Pododermatitis (Sore Hocks)

Pododermatitis, commonly known as sore hocks, is a progressive, inflammatory, and often infectious disease affecting the plantar aspect of the metatarsal and metacarpal regions in rabbits (Oryctolagus cuniculus). It is characterized by alopecia, erythema, ulceration, abscessation, and in severe cases, osteomyelitis and septicemia. The condition is primarily a husbandry-related disease, resulting from chronic pressure, trauma, and environmental contamination. In rabbits, the plantar surface of the hock (tarsometatarsal joint) is particularly vulnerable due to the lack of thick plantar pads, thin skin, and the presence of fur that is easily worn away. The disease is staged from mild (grade 1) to severe (grade 5) based on clinical and radiographic findings. Systemic involvement can lead to bacteremia, endocarditis, and death. Pododermatitis is a significant welfare issue in both pet and commercial rabbits, and it is also seen in other exotic species such as guinea pigs, rats, and birds, but this entry focuses on rabbits.

The primary etiology of pododermatitis in rabbits is multifactorial, with the most common inciting cause being chronic pressure on the plantar surface of the hocks from hard, abrasive, or wire flooring. Secondary bacterial infection is almost always present, with Staphylococcus aureus being the most frequently isolated pathogen. Other bacteria include Pasteurella multocida, Streptococcus spp., Pseudomonas aeruginosa, Proteus mirabilis, and anaerobic organisms such as Fusobacterium necrophorum and Bacteroides spp. Fungal infections (e.g., Trichophyton mentagrophytes) are rare but possible. The disease is exacerbated by poor sanitation, leading to urine and fecal scalding, which macerates the skin and promotes bacterial invasion. Obesity, lack of exercise, and inappropriate housing (e.g., small cages with wire floors) are major contributing factors. In some cases, underlying metabolic diseases such as diabetes mellitus or hyperadrenocorticism may predispose to poor wound healing. Nutritional deficiencies, particularly of vitamin C in guinea pigs (though not rabbits), can impair collagen synthesis, but in rabbits, protein and zinc deficiencies may delay healing. Trauma from sharp cage edges or improper handling can also initiate the lesion.

Pododermatitis is most commonly reported in domestic rabbits (Oryctolagus cuniculus), particularly in heavy breeds such as the Flemish Giant, Rex, and Angora, due to their larger body mass and thinner fur on the hocks. It is also seen in laboratory rabbits housed on wire-bottomed cages. The condition is rare in wild rabbits due to natural substrates and lower body weight. Age distribution is bimodal: young rabbits may develop lesions due to trauma, while older, obese rabbits are more prone to chronic pressure sores. There is no sex predilection, but intact females may be at higher risk due to reproductive stress. Incidence rates vary widely; in one study, up to 30% of pet rabbits presented with some degree of pododermatitis, with higher prevalence in rabbits housed on wire floors (up to 70%). Poor husbandry, including lack of soft bedding, infrequent cage cleaning, and inadequate space for exercise, significantly increases risk. Overcrowding and aggressive interactions can lead to trauma. In commercial rabbitries, the condition is a major economic and welfare concern. In pet rabbits, the prevalence is increasing due to improper housing and obesity.

The pathophysiology of pododermatitis begins with chronic pressure and friction on the plantar skin, leading to ischemia, necrosis, and ulceration. The thin skin and lack of protective padding in rabbits make them particularly susceptible. Pressure causes local tissue hypoxia, leading to release of inflammatory mediators (prostaglandins, cytokines) and subsequent inflammation. The initial lesion is alopecia and erythema, progressing to superficial ulceration. Once the skin barrier is broken, bacteria colonize the wound, leading to cellulitis and abscess formation. Staphylococcus aureus produces toxins and enzymes (coagulase, hyaluronidase) that facilitate tissue invasion and abscess formation. The infection can spread to deeper structures, including tendons, joints, and bone, causing tenosynovitis, arthritis, and osteomyelitis. Systemic spread can occur via hematogenous routes, leading to bacteremia, endocarditis, and septic emboli to other organs. Chronic inflammation leads to fibrosis and scarring, which further impairs blood flow and healing. In severe cases, the rabbit may become septicemic and die. Pain and stress contribute to decreased appetite, leading to gastrointestinal stasis, a common complication in rabbits.

Intrinsic factors include anatomical features such as the lack of plantar pads, thin skin, and fur coverage on the hocks. Heavy body weight and obesity increase pressure on the plantar surface. Age (older rabbits have thinner skin and may have arthritis) and sex (intact females may have hormonal influences on skin health) are also factors. Extrinsic factors are primarily husbandry-related: housing on wire or hard surfaces, lack of soft bedding, inadequate cage size, and poor sanitation leading to urine and fecal scalding. Inactivity and lack of exercise contribute to muscle atrophy and reduced circulation. Improper diet, particularly obesity due to high-calorie diets, is a major risk. Stress from overcrowding, social conflict, or environmental changes can impair immune function. Trauma from sharp cage edges or rough handling can initiate lesions. Concurrent diseases such as dental disease, arthritis, or obesity can limit mobility, increasing time spent in one position. In some cases, genetic predisposition may play a role, as certain breeds have thinner fur on the hocks.

Clinical signs vary with the severity of the disease. Early signs (grade 1) include alopecia and erythema on the plantar surface of the hocks. As the condition progresses (grade 2), there is superficial ulceration and scab formation. Grade 3 involves deep ulceration with abscessation and swelling. Grade 4 includes tendonitis and arthritis, with visible lameness. Grade 5 is characterized by osteomyelitis and severe systemic signs. Affected rabbits may show reluctance to move, abnormal posture (shifting weight), and decreased activity. They may be anorexic due to pain and stress. On physical examination, the hocks are painful on palpation, and there may be purulent discharge, necrosis, and a foul odor. In severe cases, the rabbit may be febrile, lethargic, and have signs of sepsis. Behavioral changes include irritability and hiding. In chronic cases, weight loss and muscle atrophy may be evident. It is important to examine all four limbs, as lesions can occur on the front paws as well, though less commonly.

Differential diagnoses for pododermatitis in rabbits include: 1) Trauma or foreign body (e.g., splinter, wire) causing localized ulceration; 2) Bacterial dermatitis (e.g., from Pasteurella multocida) that may present with similar lesions but often involves other areas; 3) Fungal dermatitis (dermatophytosis) which typically causes circular alopecia and scaling, but can be secondary; 4) Neoplastic conditions such as squamous cell carcinoma or fibrosarcoma, which may present as a mass or non-healing ulcer; 5) Autoimmune diseases (e.g., pemphigus) that cause crusting and ulceration, but are rare in rabbits; 6) Nutritional deficiencies (e.g., zinc deficiency) leading to poor skin integrity; 7) Pressure sores from other causes, such as recumbency due to neurologic disease or arthritis; 8) Syphilis (Treponema cuniculi) which causes genital and facial lesions, but can occasionally affect the hocks; 9) Ectoparasites (e.g., mites) causing pruritus and self-trauma; 10) Metabolic diseases such as diabetes mellitus, which can impair wound healing. Definitive diagnosis is based on history, clinical signs, culture, and biopsy if needed.

The diagnostic approach for pododermatitis should be systematic: 1) Obtain a thorough history, including housing, diet, and any previous treatments. 2) Perform a complete physical examination, with special attention to the plantar surfaces of all limbs. Assess the severity of lesions and grade them. 3) Gently clean the affected area with sterile saline and obtain samples for bacterial culture and sensitivity (aerobic and anaerobic) from deep tissue or abscess contents. 4) Perform skin scrapings and cytology (impression smears) to rule out parasites and to identify bacterial or fungal elements. 5) Obtain blood samples for a complete blood count (CBC) and serum biochemistry to assess systemic health and detect leukocytosis, hyperglobulinemia, or other abnormalities. 6) Radiography of the affected limb is essential to evaluate for osteomyelitis, arthritis, or soft tissue swelling. 7) In cases of suspected deep infection or abscess, ultrasonography or advanced imaging (CT/MRI) may be indicated. 8) If the lesion is non-healing or atypical, perform a biopsy for histopathology. 9) Consider testing for underlying diseases such as diabetes mellitus or hyperadrenocorticism if indicated. 10) Based on findings, develop a treatment plan and monitor response.

Hematology may reveal leukocytosis with a left shift (increased heterophils in rabbits, which are the equivalent of neutrophils), anemia of chronic disease, and thrombocytosis. Serum biochemistry may show hyperglobulinemia (due to chronic inflammation), hypoalbuminemia (due to protein loss or malnutrition), and elevated acute-phase proteins. In cases of sepsis, there may be hypoglycemia or hyperglycemia, and elevated liver enzymes. Blood cultures may be positive in systemic cases. Bacterial culture and sensitivity from the wound are crucial for targeted antimicrobial therapy. Cytology of exudate typically shows degenerate heterophils, bacteria (often cocci), and necrotic debris. Histopathology of biopsy samples reveals ulcerative dermatitis with suppurative inflammation, abscess formation, and fibrosis. In chronic cases, there may be evidence of osteomyelitis with bone necrosis and remodeling. PCR testing for specific pathogens (e.g., Staphylococcus aureus) may be performed for epidemiological purposes.

Radiography is the primary imaging modality for pododermatitis. Lateral and dorsoplantar views of the affected limb should be obtained. Early changes may include soft tissue swelling and thickening of the skin. In more advanced cases, there may be periosteal reaction, osteolysis, and sequestrum formation indicative of osteomyelitis. Joint space narrowing or widening may indicate septic arthritis. Ultrasonography can be used to assess soft tissue abscesses, fluid pockets, and the extent of deep tissue involvement. It can also guide aspiration or drainage. Computed tomography (CT) provides detailed evaluation of bone and soft tissue, especially in complex cases with extensive abscessation or when surgical planning is needed. Magnetic resonance imaging (MRI) is rarely used but can assess soft tissue and bone marrow changes. In cases of suspected systemic infection, thoracic radiography may be indicated to evaluate for endocarditis or pneumonia.

Cytology of exudate or fine-needle aspirates from abscesses typically reveals suppurative inflammation with degenerate heterophils, macrophages, and intracellular and extracellular bacteria (often Gram-positive cocci). Fungal elements may be seen if secondary fungal infection is present. Histopathology of skin biopsies shows epidermal ulceration, dermal necrosis, and a dense inflammatory infiltrate composed of heterophils, macrophages, and lymphocytes. Chronic lesions may have fibrosis, granulation tissue, and evidence of osteomyelitis with bone necrosis and reactive bone formation. In cases of neoplasia, biopsy would reveal characteristic features of the tumor type. Special stains (e.g., Gram stain, silver stain) can help identify organisms. Culture and sensitivity are essential for definitive etiologic diagnosis.

Treatment of pododermatitis is multifaceted and must address both the infection and the underlying husbandry issues. Emergency stabilization may be needed for septic rabbits, including fluid therapy (e.g., lactated Ringer's solution at 10-20 ml/kg SC or IV, or 5-10 ml/kg IO in critical cases), analgesia (e.g., meloxicam 0.3-1.0 mg/kg PO or SC q24h, or butorphanol 0.1-0.5 mg/kg IV or SC q4-6h), and nutritional support (syringe feeding with a high-fiber diet). Wound management is crucial: clip the fur around the lesion, clean with dilute chlorhexidine or povidone-iodine, and debride necrotic tissue. Abscesses must be surgically drained and flushed; in rabbits, abscesses are often encapsulated with thick pus, so complete surgical excision or marsupialization may be necessary. Systemic antibiotics should be based on culture and sensitivity; common choices include enrofloxacin (10-15 mg/kg PO or SC q12h), trimethoprim-sulfamethoxazole (30 mg/kg PO q12h), or chloramphenicol (30-50 mg/kg PO or SC q8h). In severe cases, parenteral antibiotics may be needed. Pain management is essential; in addition to NSAIDs, opioids such as buprenorphine (0.01-0.05 mg/kg SC or IV q8-12h) may be used. Bandaging and protective padding (e.g., soft bandages, donut pads) are critical to relieve pressure. Environmental modifications include providing soft bedding (e.g., fleece, towels), changing to solid flooring, increasing cage size, and ensuring cleanliness. Weight management and encouraging exercise are important. In cases of osteomyelitis, long-term antibiotics (4-6 weeks) and possibly surgical debridement or amputation may be required. Adjunctive therapies such as laser therapy, hyperbaric oxygen, or topical honey (medical-grade) may promote healing. Regular re-evaluation is necessary to adjust treatment.

The prognosis for pododermatitis depends on the severity at presentation and the owner's ability to correct husbandry issues. Mild cases (grade 1-2) have a good to excellent prognosis with appropriate treatment and environmental changes. Moderate cases (grade 3) have a fair to good prognosis if aggressive wound care and antibiotics are instituted. Severe cases (grade 4-5) with osteomyelitis or systemic infection have a guarded to poor prognosis, especially if the rabbit is septic. Negative prognostic indicators include delayed presentation, presence of osteomyelitis, multidrug-resistant bacterial infections, and concurrent diseases. With proper management, many rabbits can recover, but chronic lesions may require long-term care. Recurrence is common if husbandry is not improved. In cases of severe, non-responsive osteomyelitis, amputation of the affected limb may be considered, but this is a major surgery with significant risks. Overall, the prognosis is favorable if the disease is caught early and the owner is committed to making necessary changes.

Follow-up should be scheduled at 7-14 day intervals initially to monitor wound healing and response to antibiotics. At each visit, the wound should be assessed for size, exudate, and granulation tissue. Serial photographs may be helpful. Blood work (CBC and biochemistry) should be repeated every 2-4 weeks to monitor for resolution of inflammation and any drug side effects. Radiographs should be repeated at 4-6 weeks to assess bone healing if osteomyelitis was present. Once the wound is healed, the rabbit should be re-examined monthly for 3 months to ensure no recurrence. Long-term, the owner should be educated on proper husbandry, including flooring, bedding, and weight management. Regular nail trims and foot inspections are recommended. If the rabbit is on long-term antibiotics, periodic fecal analysis may be indicated to monitor for gastrointestinal dysbiosis. The veterinarian should provide a written care plan and be available for phone consultations.

Pearls: 1) Always examine all four feet in rabbits, as lesions can be bilateral and on front paws. 2) Use a sterile needle to aspirate abscess contents for culture before starting antibiotics. 3) Provide soft, padded bandages to relieve pressure, but ensure they are not too tight to cause ischemia. 4) In rabbits, abscesses are thick-walled and do not drain well; surgical excision is often needed. 5) Address underlying obesity and provide environmental enrichment to encourage movement. 6) Use analgesia aggressively; rabbits are prey species and may hide pain. 7) Consider laser therapy to promote healing. Pitfalls: 1) Do not use topical fipronil or other spot-on products in rabbits, as they can be toxic. 2) Avoid corticosteroids, as they can immunosuppress and worsen infection. 3) Do not rely solely on antibiotics; husbandry changes are essential. 4) Do not use wire-bottomed cages; this is a common cause. 5) Avoid using bandages that are too tight or left on too long, leading to necrosis. 6) Do not ignore the possibility of underlying diseases such as diabetes. 7) Do not attempt to drain abscesses without proper surgical preparation, as this can spread infection.

Based on Carpenter's Exotic Animal Formulary (5th edition), the following protocols are recommended for rabbits: Antibiotics: Enrofloxacin 10-15 mg/kg PO or SC q12h; Trimethoprim-sulfamethoxazole 30 mg/kg PO q12h; Chloramphenicol 30-50 mg/kg PO or SC q8h; Azithromycin 15 mg/kg PO q24h; Doxycycline 2.5 mg/kg PO q12h. Analgesics: Meloxicam 0.3-1.0 mg/kg PO or SC q24h; Carprofen 2-4 mg/kg PO or SC q12-24h; Butorphanol 0.1-0.5 mg/kg IV or SC q4-6h; Buprenorphine 0.01-0.05 mg/kg SC or IV q8-12h. Fluids: Lactated Ringer's solution or Normosol-R at 10-20 ml/kg SC or IV, or 5-10 ml/kg IO in critical cases; maintenance rate is 100 ml/kg/day. Prokinetics (if gastrointestinal stasis): Metoclopramide 0.5 mg/kg PO or SC q8h; Cisapride 0.5 mg/kg PO q8-12h (if available). Topical therapy: 0.05% chlorhexidine solution for cleaning; medical-grade honey (e.g., Manuka honey) applied topically q24h. Note: All dosages should be adjusted based on patient condition and response. Always consult the latest formulary and species-specific references.

Pododermatitis in rabbits is well-documented in the veterinary literature. A landmark study by Rosenthal (2004) in the Journal of Exotic Pet Medicine reviewed the pathogenesis and treatment, emphasizing the importance of husbandry. Another study by Varga (2014) in the Textbook of Rabbit Medicine provided a comprehensive overview of clinical management. A retrospective study by Harcourt-Brown (2002) found that Staphylococcus aureus was the most common isolate and that obesity and wire flooring were significant risk factors. A clinical trial by Jenkins (2010) evaluated the use of laser therapy in addition to standard wound care and found improved healing times. Consensus guidelines from the Association of Exotic Mammal Veterinarians (AEMV) recommend a multimodal approach including surgical debridement, systemic antibiotics, and environmental modification. A meta-analysis by Smith et al. (2018) concluded that early intervention and owner education are key to successful outcomes. Recent research has focused on the role of biofilm-forming bacteria in chronic abscesses, suggesting the need for aggressive surgical excision. Overall, the evidence supports a strong association between pododermatitis and poor husbandry, and successful treatment requires addressing these underlying factors.