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Objective - To examine articular
cartilage
of the distal interphalangeal (DIP) joint and distal sesamoidean impar
ligament
(DSIL) as well as the deep digital flexor tendon (DDFT) for adaptive
responses
to contact stress.
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| Sample Population - Specimens from
21
horses. |
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| Procedure - pressure-sensitive film
was
inserted between articular surfaces of the DIP joint. The digit was
subjected
to a load. Finite element models (FEM) were developed from the data.
The
navicular bone, distal phalanx, and distal attachments of the DSIL and
DDFT
were examined histologically. |
|
| Results - Analysis of
pressure-sensitive
film revealed significant increases in contact area and contact load at
dorsiflexion
in the joints between the distal phalanx and navicular bone and between
the
middle phalanx and navicular bone. The FEM results revealed compressive
and shear stresses. Histologic evaluation revealed loss of
proteoglycans
in articular cartilgae from older horses (7 to 27 years old). Tidemark
advancement
(up to 14 tidemarks) was observed in articular cartilage between the
distal
phalanx and navicular bone in older clinically normal horses. In 2
horses
with navicular syndrome, more tidemarks were evident. Clinically normal
horses had a progressive increase in proteoglycans in the DSIL and DDFT. |
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| Conclusions and Clinical Relevance -
Load
on the navicular bone and associated joints was highest during
dorsiflexion. This increased load may be responsible for microscopic
changes of tidemark
advancement and proteoglycan depletion in the articular cartilage and
of
proteoglycan production in the DSIL and DDFT. Such microscopic changes
may
represent adaptive responses to stresses that may progress and
contribute
to lameness. (AM J Vet Res 2001;61:414-424f) |