Joints of the Upper Limb (1)

The shoulder joint | Main Anatomy Index | Joints of the upper limb (2)

Joints of the Upper Limb

• The pectoral girdle (clavicle and scapula) connects the upper limb to the trunk; therefore, its articulations are included with those of the upper limb.

The Sternoclavicular Joint (p. 607)

• This is a saddle type of synovial joint and is the only bony articulation between the upper limb and the axial skeleton.

• An important function of the clavicle is to hold the upper limb away from the trunk, i.e., it acts as a strut for keeping the shoulder away from the chest to give the upper limb the maximum freedom of motion.
• The sternoclavicular joint can be readily palpated because the medial end of the clavicle lies superior to the manubrium of the sternum.

The Articular Surfaces of the Sternoclavicular Joint (p. 607)

• The enlarged medial end of the clavicle articulates in a shallow socket formed by the superolateral part of the manubrium of the sternum and the medial part of the first costal cartilage.
• Unlike most articular surfaces, the articular cartilage is mainly fibrocartilaginous.

• The articular surfaces are separated by a strong, thick, densely fibrous or fibrocartilaginous articular disc. It is located inside the joint and divides it into two synovial cavities.
• The disc is attached superiorly to the medial end of the clavicle and inferiorly to the junction of the sternum and the first costal cartilage.
• The articular disc is continuous with the anterior and posterior sternoclavicular ligaments, which are thickenings of the fibrous capsule.
• This disc prevents medial displacement of the clavicle; it is also an important shock absorber of forces transmitted along the clavicle.

The Articular Capsule of the Sternoclavicular Joint (pp. 607, 609)

• The fibrous capsule surrounds the entire joint, including the epiphysis at the medial end of the clavicle.
• Although thin inferiorly, other parts of the fibrous capsule are strong because they are reinforced by the anterior and posterior sternoclavicular ligaments and superiorly by the interclavicular ligament.

• The interclavicular ligament extends across the jugular notch of the sternum. The sternoclavicular and interclavicular ligaments are thickenings of the fibrous capsule of the joint.

• The costoclavicular ligament is a strong, extracapsular ligament. It ascends from the firs rib and its costal cartilage to the inferior margin of the medial end of the clavicle. This ligament reinforces the sternoclavicular joint laterally and limits the elevation of the medial end of the clavicle. Any movement of the clavicle, except inferior motion, tightens its fibres and is resisted.

• The synovial capsule lines the fibrous capsule and both surfaces of the articular disc. Because this disc divides the joint into two cavities, there are two synovial membranes.

• The lateral one reflects from the articular margin of the medial end of the clavicle to the margins of the articular disc.
• The medial one lines the capsule between the sternal attachments and the disc.

Movements of the Sternoclavicular Joint

• Despite the saddle-like form of its articular surfaces, this joint moves in many directions like a ball and socket joint.
• This is seen the elevation and depression of the shoulder and by protracting and retracting it.
• When the upper limb is elevated as far as possible, the clavicle is raised to about a 60-degree angle from its anatomical position.

Stability of the Sternoclavicular Joint (p. 609)

• Because of the bony surfaces involved are incongruent and the surrounding muscles offer little support, the sternoclavicular joint depends on its ligaments and articular disc for stability.
• The strong disc is largely responsible for preventing medial displacement of the clavicle (e.g., when carrying heavy suitcases). The disc prevents the medial end of the clavicle from being pushed out of its socket and superior to the manubrium.
• The sternoclavicular ligaments also help to prevent displacement of the medial end of the clavicle. These ligaments also restrain excessive protraction and elevation of the clavicle.

Blood Supply of the Sternoclavicular Joint (p. 609)

• The articular arteries are branches of the internal thoracic and suprascapular arteries.

Nerve Supply of the Sternoclavicular Joint (p. 609)

• The articular nerves are branches of the medial supraclavicular and the nerve to the subclavius muscle.

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The Acromioclavicular Joint

• This is a plane type of synovial joint that is located between the lateral end of the clavicle and the acromion of the scapula.
• It is located 2 to 3 cm medial to the acromion, which projects anteriorly from the lateral end of the spine of the scapula. The acromion forms a palpable and sometimes visible prominence, know as the "point of the shoulder".

The Articular Surfaces of the Acromioclavicular Joint (p. 609)

• The small oval articular facet on the lateral end of the clavicle articulates with a similar facet on the anterior part of the medial surface of the medial end of the acromion.
• Both articular surfaces are covered with fibrocartilage and slope inferomedially so that the clavicle tends to override the acromion and project over it.

• A wedge-shaped, incomplete fibrocartilaginous articular disc projects into the joint from the superior part of the joint and partially divides the joint cavity into two parts.

The Articular Capsule of the Acromioclavicular Joint (p. 609)

• The fibrous capsule enclosing the joint is attached to the margins of its articular surfaces.
• Although it is weak, it is strengthened superiorly by the acromioclavicular ligament and by fibres from the trapezius muscle.
• This ligament extends from the superior part of the lateral end of clavicle to the superior surface of the acromion.
• A synovial capsule lines the fibrous capsule.

The Coracoclavicular Ligament (p. 609)

• This ligament anchors the lateral part of the clavicle to the coracoid process of the scapula. It is the strongest of the ligaments that binds the clavicle to the scapula.
• It consists of two parts, the conoid and the trapezoid ligaments, which are directed in such a way that they enable the clavicle to hold the scapula and upper limb laterally.

Movements of the Acromioclavicular Joint (pp. 609, 611)

• This articulation allows the acromion to rotate on the clavicle and to move anteriorly and posteriorly.
• These movements are associated with movements of the scapula and with those at the sternoclavicular joint.

Stability of the Acromioclavicular Joint (p. 611)

• The coracoclavicular ligament, an extrinsic ligament of the acromioclavicular joint, is principally responsible for providing stability to the articulation.
• It prevents the clavicle from losing contact with the acromion of the scapula.

Blood Supply of the Acromioclavicular Joint (p. 611)

• The articular arteries are branches of the suprascapular and thoracoacromial arteries.

Nerve Supply of the Acromioclavicular Joint (p. 611)

• The articular nerves are branches of the supraclavicular, lateral pectoral, and axillary nerves.

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The Shoulder Joint

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The Elbow Joint

• This is a hinge type of synovial joint that is formed where the distal end of the humerus articulates with the proximal ends of the radius and ulna.
• The elbow is a uniaxial joint; its movements consist of flexion and extension.

The Articular Surfaces of the Elbow Joint (p. 616)

• The trochlea and capitulum of the humerus articulates with the trochlear notch of the ulna and the head of the radius, respectively.
• The articular surfaces, covered with hyaline cartilage, are most fully in contact when the forearm is in the position midway between pronation and supination and is flexed to a right angle.

The elbow joint includes three articulations:

1. The humeroulnar articulation is between the trochlea of the humerus and the trochlear notch of the ulna. They form a uniaxial hinge joint, permitting movement in one axis: flexion and extension.
2. The humeroradial articulation is between the capitulum of the humerus and the head of the radius. The capitulum fits into the slightly cupped surface of the head.
3. The proximal radioulnar joint is between the head of the radius and radial notch of the ulna. This is a pivot joint, permitting rotation of the radius about the ulna.

The Articular Capsule of the Elbow Joint (p. 616)

• The fibrous capsule completely encloses the joint. Its anterior and posterior parts are thin and weak, but collateral ligaments strengthen its sides.
• The fibrous capsule is attached to the proximal margins of the coronoid and radial fossae anteriorly, but not quite to the superior limit of the olecranon fossa posteriorly.
• Distally the fibrous capsule is attached to the margins of the trochlear notch, the anterior border of the coronoid process, and the anular ligament.

The Collateral Ligaments of the Elbow Joint (p. 616)

• These are strong triangular bands are medial and lateral thickenings of the fibrous capsule; hence, they are intrinsic ligaments.

The Radial Collateral Ligament (p. 616)

• Its apex is attached proximally to the lateral epicondyle of the humerus and its base blends with the anular ligament of the radius.

The Ulnar Collateral Ligament (p. 616)

• It is composed of anterior and posterior bands (parts), which are connected by a thinner, relatively weak oblique band.
• Its apex is attached to the medial epicondyle of the humerus.
• The strong cord-like anterior part is attached to the tubercle on the coronoid process of the ulna and the weaker fan-like posterior part is attached to the medial edge of the olecranon.
• The ulnar nerve passes posterior to the medial epicondyle and is closely applied to the ulnar collateral ligament.

The Synovial Membrane of the Elbow Joint (p. 616)

• This lines the fibrous capsule and is reflected onto the humerus, lining the coronoid and radial fossae anteriorly and the olecranon fossa posteriorly. The synovial capsule is continued into the proximal radioulnar joint.
• A redundant fold of the synovial capsule, called the sacciform recess, emerges distal to the anular ligament and facilitates rotation of the head of the radius, e.g., during supination and pronation.

Movements of the Elbow Joint (pp. 616-7)

• This joint can be flexed or extended.
• Flexion is produced by the brachialis and brachioradialis muscles, but the main flexor is the brachialis. When the forearm is supinated, the biceps brachii muscle also flexes this joint; when it is pronated, the pronator teres does.

• Flexion is limited by apposition of the anterior surfaces of the forearm and arm, by tension of the posterior arm muscles, and by the radial and ulnar collateral ligaments.

• The flexion of the forearm, or twitch of the biceps brachii that occurs following tapping of the bicipital aponeurosis without movement, is known as the biceps jerk. The reflex centre is in C5 and C6 segments of the spinal cord.

• The main extensor of the elbow joint is the triceps brachii muscle.
• Gravity and the anconeus muscle assist with this movement.

• Extension is limited by impingement of the olecranon of the ulna on the olecranon fossa of the humerus and by tension of the anterior arm muscles and collateral ligaments.
• The anconeus muscle stabilises the elbow joint and may assist in its extension.

• The extension of the forearm, or twitch of the triceps without movement that occurs following tapping of the triceps tendon, is known as the triceps jerk. The reflex centre is in C6, C7, and C8 segments of the spinal cord.

• When the forearm is fully extended and supinated in the anatomical position, the arm and forearm are not in the same line.
• This is as the articular surfaces of the distal end of the humerus are not set at a right angle to the body (shaft).
• Normally the forearm is directed laterally, forming a carrying angle of about 165 degrees. This angle permits the extended forearm to clear the side of the hip in swinging movements during walking, which is important when carrying heavy loads.
• The angle is diminished when the forearm is pronated or flexed.

Stability of the Elbow Joint (p. 617)

• In adults this joint is quite stable because of the hinge-like arrangement formed by the jaw-like trochlear notch of the ulna into which the spool-shaped trochlear of the humerus fits.
• In addition, very strong ulnar and radial collateral ligaments strengthen the joint.

Blood Supply of the Elbow Joint (p. 621)

• The articular arteries are derived from the anastomosis around the elbow, which are formed by collateral branches of the brachial and recurrent branches of the ulnar and radial arteries.

Nerve Supply of the Elbow Joint (p. 621)

• The articular nerves are derived mainly from the musculocutaneous and radial nerves, but the ulnar, median, and anterior interosseous nerves may also supply articular branches.

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