Abstract

Palatine bone luxation was diagnosed in a blue and gold macaw (Ara ararauna) based on history and physical examination findings. The bird presented with a history of recent head trauma and subsequent inability to prehend food. Physical examination findings were normal except for a hyperextended maxillary beak. Simple reduction was unsuccessful.

Detailed analysis of radiographs, anatomic descriptions and cadaver dissections revealed that the hyperextended maxillary beak was due to the dorsal luxation of the palatine bones. Surgical reduction of this luxation is achieved by introducing an intramedullary pin transversely across the infraorbital sinus dorsal to the palatine bones and hyperextending the maxillary beak while concurrently reducing the luxated palatine bones ventrally to their anatomic position. The luxation is stabilized by passing absorbable suture around the suborbital arch and jugal bones bilaterally. Reduction and stabilization were successful, but unfortunately the macaw described in this report died of anesthetic complications after surgery.

Palatine bone luxation causing hyperextension of the maxillary beak is a rare condition previously reported in only one other blue and gold macaw.¹ It can present a challenging problem since it is difficult to radiographically conceptualize the luxation and there are few sources that describe the macaw skull or the treatment for palatine luxation in detail. The objective of this paper is to provide a detailed anatomic description of the mechanism of palatine bone luxation and surgical technique for reduction.

Clinical Report

A 2-yr-old blue and gold macaw of unknown sex presented to Sonora Veterinary Surgery and Oncology in Scottsdale, Arizona with a history of head trauma 2 days previous to presentation and inability to prehend food since the traumatic incident. On physical examination the bird weighed 900 g and individual system examinations were normal except for the musculoskeletal system. The maxillary beak was locked in a hyperextended position preventing occlusion with the lower beak. There were no other outward signs of trauma. Simple manipulation did not reduce the maxillary beak.

Radiographs taken with the bird anesthetized revealed a hyperextended maxilla but the exact cause of the hyperextension was unclear. Attempts to reduce the beak were again unsuccessful. The bird was recovered from anesthesia and surgery was postponed to permit further review of the anatomic features and mechanism of palatine bone luxation. The owners were instructed to continue handfeeding soft foods until surgery was scheduled.

Anatomy

Even the most sophisticated avian anatomy texts are lacking detailed descriptions of the macaw skull. Among birds, there is great variation in skull and jaw structure. Macaws exhibit a type of upper jaw movement called prokinesis in which there is a flexible junction between the maxilla and the braincase. This junction, termed the craniofacial hinge, is an actual synovial articulation. There are several bones in the upper jaw and palate that are responsible for upward movement of the maxillary beak. The palatine bone articulates rostrally with the premaxilla and caudally with the pterygoid bone which forms a hinge joint with the quadrate bone. The jugal arch also articulates with the quadrate bone and rostrally with the upper maxilla. Thus, the quadrate bone articulates with the lower jaw, the braincase, the jugal arch and the pterygoid bone. It is the rotation of the quadrate bones rostrally which causes a gliding motion of the pterygoid, the palatine and the jugal bones allowing the maxilla to swing upward. The upper beak then extends at the craniofacial hinge to give macaws their versatile beaks.^3,6,7

In the event of severe maxillary hyperextension due to trauma, the palatine bones luxate dorsally and become hooked on the interorbital septum which is located on the ventral aspect of the braincase. In psittacines, this septum is longer, wider and thinner than the septum in domestic fowl. As the maxilla is hyperextended, the palatines slide rostrally. If a simultaneous traumatic force is applied dorsally, the palatine bones then become trapped dorsally on the rostral edge of the interorbital septum. Once this occurs, the palatines are unable to slide caudally and the maxilla remains in the hyperextended position.

Surgical Technique

The bird is placed for surgery in dorsal recumbency, the feathers are plucked bilaterally cranial and ventral to the orbit and the skin overlying the infraorbital sinus and jugal bone is aseptically prepared. Using radiographs to estimate the location of the infraorbital sinus, a stab incision approximately 2 mm ventral and 3 cm rostral to the medial canthus of the eye is made with a #15 surgical blade. A 3/32-diameter or smaller intramedullary pin is introduced through the right infraorbital sinus and exited through the opposite side using a hand chuck. The maxilla is hyperextended and simultaneous ventral pressure is exerted on the intramedullary pin displacing the palatine bones ventrally. This allows the maxilla and palatine bones to slide caudally to their anatomic positions beneath the interorbital bone. The intramedullary pin is then removed. To stabilize reduction a lateral approach is made to the jugal bone at the level of the ventral bony orbit and a 3-0 polydioxanone suture is passed around the jugal bone anchoring it to the suborbital arch. The incisions are closed with 3-0 polyglactin.⁴ Postoperative instructions include feeding soft foods and placing the bird in an enclosure that would discourage it from using its beak to climb for approximately 2 to 3 wk.

The bird in this case was treated as described above and the luxation was readily reduced and stabilized. Unfortunately, during anesthesia recovery the bird underwent cardiopulmonary arrest and despite resuscitation attempts, it died approximately 15 min after the surgical procedure concluded. Gross necropsy confirmed the initial diagnosis and ruled out that the intramedullary pin placement was the cause of death.

Conclusion

Palatine bone luxations are rare and maybe a species-specific problem which occurs only in blue and gold macaws. In the first case reported the palatine luxation was caused by the bird attempting to bite a large wooden dowel.¹ In this case, the owner accidently threw the bird down after it attempted to bite him. This suggests that a dorsal traumatic force simultaneous with maxillary hyperextension is necessary in order for the luxation to occur. Closed reduction is not successful and prehension of food is not possible with the degree of maxillary hyperextension created by the luxated palatine bones. Surgical reduction and stabilization are indicated. Once familiar with the anatomy and pathophysiology of palatine bone luxations, the surgical procedure for reduction is simple and fast. The prognosis for normal function is seemingly excellent.

Acknowledgments

We would like to thank Greg J. Harrison, DVM for sharing his personal experience with a similar case. We would also like to thank Drs. Kathy Orr and Dan Burke for contributing psittacine skulls.

Literature Cited

1.  Martin H, Ritchie BW. 1994. Orthopedic Surgical Techniques. In: Ritchie BW, Harrison GJ, Harrison LR. Avian Medicine: Principles and Application. Wingers Publishing Inc., Lake Worth, Florida, Pp. 1166.

2.  Rubel GA, Isenbugel E, Wolvekamp P. 1992. Atlas of Diagnostic Radiology in Exotic Pets. W.B. Saunders Company, Philadelphia, Pennsylvania.

3.  King AS, McLelland J. 1994. Birds—Their Structure and Function. Bailliere Tindall.

4.  Personal communication. Greg Harrison, DVM.

5.  Tankred K. 1973. Anatomy of the Chicken and Domestic Birds. Iowa State University Press, Ames, Iowa.

6.  Bamel JJ. 1993. Handbook of Avian Anatomy: Nomina Anatomica Avium. 2nd Edition. Nuttall Ornithological Publishers, Cambridge, Massachusetts.

7.  King AS, McLelland J. 1975. Outlines of Avian Anatomy. The Macmillan Publishing Company, New York.