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Bilateral valgus deformity of the distal wings (angel wing) in a Northern goshawk (Accipiter gentilis).

Abstract: A 4-week-old female Northern goshawk (Accipiter gentilis) presented with a valgus deformity of both wings resulting in dorsolateral rotation of the primary flight feathers. The condition resolved in 2 weeks after the wings were bandaged and physical therapy was performed. This type of valgus deformity is also known as angel wing. It has been frequently described in waterfowl and has been reported in bustard chicks as well as psittacine birds (budgerigars, macaws, and conures). To the best of the authors' knowledge, this is the first report in a peer-reviewed publication describing angel wing and its treatment in a raptor.

Key words: angel wing, valgus deformity, metacarpal bones, avian, birds, Northern goshawk, raptor, Accipiter gentilis

Case Report

A 4-week-old female Northern goshawk (Accipiter gentilis) presented with marked dorsolateral rotation of the primary flight feathers (remiges) of both wings (Fig 1 a and b). The deformity had become progressively more obvious since the owner acquired the bird 1 week before presentation. The bird was being hand reared and was feeding on 1-day-old chicks; it was casting and defecating well. The bird had been gaining weight and was in good body condition (830 g). It had successfully molted from its second neonate to its juvenile plumage. At the time of presentation, the bird was in the process of becoming imprinted.

[FIGURE 1 OMITTED]

Clinical examination revealed marked valgus rotation of the distal aspect of both wings. Using the convention of numbering primary remiges from 1 to 10 from the carpus distally, remiges 8-10 were fully developed, remiges 5-7 were blood feathers in the process of shedding sheaths, and remiges 3 and 4 were still fully covered by the feather sheath. No loss of motion was appreciated in any joints of the wings. Based on the clinical presentation and physical examination, the diagnosis was angel wing.

In view of the bird's young age, conservative treatment was recommended. A figure-of-eight bandage was applied to each wing such that the carpus was bandaged against the body. One layer of synthetic orthopedic padding (Soffban, BSN Medical, Bierfield, UK) was applied, followed by several layers of self-adherent, elastic bandage material (Coflex, Andover, Salisbury, UK). The owner was advised to change the bandages every 2-3 days and to perform physical therapy before bandage application. Physical therapy involved gentle manipulation of each joint of the wings from maximum flexion to maximum extension; each position was to be held for 15-20 seconds. Sessions were to be increased in number of repetitions and frequency as each level was readily tolerated. The owner was advised to feed a restricted amount of a variety of avian- and mammalian-derived food items (eg, whole 1-day-old chicks, quail, mice, hamsters, or ground rats) and a calcium/phosphorus/vitamin [D.sub.3] supplement (1 pinch/kg animal feed [1 g contains 200 mg calcium and 150 IU vitamin [D.sub.3]] every other day for 4 weeks) (Nutrobal, Vetark Animal Health, Winchester, Hants, UK).

One week after initial bandaging and initiation of physical therapy, the bird presented for follow-up examination. It had maintained good body condition, and the valgus deformity of the wings was considerably improved. However, because the rotation had not been completely corrected and no loss of range of motion was appreciated in the wings, 1 more week of regular bandage changes and physical therapy was advised.

The bird presented again 1 month after the second examination. The alular bone on each wing was rotated slightly outward, but no rotation of the carpal joints or metacarpal bones was appreciated (Fig 2a and b). Each alular bone was manually rotated into its normal anatomic position and held in place by 3-0 absorbable polydioxanone suture (PDS, Ethicon, Johnson-Johnson, St Steven-Wolane, Belgium) placed around the base of the inner proximal alular feathers and the outer distal greater primary coverts. The owner was advised to leave the sutures in place until they dissolved.

[FIGURE 2 OMITTED]

By 2 months after the third examination, the sutures had dissolved, and both of the bird's wings appeared normal. The bird's body condition was good, and it was progressing well in its training to become a hunting bird.

Discussion

Valgus rotation of the distal wing resulting in dorsolateral rotation of the primary flight feathers is known by numerous colloquial terms: angel wing, slipped wing, healed-over wing, crooked wing, sword or spear wing, rotating wing, airplane wing, straw wing, flip wing, or dropped wing. (1,2) The etiology involves a valgus deformity of the growing metacarpal bones or a rotation in the carpal joints resulting in dorsolateral rotation of the primary flight feathers, which protrude when the wing is folded to the body during rest. (1) The condition can occur both unilaterally and bilaterally. Angel wing is most frequently described in larger waterfowl, such as geese and swans, both captive and wild. (2,3) Tropical and temperate species are particularly affected. The condition is more common during warmer weather when young birds are able to use relatively more of their dietary energy for growth rather than maintenance of body temperature. Male waterfowl seem to be more frequently affected. (4) Angel wing has also been seen in budgerigars, macaws, and conures. (1) The condition has been described as the most common musculoskeletal abnormality affecting 4 species of bustard chicks 1-30 days of age. (5,6) Angel wing was noted in great bustard chicks (Otis tarda) during a reintroduction project in the United Kingdom (J. Chitty, oral communication, April 2005).

To the best of the authors' knowledge, this is the first report in a peer-reviewed publication describing the development of angel wing in a raptor. A similar valgus deformity of the metacarpal bones and carpal joint was successfully treated by one of the authors (N.E) in fast-growing larger raptors, including another Northern goshawk (male) fledgling and a gyr-peregrine hybrid fledgling (Falco rusticolus x peregrinus) (N. A. Forbes, oral communication, September 2004). (7) The condition has also been observed in snowy owl fledglings (Nyctea scandiaca) (J. Parry-Jones, oral communication, September 2004).

The juvenile Northern goshawk described in this case report mirrored predilective factors found in waterfowl. It was a young representative of a temperate species of raptor, and it presented in early June (a relatively warm month in the United Kingdom). This bird was a female;

however, interestingly, female raptor species grow larger than their male counterparts, which is the reverse of the situation usually observed in waterfowl.

The type of musculoskeletal valgus deformity seen in this bird is believed to be caused by a diet containing excessive levels of protein, which lead to increased growth rates. Compromised calcium and phosphorus intake is likely also involved in the pathophysiology; periods of fast growth and feather production also promote hypovitaminosis [D.sub.3]. Consequently, the body size increases at a faster rate than bone ossification. (5) The weight of the growing flight feathers places excessive force on the muscles and ligaments of the carpal joint and the inadequately mineralized metacarpal bones, thus exacerbating the condition. (1,2,5,8) Angel wing is usually seen during the phase of blood feather growth. High levels of protein, calcium:phosphorus (Ca : P) imbalances, and hypovitaminosis [D.sub.3] may also result in excessively rapid growth of the blood-filled (thus, relatively heavy) flight feathers carried on inadequately mineralized bone. (1) The condition is likely multifactorial, presumably involving incubation and hatching problems, genetic predisposition, environmental and management factors, and malnutrition. (1) Manganese and vitamin [D.sub.3] deficiencies are discussed as contributing factors, but growth management seems to have a greater impact. (1,5,8)

Affected waterfowl are usually those species that should naturally be eating grass containing a crude protein content of only 17%-18%. The condition increases in prevalence when these birds are fed grower pellets or cereals with a relatively higher protein content, resulting in faster growth than intended for their genetic makeup. (8) Excess available energy, excess levels of protein, rapid growth, and inadequate exercise are all considered underlying stressors. (4) These factors are well recognized to contribute to rotational deformities of the tibiotarsus in immature ostriches. (9-11) Another study investigating skeletal development in psittacine birds, however, implicated excessive levels of premature exercise in the high rate of juvenile osteodystrophy seen in hand-reared parrots. (12)

Rapid growth rate in combination with a relative imbalance in dietary levels of calcium, phosphorus, and vitamin [D.sub.3] may have contributed to the development of angel wing in the described case. The general recommendation is that growing raptors be offered as much variety as possible to ensure a balanced diet. Feeding a limited number of food types increases the risk of calcium : phosphorus (Ca : P) imbalances, excess fat intake, and vitamin and mineral deficiencies, which can result in management-related diseases, such as metabolic bone disease and musculoskeletal deformities, such as angel wing. (7) The Northern goshawk fledgling in this case report was fed 1-day-old chicks. Some studies discuss possible low levels of calcium contained in chicks this age, but other studies state that 1-day-old chicks have the correct Ca : P ratio and suitable calcium levels for growing birds of prey. (13,14) The composition of the food fed also needs to be taken into consideration. When feeding this fledgling, the owner commonly removed the yolk from the 1-day-old chicks, thus potentially reducing the amount of available vitamins, lipids, and carotenes. (15) The Ca: P ratio in deyolked 1-day-old chicks is decreased relative to that in complete 1-day-old chicks (1.17:1 and 1.3:1, respectively). (15) In some cases, fledglings demonstrating angel wing deformities may ultimately suffer from a relative Ca : P imbalance, but this may be more likely due to an excessive growth rate rather than an insufficient diet.

The fledgling in this case, as well as the other 2 fledglings diagnosed with angel wing in our hospital, were hand reared (N. A. Forbes, oral communication, September 2004). (7) This does not necessarily reflect a predilection of the condition in hand-reared birds; these birds are normally observed very closely, and a similar condition in a wild fledgling might simply go unnoticed. On the other hand, if the condition occurred commonly in wild raptors, occasional reports should have been expected. It is also noteworthy that the condition has not been described in parent-reared, captive-bred raptors. One possible explanation is that birds are hand reared for imprinting and during the process are fed excessive amounts of the best food available. During hand rearing, raptors are fed a full crop of high-quality meat at set feeding times, while parent-reared raptors are fed little and often with the parents being less selective regarding the meat fed (J. Parry-Jones and R. Jones, oral communication, September 2004). The composition and quality of the food seems to be as important as the amount fed. Obviously, the feeding of fledglings is, to a great extent, subject to the experience of the chick's individual parents or the bird owner. Hand-reared raptors are generally considered to be more active as nestlings and fledglings relative to their parent-reared counterparts. Parent-reared raptors spend the majority of the nestling time quietly in their nests being protected to a great extent by their parents (J. Parry-Jones and R. Jones, oral communication, September 2004). This low level of activity might allow the primary flight feathers to grow in the anatomically correct direction. One may speculate that excessive activity in hand-reared raptors before the maturation of the musculoskeletal system might contribute to the development of angel wing.

The diagnosis of angel wing is normally a presumptive one based on physical examination. Flexion and extension of all joints in the wing can be either normal or abnormal; sometimes joints may only exhibit an abnormal laxity. (1) In this case, the clinical picture was typical, and radiography was considered unnecessary.

If recognized early in the disease process, treatment of angel wing in juvenile birds involves the application of figure-of-eight bandages to realign the primary flight feathers with the angle of the wing in combination with control of the growth rate by use of restrictive feeding and calcium and vitamin [D.sub.3] supplementation. The correction is usually complete within 1 week. In this case, correction required a longer time, which may be explained by the fact that the bird was already 4 weeks old at initial presentation and the rotation had not been addressed within the first 24-48 hours of its being noticed. If mature birds are affected, the rotation can be corrected by osteotomy, which involves transecting the metacarpal bones, rotating the distal fragments into normal position, and transfixing the fragments by standard osteosynthesis techniques. (8)

In the case reported, the owner was advised to change the bandages every 2-3 days to avoid contracture of the musculus propatagialis longus and subsequent shortening of the propatagium. Contracture and shortening of the patagial membranes is a common consequence of wing immobilization. (16) Physical therapy aims to minimize the loss of range of motion, prevent changes in soft-tissue flexibility, improve muscular strength, and enhance muscular and cardiovascular endurance. Additionally, it serves to promote neuromuscular re-education, allowing the patient to regain coordination for normal active daily living. (17) Different forms of physical therapy include passive range-of-motion, active range-of-motion, active-assisted range-of-motion, and adjunct techniques, such as cold therapy, heat therapy, and massage. (18) Passive range-of-motion exercises are performed by manipulating the limb through its entire range of motion, from maximum flexion to maximum extension. The wing is held in each position for 15-20 seconds. (17) Active range-of-motion exercises involve the bird using the limb spontaneously, as in flying or walking, depending on the affected limb. Active assisted range-of-motion can be performed by providing a gently rocking perch, which forces the bird to move, flex, and grip to maintain balance. For example, by holding the bird on the fist and gently moving the hand up and down, the bird is forced to use its wings, and many birds held directly above a surface will paddle the legs in an attempt to walk or perch. (16) One report in pigeons discussed the success of ultrasound therapy in reversing and preventing bandaging-associated loss of wing extension but noted that osteoporosis created by bandaging was not corrected. (19) In this case, passive range-of-motion physical therapy was advised for the first 2 weeks. Once the bandages were removed, active and active-assisted range-of-motion physical therapy were recommended. The owner failed to present the bird during this period of healing. However, allowing a bird free flight in an aviary and training using normal methods will provide a variety of these movements.

References

(1.) Coles BH, Krautwald-Junghanns ME, Herrman TJ. Self-Assessment Picture Tests in Veterinary Medicine: Avian Medicine. St. Louis, MO: Mosby; 1998: 135-136.

(2.) Olsen JH. Anseriformes. In: Ritchie BW, Harrison GJ, Harrison LR, eds. Avian Medicine: Principles and Application. Lake Worth, FL: Wingers Publishing; 1994:1237-1275.

(3.) Smith K. Angel wing in captive-reared waterfowl. J Wildl Rehab. 1997;20:3-5.

(4.) Kear J. Notes on the nutrition of young waterfowl, with special reference to slipped wing. In: Duplaix-Hall N, ed. International Zoological Yearbook. London: Zoological Society; 1973;13:97-100.

(5.) Kear J. Feeding and nutrition. In: Fowler ME, ed. Zoo and Wild Animal Medicine. 2nd ed. Philadelphia, PA: WB Saunders; 1986:335-341.

(6.) Naldo JL, Bailey TA, Samour H. Musculoskeletal disorders in bustard pediatric medicine. J Avian Med Surg. 1998;12:82-90.

(7.) Forbes NA, Rees-Davies R. Practical raptor nutrition. Proc Annu Conf Assoc Avian Vet. 2000:165-171.

(8.) Forbes NA, Altman RB. Self-Assessment Colour Review of Avian Medicine. London: Manson; 1998: 129-130.

(9.) Hahulski G, Marcellin-Little DJ, Stoskopf MK. Morphologic evaluation of rotated tibiotarsal bones in immature ostriches (Struthio camelus). J Avian Med Surg. 1999;13:252-260.

(10.) Kosters J, Hornung B, Korbel R. Straussenhaltung aus der Sicht des Tierarztes. Dtsch Tierarztl Wochenschr. 1996;103:73-112.

(11.) Stewart JS. Ratites. In: Ritchie BW, Harrison GJ, Harrison LR, eds. Avian Medicine: Principles and Application. Lake Worth, FL: Wingers Publishing; 1994:1285-1326.

(12.) Harcourt-Brown N. Development of the skeleton and feathers of dusky parrots (Pionus fuscus) in relation to their behaviour. Vet Rec. 2004;154:42-48.

(13.) Dierenfeld ES, Clum NJ, Valdes EV, Oyaruz SE. Nutrient composition of whole vertebrate prey: a research update. Proc Annu Conf Assoc Zoo Aquaria. 1994:414-420.

(14.) Robbins CT. Wildlife Feeding and Nutrition. Orlando, FL: Academic Press; 1983.

(15.) Forbes NA, Flint CJ. Raptor Nutrition. Evesham, Worcestershire, UK: Honeybrook Farm Animal Foods; 2000.

(16.) Welle KR. Physical therapy in birds. Proc Annu Conf Assoc Avian Vet. 1999;247-249.

(17.) Martin HD, Ringdahl C, Scherpelz J. Physical therapy for specific injuries. In: Redig PT, Cooper JE, Remple JD, Hunter DB, eds. Raptor Biomedicine. Minneapolis, MN: University of Minnesota; 1993: 207-211.

(18.) Taylor RA. Physical therapy and rehabilitation. In: Bongura JD, Kirk RW, eds. Kirk's Current Veterinary Therapy XII: Small Animal Practice. Philadelphia, PA: WB Saunders; 1995:81-83.

(19.) Wimsatt J, Dressen P, Dennison C, Turner AS. Ultrasound therapy for the prevention and correction of contractures and bone mineral loss associated with wing bandaging in the domestic pigeon (Columba livia). J Zoo Wildl Med. 2000;31:190-195.

From the Avian and Exotic Department, Great Western Referrals, Unit 10, Berkshire House, County Park Estate, Shrivenham Road, Swindon, SN1 2NR, England.
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Article Details
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Title Annotation:Clinical Report
Author:Zsivanovits, Petra; Monks, Deborah J.; Forbes, Neil A.
Publication:Journal of Avian Medicine and Surgery
Article Type:Clinical report
Geographic Code:1USA
Date:Mar 1, 2006
Words:2855
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