Sectional anatomy for imaging professionals, 4th edition

Chapter 9. Upper Extremity

It is sometimes on one’s weakest limbs that one must lean in order to keep going.

Jean Rostand, Substance of Man

The intricate anatomy of the musculoskeletal system can make identification of the upper extremity anatomy challenging (Fig. 9.1). A basic knowledge of the anatomy and kinesiology of these areas increases the ability to identify pathology or injury that may occur.

FIG. 9.1 3D CT—healing fracture of the clavicle.

OBJECTIVES

 Identify the bony anatomy of the upper extremity.

 Identify the components that contribute to the glenoid labrum.

 Describe the joint capsules of the shoulder, elbow, and wrist.

 List and describe the ligaments and tendons of each upper extremity joint.

 Identify and state the actions of the muscles, as well as their origin and insertion sites.

 Identify the major arteries and veins of the upper extremity.

 List and identify the nerves that innervate the upper extremity.

SHOULDER

Bony Anatomy

The bony anatomy that comprises the shoulder girdle includes the clavicle, scapula, and humerus (Figs. 9.2 and 9.3).

Clavicle. The clavicle connects the upper limb to the trunk of the body and provides attachments for several muscles and ligaments. It is a long, slender bone located anteriorly that extends transversely from the sternum to the acromion process of the scapula. The widened sternal end of the clavicle articulates with the manubrium of the sternum to form the sternoclavicular (SC) joint, and its flattened acromial end articulates with the acromion process of the scapula to form the acromioclavicular (AC) joint. The medial two-thirds of the body of the clavicle is anteriorly convex, whereas the lateral one- third is flattened and anteriorly concave (Figs. 9.2-9.6).

Scapula. The scapula is a triangular-shaped flat bone that forms the posterior portion of the shoulder girdle. It has a medial margin (vertebral border), a lateral margin (axillary border), and a superior margin. The margins are separated by the superior, inferior, and lateral angles (Figs. 9.2 and 9.3). The anterior surface of the scapula, the subscapular fossa, is flat and slightly concave. The posterior surface of the scapula is divided by the scapular spine into a smaller supraspinous fossa and a larger infraspinous fossa (Fig. 9.7). Four projections of the scapula provide attachment sites for the muscles and ligaments contributing to the shoulder girdle. These include the scapular spine, acromion process, coracoid process, and glenoid process (Figs. 9.7-9.10). The scapular spine arises from the upper third of the posterior surface of the scapula and extends obliquely and laterally to give rise to the acromion process.

A communication between the supraspinous and infraspinous fossae exists at the spi- noglenoid notch, which is created where the acromion process and scapular spine converge on the posterior aspect of the scapula. Located on the anterolateral surface of the scapula is a beaklike process termed the coracoid process, which arises just medial to the glenoid process and functions to protect the shoulder joint, which lies beneath it. The coracoid process is an attachment site for the pectoralis minor, the short head of the biceps brachii, and the coracobrachialis muscles. The scapular notch is located just medial to the coracoid process on the superior margin of the scapula and allows for the passage of the suprascapular nerve (Figs. 9.2, 9.3, and 9.9).

The glenoid process, the largest of the projections, forms the lateral angle of the scapula and ends in a depression called the glenoid fossa (glenoid cavity) (Figs. 9.3 and 9.6-9.11). There are two tubercles associated with the glenoid fossa, an upper supraglenoid tubercle and a lower infraglenoid tubercle, which serve as attachment sites for the long heads of the biceps brachii and triceps brachii muscles, respectively (Figs. 9.6-9.8, 9.10, and 9.12). The shallow articular surface of the glenoid fossa joins with the relatively large articular surface of the humeral head to create the freely moving glenohumeral joint (Figs. 9.2, 9.3, 9.6, 9.9, 9.11, and 9.12).

Proximal Humerus. The humerus is a long bone that articulates with the scapula superiorly and the radius and ulna inferiorly. It consists of a proximal end, a body (shaft), and a distal end (Fig. 9.13). The proximal end is formed by the head of the humerus. Two tubercles project from the humeral head to provide attachment sites for tendons and ligaments. The lesser tubercle is located on the anterior surface of the humeral head, whereas the greater tubercle is located on the lateral surface of the humeral head (Figs. 9.12-9.15). The tubercles are separated by the intertubercular (bicipital) groove (Figs. 9.9 and 9.13-9.15). The humerus has two necks, the more proximal anatomic neck and the surgical neck, located inferior to the tubercles just distal to the humeral head (Figs. 9.13 and 9.16). In the middle of the body or shaft of the humerus, on the anterior surface, is the roughened area of the deltoid tuberosity, which provides attachment for the deltoid muscle (Fig. 9.13).

Labrum and Ligaments

The outer rim of the glenoid fossa is surrounded by a fibrocartilaginous ring termed the glenoid labrum, which functions to deepen the articular surface of the glenoid fossa (Fig. 9.17). Superiorly, the glenoid labrum blends with the tendon of the long head of the biceps brachii muscle (Fig. 9.16). In cross-section, it appears triangular (Figs. 9.14 and 9.18). The three glenohumeral ligaments (superior, middle, and inferior) thicken the fibrous capsule that surrounds the shoulder joint and contribute to the formation of the glenoid labrum (Figs. 9.14, 9.17, and 9.19). They extend from the supraglenoid tubercle of the scapula to the lesser tubercle of the humerus. The coracohumeral ligament passes from the lateral side of the coracoid process of the scapula to the greater tubercle of the humerus (Figs. 9.14 and 9.19).

The coraco- acromial ligament is another important ligament located on the anterior portion of the shoulder. As this ligament joins the coracoid process and acromion, it forms a strong bridge, termed the coracoacromial arch, which protects the humeral head and rotator cuff tendons from direct trauma and prevents displacement of the humeral head superiorly (Figs. 9.17, 9.19, and 9.20). The coracoclavicular ligaments help to maintain the position of the clavicle, in relation to the acromion, by spanning the distance between the clavicle and coracoid process of the scapula (Figs. 9.19 and 9.21-9.23). The acromioclavicular ligament, at the acromioclavicular joint, provides support for the superior surface of the shoulder (Figs. 9.17, 9.19, 9.22, and 9.24). The transverse humeral ligament is a broad band of connective tissue passing from the greater tubercle to the lesser tubercle of the humerus, forming a bridge over the intertubercular groove for protection of the long head of the biceps tendon (Figs. 9.19 and 9.27). The ligaments of the shoulder are shown in Figs. 9.20-9.35.

Articular Joint Capsule

The articular joint capsule completely encloses the shoulder joint and is quite thin and loose to allow for extreme freedom of movement. When the arm is adducted, the capsule sags to form a pouchlike area termed the axillary recess (Figs. 9.29, 9.34, and 9.36). The capsule is attached medially to the glenoid fossa of the scapula and laterally to the anatomic neck of the humerus. It is strengthened by several muscles and ligaments, including the rotator cuff muscles and the long head of the biceps brachii muscle, as well as the glenohumeral and coraco-humeral ligaments. There are two openings of the joint capsule. The first is to allow for the passage of the long head of the biceps brachii, and the second establishes a communication between the joint and the subscapularis bursa. A synovial membrane lines the fibrous capsule and extends to the glenoid labrum and neck of the humerus. The synovial membrane provides a sheath for the tendon of the long head of the biceps brachii muscle, where it passes into the joint cavity through the intertubercular groove, extending as far as the surgical neck of the humerus (Figs. 9.28-9.36).

Bursae

The tendons and ligaments of the shoulder joint are cushioned by several fluid-filled bursae. Bursae, within the shoulder, reduce friction where large muscles and tendons pass across the joint capsule. Two prominent shoulder bursae include the subacromial-subdeltoid and subscapular bursae (Figs. 9.36 and 9.37). The subacromial-subdeltoid bursa is the main bursa of the shoulder and the largest bursa within the body. Beginning at the coracoid process, the bursa extends laterally over the superior surface of the supraspinatus and infraspinatus tendons, extends beyond the acromion, and continues beneath the deltoid muscle to the greater tubercle of the humerus. This bursa cushions the rotator cuff muscles and cora- coacromial arch (Fig. 9.16). The subscapular bursa is located between the subscapularis tendon and the scapula and communicates with the synovial cavity through an opening in the joint capsule. This bursa protects the subscapularis tendon, where it passes inferior to the coracoid process and over the neck of the scapula (Fig. 9.37).

Muscles and Tendons

Numerous muscles and their tendons provide stability for the shoulder joint and movement of the upper arm. These can be separated into four muscle groups: (1) muscles that connect the upper extremity to the vertebral column, (2) muscles of the scapula, (3) muscles that connect the upper extremity to the anterior thoracic wall, and (4) muscles of the upper arm.

Muscles Connecting the Upper Extremity to the Vertebral Column

Trapezius Levator scapulae

Latissimus dorsi

Rhomboid major

Rhomboid minor

Muscles connecting the upper extremity to the vertebral column are shown in Figs. 9.38-9.42 and are described in Table 9.1.

The large triangular trapezius muscle covers the posterior aspect of the neck and superior half of the back (Fig. 9.38). It connects the upper limb to the cranium via the external occipital protuberance and to the vertebral column via the ligamentum nuchae and spinous processes of C7-T12. It inserts on the clavicle, acromion process, and scapular spine. The trapezius muscle functions to stabilize the scapula, as well as to elevate, retract, and depress the scapula.

The levator scapulae muscle lies deep in the neck and functions to elevate and rotate the scapula. It extends from the transverse processes of C1-C4 to the superior angle and medial border of the scapula above its spine (Fig. 9.38).

The latissimus dorsi muscle covers the inferior portion of the back as it extends from the spinous processes of the inferior six thoracic vertebrae, iliac crest, and inferior three or four ribs to the distal end of the intertubercular groove of the humerus. The latissimus dorsi medially rotates, extends, and adducts the humerus (Fig. 9.38).

The rhomboid muscles, major and minor, lie deep to the trapezius muscle. The rhomboid major is wider than the rhomboid minor. They parallel each other as they span from the ligamentum nuchae and spinous processes of C7-T5 to the medial border of the scapula. They function to retract the scapula and fix the scapula to the thoracic wall (Figs. 9.38-9.42).

TABLE 9.1 Muscles Connecting the Upper Extremity to the Vertebral Column

Muscle

Origin

Insertion

Primary Actions

Trapezius

External occipital protuberance, ligamentum nuchae, spinous processes of C7-T12

Clavicle, acromion process, and spine of scapula

Stabilizes, elevates, retracts, and depresses scapula

Levator scapulae

Transverse processes of C1-C4

Superior angle and medial border of scapula

Elevates scapula

Latissimus dorsi

Spinous process of T6-T12, iliac crest, and inferior three or four ribs

Distal end of intertubercular groove of the humerus

Extends, medially rotates, and adducts the humerus

Rhomboid major

Ligamentum nuchae and spinous processes of C7-T1

Medial border of scapula

Retracts scapula and fixes scapula to thoracic wall

Rhomboid minor

Spinous processes of T2-T5

Medial border of scapula

Retracts scapula and fixes scapula to thoracic wall

Muscles of the Scapula

Deltoid Teres major Teres minor Supraspinatus Infraspinatus Subscapularis

Muscles of the scapula are shown in Figs. 9.20-9.35 and 9.38-9.57 and described in Table 9.2.

The large deltoid muscle originates on the clavicle, acromion, and scapular spine to blanket the shoulder joint as it extends to insert on the deltoid tuberosity of the humerus. This powerful muscle forms the rounded contour of the shoulder and functions primarily to abduct the arm (Figs. 9.38 and 9.53).

The teres major muscle is a flat rectangular muscle that adducts and medially rotates the arm. It extends from the inferior angle of the scapula to the medial aspect or lip of the intertubercular groove of the humerus (Figs. 9.38 and 9.54A).

The four remaining muscles, supraspinatus, infraspinatus, teres minor, and subscapularis, closely surround the scapula and constitute the rotator cuff (Figs. 9.38 and 9.54-9.57). The rotator cuff provides dynamic stability to the shoulder joint and allows for adduction, abduction, and rotation of the humerus. The supraspinatus, infraspinatus, and teres minor muscles are located on the posterior aspect of the scapula. The tendons of these muscles insert on the greater tubercle of the humerus.

The supraspinatus muscle lies in the supraspinous fossa of the scapula and helps abduct the arm. The tendon of the supraspinatus muscle is the most frequently injured tendon of the rotator cuff because of possible impingement as it extends under the acromioclavicular joint and continues over the humeral head (Figs. 9.54B and 9.57).

The infraspinatus muscle is a triangular muscle that lies below the scapular spine in the infraspinous fossa. It acts to laterally rotate the arm (Fig. 9.54A).

Lying along the inferior border of the infraspinatus muscle is the elongated teres minor muscle, which also acts to laterally rotate the arm (Figs. 9.54B, 9.56, and 9.57).

The subscapularis muscle is the only muscle of the rotator cuff located on the anterior surface of the scapula; its tendon inserts on the lesser tubercle of the humerus. The subscapularis muscle acts to medially rotate the humerus (Fig. 9.55).

The majority of rotator cuff lesions are a result of chronic impingement of the supraspinatus tendon against the acromial arch. The most susceptible area is approximately 1 cm from the insertion site of the supraspinatus tendon. This location is commonly referred to as the critical zone.

TABLE 9.2 Muscles of the Scapula

Muscle

Proximal/Medial Attachment

Distal/Lateral Attachment

Primary Action

Deltoid

Clavicle, acromion process, and spine of scapula

Deltoid tuberosity of humerus

Flexes and medially rotates abductor, extensor, and lateral rotator of humerus

Teres major

Inferior angle of scapula

Intertubercular groove of humerus

Adducts and medially rotates humerus

Teres minor

Axillary border of scapula

Greater tubercle of humerus

Laterally rotates humerus and stabilizes glenohumeral joint

Supraspinatus

Supraspinous fossa of scapula

Greater tubercle of humerus

Abducts humerus and stabilizes glenohumeral joint

Infraspinatus

Infraspinous fossa of scapula

Greater tubercle of humerus

Laterally rotates humerus and stabilizes glenohumeral joint

Subscapularis

Subscapular fossa of scapula

Lesser tubercle of humerus

Medially rotates humerus and stabilizes glenohumeral joint

Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Walls

Pectoralis major Pectoralis minor Serratus anterior Subclavius

Muscles connecting the upper extremity to the anterior and lateral thoracic walls are shown in Figs. 9.39-9.42, 9.56, 9.58, 9.59, and 9.68 and described in Table 9.3.

The pectoralis muscles (major and minor), located on the anterior surface of the chest, primarily aid in the movement of the upper limb (Fig. 9.58). The large fan-shaped pectoralis major muscle, which has two heads, covers the superior part of the thorax. It spans from the sternum (sternal head), clavicle (clavicular head), cartilaginous attachments of the upper six ribs, and the aponeurosis of the external oblique muscle to the lateral aspect or lip of the intertubercular groove of the humerus. Its primary functions are to adduct, medially rotate, flex, and extend the humerus and to assist in forced inspiration. The smaller triangular-shaped pectoralis minor muscle lies beneath the pectoralis major muscle and acts to depress the scapula and assist the serratus anterior muscle in pulling the scapula forward. It extends from the coracoid process to the anterior surface of the third to fifth ribs (Fig. 9.58).

The serratus (sawlike) anterior muscle is visualized on the lateral border of the thorax. It extends from the first through eighth or ninth ribs to the medial border of the scapula. The primary action of the serratus anterior muscle is to protract and stabilize the scapula (Fig. 9.59).

TABLE 9.3 Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Wall

Muscle

Proximal/Medial Attachment

Distal/Lateral Attachment

Primary Action

Pectoralis major

Medial half of clavicle (clavicular head), manubrium and body of sternum (sternal head), aponeurosis of external oblique muscle and six upper costal cartilages

Lateral lip intertubercular groove of humerus

Adducts, medially rotates, and flexes humerus

Pectoralis minor

Anterior surface of third to fifth ribs

Coracoid process of scapula

Depresses and downwardly rotates scapula; assists in scapular protraction and stabilizes scapula

Serratus anterior

Angles of first to eighth or ninth ribs

Medial border of scapula

Rotates, stabilizes, and protracts scapula

Subclavius

First rib and cartilage

Inferior surface of clavicle

Stabilizes the clavicle and depresses the shoulder

The subclavius, a small triangular-shaped muscle that spans between the first rib and clavicle, acts to stabilize the clavicle and depress the shoulder (Fig. 9.58).

Muscles of the Upper Arm. The muscles of the upper arm can be divided into ventral and dorsal groups according to their position. The ventral group contains the biceps brachii muscle, brachialis muscle, and coraco- brachialis muscle, and the dorsal group consists of the triceps brachii muscle and anconeus muscle. These muscles are shown in Figs. 9.20-9.34, 9.43-9.52, 9.56, and 9.60-9.84 and described in Table 9.4.

Ventral Group

Biceps brachii

Brachialis

Coracobrachialis

The muscles of the ventral group are shown in Figs. 9.60-9.72.

The biceps brachii muscle is located on the anterior surface of the humerus and acts as a strong flexor of the forearm. The biceps brachii muscle is named “biceps” because of its two expanded heads of proximal attachment (long and short). The tendon of the long head arises from the supraglenoid tubercle and courses through the intertubercular (bicipital) groove to merge with the tendon from the short head. The short head of the biceps brachii muscle originates from the coracoid process and joins with the long head to create the biceps brachii muscle, which terminates in two tendons. The stronger tendon inserts on the radial tuberosity, and the other tendon creates the bicipital aponeurosis, which radiates into the fascia of the forearm (Fig. 9.60).

The brachialis muscle originates from the anterior surface of the distal humerus and covers the anterior surface of the elbow joint before inserting on the ulnar tuberosity and the coronoid process. The brachialis muscle is considered to be the most important flexor muscle of the elbow joint (Fig. 9.61).

The coracobrachialis muscle is a long, narrow muscle located in the superomedial aspect of the arm. It arises from the coracoid process along with the short head of the biceps brachii and extends to insert on the medial surface of the humerus. The primary action of the cora-cobrachialis muscle is to assist with flexion and adduction of the arm, but it also helps hold the head of the humerus within the joint capsule (Figs. 9.61).

TABLE 9.4 Muscles of the Upper Arm

Muscle

Proximal Attachment

Distal Attachment

Primary Action

Biceps brachii

Long head—supraglenoid tubercle of scapula Short head—coracoid process of scapula

Bicipital aponeurosis and radial tuberosity

Supinates and flexes forearm

Brachialis

Distal humerus

Ulnar tuberosity and coronoid process

Flexion of elbow joint

Coracobrachialis

Coracoid process of scapula

Middle third medial surface of humerus

Assists in flexing and adducting the arm

Triceps brachii

Long head—infraglenoid tubercle of scapula Medial head—posterior surface of humerus below radial groove

Lateral head—posterior surface of humerus below greater tubercle

Proximal end of olecranon process of ulna

Chief extensor of forearm, long head steadies head of humerus if abducted

Anconeus

Lateral epicondyle of humerus

Olecranon process of ulna

Assists triceps brachii in extension of elbow

Dorsal Group

Triceps brachii Anconeus

The muscles of the dorsal group are shown in Figs. 9.62-9.84.

The triceps brachii muscle is located on the posterior surface of the humerus and is the main extensor of the forearm. It is named triceps because of its three heads of proximal attachment (long, medial, and lateral). The long head of the triceps originates from the infraglenoid tubercle of the scapula, the medial head originates from the entire dorsal surface of the humerus distal to the radial groove, and the lateral head arises from the dorsal surface and lateral intermuscular septum of the humerus. All three heads join in a common tendon that inserts on the olecranon process of the ulna and the posterior joint capsule (Fig. 9.73).

The small, triangular anconeus muscle originates on the lateral epicondyle of the humerus and crosses obliquely to insert on the dorsal surface of the olecranon process, close to the tendon of the triceps brachii (Fig. 9.74). It assists the triceps brachii in extension and also provides dynamic joint stability to the lateral joint capsule.

ELBOW

The elbow is a complex hinge-pivot joint created by the articulations of the humerus, radius, and ulna. All three articulations communicate with each other within a single joint capsule. The radius and ulna are the bones of the forearm, with the radius located on the lateral side. The radioulnar and radiohumeral articulations create the pivot joint that aids in supination and pronation of the elbow. The radiohumeral and ulnohumeral articulations form the hinge joint that allows for flexion and extension (Figs. 9.75-9.78).

FIG. 9.75 Humerus. Left, Anterior view. Right, Posterior view.

FIG. 9.77 Radius and ulna. Left, Anterior view. Right, Posterior view.

Bony Anatomy

Distal Humerus. The distal portion of the humerus has two distinct prominences termed the medial and lateral condyles, with associated epicondyles, which provide attachment sites for tendons and ligaments (Fig. 9.75). The medial epicondyle serves as the site of origin for the common flexor tendon, pronator teres muscle, and medial collateral ligament, whereas the lateral epicondyle serves as the attachment site for the common extensor tendon, supinator muscle, and lateral collateral ligament. Just lateral to the medial epicondyle, along its posterior surface, is a shallow groove containing the ulnar nerve. Two depressions located on the distal humerus are the anterior coronoid fossa and the deep posterior olecranon fossa. These depressions accommodate the coronoid and olecranon processes of the proximal ulna (Figs. 9.75, 9.76, and 9.78). The distal humerus has two cartilage-covered articular surfaces—the capitellum and the trochlea—for articulation with the radius and ulna (Fig. 9.76). The lateral of the two surfaces is the capitellum, a rounded projection that articulates with the concave surface of the radial head. The trochlea is more medial and has the appearance of an hourglass if viewed in the horizontal plane. The shape of the trochlea helps keep the ulna in position during flexion between the humerus and radius (Figs. 9.75, 9.76, and 9.78A-9.81).

Radius: Proximal. The radius is a long, slender bone with a proximal portion that consists of the radial head, neck, and tuberosity. The radial head has a flat cartilage- covered depression or fossa (fovea of the radius) that articulates with the capitellum of the humerus. In addition, the articular circumference of the radial head articulates against the radial notch of the ulna during supination and pronation. The radial head is attached to the body of the radius by the narrow radial neck. Located at the distal portion of the neck on the medial side of the radius is a roughened projection termed the radial tuberosity. The radial tuberosity serves as the attachment point for the biceps brachii muscle (Figs. 9.77, 9.78A and B, and 9.79).

Because of its superficial location, the ulnar nerve is the most frequently injured nerve of the body.

Radius: Distal. The broadened distal end of the radius includes the cartilage-covered carpal articular surface, the ulnar notch, and the radial styloid process. The carpal articular surface articulates with the scaphoid and lunate bones of the wrist. The ulnar notch articulates with the ulna, and the styloid process serves as an attachment site for the extensor pollicis longus and extensor carpi radialis tendons. The dorsal surface of the radius contains several grooves that serve as passages for the extensor tendons. Along with the grooves, a prominent ridge is located on the dorsal surface termed the radial dorsal tubercle, or Lister’s tubercle, a common site for the formation of bony spurs (Figs. 9.77 and 9.78C).

Ulna: Proximal. The ulna is located medial within the forearm. The proximal ulna consists of the olecranon and coronoid processes and the trochlear and radial notches. The superficial dorsal surface is formed by the hook-shaped olecranon process, which is the attachment site for the triceps brachii muscle. The trochlear notch is a half-moon-shaped concave articular surface that curves around the trochlea of the humerus. This articulation allows for flexion and extension of the elbow. Located on the anterior portion of the distal end of the trochlear notch is a small beaklike process called the coronoid process. Just distal and lateral to the coronoid process is a flattened depression called the radial notch, which is covered by articular cartilage for articulation with the radial head. Immediately distal to the coronoid process is a roughened bony surface termed the ulnar tuberosity. The tendon of the brachialis muscle inserts on both the coronoid process and the ulnar tuberosity (Figs. 9.77, 9.78A and B, 9.80, and 9.81).

Ulna: Distal. The smaller, distal end of the ulna has two prominent projections. The larger, rounded projection is an articular eminence termed the head of the ulna. It articulates with the ulnar notch of the radius and the triangular fibrocartilage complex. The small conical projection on the medial surface is called the ulnar styloid process, which serves as the attachment site for the ulnar collateral ligament of the wrist. Another structure that is important in stabilizing and strengthening the connection between the radius and ulna is the interosseous membrane, a strong fibrous sheath stretching between the interosseous borders of both bones (Figs. 9.77 and 9.78C).

Joint Capsule and Fat Pads. The entire elbow joint is surrounded by a relatively loose joint capsule that allows for the movements of flexion and extension. The joint capsule is weaker anteriorly and posteriorly but is reinforced medially and laterally by the strong radial and ulnar collateral ligaments (discussed in the next section). Located within the olecranon and coronoid fossae are fat pads that fill the space between the synovial membrane and joint capsule (Figs. 9.79, 9.80, and 9.829.85). The fat pads help cushion the area where the olecranon and coronoid processes move during flexion and extension of the elbow. There are two clinically important bursae located in the elbow: the olecranon bursa and the bicipitoradial bursa. The olecranon bursa is located within the subcutaneous tissue overlying the olecranon process (Fig. 9.82). The bicipitoradial bursa lies between the insertion of the biceps tendon and the radial tuberosity.

FIG. 9.82 Sagittal view of elbow at midjoint.

Ligaments

The stability of the elbow joint primarily depends on the collateral ligaments, which are woven into the lateral portions of the joint capsule. The ulnar (medial) collateral ligament consists of three components: an anterior band, a posterior band, and a transverse band (ligament of Cooper) (Figs. 9.83-9.88).

The anterior band, which is the strongest, extends from the medial epicondyle of the humerus to the medial aspect of the coronoid process. The posterior band originates along with the anterior band from the medial epicondyle of the humerus and inserts on the medial aspect of the olecranon process, forming a triangular plate. The weaker transverse band stretches between the medial surfaces of the coronoid and olecranon processes to unite the anterior and posterior bands. The ulnar collateral ligament forms the floor of the cubital tunnel for passage of the ulnar nerve (Figs. 9.86-9.89).

Reinforcing the lateral side is the triangular radial (lateral) collateral ligament. The radial collateral ligament originates from the lateral epicondyle of the humerus, adjacent to and beneath the common extensor tendons, and spreads distally to insert on the annular ligament and the anterior and posterior margins of the radial notch of the ulna (Figs. 9.88 and 9.90). The annular ligament forms a fibrous ring that encircles the radial head and attaches to the anterior and posterior margins of the radial notch. It also has a narrow portion that tightens around the radial neck to prevent inferior displacement of the radius (Figs. 9.84, 9.86, and 9.90-9.92). The annular ligament is considered a key structure in the proximal radioulnar joint, allowing the head of the radius to rotate freely.

Muscles of the Forearm

One method to classify the muscles of the forearm is to use the radius, ulna, and interosseous membrane to divide them into a ventral group (the flexors) and a dorsal group (the extensors). The two groups can be further divided into superficial and deep muscles. The muscles of the forearm are described in Table 9.5.

Ventral Group—Superficial Muscles

Pronator teres Flexor carpi radialis Palmaris longus Flexor carpi ulnaris Flexor digitorum superficialis

TABLE 9.5 Muscles of the Forearm

Muscle

Origin

Insertion

Primary Actions

Ventral-Superficial Group

Pronator teres

Humeral head—common flexor tendon Ulnar head—near coronoid process of ulna

Lateral surface of radius, midshaft

Pronates and flexes forearm

Flexor carpi radialis

Common flexor tendon

Base of second metacarpal

Flexes and abducts hand

Palmaris longus

Common flexor tendon

Palmar aponeurosis

Flexes wrist

Flexor carpi ulnaris

Humeral head—common flexor tendon Ulnar head—olecranon process

Pisiform, hook of hamate, fifth metacarpal

Flexes wrist and adducts hand

Flexor digitorum superficialis

Humeral head—common flexor tendon Ulnar head—coronoid process Radial head—anterior surface of proximal half of radius

Lateral sides of middle phalanges of second to fifth fingers

Flexes middle and proximal phalanges of second to fifth fingers

Ventral-Deep Group

Flexor digitorum profundus

Anterior surface of proximal ulna

Bases of distal phalanges of second through fifth digits

Flexes distal phalanges of fourth or fifth finger at distal interphalangeal joint

Flexor pollicis longus

Anterior surface of radius and interosseous membrane

Base of distal phalanx of thumb

Flexes phalanges of thumb

Pronator quadratus

Anterior and radial aspects of distal ulna

Anterior surface of distal radius

Pronates forearm

Dorsal-Superficial Group

Brachioradialis

Proximal two-thirds of supracondylar ridge of humerus

Distal radius, base of styloid process on lateral surface

Weak forearm flexion, assists with pronation and supination

Extensor carpi radialis longus

Lateral supracondylar ridge of humerus

Dorsal aspect base of second metacarpal

Extends and abducts hand at wrist joint

Extensor carpi radialis brevis

Common extensor tendon

Dorsal aspect base of third metacarpal

Extends and abducts hand at wrist joint

Extensor digitorum

Common extensor tendon

Extensor expansions of second to fifth digits

Extends second to fifth digits at metacarpophalangeal joints

Extensor digiti minimi

Common extensor tendon

Proximal phalanx of fifth digit

Extends fifth finger at metacarpophalangeal joint

Extensor carpi ulnaris

Dorsal-Deep Group

Common extensor tendon

Dorsal aspect of base of fifth metacarpal

Extends and adducts hand at wrist joint

Abductor pollicis longus

Posterior surface of proximal ulna, radius, and interosseous membrane

Base of first metacarpal

Abducts thumb and extends thumb at carpometacarpal joint

Extensor pollicis brevis

Posterior surface of distal third of radius and ulna and interosseous membrane

Dorsal aspect of base of proximal phalanx of first digit

Extends proximal phalanx of thumb at metacarpophalangeal joint

Extensor pollicis longus

Posterior surface of middle third of ulna and interosseous membrane

Dorsal aspect of base of distal phalanx of first digit

Extends distal phalanx of thumb at interphalangeal joint

Extensor indicis

Posterior surface of distal third of ulna and interosseous membrane

Extensor expansion of second digit

Supinates forearm

Supinator

Oblique head: lateral epicondyle of humerus, radial collateral ligament Transverse head: supinator crest of ulna

Lateral, posterior, and anterior surfaces of proximal radius

Supinates forearm

All five of the superficial muscles in the ventral group have an origin from the common flexor tendon off the medial epicondyle of the humerus. These muscles are shown in Figs. 9.93-9.107.

The pronator teres muscle has two heads of origin. Its humeral head originates from the common flexor tendon, whereas the ulnar head originates near the coronoid process of the ulna. The pronator teres muscle courses obliquely before inserting on the lateral surface of the radius at midshaft. It works in conjunction with the pronator quadratus muscle to pronate the forearm (Fig. 9.93).

The flexor carpi radialis muscle originates from the common flexor tendon and is located medial to the pronator teres. Its tendon passes through the carpal tunnel of the flexor retinaculum before inserting on the palmar surface of the base of the second metacarpal. Its actions include flexion and radial deviation of the hand at the wrist joint (Fig. 9.93).

The palmaris longus muscle originates from the common flexor tendon and passes superficial to the flexor retinaculum to merge with the palmar aponeurosis. It acts to flex the hand and tighten the palmar aponeurosis (Fig. 9.93).

The flexor carpi ulnaris muscle is the most medial of the superficial muscles located in the anterior portion of the forearm. It has two heads: The humeral head originates from the common flexor tendon, and the ulnar head originates from the olecranon process. It inserts onto the pisiform, hook of the hamate, and fifth metacarpal and acts to flex and adduct (ulnar deviation) the hand at the wrist joint (Fig. 9.93).

The flexor digitorum superficialis muscle is the largest muscle of the superficial muscles in the forearm. It arises from three heads: the humeral head from the common flexor tendon, the ulnar head from the coronoid process, and the radial head from the anterior surface of the proximal half of the radius. Just before reaching the flexor retinaculum, the muscle divides into four tendons that share a common synovial sheath through the carpal tunnel. After passing under the flexor retinaculum, the tendons insert on the lateral sides of the middle phalanges of the second to fifth digits. The flexor digitorum superficialis muscle is a strong flexor of the middle and proximal phalanges of the second through fifth digits (Fig. 9.107).

Ventral Group—Deep Muscles

Flexor digitorum profundus Flexor pollicis longus Pronator quadratus

The deep muscles of the ventral group are shown in Figs. 9.94-9.107.

The flexor digitorum profundus muscle is a long, thick muscle responsible for flexing the distal interphalangeal joints of the fingers. It originates from the anterior surface of the proximal ulna and extends medially to the interosseous membrane. Similar to the flexor digitorum superficialis muscle, the flexor digitorum profundus divides into four tendons before reaching the flexor retinaculum. The four tendons pass deep in the carpal tunnel and continue distally to insert on the distal phalanges, where they pair up with the flexor digitorum superficialis tendons to provide flexion of the middle and proximal phalanges of the second through fifth digits (Fig. 9.107B).

The flexor pollicis longus muscle arises from the anterior surface of the radius and adjacent interosseous membrane and runs lateral to the flexor digitorum profundus to cover the anterior aspect of the radius. After passing through the carpal tunnel, the flexor pollicis longus tendon runs between the flexor pollicis brevis and adductor pollicis brevis muscles to insert at the base of the first distal phalanx to provide flexion to the thumb (Fig. 9.107).

The pronator quadratus, a quadrangular muscle, is the deepest muscle in the anterior aspect of the forearm. It arises from the anterior and radial aspect of the distal ulna and passes transversely to insert on the anterior surface of the distal radius. The deep fibers of this muscle help bind the radius and ulna together along with the interosseous membrane. The pronator quadratus is the prime mover in pronation of the forearm (Fig. 9.107).

Dorsal Group—Superficial Muscles

Brachioradialis Extensor carpi radialis longus Extensor carpi radialis brevis Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris

The muscles of the superficial dorsal group are shown in Figs. 9.94-9.106 and 9.108.

The brachioradialis is an extensor muscle lying along the lateral border of the forearm. This large muscle arises from the upper two-thirds of the supracondylar ridge of the humerus and attaches distally to the radial styloid process. The brachioradialis muscle flexes the forearm at the elbow and assists with pronation and supination (Figs. 9.93 and 9.108).

The extensor carpi radialis longus muscle arises just distal to the brachioradialis muscle on the lower third of the supracondylar ridge of the humerus. It runs posterior and deep to the brachioradialis to insert on the base of the second metacarpal. It acts as an extensor and abductor of the hand at the wrist joint (Fig. 9.108A and B).

The other superficial muscles (extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris) arise from a common extensor tendon attached to the lateral epicondyle of the humerus. At the level of the elbow they appear as one structure but become more distinct distally as they insert on various structures about the wrist and hand.

The extensor carpi radialis brevis muscle has components that arise from the radial collateral and annular ligaments, as well as the common extensor tendon. It runs along the dorsal surface of the wrist to insert at the base of the third metacarpal and acts to extend and abduct the hand at the wrist joint (Fig. 9.108).

The extensor digitorum muscle is the main extensor of the second to fifth digits and occupies much of the posterior surface of the forearm. It arises from the common extensor tendon and divides into four individual tendinous slips just proximal to the wrist. The four tendons run in a single synovial sheath as they pass under the extensor retinaculum. The tendons insert into the extensor expansions of the second through fifth digits, helping to form the extensor hoods (see ligaments of the finger). In addition, small slips of the tendon spread out and run to the bases of the proximal phalanges and to the capsules of the metacarpophalangeal joints. The extensor digitorum muscle extends and spreads the fingers and extends the hand at the wrist joint (Fig. 9.108).

The extensor digiti minimi muscle arises from the common extensor tendon and passes under the extensor retinaculum in its own synovial compartment. It then divides into two tendinous slips that insert on the proximal phalanx of the fifth digit to help with extension of the little finger (Fig. 9.108).

The extensor carpi ulnaris muscle is a long, slender muscle that arises from the common extensor tendon and runs along the medial and dorsal side of the ulna to insert on the base of the fifth metacarpal. Its main actions include extension of the hand at the wrist joint and adduction of the hand, resulting in ulnar deviation (Fig. 9.108).

Dorsal Group—Deep Muscles

Abductor pollicis longus Extensor pollicis brevis Extensor pollicis longus Extensor indicis Supinator

The deep muscles of the dorsal group consist of four extensors that act on either the first or second digit and include the supinator muscle. These muscles are shown in Figs. 9.94-9.104 and 9.108.

The three deep extensors that act on the first digit are the abductor pollicis longus, extensor pollicis brevis, and the extensor pollicis longus muscles. The long, slender abductor pollicis longus muscle arises from the dorsal surfaces of the ulna and radius and from the interosseous membrane. It inserts at the base of the first metacarpal to abduct and extend the thumb (Fig. 9.108).

The short extensor pollicis brevis muscle arises from the dorsal surfaces of the ulna and radius and from the interosseous membrane just distal to the abductor pollicis longus muscle. It inserts at the base of the proximal phalanx of the first digit and works together with the abductor pollicis longus muscle to extend and abduct the thumb (Fig. 9.108).

The extensor pollicis longus muscle arises from the dorsal surface of the ulna and interosseous membrane just distal to the abductor pollicis longus muscle. After passing through the extensor retinaculum, it crosses over the extensor carpi radialis longus and brevis muscles to insert at the base of the distal phalanx of the first digit. Its main action is to extend the distal phalanx of the first digit, but it can also abduct the hand (Fig. 9.108).

The extensor indicis muscle arises from the distal third of the dorsal ulna and the interosseous membrane and runs with the extensor digitorum muscle through the extensor retinaculum to insert on the dorsal aponeurosis of the second digit. It functions with the extensor digitorum muscle to extend the index finger, as if pointing (Fig. 9.108).

The supinator muscle originates from two heads: oblique and transverse. The oblique head originates from the lateral epicondyle and collateral ligament, whereas the transverse head originates from the supinator crest of the ulna. Both heads wrap laterally around the proximal radius to insert on the posterolateral and anterior surfaces of the proximal radius to supinate the forearm (Figs. 9.107 and 9.108).

WRIST AND HAND

The complex anatomy of the wrist and hand provides for a multitude of movements unmatched by any other joint of the body.

Bony Anatomy

The bony anatomy of the wrist and hand consists of the distal radius and ulna, 8 carpal bones, 5 metacarpals, and 14 phalanges (Fig. 9.109). Both the distal radius and ulna have a conical styloid process that acts as an attachment site for ligaments. The radial styloid process is located on the lateral surface of the radius, whereas the ulnar styloid process is located on the posteromedial side of the ulna. The carpal bones are arranged in proximal and distal rows. Located in the proximal row of carpal bones are the scaphoid (navicular), lunate (semilunar), triquetral (triquetrum), and pisiform bones. The pisiform is considered a sesamoid bone that is embedded in the tendon of the flexor carpi ulnaris. The distal row consists of the trapezium (greater multangular), trapezoid (lesser multangular), capitate (os magnum), and hamate (unciform) bones (Figs. 9.109-9.123). The five metacarpals are small tubular bones with a proximal end (base), distal end (head), and middle (body) portion. The 14 phalanges that make up the fingers, like the metacarpals, consist of a proximal (base), distal (head), and middle (body) portion. Each digit consists of three phalanges (proximal, middle, and distal), except for the thumb (first digit), which has only two phalanges (proximal and distal).

A fracture of the hamate may result in a nonunion injury because of the traction of associated muscles. The ulnar nerve runs close to the hook of the hamate and may be injured as well, resulting in decreased grip strength of the hand.

Joints

The joints of the wrist and hand are quite complex and consist of the following: distal radioulnar articulation, radiocarpal articulation (proximal joint of hand), midcarpal articulation (distal joint of hand), intercarpal articulations (articulations between proximal and distal carpals), carpometacarpal articulations (between carpals and meta- carpals), intermetacarpal articulations (between bases of metacarpals two through five) and interphalangeal joints (between phalanges of each digit) (Figs. 9.119-9.126).

Joints of the Wrist

Distal radioulnar joint (DRUJ)

Radiocarpal joint Midcarpal joint Intercarpal joints Carpometacarpal joints Intermetacarpal joints

The distal radioulnar joint is created when the ulnar notch of the radius moves around the articular circumference of the ulna, providing the movements of supination and pronation. The main stabilizing element of the DRUJ is an articular disk called the triangular fibro- cartilage complex (TFCC). The TFCC is a fan-shaped band of fibrous tissue that originates on the medial surface of the distal radius and traverses horizontally to insert on the ulnar styloid process. It rotates against the distal surface of the ulnar head during pronation and supination and separates the ulna from the carpal bones (Figs. 9.124-9.126).

The proximal surface of the radiocarpal articulation is formed by the articular carpal surface of the radius and the TFCC, whereas the distal surface is formed by the articular surfaces of the scaphoid, lunate, and triquetrum and the interosseous ligaments connecting them (Figs. 9.120-9.124).

The midcarpal joint is formed by the articulations between the proximal and distal carpal rows (Figs. 9.119 and 9.124).

The articulation between the carpals within each row creates the intercarpal joints (Figs. 9.119, 9.120, and 9.124).

The carpometacarpal joints are formed by the articulations between the carpus and the five metacarpals (Fig. 9.120 and 9.124). The carpometacarpal joint of the thumb is an independent joint formed by the articular surfaces of the trapezium and first metacarpal, creating a pure saddle joint. The carpometacarpal articulations of the second to fifth digits are amphiarthrotic joints with little mobility (Figs. 9.114 and 9.124).

The intermetacarpal joint exists between the bases of the metacarpals and is reinforced by the palmar and dorsal metacarpal ligaments (Fig. 9.124).

Joints of the Hand

Metacarpophalangeal (MCP)

Proximal interphalangeal (PIP)

Distal interphalangeal (DIP)

The articulation of the phalanges of the second through fifth digits creates three interphalangeal joints: the metacarpophalangeal (MCP) joints classified as condyloid joints, proximal interphalangeal (PIP), and distal interphalangeal (DIP). The proximal and distal interphalangeal joints are classified as hinge joints (Fig. 9.109). The first digit, which consists of two phalanges, has just two joints: the MCP joint, classified as a saddle joint, and an interphalangeal joint, classified as a hinge joint (Figs. 9.109 and 9.112).

Ligaments and Fascia

Numerous extrinsic and intrinsic ligaments provide additional stability to the wrist. The extrinsic ligaments reinforce the joint cavity surrounding the carpal region and include palmar and dorsal radial carpal ligaments, the radial and ulnar collateral ligaments, and the TFCC (Figs. 9.124-9.127). The many articulations between the carpal bones are supported by the intercarpal ligaments or intrinsic ligaments, which connect the carpal bones to each other (Figs. 9.124-9.126). The configuration of the intrinsic ligaments, metacarpal ligaments, and the TFCC creates five different joint compartments that can be demonstrated by arthrography: (1) compartment of the first carpometacarpal articulation, (2) common carpometacarpal compartment, (3) midcarpal (mediocarpal) compartment, (4) intermetacarpal compartment, and (5) radiocarpal compartment (Fig. 9.124). The carpal tunnel is created by the concave arrangement of the carpal bones (Figs. 9.111, 9.113, and 9.128).

FIG. 9.127 Extrinsic ligaments of wrist.

Top, Palmar view. Bottom, Dorsal view.

A thick ligamentous band called the flexor retinaculum (transverse carpal ligament) stretches across the carpal tunnel to create an enclosure for the passage of tendons and the median nerve. The flexor retinaculum inserts medially on the pisiform and hook of the hamate and spans the wrist to insert laterally on the scaphoid and trapezium (Figs. 9.128-9.137). In addition to the carpal tunnel, another tunnel called Guyon canal is formed where the ulnar extension of the flexor retinaculum continues over the pisiform and hamate. This creates a potential site for compression of the ulnar nerve (Figs. 9.128, top, and 9.132).

The extensor retinaculum (dorsal carpal ligament), located dorsally, is much thinner. It attaches medially to the ulnar styloid process, triquetrum, and pisiform, and laterally to the lateral margin of the radius (Fig. 9.129, right). Along its course, it forms six fibro-osseous tunnels for the passage of the synovial sheaths containing the extensor tendons (Figs. 9.128, bottom; 9.129, right; and 9.130-9.137).

Compression of the median nerve as it passes through the carpal tunnel is called carpal tunnel syndrome. Symptoms include pain and numbness of the fingers supplied by the median nerve.

Ligaments of the Fingers. The MCP and interphalangeal joints each have a palmar plate (ligament) and two collateral ligaments. The palmar plate (ligament) is a thick, dense fibrocartilaginous tissue that covers the palmar surface of the joints. The palmar plate runs between and is connected to the collateral ligaments, creating the floor of the interphalangeal and MCP joints (Fig. 9.138). The deep transverse metacarpal ligament (DTML) consists of a series of short ligaments that connect the palmar plate of the metacarpal heads (Fig. 9.129).

The DTML prevents separation of the metacarpals. Along the palmar surface of the fingers, the ligamentous structures of the radial and ulnar collateral ligaments, radial and ulnar accessory collateral ligaments, and palmar plates provide stability for the MCP and interphalangeal joints (Fig. 9.138). There is a fibro-osseous tunnel along the palmar aspect of each finger for the passage of the flexor tendons. The tunnel is created by well-defined areas of thickening of the tendon sheath and is called the annular pulley system. It is composed of five annular pulleys and three cruciate pulleys, which are important structures that prevent the displacement of the tendons during flexion of the fingers (Fig. 9.139). The dorsal surface of the hand and fingers contains the extensor mechanism or extensor hood. The extensor hood consists of the digital extensor tendon, extensor hood proper, and insertions of the lumbricals and interossei muscles and serves to maintain the integrity of the extensor tendons along the path of the MCP and interphalangeal joints (Figs. 9.140-9.144).

The flexor tendon pulley system of the fingers is responsible for one of the most common injuries in experienced climbers. It involves partial or complete rupture of one or more flexor tendon annular pulleys. The A2 pulley ruptures more frequently than the A4 pulley due to the common crimp grip, which places much higher force on the pulley system. Common symptoms of a pulley rupture are a loud, audible pop accompanied by pain, bowstringing of the tendon, localized swelling or tenderness, and limited mobility of the joint.

Muscles and Tendons

The numerous muscles of the forearm become tendinous just before the wrist joint. The many tendons located in the wrist can be divided into flexor (palmar) and extensor (dorsal) tendon groups (Figs. 9.129, 9.133, 9.145, and 9.146).

The flexor tendon group collectively flexes the fingers and wrist. As this group courses through the carpal tunnel, the tendons appear to be arranged in two discrete rows (Figs. 9.128, top, and 9.131). The tendons of the extensor group span the superficial surface of the wrist to extend the fingers and wrist (Figs. 9.128-9.135 and 9.137).

FIG. 9.144 Coronal, T1-weighted MRI of finger.

FIG. 9.145 Sagittal, T1-weighted MRI of wrist with flexor and extensor tendons.

Muscles of the Hand. The muscles of the hand can be divided into three groups: (1) metacarpal group (muscles of the metacarpals are considered to be the central muscles of the hand), (2) thenar group (muscles involving the thumb and creating the thenar eminence on the radial side), and (3) hypothenar group (muscles involving the fifth digit and creating the hypothenar eminence on the ulnar side). These muscles are shown in Figs. 9.147-9.154.

Metacarpal Group

Interossei

Lumbricals

The metacarpal muscle group includes the interossei and lumbrical muscles.

There are seven short interossei muscles in the metacarpal muscle group: three single-headed muscles located on the palmar surface and four double-headed muscles located on the dorsal surface (Figs. 9.140 and 9.147A and B). The three palmar interossei muscles arise from the second, fourth, and fifth metacarpals and insert on the corresponding proximal phalanges, frequently radiating into the corresponding tendons of the dorsal aponeurosis. These muscles are responsible for flexion at the MCP joints and extension at the interphalangeal joints. The dorsal interossei arise from two heads on the sides of the five metacarpal bones to insert on the proximal phalanges and radiate onto the dorsal aponeurosis. Like their palmar counterparts, the dorsal interossei flex at the MCP joints and extend at the interphalangeal joints.

The four small lumbrical muscles arise from the tendons of the flexor digitorum profundus and pass to the radial side of the corresponding finger to insert on the extensor expansion covering the dorsal surface of the finger (Figs. 9.140; 9.147, right; and 9.148). The lumbricals flex the first phalanges at the MCP joints and extend the second and third phalanges at the interphalangeal joints.

Thenar Group

Abductor pollicis brevis Flexor pollicis brevis Adductor pollicis Opponens pollicis

The abductor pollicis brevis is a thin, flat superficial muscle arising from the transverse carpal ligament, navicular, and trapezium (Figs. 9.148 and 9.149). It runs inferiorly and laterally to insert on the base of the first phalanx of the thumb to abduct the thumb.

The flexor pollicis brevis has two heads: The superficial or lateral head arises from the flexor retinaculum, and the deep or medial head arises from the trapezium, trapezoid, and capitate. This muscle inserts on the radial and ulnar base of the first phalanx to flex, adduct, and abduct the thumb (Figs. 9.148 and 9.149). Frequently, a sesamoid bone can be found in the insertion tendon on the radial side.

The adductor pollicis also has two heads: The transverse head arises from the dorsal aspect of the third metacarpal, and the oblique head arises from numerous slips off the capitate, the bases of the second and third metacarpals, and the sheath of the flexor carpi radialis tendon. The adductor pollicis inserts onto the base of the first phalanx of the thumb to provide adduction and assist in the opposition and flexion of the thumb (Figs. 9.148 and 9.149).

The opponens pollicis provides the main opposition for the thumb but also assists with adduction. It arises from the trapezium and flexor retinaculum and inserts onto the radial aspect of the first metacarpal (Figs. 9.148 and 9.149).

Hypothenar Group

Abductor digiti minimi Flexor digit minimi brevis Opponens digiti minimi

The abductor digiti minimi muscle arises from the pisiform and the flexor retinaculum to end in a flat tendon that inserts onto the ulnar base of the first phalanx of the little finger (Figs. 9.148 and 9.149). The abductor digiti minimi muscle is the main abductor of the little finger.

The flexor digiti minimi brevis muscle arises from the flexor retinaculum and the hook of the hamate. It fuses with the tendon of the abductor digiti minimi to insert on the base of the first phalanx of the fifth digit (Figs. 9.148 and 9.149). The flexor digiti minimi brevis flexes at the MCP joint.

Like the flexor digiti minimi brevis muscle, the op- ponens digiti minimi arises from the hook of the hamate and the flexor retinaculum (Fig. 9.148). It inserts on the ulnar surface of the fifth metacarpal to bring the little finger into the position for opposition.

NEUROVASCULATURE

The neurovasculature of the upper extremity is composed primarily of the branches of the axillary and brachial arteries, their accompanying deep veins, a system of superficial veins, and the brachial plexus that innervates the upper extremity.

Arterial Supply

Shoulder. The primary arteries supplying the shoulder region include the axillary and brachial arteries (Fig. 9.155). The axillary artery begins at the lateral border of the first rib as a continuation of the subclavian artery. It ends at the inferior border of the teres major muscle, where it passes into the arm and becomes the brachial artery. The axillary artery and its branches supply blood to numerous thoracic and shoulder structures, including the first and second intercostal spaces; the axillary lymph nodes; the mammary gland in women; and the scapular, serratus anterior, pectoral, latissimus dorsi, deltoid, and triceps brachii muscles. The branches of the axillary artery typically include the superior thoracic, thoracoacromial, lateral thoracic, subscapular, and anterior and posterior humeral circumflex arteries. The brachial artery is the principal arterial supply to the arm. It courses inferiorly on the medial side of the humerus and then continues anterior to the cubital fossa of the elbow. The brachial artery is relatively superficial and palpable throughout its course. It accompanies the median nerve, which crosses anterior to the artery in the middle of the arm. During its course, the brachial artery gives rise to numerous muscular branches, which include the profunda brachii, superior ulnar collateral, and inferior ulnar collateral arteries (Figs. 9.155A-9.160).

Elbow. The brachial artery divides at the cubital fossa into the radial and ulnar arteries (Fig. 9.155A).

The radial artery begins at the level of the head of the radius within the anterior compartment of the forearm. It courses beneath the brachioradialis muscle and then continues its course just deep to the skin, along the lateral side of the anterior forearm to the wrist. It passes anterior to the radial styloid process to enter the hand. The most proximal branch of the radial artery is the radial recurrent artery, which supplies the brachioradialis, supinator, and brachialis muscles and the elbow joint. Within the forearm, the radial artery gives off several direct muscular branches. The ulnar artery also gives rise to several branches that supply the elbow and forearm. The first branch of the ulnar artery is the anterior ulnar recurrent artery, which supplies the brachialis and pronator teres muscles. It courses just anterior to the medial condyle of the humerus to anastomose with the inferior ulnar collateral branch of the brachial artery. The posterior ulnar recurrent artery courses behind the medial epi- condyle of the humerus to anastomose with the superior ulnar collateral branch of the brachial artery. It supplies the flexor carpi ulnaris, pronator teres, and anconeus muscles. The common interosseous artery branches from the ulnar artery and almost immediately bifurcates into the anterior and posterior interosseous arteries. These arteries and their branches supply the median nerve, deep flexor and extensor muscles of the forearm, superficial extensor muscles of the forearm, and radius and ulna (Figs. 9.155, 9.156B and C, 9.157, 9.159, and 9.160).

Wrist and Hand. The terminal branches of the radial and ulnar arteries form the palmar arches of the wrist and hand. These arches emit branches that serve the wrist, palm, and digits (Figs. 9.155, 9.156C, and 9.157). The palmar radiocarpal arch or network is formed by the palmar carpal branches from the radial and ulnar arteries; the anterior interosseous artery, also a branch of the ulnar artery; and a recurrent branch from the deep palmar arch. These vessels supply the carpal bones and joints (Fig. 9.155A and C). The dorsal radiocarpal arch or network is formed by dorsal carpal branches of the radial and ulnar arteries. The dorsal carpal arch also receives contributions from the anterior and posterior interosseous arteries. The arch lies close to the dorsal surface of the carpals and gives rise to three dorsal metacarpal arteries and branches that supply the distal regions of the ulna and radius, carpal bones, and intercarpal joints (Fig. 9.155). The superficial palmar branch of the radial artery anastomoses with the superficial palmar branch of the ulnar artery to form the superficial palmar arch. This arch gives rise to three common palmar digital arteries that anastomose with the palmar metacarpal arteries from the deep palmar arch (Fig. 9.155A and C). The deep palmar arch is formed by deep palmar branches of the radial and ulnar arteries and is located approximately 1 cm proximal to the superficial palmar arch. The deep palmar arch also gives rise to a recurrent branch that anastomoses with the palmar carpal branches of the radial and ulnar arteries (Fig. 9.155A).

Venous Drainage

The veins of the upper extremity are divided into deep and superficial groups (Fig. 9.161). Numerous anastomoses occur between the groups. The superficial venous system consists of extensive venous networks that are especially well developed within the upper extremity along with their accompanying arteries of the same name. The deep veins are often double and repeatedly anastomose with one another.

Shoulder. The veins of the upper arm include the brachial, cephalic, and basilic (Fig. 9.161). The two deep brachial veins ascend the arm, one on either side of the brachial artery. The brachial veins begin in the elbow from the union of the ulnar and radial veins and end in the axillary vein near the lower margin of the subscapularis muscle. The two deep brachial veins may join to form one brachial vein during part of their course. The superficial veins of the upper arm include the cephalic and basilic. The cephalic vein courses from the radial side of the dorsal venous arch of the hand and then ascends to the midpoint of the forearm, where it curves around to the ventral surface of the forearm and ascends the lateral aspect of the upper arm, along the anterolateral border of the biceps brachii muscle, to open into the axillary vein, just below the clavicle. It drains the superficial parts of the lateral hand and lateral forearm. The basilic vein originates from the medial end of the dorsal venous arch of the hand. It then ascends the ulnar side of the forearm, along the medial surface of the biceps brachii muscle in the upper arm, to form the axillary vein. The basilic vein drains the superficial parts of the medial side of the hand and medial side of the forearm. The large axillary vein lies on the medial side of the axillary artery. It extends from the lower border of the teres major muscle to the lateral surface of the first rib to continue as the subclavian vein. The axillary vein receives tributaries that correspond to the branches of the axillary artery (Figs. 9.158 and 9.161).

Elbow. The large deep vein of the elbow is the brachial vein, which is formed by the union of the radial and ulnar veins (Fig. 9.159).

The superficial veins of the elbow include the cephalic, median cubital, basilic, and intermediate (median) antebrachial veins. The cephalic vein courses along the radial side of the elbow and may give rise to the median cubital vein, which ascends in an oblique and medial course to create an anastomosis between the basilic and cephalic veins (Fig. 9.161). The median cubital vein is a common site for venipuncture. The basilic vein courses along the posteromedial aspect of the forearm, crosses the elbow, then takes a deep course in the axilla to join the brachial vein. The intermediate (median) antebrachial vein transports blood from the superficial palmar venous arch and anterior forearm. It ascends the ventral side of the forearm on the ulnar side and typically ends in the basilic vein (Figs. 9.94-9.102).

Wrist and Hand. The superficial venous system forms a network at the dorsum of the hand termed the dorsal venous network (arch). It is fed by the subcutaneous dorsal metacarpal veins of the fingers and continues to the distal forearm, where it drains into three major superficial veins: the cephalic, basilic, and intermediate (median) antebrachial veins of the forearm (Figs. 9.128 and 9.130-9.133). These large superficial veins anastomose frequently as they course superiorly. The deep and superficial palmar venous arches of the hand empty into the radial and ulnar veins that then unite to form the brachial vein of the arm (Fig. 9.161).

Innervation

The brachial plexus, also described in Chapter 4, is a large network of nerves that innervate the upper limb (Figs. 9.22, 9.23, 9.47, and 9.162). It extends from the neck into the axilla. The brachial plexus is formed by the union of the ventral rami of nerves C5-C8 and the greater part of the T1 ventral ramus. The ventral rami from C5 and C6 unite to form a superior trunk, the ventral ramus of C7 continues as the middle trunk, and the ventral rami of C8 and T1 unite to form an inferior trunk.

Each of these trunks divides into an anterior and posterior division. The anterior divisions supply the anterior (flexor) parts of the upper limb, and the posterior divisions supply the posterior (extensor) parts of the upper limb. These divisions form three cords (posterior, lateral, and medial), which continue to divide to form the median, ulnar, musculocutaneous, and radial nerves (sequential Figs. 9.62-9.67). These nerves supply the muscles of the forearm and hand. The median nerve descends the cubital fossa deep to the median cubital vein. It supplies the pronator teres muscle of the arm and all the superficial and deep flexor muscles of the forearm, except the flexor carpi ulnaris muscle. It gives off an anterior interosseous branch that descends within the forearm to supply the flexor digitorum profundus muscle. The median nerve courses through the carpal tunnel of the wrist, typically superficial to the flexor tendons (Fig. 9.163). It supplies the flexors of the hand, the skin of the wrist, the thenar eminence, the palm of the hand, and the sides of the first three digits and the lateral half of the fourth. At the elbow, the ulnar nerve passes between the medial epicondyle of the humerus and the olecranon process within the cubital tunnel to enter the medial side of the flexor compartment of the forearm (Figs. 9.87 and 9.162). Posterior to the medial epicondyle, the ulnar nerve is superficial and easily palpable. It supplies the flexor carpi ulnaris muscle and the medial side of the flexor digitorum profundus muscle in the forearm before entering the hand. The ulnar nerve passes under the flexor retinaculum, along with the ulnar artery, to enter the palmar compartment of the hand (Fig. 9.163). At this point, the ulnar nerve divides into superficial and deep terminal branches that supply the ulnar flexors of the hand, as well as the skin on the medial side of the palm, medial half of the dorsum of the hand, fifth digit, and medial half of the fourth digit. The musculocutaneous nerve descends to the lateral side of the arm and elbow to innervate the flexors in the arm and the skin of the forearm, wrist, and thenar region of the hand (Fig. 9.162). It emits branches that supply both heads of the biceps brachii muscle, the brachialis muscle, and the elbow joint. It innervates the skin of the dorsal surface of the arm. A continuation of the musculocutaneous nerve is the lateral cutaneous nerve, which terminates into cutaneous branches that supply the skin covering the radial side of the wrist and the thenar eminence. The radial nerve is the largest branch of the brachial plexus. It passes inferolaterally around the body of the humerus in the radial groove (Fig. 9.162). It continues inferiorly between the brachialis and brachioradialis muscles to the level of the lateral epicondyle of the humerus, where it divides into deep and superficial branches. The deep branches supply all the extensors in the arm and forearm, and the cutaneous branches innervate the skin on the dorsal side of the arm and hand. The superficial branch, the direct continuation of the radial nerve, is entirely sensory. It supplies the skin and fascia over the lateral two-thirds of the dorsum of the hand, the dorsum of the thumb, and the proximal parts of the lateral three and a half digits on their dorsal surfaces (Figs. 9.93-9.102).

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