Page 240 - Adams and Stashak's Lameness in Horses, 7th Edition

206 Chapter 3

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d d

a a
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Figure 3.27. Dorsoproximal to distopalmar oblique (D30Pr‐
DiPaO) projection of a normal metacarpophalangeal joint, showing
an example of the structures that should be evaluated around a
Figure 3.26. Lateromedial (LM) projection of the distal radius joint. (a) Joint margins. (b) Subchondral bone. (c) “Joint space”
with radiographic changes, consistent with osteomyelitis. Note the (articular cartilage). (d) Areas for collateral ligament attachment.
irregular and discontinued periosteal reaction with lysis of the (e) Joint capsule and general joint alignment.
craniodistal cortex of the distal radius and adjacent ill‐defined
increased medullary opacity and soft tissue thickening. On the most
proximal aspect of the lesion, the cranial cortex is wider and tissue within muscle fascial planes can be identified
presents a circular mineral opacity with a surrounding radiolucent around some normal joints. Visibility and location of
rim and sclerosis, suggesting the presence of a sequestrum (arrow). adipose tissue may change with inflammation or joint
Source: Courtesy of Dr. Gary Baxter. capsule distension or thickening. The normal location
and the presence of fat bodies vary, depending on the
joint and animal being examined.
• Localized increased bone densities (sclerosis), which Joint margins are bony regions at the edge of articu­
are produced within the host bone, e.g. thick cortices, lar cartilage that also coincide with the edge of the sub­
and in which a sequestrum sometimes may be identi­ chondral bone. Articular cartilage, the periosteum, and
fied within the sclerotic and lytic bone patterns. the joint capsule meet in this region. In the normal joint,
• Periosteal bone production, which is usually abun­ the margins are smooth and blend with the surrounding
dant with a well‐defined irregular or smooth border. bone structures. Subchondral bone is a dense, compact
• It is often impossible to determine radiographically bony zone 1–3 mm in width and adjacent to the articu­
whether chronic osteomyelitis is active or inactive. lar cartilage. The subchondral bone surface adjacent to
This diagnosis is best determined by physical exami­ the articular cartilage is smooth and even.
nation, clinical signs, or other imaging techniques, The area referred to as radiographic “joint space” is
such as nuclear scintigraphy. not an actual space but is composed of articular carti­
lage with a thin layer of synovial fluid between the
Radiology of Synovial Joints opposing cartilaginous surfaces. It appears radiolucent
on a radiograph, compared with the adjacent radio­
Radiographic evaluation of joints in the equine limb paque subchondral bone. The joint space should be of
is an important part of the diagnostic workup for lameness even thickness throughout a specific joint, but thickness
and encompasses evaluation of multiple components, differs from joint to joint; e.g. the distal interphalangeal
including soft tissue structures (both intracapsular and joint space is wider than the proximal interphalangeal
extracapsular); joint margins; subchondral bone; joint joint space, which is wider than the metacarpophalan­
space and alignment; and ligament, tendon, and joint geal joint space.
capsule attachment areas (Figure 3.27). Ligaments, tendons, and the joint capsule, which
attach periarticularly, add stability to the joint. The
attachment areas vary with the joint and may be located
Normal Joint Structures at different distances both proximal and distal to the
The joint capsule and periarticular soft tissue struc­ joint margins. It is important to know regions of insertion
tures should not be distended. Fat bodies and adipose for ligaments and tendons around specific joints.