Page 68 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.2 The foal and developing animal 43

VetBooks.ir 1.74 1.75

Fig. 1.74 Dorsopalmar radiograph of the distal Fig. 1.75 Another case of teratological polydactyly in
right forelimb of a foal with the teratological form of the right forelimb of a Cob foal.
polydactyly. Note the duplication of the distal end of
the metacarpus and two formed digits.

the extra digit at its base, with no functional distur- junctions) and pelvis. A single dominant autosomal
bance or cosmetic blemish. gene has been cited as the cause, and affected indi-
Adactyly refers to the absence of all or part of a viduals pass the trait to approximately half of their
normal digit and has been reported in the forelimb offspring. Histologically, the exostoses have cancel-
of a Welsh Mountain foal with a contralateral fore- lous bone capped by hyaline cartilage and appear to
limb polydactyly. be osteochondromas. They remain benign and no
transformation to malignancy has been reported.
HEREDITARY MULTIPLE EXOSTOSIS The exostoses vary in morphology from smooth
(MULTIPLE OSTEOCHONDROMA, and rounded to ‘spur-like’. As the foal matures, the
MULTIPLE CARTILAGINOUS swellings on the limbs tend not to enlarge, but those
EXOSTOSIS, DIAPHYSEAL ACLASIS at other sites enlarge until maturity is attained.
OR ENDOCHONDROMATOSIS) Lameness is present if the exostosis impinges on
surrounding muscles or tendons. Radiography and
Hereditary multiple exostosis is an uncommon, ultrasonography can confirm the exact location and
hereditary, skeletal disorder characterised by many extent of the exostoses.
bony projections, often bilateral and symmetrical, No treatment for the condition is known. The
on the long bones, ribs (near the costochondral owner should be informed of the hereditary nature