Page 62 - Adams and Stashak's Lameness in Horses, 7th Edition

28 Chapter 1

of the synovial lining of the joint project under the ori­ and distal parts of the greater tubercle, distal to the inser­
gins of the extensor carpi ulnaris and the digital flexor tion of the supraspinatus (Figure 1.30). The partly carti­
VetBooks.ir joint is supplied by branches from the transverse cubital eminence by adipose tissue and a synovial bursa that
laginous tendon is protected from the underlying caudal
muscles and into the radioulnar articulation. The elbow
may communicate with the shoulder joint cavity. The
artery cranially and a branch from the collateral ulnar
artery caudally. tendon is the main lateral support of the shoulder joint.
The articular surface of the radius features a concave It is assisted by the teres minor, a smaller muscle deep to
fovea, partially subdivided by two sagittal ridges. This the infraspinatus and arising from the infraspinous fossa,
surface plus the trochlear notch of the ulna articulates the caudal border, and a small tubercle on the distal end
with the humerus, forming a hinge joint. The articular of the scapula. It inserts proximal to and on the deltoid
angle can range from approximately 60° to 150°. 16 tuberosity. The teres minor muscle flexes the joint and,
together with the infraspinatus, abducts the arm. The
infraspinatus also rotates the arm laterad. The infraspi­
Arm and Shoulder
natus muscle is supplied by the suprascapular nerve, and
The “arm” (L. brachium) is the region of the limb the teres minor by the axillary nerve.
between the elbow and shoulder (scapulohumeral) joints. The subscapularis muscle stabilizes the shoulder joint
Within the superficial fascia over the lateral aspect of the medially. This adductor of the arm originates in the sub­
shoulder and arm, the cutaneous omobrachialis muscle scapular fossa of the scapula and inserts on the lesser
arises in the region lateral to the scapula and extends as tubercle of the humerus. Caudal support to the joint is
far distal as the elbow joint (Figure 1.28). The cutaneous rendered by the long head of the triceps brachii, the only
muscle is innervated by the intercostobrachial nerve head of this muscle originating from the scapula.
(a branch of the lateral thoracic nerve). The intercosto­
brachial nerve and branches of the axillary, radial, and
spinal nerves provide cutaneous sensation to this region. Flexor Muscles of the Shoulder Joint
Superficial blood vessels are branches of the caudal In addition to the long head of the triceps brachii
circumflex humeral vessels. muscle, four muscles flex the shoulder joint: laterally,
The cleidobrachialis muscle (distal part of the bra­ the deltoideus and teres minor; medially, the teres major
chiocephalicus) covers the craniolateral aspect of the and coracobrachialis; and the latissimus dorsi. The first
shoulder joint on the way to its insertion on the deltoid three muscles are innervated by branches from the axil­
tuberosity, humeral crest, and the fascia of the arm lary nerve; the coracobrachialis, by the musculocutane­
(Figure 1.29). When the head and neck are fixed and the ous nerve; and the latissimus dorsi, by the thoracodorsal
limb is free to swing, this muscle acts as an extensor of nerve.
the shoulder joint, drawing the forelimb forward. With The deltoideus lies on the lateral surface of the tri­
the limb fixed on the ground, its contraction draws the ceps brachii and partly on the infraspinatus and teres
head and neck into lateral flexion. minor muscles. It originates from the caudal border of
the scapula and the scapular spine via the aponeurosis
covering the infraspinatus and inserts on the deltoid
Muscles Substituting for Shoulder Joint Ligaments
tuberosity of the humerus and the brachial fascia
Cranially, the dense, partly cartilaginous tendon of (Figure 1.30).
the biceps brachii muscle originates on the supraglenoid The teres major muscle extends from the caudal bor­
tubercle of the scapula and occupies the intertubercular der of the scapula and crosses the medial surface of the
groove of the humerus. A connective tissue band extends triceps brachii to the teres major tuberosity of the
from the lesser tubercle to the greater tubercle, serving humerus, where it inserts in common with the latissimus
as a retinaculum for the biceps tendon. A bursa lies dorsi muscle (Figure 1.27).
under the tendon, partially extending around its sides. The coracoid process of the scapula gives origin to the
A tendinous band (an “internal tendon”) is continuous coracobrachialis muscle that crosses the medial aspect of
from the tendon of origin distad through the muscle. In the shoulder joint to attach to the humerus just proximal
addition to the muscle’s primary function of elbow flex­ to the teres major tuberosity and on the middle of the
ion, the internal tendon of the biceps brachii passively cranial surface of the bone. A bursa lies between the ten­
fixes the elbow and shoulder in the standing position. don of origin of the coracobrachialis and the tendon of
The musculocutaneous nerve supplies the biceps insertion of the subscapularis muscle. 30
brachii.
The supraspinatus muscle arises in the supraspinous
fossa, the spine, and cartilage of the scapula. It divides Shoulder Joint
distally to attach to the greater and lesser tubercles of The fibrous joint capsule of the shoulder joint attaches
the humerus, serving with the bicipital tendon to stabi­ up to 2 cm from the margins of the articular surfaces.
lize the shoulder joint cranially and to a smaller degree Two elastic glenohumeral ligaments reinforce the joint
laterally (Figure 1.30). The supraspinatus is a shoulder capsule on its cranial side as they diverge from the supra­
extensor; it is innervated by the suprascapular nerve, glenoid tubercle to the humeral tuberosities. A very small
which reaches the supraspinous fossa by coursing articularis humeri muscle lies on the flexion surface of
between the subscapularis and supraspinatus muscles the joint capsule, extending from the caudal part of the
and then wrapping around the distal fourth of the cra­ scapula to the caudal surface of the humerus just distal
nial border of the scapula. to the head. Innervated by the axillary nerve, the articu­
The infraspinatus muscle extends from the scapular laris humeri muscle tenses the joint capsule during flex­
cartilage and infraspinous fossa to insert on the caudal ion of the shoulder joint.