Introduction

Pododermatitis, or bumblefoot, is a common podal condition of birds of prey. It is particularly prevalent in large falcons of the genus Falco such as the peregrine and gyrfalcons.^1,2 Many other birds of prey, such as owls, eagles, and hawks, are commonly diagnosed with this disease.

The disease is characterized by inflammation and infection of the plantar aspects of the feet, particularly at the central metatarsal pad and the proximal digital pads. Several grading systems have been developed to consistently assess and standardize the severity of lesions.^3-5

A grading system for falcon pododermatitis lesions used by the author⁵

Infection may progress to involve the skin, fibrous metatarsal and digital pads, subcutaneous tissue, superficial and deep flexor tendons, bones, and articulations. Lesions may be as mild as plantar erythema, loss of papillae, and thinning of the skin, and can be as severe as plantar abscessation, tendinitis and tendon ruptures, osteomyelitis, and loss of function.

Various bacterial pathogens have been isolated from pododermatitis lesions, with Staphylococcus spp. being reported most often.⁴ Proposed risk factors include obesity, poor perch design (roughness of the surface, poor distribution of weight loading over the plantar surface, cleanliness, incorrect shape), nutritional deficiencies, lack of exercise, abrupt decrease of exercise (e.g., after the hunting or show season), disrupted blood supply to the affected area, diseases of the contralateral limb, overgrown talons, and repeated trauma to the central metatarsal pad (poor aviary design, foreign bodies, prey bites, repeated improper landing).^1,3,6-8

Chronic pododermatitis has also been suggested to cause chronic systemic inflammation that may promote systemic amyloidosis in gyrfalcons and immune suppression through chronic stress and pain.^4,9,10 Chronic foot infection may also serve as a portal of entry for a variety of pathogens and has been associated with sepsis and tetanus.¹¹ Self-puncture by the hallux can also occur in birds of prey or self-trauma from grasping cage wires and hanging on the side of aviaries.

Diagnosis

The diagnosis is initially based on observation and grading of the lesions. Radiographs of the pelvic limbs help further staging the disease and the presence of osteomyelitis or septic arthritis typically warrants euthanasia. Radiographs may also detect orthopedic issues on the contralateral limb that may be a predisposing factor.

Thermal imaging has also been used to screen for inflammation. Active lesions (infections) tend to be warmer than the surrounding tissues or the contralateral foot. Chronic lesions with a central scab tend to look cooler over the scab area. Thermal imaging may also be useful to monitor the response to therapy with a decrease in foot temperature over time.

Bacterial culture and sensitivity is usually performed from samples collected during debridement surgeries. Fine-needle aspiration of a swollen foot is generally not recommended for this purpose. Culture of synovial fluid may be performed if septic arthritis is suspected. Aerobic and anaerobic culture is recommended as anaerobic bacteria have also been recovered from these lesions. In the case of a persistent wound on the central metatarsal pad, a surface cytology may help screen for fungal elements such as yeasts.

Treatment

The prevention and treatment of falcon pododermatitis is challenging, especially since birds are bipedal animals, lesions are located on a high weight-bearing area that heals poorly and is prone to soiling, and there are few scientific studies on therapeutic and preventative modalities. Current treatment depends on severity and may include a combination of surgical debridement of necrotic and infected tissues, implantation of sustained-release antibiotic compounds (PMMA beads or antibiotic-containing hydrogels), skin flaps and grafts, chronic wound bandaging, silicone shoes to further relieve pressure on the central metatarsal pads, changes in perching surfaces, increased flight time, and prescribed weight loss.^1,3,5,12-16

Most mild cases (grades I–II) can be treated conservatively with reducing risk factors, chronic bandages, and antibiotic therapy. Other cases may benefit from surgical debridement. It is often beneficial that birds receive 1–2 weeks of antibiotic treatment prior to attempting surgical debridement, so the infection may be more circumscribed and/or with a decreased level of cellulitis. Surgical debridement is straightforward and consists of first removing the central scab that is often present on the central metatarsal pad, and then assessing the underlying tissue. Often there is a core of necrotic tissue that needs to be removed.

Once the necrotic tissue has been excised, a culture should be taken and submitted for aerobic and anaerobic culture, and the wound abundantly flushed with sterile saline. A sustained-release antibiotic compound may be placed in the wound such as antibiotic/poloxamer combination, Doxirobe® gel, or PMMA beads (they may have to be removed at a later stage). Then, the skin edges are freshened taking care to remove just the minimum required.

The skin is then closed using small sutures (5-0 or smaller) in a tension-relieving pattern (mattress sutures or far-near-near-far pattern) on a taper needle. Colloid ointment and a non-adherent contact layer with an interdigital bandage should then be placed. In falcons, the skin heals relatively slowly, and it is not uncommon for the wound to dehisce. The sutures need to be removed when the skin seems to be healed (approximately 2 weeks), so the knots do not become a nidus for infection on a surface that can easily become soiled or lead to small pressure points.

Systemic antibiotics are also recommended such as amoxicillin/acid clavulanic, enrofloxacin or marbofloxacin (once a day), or clindamycin. Regional limb perfusion may be used to achieve high tissue levels of antibiotics.^17,18 It consists of placing a catheter distally in the medial metatarsal vein, injecting an antibiotic, and placing a tourniquet medially for no more than 15 minutes. Combinations of beta-lactams (ampicillin, cephalosporins) and amikacin are frequently used in regional limb perfusion. The procedure can be repeated as needed such as once a week for 2–3 weeks.

In addition to topical and systemic antimicrobial treatment, it is accepted that weight load on the affected area should be reduced in order to promote vascularization (by decreasing occlusion/compression of the local capillary network) and promote normal wound healing. Better redistribution of the weight load over the entire plantar surface, or reduction of weight load on susceptible areas such as the central metatarsal pad, are also recommended to prevent development of bumblefoot lesions. This is typically achieved by using foot bandages and/or a variety of perch designs and surfaces. A variety of bandage types and recommendations for changes in perching have been suggested in the literature.³ Most bandaging options consist of providing an ointment for a wound or to soften a scab over the central metatarsal pad, placing a non-adhesive bandage (such as Telfa-pad®), and then some sort of padding to relieve pressure over the central metatarsal pad and better redistribute the pressure to other areas of the foot.

The interdigital bandage with cotton padding is the most commonly used simple bandage. Bandages with additional padding or that remove pressure from the centre of the foot include bandages using pool noodles, custom-made silicone shoe, neoprene, yoga mat, and ball bandages. The same principle applies to perching surfaces whereby the pressure is more evenly distributed across the plantar surface and can act as shock absorber during landing. Artificial turf is frequently used for this purpose as well as neoprene. Neoprene provides more relief but is also harder to clean.

A recent study investigating foot bandages—perching surface combinations in falcons found that silicone shoes provided the greatest decrease in weight loading on the central metatarsal pad followed by interdigital bandages in combination with neoprene or artificial turf surface.¹⁹ As the plantar epithelium and fibrous metatarsal pad are relatively slow to heal, particularly in falcons, frequent wound care and bandage changes are paramount to treatment success and may be carried out over several months.

Recurrence of pododermatitis after resolution of initial lesions is common. Advanced cases respond poorly to treatment and typically require humane euthanasia.

References

1.  Lierz M. Aspects of the pathogenesis of bumblefoot in falcons. Proc Eur Assoc Avian Vet. Tenerife, Spain. Published online. 2003:178–184.

2.  Naldo JL, Samour JH. Causes of morbidity and mortality in falcons in Saudi Arabia. Journal of Avian Medicine and Surgery. 2004;18(4):229–241.

3.  Bailey T, Lloyd C. Raptors: disorders of the feet. In: Chitty J, Lierz M, eds. BSAVA Raptors, Pigeons, and Passerine Birds. BSAVA; 2008:176–189.

4.  Oaks J. Immune and inflammatory responses in falcon staphylococcal pododermatitis. In: Redig P, Cooper J, Remple J, Hunter D, eds. Raptor Biomedicine. University of Minnesota Press; 1993:72–87.

5.  Remple J. Raptor bumblefoot: a new treatment technique. In: Redig P, Cooper J, Remple D, Hunter D, eds. Raptor Biomedicine. University of Minnesota Press; 1993:173–179.

6.  Remple J, Al-Ashbal A. Raptor bumblefoot: another look at histopathology and pathogenesis. In: Redig P, Cooper J, Remple J, Hunter D, eds. Raptor Biomedicine. University of Minnesota Press; 2000:92–98.

7.  Rodriguez-Lainz AJ, Hird DW, Kass PH, Brooks DL. Incidence and risk factors for bumblefoot (pododermatitis) in rehabilitated raptors. Preventive Veterinary Medicine. 1997;31(3–4):175–184.

8.  Mueller M. Studies on bumblefoot in falcons used for hunting in the United Arab Emirates. Published online. 1989.

9.  Caliendo V, McKinney P, Bailey T, Kinne J, Wernery U. Serum amyloid A as an indicator of health status in falcons. Journal of Avian Medicine and Surgery. 2013;27(2):83–89.

10.  Tarello W. A possible relationship between bumblefoot responsive to potassium arsenite and micrococci in the blood of three birds of prey. Acta Veterinaria Hungarica. 2002;50(2):143–150.

11.  Beaufrère H, Laniesse D, Stickings P, et al. Generalized tetanus in a gyrfalcon (Falco rusticolus) with pododermatitis. Avian Diseases. 2016;60(4):850–855.

12.  Kummrow M, Murray M, Bailey T. Successful treatment of severe bumblefoot in a peregrine falcon (Falco peregrinus) utilizing intralesional doxycycline. Falco. 2010;(36):21–22.

13.  Remple J. A multifaceted approach to the treatment of bumblefoot in raptors. Journal of Exotic Pet Medicine. 2006;15(1):49–55.

14.  Remple J, Forbes N. Antibiotic-impregnated polymethyl methacrylate beads in the treatment of bumblefoot in raptors. In: Lumeij J, Remple J, Redig P, Lierz M, Cooper J, eds. Raptor Biomedicine III. Zoological Education Network; 2000:255–266.

15.  Riddle K, Hoolihan J. A form-fitting, composite-casting method for avian appendages. In: Redig P, Cooper J, Remple D, Hunter D, eds. Raptor Biomedicine. University of Minnesota Press; 2000:161–164.

16.  Sander S, Whittington JK, Bennett A, Burgdorf-Moisuk A, Mitchell MA. Advancement flap as a novel treatment for a pododermatitis lesion in a red-tailed hawk (Buteo jamaicensis). Journal of Avian Medicine and Surgery. 2013;27(4):294–300.

17.  Ratliff CM, Zaffarano BA. Therapeutic use of regional limb perfusion in a chicken. Journal of Avian Medicine and Surgery. 2017;31(1):29–32.

18.  Knafo SE, Graham JE, Barton BA. Intravenous and intraosseous regional limb perfusion of ceftiofur sodium in an avian model. American Journal of Veterinary Research. 2019;80(6):539–546.

19.  Barboza T, Beaufrère H, Moens N. Effects of perching surfaces and foot bandaging on central metatarsal foot pad weight loading of the peregrine falcon (Falco peregrinus). Journal of Avian Medicine and Surgery. 2020;34(1):9–16.