However, because of the young age of the bird, together with low frontal bone density, this transsinus pin was unstable. As an alternative, dental acrylic shell was placed over the rhinotheca to apply corrective pressure toward the correct rotational rhinothecal alignment. The acrylic shell provided the stability required while still being relatively lightweight.

In fracture repair in birds, positive-profile pins are less likely to break, which is useful in birds weighing >1 kg. (27) However positive-threaded pins are more likely to cause iatrogenic damage in small, brittle avian bones and their greater strength is not required. In view of the diameter of the mandible, size and weight were considered to be limiting factors. Negative-threaded pins could have been used, but in this case smooth Steinmann pins were chosen because less trauma would arise in placement and removal. Smooth pins are more likely to loosen than threaded pins; however, smooth pins achieved good stabilization without complications in the current case. The horny lamellae, localized at the edges of the rhamphotheca and used in apprehension of food (28) were not affected by the positioning of the pins.

The latency period is the time between the osteotomy and the beginning of the distraction. Classically, this is between 2 to 7 days in both human and veterinary medicine. In people, the period is between 3 and 5 days for the use of the rigid external distraction (RED) system for maxillary fractures. (29) The latency period used in a study in chickens (30) and in the yellow-napped Amazon parrot was 7 days (17); in the cases of the owl and the falcon, (18) distraction started the day after the surgery. Results of a recent study in sheep indicated that a change in latency does not alter the properties of the regenerated bone in mandibular distraction osteogenesis, and that no latent interval is required at all in craniofacial distraction. (31) With these considerations in mind, no latency period was applied in this case.

The distraction rate takes into account the bone distance moved per day, while the distraction rhythm is number of movements each day. (29) The rate reported in veterinary medicine is usually between 0.75 and 2 mm/d. (32) With the RED systems, the rate is usually I mm/d. (29) In a study of varying rates of distraction (1, 2, 3, and 4 mm/d) in sheep, bone formation was achieved in all groups, but 1 mm/d achieved the strongest biomechanical and histologic properties. (33) The distraction rate in the Amazon parrot was 1 mm/d (17) and in the study in chickens, 0.75 mm/d. (30) In this swan, a rate of 1 mm was considered appropriate; the bone defect was small, and the gap created was relatively small. The expected further rate of growth of the rostrum mandibulare was also taken into account, and the distraction rate was decreased on the second distraction given the reduced growth rated expected in the patient.

Ilizarov reported that higher rhythms produce significantly greater bone formation than lower rhythms. (15) With the RED devices in humans, the distraction rhythm is 2 times/d (0.5 mm each time, 1 mm/d (29)). In a study in chickens, an increased distraction rhythm improved osteogenesis during bone lengthening in skeletally mature long bones. (30) In an Amazon parrot, a rhythm of 3 times a day was stated to achieve a good outcome. (17) We chose a rhythm of 2 times/d to avoid stress and to limit human interaction associated with more frequent handling.

Consolidation occurs when the distraction ceases. Many factors play a role in consolidation, in particular, weight bearing, stress of use, and appropriate positioning of the affected limb in long bones. (29)

Complications associated with distraction osteogenesis are muscle contraction, subluxation, nerve and vascular injury, and premature or delayed consolidation. (32) In a retrospective study in people with RED devices, 42 complications occurred in 21 patients treated with a RED, 93% of which were related to the pins. The most frequent problems were loosening of the pins (43%) and frame displacement (29%), with 25% of the latter cases caused by trauma. (29) In this swan, radiographs revealed loosening of some pins 21 days after the second surgery, but healing was correct without excessive callus. Some osteolysis was associated with one pin. Avian mandibular fractures should be addressed in 2 stages: repair of the bone, and repair and alignment of the gnathotheca (lower keratinized beak). (34) In the present case, the gnathotheca and skin healed well once the mandible was aligned.

The main complication in this swan was the recurrence of the misalignment after the initial surgery. This recurrence was caused by early consolidation before completion of growth of the contralateral rami, such that the lateral deviation recurred. Repeating the procedure resolved this complication; in retrospect, the initial distraction osteogenesis should have been continued for a longer time, until the swan was fully grown.

Techniques previously described in other species were applied in this swan. Distraction osteogenesis may be usefully applied in avian medicine; cost was relatively inexpensive in this case, and despite the considerations, the surgical procedure is a relatively easy, based on an osteotomy and pin placement. Although more studies need to be done, this technique appears promising and applicable in avian patients.

Daniel Calvo Carrasco, LV, CertAVP, MRCVS, Thomas A. G. Dutton, BVM&S, CertAVP (ZooMed), MRCVS, Naomi Shimizu, DVM, MRCVS, Mikel Sabater, LV, CertZooMed, Dipl ECZM (Avian), MRCVS, and Neil A. Forbes, BVetMed, Dipl ECZM (Avian), FRCVS

From Great Western Exotics, Vets Now Referrals Swindon, Unit 10 Berkshire House, County Business Park, Shrivenham Road, Swindon, SN1 2LD, Wiltshire, UK.

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Title Annotation:Clinical Report
Author:Carrasco, Daniel Calvo; Dutton, Thomas A.G.; Shimizu, Naomi; Sabater, Mikel; Forbes, Neil A.
Publication:Journal of Avian Medicine and Surgery
Article Type:Report
Date:Mar 1, 2016
Words:4374
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