Page 235 - Adams and Stashak's Lameness in Horses, 7th Edition

Diagnostic Imaging 201

problems or abnormal weight bearing. To formulate a Cortical Changes
correct diagnosis, the clinician should note fundamental Cortical changes that can be identified radiographi­
VetBooks.ir and any associated soft tissue changes on equine limb cally consist of defects, erosions, lysis, and changes in
bone response patterns and distribution within bones
thickness. Cortical defects seen most frequently in
radiographs. The clinician also should be able to differ­
entiate whether these changes are a response to patho­ equine extremities are caused by fractures. Fractures
must be differentiated from nutrient foramina (Figure 3.15),
logic processes or secondary to normal bone modeling physeal lines, and edge enhancement shadows caused by
as adaptation to a particular athletic activity. superimposed bones. Long bone cortical stress fractures
may not be evident in all cases as a distinct fracture line
(Figure 3.16); a periosteal and/or endosteal reaction
Periosteal Reactions may be the only visible radiographic change (Figure 3.17).
When a long bone fracture is suspected but not visible
The periosteum is stimulated when elevated by hem­ radiographically, it is essential to continue to treat
orrhage, purulent material, edema, or infiltrating neo­ the patient conservatively as though there were a fracture
plastic cells. In the horse, direct trauma, extension of and utilize further imaging including nuclear scintigraphy
soft tissue infections, and avulsion of ligaments, tendons, and/or repeat radiographs in approximately 10 days.
and/or joint capsules are most frequently associated Cortical lysis is usually caused by infection and typi­
with periosteal new bone production. Periosteal bone cally has a permeative and/or moth‐eaten pattern. A
production may be acute or chronic (Figure 3.14). Acute sequestrum also may be associated with a focal area of
periosteal bone production has an irregular, indistinct cortical lysis (Figure 3.18). In such cases, a dense seques­
border and may be continuous or interrupted, lami­ tered piece of bone can be identified surrounded by a
nated, or speculated. Acute periosteal reaction is usually lytic zone (cloaca), which in turn is surrounded by bone
active. Chronic periosteal bone production has a smooth, sclerosis, producing an involucrum within the parent
well‐defined border, is solid, and often blends with the bone.
adjacent cortex. This type of periosteal reaction is usu­ Cortical erosion changes can extend from either the
ally inactive and often indicates a healed process such as endosteal or the periosteal surface. In the horse, they are
a healed fracture or previous active periosteal bone pro­ most frequently encountered adjacent to the periosteal
duction that has changed to a chronic, probably inactive surface. Erosive changes with an irregular border usu­
stage (Figure 3.14).
ally result from infiltration into the bone and are most
often caused by infectious processes. Cortical erosive
areas with a smooth border are the result of pressure

Figure 3.14. Dorsolateral to palmaromedial oblique (DLPMO) Figure 3.15. Lateromedial (LM) projection of the pastern. A
projection of the metacarpus. Note the smooth periosteal reaction radiolucent line is seen through the dorsal cortex of the mid portion
and cortical thickening of the mid‐distal diaphysis of MCII, consist­ of the first phalanx (arrow). This is a nutrient foramen that should
ent with a chronic exostosis. not be mistaken for a fracture.