Functional anatomy of the cartilage of the distal phalanx and digital cushion in the equine foot and a hemodynamic flow hypothesis of energy dissipation.
OBJECTIVE
To examine macro- and microscopic characteristics of cartilage of the distal phalanx (ungual cartilage [UC]) and digital cushion in the equine foot and to relate them to the foot's function of energy dissipation.


METHODS
85 horses and 5 foals of various breeds and ages.


METHODS
Feet, obtained at necropsy, were perfused with India ink (n = 30), latex (5), or polymer plastic (10). Select feet were examined histologically for tissue architecture and to identify elastic fibers. Immunochemistry to identify substance P peptides in nerves (feet from foals) and gold chloride impregnation of axons (n = 10) were performed. Feet were sectioned transversely (n = 27) or coronally (62 feet in a matched-paired study). Ungual cartilage was measured at the navicular bone. Digital cushions were examined for relative tissue composition between forefeet and hind feet.


RESULTS
Ungual cartilage formed an axial projection that extended towards the midline to overlie the bars, and dorsally along the semilunar line of the distal phalanx. Ungual cartilage of forefeet was significantly larger than that of hind feet. The digital cushion was composed of fat and elastic tissues in feet with thin UC, or fibrous and fibrocartilaginous tissue and elastic tissue in feet with thicker UC. Sensory nerves and an extensive network of venovenous anastomoses were found in the UC.


CONCLUSIONS
Ungual cartilage and the digital cushion provide the basis for a hemodynamic flow hypothesis of energy dissipation. Maximum energy dissipation depends on proper hoof preparation and shoeing.
Department of Anatomy, College of Veterinary Medicine, Michigan State University, East Lansing 48824-1316, USA.
R M
RM
Bowker
K K
KK
Van Wulfen
S E
SE
Springer
K E
KE
Linder
D000375:Aging; D000818:Animals; D002358:Cartilage, Articular / Q000033:anatomy & histology* / Q000098:blood supply* / Q000294:innervation; D005529:Foot Bones / Q000033:anatomy & histology* / Q000098:blood supply; D005552:Forelimb; D006439:Hemodynamics; D006736:Horses / Q000033:anatomy & histology*; D009475:Neurons, Afferent / Q000166:cytology; D013045:Species Specificity; D014034:Toes / Q000033:anatomy & histology / Q000098:blood supply; D014680:Veins / Q000033:anatomy & histology*