CHAPTER 1 Introduction to the Upper Limb The upper limb is the organ of the body, responsible for manual activities. It is freely movable, especially its distal segment the hand, which is adapted for grasping and manipulating the objects. A brief description of comparative anatomy of the limbs would facilitate understanding of their structure and function. All the terrestrial vertebrates possess four limbs-a pair of forelimbs and a pair of hindlimbs. In quadrupeds such as dogs and buffaloes, both forelimbs and hindlimbs are evolved for transmission of body weight and locomotion. In human beings, due to evolution of erect posture, the function of weight bearing and locomotion is performed only by the hind limbs (lower limbs), while upper limbs are spared for prehensile/manipulative activities, such as grasping, holding, picking, etc. (Fig. 1.1). There are three types of grips: (a) power grip, (b) hook grip, and (c) precision grip. The power and hook grips are primitive in nature, hence found in higher primates. The precision grip is characteristic of human beings hence only humans can properly hold a pen, pencil, needles, instruments, etc. As a result, human beings could make advancements in arts, craft, and technology, of course, with the help of intelligence. To suit the prehensile activities, the following changes took place in the upper limbs of humans during evolution: 1. Appearance of joints permitting rotatory movements of the forearm, viz. supination and pronation. 2. Addition of clavicle to act as a strut and keep upper limb away from the body for prehension. 3. Rotation of thumb to 90° for opposition. 4. Suitable changes for free mobility of the fingers and hand. N.B. The human hand with its digits can perform complex skilled movements under the control of the brain. Hence man is considered as the master mechanic of the animal world. The disabling effects of an injury to the upper limb, particularly B Hindlimbs Forelimbs Upper limb (forelimb) Lower limbs (hindlimbs) Fig. 1.1 Position of limbs: A, in quadrupeds; B, in humans.2 Textbook of Anatomy: Upper Limb and Thorax that of hand is far more than the extent of an injury. Therefore, a sound understanding of its structure and functions is of great clinical significance the ultimate aim of treating any ailment of the upper limb being to restore its function. The upper limbs are connected to the trunk by a pectoral girdle. The limb girdle is defined as the bones which connect the limbs to the axial skeleton. The pectoral girdle is composed of two bones - scapula and clavicle. The scapula is connected to the clavicle by the acromioclavicular joint, and the clavicle is attached to the axial skeleton by the sternoclavicular joint. The pectoral girdle is not a complete girdle because it is attached to the axial skeleton only anteriorly. The primary function of the pectoral girdle is to provide attachment to numerous muscles, which move the arm and forearm. It is not weight bearing and is, therefore, more delicate as compared to the pelvic girdle. Note that pelvic girdle is a complete girdle. N.B. Only one small joint (sternoclavicular joint) connects the skeleton of upper limb to the rest of the skeleton of the body. Shoulder Clavicle Scapula (brachium) Arm Humerus PARTS OF THE UPPER LIMB For descriptive purposes, the upper limb is divided into the following four parts (Fig. 1.2): 1. Shoulder. 2. Arm or brachium. 3. Forearm or antebrachium. Forearm (antebrachium) Radius Ulna 4. Hand. The shoulder region includes: (a) axilla or armpit, (b) scapular region or parts around the scapula (shoulder blade), and (c) pectoral or breast region on the front of the chest. The bones of the shoulder region are the clavicle (collar bone) and the scapula (shoulder blade). They articulate with each other at the acromioclavicular joint and form the shoulder girdle. The shoulder girdle articulates with the rest of the skeleton of the body only at the small sternoclavicular joint. The arm is the part of the upper limb between the shoulder and elbow (or cubitus). The bone of the arm is humerus, which articulates with the scapula at the shoulder joint and upper ends of radius and ulna at the elbow joint. The forearm is the part of the upper limb between the elbow and the wrist. The bones of the forearm are radius and ulna. These bones articulate with humerus at the elbow joint and with each other forming radio-ulnar joints. The hand (or manus) consists of the following parts: (a) wrist or carpus, (b) hand proper (or metacarpus), and (c) digits (thumb and fingers). Hand Carpus (wrist) Metacarpus Phalanges Fig. 1.2 Parts of the upper limb. The wrist consists of eight carpal bones arranged in two rows, each consisting of four bones. The carpal bones articulate (a) with each other at intercarpal joints, (b) proximally with radius forming radio-carpal wrist joint, and (c) distally with metacarpal bones at carpometacarpal joints.Table 1.1 Parts of the upper limb Subdivisions Shoulder region Pectoral region Axilla Scapular region Arm Forearm Hand Wrist (carpus) Hand proper (metacarpus) Digits The hand proper consists of five metacarpal bones numbered one to five from lateral to medial side in anatomical position. They articulate (a) proximally with distal row of carpal bones forming carpometacarpal joints, (b) with each other forming intermetacarpal joints, and (c) distally with proximal phalanges forming metacarpophalangeal joints. The digits are five and numbered 1 to 5 from lateral to medial side. The first digit is called thumb and remaining four digits are fingers. Each digit is supported by three short long bones the phalanges except thumb, which is supported by only two phalanges. The phalanges form metacarpophalangeal joints with metacarpals and interphalangeal joints with one another. The first carpometacarpal joint has a separate joint cavity hence movements of thumb are much more free than that of any digit/finger. N.B. The functional value of thumb is immense. For example, in grasping, the functional value of thumb is equal to other four digits/fingers. Therefore, loss of thumb alone is as disabling as the loss of all four fingers. The subdivisions, bones and joints of different parts of the upper limb are summarized in Table 1.1. COMPARISON AND CONTRAST BETWEEN THE UPPER AND LOWER LIMBS Both the upper and lower limbs are built on the same basic principle. Each limb is made up of two portions: proximal and distal. The proximal part is called limb girdle and attaches the limb to the trunk. The distal part is free and consists of proximal, middle, and distal segments, which are referred to Joints Bones Clavicle Scapula Part Humerus Radius Ulna Carpal bones Metacarpal bones Phalanges Sternoclavicular Acromioclavicular Shoulder Elbow Radio-ulnar Wrist/radio-carpal Intercarpal Carpometacarpal Intermetacarpal Metacarpophalangeal Proximal and distal interphalangeal as arm, forearm, and hand respectively in the upper limb, and thigh, leg, and foot respectively in the lower limb. The homologous parts of the upper and lower limbs are enumerated in Table 1.2. A short account of the development of the limbs further makes it easier to understand the differences between the upper and lower limbs (Fig. 1.3). The development of upper and lower limbs begins in the 4th week of intrauterine life (IUL). A pair of small elevations appears on the ventrolateral aspect of the embryo called limb buds. The anterior pair of the upper limb buds appears opposite the lower cervical segments. The posterior pair of lower limb buds appears 3 or 4 days later at the level of lumbar and upper sacral segments. Thus during an early stage of development all the four limbs appear as paired limb buds. First they are simple flipper-like appendages so that the upper and lower limbs are similar in their appearance. Each has dorsal and ventral surfaces, and preaxial and postaxial borders. The preaxial border faces towards the head. Later in Table 1.2 Homologous parts of the upper and lower limbs Upper limb Shoulder/pectoral girdle Shoulder joint Arm Elbow joint Forearm Wrist joint Hand (a) Carpus (b) Metacarpus (c) Fingers* Lower limb Hip girdle/pelvic girdle Hip joint Thigh Knee joint Leg Ankle joint Foot (a) Tarsus (b) Metatarsus (c) Toes* *First digit in hand is termed thumb and first digit in foot is termed great toe.4 Textbook of Anatomy: Upper Limb and Thorax Upper limb bud D 90° lateral rotation Thumb Thumb Lower limb bud Big toe 90° medial rotation Big toe Fig. 1.3 Development of the limbs. Table 1.3 Differences between the upper and lower limbs Upper limb Function Bones Joints Prehension (i.e., manipulation of objects by grasping) Smaller and weaker Smaller and less stable Muscles Girdle Smaller and attached to smaller bony areas Antigravity muscles less developed Pectoral girdle (a) Made up of two bones, clavicle and scapula (b) No articulation with vertebral column (c) Articulation with axial skeleton is very small through sternoclavicular joint Preaxial border Faces laterally Lower limb Locomotion and transmission of weight Larger and stronger Larger and more stable Larger and attached to larger bony areas Antigravity muscles more developed Pelvic girdle (a) Made up of single bone, the hip bone* (b) Articulates with vertebral column (c) Articulation with axial skeleton is large, through sacroiliac joint Faces medially *The hip bone essentially consists of three components: ilium, ischium, and pubis, which later fuse to form a single bone. the development, the ends of limb buds become expanded and flattened to form the hand and foot plates in which the digits develop. The digits nearest to the preaxial border are thumb and big toe in the upper and lower limbs, respectively. The limbs then rotate. The lower limb buds rotate medially through 90 deg so that their preaxial border faces medially and their extensor surface faces forwards. The upper limb buds on the other hand rotate laterally through 90 deg so that their preaxial border faces laterally their extensor surface faces backwards. The differences between the upper and lower limbs are listed in Table 1.3. TRANSMISSION OF FORCE IN THE UPPER LIMB (Fig. 1.4) The pectoral girdle on each side consists of two bones: clavicle and scapula, only clavicle is attached to the rest of skeleton by a small joint-the sternoclavicular joint. The two bones of girdle are joined together by even smaller joint, the acromioclavicular joint. The clavicle is attached to the scapula by a strong coracoclavicular ligament (strongest ligament in the upper limb), and the clavicle is anchored to the 1st costal cartilage by the costoclavicular ligament.Coracoclavicular ligament Acromioclavicular joint Clavicle Sternoclavicular joint Costoclavicular ligament Scapula Humerus Humero-ulnar joint Radius Ulna Interosseous membrane Fig. 1.4 Transmission of force in the upper limb. Forces of the upper limb are transmitted to the axial skeleton by clavicle through costoclavicular ligament and sternoclavicular joint. The lines of force transmission in the upper limb are shown in Flowchart 1.1. BONES OF THE UPPER LIMB They are already described with parts of the upper limb (for details see Page 2). MUSCLES OF THE UPPER LIMB The muscles of upper limb include (a) the muscles that attach the limb and girdle to the body and (b) the muscles of arm, forearm, and hand. The deltoid muscle covers the shoulder like a hood and is commonly used for intramuscular injections. The arm and forearm are invested in the deep fascia like a sleeve and are divided into anterior and posterior compartments by intermuscular septa. The muscles of anterior and posterior compartments mainly act synergistically to carry out specific functions. The muscles of anterior compartment are mainly flexors and those of posterior compartment extensors. The muscles of hand are responsible for its various skilled movements such as grasping, etc. NERVES OF THE UPPER LIMB (Fig. 1.5) The nerve supply to the upper limb is derived from the brachial plexus (formed by ventral rami of C5 to C8 and T1 spinal nerves). The five main branches of brachial plexus are axillary, musculocutaneous, median, ulnar, and radial nerves. The axillary nerve supplies the deltoid and teres minor muscles. Sternoclavicular joint and costoclavicular ligament Axial skeleton Clavicle Coracoclavicular ligament Humerus Shoulder joint Scapula Radius Interosseous membrane Elbow joint Wrist joint Hand Ulna 罩 Force Flowchart 1.1 Lines of force transmission in the upper limb.Musculocutaneous nerve Radial nerve Median nerve Ulnar nerve Deep branch of radial nerve (posterior interosseous nerve) Superficial branch of radial nerve (superficial radial nerve) Axillary nerve Radial nerve Ulnar nerve Deep branch of radial nerve (posterior interosseous nerve) Fig. 1.5 Main nerves of the upper limb. A, anterior aspect; B, posterior aspect. The musculocutaneous, median, and ulnar nerves supply the muscles of anterior (flexor) compartments of the arm and forearm. The radial nerve supplies the muscles of the posterior (extensor) compartments of the arm and forearm. N.B. All the intrinsic muscles of the hand are supplied by the ulnar nerve except muscles of thenar eminence and first two lumbricals. ARTERIES OF THE UPPER LIMB (Fig. 1.6) The blood to the upper limb is supplied by four main arteries: axillary, brachial, radial, and ulnar. The axillary is the continuation of subclavian artery. At the lower border of the teres major muscle its name is changed to brachial artery. The brachial artery continues down the arm and just distal to the elbow joint, it divides into radial and ulnar arteries, which follow the bones, after which they are named. In the hand, radial artery terminates by forming the deep palmar arch and ulnar artery terminates by forming the superficial palmar arch. The axillary artery supplies the shoulder region. The brachial artery supplies the anterior and posterior compartments of the arm. The radial and ulnar arteries supply the lateral and medial parts of the forearm, respectively.Subclavian artery- Common carotid artery Brachiocephalic artery/trunk Axillary artery Profunda brachii artery Brachial artery Radial artery Ulnar artery Deep palmar arch Superficial palmar arch Fig. 1.6 Arteries of the upper limb. VEINS OF THE UPPER LIMB The deep veins of the upper limb follow the arteries and run superiorly towards the axilla, where axillary vein travels superiorly and becomes subclavian vein at the outer border of the 1st rib. The subclavian vein continues towards the root of the neck where it joins the internal jugular vein to form the brachiocephalic vein. The two brachiocephalic veins (right and left) join each other to form superior vena cava, which drains into the heart. The superficial veins of the upper limb originate from the dorsal venous arch of the hand. The lateral end of the dorsal venous arch forms the cephalic vein, which runs along the lateral aspect of the upper limb and terminates into the axillary vein in the axilla. The medial end of the dorsal venous arch forms the basilic vein, which ascends along the medial aspect of the upper limb and empties into the axillary vein as well. Anterior to the elbow, the cephalic vein is connected to the basilic vein via the median cubital vein. LYMPHATICS OF THE UPPER LIMB The lymphatics of the upper limb originate in the hand. The superficial lymph vessels follow the superficial veins. The deep lymph vessels follow the deep arteries (viz. radial, ulnar, and brachial) and pass superiorly to the axilla where they drain into the axillary lymph nodes.Clinical correlation Injuries of the upper limb: The human upper limb is meant for prehension, i. e., grasping, and not for locomotion and transmission of weight. The mechanism of grasping is provided by hand with the four fingers flexing against the opposable thumb. The upper limb is therefore light built, i.e., its bones are smaller and weaker, joints are smaller and less stable, etc. Hence, it is more prone to injuries such as dislocation, fractures, etc. Dislocations: The common dislocations in the upper limb are dislocations of shoulder joint (most commonly dislocated joint in the body), elbow joint, and lunate bone of the hand. Fractures: The common fractures in the upper limb are fracture of clavicle (most commonly fractured bone in the body), humerus, radius, and scaphoid. The scaphoid is the most commonly fractured bone of the hand. Nerve injuries: The common nerve injuries in the upper limb are injuries of brachial plexus, median nerve, radial nerve, and ulnar nerve. The compression of median nerve at wrist is most common peripheral neuropathy in the body. The three major nerves of the upper limb (e.g., radial, median, and ulnar) have predilection of involvement in leprosy. The ulnar nerve can be easily palpated behind the medial epicondyle of the humerus. Sites for the intramuscular and intravenous injections: The intramuscular injection is most commonly given in the shoulder region in deltoid muscle; intravenous injection is most commonly given in the superficial veins in front of elbow and the dorsum of hand. Sites for feeling arterial pulsations: The arterial pulsation is most commonly felt and auscultated on the medial side of the front of elbow for recording of blood pressure. The arterial pulse is most commonly felt on the lateral side of the front of distal forearm of recording pulse rate.Introduction to the Upper Limb 9 Golden Facts to Remember Most important function of hand Most important feature of human hand Only point of bony contact between the upper limb and chest Part of the upper limb having largest representation in the brain Most important digit of the hand Prehension (i.e., grasping) Opposition of thumb and precision grip Sternoclavicular joint Hand Thumb1.

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