Page 242 - Adams and Stashak's Lameness in Horses, 7th Edition

208 Chapter 3

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Figure 3.31. Medial (left) and lateral (right) stressed dorso­
palmar views of the metacarpophalangeal joint. There is soft tissue
swelling along the lateral aspect of the joint. On the lateral stress
view, there is asymmetric widening of the lateral aspect of the joint.
This is not seen on the medial aspect of the joint during medial
Figure 3.30. Lateromedial (LM) projection of the distal limb. stress. These findings are indicative of severe damage or rupture of
Severe chronic degenerative changes are present on the proximal the lateral collateral ligaments of the fetlock joint.
and to a lesser degree the distal interphalangeal joints consistent
with osteoarthritis (high and low “ringbone”). Note the marked
undulating bone proliferation (osteophytes and enthesophytes) on injury or contracture; abnormal bone growth, i.e. angu­
the dorsal aspect of P1 and P2 and extensor process of P3; there is lar limb deformities in foals; and healed, malaligned
severe narrowing of the proximal interphalangeal joint with adjacent fractures. Chronic alignment abnormalities predispose
subchondral bone sclerosis. Enthesophytes are also seen on the the joint to OA from abnormal weight bearing and stress
palmar aspect of distal P1 and proximal P2. Source: Courtesy of Dr. distribution through the joint.
Gary Baxter.
Radiographic Changes with Specific Joint Conditions
lesions are seen with osteochondrosis or repetitive As discussed above, there are cardinal radiographic
trauma, which may develop into subchondral cyst‐like
lesions. Focal subchondral lytic areas associated with changes associated with joint disease. Some of the changes
are seen across multiple types of joint disease, whereas
bone fragments are seen with osteochondritis dissecans
and traumatic arthritis lesions from chronic microfrac­ other findings are predominant for specific types of path­
ologic processes. Below is a summary of typical radio­
tures in the subchondral bone.
The joint space width may be increased or decreased. graphic findings of specific joint conditions.
Increased joint space associated with marked subchon­
dral bone lysis can be seen with extensive septic arthritis OsteOarthritis
(Figure 3.29). A decreased joint space, either general or
OA is a common pathologic process in horses. The
localized within the joint, is associated with cartilagi­ changes seen radiographically are secondary to inflam­
nous lesions and degeneration and occurs predominately
with OA. Decreased joint space is usually accompanied mation and degenerative processes within the joint,
predominantly those affecting the articular cartilage.
by subchondral bone sclerosis (Figure 3.30). It is impor­
tant to be sure that the patient is standing squarely to The degree of secondary change not only is somewhat
dependent on the severity and chronicity of the disease
avoid positional joint space narrowing. 11
Periarticular enthesophytes are usually associated process but also can vary by joint, as some joints are
with joint capsule, ligament, or tendon damage or avul­ more prone to secondary osteoarthritic changes than
sion from their bony attachments (Figure 3.13). The others (Figures 3.28, 3.30, and 3.32). The following are
radiographic changes seen in OA of the horse:
location, larger area of bone change, and typically more
undulating margins of enthesophytes typically help dis­ • Periarticular osteophytes.
tinguish them from osteophytes; however, in some loca­ • Subchondral bone sclerosis.
tions such as the dorsoproximal third metatarsal bone, • Narrowed joint space, which may involve all or only
it can be difficult to differentiate enthesopathy from part of the joint; distinct, smooth borders remain on the
osteophytosis. subchondral bone adjacent to the articular cartilage.
Alignment abnormalities may consist of subluxation • Focal or multifocal, well‐defined subchondral bone
or luxation of a joint or may simply result in an abnor­ lysis, most frequently in low‐motion joints.
mal degree of flexion or extension of a joint in a resting • Degenerative subchondral cyst‐like lesions secondary
position. Abnormal joint alignment may be associated to chronic subchondral bone and articular cartilage
with ligament laxity and/or injury (Figure 3.31); tendon injury.