Bovine Lower Limb - Anatomy & Physiology

()Map MUSCULOSKELETAL SYSTEM (Map)

Cattle are artiodactyl unguligrade animals. Unguligrade means that they bear their weight on a horny covering (hoof) that surrounds their distal phalanges, artiodactyl means that they bear weight on an even number of digits. They are virtually identical in their structure in the hindlimb and forelimb. The main differences are in the forelimb we have metacarpals and the metacarpophalangeal joint, the hindlimb equivalents are the metatarsals and the metatarsophalangeal joint. Also in anatomical planes we use the term palmar for forelimb and plantar for hindlimb. These terms are all interchangable in the below article depending on whether you want to talk about the fore or hindlimb.

Bones

Metacarpals and Metatarsals

• The arrangement of the metatarsals are similar to those of the metacarpals.
• Metacarpal III and IV fuse in the fetus to form the large metacarpal bone. The site of fusion is marked by vascular grooves on the dorsal and palmar surfaces of the shaft of the bone. Metacarpal V remains only as a small lateral remnant.
• The distal end has two seperate articular surfaces seperated by the sagittal intertrochlear notch. The articular surfaces have two condyles seperated by a sagittal ridge.
• The dorsal aspect of the proximal end has a tuberosity for muscular attachment.

Phalanges

• The proximal phalanx tends to be triangular with the interdigital surface being flattened. The proximal end is concave with a sagittal groove so it can articulate with the metacarpal bone, the palmar aspect has facets for the sesamoid bones. The distal head has two convex areas seperated by a sagittal concavity.
• The middle phalanx is three sided and 2/3rds the length of the proximal one. The proximal end is made up of two concavities and a sagittal ridge. The distal end resembles that of the proximal phalanx.
• The distal phalanx is pointed, the proximal end has two articular surfaces seperated by a ridge. The solar surface is flattened and has a flexor tubercle for the attachment of the deep digital flexor tendon. The axial surface faicng the other digit is also flattened. The abaxial surface is is rounded and is the parietal surface of the claw.
• Just distal to the metacarpophalangeal joint on the palmar aspect of the limb lie a pair of conical accessory claws. These are covered with horn and often contain dense connective tissue and small nodules of bone.

Joints

Metacarpophalangeal/Fetlock Joint

• Movement - flexion and extension.
• The cow has a pair of fetlock joints involving the metacarpal bone, the two proximal phalanges and two pairs of sesamoid bones. These sesamoids articulate with the proximal palmar edge of the proximal phalanges
• Cattle have a joint capsule for the articulation of each digit with the palmar parts communicating.
• Collateral ligaments - bind the the furrow between the two articulating areas of the metacarpal bone to the proximal phalanx.
• Interdigital intersesamoid ligament - units the axial sesamoids of each digit together.
• Interdigital phalangosesamoid ligaments - a pair of ligaments that cross each other as they connect thesesamoid of one digit to the proximal phalanx of the other.
• Proximal interdigital ligament - connects the proximal halves of the two digits. Not technically part of the fetlock joint, it is absent in sheep.
• Collateral sesamoid ligaments - connect the outer aspect of the sesamoids to the proximal phalanx and there is a distinct branch that attaches to the metacarpal bone.
• Distal sesamoid ligaments - a collection of ligaments that are very marked in the horse. They connect the distal surface of the sesamoids to the plamar aspect of the phalanx. These are:
  • Short ligaments - connect the axial base of the sesamoids to the lateral/medial aspect on the palmar margin of the proximal phalanx. These are the deepest of the ligaments.
  • Cruciate ligaments - paired ligaments from the base of the sesamoids that diagonally cross to attach to the proximal phalanx. It lies superficial to the short ligaments.

Proximal Interphalangeal/Pastern Joint

• Movement - flexion and extension.
• The joint capsule is simple and attaches by thr articular margins of the two phalanges.
• Collateral ligaments - connect the distal end of the proximal phalanx to the proximal end of the middle phalanx. They lie in a vertical direction rather than along the bone axis.

Distal Interphalangeal/Coffin Joint

• Movement - extension, slight flexion.
• A distal sesamoid is closely associated with the distal phalanx, which has a navicular bursa present like in the horse.
• The joint capsule attaches to the articular periphery. There is a dorsal recess under the extensor tendons and a palmar one that runs to about half the height of the middle phalanx.
• Collateral ligaments - connect the distal part of the middle phalanx to the sides of the proximal distal phalanx.
• Dorsal ligament - yellow elastic tissue connecting the proximal dorsal border of the middle phalanx to the extensor process of the distal phalanx.
• Distal sesamoid ligaments' - connect the distal border of the distal sesamoid bone to the flexor surface of the distal phalanx and has axial and abaxial parts.
• Collateral sesamoid ligaments - fibroelastic ligaments that attach the middle phalanx to the proximal border of the navicular bone.
• Distal interdigital ligaments- cruciate ligaments that attach the abaxial aspect of the proximal end of the middle phalanx to the axial surface of the opposing distal phalanx and distal sesamoid.

Musculature

Interosseous/Suspensory ligament

• Function - support of the metacarpophalangeal joints.
• Origin - palmar aspect of the proximal end of the metacarpal bones, distal row of carpal bones and the joint capsule of the carpus.
• Insertion - At the distal third of the metacarpal bone it divides into three. The lateral branch further splits in two, attaches to the proximal sesamoids of the fetlock and then continue round dorsally on the proximal lateral phalanx and attach to the lateral digital extensor tendon. The medial branch is likewise arranged but attaches to the medial digital extensor tendon. The middle branch dives between the groove of the distal part of the metacarpal bone and divides into two branches that attach to the tendons of the common digital extensor tendon.

Forelimb

Superficial digital flexor

• Function - flexion of the digits
• Origin - medial epicondyle of the humerus
• Insertion - solar surface of the middle phalanges

Deep digital flexor

• Function - flexion of the digits
• Origin - medial epicondyle of the humerus, proximal radius and ulna
• Insertion - solar surfaces of distal phalanges

Common digital extensor

• Function - extensor of the digits
• Origin - lateral epicondyle of the humerus and the ulna.
• Insertion - It splits in two at the level of the fetlock, each branch then inserting on the extensor process of each distal phalanx.

Medial digital extensor

• Function - extensor of the medial digit
• Origin - lateral epicondyle
• Insertion - by two branches to the middle and distal medial phalanges.

Lateral digital extensor

• Function - extensor of the digits
• Origin - lateral ligament of the elbow, lateral tuberosity of the radius, ulna.
• Insertion - by two branches to the middle and distal lateral phalanges.

Hindlimb

Long Digital Extensor

• Origin - extensor fossa of the lateral femoral condyle.
• Insertion - It splits in two at the level of the fetlock, each branch then inserting on the extensor process of each distal phalanx.

Medial digital extensor

• Function - extensor of the medial digit
• Origin - extensor fossa of the lateral femoral condyle.
• Insertion - the middle medial phalanx.

Lateral Digital Extensor

• Origin - lateral ligament of the stifle, lateral condyle of the tibia.
• Insertion - on the dorsal aspect of the middle lateral phalanx.

Superficial Digital Flexor

• Origin - Supracondylar tuberosity of the femur.
• Insertion - solar surfaces of the middle phalanges.

Deep Digital Flexor

• Origin - lateral tibial condyle, fibula, interosseous ligament.
• Insertion - the solar surface of the distal phalanx.

Vasculature

• Arteries of the Forelimb
• Veins of the Forelimb
• Lymphatics of the Forelimb
• Arteries of the Hindlimb
• Veins of the Hindlimb
• Lymphatics of the Hindlimb

Innervation

Innervation of the Hindlimb

The Bovine Claw

The claws of a cow resemble a disc split in half, hence the term cloven-hoof. The split is named the interdigital cleft and gives rise to the flattened axial surface, the abaxial surface is the remaining rounded surface of the claw. The claw is divided into three regions:

• Sole - slightly concave region on the point of the sole
• Bulb - slightly convex region at the heel of the sole
• Wall - on its abaxial aspect it is convex and merges with the bulb, dorsally it reflects acutely to the convex axial wall. The junction with the bulb has a groove called the axial cleft.

The dermis of the wall is very similar to the horse and is arranged in laminae. This interdigitates with the epidermal horn that is produced by the papillous coronary region. The horn on the sole and bulb is also produced by papillae. The hpodermis in the bulb forms a pad of fibrous elastic tissue called the digital cushion.