Condylar Joint

■ Temporomandibular Joint_

Overview, Bony Structures, and Joints. The temporomandibular joint is the most active joint in the body, opening and closing up to 2000 times a day. It is formed by the fossa and articular tubercle of the temporal bone and the condyle of the mandible. It lies midway between the external acoustic meatus and the zygomatic arch.

bone and the condyle of the mandible. It lies midway between the external acoustic meatus and the zygomatic arch.

A fibrocartilaginous disc cushions the action of the condyle of the mandible against the synovial membrane and capsule of the articulating surfaces of the temporal bone. Hence, it is a condylar synovial joint.

Muscle Groups and Additional Structures. The principal muscles opening the mouth are the external pterygoids. Closing the mouth are the muscles innervated by Cranial Nerve V, the trigeminal nerve (see p. 538)—the masseter, the temporalis, and the internal pterygoids.

H The Shoulder_

Overview. The shoulder is distinguished by wide-ranging movement in all directions. The humerus virtually dangles from the scapula, suspended from the shallow glenoid fossa by the joint capsule, the intra-articular capsular ligaments, the glenoid labrum, and a meshwork of muscles and tendons. The shoulder derives its mobility from a complex interconnected structure of four joints, three large bones, and three principal muscle groups, often referred to as the shoulder girdle. The clavicle and acromion stabilize the shoulder girdle, allowing the humerus to swing out and away from the body, giving the shoulder its remarkable range of motion.

Bony Structures. The bony structures of the shoulder include the humerus, the clavicle, and the scapula. The scapula is anchored to the axial skeleton only by the sternoclavicular joint and inserting muscles, often called the scapulothoracic articulation since it is not a true joint.

Identify the manubrium, the sternoclavicular joint, and the clavicle. With your fingers, trace the clavicle laterally. Now, from behind, follow the bony spine of the scapula laterally and upward until it becomes the acromion, the summit of the shoulder. Its upper surface is rough and slightly convex. Identify the anterior tip of the acromion (A) and mark it with ink. With your index finger on top of the acromion, just behind its tip, press medially to find the slightly elevated ridge that marks the distal end of the clavicle at the acromioclavicular joint (shown by the arrow). Move your finger laterally and down a short step to the next bony prominence, the greater tubercle of the humerus (B). Mark this with ink. Now sweep your finger medially until you feel a large bony prominence, the coracoid process of the scapula (C). Mark this also. These three points—the tip of the acromion, the greater tubercle of the humerus, and the coracoid process—orient you to the anatomy of the shoulder.

Joints. Three different joints articulate at the shoulder:

■ The glenohumeral joint. In this joint, the head of the humerus articulates with the shallow glenoid fossa of the scapula. This joint is deeply situated and not normally palpable. It is a ball-and-socket joint, allowing the arm its wide arc of movement—flexion, extension, abduction (movement away from the trunk), adduction (movement toward the trunk), rotation, and circumduction.

■ The sternoclavicular joint. The convex medial end of the clavicle articulates with the concave hollow in the upper sternum.

■ The acromioclavicular joint. The lateral end of the clavicle articulates with the acromion process of the scapula.

Muscle Croups. Three groups of muscles attach at the shoulder:

The Scapulohumeral Group.

This group extends from the scapula to the humerus and includes the muscles inserting directly on the humerus, known as CCSITS musclesv of the rotator cuff:

■ Supraspinatus—runs above the glenohumeral joint; inserts on the greater tubercle

■ Infraspinatus and teres minor— cross the glenohumeral joint posteriorly; insert on the greater tubercle

■ Subscapularis (not illustrated)— originates on the anterior surface of the scapula and crosses the joint anteriorly; inserts on the lesser tubercle.

Axioscapular group

Posterior view

Axioscapular group (pulls shoulder backward)

Scapulohumeral group (rotates shoulder laterally; includes rotator cuff)

Posterior view

Axioscapular group (pulls shoulder backward)

Scapulohumeral group (rotates shoulder laterally; includes rotator cuff)

The scapulohumeral group rotates the shoulder laterally (the rotator cuff) and depresses and rotates the head of the humerus. (See pp. 526-527 for discussion of rotator cuff injuries.)

The Axioscapular Group.

This group attaches the trunk to the scapula and includes the trapezius, rhomboids, serratus anterior, and levator scapulae. These muscles rotate the scapula.

The Axiohumeral Group.

This group attaches the trunk to the humerus and includes the pec-toralis major and minor and the latis-simus dorsi. These muscles produce internal rotation of the shoulder.

The biceps and triceps, which connect the scapula to the bones of the forearm, are also involved in shoulder movement, particularly abduction.

Additional Structures. Also important to shoulder movement are the articular capsule and bursae. Surrounding the glenohumeral joint is a fibrous articular capsule formed by the tendon insertions of the rotator cuff and other capsular muscles. The loose fit of the capsule allows the shoulder bones to separate, and contributes to the shoulder's wide range of movement. The capsule is lined by a synovial membrane with two outpouchings—the subscapular bursa and the synovial sheath of the tendon of the long head of the biceps.

To locate the biceps tendon, rotate the arm externally and find the tendinous cord that runs just medial to the greater tubercle. Roll it under your fingers. This is the tendon of the long head ofthe biceps. It runs in the bicipital groove between the greater and lesser tubercles.

The principal bursa of the shoulder is the subacromial bursa, positioned between the acromion and the head of the humerus and overlying the supra-spinatus tendon. Abduction of the shoulder compresses this bursa. Normally, the supraspinatus tendon and the subacromial bursa are not palpable. However, if the bursal surfaces are inflamed (subacromial bursitis), there may be tenderness just below the tip of the acromion, pain with abduction and rotation, and loss of smooth movement.

H The Elbow_

Overview, Bony Structures, and Joints. The elbow helps position the hand in space and stabilizes the lever action of the forearm. The elbow

Anterior view Axiohumeral group (rotates shoulder internally)

joint is formed by the humerus and the two bones of the forearm, the radius and the ulna. Identify the medial and lateral epicondyles of the humerus and the olecranon process of the ulna.

These bones have three articulations: the humeroulnar joint, the radio-humeral joint, and the radioulnar joint. All three share a large common articular cavity and an extensive synovial lining.

Muscle Groups and Additional Structures. Muscles traversing the elbow include the biceps and brachio-radialis (flexion), the triceps (extension), the pronator teres (pronation), and the supinator (supination).

Humerus

Medial epicondyle

Humeroulnar joint Radioulnar joint—

Pronator teres

Humerus

Medial epicondyle

Humeroulnar joint Radioulnar joint—

Pronator teres

Lateral epicondyle

Radiohumeral joint

— Brachioradialis

Radius

LEFT ELBOW—ANTERIOR VIEW

Lateral epicondyle

Radiohumeral joint

— Brachioradialis

Radius

LEFT ELBOW—ANTERIOR VIEW

Note the location of the olecranon bursa between the olecranon process and the skin. The bursa is not normally palpable but swells and becomes tender when inflamed. The ulnar nerve runs posteriorly between the medial epicondyle and the olecranon process. On the ventral forearm, the median nerve is just medial to the brachial artery.

Synovial membrane

(distended)

Radial nerve

Synovial membrane

(distended)

Radial nerve

Ulnar nerve

Olecranon process

Medial epicondyle

Olecranon bursa

LEFT ELBOW—POSTERIOR VIEW

Ulnar nerve

Olecranon process

Medial epicondyle

Olecranon bursa

LEFT ELBOW—POSTERIOR VIEW

The Wrist and Hands

Bony Structures. The wrist includes the distal radius and ulna and eight small carpal bones. At the wrist, identify the bony tips of the radius and the ulna.

The carpal bones lie distal to the wrist joint within each hand. Identify the caipal bones, each of the five metacarpals, and the proximal, middle, and distal phalanges. Note that the thumb lacks a middle phalanx.

Joints. The numerous joints of the wrist and hand lend unusual dexterity to the hands.

Wrist joints. The wrist joints include the radiocarpal or wrist joint, the distal radioulnar joint, and the intercarpal joints. The joint capsule, articular disc, and synovial membrane of the wrist join the radius to the ulna and to the proximal caipal bones. On the dorsum of the wrist, locate the groove of the radiocarpal joint.

Intercarpal joints

Distal radioulnar joint

Radiocarpal joint

Radiocarpal joint

Intercarpal joints

Distal radioulnar joint

Proximal interphalangeal joint (PIP)

Metacarpophalangeal joint (MCP)

Trapezoid Trapezium Scaphoid

Radius

Overview. The wrist and hands form a complex unit of small, highly active joints used almost continuously during waking hours. There is little protection from overlying soft tissue, increasing vulnerability to trauma and disability.

Distal interphalangeal joint (DIP)

Proximal interphalangeal joint (PIP)

Metacarpophalangeal joint (MCP)

Trapezoid Trapezium Scaphoid

Capitate Hamate Triquetrum Lunate

Radius

Hand joints. The joints of the hand include the metacarpophalangeal joints (MCPs), the proximal interphalangeal joints (PIPs), and the distal interphalangeal joints (DIPs). Flex the hand and find the groove marking the MCP joint of each finger. It is distal to the knuckle and is best felt on either side of the extensor tendon.

Metacarpophalangeal joint

Muscle Croups. Wrist flexion arises from the two carpal muscles, located on the radial and ulnar surfaces. Two radial and one ulnar muscle provide wrist extension. Supination and pronation result from muscle contraction in the forearm.

The thumb is powered by three muscles that form the thenar eminence and provide flexion, abduction, and opposition. The muscles of extension are at the base of the thumb along the radial margin. Movement in the digits depends on action of the flexor and extensor tendons of muscles in the forearm and wrist.

The intrinsic muscles of the hand attaching to the metacarpal bones are involved in flexion (lumbricals), abduction (dorsal interossei), and adduction (palmar interossei) of the fingers.

Additional Structures. Soft-tissue structures, especially tendons and tendon sheaths, are extremely important in the wrist and hand. Six extensor tendons and two flexor tendons pass across the wrist and hand to insert on the fingers. Through much of their course these tendons travel in tunnellike sheaths, generally palpable only when swollen or inflamed.

Be familiar with the structures in the carpal tunnel, a channel beneath the palmar surface of the wrist and proximal hand. The canal contains the sheath and flexor tendons of the fore-ami muscles and the median nerve.

Holding the tendons and tendon sheath in place is a transverse ligament, the flexor retinaculum. The median nerve lies between the flexor retinaculum and the tendon sheath. It provides sensation to the palm and the palmar surface of most of the thumb, the second and third digits, and half of the fourth digit. It also innervates the thumb muscles of flexion, abduction, and opposition.

Flexor retinaculum Carpal tunnel Median nerve

Was this article helpful?

0 0
Anxiety and Depression 101

Anxiety and Depression 101

Everything you ever wanted to know about. We have been discussing depression and anxiety and how different information that is out on the market only seems to target one particular cure for these two common conditions that seem to walk hand in hand.

Get My Free Ebook


Post a comment