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Hoof - Anatomy & Physiology (view source)
Revision as of 12:56, 31 August 2015
, 12:56, 31 August 2015→Deeper structures of the foot
[[File:Horse_hoof_wild_bare_sagittal.jpg|thumb|200px|right|Saggital section through horse hoof.]]
[[File:Horse_hoof_wild_bare_sagittal.jpg|thumb|200px|right|Saggital section through horse hoof.]]
Enclosed within the hoof capsule are the bony structures – the distal phalanx, distal end of the middle phalanx, the distal interphalangeal joint, and the distal sesamoid bone (navicular). There are also soft tissue structures including ligaments, cartilage, the digital cushion and the insertions of the common digital extensor tendon and the deep digital flexor tendon.
Enclosed within the hoof capsule are the bony structures – the distal phalanx, distal end of the middle phalanx, the distal interphalangeal joint, and the distal sesamoid bone (navicular). There are also soft tissue structures including ligaments, cartilage, the digital cushion and the insertions of the common digital extensor tendon and the deep digital flexor tendon.
===Ungual (collateral) cartilages===
The ungual cartilages are extensions of the distal phalanx (Plll) that extend caudally and dorsally from the medial and lateral margins of Plll, curving inwards towards each other in the heel region. The cartilages extend just beyond the confines of the hoof capsule making them palpable just above the coronary band at the lateral and medial edges of the foot. The ungual cartilages can ossify resulting in ‘side bones’ which have the potential for fracturing. The cartilages can also become infected resulting in the condition known as ‘quittor’.
The cartilages are securely attached to the other internal structures of the foot by a series of ligaments that extend from the medial and lateral cartilages to the distal and middle phalanx, the navicular bone, and the digital cushion.
===Collateral ligaments.===
The distal interphalangeal joint is enclosed within the hoof capsule. It is stabilised by the medial and lateral collateral ligaments which form part of the joint capsule, connecting the distal end of Pll with the proximal edge of Plll.
===Annular ligaments===
The annular ligament has its origins on the medial and lateral surfaces of distal Pl. It is the most superficial structure in the region, lying just beneath the skin and fusing with the DDFT where it enters the hoof capsule. Once inside the hoof the annular ligament merges with the fibrous attachments of the ungual cartilages and digital cushion, and continues with the DDFT down to its insertion onto Plll.
===Sesamoidean ligaments===
The dorsal border of the navicular bone is held securely to the palmar/plantar surface of the distal phalanx by the distal sesamoidean ligament and to the proximal phalanx via the proximal interphalangeal collateral ligaments by means of a pair of medial and lateral collateral sesamoidean ligaments.
===Navicular bursa===
The navicular bone (distal sesamoid bone) lies between the second and third phalanges and the deep digital flexor tendon. Associated with it is a fluid-filled sac that reduces friction between the bone and the DDFT that lies over the top of it— the navicular bursa. Inflammation in the region is involved in navicular disease which is a common cause of lameness.
===Digital Cushion===
The digital cushion is the internal tissue deep to the frog. It lies between the ungual cartilages and is comprised of collagenous, elastic tissue infiltrated by adipose tissue. At the bulbs of the heel, it is subcutaneous and is soft and loose in texture. It has connection with the digital annular ligament and, at the apex to the deep digital flexor tendon at its point of insertion on the distal phalanx. It acts as one of the major shock absorbers of the foot. When the limb is weight bearing, the increase in pressure and change in shape of the digital cushion and the frog compress the veins in the foot aiding venous return.
===Blood supply to the digit===
The main vessels supplying the digit in the forelimb are the medial and lateral palmar digital aa, both of which arise from the median a. In the digit of the hind limb the medial and lateral digital aa. are a continuation of the metatarsal a. and are also contributed to by the medial and lateral plantar aa. which branch from the sapheneous a.
The digital arteries give rise to numerous branches forming rich networks for the vascular tissues. Many anastomoses occur. The terminal branches of the main vessels finally enter a bony canal in the distal phalanx. Venous drainage is similar with the most distal vessels being the medial and lateral palmar/plantar digital veins. The compressive action of the hoof on the soft tissues within during locomotion generates an important function promoting venous return.
Normal equine digital vasculature anatomy can be divided into five major areas of perfusion:
1. Coronary plexus
2. Dorsal lamellar plexus
3. Circumflex vessels
4. Terminal arch
5. Heel perfusion
Loss of perfusion to the lamella vessels, circumflex vessels, and terminal arch indicates a poor prognosis without aggressive therapy.
===Microcirculation in the dermal laminae===
Numerous arteriovenous anastomoses occur which are of a somewhat unusual type. Under normal circumstances these are closed and as a result circulation within the capillary beds of the dermal laminae occurs. Certain systemic pathologies may result in opening of these AV anastomoses resulting in ischaemia of the laminae. This in turn results in the hoof wall separating from the distal phalanx producing the disease termed “laminitis”, which can be either acute or chronic.
===Innervation of the equine digit===
The digit of the forelimb is innervated by the medial and lateral digital nerves. The medial digital n. is a continuation of the median n. and the lateral digital n. is derived from both median and ulnar nerves. These run on the palmar aspect of the digit in close proximity to the main arteries and veins. They give rise to several dorsal branches which supply dorsally located areas.
The pelvic limb digit is innervated on the dorsal aspect by the common digital nn. Derived from the fibular n. The plantar aspect is innervated by the medial and lateral digital nn which originate from the tibial n.
In addition to their normal importance in supplying innervation to the sensitive tissues of the equine digit these nerves are also of considerable clinical importance as they are utilized for the procedure termed diagnostic nerve blocks.
==Structure and Function==
==Structure and Function==