Heterotopic Ossification With Concurrent Chronic Osteomyelitis of the Leg Following Licking of a Wound by a Domesticated Dog

HO, or ectopic ossification, is the aberrant formation of bone within soft tissues; it is most prevalent at the hip.¹ Chronic osteomyelitis manifests as intermittent or persistent pain, erythema, or swelling, sometimes with sequestra or draining sinus tracts. HO concurrent with chronic osteomyelitis is extremely rare.² HO can induce chronic osteomyelitis, and chronic osteomyelitis may mimic HO.^3,4

To the authors’ knowledge, this report presents the first case in the English-language literature of wound infection and mature HO with chronic osteomyelitis caused by a mixed infection of Pasteurella canis, Peptoniphilus coxii, Peptostreptococcus canis, and Fusobacterium nucleatum following licking of a wound by a domesticated dog.

A 49-year-old female with a painful, swollen, and purulent wound, measuring 2.5 cm × 1.5 cm, of the right leg with exposed bone was referred to the authors’ (SJW) clinic after undergoing an unsuccessful 3-month treatment regimen at a local clinic for an open wound of the right leg resulting from a fall from a motorcycle (Figure 1A). The wound was covered with dressings for the first week after the motorcycle injury, followed by open wound care with application of povidone-iodine. The wound seemed improved in the first few weeks; however, infection symptoms emerged approximately 2 months after the motorcycle injury. The patient recalled that her dog had licked the wound several times 1 week after the accident, during the period of open wound care.

The patient’s past medical history included a snakebite (type of snake unknown) on the right leg followed by repeated debridement and skin graft owing to wound complications in childhood. No fever, chills, or other systemic symptoms were evident at presentation to the authors of this case report. An irregular calcification of the lateral right distal fibula was evident on radiographs (Figure 1B, C). Neither white blood cell count, high-sensitivity C-reactive protein level, nor erythrocyte sedimentation rate was elevated according to blood test results. Empirical antibiotic therapy consisting of cephradine 500 mg every 6 hours was prescribed in the OPD. Pus culture was positive for P canis and Pasteurella stomatis. Mature HO with soft tissue inflammation on the lateral aspect of the distal right leg was evident on computed tomography scans (Figure 1D).

The patient was admitted for sequestrectomy and debridement after a 3-week OPD treatment. She received 2 cycles of NPWT (3 days per cycle) postoperatively, followed by open wound care for 1 week, after which she underwent debridement and STSG followed by 3 weeks of IV ampicillin 2 g plus sulbactam 1 g every 6 hours. The patient was discharged in stable condition followed by OPD treatments. The wound healed 2 months after discharge.

Pathologic evaluation was positive for bone tissue with necrosis, inflammatory cell infiltration, granulation tissue, and fibrosis of the marrow area for the resected HO. These findings are consistent with chronic osteomyelitis. The cultured resected tissue and sequestra was positive for P canis, P coxii, P canis, and F nucleatum.

To the authors’ knowledge, this is the first documented case in the English-language literature of chronic osteomyelitis caused by a mixed infection of P canis, P coxii, P canis, and F nucleatum in mature HO.

Full maturation of HO can take up to 12 to 18 months.⁵ The patient in this case report was referred to the authors’ hospital 3 months after sustaining a motorcycle injury. At that time, HO resulting from the motorcycle injury wound may have been in the immature stage. However, this patient presented with mature HO, possibly as a result of wound complications, repetitive inflammation, and surgeries in childhood following a snakebite on the right leg, which may have resulted in decreased end organ perfusion. Microvascular constriction resulting from hypovolemia and inflammatory cytokines facilitates HO formation.¹ In this case, the recent motorcycle injury resulted in an open wound around the HO, repeated wound licking by a dog resulted in colonization of pathogens from the dog’s saliva, and inappropriate nursing by the patient herself resulted in swelling, erythema, and pus of the poorly perfused fibrotic wound. Management of chronic osteomyelitis consists of debridement and sequestrectomy with antimicrobial therapy and soft tissue or bone reconstruction, if necessary.⁶ Antibiotics should be tailored to the bacterial culture and susceptibility testing results.

Wounds should be protected from not only pet bites or scratches but also pet licking, especially for poor perfusion of focal or grafted tissues in patients who are immunocompromised. There are few case reports describing septicemia, prosthetic joint infection, osteomyelitis, and septic arthritis, along with wound infection, following dog licking of a wound. In contrast, there are complete guidelines for managing an animal bite. Repetitive wound licking results in accumulation of bacteria from the respiratory tract and/or oral cavity of an animal to the human’s wound through saliva; this may not be painful and thus, patients delay seeking medical assistance, which tends to result in chronic polymicrobial infections. In contrast, animal bites are painful, with short-term contact, and patients usually seek early medical care. Thus, should infection occur after an animal bite, the infection is acute rather than chronic.

Five cases of P canis osteomyelitis have been reported in the English-language literature.⁷P canis is a Gram-negative coccobacillus that resides mainly in the oral cavity, nasopharynx, or intestine of domestic animals; it can cause a variety of infections that lead to osteomyelitis, septic arthritis, peritonitis, and bacteremia.^7-9P stomatis has been isolated from the mouth and respiratory tract of dogs and cats, and it was reported in a boy with a wound infection following a dog bite and an elderly patient with catastrophic diffuse hemorrhagic shock.¹⁰

The patient discussed in the current report is the first case of documented osteomyelitis and soft tissue infection caused by P coxii, which is an anaerobic Gram-positive coccus that was isolated from human clinical specimens in 2011.¹¹P canis was first isolated from the oral subgingival plaque of Labrador retrievers in 2012 and has been reported in a female patient with prosthetic joint infection.¹² F nucleatum is an anaerobic Gram-positive oral commensal bacterium related to dental biofilm. Twenty-two cases of
F nucleatum osteomyelitis have been reported, mostly in boys older than 4 years.¹³ All the aforementioned bacteria can be found as normal flora in the oral cavity or respiratory tract of dogs; thus, it is reasonable to postulate that these bacteria for chronic osteomyelitis concurrent with HO in the patient in this case report were introduced by repetitive wound licking by the dog.

This case report has limitations. The patient did not receive hyperbaric oxygen therapy. Delayed wound healing may have resulted from poor tissue perfusion in the patient’s right leg. Additionally, the patient experienced chronic inflammation of, underwent repeated operations to, and experienced diffuse scarring in the right leg.

Wound bed preparation is the process of removing barriers to maximize the potential for successful healing, which is accomplished primarily through debridement. Adjunctive wound treatment methods include NPWT and hyperbaric oxygen therapy. NPWT is used to remove exudates, bacteria, and debris; increase blood flow; and enhance cellular proliferation, thus promoting earlier wound closure.¹⁴ To the authors’ knowledge, this is the first reported case in which NPWT was used in the management of a wound involving HO and chronic osteomyelitis.

Authors: Liang-Chen Huang, MD¹; Ya Hui Wang, MD^2,3; Tsing-Li Lin, MD⁴; Wei-Cheng Hung, MD⁴; and Shyu-Jye Wang, MD^5,6

Affiliations: ¹Department of Surgery, En Chu Kong Hospital, New Taipei City 237, Taiwan; ²Department of Ophthalmology, Taipei Municipal Wanfang Hospital, Taipei 116, Taiwan; ³School of Medicine, Taipei Medical University, Taipei 110, Taiwan; ⁴Department of Orthopedics, China Medical University Hospital, Taichung 404, Taiwan; ⁵Department of Surgery, Country Hospital, Taipei 106, Taiwan; ⁶Department of Surgery, Chung Shan Hospital, Taipei 106, Taiwan

Disclosure: The authors disclose no financial or other conflicts of interest.

Correspondence: Shyu-Jye Wang, MD; No. 11, Aly. 112, Sec. 4, Ren'ai Rd., Da’an Dist., Taipei City 106, Taiwan; sjwang1214@yahoo.com.tw