Textbook of Anatomy: Upper Limb and Thorax (Volume I) PDF

TEXTBOOK OF ANATOMY UPPER LIMB AND THORAX TEXTBOOK OF ANATOMY UPPER LIMB AND THORAX Volume I Second Edition Vishram Singh, MS, PhD Professor and Head, Department of Anatomy Pr...

TEXTBOOK OF ANATOMY UPPER LIMB AND THORAX TEXTBOOK OF ANATOMY UPPER LIMB AND THORAX Volume I Second Edition Vishram Singh, MS, PhD Professor and Head, Department of Anatomy Professor-in-Charge, Medical Education Unit Santosh Medical College, Ghaziabad Editor-in-Chief, Journal of the Anatomical Society of India Member, Academic Council and Core Committee PhD Course, Santosh University Member, Editorial Board, Indian Journal of Otology Medicolegal Advisor, ICPS, India Consulting Editor, ABI, North Carolina, USA Formerly at: GSVM Medical College, Kanpur King George’s Medical College, Lucknow Al-Arab Medical University, Benghazi (Libya) All India Institute of Medical Sciences, New Delhi ELSEVIER A division of Reed Elsevier India Private Limited Textbook of Anatomy: Upper Limb and Thorax, Volume I, 2e Vishram Singh © 2014 Reed Elsevier India Private Limited First edition 2010 Second edition 2014 All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the Publisher. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). ISBN: 978-81-312-3729-8 e-book ISBN: 978-81-312-3625-3 Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. With respect to any drug or pharmaceutical products identified, readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose or formula, the method and duration of administration, and contraindications. It is the responsibility of practitioners, relying on their own experience and knowledge of their patients, to make diagnoses, to determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Please consult full prescribing information before issuing prescription for any product mentioned in this publication. The Publisher Published by Reed Elsevier India Private Limited Registered Office: 305, Rohit House, 3 Tolstoy Marg, New Delhi-110 001 Corporate Office: 14th Floor, Building No. 10B, DLF Cyber City, Phase II, Gurgaon-122 002, Haryana, India Senior Project Manager-Education Solutions: Shabina Nasim Content Strategist: Dr Renu Rawat Project Coordinator: Goldy Bhatnagar Copy Editor: Shrayosee Dutta Senior Operations Manager: Sunil Kumar Production Manager: NC Pant Production Executive: Ravinder Sharma Graphic Designer: Milind Majgaonkar Typeset by Chitra Computers, New Delhi Printed and bound at Thomson Press India Ltd., Faridabad, Haryana  Dedicated to My Mother Late Smt Ganga Devi Singh Rajput an ever guiding force in my life for achieving knowledge through education My Wife Mrs Manorama Rani Singh for tolerating my preoccupation happily during the preparation of this book My Children Dr Rashi Singh and Dr Gaurav Singh for helping me in preparing the manuscript My Teachers Late Professor (Dr) AC Das for inspiring me to be multifaceted and innovative in life Professor (Dr) A Halim for imparting to me the art of good teaching My Students, Past and Present for appreciating my approach to teaching anatomy and transmitting the knowledge through this book  Preface to the Second Edition It is with great pleasure that I express my gratitude to all students and teachers who appreciated, used, and recommended the first edition of this book. It is because of their support that the book was reprinted three times since its first publication in 2009. The huge success of this book reflects appeal of its clear, unclustered presentation of the anatomical text supplemented by perfect simple line diagrams, which could be easily drawn by students in the exam and clinical correlations providing the anatomical, embryological, and genetic basis of clinical conditions seen in day-to-day life in clinical practice. Based on a large number of suggestions from students and fellow academicians, the text has been extensively revised. Many new line diagrams and halftone figures have been added and earlier diagrams have been updated. I greatly appreciate the constructive suggestions that I received from past and present students and colleagues for improvement of the content of this book. I do not claim to absolute originality of the text and figures other than the new mode of presentation and expression. Once again, I whole heartedly thank students, teachers, and fellow anatomists for inspiring me to carry out the revision. I sincerely hope that they will find this edition more interesting and useful than the previous one. I would highly appreciate comments and suggestions from students and teachers for further improvement of this book. “To learn from previous experience and change accordingly, makes you a successful man.” Vishram Singh  Preface to the First Edition This textbook on upper limb and thorax has been carefully planned for the first year MBBS students. It follows the revised anatomy curriculum of the Medical Council of India. Following the current trends of clinically-oriented study of Anatomy, I have adopted a parallel approach – that of imparting basic anatomical knowledge to students and simultaneously providing them its applied aspects. To help students score high in examinations the text is written in simple language. It is arranged in easily understandable small sections. While anatomical details of little clinical relevance, phylogenetic discussions and comparative analogies have been omitted, all clinically important topics are described in detail. Brief accounts of histological features and developmental aspects have been given only where they aid in understanding of gross form and function of organs and appearance of common congenital anomalies. The tables and flowcharts summarize important and complex information into digestible knowledge capsules. Multiple choice questions have been given chapter-by-chapter at the end of the book to test the level of understanding and memory recall of the students. The numerous simple 4-color illustrations further assist in fast comprehension and retention of complicated information. All the illustrations are drawn by the author himself to ensure accuracy. Throughout the preparation of this book one thing I have kept in mind is that anatomical knowledge is required by clinicians and surgeons for physical examination, diagnostic tests, and surgical procedures. Therefore, topographical anatomy relevant to diagnostic and surgical procedures is clinically correlated throughout the text. Further, Clinical Case Study is provided at the end of each chapter for problem-based learning (PBL) so that the students could use their anatomical knowledge in clinical situations. Moreover, the information is arranged regionally since while assessing lesions and performing surgical procedures, the clinicians encounter region-based anatomical features. Due to propensity of fractures, dislocations and peripheral nerve lesions in the upper limb there is in-depth discussion on joints and peripheral nerves. As a teacher, I have tried my best to make the book easy to understand and interesting to read. For further improvement of this book I would greatly welcome comments and suggestions from the readers. Vishram Singh  Acknowledgments At the outset, I express my gratitude to Dr P Mahalingam, CMD; Dr Sharmila Anand, DMD; and Dr Ashwyn Anand, CEO, Santosh University, Ghaziabad, for providing an appropriate academic atmosphere in the university and encouragement which helped me in preparing this book. I am also thankful to Dr Usha Dhar, Dean Santosh Medical College for her cooperation. I highly appreciate the good gesture shown by Dr PK Verma, Dr Ruchira Sethi, Dr Deepa Singh, and Dr Preeti Srivastava for checking the final proofs. I sincerely thank my colleagues in the Department, especially Professor Nisha Kaul and Dr Ruchira Sethi for their assistance. I gratefully acknowledge the feedback and support of fellow colleagues in Anatomy, particularly,  Professors AK Srivastava (Head of the Department) and PK Sharma, and Dr Punita Manik, King George’s Medical College, Lucknow.  Professor NC Goel (Head of the Department), Hind Institute of Medical Sciences, Barabanki, Lucknow.  Professor Kuldeep Singh Sood (Head of the Department), SGT Medical College, Budhera, Gurgaon, Haryana.  Professor Poonam Kharb, Sharda Medical College, Greater Noida, UP.  Professor TC Singel (Head of the Department), MP Shah Medical College, Jamnagar, Gujarat.  Professor TS Roy (Head of the Department), AIIMS, New Delhi.  Professors RK Suri (Head of the Department), Gayatri Rath, and Dr Hitendra Loh, Vardhman Mahavir Medical College and Safdarjang Hospital, New Delhi.  Professor Veena Bharihoke (Head of the Department), Rama Medical College, Hapur, Ghaziabad.  Professors SL Jethani (Dean and Head of the Department), and RK Rohtagi, Dr Deepa Singh and Dr Akshya Dubey, Himalayan Institute of Medical Sciences, Jolly Grant, Dehradun.  Professors Anita Tuli (Head of the Department), Shipra Paul, and Shashi Raheja, Lady Harding Medical College, New Delhi.  Professor SD Joshi (Dean and Head of the Department), Sri Aurobindo Institute of Medical Sciences, Indore, MP. Lastly, I eulogize the patience of my wife Mrs Manorama Rani Singh, daughter Dr Rashi Singh, and son Dr Gaurav Singh for helping me in the preparation of this manuscript. I would also like to acknowledge with gratitude and pay my regards to my teachers Prof AC Das and Prof A Halim and other renowned anatomists of India, viz. Prof Shamer Singh, Prof Inderbir Singh, Prof Mahdi Hasan, Prof AK Dutta, Prof Inder Bhargava, etc. who inspired me during my student life. I gratefully acknowledge the help and cooperation received from the staff of Elsevier, a division of Reed Elsevier India Pvt. Ltd., especially Ganesh Venkatesan (Director Editorial and Publishing Operations), Shabina Nasim (Senior Project Manager- Education Solutions), Goldy Bhatnagar (Project Coordinator), and Shrayosee Dutta (Copy Editor). Vishram Singh  Contents Preface to the Second Edition vii Preface to the First Edition ix Acknowledgments xi Chapter 1 Introduction to the Upper Limb 1 Chapter 2 Bones of the Upper Limb 10 Chapter 3 Pectoral Region 34 Chapter 4 Axilla (Armpit) 48 Chapter 5 Back of the Body and Scapular Region 58 Chapter 6 Shoulder Joint Complex (Joints of Shoulder Girdle) 72 Chapter 7 Cutaneous Innervation, Venous Drainage and Lymphatic Drainage of the Upper Limb 83 Chapter 8 Arm 92 Chapter 9 Forearm 105 Chapter 10 Elbow and Radio-ulnar Joints 126 Chapter 11 Hand 137 Chapter 12 Joints and Movements of the Hand 161 Chapter 13 Major Nerves of the Upper Limb 172 Chapter 14 Introduction to Thorax and Thoracic Cage 185 Chapter 15 Bones and Joints of the Thorax 196 Chapter 16 Thoracic Wall and Mechanism of Respiration 211 Chapter 17 Pleural Cavities 227 Chapter 18 Lungs (Pulmones) 234 Chapter 19 Mediastinum 249 xiv Contents Chapter 20 Pericardium and Heart 256 Chapter 21 Superior Vena Cava, Aorta, Pulmonary Trunk, and Thymus 283 Chapter 22 Trachea and Esophagus 292 Chapter 23 Thoracic Duct, Azygos and Hemiazygos Veins, and Thoracic Sympathetic Trunks 302 Multiple Choice Questions 311 Index 325  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 forelimbs and a pair of hindlimbs. In quadrupeds such as Hindlimbs dogs and buffaloes, both forelimbs and hindlimbs are A 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 Upper limb humans can properly hold a pen, pencil, needles, (forelimb) 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 Lower limbs (hindlimbs) hand. N.B. The human hand with its digits can perform complex skilled movements under the control of the brain. Hence man B is considered as the master mechanic of the animal world. The disabling effects of an injury to the upper limb, particularly 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 Clavicle ailment of the upper limb being to restore its function. Shoulder 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 Scapula 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, Arm (brachium) more delicate as compared to the pelvic girdle. Note that Humerus 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. PARTS OF THE UPPER LIMB For descriptive purposes, the upper limb is divided into the following four parts (Fig. 1.2): 1. Shoulder. Ulna Forearm Radius 2. Arm or brachium. (antebrachium) 3. Forearm or antebrachium. 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 Carpus (wrist) chest. The bones of the shoulder region are the clavicle (collar Metacarpus bone) and the scapula (shoulder blade). They articulate with each other at the acromioclavicular joint and form the Hand shoulder girdle. The shoulder girdle articulates with the rest Phalanges 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 Fig. 1.2 Parts of the upper limb. 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 The wrist consists of eight carpal bones arranged in two ulna. These bones articulate with humerus at the elbow joint rows, each consisting of four bones. The carpal bones and with each other forming radio-ulnar joints. articulate (a) with each other at intercarpal joints, The hand (or manus) consists of the following parts: (b) proximally with radius forming radio-carpal wrist (a) wrist or carpus, (b) hand proper (or metacarpus), and joint, and (c) distally with metacarpal bones at (c) digits (thumb and fingers). carpometacarpal joints.  Introduction to the Upper Limb 3 Table 1.1 Parts of the upper limb Part Subdivisions Bones Joints Shoulder region Pectoral region Clavicle Sternoclavicular Axilla Scapula Acromioclavicular Scapular region Arm — Humerus Shoulder Forearm — Radius Elbow Ulna Radio-ulnar Hand Wrist (carpus) Carpal bones – Wrist/radio-carpal – Intercarpal Hand proper (metacarpus) Metacarpal bones – Carpometacarpal – Intermetacarpal Digits Phalanges – Metacarpophalangeal – Proximal and distal interphalangeal The hand proper consists of five metacarpal bones as arm, forearm, and hand respectively in the upper limb, numbered one to five from lateral to medial side in and thigh, leg, and foot respectively in the lower limb. The anatomical position. They articulate (a) proximally with homologous parts of the upper and lower limbs are distal row of carpal bones forming carpometacarpal enumerated in Table 1.2. joints, (b) with each other forming intermetacarpal joints, A short account of the development of the limbs further and (c) distally with proximal phalanges forming makes it easier to understand the differences between the metacarpophalangeal joints. upper and lower limbs (Fig. 1.3). The digits are five and numbered 1 to 5 from lateral to The development of upper and lower limbs begins in the medial side. The first digit is called thumb and remaining 4th week of intrauterine life (IUL). A pair of small elevations four digits are fingers. Each digit is supported by three appears on the ventrolateral aspect of the embryo called limb short long bones—the phalanges except thumb, which is buds. The anterior pair of the upper limb buds appears supported by only two phalanges. The phalanges form opposite the lower cervical segments. The posterior pair of metacarpophalangeal joints with metacarpals and lower limb buds appears 3 or 4 days later at the level of interphalangeal joints with one another. The first lumbar and upper sacral segments. Thus during an early carpometacarpal joint has a separate joint cavity hence stage of development all the four limbs appear as paired limb movements of thumb are much more free than that of any buds. First they are simple flipper-like appendages so that the digit/finger. upper and lower limbs are similar in their appearance. Each has dorsal and ventral surfaces, and preaxial and postaxial N.B. The functional value of thumb is immense. For borders. The preaxial border faces towards the head. Later in example, in grasping, the functional value of thumb is equal to other four digits/fingers. Therefore, loss of thumb alone is Table 1.2 Homologous parts of the upper and lower limbs as disabling as the loss of all four fingers. Upper limb Lower limb The subdivisions, bones and joints of different parts of Shoulder/pectoral girdle Hip girdle/pelvic girdle the upper limb are summarized in Table 1.1. Shoulder joint Hip joint Arm Thigh COMPARISON AND CONTRAST BETWEEN Elbow joint Knee joint THE UPPER AND LOWER LIMBS Forearm Leg Wrist joint Ankle joint Both the upper and lower limbs are built on the same basic Hand Foot principle. Each limb is made up of two portions: proximal (a) Carpus (a) Tarsus and distal. (b) Metacarpus (b) Metatarsus The proximal part is called limb girdle and attaches the (c) Fingers* (c) Toes* limb to the trunk. The distal part is free and consists of *First digit in hand is termed thumb and first digit in foot is termed great proximal, middle, and distal segments, which are referred to toe. 4 Textbook of Anatomy: Upper Limb and Thorax Upper limb bud Thumb 90° lateral rotation Thumb Big toe Lower limb bud 90° medial rotation Big toe Fig. 1.3 Development of the limbs. Table 1.3 Differences between the upper and lower limbs Upper limb Lower limb Function Prehension (i.e., manipulation of objects by Locomotion and transmission of weight grasping) Bones Smaller and weaker Larger and stronger Joints Smaller and less stable Larger and more stable Muscles Smaller and attached to smaller bony areas Larger and attached to larger bony areas Antigravity muscles less developed Antigravity muscles more developed Girdle Pectoral girdle Pelvic girdle (a) Made up of two bones, clavicle and scapula (a) Made up of single bone, the hip bone* (b) No articulation with vertebral column (b) Articulates with vertebral column (c) Articulation with axial skeleton is very small (c) Articulation with axial skeleton is large, through through sternoclavicular joint sacroiliac joint Preaxial border Faces laterally 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 TRANSMISSION OF FORCE IN THE and flattened to form the hand and foot plates in which the digits develop. The digits nearest to the preaxial border are UPPER LIMB (Fig. 1.4) thumb and big toe in the upper and lower limbs, respectively. The limbs then rotate. The pectoral girdle on each side consists of two bones: The lower limb buds rotate medially through 90° so that clavicle and scapula, only clavicle is attached to the rest of their preaxial border faces medially and their extensor skeleton by a small joint—the sternoclavicular joint. The two surface faces forwards. The upper limb buds on the other bones of girdle are joined together by even smaller joint, the hand rotate laterally through 90° so that their preaxial border acromioclavicular joint. The clavicle is attached to the faces laterally their extensor surface faces backwards. scapula by a strong coracoclavicular ligament (strongest The differences between the upper and lower limbs are ligament in the upper limb), and the clavicle is anchored to listed in Table 1.3. the 1st costal cartilage by the costoclavicular ligament.  Introduction to the Upper Limb 5 Forces of the upper limb are transmitted to the axial Coracoclavicular skeleton by clavicle through costoclavicular ligament and ligament Clavicle sternoclavicular joint. The lines of force transmission in the Sternoclavicular upper limb are shown in Flowchart 1.1. joint Acromioclavicular joint BONES OF THE UPPER LIMB They are already described with parts of the upper limb (for details see Page 2). Costoclavicular ligament Scapula MUSCLES OF THE UPPER LIMB The muscles of upper limb include (a) the muscles that Humerus 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 Humero-ulnar joint sleeve and are divided into anterior and posterior compartments by intermuscular septa. The muscles of anterior and posterior compartments mainly act Ulna synergistically to carry out specific functions. The muscles of Radius anterior compartment are mainly flexors and those of Interosseous posterior compartment extensors. membrane 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 Fig. 1.4 Transmission of force in the upper limb. muscles. Sternoclavicular joint and costoclavicular ligament Clavicle Axial skeleton Coracoclavicular ligament Shoulder joint Humerus Scapula Inte ro Radius mem sseous Elbow joint bran e Wrist joint Ulna Hand Force Flowchart 1.1 Lines of force transmission in the upper limb. 6 Textbook of Anatomy: Upper Limb and Thorax Axillary nerve Musculocutaneous nerve Radial nerve Radial nerve Median nerve Ulnar nerve Ulnar nerve Deep branch of radial nerve (posterior interosseous Deep branch of nerve) radial nerve (posterior interosseous Superficial branch of nerve) radial nerve (superficial radial nerve) A B Fig. 1.5 Main nerves of the upper limb. A, anterior aspect; B, posterior aspect.  The musculocutaneous, median, and ulnar nerves supply The axillary is the continuation of subclavian artery. At the muscles of anterior (flexor) compartments of the arm the lower border of the teres major muscle its name is and forearm. changed to brachial artery. The brachial artery continues  The radial nerve supplies the muscles of the posterior down the arm and just distal to the elbow joint, it divides (extensor) compartments of the arm and forearm. into radial and ulnar arteries, which follow the bones, after which they are named. In the hand, radial artery terminates N.B. All the intrinsic muscles of the hand are supplied by by forming the deep palmar arch and ulnar artery terminates the ulnar nerve except muscles of thenar eminence and first by forming the superficial palmar arch. two lumbricals.  The axillary artery supplies the shoulder region. ARTERIES OF THE UPPER LIMB (Fig. 1.6)  The brachial artery supplies the anterior and posterior compartments of the arm. The blood to the upper limb is supplied by four main  The radial and ulnar arteries supply the lateral and medial arteries: axillary, brachial, radial, and ulnar. parts of the forearm, respectively.  Introduction to the Upper Limb 7 Common carotid artery Subclavian 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. into the axillary vein in the axilla. The medial end of the VEINS OF THE UPPER LIMB dorsal venous arch forms the basilic vein, which ascends The deep veins of the upper limb follow the arteries and run along the medial aspect of the upper limb and empties into superiorly towards the axilla, where axillary vein travels the axillary vein as well. Anterior to the elbow, the cephalic superiorly and becomes subclavian vein at the outer border vein is connected to the basilic vein via the median cubital of the 1st rib. The subclavian vein continues towards the root vein. of the neck where it joins the internal jugular vein to form the brachiocephalic vein. The two brachiocephalic veins LYMPHATICS OF THE UPPER LIMB (right and left) join each other to form superior vena cava, which drains into the heart. The lymphatics of the upper limb originate in the hand. The The superficial veins of the upper limb originate from superficial lymph vessels follow the superficial veins. The the dorsal venous arch of the hand. The lateral end of the deep lymph vessels follow the deep arteries (viz. radial, ulnar, dorsal venous arch forms the cephalic vein, which runs and brachial) and pass superiorly to the axilla where they along the lateral aspect of the upper limb and terminates drain into the axillary lymph nodes. 8 Textbook of Anatomy: Upper Limb and Thorax Clinical correlation – Nerve injuries: The common nerve injuries in the upper limb are injuries of brachial plexus, median nerve, radial Injuries of the upper limb: The human upper limb is nerve, and ulnar nerve. The compression of median meant for prehension, i.e., grasping, and not for locomotion nerve at wrist is most common peripheral neuropathy in and transmission of weight. The mechanism of grasping is the body. The three major nerves of the upper limb (e.g., provided by hand with the four fingers flexing against the radial, median, and ulnar) have predilection of opposable thumb. The upper limb is therefore light built, involvement in leprosy. The ulnar nerve can be easily i.e., its bones are smaller and weaker, joints are smaller palpated behind the medial epicondyle of the humerus. and less stable, etc. Hence, it is more prone to injuries Sites for the intramuscular and intravenous injections: such as dislocation, fractures, etc. – The intramuscular injection is most commonly given in – Dislocations: The common dislocations in the upper the shoulder region in deltoid muscle; limb are dislocations of shoulder joint (most commonly – intravenous injection is most commonly given in the dislocated joint in the body), elbow joint, and lunate superficial veins in front of elbow and the dorsum of bone of the hand. hand. – Fractures: The common fractures in the upper limb Sites for feeling arterial pulsations: The arterial pulsation are fracture of clavicle (most commonly fractured is most commonly felt and auscultated on the medial side bone in the body), humerus, radius, and scaphoid. of the front of elbow for recording of blood pressure. The The scaphoid is the most commonly fractured bone of arterial pulse is most commonly felt on the lateral side of the hand. the front of distal forearm of recording pulse rate.  Introduction to the Upper Limb 9 Golden Facts to Remember " Most important function of hand Prehension (i.e., grasping) " Most important feature of human hand Opposition of thumb and precision grip " Only point of bony contact between the upper Sternoclavicular joint limb and chest " Part of the upper limb having largest Hand representation in the brain " Most important digit of the hand Thumb  CHAPTER 2 Bones of the Upper Limb The study of bones of the upper limb is important to Clavicle (1) understand the general topography of the upper limb and the attachment of various muscles and ligaments. The students must read the features and attachments of the bones Shoulder joint before undertaking the study of the upper limb. The study of bones also helps to understand the position Sternoclavicular joint of various articulations, wide range of the movements executed by the upper limb and the genesis of various fractures, which are common in the upper limb bones. Scapula (1) Each upper limb contains 32 bones (Fig. 2.1), viz.   Scapula, the shoulder blade (1). Bones of the pectoral Humerus (1)  Clavicle, the collar bone (1). girdle  Humerus, the bone of arm (1).  Radius and ulna, the bones of forearm (2).  Carpal bones, the bones of wrist (8).  Metacarpals, the bones of hand (5).  Phalanges, the bones of digits (fingers) (14). Elbow joint CLAVICLE The clavicle (L. clavicle = key) or collar bone is the long bone, with a slight S-shaped curve. It is located horizontally on the Ulna (1) Radius (1) anterior aspect of the body at the junction of root of the neck and trunk. It articulates medially with the sternum and 1st rib cartilage and laterally with the acromion process of the scapula. It is subcutaneous and hence it can be palpated through its entire extent. It is the only bony attachment Wrist joint between the trunk and upper limb. Carpal bones (8) Metacarpals (5) FUNCTIONS Phalanges (14) The functions of the clavicle are as follows: 1. It acts as a strut for holding the upper limb far from the trunk so that it can move freely. This allows free swing of the upper limb for various prehensile acts such as holding, catching, etc. Fig. 2.1 Bones of the upper limb.  Bones of the Upper Limb 11 2. It transmits forces from the upper limb to the axial Shaft skeleton (sternum). The shaft is curved. Its medial two-third is round and convex 3. It provides an area for the attachment of muscles. forwards, and its lateral one-third is flattened and concave forwards. The inferior surface of the shaft possesses a small PECULIARITIES longitudinal groove in its middle third. The peculiar features of the clavicle are as follows: 1. It is the only long bone which lies horizontally. ANATOMICAL POSITION AND SIDE DETERMINATION 2. It has no medullary cavity. The side of clavicle can be determined by holding the bone 3. It is subcutaneous throughout its extent. horizontally in such a way that its flattened end is on the 4. It is the first bone to start ossifying (between the fifth lateral side and its enlarged quadrilateral end is on the and sixth week of intrauterine life) and last bone to medial side. The convexity of its medial two-third and complete its ossification (at 25 years). concavity of its lateral one-third face forwards with 5. It is the only long bone which ossifies by two primary longitudinal groove in the middle third of shaft facing centers. inferiorly. 6. It is the only long bone which ossifies in membrane except for its medial end (cf. long bones ossify in cartilage). FEATURES AND ATTACHMENTS (Fig. 2.3) 7. It may be pierced through and through by cutaneous nerve (intermediate supraclavicular nerve). Lateral End/Acromial End It is flattened above downwards. An oval facet on this end PARTS articulates with the facet on the medial margin of the The clavicle consists of three parts: two ends (medial and acromion to form acromioclavicular joint. The lateral end lateral) and a shaft (Fig. 2.2): provides attachment to fibrous capsule of acromioclavicular joint. Ends Medial End/Sternal End 1. The lateral (acromial) end is flattened above downwards and articulates with medial margin of the acromion The enlarged medial end has a saddle-shaped articular process. surface, which articulates with the clavicular notch of 2. The medial (sternal) end is enlarged and quadrilateral. manubrium sterni to form sternoclavicular joint. It provides It articulates with the clavicular notch of the manubrium attachment to (a) fibrous capsule (b) articular disc, and sterni. (c) interclavicular ligament. Post. Sternal end Lat. Med. Acromial end A Ant. Trapezoid ridge Shaft Conoid Post. tubercle Acromial end Sternal end Lat. Med. Ant. Subclavian groove (groove for Rough impression for B subclavius muscle) costoclavicular ligament Fig. 2.2 Right clavicle: A, superior aspect; B, inferior aspect. 12 Textbook of Anatomy: Upper Limb and Thorax Trapezius Sternocleidomastoid Post. Lat. Med. Ant. Deltoid A Pectoralis major Capsule of Capsule of acromioclavicular sternoclavicular joint Pectoralis major joint Deltoid Post. Articular surface for acromion Lat. Med. Trapezius Ant. Subclavius Costoclavicular Articular Trapezoid Conoid ligament facet for part part manubrium Coracoclavicular B ligament Fig. 2.3 Right clavicle showing attachments of the muscles and ligaments: A, superior surface; B, inferior surface. Shaft Anterior surface: It is convex forwards and gives origin to The shaft of the clavicle is divided into two parts: lateral one- clavicular head of pectoralis major. third and medial two-third. The medial two-third of shaft is Posterior surface: It is concave backwards and gives origin convex forward and lateral one-third is concave forward. to sternohyoid muscle near its medial end. The lateral part of this surface forms the anterior boundary of cervico-axillary Lateral One-third canal and is related to the following structures: It is flattened from above downwards. It has two surfaces, i.e., 1. Trunks of brachial plexus. superior and inferior, and two borders, i.e., anterior and 2. Third part of subclavian artery. posterior. Superior surface: The clavicular head of sternocleido- mastoid muscle originates from medial half of this surface. Surfaces Inferior surface: It presents the following features: Superior surface: It is subcutaneous between the attachments of deltoid and trapezius. 1. Costoclavicular ligament is attached to an oval Inferior surface: It presents a conoid tubercle and impression at its medial end. trapezoid ridge, which provide attachments to conoid and 2. Subclavius muscle is inserted into the subclavian groove trapezoid parts of coracoclavicular ligament, respectively. on this surface. The conoid tubercle is located on the inferior surface near 3. Clavipectoral fascia is attached to the margins of the posterior border at the junction of the lateral one-fourth subclavian groove. and medial three-fourth of the clavicle. The trapezoid ridge 4. Nutrient foramen of clavicle is located on the lateral end extends forwards and laterally from conoid tubercle. of the subclavian groove. The muscles and ligaments attached to the clavicle are Borders given in Table 2.1. Anterior border: It is concave forwards and gives origin to deltoid muscle. A small tubercle called deltoid tubercle may Table 2.1 Muscles and ligaments attached to the clavicle be present on this border. Posterior border: It is convex backwards and provides Muscles Ligaments insertion to the trapezius muscle. Pectoralis major Coracoclavicular Sternocleidomastoid (clavicular head) Costoclavicular Medial Two-third Deltoid Interclavicular It is cylindrical in shape and presents four surfaces: anterior, Trapezius posterior, superior, and inferior. Subclavius  Bones of the Upper Limb 13 Table 2.2 Ossification centers of the clavicle Clinical correlation Site of appearance Time of appearance Time of fusion Fracture of clavicle (Fig. 2.4): The clavicle is the most commonly fractured bone in the body. It commonly fractures Two primary centres 5–6 weeks of 45th day of at the junction of its lateral one-third and medial two-third (medial and lateral) in intrauterine life IUL due to blows to the shoulder or indirect forces, usually as a the shaft (IUL) result of strong impact on the hand or shoulder, when Secondary centre at 19–20 years (2 years 25th year person falls on the outstretched hand or the shoulder. When fracture occurs, the lateral fragment is displaced downward sternal end earlier in female) by the weight of the upper limb because trapezius alone is Secondary centre at the 20th year Fuses unable to support the weight of the upper limb. In addition, acromial end immediately the lateral fragment is drawn medially by shoulder adductors (occasional) viz. teres major, etc. The medial fragment is slightly elevated by the sternocleidomastoid muscle. The characteristic clinical picture of the patient with fractured clavicle is that of a man/woman supporting his sagging upper limb with the opposite hand. The fracture at the junction of lateral one- third and medial two-third occurs because: OSSIFICATION (Fig. 2.5) (a) This is the weakest site. The ossification of clavicle is membranocartilaginous. (b) Two curvatures of clavicle meet at this site. Whole of it ossifies in the membrane except its medial end (c) The transmission of forces (due to impact) from the clavicle to scapula occur at this site through which ossifies in the cartilage. The clavicle begins to ossify coracoclavicular ligament. before any other bone in the body. It ossifies by four ossification centres – two primary centres for shaft and two secondary centres, one for each end. N.B. The site of appearance, time of appearance, and time of fusion of various centres is given in the Table 2.2. The clavicle is absent in animals in which the upper limbs are used only for walking and weight transmission, and not for grasping such as horse, etc. N.B. Growing end of clavicle: The sternal end of clavicle is its growing end, because epiphysis at this end appears at One of the two primary centers of clavicle is regarded as the age of 19–20 years and unites with the shaft at the age precoracoid element of reptilian shoulder girdle. of 25 years. It is the last of all the epiphyses in the body to fuse with the shaft. The radiological appearance of this epiphysis in females confirms their bone age for legal Sternocleidomastoid consent to marriage. A B Clinical correlation Congenital anomalies: Clavicular dysostosis: It is a clinical condition in which medial and lateral parts of clavicle remain separate due to nonunion of two primary centers of ossification. Cleidocranial dysostosis: It is a clinical condition characterized by partial or complete absence of clavicle associated with defective ossification of the skull bones. Muscle spasm (Teres major and Pectoralis major) Acromial end Sternal end Two primary Secondary centre centres Secondary centre at the acromial end at the sternal end Fig. 2.4 Clavicle fracture: A, medial fragment; B, lateral (occasional) fragment. (Source: Fig. 2.1, Page 51, Clinical and Surgical Anatomy, 2e, Vishram Singh. Copyright Elsevier 2007, All rights reserved.) Fig. 2.5 Ossification of the clavicle. 14 Textbook of Anatomy: Upper Limb and Thorax Coracoid process Spinous process Acromion process Suprascapular Superior border notch Superior angle Glenoid cavity (lateral angle) Supraglenoid tubercle Oblique ridges for attachment of Infraglenoid tubercle small intramuscular tendons of subscapularis Medial border Lateral border A Inferior angle Facet for acromioclavicular joint Suprascapular notch Acromion process Spine/spinous process Supraspinous fossa Later border of acromion Spinoglenoid notch Upper lip of spine Suprascapular nerve Lower lip of spine Infraglenoid tubercle Infraspinous fossa Lateral border Medial border B Fig. 2.6 Right scapula: A, anterior aspect; B, posterior aspect.  Bones of the Upper Limb 15 SCAPULA FEATURES AND ATTACHMENTS (Fig. 2.7) Surfaces The scapula (shoulder blade) is a large, flattened, and triangular bone located on the upper part of the posterolateral Costal surface (subscapular fossa) aspect of the thorax, against 2nd to 7th ribs. 1. It is concave and directed medially and forwards. 2. It presents three longitudinal ridges, which provide attachment to the intramuscular tendons of PARTS (Fig. 2.6) subscapularis muscle. The scapula is highly mobile and consists of four parts: a 3. The subscapularis muscle (a multipennate muscle) body and three processes—spinous, acromion, and coracoid. arises from the medial two-third of subscapular fossa/ costal surface except near the neck where a subscapular N.B. Some authorities divide scapula into three parts, viz. bursa intervenes between the neck and the subscapular head, neck, and body. tendon. 4. The serratus anterior muscle is inserted on this surface Body along the medial border and inferior angle. The body is triangular, thin, and transparent. It presents the following features: Dorsal surface 1. Two surfaces: (a) costal and (b) dorsal. 1. The dorsal surface is convex and presents a shelf-like 2. Three borders: (a) superior, (b) lateral, and (c) medial. projection called spinous process. 3. Three angles: (a) inferior, (b) superior, and (c) lateral. 2. The spinous process divides the dorsal surface into supraspinous and infraspinous fossae. The upper, The dorsal surface presents a shelf-like projection on its supraspinous fossa is smaller (one-third) and lower, upper part called spinous process. infraspinous fossa is larger (two-third). The lateral angle is truncated to form an articular 3. The spinoglenoid notch lies between lateral border of surface—the glenoid cavity. the spinous process and the dorsal surface of the neck of The lateral angle is thickened and called head of the scapula. Through this notch supraspinous fossa scapula, which is connected to the plate-like body by an communicates with the infraspinous fossa and inconspicuous neck. suprascapular nerve and vessels pass from supraspinous fossa to the infraspinous fossa. Processes 4. The supraspinatus muscle arises from medial two-third There are three processes. These are as follows: of supraspinous fossa. 1. Spinous process. 5. The infraspinatus muscle arises from medial two-third 2. Acromion process. of infraspinous fossa. 3. Coracoid process. 6. The teres minor muscle arises from the upper two-third of the dorsal surface of lateral border. This origin is The spinous process is a shelf-like bony projection on the interrupted by the circumflex scapular artery. dorsal aspect of the body. 7. The teres major muscle arises from the lower one-third The acromion process projects forwards almost at right of the dorsal surface of lateral border and inferior angle angle from the lateral end of the spine. The coracoid process is like a bird’s beak. It arises from of scapula. the upper border of the head and bends sharply to project 8. The latissimus dorsi muscle also arises from dorsal superoanteriorly. surface of the inferior angle by a small slip. ANATOMICAL POSITION AND SIDE DETERMINATION Borders Superior border The side of the scapula can be determined by holding the 1. The superior border is the shortest border and extends scapula in such a way that: between superior and lateral angles. 1. The glenoid cavity faces laterally, forwards, and slightly 2. The suprascapular notch is present on this border near upwards (at an angle of 45° from the coronal plane). the root of coracoid process. 2. The coracoid process is directed forwards. 3. The suprascapular notch is converted into suprascapular 3. The shelf-like spinous process is directed posteriorly. foramen by superior transverse (suprascapular) ligament. 16 Textbook of Anatomy: Upper Limb and Thorax Pectoralis minor Coracoacromial ligament Coracoclavicular ligament Short head of biceps brachii and Suprascapular ligament coracobrachialis Superior angle Capsule of shoulder joint Inferior belly of omohyoid Glenoid cavity (lateral angle) Long head of triceps Serratus anterior Subscapularis A Inferior angle Trapezius Coracoacromial ligament Suprascapular ligament Deltoid Superior angle Glenoid cavity Levator scapulae (lateral angle) Capsule of shoulder joint Supraspinatus Long head of triceps Rhomboideus minor Circumflex scapular artery Infraspinatus Teres minor Rhomboideus major Teres major Latissimus dorsi B Inferior angle Fig. 2.7 Right scapula showing attachments of the muscles and ligaments: A, costal surface; B, dorsal surface.  Bones of the Upper Limb 17 4. The suprascapular artery passes above the ligament and Processes suprascapular nerve passes below the ligament, through Spinous process (spine of scapula) suprascapular foramen. (Mnemonic: Air force flies above 1. It is a triangular shelf-like bony projection, attached to the Navy, i.e., A: artery is above and N: nerve is below the the dorsal surface of scapula at the junction of its upper ligament.) one-third and lower two-third. 5. The inferior belly of omohyoid arises from the superior 2. It divides the dorsal surface of scapula into two parts— border near the suprascapular notch. upper supraspinous fossa and lower infraspinous fossa. Lateral border 3. The spine has two surfaces—(a) superior and (b) inferior, and three borders—(a) anterior, (b) posterior, and 1. The lateral border is the thickest border and extends (c) lateral. from inferior angle to the glenoid cavity. 2. The infraglenoid tubercle is present at its upper end, Surfaces just below the glenoid cavity. (a) The superior surface of spine forms the lower boundary 3. The long head of triceps muscle arises from the infra- of supraspinous fossa and gives origin to supraspinatus. glenoid tubercle. (b) The inferior surface of spine forms the upper limit of infraspinous fossa and gives origin to infraspinatus. N.B. Lateral border of scapula is thick because it acts as fulcrum during rotation of the scapula. Borders (a) The anterior border of spine is attached to the dorsal Medial border (vertebral border) surface of scapula. 1. It extends from superior angle to the inferior angle. (b) The lateral border of spine bounds the spinoglenoid 2. It is thin and angled at the root of spine of scapula. notch through which pass suprascapular nerve and 3. The serratus anterior muscle is inserted on the costal vessels from supraspinous fossa to infraspinous fossa. surface of the medial border and the inferior angle. (c) The posterior border of spine is also called crest of spine. Trapezius is inserted to the upper lip of crest of spine, 4. The levator scapulae muscle is inserted on the dorsal while posterior fibres of deltoid take origin from its aspect of the medial border from superior angle to the lower lip. root of spine. 5. The rhomboideus minor muscle is inserted on the Acromion process (acromion) dorsal aspect of the medial border opposite the root of spine. 1. It projects forwards almost at right angle from the lateral end of spine and overhangs the glenoid cavity. 6. The rhomboideus major muscle is inserted on the dorsal 2. Its superior surface is subcutaneous. aspect of the medial border from the root of spine to the inferior angle. 3. It has a tip, two borders (medial and lateral), and two surfaces (superior and inferior). Angles 4. The medial and lateral borders of acromion continue with the upper and lower lips of the crest of the spine of Inferior angle: It lies over the 7th rib or the 7th intercostal scapula, respectively. space. 5. Its superior surface is rough and subcutaneous. Superior angle: It is at the junction of superior and medial 6. Its inferior surface is smooth and related to subacromial borders, and lies over the 2nd rib. bursa. 7. The medial border of acromion provides insertion to Lateral angle (head of scapula) the trapezius muscle. Near the tip, medial border 1. It is truncated and bears a pear-shaped articular cavity presents a circular facet, which articulates with the called the glenoid cavity, which articulates with the head lateral end of clavicle to form the acromioclavicular of humerus to form glenohumeral (shoulder) joint. joint. 2. A fibrocartilaginous rim, the glenoid labrum is attached 8. The lateral border of acromion gives origin to to the margins of glenoid cavity to deepen its concavity. intermediate fibres of the deltoid muscle. 3. The capsule of shoulder joint is attached to the margins 9. The coracoacromial ligament is attached to the tip of of glenoid cavity, proximal to the attachment of glenoid acromion. labrum. 10. The acromial angle is at the junction of lateral border of 4. The long head of biceps brachii arises from supraglenoid acromion and lateral border of the crest of the spine of tubercle. This origin is intracapsular. scapula. 18 Textbook of Anatomy: Upper Limb and Thorax Coracoid process Clinical correlation 1. It arises from the upper part of the head of scapula and bent sharply so as to project forwards and slightly Sprengel’s deformity of the scapula (congenital high laterally. scapula): The scapula develops in the neck region during intrauterine life and then migrates downwards to its adult 2. The coracoid process provides attachment to three position (i.e., upper part of the back of the chest). Failure muscles—short head of biceps brachii, coracobrachialis, of descent leads to Sprengel’s deformity of the scapula. In and pectoralis minor, and three ligaments— this condition the scapula is hypoplastic and situated in the coracoacromial, coracoclavicular, and coracohumeral. neck region. It may be connected to the cervical part of 3. The short head of biceps brachii and coracobrachialis arise vertebral column by a fibrous, cartilaginous, or bony bar called omovertebral body. An attempt to bring down from its tip by a common tendon. scapula by a surgical procedure may cause injury to the 4. The pectoralis minor muscle is inserted on the medial brachial plexus. border of the upper surface. 5. The coracoacromial ligament is attached to its lateral border. HUMERUS 6. The conoid part of the coracoclavicular ligament (rhomboid ligament) is attached to its knuckle. The humerus is the bone of arm. It is the longest and 7. The trapezoid part of the coracoclavicular ligament strongest bone of the upper limb. (rhomboid ligament) is attached to a ridge on its superior aspect between the pectoralis minor muscle PARTS (Fig. 2.8) and coracoacromial ligament. The humerus is a long bone and consists of three parts: 8. The coracohumeral ligament is attached to its root upper end, lower end, and shaft. adjacent to the glenoid cavity. N.B. Upper End In living individual, the tip of coracoid process can be The upper end presents the following five features: palpated 2.5 cm below the junction of lateral one-fourth 1. Head. and medial three-fourth of the clavicle. 2. Neck. In reptiles, coracoid process is a separate bone, but in 3. Greater tubercle. humans it is attached to scapula and thus it represents 4. Lesser tubercle. atavistic epiphysis. 5. Intertubercular sulcus. The head is smooth and rounded, and forms less than half OSSIFICATION of a sphere. It is directed medially backwards and upwards. It The ossification of scapula is cartilaginous. The cartilaginous articulates with the glenoid cavity of scapula to form the scapula is ossified by eight centres—one primary and seven glenohumeral (shoulder) joint. secondary. Lower End The primary centre appears in the body. The secondary centres appear as follows: The lower end presents the following seven features: 1. Two centres appear in the coracoid process. 1. Capitulum, a lateral rounded convex projection. 2. Two centres appear in the acromion process. 2. Trochlea, a medial pulley-shaped structure. 3. One centre appears each in the (a) medial border, 3. Radial fossa, a small fossa above the capitulum. (b) inferior angle, and (c) in the lower part of the rim of 4. Coronoid fossa, a small fossa above the trochlea. glenoid cavity. 5. Medial epicondyle, a prominent projection on the medial side. The primary centre in the body and first secondary centre 6. Lateral epicondyle, a prominent projection on the in the coracoid process appears in eighth week of lateral side but less than the medial epicondyle. intrauterine life (IUL) and first year of postnatal life, 7. Olecranon fossa, a large, deep hollow on the posterior respectively and they fuse at the age of 15 years. aspect above the trochlea. All other secondary centres appear at about puberty and fuse by 20th year. Shaft N.B. First coracoid centre represents precoracoid element The shaft is a long part of bone extending between its upper and second coracoid (subcoracoid) centre represents and lower ends. It is cylindrical in the upper half and coracoid proper of reptilian girdle. flattened anteroposteriorly in the lower half.  Bones of the Upper Limb 19 Anatomical neck Anatomical neck Impression for supraspinatus Greater tubercle Head Head Impression for Lesser tubercle infraspinatus Impression for Lateral lip teres minor Surgical neck Surgical neck Medial lip Bicipital groove Spiral groove Deltoid tuberosity Deltoid tuberosity Shaft of humerus Shaft of humerus Coronoid fossa Lateral supracondylar ridge Medial supracondylar ridge Radial fossa Lateral epicondyle Olecranon fossa Medial epicondyle Medial epicondyle Capitulum Lateral epicondyle A Trochlea B Trochlea Fig. 2.8 Right humerus: A, anterior view; B, posterior view. ANATOMICAL POSITION AND SIDE DETERMINATION 3. The olecranon fossa on the lower flattened end faces posteriorly. The side of humerus can be determined by holding it vertically in such a way that: FEATURES AND ATTACHMENTS (Fig. 2.9) 1. The rounded head at the upper end faces medially, backwards and upwards. Upper End Head 2. The lesser tubercle, greater tubercle, and vertical groove 1. It is smooth, rounded and forms one-third of a sphere. (intertubercular groove) at the upper end faces 2. It is covered by an articular hyaline cartilage, which is anteriorly. thicker in the center and thinner at the periphery. 20 Textbook of Anatomy: Upper Limb and Thorax Neck Surgical neck The humerus has three necks: 1. It is short constriction in the upper end of the shaft Anatomical neck below the greater and lesser tubercles/below the 1. It is constriction at the margins of the rounded head. epiphyseal line. 2. It provides attachment to the capsular ligament of the 2. It is related to axillary nerve and posterior and anterior shoulder joint, except—superiorly where the capsule is circumflex humeral vessels. deficient, for the passage of tendon of long head of 3. It is the most important feature of the proximal end of biceps brachii, medially the capsule extends down from the humerus because it is weaker than the more proximal the anatomical neck to the shaft for about 1–2 cm. regions of the bone, hence it is one of sites where the Supraspinatus Supraspinatus Head Head Infraspinatus Capsular ligament of Capsular ligament of Subscapularis shoulder joint shoulder joint Teres minor Pectoralis major Latissimus dorsi Lateral head of triceps Teres major Spiral groove Deltoid Deltoid Coracobrachialis Brachialis Medial head of triceps Brachioradialis Extensor carpi radialis longus (ECRL) Pronator teres Common extensor origin Capsular ligament of Capsular ligament of elbow joint elbow joint Common flexor origin Capitulum Anconeus A Trochlea B Fig. 2.9 Right humerus showing attachments of the muscles and ligaments: A, anterior aspect; B, posterior aspect.  Bones of the Upper Limb 21 humerus commonly fractures leading to damage of Lateral border associated nerves and vessels. 1. Its upper part is indistinct while its lower part is Morphological neck prominent where it forms the lateral supracondylar ridge. Above the lateral supracondylar ridge, it is ill- 1. It is the junction between diaphysis and epiphysis. defined but traceable to the posterior part of the greater 2. It is represented by an epiphyseal line in the adult bone. tubercle. 3. It is a true junction of head with the shaft. 2. About its middle, this border is crossed by the radial Greater tubercle groove from behind. 1. It is the most lateral part of the proximal end of humerus. 3. The lower part of this border, lateral supracondylar 2. Its posterosuperior aspect bears three flattened facet-like ridge, provides attachment to the lateral intermuscular impressions: upper, middle, and lower, which provide septum. attachment to supraspinatus, infraspinatus, and teres minor muscles, respectively. Surfaces Anterolateral surface Mnemonic: SIT, (supraspinatus, infraspinatus, teres minor).