Page 47 - Adams and Stashak's Lameness in Horses, 7th Edition

Functional Anatomy of the Equine Musculoskeletal System 13

lies deep to each tendon. Small but common subcutaneous around the middle phalanx. Branches from the palmar
bursae may occur on the palmar surface of the fetlock portion of the arterial circle supply an anastomotic
VetBooks.ir the extensor branch of the suspensory ligament. 30 arteries that enter the foramina along the proximal bor­
proximal navicular plexus; this gives rise to several small
joint and on the lateral aspect of the joint just proximal to
The palmar part of the fetlock joint capsule is thicker
The bone receives approxi­
der of the navicular bone.
9,18
and more voluminous than the dorsal part. A consistent mately one‐third of its blood supply from this plexus.
bursa deep to the digital flexor tendons at the distal end Immediately distal to the distal sesamoid bone, each
of the cannon bone lies against the thickened capsule digital artery gives off one to three small arteries that
and may communicate with the joint cavity. The pal­ supply the distolateral border of the navicular bone. The
16
mar recess (pouch) of the fetlock joint capsule extends digital arteries further give rise to branches that form
proximad between the cannon bone and the suspensory a distal navicular plexus within the distal sesamoid
ligament. This pouch is palpable and even visible in the impar ligament. Six to nine distal navicular arteries
presence of joint effusion. from the plexus enter the distal sesamoid bone through
Support for the fetlock and stabilization during weight‐ the distal border. These supply the distal two‐thirds
bearing and locomotion is rendered by the suspensory of the distal sesamoid bone. 18
apparatus, a part of the stay apparatus. The suspen­ Near the level of the pastern joint, a prominent bul­
sory apparatus of the fetlock comprises the suspensory bar artery (artery of the digital cushion) arises from each
ligament (interosseus medius muscle) and its extensor digital artery (Figure 1.8). Their branches supply the
branches to the common digital extensor tendon, the frog, the digital cushion, palmar part of the cuneate
proximal sesamoids embedded in the palmar ligament, corium, laminar corium of the heel and bar, and palmar
and the distal sesamoidean ligaments extending from the parts of the perioplic and coronary coria. A small coro­
bases of the proximal sesamoid bones to the proximal nal artery arises from either the digital artery or the bul­
and middle phalanges. bar artery, and its branches supply the heel and perioplic
corium.
Within the foot opposite each end of the navicular
Blood Vessels of the Digit and Fetlock bone, an artery to the dermal laminae of the heel arising
from the digital artery has been noted on radiographic
arterIal Supply
angiograms. 10,18 At the level of the palmar process of the
The arterial supply to the digit and fetlock of the tho­ distal phalanx, the digital artery gives off the dorsal
racic limb is derived principally from the medial palmar branch of the distal phalanx and then continues distad
artery. This substantial vessel divides in the distal fourth to form the terminal arch within the distal phalanx. The
of the metacarpus between the digital flexor tendons dorsal branch of the distal phalanx gives off a small
and the suspensory ligament into the medial and lateral artery supplying the digital cushion and corium of the
digital arteries. An anastomotic branch from the distal frog and then passes through a notch or foramen in
deep palmar arch unites with the lateral digital artery to the palmar process. Emerging onto the dorsal side of the
form the superficial palmar arch. Branches from this distal phalanx, the dorsal branch of the distal phalanx
arch directly supply the fetlock joint (Figure 1.8). bifurcates. One branch supplies the corium of the heels
Each digital artery becomes superficial on the fetlock. and quarters; the other courses dorsad in a bony sulcus
The artery lies palmar to its satellite vein, running to supply the corium of the toe and to form anastomoses
between the palmar digital nerve and its dorsal branch with other arteries on the distal phalanx (Figure 1.8).
(Figures 1.14 and 1.15). As each digital artery courses The continuation of the digital artery enters a solar
distad over the fetlock, it gives off branches to the fet­ foramen and anastomoses with the contralateral artery to
lock joint, digital extensor and flexor tendons, digital form the terminal arch within the solar canal (Figure 1.8).
synovial sheath, ligaments, fascia, and skin. Branches from the terminal arch course through the bone,
Distal to the fetlock, the digital arteries run parallel 4 or 5 of them emerging through foramina on the parietal
with the borders of the DDFT, giving off branches that surface to supply the proximal part of the laminar corium;
create encircling anastomoses around the proximal and another 8–10 vessels emerge through foramina near the
middle phalanges. The anastomosis associated with the solar border of the bone and anastomose to form the
proximal phalanx is created from dorsal and palmar prominent marginal artery of the sole. This artery sup­
branches of the proximal phalanx that encircle the digit plies the solar and cuneate coria.
(Figure 1.8). The palmar branch joins the contralateral The arterial network of the corium can be divided
vessel between the straight and oblique sesamoidean liga­ into three regions with independent blood supplies: (1)
ments. The dorsal branch anastomoses with the contralat­ the dorsal coronary corium, (2) the palmar part of the
eral vessel deep to the common digital extensor tendon. coronary corium and laminar corium, and (3) the dorsal
At the level of the middle phalanx, dorsal and palmar laminar corium and solar corium. Other regions are
32
branches again arise. The dorsal branch of the middle supplied by multiple other small arteries. Angiographic
phalanx anastomoses with the contralateral branch studies indicate that blood flow within dermal laminae
deep to the common digital extensor tendon to form a is from distal to proximal. 10,32
coronary arterial circle. This vascular complex supplies Branches of the digital arteries in the hindfoot are
branches to the distal interphalangeal joint, common essentially the same as in the forefoot except for the blood
digital extensor tendon, perioplic and coronary coria, supply to the distal sesamoid bone. In 50% of hindfeet
fascia, and skin. The palmar branches of the middle pha­ examined in a definitive study, the collateral arch from
lanx run parallel to the proximal border of the distal the plantar branches of the middle phalanx supplied the
sesamoid bone, uniting to complete the arterial circle primary arteries to the proximal navicular network. 18