Page 873 - Adams and Stashak's Lameness in Horses, 7th Edition

Principles of Musculoskeletal Disease 839

to treat acute osteomyelitis in humans and animals in Infectious Physitis
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conjunction with antimicrobials. Many times the pain Hematogenous infections of the physes are not
VetBooks.ir associated joint, and lavage of the joint can provide sig­ uncommon in foals and have similar predisposing fac­
is due to acute synovitis from infection spreading to an
tors as other bone and joint infections in foals. The phy­
nificant pain relief and treatment.
If there is no response to medical therapy and/or the sis is often the initial location of hematogenous bacteria
osteomyelitis is localized, then surgery in conjunction and infection, which can subsequently spread to the
neighboring epiphysis and joint (Figure 7.37). Multiple
with medical therapy is recommended. If the lesion can physes can be infected simultaneously, but this is uncom­
be accessed through a joint, which is often seen with mon. Clinical signs, radiographic findings, and treat­
hematogenous infections, then arthroscopy should be ment are similar to other bone infections. However,
used to remove the damaged bone. A sample of the bone foals with primary infectious physitis without accompa­
should be obtained at surgery and submitted for culture nying septic arthritis might demonstrate a stiff gait at
and sensitivity testing. Debridement of infected fractures most in multiple limbs. Pinpoint palpation over the phy­
or open wounds should be performed to remove avascu­ sis can oftentimes elicit a significant pain response, mak­
lar bone and infected soft tissue and to decrease bacterial ing radiographic evaluation critical to early diagnosis.
numbers. Cancellous bone grafting is often utilized with
infections of fractures to speed fracture healing. However,
a major priority for treatment of osteomyelitis associated Bone Cysts
with fractures is to achieve stability of the fracture.
Stability needs to be maintained not only for fracture True bone cysts (here defined as those other than
healing but also to limit the spread of infection. Loose SCLs) that occur in other species (primarily aneurys­
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implants should be removed, and fracture stability mal and unicameral) have been reported to occur rarely
achieved by other means such as re‐plating, external fix­ in horses. 8,45,112 The most common site appears to be
ators, interlocking nails, external immobilization, or a the mandible. Unicameral bone cysts are defined as
combination of these techniques. If it is impossible to sta­ solitary intraosseous cysts lined by thin connective tis­
bilize the fracture either with internal fixation, external sue membranes. Aneurysmal bone cysts are defined
45
fixation, or both, euthanasia may be the only alternative as expansile lesions consisting of anastomosing cavern­
since it is unlikely that the infection will resolve. ous spaces filled with unclotted blood and lined with
Other methods used to treat osteomyelitis include fibrous walls of varying thickness. 61
regional perfusion of antimicrobials directly into the These cysts usually contain osteoid tissue or osseous
61
medullary cavity of the bone or within the vascular sys­ components, without elastic laminae or muscle layers.
tem of the limb. 127,129,130 The goal is to obtain very high Aneurysmal and unicameral bone cysts are more charac­
tissue concentrations of antibiotics to achieve better teristic of true cystic lesions since they do not involve an
bacterial kill. A tourniquet should be placed above and articular surface and are usually solitary, expansile,
below the site of infusion and maintained for a mini­ intraosseous lesions. The majority of these true bone
mum of 20–30 minutes to achieve optimal results. 7,127–129 cysts reported in dogs and people occur in the distal or
In addition, antimicrobial‐impregnated PMMA may be proximal metaphyses of long bones.
placed locally into the wound to achieve high antibiotic The cause of aneurysmal and unicameral bone cysts
concentrations in and around the fracture. 40,116 The anti­ in any species is uncertain. Unicameral cysts are thought
microbials are incorporated into the PMMA during to result from the encapsulation and alteration of a
mixing and will elute from the PMMA into the wound focus of intramedullary hemorrhage supposedly from
for several days to weeks after they are placed. The trauma. Alternatively, trauma results in a disturbance in
PMMA is usually molded into bead or cigar shapes and endochondral ossification, resulting in a cystic defect
placed adjacent to the implants, fracture, or site of infec­ within the metaphysis. Aneurysmal bone cysts are gen­
15
tion. The use of antibiotic‐impregnated PMMA is erally believed to develop secondary to a preexisting
40
thought to greatly improve our ability to successfully lesion such as fibrous dysplasia, hematoma from trauma
113
treat iatrogenic osteomyelitis in horses such as those or bleeding disorders, or neoplasia. An aneurysmal
associated with internal fixation. 40 bone cyst of the distal metaphysis of the metatarsus in a
horse was thought to be caused by trauma. Whether
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the pathogenesis of aneurysmal and unicameral bone
PrognosIs
cysts and SCLs are interrelated is controversial. Most of
The prognosis for foals with hematogenous osteo­ the evidence (including pathogenesis and clinical char­
myelitis is variable but is usually poor if multiple sites acteristics) suggest that SCLs, at least in horses, are a
are involved. However, if the site of osteomyelitis can distinctly separate clinical entity from aneurysmal or
be thoroughly debrided, then the infection can usually unicameral bone cysts. Additionally, aneurysmal and
6
be resolved. The prognosis with traumatic osteomyelitis unicameral bone cysts can be difficult to differentiate
is also variable depending on the bone involved and the from some bone tumors in horses (Figure 7.43).
duration and severity of the infection. Traumatic osteo­ Treatment of true bone cysts in horses usually involves
myelitis is usually less difficult to resolve than iatrogenic surgical curettage of the lesion with or without autoge­
infections. Osteomyelitis following internal fixation of a nous cancellous bone grafting. Spontaneous resolution
fracture is one of the most difficult diseases to success­ of the cyst may also occur, and some bone cysts in peo­
fully resolve in horses. 7,40 Therefore the prognosis for ple respond to intralesional steroid injections. The
61
these animals is extremely guarded particularly for adult prognosis for resolution of bone cysts in horses is usu­
horses. ally good depending on the location of the cyst.