Human Anatomy - Elbow Joint and Muscles PDF

Human Anatomy Professor Mangiavini 10/11/2023 Anatomy Sbobina (n.5) THE UPPER LIMBS ELBOW JOINT AND MUSCLES The elbow is a single joint between three bone...

Human Anatomy Professor Mangiavini 10/11/2023 Anatomy Sbobina (n.5) THE UPPER LIMBS ELBOW JOINT AND MUSCLES The elbow is a single joint between three bones, with one single cavity, but functionally and physiologically there are two joints inside: 1. The true or proper elbow joint: it is formed between the trochlear notch of the ulna and the trochlea of the humerus and between the head of the radius and the capitulum of the humerus; it allows the movements of flexion and extension. 2. The superior or proximal radioulnar joint: it is formed between the proximal part of the radius and the proximal part of the ulna; together with the inferior or distal radioulnar joint (that belongs to the wrist), it allows the movements of pronation and supination. TRUE OR PROPER ELBOW JOINT In the true elbow joint we can recognise two articular surfaces at the level of the arm: The trochlea: on the distal part of the humerus, the trochlea articulates with the proximal epiphisis of the ulna (the trochlear notch of the ulna, that has a coronoid process anteriorly and an olecranon process posteriorly); it has a central groove. The capitulum humeri or capitellum: on the distal part of the humeus, the capitellum articulates with the head of the radius; it is lateral with respect to the trochlea. The complex formed by the trochlea and the capitellum is like a ball and spool threaded on to the same axis, and this axis constitutes basically the axis of flection and extension of the elbow. The distal end of the humerus (trochlea + capitellum) has the shape of an artist’s palette and is flattened antero-posteriorly. In the anterior part of the distal humerus, we have the coronoid fossa that recieves the coronoid process of the ulna during flexion. In the posterior part of the distal humerus, we have the olecranon fossa that recieves the olecranon process of the ulna during extension. The shape of the distal end of the humerus and the proximal end of the ulna and the presence of these fossae is essential to allow greater range of motion in flexion and extension: − The fossae allow the trochlear notch of the ulna (semilunar surface) to glide over the trochlea of the humerus, delaying the impact of the ulna with the humerus; − The distal end of the humerus points anteriorly, making a 45° angle with the diaphysis of the humerus; − The proximal end of the ulna (trochlear notch) also points anteriorly and superiorly with a 45° angle. So, the anterior projections of the articular surfaces and their 45° orientation allow for a greater range of movement (both flexion and extension, but extension is less important in the elbow); without this organization, the maximum range of movement would be about only 90°. Paolo Bruno, Edoardo L’Ingesso Pag.1 Human Anatomy Professor Mangiavini 10/11/2023 Then, we also have two articular surfaces at the level of the forearm, corresponding to those of the humerus: The head of the radius: on the proximal part of the radius, it is concave and corresponds to the convexity of the capitellum. The trochlear notch of the ulna: on the proximal part of the ulna, it extends anteriorly and inferiorly from the coronoid process and posteriorly and superiorly from the olecranon process; it glides over the trochlea. LIGAMENTS OF THE TRUE ELBOW JOINT At the level of the true elbow joint (joint between humerus, ulna and radius) we have 2 main ligaments:  The medial or ulnar collateral ligament: it goes from the medial epicondyle of the humerus to the medial border of the trochlear notch; it has the function to strengthen the joint capsule and stabilise the true elbow joint (especially in extention); it is formed by: − The anterior fibers (green in the image); − The posterior fibres (pink in the image); − The intermediate fibres or transverse ligament of Cooper (blue in the image):  The lateral or radial collateral ligament: it goes from the lateral epicondyle of the humerus to the head of the radius, it has the function to strengthen the anular ligament, which stabilises the radioulnar joint (it stabilises the head of the radius close to the proximal epiphysis of the ulna at the level of the radial notch of the ulna); It is formed by: − The anterior fibers: they strengthen the anular ligament posteriorly; − The intermediate fibers: they strengthen the anular ligament anteriorly; − The posterior fibers. MUSCLES OF THE ELBOW (1) The muscles of the elbow, that act at the level of the true elbow joint, can be divided into flexors and extensors [the only possible movements are flexion and extension]. FLEXOR MUSCLES The three main flexor muscles (part of the arm) are the biceps, the brachio-radialis and the brachialis muscles. Then we have also some accessory muscles (part of the forearm): the extensor carpi radialis longus and the pronator teres. The flexor muscles, and especially the biceps, work at their greatest efficiency when the elbow is flexed at 90°, because, if the elbow is extended, the direction of the forces is nearly parallel to the axis of the arm; so, it is more difficult to flex, we need more force. Paolo Bruno, Edoardo L’Ingesso Pag.2 Human Anatomy Professor Mangiavini 10/11/2023  Brachialis: it originates from the anterior middle part of the humerus and inserts into the anterior tuberosity of the ulna. It is a flexor of the elbow.  Brachio-radialis: it originates from the lateral supracondylar ridge of the humerus and inserts into the styloid process of the radius (distal process of the radius). It is a flexor of the elbow, but also important for prono-supination (supinator only in extreme pronation; pronator only in extreme supination).  Biceps brachii: it is formed by a short head and a long head that originate from the scapula (short from the coracoid process; long from the supraglenoid tubercle) and fuse together in a single tendon that inserts in the radial tuberosity. It is the main flexor of the elbow, but also the main supinator. EXTENSOR MUSCLES The main extensor muscle is the triceps. Then we also have an accessory muscle called the anconeus.  Triceps brachii: it has three parts: the medial head (originates from the medial posterior surface of the humerus, close to the radial groove), the lateral head (originates from the lateral posterior border of the humerus) and the long head (originates from the inferior tubercle of the glenoid cavities). The three heads unite into a common tendon that inserts at the level of the olecranon process. KINEMATICS (1): FLEXION AND EXTENSION Again, at the level of the true elbow joint, the only movements allowed are flexion and extension. Although, since the anatomical position of reference corresponds to complete extension, the max extension of the elbow is zero by definition, with the exception of some subjects (especially women) with ligament laxity that allows 5-10° hyperextension (forearm goes a little bit posterior to the arm). Flexion is the movement that brings the forearm close to the arm. We need to distinguish between active and passive flection: − Active flexion: can reach up to 145° (average value); the reason is that the volume of the contracted flexor muscle limits the flexion range; − Passive flexion: can reach up to 160° (average value); it is limited by the tension/stretching of the triceps, by the tension/stretching of the posterior capsular ligament and by the impact of the head of the radius against the radial fossa and of the coronoid process against the coronoid fossa. SUPERIOR RADIOULNAR JOINT (SRU) It is the second joint that forms the elbow (together with the true elbow joint), and it is a trochoid joint with cylindrical surfaces; thanks to this joint the radius rotates on the radial notch of the ulna. The two cylindrical surfaces are: The head of the radius: covered by articular cartilage; The fibro-osseus ring: it is formed by the radial notch of the ulna, which is covered by articular cartilage and separated from the trochlear notch by a blunt ridge, and by the anular ligament, which surrounds the head of the radius, attaching to the anterior and posterior margins of the radial notch of the ulna. Paolo Bruno, Edoardo L’Ingesso Pag.3 Human Anatomy Professor Mangiavini 10/11/2023 The anular ligament is a ligament because it stabilizes and keeps in place the head of the radius, but also allows for the movement of rotation. The superior radioulnar joint is also stabilized by another ligament, the quadrate ligament, which is a little bit distal to the anular ligament and it connects the distal and inferior part of the radial notch to the neck of the radius. [Applied anatomy: Nursemaid’s elbow → This joint is very important. In children, one of the most common traumas is the subluxation (dislocation) of this joint just by performing traction on their arm. This is because in small children (up to 6 years) we have an increased laxity of the anular ligament: it is more elastic, so the head of the radius can slip off. This condition is called Nursemaid’s elbow, but also painful pronation because the child keeps the forearm in pronation and any movement causes pain. It is very easy to solve this condition performing a simple maneuver: we supinate and flex the elbow and the head of the radius goes back into the anular ligament.] INFERIOR RADIOULNAR JOINT (IRU) The inferior radioulnar joint is NOT part of the elbow, but it is anatomically part of the wrist joint. We introduce it now, talking about the elbow, because, together with the superior radioulnar joint it allows for the movement of rotation, so pronation and supination. It is the mirror joint of the SRU: in this case we have the rotation of the head of the ulna over the ulnar notch of the radius. MUSCLES OF THE ELBOW (2) The muscles of the elbow, that act at the level of the SRU and IRU, can be divided into pronators and supinators. In general, the pronator muscle are less powerful than the supinator muscles, and in normal condition the range of prono-supination is about 180° (90° of pronation and 90° of supination) SUPINATOR MUSCLES  Supinator: it is a muscle wound around the neck of the radius (it surrounds it) and acts by unwinding, allowing rotation and bringing back the radius on the lateral side of the ulna [movement explained in next paragraph: KINEMATICS (2)].  Biceps brachii: the main supinator is again the biceps (most efficient at 90° angle). Paolo Bruno, Edoardo L’Ingesso Pag.4 Human Anatomy Professor Mangiavini 10/11/2023 PRONATOR MUSCLES  Pronator quadratus: it is a muscle wrapped around the distal end of the ulna, and it acts by unwinding so that the radius rotates on the ulna and crosses it distally.  Pronator teres: it originates from the medial epicondyle of the humerus and inserts into the radius; it acts by traction but its action is very weak, especially if the elbow is extended. KINEMATICS (2): PRONATION AND SUPINATION At the level of the radioulnar joint, we can have also a movement of rotation, which is the movement of the forearm about its longitudinal axis. These movements, as we said, are possible thanks to the superior radioulnar joint (SRU), which anatomically belongs to the elbow and to the inferior radioulnar joint (IRU), which anatomically belongs to the wrist. In supination, the radius and the ulna are parallel to each other, they lie side by side with the ulna on the medial side and the radius on the lateral side. In pronation, the radius rotates over the ulna, so they are no longer parallel to each other, but they cross each other: the radius is lateral to the ulna proximally (near elbow), but becomes medial distally (near wrist); this is possible thanks to the shape of the radius with its angulation that allows the rotation of the ulna, and thanks to the interosseous membrane that keeps together the two bones. WRIST JOINT AND MUSCLES THE WRIST: ARTICULAR STRUCTURES The wrist is the distal joint of the upper limb and allows the hand, which is the effector segment, to assume the optimal position for prehension. It has two degrees of freedom: the first one is flection and extension, the second one is adduction and abduction. It is an articular joint (it is not a single joint), formed by two joints: The radio-carpal (RC) joint (wrist joint): it is the joint between the distal epiphysis of the radius and the proximal row of carpal bones; The mid-carpal (MC) joint: it is the joint between the first row of carpal bones and the second row of carpal bones. The ulna is NOT part of the wrist joint: it doesn’t articulate with the carpal bones, and so there is a space between the carpal bones and the ulna. This is one of the reasons why the range of adduction of the wrist is higher than the one of abduction. Paolo Bruno, Edoardo L’Ingesso Pag.5 Human Anatomy Professor Mangiavini 10/11/2023 RADIOCARPAL JOINT The RC joint is an ellipsoidal joint and it has two concavities: − a transverse concavity, important for the movements of adduction and abduction; − an antero-posterior concavity, that is related to movements of flexion and extension. The proximal articular surface of the RC joint is the distal surface of the radius and can be divided into concave parts: laterally, the concavity for the scaphoid bone, and medially, the concavity for the lunate bone. Medially, we do not have the direct involvement of the ulna (it is not part of this joint) because there is an articular disc connecting the distal ulna with the distal radius. At this level, there is a communication between the inferior radio-ulnar joint and radio-carpal joint. The distal surface of the radio-carpal joint consists of the proximal surfaces of these three bones: the scaphoid, the lunate and the triquetrum (in order from lateral to medial), joint together by interosseous ligaments. These bones are covered by articular cartilage, forming basically a continuous surface articulating with the distal radius. There is also another small bone which is not part of the radio-carpal joint but it is considered part of the first row of the carpal bones: the pisiform bone, that articulates with the triquetrum bone on the palmar surface on the ulnar side. MIDCARPAL JOINT The MC joint is the joint between the first row and the second row of carpal bones. The second row (distal row) of carpal bones comprehends the trapezium, the trapezoid, the capitate (the biggest of the carpal bones) and the hamate bones (laterally to medially); all these bones are linked by interosseous ligaments. Paolo Bruno, Edoardo L’Ingesso Pag.6 Human Anatomy Professor Mangiavini 10/11/2023 The trapezium articulates proximally articulates with the scaphoid and distally with the first metacarpal bone. The joints of these connections are the ones particularly vulnerable to arthritis. The trapezoid articulates proximally with the scaphoid and distally with the second metacarpal bone. The capitate articulates proximally with the scaphoid and with the lunate and distally with the third and fourth metacarpal bones. The hamate articulates proximally with the lunate and the triquetrum and distally fourth and fifth metacarpal bones. So, these are the proximal and distal surfaces: PROXIMAL SURFACE → The scaphoid bone that has two articulating surfaces distally for trapezium and trapezoid and a deep concave medial surface for the capitate. The lunate that has a semilunar cavity for the capitate and an articular surface for the hamate. The triquetrum that articulates distally with the proximal surface of the hamate. DISTAL SURFACE → The proximal surfaces of the trapezium and trapezoid. The head of the capitate in contact with the scaphoid and the lunate. The proximal surface of the hamate, which is mostly in contact with the triquetrum, and its small lateral facet in contact with the lunate. LIGAMENTS OF THE RC JOINT The main ligaments of the radio-carpal joint are organized in two groups: − The collateral ligaments (present in the elbow, wrist, fingers, knees, ankles), that limit the movements of adduction and abduction. − The anterior and posterior ligaments, that stabilize the joints antero-posteriorly and limit the movements of flexion and extension. COLLATERAL LIGAMENTS The lateral or radial collateral ligament (RCL) is attached to the styloid process of the radius and the scaphoid bone. It is made up of two bands: a posterior band, running from the styloid to below the lateral aspect of the proximal articular surface of the scaphoid, and an anterior band, very thick and strong, stretching from the anterior edge of the radial styloid to the anterior surface of the scaphoid. The medial or ulnar collateral ligament (UCL) is attached to the styloid process of the ulna and the pisiform and triquetrum bones. As the lateral one, it divides in a posterior band, inserted into the triquetrum, connecting the ulnar styloid process to the triquetrum bone, and an anterior band inserted into the pisiform, connecting the styloid process to the pisiform. This ligament adds support to a small disc of cartilage where the ulna meets the wrist joint: this structure is called triangular fibrocartilage complex (TFCC). Paolo Bruno, Edoardo L’Ingesso Pag.7 Human Anatomy Professor Mangiavini 10/11/2023 TRIANGULAR FIBROCARTILAGE COMPLEX The triangular fibrocartilage complex (TFCC) is a sort of meniscus that stabilizes the wrist at the distal radioulnar joint. It acts like a pillow that prevents damage of articular cartilage during abduction/adduction. It also acts as a focal point (pivot) for force transmitted across the wrist to the ulnar side. Palmarly, the TFCC inserts into the lunate and triquetrum via the ulnolunate ligament, the ulnotriquetral ligament and the radioulnar ligament. It prevents damages of the articular surface during adduction thanks to a sort of meniscus present deeper into the ligaments. Dorsally the TFCC inserts into the lunate and triquetrum via the dorsal radioulnar ligament, the extensor carpi ulnaris and the UCL. Lesions of the TFCC are common in boxing and lead to pain and limitation in the adduction; they can be repaired arthroscopically. ANTERIOR AND POSTERIOR LIGAMENTS The anterior ligament (or anterior ligamentous complex) is attached to the anterior edge of the distal surface of the radius and the neck of the capitate. It is important to limit the extension of the wrist and composed of two bands: the palmar radiocarpal ligament, divided laterally in the radio-capitate band that stabilizes the radius with the capitate, and medially the radio- triquetral band that stabilizes the radius to the triquetrum bone; the palmar ulnocarpal ligament, divided laterally in the ulnolunate band and medially in the ulnotriquetral band. The posterior ligament (or posterior ligamentous complex) stabilizes the wrist joint at the dorsal level, limiting the flexion movement. As the anterior ligament, it is composed of two bands: the dorsal radiocarpal ligament, divided in the radio- lunate and in the radio-triquetral bands; the dorsal intercarpal ligament. Paolo Bruno, Edoardo L’Ingesso Pag.8 Human Anatomy Professor Mangiavini 10/11/2023 ACTION OF THESE LIGAMENTS − During adduction, which brings the ulnar side of the hand closer to the ulnar side of the forearm, the lateral ligament is stretched and the medial ligament is loose (movement limited by the lateral ligament). − During abduction, in which the opposite of adduction occurs, the medial ligament is stretched while the lateral ligament is loose. − During flexion, the posterior ligaments are stretched. − During extension, the anterior ligaments are stretched. LIGAMENTS OF THE MC JOINT The radio-capitate ligament: it runs obliquely distally and medially from the lateral portion of the anterior border of the distal surface of the radius to the anterior aspect of the neck of the capitate. The triquetro-capitate ligament: it runs obliquely distally and laterally from the anterior aspect of the triquetrum to the neck of the capitate, where it helps to form a true ligamentous complex with the other preceding ligaments. The scapho-trapezium ligament: short but broad and stout, linking the scaphoid tubercle, the anterior aspect of the trapezium above its oblique crest and the trapezoid. The scapho-lunate ligament: it connects scaphoid to the lunate ligament; lesions to this ligament lead to the instability of the mid-carpal joint and subluxation of the lunate bone. The triquetro-hamate ligament: in effect constituting the medial ligament of the mid- carpal joint and connects the triquetrum to the hamate. The piso-hamate ligament: it connects the pisiform to the hook of the hamate. Paolo Bruno, Edoardo L’Ingesso Pag.9 Human Anatomy Professor Mangiavini 10/11/2023 MUSCLES OF THE FOREARM There are 17 muscles crossing the elbow joint: they control the movements of the wrist, of the hand and of the elbow. The majority of these muscles originate from the medial and lateral epicondyles of the humerus. The tendons of these muscles pass through the distal part of the forearm and continue into the wrist, hand and fingers. FLEXOR-PRONATOR MUSCLES The flexor-pronator muscles are mostly present in the anterior compartment and have approximately twice the bulk and strength of the extensor muscles of the posterior compartment. They are separated from the extensor muscles of the forearm by the radius and ulna and, in the distal two thirds of the forearm, by the interosseous membrane that connects them. The tendons of most flexor muscles are located on the anterior surface of the wrist and are surrounded by a synovial membrane which produces synovial fluid that allows the sliding of the tendons. They are held in place by the palmar carpal ligament and by the transverse carpal ligament (flexor retinaculum). The transverse carpal ligament underneath has the medial nerve together with the flexor tendons and for this reason, if a problem persists at the level of these ligaments, there could be a compression of the medial nerve leading to paresthesia of the first, second, third and half of the fourth finger on the palmar side and also decreased force, especially in muscles of the first finger. The compression can be caused by hormonal changes leading to thickening of these ligaments during pregnancy. Starting from the anterior compartment of the forearm, it is possible to divide the flexor muscles into three layers: 1. Superficial layer: it consists of four muscles (pronator teres, flexor carpi radialis, palmaris longus and flexor carpi ulnaris) that originate from the medial epicondyle of the humerus, all attached to it thanks to the common flexor attachment tendon. Pronator teres: it is the most lateral of the muscles of the superficial layer and originates from the medial epicondyle of the humerus and from the coronoid process of the ulna; laterally, it inserts in the lateral surface of the radius. Its action is the internal rotation of the elbow joint bringing the forearm in a prone position, but also cooperates in the flexion of the elbow joint. Flexor carpi radialis: it is located medially to the pronator teres; it originates from the medial epicondyle of the humerus and inserts at the base of the second metacarpal. Its action is the flexion of the wrist and of the midcarpal joints and the abduction of the hand; it also cooperates in the flexion of the elbow joint and in the pronation of the forearm and hand. Paolo Bruno, Edoardo L’Ingesso Pag.10 Human Anatomy Professor Mangiavini 10/11/2023 Palmaris longus: it is located between the flexor carpi radialis and the flexor carpi ulnaris; originates from the medial epicondyle of the humerus, and terminates in the palmar aponeurosis, which is a sort of a fibrous tissue surrounding all the carpal region; its action is helping the flexion of the wrist and of the midcarpal joints. It is a weak muscle and for this reason it is possible to use it in case of necessity to repair another tendon in other regions of the body. Flexor carpi ulnaris: it originates from the medial epicondyle of the humerus and terminates at the level of the pisiform bone, bounding the hook of hamate and the fifth metacarpal bone. Its action is flexing and adducting the hand. 2. Intermediate layer: it consists of one muscle: the flexor digitorum superficialis, that originates from the medial epicondyle of the humerus and terminates in the middle phalanx of the fourth digit. It allows the flexion at the level of the metacarpal-phalangeal joint and proximal interphalangeal joints of the digits except for the pollicis, and it also cooperates to the flexion of the wrist and of the elbow joints. 3. Deep layer: it consists of three muscles (flexor digitorum profundus, flexor pollicis longus, and pronator quadratus). Flexor digitorum profundus: it originates from the anterior and medial surfaces of the ulna and it divides into four tendons (corresponding to the digits with the exception of the pollicis). It controls the flexion of the distal interphalangeal joints and cooperates to the flexion of the proximal interphalangeal and metacarpophalangeal joints. Flexor pollicis longus: it originates from the anterior surface of the radius and it reaches the distal phalanx of the first finger, the thumb (which has two phalanges differently from the other fingers, the proximal and the distal phalanx, with no middle phalanx). It regulates the flection of the interphalangeal joint of the thumb. Pronator quadratus: it is the deepest muscle of the anterior muscles of the forearm; it originates from the anterior surface of the ulna and terminates at the anterior surface of the radius; its action is the internal rotation of the elbow joint bringing the forearm and hand in prone position. Paolo Bruno, Edoardo L’Ingesso Pag.11