Page 858 - Adams and Stashak's Lameness in Horses, 7th Edition

824 Chapter 7

have been described as resulting from an infolding of
abnormal cartilage into the underlying bony spongi­
VetBooks.ir matrix remains nonmineralized so that osteoclasts and
osa. The infolded cartilage becomes necrotic and its
6
blood vessels do not migrate into the defect to enable
repair of the defective cartilage and bone. The cystic
lining is made up of fibrous tissue with active fibropla­
sia and capillary proliferation present in the tissue adja­
cent to the bone. The cyst lining has been shown
experimentally to contain significant inflammatory
mediators that likely contribute to the formation and
progression of the cyst. 90
Treatment of SCLs involves the use of either intra‐
articular medications (combined with systemic joint
therapies), surgical debridement of the lesion, surgical A
debridement with bone graft, surgical debridement with
augmentative therapies such as chondrocytes or stem
cells, intralesional injection with corticosteroids, or tran­
scystic screw placement (with or without intralesional
therapy). 41,98,124 Because of the variable prognosis in
horses with debridement of the lesion alone, additional
treatment(s) of the bone defect is(are) being attempted by
some surgeons. These include packing the entire defect
with cancellous bone or packing the depth of the lesion
with cancellous bone and filling the remaining bone
defect with fibrin‐laden chondrocytes containing growth
factors. The goals of the latter treatment are to promote
healing of both the bone and articular cartilage defects.
Although nonsurgical treatment was usually recom­
mended initially in most horses because of the variable
success with surgical debridement of the lesions with or
without the adjunctive treatments, the use of intrale­
sional corticosteroid injections appears to give a more
dependable prognosis. Use of a transcondylar screw
reportedly eliminated lameness in 75% of treated horses B
but was reported to be less successful in horses >3 years
of age. 98 Figure 7.19. Three‐dimensional computed tomographic images
of the third metacarpal condyles, demonstrating the adaptation of
bone to exercise in foals. In this example, subchondral bone density
Effects of Exercise on the Immature Skeleton shortly after birth is homogeneous across the joint surface (A);
however, after 6 months (B), the subchondral bone density increases
Exercise can have a profound effect on the musculo­ in the areas that articulate with the proximal sesamoid bones (arrow)
skeletal system beginning at birth, and there has been and the dorsal aspect of the first phalanx (arrowhead).
considerable interest in the effects of early exercise on
foals in an attempt to strengthen the system to reduce
the incidence of injuries later in life. In initial studies by nificant effects on articular cartilage. Namely, exercised
van de Lest et al., foals that were box stall rested were foals had significantly higher viable chondrocyte con­
more likely to have reduced development than foals that tent in their joints than pasture‐reared foals, and they
were turned out full time and those that were turned out had less gross lesions in the carpi at 18 months of age. 24,54
intermittently along with box stall rest. Lepeule et al. However, there was no effect on articular cartilage
58
have also shown an association between irregular exer­ changes that occurred in the palmar aspect of the par­
cise soon after birth and poor osteoarticular status. asagittal groove in the fetlock joints, a site of fracture
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78
The first author (CEK) has performed density studies in and OA. In the carpus though, Kim et al. showed that
foals before and after exercise and found that prior to the incidence of gross lesions was significantly lower in
54
exercise, the subchondral bone pattern is blank, but at 6 the exercised group compared with the control group.
months of age, the density pattern reflects the articula­ Subchondral bone formation was increased, but the
tion between the joint surfaces (Figure 7.19). overall bone content and density were no different
In an attempt to strengthen musculoskeletal tissues between the groups. Overall, enforced galloping exercise
later in life, a large study was performed in which foals did not produce negative effects and actually provided
that had additional exercise early in life were compared benefit to the joints.
with those that were turned out. The goal was to pro­ Clinically, lack of exercise seems to have a profound
vide galloping exercise in addition to normal pasture effect on bone. For instance, it is not uncommon for
turnout to a group of foals and compare tissue responses young foals to fracture their proximal sesamoid bones
as yearlings and as 3‐year‐olds. The investigators found during normal pasture exercise after being confined,
minimal effects on tendons and ligaments, but fairly sig­ usually in a hospital setting (Figure 7.20). The stall