Handbook of the Human Body

8/3/2019 Handbook of the Human Body

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Handbook of the Human Body:

Shoulder joint :

The glenohumeral, or shoulder joint, is the point of articulation between the glenoid cavity of the

scapula (shoulder blade) and the head of the humerus (bone of the upper arm). It is a ball-and-

socket synovial (fluid-filled) joint constructed to allow the upper limb a very wide range of

movement.

Articular surface:

To permit a wide range of movement, the head of the humerus provides a large articular surface.

The glenoid cavity of the scapula, deepened by a ring of tough fibrocartilage (the glenoid labrum),

offers only a shallow socket. The resulting ball-and-socket is so shallow that the joint needs to be

held firmly together by the surrounding muscles and ligaments. A thin layer of smooth articular (or

hyaline) cartilage allows the bones to slip over each other with minimum friction.

Joint Capsule:

The shoulder joint is surrounded by a loose capsule of fibrous tissue. This capsule is lined by the

synovial membrane which covers all the inner surfaces of the joint except those covered with

articular cartilage. The cells of this synovial membrane secrete synovial fluid, a viscous liquid which

lubricates and nourishes the joint.

Ligaments of the shoulder joint :

The ligaments around any joint contribute to its stability by holding the bones firmly together. In the

shoulder joint, the main stabilizers are the surrounding muscles, but ligaments also play a role.

Stabilizing ligaments:

The fibrous joint capsule has ligaments within it which help to strengthen the joint.

y The glenohumeral ligaments are three weak, fibrous bands which reinforce the front of the

capsule.

y The coracohumeral ligament is a strong, broad band which strengthens the upper aspect of

the capsule. Although not actually part of the glenohumeral joint itself, the coraco-acromial

ligament is important as it spans the gap between the acromion and the coracoid process of

the scapula. The arch of bone and ligament is so strong that even if the humerus is forcibly

pushed up, it will not break; the clavicle or the humerus will give way first

y The transverse humeral ligament runs from the greater to the lesser tuberosity of the

humerus, creating a tunnel for the passage of the biceps brachii tendon in its synovial

sheath.

Movements of the shoulder joints:

The movements of the shoulder joint take place around three axis: a horizontal axis through the

centre of the glenoid fossa; axis perpendicular to this (front-back) through the humeral head; and a



third axis running vertically through the shaft of the humerus. These give the axes of flexion and

extension, adduction (movement towards the body) and adduction (movements away from the

body), and medial (internal) and lateral (external) rotation respectively. A combination of these

movements can allow a circular motion of the limb called circumduction.

ShoulderMuscles:

Many of the muscles involved in these movements are attached to the pectoral girdle (the clavicles

and scapulae). The scapula has muscles attached to its rear and front surfaces and the coracoid

process, a bony projection. Some muscles arise directly from the trunk (pectoralis major and

latissimus dorsi). Other muscles influence the movement of the humerus even though they are not

attached to it directly (such as trapezius). They do this by moving the scapula, and hence the

shoulder joint.

Rotation of the arm and rotator cuff

The pectoralis major, anterior fibres of deltoid, teres major and latissimus dorsi muscles also cause

medial rotation of the humerus.

Rotator Cuff:

The most powerful medial rotator, however, is subscapularis. This muscle occupies the entire front

surface of the scapula, and attaches to the joint capsule around the lesser tuberosity of the

humerus. Subscapularis is one of a set of four short muscles, collectively called the rotator cuff,

which attach to and strengthen the joint capsule. In addition, they pull the humerus into the socket

of the joint (glenoid fossa), increasing contact of the bony elements. This is the most important

factor contributing to the stability of the joint. The other muscles of the group are supraspinatus,

infraspinatus and teres minor. These latter three muscles attach to the three facets on the greater

tuberosity of the humerus. Infraspinatus and teres minor are lateral rotators of the shoulder joint,

together with the posterior fibres of the deltoid. Injury to the rotator cuff muscles is disabling,

because the stability of the humerus in the joint is lost. The other muscles of the arm lose the abilityto move the humerus correctly, resulting in dislocation of the joint.

Axilla:

Vessels, nerves and lymphatics serving the upper limb all pass through the axilla. The structures lie

embedded in fatty connective tissue, which occupies the axillary space.

The axillary artery:

The axillary artery and its branches supply oxygenated blood to the upper limb. As it passes through

the axilla this artery gives off several branches which supply the surrounding structures of the

shoulder and pectoral regions.

The axillary vein:

The axillary vein runs through the axilla on the medial side of the axillary artery. The pattern of the

veins and venous drainage is variable but the axillary vein, in general, receives blood from tributary

veins that match the branches of the axillary artery.

Nerves in the Axilla:

The nerves which lie in the axilla are part of a complex network known as the branchial plexus.



Lymphatics:

Within the fatty connective tissue of the axilla lie a series of groups of lymph nodes which are

connected by lymphatic vessels. Lymph nodes are scattered throughout the fat of the axilla.

The clavipectoral fascia:

The clavipectoral fascia descends to enclose the subclavius muscle and the pectoralis minor muscle

and then joins with the overlying axillary fascia in the base of the axilla. The part of the clavipectoral

fascia that lies above the pectoralis minor muscle is known as the costocorcoid membrane and is

pierced by the nerve which supplies the overlying pectoralis minor muscle. Below the pectoralis

minor muscle, the fascia becomes the suspensory ligament of the axilla, which attaches to the skin

of the armpit and is responsible for pulling that skin up when the arm is raised. The clavipectoral

fascia is continuous with the brachial fascia, which envelops the arm like a sleeve. The fascia is

pierced by a number of veins, arteries and nerves. These are the cephalic vein, the thoracoacromial

artery (a branch of the axillary artery) and the lateral pectoral nerve.

Structure of the humerus:

At the top of the humerus (the proximal end) lays the smooth, hemispherical head that fits into theglenoid cavity of the scapula at the shoulder joint. Behind the head is a shallow constriction known

as the anatomical neck of the humerus, which separates the head from two bony prominences, the

greater and the lesser tuberosities. These are sites for muscle attachment and are separated by the

intertubercular (or bicipital) groove.

The shaft:

At the upper end of the shaft is the slightly narrowed surgical neck of the humerus- a common site

for fractures. The relatively smooth shaft has two distinctive features. About half way down the

shaft, on the lateral (outer) side, lies the deltoid tuberosity, a raised site of attached of the deltoid

muscle. The second feature is the radial (or spiral) groove which runs across the back of the middle

part of the shaft. This depression marks the path of the radial nerve and the profunda brachii artery.

Ridges at each side of the lower shaft pass down to end in the prominent medial (inner) and lateral

epicondyles. There are two main parts to the articular surface: the trochlea, which articulates with

the ulna; and the capitulum, which articulates with the radius.

Inside the humerus:

Long bones are elongated in shape and longer than they are wide. Most of the bones of the limbs

are long bones, even the small bones of the fingers, and as such they have many features in common

with the humerus. The humerus consists of a diaphysis, or shaft, with an epiphysis (expanded head)

at each end. The diaphysis is a tubular construction with an outer layer of dense, thick bone

surrounding a central medulla (inner region) containing fat cells. The epiphyses of the humerus are,

at the upper end, the head and at the lower end the condylar region. These are composed of a thin

layer of compact bone covering cancellous (spongy) bone which make up the greater volume.

Bone surface:

The surface of the humerus (and all long bones) is covered by a thick membrane, the periosteum.

The articular surfaces at the joints are the only parts of the bone not covered by the periosteum.

These surfaces are covered by tough articular (or hyaline) cartilage which is smooth, allowing the

bones to glide over each other. The outer compact bone receives its blood supply from the arteries



of the periosteum, and will die if that periosteum is stripped off, while the inner parts of the bone

are supplied by occasional nutrient arteries which pierce the compact bone.

Ulna and Radius:

The ulna and radius are the two parallel long bones of the forearm and lie between the elbow and

the wrist joints. The ulna lies on the same side as the little finger (medially), while the radius lies on

the same side as the thumb (laterally). The radio-ulnar joints allow the ulna and radius to rotate

around each other in the movements peculiar to the forearm known as pronation (rotating the

forearm so that the palm faces down), and supination (rotating the forearm so that the palm faces

up).

The ulna:

The Ulna is longer than the radius and is the main stabilizing bone of the forearm. It has a long shaft

with two expanded ends. The upper end of the ulna has two prominent projections, the olecranon

and the coronoid process, which are separated by the deep trochlear notch, which articulates with

the trochlea of the humerus. On the lateral (outer) side of the coronoid process, there is a small,

rounded recess (the radial notch), which is the site of articulation of the upper end of the ulna withthe neighbouring head of the radius. The head of the ulna is separated from the wrist joint by an

articular disc and does not play much part in the wrist joint itself.

The Radius:

Like the ulna, the radius has a long shaft with upper and lower expanded ends. While the ulna is the

forearm bone which contributes most to the elbow, the radius plays a major part in the wrist joint.

Head of the Radius:

The disc-like head of the radius is concave above, where it articulates with the capitulum of the

humerus in the elbow joint. The cartilage that covers this concavity continues down over the head,

especially on the side nearest to the ulna, to allow the smooth articulation of the head of the radiuswith the radial notch at the upper end of the ulna.

The shaft:

The shaft of the radius becomes progressively thicker as it continues down to the wrist. It also has a

sharp edge for attachment of the interosseous membrane. On the inner side, next to the ulna, there

is a concavity (the ulnar notch), which is the site for articulation with the head of the ulna. Extending

from the opposite side is the radial styloid process, a blunt cone which projects a little further down

then the ulnar styloid process. At the back of the end of the radius, and easily felt at the back of the

wrist, is the dorsal tubercle.

Elbow:

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Handbook of the Human Body