Osteomyelitis

Chapter 121 Osteomyelitis



Callum W. Hay


Osteomyelitis is caused by infection of bone and associated structures (soft tissue, periosteum, and endosteum). Osteomyelitis is invariably caused by an infectious agent such as bacteria or fungi. Acute onset osteomyelitis is rare and generally does not show detectable radiographic changes until 5 to 10 days after bone inoculation. Chronic osteomyelitis is seen as a complication from orthopedic surgery, extension of tooth infection into bone (with periodontal disease), or from nail bed infections. Osteomyelitis can mimic other diseases such as panosteitis, hypertrophic osteodystrophy, and neoplasia and should be differentiated from these.



ETIOLOGY



Bacteria



• The common routes of bacterial infection are outlined in Table 121-1.


Table 121-1 ROUTES OF INFECTION IN OSTEOMYELITIS


Open reduction and internal fixation of fractures; other orthopedic intervention


Open fractures


Extension from soft tissue infection (periodontal disease, rhinitis, otitis media)


Traumatic injuries and bite wounds


Penetrating foreign bodies, including sticks and grass awns


Gunshot injury


Hematogenous


Prosthetic joint replacement surgery




Key Point


Chronic bacterial osteomyelitis is the most common form seen in veterinary medicine.



• Orthopedic surgical procedures allow introduction of bacteria from the patient’s skin or from implants placed in the wound (bone plates, suture). Direct inoculation from the surgeon’s skin or apparel is also possible.

• Chronic periodontal disease with extension of infection into the mandible or maxilla can lead to chronic osteomyelitis and bone weakening. The mandible of small dogs can be susceptible to iatrogenic fracture during tooth extraction, if significant osteomyelitis is present.

• Nail bed infections acquired from trauma and the environment can extend into phalanges and digits (see Chapter 63).



Key Point


Osteomyelitis is often propagated by local tissue environmental factor(s), which over whelm the body’s own natural defense mechanisms. These include poor vascularity, necrotic bone or soft tissue, foreign material such as metallic orthopedic implants or methyl methacrylate, and especially fracture instability.



• Beta-lactamase–producing Staphylococcus aureus bacteria cause a large majority of infections. Other common bacteria are Pseudomonas aeroginosa; Escherichia coli; and Streptococcus, Bacteroides, Actinomyces, and Clostridium species.

• Bacteria produce a mucopolysaccharide coating called glycocalyx, which protects bacteria from phagocytes, antibiotics, and antibodies. Bacterial colonization of orthopedic implants or necrotic bone allows reinfection once antibiotic therapy is stopped.


Fungi


Fungal entry into the respiratory tract can lead to osteomyelitis from hematogenous spread. Direct contamination through an open wound is possible, but rare. Most infections will occur in the vertebral bodies/disks or in the bones of the skull.


Coccidioides, Blastomyces, Histoplasma, Cryptococcus, and Aspergillus spp. can all cause fungal osteomyelitis.



DIAGNOSIS



History



• Osteomyelitis can be preceded by orthopedic surgery, penetrating trauma, chronic dental disease, injury to the toes/foot pads, or possibly known travel to an endemic fungal region.


Physical Examination



• The patient may have evidence of lameness, inappetence, malaise, elevated body temperature, muscle atrophy, and pain on direct palpation of affected area(s).

• Patients who have had orthopedic surgery may have obvious instability at the fracture site or exterior migration of pins. A draining tract may develop distal to the surgical site (Fig. 121-1). Exudate from a tract is not necessarily copious and can appear minimal, especially if the patient is frequently licking the site.

• Small-breed dogs with severe dental disease with mandibular involvement may be very painful on oral manipulation. Pathologic fractures (either precipitated iatrogenically from tooth extraction or from trauma) are easily palpable under general anesthesia.

• Swelling, heat, pain, and possibly a draining tract may be seen in patients with digital osteomyelitis.

• Mucopurulent nasal discharge, coughing, or pulmonary crackles/wheezes may be observed in patients with disseminated fungal infections (see Chapter 20).

image

Figure 119-1 Chronic osteomyelitis with sequestrum, loose unstable implants, and involucrum walling off the focus of infection. These conditions favor chronic bacterial infection, and purulent exudate drains through a dependent sinus.



Hematology



• Acute systemic infection may cause a neutrophilic leukocytosis; however, chronic osteomyelitis may not cause significant hematologic abnormalities.


Diagnostic Imaging



Survey Radiography



• Acute osteomyelitis will not be readily apparent for 10 to 14 days after initial inoculation.

Related posts:

  1. Feline Infectious Peritonitis (Feline Coronavirus)
  2. Borreliosis (Lyme Disease)
  3. Immune-Mediated Dermatoses
  4. Otitis Media and Otitis Interna

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Osteomyelitis

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