Snell's Clinical Anatomy by Regions, 10e - Upper Limb Anatomy (PDF)

3 Upper Limb For additional ancillary materials related to this chapter, please visit thePoint. A 64-year-old woman fell down the stairs and was admitted to the emergency department with severe left shoulder pain. While she was sitting up, her left arm was by her side and her le...

3 Upper Limb For additional ancillary materials related to this chapter, please visit thePoint. A 64-year-old woman fell down the stairs and was admitted to the emergency department with severe left shoulder pain. While she was sitting up, her left arm was by her side and her left elbow was flexed and supported by her right hand. Inspection of the left shoulder showed loss of the normal rounded curvature and evidence of a slight swelling below the left clavicle. The clinician then systematically tested the cutaneous sensibility of the left upper limb and found severe sensory deficits involving the skin of the back of the arm down as far as the elbow, the lower lateral surface of the arm down to the elbow, the middle of the posterior surface of the forearm as far as the wrist, the lateral half of the dorsal surface of the hand, and the dorsal surface of the lateral three and a half fingers proximal to the nail beds. A diagnosis of subcoracoid dislocation of the left shoulder joint was made, complicated by damage to the axillary and radial nerves. The head of the humerus was displaced downward to below the coracoid process of the scapula by the initial trauma and was displaced further by the pull of the muscles (subscapularis, pectoralis major). The loss of shoulder curvature was caused by the displacement of the humerus (greater tuberosity) medially so that it no longer pushed the overlying muscle (deltoid) laterally. The extensive loss of skin sensation to the left upper limb was the result of damage to the axillary and radial nerves. For a clinician to be able to make a diagnosis in this case and to be able to interpret the clinical findings, he or she must have considerable knowledge of the anatomy of the shoulder joint. Furthermore, the clinician must know the relationship of the axillary and radial nerves to the joint and the distribution of these nerves to the parts of the upper limb. CHAPTER OUTLINE Overview Osteology Clavicle Scapula Humerus Radius Ulna Carpal Bones Metacarpal Bones Phalanges Upper Limb Regions Pectoral Region Scapular Region Axilla Arm Elbow and Cubital Fossa Forearm Wrist Hand Muscles Pectoral Region Back and Scapular Region Arm Forearm Hand Nerves Spinal Accessory Nerve (Cranial Nerve XI) Brachial Plexus Skin Branches from Brachial Plexus Roots Branches from Brachial Plexus Lateral Cord Branches from Brachial Plexus Medial Cord Branches from Brachial Plexus Posterior Cord Musculocutaneous Nerve  Median Nerve Ulnar Nerve Axillary Nerve Radial Nerve Vasculature Arteries Veins Lymph Axillary Lymph Nodes Superficial and Deep Lymph Vessels Joints Sternoclavicular Joint Acromioclavicular Joint Glenohumeral Joint (Shoulder Joint) Elbow Joint Proximal Radioulnar Joint Interosseous Membrane Distal Radioulnar Joint Wrist Joint (Radiocarpal Joint) Hand and Finger Joints Hand as Functional Unit Radiographic Anatomy Surface Anatomy Anterior Surface of Chest Posterior Surface of Shoulder Breast Elbow Region Wrist and Hand LEARNING OBJECTIVES The purpose of this chapter is to review the basic anatomy of the upper limb, including the breast, in order to understand normal functional relationships and the basis for common limb injuries, pain, motor deficits, congenital defects, medical imaging, and general surface examination. 1. Identify the bones of the upper limb and their major features. Describe  the functional aspects of these structures. Identify these structures in standard medical imaging. 2. Identify the specific anatomical regions of the upper limb. 3. Describe the general structure of the female breast and its relationship to the thoracic wall. Describe the lymphatic drainage of the breast and the anatomical bases for various degrees of mastectomy. 4. Define the boundaries of the axilla and identify its contents. 5. Define the boundaries of the cubital fossa and identify its contents. 6. Describe the major steps in the development of the upper limb. 7. Define the components of the shoulder complex. Identify the muscles of the shoulder, indicating their attachments, innervation, and major actions. 8. Identify the muscles composing the “rotator cuff.” Describe the functional significance of this group. 9. Identify the quadrangular and triangular spaces of the shoulder. Describe the functional significance of each. 10. Define the osseofascial compartments of the upper limb. Identify the muscles contained in each compartment. Describe the attachments, innervation, and major actions of each muscle. Describe the innervation of each compartment as a whole and the major actions governed by that innervation. Predict the functional consequences of loss of action of each muscle and each compartment. 11. Describe the mechanisms of pronation and supination. Note the muscles involved, their sites of attachment, and their innervation. 12. Define the carpal tunnel. Note the relationships of tendons, nerves, and blood vessels to the carpal tunnel. Describe the clinical significance of this arrangement in the context of carpal tunnel syndrome. 13. Define the movements of the thumb and fingers. Describe the interaction of extrinsic and intrinsic muscles, retinacula, and fibrous digital sheaths in producing precision hand movement. Describe the relationship between the extensors of the digits and the lumbrical and interosseous muscles. Define the role of this arrangement in the production of precision hand movement. 14. Describe the arrangement of synovial sheaths in the wrist and hand. Explain the clinical significance of such a patterning. 15. Define the “anatomical snuffbox” and identify its major contents. 16. Identify the brachial plexus and its component parts, from spinal  segmental sources to terminal branches. 17. Trace the course of motor and cutaneous innervation in the upper limb. Identify the spinal segmental level(s) of origin and relationship to the brachial plexus of each major peripheral nerve. Predict the functional consequences of lesions to specific spinal levels, parts of the brachial plexus, and individual peripheral nerves. 18. Trace the flow of blood from the subclavian artery to and through the upper limb by describing the courses and branching patterns of the major arteries and veins. Identify the territories supplied and drained by the major vessels. Note the main collateral routes around the shoulder and elbow. Describe the composition and anastomoses of the palmar arterial arches. 19. Describe the pattern of lymphatic drainage of the upper limb, including the relationship of this drainage to that of the axilla and breast. 20. Identify the bony components, major ligaments, key accessory structures (e.g., intra-articular discs), and movements permitted at the shoulder, elbow, and wrist joints. Describe the characteristic features of the major traumas to each joint. 21. Identify the major features of the upper limb in standard medical images. 22. Locate the surface projections and palpation points of the major structures of the upper limb in a basic surface examination. OVERVIEW The upper limb is a multijointed lever that is freely movable on the trunk at the shoulder joint. Its primary function is to maneuver the hand into positions where the hand can manipulate objects. The hand is a highly evolved organ with the unique ability to grasp items in both coarse and fine ways. Much of the importance of the hand centers on the pincer-like opposable action of the thumb, which enables the tip of the thumb to contact the tips of the other digits. The upper limb is organized into the shoulder region, the arm, the cubital fossa, the forearm, the wrist, and the hand. The arm, forearm, and hand are compartmentalized into working units. Each compartment has its own muscles that perform both group and individual functions and its own distinct nerve and blood supply. The physician commonly encounters pain, fractures, dislocations, and nerve injuries of the upper limb. Wrist and hand injuries deserve particular attention because of the importance of preserving as much function of the thumb as possible. OSTEOLOGY The upper limb is a component of the appendicular skeleton. The bones included here are the clavicle, scapula, humerus, ulna, radius, carpal bones, metacarpal bones, and phalanges. The clavicle and scapula form the shoulder girdle. The humerus defines the arm, whereas the radius and ulna delineate the forearm. The carpal bones form the wrist, and the metacarpals and phalanges constitute the hand. This section provides a comprehensive description of the bones of the upper limb and their significant features. Rather than relegating learning this material to a painful exercise in rote memorization of meaningless words, try to understand the terminology (e.g., what is the difference between a tubercle and a tuberosity?) in order to better appreciate the application of the anatomy. Most importantly, ask yourself functional questions when you examine the bones themselves, such as the following: Is this a right or left element? What articulates with this structure/area? What attaches to this structure? Is this structure palpable? Can this structure be identified in a standard radiographic image? Are there any important neurovascular relations to this region/structure? Clavicle Also known as the “collar bone,” the clavicle (clavicul- is Latin for “key”) is located between the sternum and the scapula and lies horizontally across the root of the neck. It is roughly S-shaped and resembles a large, old-style key. The clavicle forms a light strut that connects the upper limb to the thorax and allows the limb to move freely from the trunk. It is the first bone to begin ossification. The clavicle is subcutaneous and easily palpable along its entire length.  The sternal extremity (Fig. 3.1) is the blunt, thickened, proximal (medial) end of the clavicle. It articulates with the clavicular notch of the sternum through a compound synovial joint containing an articular disc. The acromial extremity is the flattened distal (lateral) end of the clavicle. It articulates with the acromion process of the scapula. The conoid tubercle (cono- is Greek for “pine cone”) is a small, roughened elevation on the inferior surface, near the acromial end. This serves as the attachment area for the conoid ligament part of the coracoclavicular ligament. The important muscles and ligaments attached to the clavicle are shown in Figures 3.1 and 3.2. Figure 3.1 Muscle attachments to the bones of the thorax, clavicle, scapula, and humerus. Figure 3.2 Important muscular and ligamentous attachments to the right clavicle. A. Superior surface. B. Inferior surface. Clinical Notes Clavicle Fracture The clavicle is a strut that holds the arm laterally so that it can move freely on the trunk. It is the sole link between the upper limb and the axial skeleton, and so transmits all forces from the upper limb to the trunk. Unfortunately, because of its position, it is easily exposed to trauma. It is the most commonly fractured bone in the body. The fracture usually occurs as a result of a fall on the shoulder or outstretched hand. The force is transmitted along the clavicle, which breaks at its weakest point, the junction of the middle and outer thirds. After the fracture, the lateral fragment is depressed by the weight of the arm and is pulled medially and forward by the strong adductor muscles of the shoulder joint, especially the pectoralis major. The medial end is tilted upward by the sternocleidomastoid muscle. The close relationship of the supraclavicular nerves to the clavicle may result in their involvement in callus formation after fracture of the bone. This may be the cause of persistent pain over the side of the neck. Clavicular Compression of Brachial Plexus, Subclavian Artery, and Subclavian Vein The interval between the clavicle and the first rib in some patients may become narrowed and thus is responsible for compression of nerves and blood vessels. (See discussion of thoracic outlet syndrome in Chapter 4.) Scapula Also known as the “shoulder bone,” the scapula (scapul- is Latin for “shoulder blade”) is a large, flat, triangular bone that lies on the posterior chest wall between the second and seventh ribs. It articulates with the acromial extremity of the clavicle and the head of the humerus. The major defining features of the scapula are its three borders (superior, medial, lateral), three angles (superior, inferior, lateral), two surfaces (dorsal, costal), and three large bony processes (spine, acromion, coracoid), as shown in Figure 3.3. Figure 3.3 Important muscular and ligamentous attachments to the right scapula. A. Anterior surface. B. Posterior surface. The superior border is the short, thin, superior edge of the scapula. A notch (the scapular notch) is located on the lateral aspect of the superior border, near the base of the coracoid process. The superior transverse scapular ligament bridges the notch. Normally, the suprascapular artery passes superior to this ligament, whereas the suprascapular nerve passes inferior to it (remember: the Army goes over the bridge; the Navy goes under the bridge). The medial (vertebral) border is the long, medial edge of the scapula, located closest to the vertebral column. The lateral (axillary) border is the thickened, lateral edge of the scapula, located closest to the axilla. The junction of the superior and medial borders forms the superior angle of the scapula. The junction of the medial and lateral borders forms the inferior angle. The inferior angle of the scapula can be palpated easily in the living subject and marks the level of the seventh rib and the spine of the seventh thoracic vertebra. The junction of the superior and lateral borders forms the lateral angle. The lateral angle of the scapula is the thickest and most complex part of the scapula. It is composed mainly of a broadened process (the head of the scapula) that is connected to the rest of the bone by a slight constriction (the neck of the scapula). The lateral surface of the head forms a shallow articular surface, the glenoid cavity or fossa (glen- is Greek for “pit” or “socket”), for the head of the humerus. A fibrocartilage ring (glenoid labrum) rims the margin of the glenoid cavity and serves to broaden and deepen the joint cavity. A small elevation (supraglenoid tubercle) is located at the apex of the glenoid cavity, near the base of the coracoid process. A roughened area (infraglenoid tubercle) is located immediately inferior to the glenoid cavity. The dorsal (posterior) surface of the scapula is subdivided into two unequal-sized regions by the spine of the scapula. The smaller, troughlike area superior to the spine is the supraspinous fossa. The much larger area inferior to the spine is the infraspinous fossa. The spine is the large, triangular ridge that runs laterally from the medial border of the scapula to merge into the acromion process. The lateral border of the spine blends into the neck of the scapula and forms a notchlike passageway (spinoglenoid, or greater scapular, notch) that connects the supraspinous fossa with the infraspinous fossa. This allows the suprascapular nerve and vessels to pass between these fossae. The acromion (acromi- is Greek for “point of the shoulder”) is the broad, flat lateral extension of the spine of the scapula. This forms the easily palpable tip of the shoulder. It partly roofs over the glenoid cavity and provides an articulation with the clavicle at the acromioclavicular joint. The costal (ventral, anterior) surface of the scapula lies against the posterior aspect of the rib cage. A large part of this surface forms a shallow concavity, the subscapular fossa. The coracoid process (coraco- is Greek for “like a crow’s beak”) is a thick, beaklike structure that projects anterolaterally from the junction of the neck and lateral end of the superior border of the scapula. It can be palpated via deep pressure through the anterior part of the deltoid muscle, inferior to the lateral end of the clavicle. The main muscles and ligaments attached to the scapula are shown in Figures 3.1 and 3.3. Clinical Notes Scapular Fractures Fractures of the scapula are usually the result of severe trauma, such as occurs in run-over accident victims or in occupants of automobiles involved in crashes. Injuries are usually associated with fractured ribs. Most fractures of the scapula require little direct treatment because the muscles on the anterior and posterior surfaces adequately splint the fragments. Dropped Shoulder and Winged Scapula The position of the scapula on the posterior wall of the thorax is maintained by the tone and balance of the muscles attached to it. If one of these muscles is paralyzed, the balance is upset, as in dropped shoulder, which occurs with paralysis of the trapezius, or winged scapula (Fig. 3.4), caused by paralysis of the serratus anterior. Such imbalance can be detected by careful physical examination. Figure 3.4 Winging of the right scapula. Humerus The humerus (humer- is Latin for “shoulder”) is located in the arm (brachium) and is the longest bone of the upper limb. Proximally, the humerus articulates with the glenoid cavity of the scapula, at the glenohumeral (shoulder) joint. Distally, it articulates with the head of the radius and the trochlear notch of the ulna, at the elbow joint. The humerus can be divided into three main regions: (1) proximal extremity, (2) body or shaft, and (3) distal extremity. The major muscles and ligaments attached to the humerus are shown in Figures 3.1 and 3.5. Figure 3.5 Important muscular and ligamentous attachments to the right humerus. A. Anterior surface. B. Posterior surface. Proximal Extremity The head is the round, smooth, proximal end of the humerus. It forms about one third of a sphere and is oriented medially, superiorly, and slightly posteriorly. It articulates with the glenoid cavity of the scapula to form the glenohumeral joint in the shoulder joint complex. The greater tubercle is the large, roughened elevation on the lateral proximal end of the humerus, lateral to the head. The lesser tubercle is the small, roughened elevation on the anterior proximal end of the humerus, inferior to the head and medial to the greater tubercle. The anatomical neck is the slightly constricted region surrounding the articular surface of the head. The articular capsule of the glenohumeral joint attaches along the inferior edge of the anatomical neck. Fractures here generally are rare but may be more frequent in the elderly. The surgical neck is the constricted area immediately inferior to the greater and lesser tubercles. This forms the interface between the proximal extremity and the shaft of the humerus. The surgical neck has important relations with the axillary nerve and the anterior and posterior circumflex humeral vessels. Fractures here are common. The intertubercular (bicipital) groove is the deep groove on the anterior surface of the humerus that separates the greater and lesser tubercles. It houses the tendon of the long head of the biceps brachii muscle and extends into the upper third of the shaft of the humerus. Body/Shaft The deltoid tuberosity (delt as in the triangular Greek letter “delta”) is the roughened triangular elevation on the anterolateral surface of the midshaft of the humerus. This serves as the attachment area for the deltoid muscle. The posterior edge of the tuberosity defines the groove for the radial nerve. The groove (sulcus) for the radial nerve (radial groove, spiral groove) is the shallow depression that spirals around the posterior and lateral aspects of the midshaft of the humerus. The groove is most distinct where it lies between the deltoid tuberosity and the upper end of the lateral supracondylar ridge. It has important relations with the radial nerve and the profunda brachii vessels. Fractures of the midshaft humerus are common, especially inferior to the deltoid tuberosity, and may affect the radial groove and its contents. The medial supracondylar ridge is the narrow ridge running proximally from the medial epicondyle, forming the lower medial border of the humerus. The lateral supracondylar ridge is the narrow ridge running proximally from the lateral epicondyle, forming the lower lateral border of the humerus. Distal Extremity The lateral epicondyle is the small, roughened projection on the distal, lateral side of the humerus, proximal to the capitulum. It is readily palpable. The common extensor tendon (tendon of origin for several superficial forearm extensor muscles) attaches here. Inflammation of this tendon is termed “lateral epicondylitis” (“tennis elbow”). The medial epicondyle is the large, knoblike projection on the distal, medial side of the humerus, proximal to the trochlea. It is easily palpable and forms an important surface landmark in the arm. The ulnar nerve crosses the posterior surface of this epicondyle in the shallow ulnar sulcus and is susceptible to injury here (e.g., via blunt trauma or bony fracture). The nerve can be palpated and rolled against the epicondyle. Stimulation of the nerve by contact against the epicondyle elicits the characteristic “funny bone” response of tingling sensations in the medial border of the hand and fifth digit. (So, why is the funny bone funny? Because it borders on the “humerus.”) The capitulum (capit- is Latin for “head”—in this grammatical case, “little head”) is the rounded, half-spherical, articular process at the distal, lateral end of the humerus. It lies immediately lateral to the trochlea. The capitulum articulates with the head of the radius. The shapes of these structures allow both flexion/extension and rotation at the humeroradial joint. The trochlea (trochle- is Greek for “pulley”) is the pulley-shaped articular process at the distal, medial end of the humerus. It lies immediately medial to the capitulum. The trochlea articulates with the trochlear notch of the ulna. The shapes of the articulated trochlea and trochlear notch (plus the presence of the humeroradial joint) limit lateral movements of the ulna, resulting in essentially a hinge action at the humeroulnar joint. The coronoid fossa is the depression on the distal, anterior end of the humerus, immediately proximal to the trochlea. This receives the coronoid process of the ulna when the elbow is fully flexed. The radial fossa is the shallow depression on the distal, anterior end of the humerus, immediately proximal to the capitulum. This receives the margin of the head of the radius when the elbow is fully flexed. The olecranon fossa is the deep depression on the distal, posterior end of the humerus, immediately proximal to the trochlea. This holds the apex of the olecranon process of the ulna when the elbow is extended.  Clinical Notes Proximal End of Humerus Fracture Refer to Figure 3.6A to visualize the fractures described here. Figure 3.6 A. Common fractures of the humerus. B. Common fractures of the radius and ulna. The red arrows indicate the direction of displacement of the bony fragments on the site of the fracture line and the pull of the responsible muscles. CF, pull of common flexure muscles; D, deltoid; PM, pectoralis major; S, supraspinatus; SUB, subscapularis; TR, triceps. Humeral Head Fracture Fractures of the humeral head can occur during the process of anterior and posterior dislocations of the shoulder joint. The fibrocartilaginous glenoid labrum of the scapula produces the fracture, and the labrum can become jammed in the defect, making reduction of the shoulder joint difficult. Greater Tuberosity Fracture The greater tuberosity of the humerus can be fractured by direct trauma, displaced by the glenoid labrum during dislocation of the shoulder joint, or avulsed by violent contractions of the supraspinatus muscle. The bone fragment will hold the attachments of the supraspinatus, teres minor, and infraspinatus muscles, whose tendons form part of the rotator cuff. When associated with a shoulder dislocation, severe tearing of the rotator cuff with the fracture can result in the greater tuberosity remaining displaced posteriorly after the shoulder joint has been reduced. In this situation, open reduction of the fracture is necessary to attach the rotator cuff back into place. Lesser Tuberosity Fracture Occasionally, a lesser tuberosity fracture accompanies posterior dislocation of the shoulder joint. The bone fragment receives the insertion of the subscapularis tendon, a part of the rotator cuff. Surgical Neck Fracture The surgical neck of the humerus, which lies immediately distal to the lesser tuberosity, can be fractured by a direct blow on the lateral aspect of the shoulder or in an indirect manner by falling on the outstretched hand. The axillary nerve and circumflex humeral blood vessels have close relations to the surgical neck and can be readily damaged in association with a fracture here. Shaft of Humerus Fracture Fractures of the humeral shaft are common; displacement of the fragments depends on the relation of the site of fracture to the insertion of the deltoid muscle. When the fracture line is proximal to the deltoid insertion, the pectoralis major, latissimus dorsi, and teres major muscles adduct the proximal fragment; the deltoid, biceps, and triceps pull the distal fragment proximally. When the fracture is distal to the deltoid insertion, the proximal fragment is abducted by the deltoid, and the biceps and triceps pull the distal fragment proximally. The radial nerve can be damaged where it lies in the spiral groove on the posterior surface of the humerus under cover of the triceps muscle. Distal End of Humerus Fracture Supracondylar fractures are common in children and occur when the child falls on the outstretched hand with the elbow partially flexed. Injuries to the median, radial, and ulnar nerves are not uncommon, although function usually quickly returns after reduction of the fracture. Damage to or pressure on the brachial artery can occur at the time of the fracture or from swelling of the surrounding tissues; the circulation to the forearm may be interfered with, leading to Volkmann’s ischemic contracture (see the Clinical Notes on the forearm). The medial collateral ligament of the elbow can avulse the medial epicondyle if the forearm is forcibly abducted. The ulnar nerve can be injured at the time of the fracture, can become involved later in the repair process of the fracture (in the callus), or can undergo irritation on the irregular bony surface after the bone fragments are reunited. Radius The radius (radi- is Latin for “spoke” or “ray”) is the bone on the lateral side of the forearm (antebrachium). Proximally, it articulates with both the capitulum of the humerus and the radial notch of the ulna, in the elbow joint. Distally, it articulates with the head of the ulna and the scaphoid and lunate bones, in the wrist. During pronation and supination, the radius rotates about its long axis at its proximal end and circumducts the ulna at its distal end. The major muscles and ligaments attached to the radius are shown in Figure 3.7. Figure 3.7 Important muscular and ligamentous attachments to the radius and the ulna. A. Anterior surface. B. Posterior surface. The head is the expanded, round, proximal end of the radius. Its proximal surface is a shallow concavity for articulation with the capitulum of the radius. Its periphery articulates with the radial notch of the ulna. The head is held in place against the ulna by the encircling anular ligament. Note that the head of the radius is at its proximal end, whereas the head of the ulna is at its distal end. The neck is the constricted area immediately distal to the head. The radial tuberosity is the raised, mostly roughened area on the anteromedial, proximal aspect of the radius, just distal to the neck. This is the insertion site of the biceps brachii muscle. The body (shaft) is the elongated midportion of the radius. It widens along its proximal to distal extent. The medial border of the shaft forms a sharp crest (the interosseous border) for the attachment of the interosseous membrane that binds together the radius and ulna. The ulnar notch is the shallow depression on the distal, medial aspect of the radius. This is the articular surface for the head of the ulna. The styloid process (styl- is Greek for “pointed instrument”) is the distal projection from the lateral, distal aspect of the radius. This extends lateral to the proximal row of carpal bones. The carpal articular surface forms the distal surface of the radius. This area articulates with the scaphoid (laterally) and lunate (medially) bones. Ulna The ulna (ulna is Latin for “elbow”) lies on the medial side of the forearm (antebrachium). Proximally, the ulna articulates with both the trochlea of the humerus and the head of the radius, in the elbow joint. Distally, it articulates with the ulnar notch of the radius. Its large, hook-shaped proximal end characterizes the bone. The major muscles and ligaments attached to the ulna are shown in Figure 3.7. The olecranon (olecran- is Greek for “elbow”) is the easily palpable proximal end of the ulna that forms the “point” of the elbow. It is the insertion site of the triceps brachii muscle. The beaklike tip of the olecranon fits into the olecranon fossa of the humerus when the elbow is extended. The coronoid process (coron- is Greek for “resembling a crow”) is the anterior projection forming the inferior end of the hooklike proximal end of the ulna. It contributes to the formation of the trochlear notch. The trochlear notch is the large, crescent-shaped notch on the anterior aspect of the proximal end of the ulna. It is formed by the articular surfaces of the olecranon and the coronoid process and articulates with the trochlea of the humerus. The radial notch is the shallow, smooth notch on the lateral aspect of the coronoid process, immediately distal to the trochlear notch. It is the articular surface for the head of the radius. The ulnar tuberosity is the anterior, distal, roughened aspect of the coronoid process. This serves as the insertion area for the brachialis muscle. The body (shaft) is the elongated midportion of the ulna. In contradistinction to the radius, the body of the ulna tapers along its proximodistal length. The posterior aspect of the body is rounded and subcutaneous and easily palpable along its entire length. The lateral border of the shaft forms a sharp crest (the interosseous border) for the attachment of the interosseous membrane. The head is the small, rounded distal end of the ulna. This has an articular surface on its lateral side for contact with the ulnar notch of the radius. However, the distal end of the head is separated and excluded from the wrist joint by an articular disc. The styloid process is a small projection from the posterolateral, distal end of the ulna. Clinical Notes Ulnar and Radial Fractures Fractures of the head of the radius can occur from falls on the outstretched hand. As the force is transmitted along the radius, the head of the radius is driven sharply against the capitulum, splitting or splintering the head (see Fig. 3.6B). Fractures of the neck of the radius occur more often in young children from falls on the outstretched hand (see Fig. 3.6B). Fractures of the shafts of the radius and ulna may or may not occur together (see Fig. 3.6B). Displacement of the fragments is usually considerable and depends on the pull of the attached muscles. The supinator and biceps brachii muscles supinate the proximal fragment of the radius. The pronator quadratus muscle pronates and medially deviates the distal fragment of the radius. The strength of the brachioradialis and extensor carpi radialis longus and brevis muscles shortens and angulates the forearm. In fractures of the ulna, the ulna angulates posteriorly. To restore the normal movements of pronation and supination, the normal anatomic relationship of the radius, ulna, and interosseous membrane must be regained. A fracture of one forearm bone may be associated with a dislocation of the other bone (e.g., in Monteggia’s fracture, a force applied from behind fractures the shaft of the ulna). There is a bowing forward of the ulnar shaft and an anterior dislocation of the radial head with rupture of the anular ligament. In Galeazzi’s fracture, the proximal third of the radius is fractured and the distal end of the ulna is dislocated at the distal radioulnar joint. Fractures of the olecranon process can result from a fall on the flexed elbow or from a direct blow. Depending on the location of the fracture line, the bony fragment may be displaced by the pull of the triceps muscle, which is inserted on the olecranon process (see Fig. 3.6). Avulsion fractures of part of the olecranon process can be produced by the pull of the triceps muscle. Good functional return after any of these fractures depends on the accurate anatomic reduction of the fragment. Colles’ fracture is a fracture of the distal end of the radius resulting from a fall on the outstretched hand. It commonly occurs in patients older than 50 years. The force drives the distal fragment posteriorly and superiorly, and the distal articular surface is inclined posteriorly (Fig. 3.8A). This posterior displacement produces a posterior bump, sometimes referred to as the “dinner-fork deformity” because the forearm and wrist resemble the shape of that eating utensil. Failure to restore the distal articular surface to its normal position will severely limit the range of flexion of the wrist joint. Smith’s fracture is a fracture of the distal end of the radius and occurs from a fall on the back of the hand (see Fig. 3.8B). It is a reversed Colles’ fracture because the distal fragment is displaced anteriorly. Figure 3.8 Fractures of the distal end of the radius. A. Colles’ fracture. B. Smith’s fracture. Olecranon Bursitis A small subcutaneous bursa is present over the olecranon process of the ulna, and repeated wear or trauma often produces chronic bursitis. Carpal Bones The carpal (carp- is Greek for wrist) bones are the eight small bones comprising the wrist (Figs. 3.9 and 3.10). These are arranged in two rows (proximal and distal), with four bones in each row. The arrangement of the bones forms a deep concave groove on the ventral aspect of the wrist. This groove is roofed over by a strong ligamentous band (the flexor retinaculum), thus forming the osseofascial carpal tunnel. The carpal tunnel conveys several flexor tendons and the median nerve into the hand. Compression of the tunnel space and/or trauma to its contents results in carpal tunnel syndrome. The bones of the hand are cartilaginous at birth. The capitate begins to ossify during the 1st year, and the others begin to ossify at intervals thereafter until the 12th year, when all the bones are ossified. Figure 3.9 Important muscular attachments to the anterior surfaces of the bones of the hand. Figure 3.10 Important muscular attachments to the posterior surfaces of the bones of the hand. Learn the carpal bones as an articulated group, rather than as individually separate items. A mnemonic helpful for remembering the carpal bones is “Some lovers try positions that they cannot handle.” The first letter of each word represents the first letter of each carpal bone, arranged by row (proximal row first), from lateral to medial. Proximal Row From lateral to medial: scaphoid, lunate, triquetrum, and pisiform. The scaphoid and lunate bones articulate with the carpal articular surface of the radius. The scaphoid (scaph- is Greek for something hollowed out, such as a “bowl,” “boat,” or “trough”) is the largest, most lateral carpal bone of the proximal row. The scaphoid is located in the floor of the anatomical snuffbox. It is fractured frequently by impact on the base of the hand when the wrist is hyperextended and abducted, as when trying to break a fall with the outstretched hand. The lunate (lun- is Latin for “moon”) is the roughly semilunar-shaped carpal bone located between the scaphoid and triquetrum. The triquetrum (triquetr- is Latin for “triangular”) is the roughly pyramidal- shaped, most medial bone in the proximal carpal row. The pisiform lies anterior to the triquetrum. The pisiform (pis- is Greek for “pea”) is the small, pea-shaped, sesamoid bone formed in the tendon of the flexor carpi ulnaris muscle. Distal Row From lateral to medial: trapezium, trapezoid, capitate, and hamate. These bones articulate distally with the metacarpal bones of the hand. The trapezium (trapez- is Greek for “table”) is the most lateral carpal bone of the distal row. It forms a saddle joint with the first metacarpal bone, thus allowing the great mobility of the thumb. Remember “The thumb swings on the trapezium.” The trapezoid is the bone located between the trapezium and the capitate and is named for its trapezoid shape. The capitate (recall that capit means “head”) is the central and largest carpal bone, located between the trapezoid and the hamate. It is named for its rounded head, which sits in the concavity formed by the scaphoid and lunate bones. Forces generated in the hand (as during a punching blow with the fist) are transmitted through the third metacarpal bone to the capitate, then proximally through the lunate to the radius. The hamate (hamat is Latin for “hooked”) is the most medial bone in the distal carpal row. Its distinguishing feature is the hamulus (hook), which is one of the attachment points of the flexor retinaculum. Metacarpal Bones The metacarpal bones are the five bones located between the carpal bones and the phalanges of the hand (see Figs. 3.9 and 3.10). These comprise the body of the hand, whereas the phalanges make up the fingers. The bones are identified by number (1–5), starting with the most lateral unit (i.e., metacarpal 1 aligns with the thumb). Each bone has a base, a body, and a head. The base is the expanded proximal end of the bone. It articulates with the distal row of carpal bones. The body (shaft) is the elongate, slender midportion of the bone. The shaft of each metacarpal bone is slightly concave anteriorly and is triangular in transverse section. It has posterior, lateral, and medial surfaces. The head is the rounded distal end of the bone. It articulates with the proximal phalanx of the corresponding digit and forms a knuckle of the hand. The first metacarpal bone of the thumb is the shortest and most mobile. It does not lie in the same plane as the others but occupies a more anterior position. It is also rotated medially through a right angle so that its extensor surface is directed laterally rather than posteriorly. Phalanges The phalanges (phalan- is Greek for “battle line”; phalanx = singular; phalanges = plural) are the bones that comprise the digits of the hand (see Figs. 3.9 and 3.10). As with the metacarpals, each has a base, body (shaft), and head. The thumb has 2 phalanges (proximal and distal), whereas each other digit has 3 phalanges (proximal, middle, distal). Thus, each hand has 14 phalanges in total. The base of each proximal phalanx articulates with the head of the corresponding metacarpal bone. The base of the middle or distal phalanx articulates with the head of the next most proximal phalanx. The body of each distal phalanx is very short. The head of each proximal and middle phalanx articulates with the base of the next most distal phalanx. Clinical Notes Hand Bone Injury Fracture of the scaphoid bone is common in young adults; unless treated effectively, the fragments will not unite, and permanent weakness and pain of the wrist will result, with the subsequent development of osteoarthritis. The fracture line usually goes through the narrowest part of the bone, which, because of its location, is bathed in synovial fluid. The blood vessels to the scaphoid enter its proximal and distal ends, although the blood supply is occasionally confined to its distal end. If the latter occurs, a fracture deprives the proximal fragment of its arterial supply, and this fragment undergoes avascular necrosis. Deep tenderness in the anatomic snuffbox (see the following discussion of the wrist) after a fall on the outstretched hand in a young adult is suspicious for a fractured scaphoid. Dislocation of the lunate bone occasionally occurs in young adults who fall on the outstretched hand in a way that causes hyperextension of the wrist joint. Involvement of the median nerve is common. Fractures of the metacarpal bones can occur as a result of direct violence, such as the clenched fist striking a hard object. The fracture always angulates dorsally. The “boxer’s fracture” commonly produces an oblique fracture of the neck of the fifth and sometimes the fourth metacarpal bones. The distal fragment is commonly displaced proximally, thus shortening the finger posteriorly. Bennett’s fracture is a fracture of the base of the metacarpal of the thumb caused when violence is applied along the long axis of the thumb or the thumb is forcefully abducted. The fracture is oblique and enters the carpometacarpal joint of the thumb, causing joint instability. Fractures of the phalanges are common and usually follow direct injury. UPPER LIMB REGIONS The upper limb is divided into the shoulder, arm, elbow, forearm, wrist, and hand. The shoulder is a complex region connecting the trunk with the upper limb and can be considered as three parts: pectoral region, scapular region, and axilla. The arm (upper arm, brachium) is the proximal segment of the upper limb from the shoulder to the elbow. In contrast, in the lower limb, the leg is the more distal segment from the knee to the ankle. Remember, spelling does matter because sometimes one or two letters can make a major difference in the location you are describing (e.g., “brachial” vs. “bronchial” vs. “branchial”). The elbow is the area connecting the arm with the forearm. The cubital fossa is a depression across the front of the elbow. The forearm (lower arm, antebrachium) is the segment of the upper limb from the elbow to the wrist. The wrist (carpus) is a complex of small bones connecting the forearm and hand. The hand (manus), a very important organ, is located at the distal end of the upper limb. Pectoral Region The pectoral region is the anterior aspect of the shoulder. Although this area may be considered part of the anterior thoracic wall, several structures here (e.g., pectoral muscles) connect with and function as part of the upper limb, thus uniting these areas. The pectoral region also houses the breasts. The general topography of the pectoral region is shown in Figures 3.11 through 3.13. Figure 3.11 Pectoral region and axilla. Figure 3.12 Pectoral region and axilla; the pectoralis major muscle has been removed to display the underlying structures. Figure 3.13 Pectoral region and axilla; the pectoralis major and minor muscles and the clavipectoral fascia have been removed to display the underlying structures. Breasts Strictly speaking, the breasts are not anatomically part of the upper limb. However, they are situated in the pectoral region, and their blood supply and lymphatic drainage are largely related to the armpit. The clinical importance of the breasts cannot be overemphasized. Location and Description The breasts are specialized accessory glands of the skin that secrete milk. They are present in both sexes and share similar structure in males and immature females. The nipples are small and surrounded by a colored area of skin called the areola (Fig. 3.14). The breast tissue consists of a system of ducts embedded in connective tissue that does not extend beyond the margin of the areola. Figure 3.14 Mature breast in the female. A. Anterior view with skin partially removed to show internal structure. B. Sagittal section. C. The axillary tail, which pierces the deep fascia and extends into the axilla. Puberty At puberty in females, the breasts gradually enlarge and assume their hemispherical shape under the influence of ovarian hormones. The ducts elongate, but the increased size of the glands is mainly from the deposition of fat. The base of the breast extends from the second to sixth rib and from the lateral margin of the sternum to the midaxillary line. The greater part of the gland lies in the superficial fascia. An extension of the gland called the axillary tail (see Fig. 3.14C) continues upward and laterally, pierces the deep fascia at the lower border of the pectoralis major muscle, and enters the axilla. Each breast consists of 15 to 20 lobes, which radiate out from the nipple (see Fig. 3.14A). The main duct from each lobe opens separately on the summit of the nipple and possesses a dilated ampulla just before its termination. The base of the nipple is surrounded by the areola. The underlying areolar glands produce tiny tubercles on the areola. The lobes of the gland are separated by fibrous septa that serve as suspensory ligaments (see Fig. 3.14B). A space filled by loose connective tissue called the retromammary space lies deep to the breast and superficial to the underlying pectoral muscles. Young Women In young women, the breasts tend to protrude forward from a circular base. Pregnancy Early In the early months of pregnancy, the duct system rapidly increases in length and branching (Fig. 3.15). The secretory alveoli develop at the ends of the smaller ducts, and the connective tissue becomes filled with expanding and budding secretory alveoli. The vascularity of the connective tissue also increases to provide adequate nourishment for the developing gland. The nipple enlarges, and the areola becomes darker and more extensive as a result of increased deposits of melanin pigment in the epidermis. The areolar glands enlarge and become more active. Figure 3.15 Extent of the development of the ducts and secretory alveoli in the breasts in both sexes at different stages of activity. Late During the second half of pregnancy, the growth process slows. However, the breasts continue to enlarge, mostly because of the distention of the secretory alveoli with the fluid secretion called colostrum. Postweaning The breasts return to their inactive state once the baby has been weaned. The remaining milk is absorbed; the secretory alveoli shrink, and most of them disappear. The interlobular connective tissue thickens. The breasts and the nipples shrink and return nearly to their original size. The pigmentation of the areola fades, but the area never lightens to its original color. Postmenopause The breast atrophies after the menopause (see Fig. 3.15). Most of the secretory alveoli disappear, leaving behind the ducts. The amount of adipose tissue may increase or decrease. The breasts tend to shrink in size and become more pendulous. The atrophy after menopause is caused by the absence of ovarian estrogens and progesterone. Blood Supply The arterial supply to the breasts includes the perforating branches of the internal thoracic artery and the intercostal arteries. The axillary artery also supplies the gland via its lateral thoracic and thoracoacromial branches. The veins correspond to the arteries. Lymph Drainage The lymph drainage of the mammary gland is of great clinical importance because of the frequent development of cancer in the gland and the subsequent dissemination of the malignant cells along the lymph vessels to the lymph nodes. The lateral quadrants of the breast drain into the anterior axillary or pectoral group of nodes (Fig. 3.16) (situated just posterior to the lower border of the pectoralis major muscle). The medial quadrants drain by means of vessels that pierce the intercostal spaces and enter the internal thoracic group of nodes (situated within the thoracic cavity along the course of the internal thoracic artery). A few lymph vessels follow the posterior intercostal arteries and drain posteriorly into the posterior intercostal nodes (situated along the course of the posterior intercostal arteries); some vessels communicate with the lymph vessels of the opposite breast and with those of the anterior abdominal wall. Figure 3.16 Lymph drainage of the breast. Clinical Notes Witch’s Milk in Newborns While the fetus is in the uterus, the maternal and placental hormones cross the placental barrier and cause proliferation of the duct epithelium and the surrounding connective tissue. This proliferation may cause swelling of the mammary glands in both sexes during the 1st week of life. In some cases, a milky fluid called witch’s milk may be expressed from the nipples. The condition is resolved spontaneously as the maternal hormone levels in the child fall. Clinical Notes Breast Examination The breast is one of the common sites of cancer in women. It is also the site of different types of benign tumors and may be subject to acute inflammation and abscess formation. For these reasons, clinical personnel must be familiar with the development, structure, and lymph drainage of this organ. With the patient undressed to the waist and sitting upright, first inspect the breasts for symmetry. Some degree of asymmetry is common and is the result of unequal breast development. Any swelling should be noted. An underlying tumor, a cyst, or abscess formation can cause a swelling. Carefully examine the nipples for evidence of retraction. A carcinoma within the breast substance can cause retraction of the nipple by pulling on the lactiferous ducts. Next, ask the patient to lie down so that the breasts can be palpated against the underlying thoracic wall. Finally, ask the patient to sit up again and raise both arms above her head. With this maneuver, a carcinoma tethered to the skin, the suspensory ligaments, or the lactiferous ducts produces dimpling of the skin or retraction of the nipple. Mammography Mammography is a radiographic examination of the breast (Fig. 3.17). This technique is extensively used for screening the breasts for benign and malignant tumors and cysts. Extremely low doses of x-rays are used so that the dangers are minimal, and the examination can be repeated often. Its success is based on the fact that a lesion measuring only a few millimeters in diameter can be detected long before it is felt by clinical examination. Figure 3.17 Mediolateral mammogram showing the glandular tissue supported by the connective tissue septa. Supernumerary and Retracted Nipples Supernumerary nipples occasionally occur along a line extending from the axilla to the groin; they may or may not be associated with breast tissue (see the Embryology Notes below). This minor congenital anomaly may result in a mistaken diagnosis of warts or moles. A long-standing retracted nipple is a congenital deformity caused by a failure in the complete development of the nipple. A retracted nipple of recent occurrence is usually caused by an underlying carcinoma pulling on the lactiferous ducts. Importance of Fibrous Septa The interior of the breast is divided into 15 to 20 compartments that radiate from the nipple by fibrous septa (suspensory ligaments) that extend from the deep surface of the skin. Each compartment contains a lobe of the gland. Normally, the skin feels completely mobile over the breast substance. However, a scirrhous carcinoma or a disease such as a breast abscess may apply traction to the fibrous septa that causes dimpling of the skin. Breast Abscess An acute infection of the mammary gland may occur during lactation. Pathogenic bacteria gain entrance to the breast tissue through a crack in the nipple. Because of the presence of the fibrous septa, the infection remains localized to one compartment or lobe to begin with. Abscesses should be drained through a radial incision to avoid spreading of the infection into neighboring compartments; a radial incision also minimizes the damage to the radially arranged ducts. Lymph Drainage and Breast Carcinoma The importance of knowing the lymph drainage of the breast in relation to the spread of cancer from that organ cannot be overemphasized. The lymph vessels from the medial quadrants of the breast pierce the second, third, and fourth intercostal spaces and enter the thorax to drain into the lymph nodes alongside the internal thoracic artery. The lymph vessels from the lateral quadrants of the breast drain into the anterior or pectoral group of axillary nodes. Therefore, a cancer occurring in the lateral quadrants of the breast tends to spread to the axillary nodes. Thoracic metastases are difficult or impossible to treat, but the lymph nodes of the axilla can be removed surgically. Approximately 60% of carcinomas of the breast occur in the upper lateral quadrant. The lymphatic spread of cancer to the opposite breast, to the abdominal cavity, or into the lymph nodes in the root of the neck is caused by obstruction of the normal lymphatic pathways by malignant cells or destruction of lymph vessels by surgery or radiotherapy. The cancer cells are swept along the lymph vessels and follow the lymph stream. The entrance of cancer cells into the blood vessels accounts for the metastases in distant bones. In patients with localized cancer of the breast, most surgeons do a simple mastectomy or a lumpectomy, followed by radiotherapy to the axillary lymph nodes and/or hormone therapy. In patients with localized cancer of the breast with early metastases in the axillary lymph nodes, most authorities agree that radical mastectomy offers the best chance of cure. In patients in whom the disease has already spread beyond these areas (e.g., into the thorax), simple mastectomy, followed by radiotherapy or hormone therapy, is the treatment of choice. Radical mastectomy is designed to remove the primary tumor and the lymph vessels and nodes that drain the area. This means that the breast and the associated structures containing the lymph vessels and nodes must be removed en bloc. The excised mass is therefore made up of the following: a large area of skin overlying the tumor and including the nipple; all the breast tissue; the pectoralis major and associated fascia through which the lymph vessels pass to the internal thoracic nodes; the pectoralis minor and associated fascia related to the lymph vessels passing to the axilla; all the fat, fascia, and lymph nodes in the axilla; and the fascia covering the upper part of the rectus sheath, the serratus anterior, the subscapularis, and the latissimus dorsi muscles. The axillary blood vessels, the brachial plexus, and the nerves to the serratus anterior and the latissimus dorsi are preserved. Some degree of postoperative edema of the arm is likely to follow such a radical removal of the lymph vessels draining the upper limb.  A modified form of radical mastectomy for patients with clinically localized cancer is also a common procedure and consists of a simple mastectomy in which the pectoral muscles are left intact. The axillary lymph nodes, fat, and fascia are removed. This procedure removes the primary tumor and permits pathologic examination of the lymph nodes for possible metastases. Male Breast Carcinoma Carcinoma in the male breast accounts for about 1% of all carcinomas of the breast. This fact tends to be overlooked when examining the male patient. Because the amount of breast tissue in the male is small, the tumor can usually be felt with the flat of the examining hand in the early stages. However, the prognosis is relatively poor in the male, because the carcinoma cells can rapidly metastasize into the thorax through the small amount of intervening tissue. Embryology Notes Breast Development In the early embryo, a linear thickening of ectoderm appears called the milk ridge, which extends from the axilla obliquely to the inguinal region. In animals, several mammary glands are formed along this ridge. In the human, the ridge disappears except for a small part in the pectoral region. This localized area thickens, becomes slightly depressed, and sends off 15 to 20 solid cords, which grow into the underlying mesenchyme. Meanwhile, the underlying mesenchyme proliferates, and the depressed ectodermal thickening becomes raised to form the nipple. At the 5th month, the areola is recognized as a circular pigmented area of skin around the future nipple. Polythelia Supernumerary nipples occasionally occur along a line corresponding to the position of the milk ridge. They are liable to be mistaken for moles. Retracted or Inverted Nipple Retracted nipple is a failure in the development of the nipple during its later stages. It is important clinically, because normal suckling of an infant cannot take place and the nipple is prone to infection (also see the Clinical Notes above). Micromastia An excessively small breast on one side occasionally occurs, resulting from lack of development. Macromastia Diffuse hypertrophy of one or both breasts occasionally occurs at puberty in otherwise normal girls. Gynecomastia Unilateral or bilateral enlargement of the male breast occasionally occurs, usually at puberty. The cause is unknown, but the condition is probably related to some form of hormonal imbalance. Scapular Region The scapular region is the posterior aspect of the shoulder. Although this area may be considered part of the back and/or posterior thoracic wall, several structures here (e.g., trapezius and latissimus dorsi muscles) connect with and function as part of the upper limb, thus uniting these areas. Musculoskeletal and Neurovascular Structures The underlying bones of the back are shown in Figure 3.18 and are described in detail in Chapter 2 (The Back). Details of the scapula were described earlier in this chapter. The general topography of the scapular region is shown in Figures 3.19 and 3.20. Figure 3.18 Bones of the back. Figure 3.19 Superficial and deep muscles of the back. Figure 3.20 Muscles, nerves, and blood vessels of the scapular region. Note the close relation of the axillary nerve to the shoulder joint. Quadrangular Space The quadrangular space is an intermuscular space, located immediately below the glenohumeral (shoulder) joint (see Fig. 3.20). It is bounded above by the subscapularis and teres minor muscles and the capsule of the shoulder joint and below by the teres major muscle. It is bounded medially by the long head of the triceps and laterally by the surgical neck of the humerus. The significance of the quadrangular space is that the axillary nerve and the posterior circumflex humeral vessels emerge through this space to reach their terminal destinations in the shoulder. Axilla The axilla, or armpit, is a pyramid-shaped space between the upper part of the arm and the side of the chest (Fig. 3.21). It forms an important passage for nerves, blood vessels, and lymph channels as they travel between the root of the neck to the upper limb. The upper end of the axilla, or apex, is directed into the root of the neck and is bounded in front by the clavicle, behind by the upper border of the scapula, and medially by the outer border of the first rib. The lower end, or base, is bounded in front by the anterior axillary fold (formed by the lower border of the pectoralis major muscle), behind by the posterior axillary fold (formed by the tendons of the latissimus dorsi and teres major muscles), and medially by the chest wall. Figure 3.21 Right axilla. A. Axillary inlet from above. B. Axillary walls. C. Axillary outlet. Axillary Walls The four walls of the axilla are constructed as follows: Anterior wall: By the pectoralis major, subclavius, and pectoralis minor muscles (Fig. 3.22; also see Figs. 3.11 through 3.13) Posterior wall: By the subscapularis, latissimus dorsi, and teres major muscles (Fig. 3.23; also see Figs. 3.11 through 3.13 and 3.22) Medial wall: By the upper four or five ribs and the intercostal spaces covered by the serratus anterior muscle (see Figs. 3.11 through 3.13, 3.22, and 3.23) Lateral wall: By the coracobrachialis and biceps brachii muscles in the bicipital groove of the humerus (see Figs. 3.12, 3.13, 3.22, and 3.23) Figure 3.22 Structures that form the walls of the axilla. The red arrow indicates the lateral wall. A. Anterior wall. B. Posterior wall. C. Medial wall. D. Lateral wall. The skin stretching between the anterior and posterior walls forms the base of the axilla (see Fig. 3.22). Details of the muscles forming the walls of the axilla are summarized later in this chapter in Tables 3.3 through 3.5.  The axilla contains the axillary artery and its branches, which supply blood to the upper limb; the axillary vein and its tributaries, which drain blood from the upper limb; and lymph vessels and lymph nodes, which drain lymph from the upper limb, the breast, and the skin of the trunk as far down as the level of the umbilicus. The brachial plexus, an important nerve network that innervates the upper limb, lies among these structures. The contents of the axilla are embedded in fat. Figure 3.23 Dissection of the right axilla. The pectoralis major and minor muscles and the clavipectoral fascia have been removed to display the underlying structures. Pectoralis Minor The pectoralis minor is a thin triangular muscle that lies deep to the pectoralis major (see Fig. 3.12). It arises from the third, fourth, and fifth ribs and runs upward and laterally to insert into the coracoid process of the scapula. Thus, it crosses the axilla and divides the area into three subregions (proximal, deep, and distal to the muscle) that are useful in describing the course of the axillary artery and the lymph drainage of the area (see the descriptions of the axillary artery and lymph drainage below). Clavipectoral Fascia The clavipectoral fascia is a strong sheet of connective tissue lying immediately deep to the pectoralis major muscle (see Figs. 3.12 and 3.22). Superiorly, it attaches to the clavicle. Inferiorly, it splits to enclose the subclavius and pectoralis minor muscles and then continues downward as the suspensory ligament of the axilla and joins the fascial floor of the armpit. The lateral pectoral nerve, cephalic vein, branches of the thoracoacromial artery, and lymphatic channels from the infraclavicular nodes pierce the clavipectoral fascia in order to make their superficial–deep connections. Arm The arm (upper arm; brachium) is the proximal segment of the upper limb from the shoulder to the elbow. Osseofascial Compartments The arm is enclosed in a sheath of deep fascia (Fig. 3.24; also see Chapter 1, Introduction). Two fascial intermuscular septa, one on the medial side and one on the lateral side, extend inward from this sheath and are attached to the medial and lateral supracondylar ridges of the humerus, respectively. In this way, the upper arm is divided into an anterior and a posterior osseofascial compartment, each having a set of muscles, nerves, and arteries (Figs. 3.25 through 3.27; also see Fig. 3.24 and Table 3.1). Also, these and additional structures pass through each compartment on route to more distal areas. Figure 3.24 Cross section of the upper arm just below the level of insertion of the deltoid muscle. Note the division of the arm into anterior and posterior compartments by the humerus and the medial and lateral intermuscular septa. Figure 3.25 Anterior view of the upper arm. The middle portion of the biceps brachii has been removed to show the musculocutaneous nerve lying in front of the brachialis. Figure 3.26 Anterior view of the upper arm showing the insertion of the deltoid and the origin and insertion of the brachialis. Figure 3.27 Posterior view of the upper arm. The lateral head of the triceps has been divided to display the radial nerve and the profunda artery in the spiral groove of the humerus. Table 3.1 Contents of Arm Osseofascial Compartments Structures Passing through Anterior Osseofascial Compartment The musculocutaneous nerve, median nerve, ulnar nerve, brachial artery, and basilic vein pass through this region. The radial nerve is present in the lower part of the compartment. Structures Passing through Posterior Osseofascial Compartment The radial nerve, ulnar nerve, and profunda brachii vessels pass through this region. Elbow and Cubital Fossa The elbow is the area connecting the arm with the forearm. The cubital fossa is a triangular depression that lies in the anterior aspect of the elbow (Figs. 3.28 and 3.29). This fossa is important because it conveys several major structures between the arm and forearm. Figure 3.28 The cubital fossa and anterior surface of the forearm in a young man. Figure 3.29 Right cubital fossa. Cubital Fossa Boundaries  Laterally: Brachioradialis muscle Medially: Pronator teres muscle Base: Imaginary line drawn between the two epicondyles of the humerus forming the base of the triangle Floor: Supinator muscle laterally; the brachialis muscle medially Roof: Skin and fascia, reinforced by the bicipital aponeurosis Cubital Fossa Contents The cubital fossa (see Fig. 3.29) contains the following structures, enumerated from the medial to the lateral side: the median nerve, the bifurcation of the brachial artery into the ulnar and radial arteries, the tendon of the biceps muscle, and the radial nerve and its deep branch. Forearm The forearm (lower arm; antebrachium) is the segment of the upper limb from the elbow to the wrist. Osseofascial Compartments The forearm is enclosed in a sheath of deep fascia, which is attached to the periosteum of the posterior subcutaneous border of the ulna (Fig. 3.30). The interosseous membrane (see Figs. 3.30, 3.33, and 3.35) is a strong ligamentous band that unites the shafts of the radius and the ulna and also provides additional surface area for the attachments of neighboring muscles. This wrapping sheet of deep fascia, together with the interosseous membrane and fibrous intermuscular septa, divides the forearm into three osseofascial compartments: anterior, lateral, and posterior. Each compartment contains a set of muscles, nerves, and arteries (Figs. 3.34 and 3.35 and Table 3.2; also see Figs. 3.30 through 3.33). Figure 3.30 Cross-section of the forearm at the level of insertion of the pronator teres muscle. Table 3.2 Contents of Forearm Osseofascial Compartments Figure 3.31 Anterior view of the forearm. The middle portion of the brachioradialis muscle has been removed to display the superficial branch of the radial nerve and the radial artery. Figure 3.32 Anterior view of the forearm. Most of the superficial muscles have been removed to display the flexor digitorum superficialis, median nerve, superficial branch of the radial nerve, and radial artery. Note that the ulnar head of the pronator teres separates the median nerve from the ulnar artery. Figure 3.33 Anterior view of the forearm showing the deep structures. Figure 3.34 Posterior view of the forearm. Parts of the extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris have been removed to show the deep branch of the radial nerve and the posterior interosseous artery. Figure 3.35 Posterior view of the forearm. The superficial muscles have been removed to display the deep structures. Wrist The wrist (carpus) is a complex of the eight small carpal bones that connect the forearm and hand (see Figs. 3.9 and 3.10). Before learning the anatomy of the hand, having a sound knowledge of the arrangement of the tendons, arteries, and nerves in the region of the wrist is essential. From a clinical standpoint, the wrist is a common site for injury. Flexor and Extensor Retinacula The flexor and extensor retinacula are strong bands of deep fascia that hold the long flexor and extensor tendons in position at the wrist. Flexor Retinaculum The flexor retinaculum is a thickening of deep fascia that holds the long flexor tendons in position at the wrist. It stretches across the front of the wrist and converts the concave anterior surface of the wrist into an osseofascial tunnel, the carpal tunnel, for the passage of the median nerve and the flexor tendons of the thumb and fingers (Figs. 3.36 through 3.38). It attaches medially to the pisiform bone and the hook of the hamate and laterally to the tubercle of the scaphoid and the trapezium bones. The attachment to the trapezium consists of superficial and deep parts and forms a synovial-lined tunnel for passage of the tendon of the flexor carpi radialis. The proximal border of the retinaculum corresponds to the distal transverse skin crease in front of the wrist and is continuous with the deep fascia of the forearm. The distal border is attached to the palmar aponeurosis (see Fig. 3.37). Figure 3.36 Cross section of the hand showing the relation of the tendons, nerves, and arteries to the flexor and extensor retinacula. Figure 3.37 Anterior view of the palm of the hand. The palmar aponeurosis has been left in position. Figure 3.38 Dissection of the front of the left forearm and hand showing the superficial structures. Extensor Retinaculum The extensor retinaculum is a thickening of deep fascia that stretches across the back of the wrist and holds the long extensor tendons in position (Figs. 3.39 and 3.40; also see Fig. 3.34). It converts the grooves on the posterior surface of the distal ends of the radius and ulna into six separate tunnels for the passage of the long extensor tendons. Each tunnel is lined with a synovial sheath, which extends proximal and distal to the retinaculum on the tendons. The tunnels are separated from one another by fibrous septa that extend from the deep surface of the retinaculum to the underlying bones (see Fig. 3.36). The retinaculum attaches medially to the pisiform bone and the hook of the hamate and laterally to the distal end of the radius. The proximal and distal borders of the retinaculum are continuous with the deep fascia of the forearm and hand, respectively. Figure 3.39 Dorsal surface of the hand showing the long extensor tendons and their synovial sheaths. Figure 3.40 Dissection of the dorsal surface of the right hand showing the long extensor tendons and the extensor retinaculum. Anterior Wrist Structures Recognizing the structures contained within the carpal tunnel versus those located outside the tunnel (i.e., which structures pass superficial versus deep to the flexor retinaculum) is a topic of notable concern in the wrist. The following structures pass superficial to the flexor retinaculum (outside the carpal tunnel), in medial to lateral sequence (see Fig. 3.36): Flexor carpi ulnaris tendon, ending on the pisiform bone (this tendon does not actually cross the flexor retinaculum but is included for the sake of completeness) Ulnar nerve, lying lateral to the pisiform bone Ulnar artery, lying lateral to the ulnar nerve Palmar cutaneous branch of the ulnar nerve Palmaris longus tendon (if present), passing to its insertion into the flexor retinaculum and the palmar aponeurosis Palmar cutaneous branch of the median nerve The following structures pass deep to the flexor retinaculum (within the carpal tunnel), from medial to lateral (Fig. 3.41; also see Fig. 3.36): Figure 3.41 Anterior view of the palm of the hand. The palmar aponeurosis and the greater part of the flexor retinaculum have been removed to display the superficial palmar arch, the median nerve, and the long flexor tendons. Segments of the tendons of the flexor digitorum superficialis have been removed to show the underlying tendons of the flexor digitorum profundus. Flexor digitorum superficialis tendons and, deep to these, the tendons of the flexor digitorum profundus (both groups of tendons share a common synovial sheath)  Median nerve Flexor pollicis longus tendon, surrounded by a synovial sheath Flexor carpi radialis tendon, going through a split in the flexor retinaculum (synovial sheath surrounds the tendon) Posterior Wrist Structures The following structures pass superficial to the extensor retinaculum, from medial to lateral (see Fig. 3.36): Dorsal (posterior) cutaneous branch of the ulnar nerve Basilic vein Cephalic vein Superficial branch of the radial nerve The following structures pass deep to the extensor retinaculum from medial to lateral, within the six extensor tunnels of the retinaculum: Extensor carpi ulnaris tendon, which grooves the posterior aspect of the head of the ulna Extensor digiti minimi tendon, situated posterior to the distal radioulnar joint Extensor digitorum and extensor indicis tendons, sharing a common synovial sheath and situated on the lateral part of the posterior surface of the radius Extensor pollicis longus tendon, winding around the medial side of the dorsal tubercle of the radius Extensor carpi radialis longus and brevis tendons, sharing a common synovial sheath and situated on the lateral part of the posterior surface of the radius Abductor pollicis longus and extensor pollicis brevis tendons, having separate synovial sheaths but sharing a common compartment Carpal Tunnel The carpus is deeply concave on its anterior surface and forms a bony gutter. The gutter is converted into a tunnel, the carpal tunnel, by the covering flexor retinaculum (see Fig. 3.36). The long flexor tendons to the fingers and thumb pass through the tunnel and are accompanied by the median nerve. The four separate tendons of the flexor digitorum superficialis muscle are arranged in anterior and posterior rows, those to the middle and ring fingers lying superficial to those of the index and little fingers. The four tendons diverge and become arranged on the same plane at the distal border of the flexor retinaculum (see Fig. 3.41). The tendons of the flexor digitorum profundus muscle are on the same plane as one another and lie deep to the superficialis tendons. All eight tendons of the flexor digitorum superficialis and profundus invaginate a common synovial sheath from the lateral side (see Fig. 3.36). This allows the arterial supply to the tendons to enter them from the lateral side. The tendon of the flexor pollicis longus muscle runs through the lateral part of the tunnel in its own synovial sheath. The median nerve passes deep to the flexor retinaculum in a narrow space between the tendons of the flexor digitorum superficialis and the flexor carpi radialis muscles. Clinical Notes Carpal Tunnel Syndrome The carpal tunnel is tightly packed with the long flexor tendons of the fingers, with their surrounding synovial sheaths, and with the median nerve (see Fig. 3.36). Any condition that significantly decreases the size of the carpal tunnel and compresses its contents is a carpal tunnel syndrome. See the Clinical Notes on the median nerve for further details. “Anatomic Snuffbox” The anatomic snuffbox is a small triangular skin depression on the posterolateral side of the wrist that is bounded medially by the tendon of the extensor pollicis longus and laterally by the tendons of the abductor pollicis longus and extensor pollicis brevis (see Figs. 3.34 and 3.105B,C). Its clinical importance lies in the fact that the scaphoid bone is most easily palpated here and that the pulsations of the radial artery can be felt here (see Fig. 3.105B). Hand The hand (manus), a very important organ, is located at the distal end of the upper limb. Much of the importance of the hand depends on the pincer-like action of the thumb, which enables us to grasp objects between the tips of the thumb and index finger. The anterior (ventral) side of the hand is its palmar (volar) surface. The posterior aspect is the dorsal surface. In identifying the individual digits, the thumb (pollux) is digit 1, with the other numbers following sequentially from lateral to medial. Skin The skin of the palm of the hand is thick and hairless. It is bound down to the underlying deep fascia by numerous fibrous bands. The skin shows many flexure creases at the sites of skin movement, which are not necessarily placed at the site of joints. Sweat glands are present in large numbers. The skin on the dorsum of the hand is thin, hairy, and freely mobile on the underlying tendons and bones. Deep Fascia The deep fascia of the wrist and palm is thickened to form the flexor retinaculum (described previously) and the palmar aponeurosis. Palmar Aponeurosis The palmar aponeurosis is triangular and occupies the central area of the palm (see Fig. 3.37). The apex of the palmar aponeurosis is attached to the distal border of the flexor retinaculum and receives the insertion of the palmaris longus tendon. The base of the aponeurosis divides at the bases of the fingers into four slips. Each slip divides into two bands, one passing superficially to the skin and the other passing deeply to the root of the finger. Here, each deep band divides into two, which diverge around the flexor tendons and finally fuse with the fibrous flexor sheath and the deep transverse ligaments. The medial and lateral borders of the palmar aponeurosis are continuous with the thinner deep fascia covering the hypothenar and thenar muscles. From each of these borders, fibrous septa pass deeply into the palm and take part in the formation of the palmar fascial spaces (see below). The function of the palmar aponeurosis is to give firm attachment to the overlying skin and so improve the grip and to protect the underlying tendons. Clinical Notes Dupuytren Contracture Dupuytren contracture is a localized thickening and contracture of the palmar aponeurosis, which limits hand function and may eventually disable the hand. It commonly starts near the root of the ring finger and draws that finger into the palm, flexing it at the metacarpophalangeal joint. Later, the condition involves the little finger in the same manner. In long-standing cases, the pull on the fibrous sheaths of these fingers results in flexion of the proximal interphalangeal joints. The distal interphalangeal joints are not involved and are actually extended by the pressure of the fingers against the palm. Surgical division of the fibrous bands followed by physiotherapy to the hand is the usual form of treatment. The alternative treatment of injection of the enzyme collagenase into the contracted bands of fibrous tissue has been shown to significantly reduce the contractures and improve mobility. Fascial Spaces of Palm Normally, the fascial spaces of the palm are potential spaces filled with loose connective tissue. Their boundaries are important clinically because they may limit the spread of infection in the palm.  The triangular palmar aponeurosis fans out from the distal border of the flexor retinaculum (see Fig. 3.37). From its medial border, a fibrous septum passes backward and is attached to the anterior border of the fifth metacarpal bone (Fig. 3.42C). Medial to this septum is a fascial compartment containing the three hypothenar muscles. From the lateral border of the palmar aponeurosis, a second fibrous septum passes obliquely backward to the anterior border of the third metacarpal bone. Usually, the septum passes between the long flexor tendons of the index and middle fingers. This second septum divides the palm into the thenar space, which lies lateral to the septum (and must not be confused with the fascial compartment containing the thenar muscles), and the midpalmar space, which lies medial to the septum. Proximally, the thenar and midpalmar spaces are closed off from the forearm by the walls of the carpal tunnel. Distally, the two spaces are continuous with the appropriate lumbrical canals (Fig. 3.42A). Figure 3.42 Palmar and pulp fascial spaces. A. Anterior view of the hand showing the positions of the thenar and midpalmar spaces and their continuities with the lumbrical canals. B. Sagittal section through a finger showing the pulp space and arterial supply to the distal phalanx. C. Transverse section through the hand showing the fascial spaces of the palm. The thenar space contains the first lumbrical muscle and lies deep to the long flexor tendons to the index finger and superficial to the adductor pollicis muscle (Fig. 3.42A,C). The midpalmar space contains the second, third, and fourth lumbrical muscles and lies posterior to the long flexor tendons to the middle, ring, and little fingers. It lies superficial to the interosseous muscles and the third, fourth, and fifth metacarpal bones. The lumbrical canal is a potential space surrounding the tendon of each lumbrical muscle and is normally filled with connective tissue. Proximally, it is continuous with one of the palmar spaces. Clinical Notes Fascial Spaces of Palm and Infection The fascial spaces of the palm (see Fig. 3.42A,C) are clinically important because they can become infected and distended with pus as a result of the spread of infection in acute suppurative tenosynovitis. Rarely, they can become infected after penetrating wounds such as falling on a dirty nail. Finger Pulp Spaces The deep fascia of the pulp of each finger fuses with the periosteum of the terminal phalanx just distal to the insertion of the long flexor tendons and closes off a fascial compartment known as the pulp space (see Fig. 3.42B). Each pulp space is subdivided by the presence of numerous septa, which pass from the deep fascia to the periosteum. The terminal branch of the digital artery that supplies the diaphysis of the terminal phalanx runs through the pulp space, which is filled with fat. The digital artery branch to the epiphysis of the distal phalanx does so proximal to the pulp space. Clinical Notes Pulp Space Infection (Felon) The pulp space of the fingers is a closed fascial compartment situated anterior to the terminal phalanx of each finger (see Fig. 3.42B). Infection of such a space is common and serious, occurring most often in the thumb and index finger. Bacteria are usually introduced into the space by pinpricks or sewing needles. Because each space is subdivided into numerous smaller compartments by fibrous septa, the accumulation of inflammatory exudate within these compartments causes the pressure in the pulp space to quickly rise. If the infection is left without decompression, infection of the terminal phalanx can occur. In children, the blood supply to the diaphysis of the phalanx passes through the pulp space, and pressure on the blood vessels could result in necrosis of the diaphysis. The proximally located epiphysis of this bone is saved because it receives its arterial supply just proximal to the pulp space. The close relationship of the proximal end of the pulp space to the digital synovial sheath accounts for the involvement of the sheath in the infectious process when the pulp space infection has been neglected. MUSCLES Pectoral Region The muscles and major neurovascular structures of the pectoral region are shown in Figures 3.11, 3.12, and 3.13. The muscles of the pectoral region are summarized in Table 3.3. Table 3.3 Pectoral Region Muscles aThe predominant nerve root supply is indicated by boldface type. Clinical Notes Absent Pectoralis Major Occasionally, parts of the pectoralis major muscle may be absent. The sternocostal origin is the most commonly missing part, and this causes weakness in adduction and medial rotation of the shoulder joint. Back and Scapular Region The superficial group of muscles of the back (Chapter 2, The Back: trapezius, latissimus dorsi, levator scapulae, rhomboid major, rhomboid minor) connects the shoulder girdle with the vertebral column. However, developmentally (except for the trapezius) and functionally, these are upper limb muscles and, as such, are included here (Table 3.4; also see Fig. 3.19). Table 3.4 Back Superficial Muscles aThe predominant nerve root supply is indicated by boldface type. The muscles of the scapular region connect the shoulder girdle with the upper part of the humerus and are largely concerned with abduction and rotation of the arm. The muscles and major neurovascular structures of the scapular region are shown in Figures 3.19 and 3.20. The muscles are summarized in Table 3.5. Table 3.5 Scapular Region Muscles aThe predominant nerve root supply is indicated by boldface type. Rotator Cuff The tendons of the subscapularis, supraspinatus, infraspinatus, and teres minor muscles are fused to the underlying capsule of the shoulder joint. Because of this relationship, these four muscles are referred to as the “rotator cuff.” The cuff plays a very important role in stabilizing the glenohumeral (shoulder) joint. The tone of these muscles assists in holding the head of the humerus in the glenoid cavity of the scapula during movements at the shoulder joint. The cuff lies on the anterior, superior, and posterior aspects of the joint. The cuff is deficient inferiorly, and this is a site of potential weakness. Clinical Notes Rotator Cuff Tendinitis Lesions of the rotator cuff are a common cause of pain in the shoulder region. Failure of the cuff is due to either wear or tear. Wear is age related. Inflammation or tearing is associated with excessive repetitive use. Overused overhead movements of the upper limb, such as seen in baseball pitchers, tennis players, and swimmers, may be the cause of tendinitis, although many cases appear spontaneously. The supraspinatus is the most commonly injured muscle in the rotator cuff. During abduction of the shoulder joint, the supraspinatus tendon is exposed to friction against the acromion (Fig. 3.43). Under normal conditions, the amount of friction is reduced to a minimum by the large subacromial bursa, which extends laterally beneath the deltoid. Degenerative changes in the bursa are followed by degenerative changes in the underlying supraspinatus tendon, and these may extend into the other tendons of the rotator cuff. Clinically, the condition is known as subacromial bursitis, supraspinatus tendinitis, or pericapsulitis. It is characterized by the presence of a spasm of pain in the middle range of abduction, when the diseased area impinges on the acromion. Extensive acute traumatic tears are best repaired surgically as soon as possible. Small chronic cuff injuries are best managed without surgery using nonsteroidal anti-inflammatory drugs and muscle exercises. Figure 3.43 Subacromial bursitis, supraspinatus tendinitis, or pericapsulitis showing the painful arc in the middle range of abduction, when the diseased area impinges on the lateral edge of the acromion. Supraspinatus Tendon Rupture In advanced cases of rotator cuff tendinitis, the necrotic supraspinatus tendon can become calcified or rupture. Rupture of the tendon seriously interferes with the normal abduction movement of the shoulder joint. Recall that the main function of the supraspinatus muscle is to hold the head of the humerus in the glenoid fossa at the commencement of abduction. The patient with a ruptured supraspinatus tendon is unable to initiate abduction of the arm. However, if the arm is passively assisted for the first 15° of abduction, the deltoid can then take over and complete the movement to a right angle. Arm The muscles and major neurovascular structures of the arm are shown in Figures 3.24 through 3.27. The muscles are summarized in Table 3.6. Table 3.6 Arm Muscles aThe predominant nerve root supply is indicated by boldface type. Osseofascial Compartments The muscles of the arm are organized in two osseofascial compartments, anterior and posterior. The muscles influence the shoulder and/or elbow joints, with the anterior compartment muscles acting mainly as flexors and the posterior compartment muscle producing mainly extension. The musculocutaneous nerve supplies the entire anterior compartment, whereas the radial nerve innervates the posterior compartment. Biceps Brachii Muscle The biceps brachii is a component of the anterior compartment of the arm. It is a powerful flexor of the elbow joint and a weak flexor of the shoulder joint. Additionally, the biceps brachii is a powerful supinator, especially during supination against resistance. You can test the supination action when using the right arm to twist a corkscrew into the cork or driving a screw into wood with a screwdriver. Interestingly, this test works only when using the right arm and not the left. Clinical Notes Biceps Brachii and Shoulder Joint Osteoarthritis The tendon of the long head of biceps is attached to the supraglenoid tubercle within the shoulder joint. Advanced osteoarthritic changes in the joint can lead to erosion and fraying of the tendon by osteophytic outgrowths, and rupture of the tendon can occur. Forearm The muscles and major neurovascular structures of the forearm are shown in Figures 3.30 through 3.35. The muscles are summarized in Tables 3.7 to 3.9. Table 3.7 Muscles of Anterior Forearm Osseofascial Compartment aThe predominant nerve root supply is indicated by boldface type. Table 3.8 Muscles of Lateral Forearm Osseofascial Compartment aThe predominant nerve root supply is indicated by boldface type. Table 3.9 Muscles of Posterior Forearm Osseofascial Compartment aThe predominant nerve root supply is indicated by boldface type. Osseofascial Compartments The muscles of the forearm are organized in three osseofascial compartments: anterior, lateral, and posterior. The muscles influence the elbow, wrist, and digits. The anterior compartment muscles produce mainly flexion or pronation, whereas the lateral and posterior compartment muscles produce mainly extension or supination. The median and ulnar nerves supply the anterior compartment, whereas the radial nerve innervates the lateral and posterior compartments. Anterior Osseofascial Compartment Muscles The muscles of the anterior osseofascial compartment are arranged in three groups: superficial, intermediate, and deep. Note that the superficial group muscles possess a common tendon of origin that is attached to the medial epicondyle of the humerus. Superficial group: Flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres Intermediate group: Flexor digitorum superficialis Deep group: Flexor digitorum profundus, flexor pollicis longus, and pronator quadratus Lateral Osseofascial Compartment Muscles The brachioradialis and extensor carpi radialis longus muscles are the two members of the lateral osseofascial compartment. Some authors regard this group as part of the posterior osseofascial compartment. Note that the brachioradialis is an exception to the general functional theme of the lateral and posterior forearm compartments in that it is a significant flexor of the elbow rather than an extensor. Posterior Osseofascial Compartment Muscles The muscles of the posterior osseofascial compartment are arranged in two groups: superficial and deep. The superficial group muscles possess a common tendon of origin that is attached to the lateral epicondyle of the humerus. Superficial group: Extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus  Deep group: Supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis Clinical Notes Forearm Compartment Syndrome The forearm compartments are tightly packed spaces with very little extra room. Any edema can cause secondary compression of the blood vessels; the veins are first affected and later the arteries. Soft tissue injury is a common cause, and early diagnosis is critical. Early signs include altered skin sensation (caused by ischemia of the sensory nerves passing through the compartment), pain disproportionate to any injury (caused by pressure on nerves within the compartment), pain on passive stretching of muscles that pass through the compartment (caused by muscle ischemia), tenderness of the skin over the compartment (a late sign caused by edema), and absence of capillary refill in the nail beds (caused by pressure on the arteries within the compartment). Once the diagnosis is made, the deep fascia must be incised surgically to decompress the affected compartment. A delay of as little as 4 hours can cause irreversible damage to the muscles. Volkmann’s Ischemic Contracture Volkmann’s ischemic contracture is a contracture of the muscles of the forearm that commonly follows fractures of the distal end of the humerus or fractures of the radius and ulna. In this syndrome, a localized segment of the brachial artery goes into spasm, reducing the arterial flow to the flexor and the extensor muscles so that they undergo ischemic necrosis. The flexor muscles are larger than the extensor muscles, and they are therefore the ones mainly affected. The muscles are replaced by fibrous tissue, which contracts, producing the deformity. An overtight cast usually causes the arterial spasm, but in some cases, the fracture itself may be responsible. The deformity can be explained only by understanding the anatomy of the region. Three types of deformity exist:  The long flexor muscles of the carpus and fingers are more contracted than the extensor muscles, and the wrist joint is flexed; the fingers are extended. If the wrist joint is extended passively, the fingers become flexed. The long extensor muscles to the fingers, which are inserted into the extensor expansion that is attached to the proximal phalanx, are greatly contracted; the metacarpophalangeal joints and the wrist joint are extended, and the interphalangeal joints of the fingers are flexed. Both the flexor and extensor muscles of the forearm are contracted. The wrist joint is flexed, the metacarpophalangeal joints are extended, and the interphalangeal joints are flexed. Absent Palmaris Longus The palmaris longus muscle may be absent on one or both sides of the forearm in about 10% of people. Others show variation in form, such as a centrally or distally placed muscle belly in the place of a proximal one. Because the muscle is relatively weak, its absence produces no disability. Tennis Elbow A partial tearing or degeneration of the origin of the superficial extensor muscles from the lateral epicondyle of the humerus causes tennis elbow. It is characterized by pain and tenderness over the lateral epicondyle of the humerus, with pain radiating down the lateral side of the forearm; it is common in tennis players and violinists. Stenosing Synovitis of Abductor Pollicis Longus and Extensor Pollicis Brevis Tendons As a result of repeated friction between these tendons and the styloid process of the radius, they sometimes become edematous and swell. Later, fibrosis of the synovial sheath produces a condition known as stenosing tenosynovitis in which movement of the tendons becomes restricted. Advanced cases require surgical incision along the constricting sheath. Extensor Pollicis Longus Tendon Rupture Rupture of this tendon can occur after fracture of the distal third of the radius. Roughening of the dorsal tubercle of the radius by the fracture line can cause excessive friction on the tendon, which can then rupture. Rheumatoid arthritis can also cause rupture of this tendon. Hand The muscles and major neurovascular structures of the hand are shown in Figures 3.44 and 3.45 (also see Figs. 3.34, 3.35, and 3.37 through 3.41). The compartments of the hand are outlined in Table 3.10. The intrinsic (small) muscles are summarized in Table 3.11. Figure 3.44 Anterior view of the palm of the hand. The long flexor tendons have been removed from the palm, but their method of insertion into the fingers is shown. Figure 3.45 Anterior view of the palm of the hand showing the deep palmar arch and the deep terminal branch of the ulnar nerve. The interossei are also shown. Table 3.10 Osseofascial Compartments of Hand Table 3.11 Intrinsic Hand Muscles aThe predominant nerve root supply is indicated by boldface type. Osseofascial Compartments The muscles of the hand can be described as either extrinsic or intrinsic muscles. Extrinsic muscles are those that originate outside of the hand proper (in the forearm) and insert within the hand via long tendons. Intrinsic muscles (small muscles) of the hand are those that both originate and insert within the hand. Both the extrinsic and intrinsic muscles are organized in five osseofascial compartments within the hand. Four compartments (thenar, hypothenar, central [midpalmar], and interosseous) are located in the palmar aspect of the hand. One compartment (dorsal/extensor) is related to the dorsum of the hand. Fibrous Flexor Sheaths The anterior surface of each finger, from the head of the metacarpal to the base of the distal phalanx, is provided with a strong fibrous sheath that is attached to the sides of the phalanges (Fig. 3.46; also see Fig. 3.44). The proximal end of the fibrous sheath is open, whereas the distal end of the sheath is closed and is attached to the base of the distal phalanx. The sheath and the bones form a blind tunnel, which contains the flexor tendons of the finger. In the thumb, the osseofibrous tunnel contains the tendon of the flexor pollicis longus. In the case of the four medial fingers, the tunnel is occupied by the tendons of the flexor digitorum superficialis and profundus (see Fig. 3.46B). The fibrous sheath is thick over the phalanges but thin and lax over the joints. Figure 3.46 Fibrous and synovial flexor sheaths in the hand. A. Anterior view of the palm of the hand. B. Cross section of a finger. Synovial Flexor Sheaths In the hand, the tendons of the flexor digitorum superficialis and profundus muscles invaginate a common synovial sheath from the lateral side (see Fig. 3.36). The medial part of this common sheath extends distally without interruption on the tendons of the little finger (see Fig. 3.46A). The lateral part of the sheath stops abruptly on the middle of the palm, and the distal ends of the long flexor tendons of the index, the middle, and the ring fingers acquire digital synovial sheaths as they enter the fingers. The flexor pollicis longus tendon has its own synovial sheath that passes into the thumb. These sheaths allow the long tendons to move smoothly, with a minimum of friction, beneath the flexor retinaculum and the fibrous flexor sheaths. The synovial sheath of the flexor pollicis longus (sometimes referred to as the radial bursa) communicates with the common synovial sheath of the superficialis and profundus tendons (sometimes referred to as the ulnar bursa) at the level of the wrist in about 50% of subjects. The vincula longa and brevia are small vascular f