372 SHUPE
Irritation, trauma, and shearing action also are correlated with the degree and
extent of the lesions. Faulty conformation and malalignment of joints seem to
predispose the intra-articular tissues to greater stress and wear.
The initial stages of degenerative changes seem to occur in the articular
cartilage. The normally wet, smooth and glistening cartilage takes on a dull, dry,
opaque, yellowish and granular appearance. Small clefts and fissures then appear,
followed by splitting and fibrillation of the articular cartilage (so-called asbestos
fibers). Progressive erosion of the cartilage continues until the underlying bone
is exposed. The exposed bone slowly becomes smooth, polished, and, at times,
grooved. These lesions cause further malalignment and malposition of joints
resulting in a slow, progressive, vicious cycle in which the injury is constantly
aggravated and extended.
The degree of involvement of joint capsules and the amount of joint fluid vary
with the severity of the case and the individual animal. In advanced stages and
in cases complicated by concurrent inflammatory reactions, fibrosis and thickening
of the joint capsules occur simultaneously with an increase in the amount of
joint fluid, which contains more protein, masses of fibrin, an increased number of
nucleated white cells, and, in cases leading to sequestration, pieces of bone and
cartilage, and free joint bodies. Intra-articular ligaments and structures show
varying degrees of fragmentation and shredding. Synovial villi become thickened
and fibrotic. Fibrosis and hemorrhage of the periarticular tissue are sometimes
evident, depending upon the duration and extent of the disease process.
.,_[ ~ .Asthediseaseprogresses, overgrowths,which arecompensatorychanges,
appear. Osteophytic growths along articular margins become evident; and new
outgrowths of bone of varying sizes, shapes, and density appear along articular
borders (fig. 2). The density of the bone adjacent to the eroded areas is con-
Figure 2. Proximal ends of femoral bones from two 10-year-old dairy cows. Left
Degenerative arthritis; Right Normal.
siderably increased. Chondrification, followed by ossification of the associated
tendons and joint capsule, was marked in several cases that had numerous,
various-sized osteophytic structures within the joint capsule (fig. 3).