Anatomy of the Upper Limb (Locomotor System) PDF

**ANATOMY LOCOMOTOR SYSTEM KEY INFO** **[Upper Limb]** - Primarily composed of 3 bones: clavicle, scapula, and humerus. - The scapula has 3 main processes, and a rather complex shape. It is a flat bone, slightly concave from the frontal view, and convex from the posterior one. From th...

**ANATOMY LOCOMOTOR SYSTEM KEY INFO** **[Upper Limb]** - Primarily composed of 3 bones: clavicle, scapula, and humerus. - The scapula has 3 main processes, and a rather complex shape. It is a flat bone, slightly concave from the frontal view, and convex from the posterior one. From the posterior view we can see a spine, called spine of the scapula (first process) which divides the two fossae, one inferior called infraspinous fossa, and one superior called supraspinous fossa. From these, there is the origination of the infraspinatus and the supraspinatus muscles, respectively. The Acromion is the second process, and is a continuation of the spine of the scapula, which ends superiorly and laterally. The coracoid process is the third process of the scapula and the only one that cannot be palpated. It is rather deep and is found anteriorly. It is greatly involved in the origin/insertion of 3 muscles, as well as taking part in a series of ligaments. - Anteriorly, being the scapula concave from this angle, there is a large fossa, called subscapular fossa, from where the subscapularis muscle originates. - The glenoid fossa is a major part of the scapula, located laterally below the acromion, where the glenohumeral joint between the scapula and the humerus will take place. This joint is the most moveable of the entire body, which at the same time it is the easiest to dislocate. This type of joint is a ball and socket joint (as the glenoid fossa is indeed an empty hole -- socket -- whereas the proximal epiphysis of the humerus is a essentially a spherical structure that can easily insert into the cavity). - The shoulder is the most movable joint, allowing 3 different movements around 3 different axes. It is composed of a total of 5 joints, of which only 3 are true in nature. These are: sternoclavicular joint, acromioclavicular joint, glenohumeral joint (humeroscapular), scapulothoracic joint, and subacromial joint. These last two are false joints. - The difference between true and false joints is that true joints are actual synovial joints, with a series of ligaments to inhibit excess movement, and with articular discs and fibrous cartilage, whereas false joints are simply empty areas within the structure that enable the sliding of muscles and tendons. - The scapulohumeral joint (glenohumeral joint) is the most important as it is the most mobile in our body. It indeed enables movement around 3 axes (has 3 degrees of freedom). It is a true synovial joint, of the ball and socket type. It constitutes in a proximal epiphysis (head of the humerus) which is spherical in structure, forming a joint with the glenoid cavity of the scapula. The head of the humerus, with respect to the shaft, forms an angle of 135-140°, as it points superiorly, medially, and slightly posteriorly, with respect to the diaphysis. Also, from the frontal view it makes a retrotorsion angle of 30°. - The proximal epiphysis of the humerus has 2 tubercles, one anterior called lesser tubercle, and one lateral and slightly posterior called greater tubercle. These are important insertion sites for a series of muscles that act on the glenohumeral joint, and that provide movement to the entire shoulder girdle. Between the two tubercles is a canal, the humeral canal, from which the tendon of the long head of the biceps brachii passes, after originating from the supraglenoid tubercle of the scapula, indeed above the glenoid cavity. - The glenoid cavity is much smaller compared to the size of the head of the humerus (as it indeed it covers only a quarter of its size). The presence of the glenoid labrum, a layer of fibrocartilage located inside the glenoid cavity, is crucial as it provides greater congruency between the proximal epiphysis and the cavity itself, crucial to provide stability to the joint. The fact that the head is larger than the cavity itself is important as it enables the shoulder to undergo the large number of movements it can undergo. - The glenoid cavity points anteriorly, laterally, and slightly superiorly. - The main ligaments of the glenohumeral joint are: superior, middle, and inferior glenohumeral ligaments, transverse humeral ligament (between the lesser and greater tubercles), and the coracohumeral ligament, between the coracoid process of the scapula and the superior aspects of the greater and lesser tubercles of the surgical neck of the humerus. - The acromioclavicular ligament is another true joint. It is constituted of articular cartilage and synovial fluid, and is kept very stable through the presence of 3 main ligaments: the acromioclavicular ligament, indeed between the distal end (acromial end) of the clavicle and the medial aspect of the acromion, the conoid ligament, between the medial aspect of the coracoid process and the inferior portion of the acromial end of the clavicle, and the trapezoid ligament, more lateral on the coracoid process, with insertion close to that of the conoid ligament. - The sternoclavicular ligaments is the third true joint of the upper limb. It indeed connects the upper limb with the thorax. It is between the proximal (sternal) end of the clavicle and the superior-lateral surface of the manubrium of the sternum. The joint constituted of an articular cartilage, synovial fluid, and several articular discs that protect bones from grinding between one another. The joint actually involves also the cartilage of the first rib, as one of the ligaments is indeed between the inferior aspect of the sternal end of the clavicle and the first rib cartilage (through the costoclavicular ligament). The other 3 ligaments instead connect the manubrium of sternum with the clavicle. These are the anterior sternoclavicular ligament (located anteriorly), the posterior sternoclavicular ligament (located posteriorly), and the interclavicular ligament (located between the anterior and posterior sternoclavicular ligaments). The main role of this joint is to limit movement of the clavicle with the sternum (similar to the acromioclavicular joint), by providing also strength and resistance. - The subacromial joint is the first false joint of the shoulder girdle. It is indeed an area where the subacromial bursa is located, confined superiorly by the acromion process, the coracoacromial ligament, and the acromial part of the deltoid, and inferiorly by the subscapularis muscle tendon and the head of the humerus. This area is essential to enable the proper function of the rotator cuff muscles, and the presence of the subacromial bursa serves to maintain this space sufficiently enlarged. In fact, a decrease in the size of the subacromial area may lead to subscapularis tendon impingement with the acromion process and/or coracoacromial ligament, which over time may lead to the complete tear of the tendon. - Note that the subacromial bursa is found inside the subacromial joint and it covers the superior surface of the subscapularis tendon. - The scapulothoracic joint is the second and last false joint of the shoulder girdle. It constitutes and area between the anterior surface of the scapula (subscapular fossa, where the subscapularis is located) and the posterior aspect of the thoracic cage, specifically where the serratus anterior is located. This joint serves to grant an area between the two muscles, enabling movement of the scapula and inhibiting muscles from grinding one against the other. It has a main role in scapula kinematics. - The coracohumeral ligament is of pivotal importance for the stability of the glenohumeral joint. It connects the dorsa-lateral aspect of the coracoid process with the surgical neck of the humerus, specifically at the superior aspects of the lesser and greater tubercles. It also makes a tunnel through which the tendon of the long head of the biceps brachii passes through, as it originates from the supraglenoid tubercle of the scapula (above the glenoid cavity). - The inferior, middle, and superior glenohumeral ligaments serve, as the coracohumeral ligament, to provide stability and limit excessive movement of the shoulder joint. These ligaments primarily avoid over extension and over abduction of the joint. The inferior glenohumeral ligament is crucial as it inhibits humeral dislocation as a result of over abduction. Tearing of this ligament would drastically increase chances of shoulder dislocation. - Tendons of the biceps brachii (both the short and long heads) play a crucial role in the abductive activity of the rotator cuff as when undergoing abduction the long head tendon presses from downwards the humeral head to prevent superior dislocation, and the short head instead presses upwards to prevent inferior dislocation of the humeral head. Together, the two tendons push the humeral head into the glenoid cavity, ensuring no dislocation. - The long head of the biceps brachii originates from the supraglenoid tubercle of the glenoid cavity of the scapula, whereas the short head of the biceps brachii originates from the lateral aspect (apex) of the coracoid process). Both muscles converge into a single tendon that inserts into the radial tuberosity, located on the medial surface of the superior portion of the shaft of the radius. - The arm is constituted by the humerus, which has its proximal end forming the glenohumeral joint, and a series of attachment sites (in the greater and lesser tubercle crests) for muscles. The diaphysis (shaft) constitutes in a deltoid tuberosity, which is the site of insertion of the deltoid muscle tendon, and the radial groove, which is a groove in which the radial nerve passes through. The distal end of the humerus is instead involved in the formation of the elbow joint, articulating medially with the ulna and laterally with the radius. - The coracobrachialis originates from the coracoid process of the scapula, just behind the short head of the biceps brachii, and inserts into the medial third of the diaphysis of the humerus. - The brachialis muscle is the last anterior view muscle of the arm, originating below the deltoid tuberosity of the humerus (located laterally), and inserting into the tuberosity of the ulna (located medially, just under the proximal head). - From the posterior view, the triceps brachii has three different muscle bellies, each originating from a different part of the shoulder girdle, yet all inserting into the olecranon process of the ulna. - The long head of the triceps brachii originates from the infraglenoid tubercle of the scapula, just below the glenoid fossa. The lateral head of the triceps brachii instead originates from the posterior surface of the humerus, just above the radial groove. The medial head instead originates from the posterior surface of the humerus, inferior to the radial groove. Again, all three heads converge into a single tendon that inserts into the olecranon of the ulna. - The long head of the triceps brachii has a double effect, on both the stability of the glenohumeral joint and the extension of the elbow joint (essentially extension of the arm and extension of the shoulder). The medial and lateral heads instead only act on the elbow joint, as their origin is intrinsic within the humerus. - The humerus is a long bone, constituting of a distal epiphysis that articulates medially with the ulna and laterally with the radius. This distal portion possesses two condyles, one medial and one lateral, which extend as epicondyles (medial and lateral), which are the origin sites of most muscles of the forearm. - The lateral condyle extends as a structure known as capitulum which articulates with the radius laterally. The radius will articulate with the capitulum by the shape of the head of the radius (spherical) and that of the capitulum, which is instead slightly concave. - The medial condyle extends as the trochlea, and is the articular portion of the medial humerus with the ulna. The ulna has a semilunar face, and two processes. One is the coronoid process (anterior), and the other is the olecranon (posterior). - Flexion and extension of the forearm is enabled by the hinge-like motion of the trochlear notch around the trochlea of the humerus. In the fully extended form, when the arm and forearm have an angle of 0° (all the limb is straight), the olecranon is inside of the olecranon fossa, and the coronoid process is instead located anteriorly and below the coronoid fossa. During flexion, when the arm is bent (through the action of the biceps brachii, brachialis, and brachioradialis muscles), the trochlear notch rotates in posteroanterior direction making the olecranon come out of the olecranon fossa, and at the same time making the coronoid process enter into the coronoid fossa. The maximum degree of flexion is 150°. The radial fossa instead remains empty when the forearm is in complete extension, whereas is occupied by the proximal epiphysis of the radius when the forearm is in flexion. - There are three main ligaments in the elbow joint: medial collateral ligament (ulnar ligament), the lateral collateral ligament (radial ligament), and the annular ligament (which stabilises the head of the radius to the radial notch of the ulna in the radioulnar joint). - True elbow joint: involves 3 bones: humerus, radius, and ulna. Radius and humerus connect together via the radial collateral ligament and through the capitulum, which is the articular radial portion of the humerus, and the ulna and humerus articulate with each other through the trochlear notch of the ulna and the trochlea of the humerus. This joint enables flexion and extension of the forearm. - The radioulnar joint (proximal located at the elbow joint, distal located at the wrist joint) enables supination and pronation, essentially by rotating the radius on top of the ulna. - The medial collateral ligament consists of 3 fibres: anterior, posterior, and intermediate (also known as transverse ligament of Cooper). - The lateral collateral ligament consists also of 3 fibres: anterior, intermediate, and posterior. - Both collateral ligaments extend from the medial and lateral epicondyle of the humerus (respectively) to the head of the ulna and radius (respectively). - The elbow can undergo only flexion and extension. Flexion is performed by 3 muscles of the arm: biceps brachii, brachialis, brachioradialis. - The brachialis originates just below the deltoid tuberosity of the humerus and inserts into the coronoid process and tuberosity of the ulna. - The radiocarpal joint is of crucial importance for limiting excess movement of the wrist joint. This is allowed by the presence of both collateral ligaments (that limit adduction and abduction), and anterior and posterior ligaments that limit flexion and extension. - Collateral ligaments of the radiocarpal joint are 2: radial collateral and ulnar collateral. Radial collateral extends from the styloid process of the radius to the styloid process of the scaphoid bone. Ulnar collateral extends from styloid process of ulna to the medial aspect of the triquetrum and pisiform bones. - The triangular fibrocartilage complex connects the ulna with the wrist joint, and adds stability, also enabling the actual connection between the ulna and the triquetrum and pisiform to occur, as the ligaments are not direct (as instead does the radius with the radial collateral ligament). - The triangular fibrocartilage complex (TFCC) reinforces the radioulnar joint by acting as a sort of meniscus between the radius and ulna with 3 ligaments: the ulnotriquetral ligament (connecting the ulna with the triquetrum), the ulnolunate ligament (connecting the ulna with the lunate), and the radioulnar ligament (connecting the distal head of the ulna with the ulnar notch of the radius). - The TFCC prevents damages during adduction, through the presence of ligaments. - The anterior (palmar) ligamentous complex is constructed by two main ligaments: palmar radiocarpal ligament and the palmar ulnocarpal ligament. The radiocarpal ligament is constituted by a ligament of the radius with the capitate bone (laterally), and another ligament with the triquetrum (medially). The ulnocarpal ligament instead consists of a ligament of the ulna with the triquetrum (medially) and a ligament with the lunate (laterally). The palmar radiocarpal and ulnocarpal ligaments are crucial to limit extension of the wrist. - The posterior (dorsal) ligamentous complex is again constituted of two ligaments: dorsal radiocarpal ligament and the dorsal intercarpal ligament. The dorsal radiocarpal ligament is itself constituted of two ligaments that connect one the radius with the lunate bone (laterally) and the other the radius with the triquetrum (laterally). The role of the dorsal ligamentous complex is to limit over flexion of the wrist. - During adduction (ulnar hand side closer to ulnar forearm side) the radial collateral ligament is stretched whereas the ulnar collateral ligament is relaxed. Over adduction is limited by the radial collateral ligament. - During abduction (radial hand side closer to the radial forearm side) the ulnar collateral ligament is stretched, and the radial collateral ligament is relaxed. Over abduction is limited by the ulnar collateral ligament, despite it being already limited by anatomy, due to the presence of the scaphoid bone. - Over flexion is limited by the dorsal ligamentous complex (dorsal radiocarpal ligament and dorsal intercarpal ligament). Over extension is limited by the palmar ligamentous complex (palmar radiocarpal ligament and palmar ulnocarpal ligament). - Ligaments of the metacarpal joint are rather simple, as they connect the 8 bones that constitute the metacarpal bone complex (in lateromedial direction, first row and second row: scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate) directly indicating the name of the two bones involved, for instance the scapho-lunate ligament is a horizontal ligament that connects the medial aspect of the scaphoid bone with the lateral aspect of the lunate bone. - **Muscles from trunk to shoulder girdle** - Serratus anterior: - Originates from 1^st^ to 9^th^ rib - Inserts into medial border of the scapula - Performs abduction and upward rotation of scapula - Trapezius: - 3 components: descending, transverse, ascending trapezius - Originates from occipital bone and spinous processes of C7 through T12 - Inserts into acromion and spine of the scapula - Performs adduction, downward-upward rotation, and elevation-depression of the scapula - Rhomboid minor and major: - Originate from spinous process and nuchal ligament of C5 to T4 - inserts into medial border of the scapula - Perform adduction, downward rotation, and elevation of the scapula - Pectoralis minor: - Originates from the second to fifth rib - Inserts into the coracoid process of the scapula - Performs depression and ventral tilt of the scapula, and elevation of the second to fifth ribs - Levator scapulae: - Originates from the transverse process of the upper cervical vertebrae - Inserts into the superior medial border (above the rhomboid minor and major) of the scapula - Performs elevation and downward rotation of the scapula, and ipsilateral rotation and flexion of the head - **Muscles from shoulder girdle to humerus** - Deltoid: - 3 components - Originates from the spine of the scapula, acromion process, and acromial end of the clavicle - Inserts as a single tendon into the deltoid tuberosity, located medially on the shaft of the humerus - Performs abduction of glenohumeral joint. Clavicular part performs flexion and spinal part performs extension of glenohumeral joint - Supraspinatus: - Originates from the supraspinal fossa - Inserts into uppermost facet of greater tubercle - Performs abduction of glenohumeral joint - Infraspinatus: - Originates from the infraspinous fossa - Inserts into the middle facet of the greater tubercle - Performs external rotation of the glenohumeral joint - Teres minor: - Originates from the lateral border of the scapula - Inserts into the lower facet of the greater tubercle - Performs external rotation of the glenohumeral joint - Subscapularis: - Originates from the subscapular fossa - Inserts into the lesser tubercle - Performs internal rotation (also adduction, extension, and flexion depending on arm position) of the glenohumeral joint - Teres major: - Originates from the inferior angle of the scapula - Inserts into the crest of the lesser tubercle - Performs internal rotation, adduction, and extension of the glenohumeral joint - Pectoralis major: - Originates from the second to seventh rib, sternal end of the scapula, and sternum - Inserts into the crest of the greater tuberosity of the humerus - Performs adduction and internal rotation of the glenohumeral joint. Clavicular head also performs flexion - Latissimus dorsi: - Originates from spinous process of T6 to the crest of the ilium - Inserts into the crest of the lesser tubercle, proximal to teres major - Performs external rotation, extension, and adduction of the glenohumeral joint (also performs scapular depression) - Motor muscles of supination: - Supinator muscle - Biceps brachii - Motor muscles of pronation: - Pronator quadratus - Pronator teres - Tendons of most flexor muscles are kept in place by the palmar carpal ligament and the transverse carpal ligament (flexor retinaculum), all located on the palmar side of the - **Flexor-pronator muscles** - Superficial layer: - Pronator Teres - Palmaris longus - Flexor carpi radialis - Flexor carpi ulnaris - All muscles originate from the medial epicondyle of the humerus (through the common flexor attachment tendon). The order in lateromedial direction is pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. - Insertions and actions: - Pronator teres: lateral middle surface of the radius; performs pronation and flexion of the arm. - Flexor carpi radialis: base of the second metacarpal bone; flexes and abducts the wrist. - Palmaris longus: distal half of flexor retinaculum and palmar aponeurosis; flexes the wrist and tenses the aponeurosis. - Flexor carpi ulnaris: pisiform bone, hook of the hamate bone, and fifth metacarpal bone; flexes and adducts the wrist. - Intermediate layer: - Flexor digitorum superficialis - This is the single muscle that consists this intermediate layer. - Originates from the medial epicondyle and coronoid process of the humerus - Inserts into the shafts of the middle phalanges of the four digits (excluding the thumb) - Performs flexion of the middle phalanges at the proximal interphalangeal joint, also flexing the proximal phalanges to the metacarpophalangeal joint. Has an effect on wrist flexion as well - Deep layer: - Flexor digitorum profundus - Originates from anterior and medial aspects of the proximal ulna superior ¾ of the shaft of the ulna (close to the coronoid process), and interosseous membrane - Inserts into the base of the distal phalanges of the second through fifth digits - Performs flexion of the distal interphalangeal joint - Flexor pollicis longus - Originates from the anterior surface of the radius and adjacent interosseous membrane - Inserts into the base of the distal phalanx of the first digit - Performs phalanx flexion of the first digit - Pronator quadratus - Originates from the anterior aspect of the distal quarter of the ulna - Inserts into the anterior aspect of the distal quarter of the radius - Performs pronation of the forearm, superimposing the radius on top of the ulna - Extensor-supinator muscles are located, differently from flexor-pronator muscles, on the posterior aspect of the forearm, and have the main functions of extension and supination of the forearm (and also perform abduction and adduction, depending on their insertion). Extensors that insert into the radius are primarily abductors, and extensors that insert into the ulna are primarily adductors. - Extensor-supinator muscles are kept in place by the presence of the extensor retinaculum, that has the same role as the palmar carpal ligament (indeed it is a dorsal continuation of the palmar carpal ligament) and the flexor retinaculum, with the difference that extensor tendons are kept in place in this single area. - **Extensor muscles** - Superficial layer: - Brachioradialis - Originates from the proximal 2/3^rds^ of the lateral supracondylar ridge of the humerus - Inserts into the lateral distal portion of the radius, proximal to the styloid process - Performs flexion of the forearm - Extensor carpi radialis longus - Originates from the lateral supracondylar ridge of the humerus - Inserts into the dorsal aspect of the base of the second metacarpal bone (index finger) - Performs extension and abduction of the hand at the wrist joint - Extensor carpi radialis brevis - Originates from the lateral epicondyle of the humerus - Inserts in the dorsal aspect of the base of the third metacarpal bone - Performs extension and abduction of the hand at the wrist joint - Extensor digitorum - Originates from the lateral epicondyle of the humerus - Inserts into the distal phalanges of the second through fifth digits - Performs extension of the digits at the metacarpophalangeal and interphalangeal joints - Extensor digiti minimi - Originates from the lateral epicondyle of the humerus - Inserts into the distal phalanx of the fifth digit - Performs extension of the fifth digit at the metacarpophalangeal and interphalangeal joints - Extensor carpi ulnaris - Originates from the lateral epicondyle of the humerus - Inserts into the dorsal base of the fifth metacarpal bone - Performs extension and adduction the hand at the wrist joint - Deep layer: - Supinator - Originates from the lateral epicondyle of the humerus, crest of the ulna, and supinator fossa - Inserts into the lateral, posterior, and anterior surfaces of the proximal third of the radius - Performs supination of the forearm - Extensor indicis - Originates from the posterior surface of the distal third of the ulna and interosseous membrane - Inserts into the dorsal base of the distal phalanx of the index finger - Performs independent extension of the second digit and helps with hand extension - Abductor pollicis longus - Originates from the posterior surfaces of the proximal halves of the ulna, radius, and interosseous membrane - Inserts into the dorsal base of the first metacarpal bone - Performs independent abduction of the thumb - Extensor pollicis longus - Originates from the posterior surface of the middle third of the ulna and interosseous membrane - Inserts into the dorsal base of the distal phalanx of the first digit - Performs individual extension of the thumb at the metacarpophalangeal and interphalangeal joints - Extensor pollicis brevis - Originates from the posterior surface of the distal third of the radius and interosseous membrane - Inserts into the dorsal base of the proximal phalanx of the first digit - Performs individual extension of the thumb at the metacarpophalangeal joint and the carpometacarpal joint - Muscles of the hand can be both intrinsic (originate and insert in the hand) or extrinsic (insert into the hand, but originate from adjacent structures, such as the humerus, radius, and ulna). - Extrinsic flexor-pronators of the hand are: flexor carpi radialis, flexor carpi ulnaris, palmaris longus, flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus. Total of 6. - Extrinsic extensor-supinators of the hand are: extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum, extensor pollicis longus, extensor pollicis brevis, abductor pollicis longus, extensor digiti minimi, extensor indicis. Total of 9. - Intrinsic muscles of the hand are instead divided into 4 subcategories: thenar and abductor muscles, hypothenar muscles, lumbrical muscles, and intraossei muscles. - Thenar muscles are the: abductor pollicis brevis, opponens pollcis, flexor pollicis brevis, and adductor pollicis. - Hypothenar muscles are the: palmaris brevis, abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi. - Lumbrical muscles are both unipennate and bipennate. Starting from the index finger moving medially to the fifth digit, we have on the second and third digit the unipennate lumbrical muscle, and on the fourth and fifth digits the bipennate lumbrical muscles. They contribute to the flexion of the metacarpophalangeal joints and extension of the proximal interphalangeal joints. - Intraossei muscles divide in palmar intraossei muscles and dorsal intraossei muscles. Palmar intraossei muscles are 3 and are unipennate, whereas dorsal intraossei muscles are 4 and are bipennate.