ANATOMY LOCOMOTOR SYSTEM KEY INFO 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 the posterio...

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 o Serratus anterior: § Originates from 1st to 9th rib § Inserts into medial border of the scapula § Performs abduction and upward rotation of scapula o 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 o 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 o 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 o 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 o 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 o Supraspinatus: § Originates from the supraspinal fossa § Inserts into uppermost facet of greater tubercle § Performs abduction of glenohumeral joint o Infraspinatus: § Originates from the infraspinous fossa  § Inserts into the middle facet of the greater tubercle § Performs external rotation of the glenohumeral joint o 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 o 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 o 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 o 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 o 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 internal rotation, extension, and adduction of the glenohumeral joint (also performs scapular depression) Motor muscles of supination: o Supinator muscle o Biceps brachii Motor muscles of pronation: o Pronator quadratus o 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 o 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: o Pronator teres: lateral middle surface of the radius; performs pronation and flexion of the arm. o Flexor carpi radialis: base of the second metacarpal bone; flexes and abducts the wrist. o Palmaris longus: distal half of flexor retinaculum and palmar aponeurosis; flexes the wrist and tenses the aponeurosis.  o Flexor carpi ulnaris: pisiform bone, hook of the hamate bone, and fifth metacarpal bone; flexes and adducts the wrist. o 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 o 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 o Superficial layer: § Brachioradialis Originates from the proximal 2/3rds 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 o 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. Lower Limb The lower limb consists of the pelvic girdle and the attached component that forms the free lower limb, just as the shoulder girdle for the free upper limb. The pelvic girdle consists posteriorly of the sacrum (composed of 5 sacral vertebrae and 4 coccygeal vertebrae essentially fused together into a single bone structure – in younger individuals the 5 sacral vertebrae have some little synovial fluid between them, but soon becomes solidified, fusing the vertebrae together). The sacrum is attached laterally on both sides by the ilium, which is attached, through a series of ligaments, inferiorly and posteriorly to the ischium and inferiorly and anteriorly to the pubis. The two pubic bones on both sides attach together anteriorly and medially through the pubic symphysis. The acetabulum is the articulating portion of the hip structure (ilium, ischium, and pubis) that will host the head of the femur. It possesses itself, just as the glenoid cavity, of an acetabular labrum, which improves the congruency and total articulating surface area for the femoral head. Remember that the acetabular labrum, just as the glenoid labrum, is a fibrocartilaginous layer. The ilium is the largest bone of the hip and is the one attached to the sacrum laterally and posteriorly via the sacroiliac joint. The ilium consists medially and inferiorly of a body, which forms the major part of the acetabular structure, together with the ischium and pubis. The body is mainly responsible for weight bearing and distribution. The superior medial aspect instead constitutes the ala, which is the concave portion of the ilium. The ala is responsible for the formation of the iliac fossa, where a number of gluteal muscles insert, including the iliacus muscle for instance. The ilium also possesses a crest, both anterior and posterior, which provides a total of 4 bony tuberosities. Ligaments and tendons attach on the anterior inferior and anterior superior iliac spines, where other muscles instead insert and originate from the posterior inferior and posterior superior iliac spines. The posterior inferior iliac spine is also a checkpoint for the recognition of the greater sciatic notch.  The ischium is the posteroinferior bone of the hip. It consists of a body and two rami: the superior ramus and the inferior ramus. The superior ramus is connected to the ilium and the body of the ischium, and defines the posteroinferior aspect of the acetabulum. The body then proceeds with the inferior ramus which is instead attached to the pubic bone. At this point, the inferior ramus of the ischium attaches to the inferior ramus of the pubis and forms the ischiopubic ramus, which defined the inferior portion of the obturator foramen. The ischium possesses two major tuberosities: the ischial spine, responsible for the formation of the posteroinferior margin of the greater sciatic notch, and the ischial tuberosity, located inferiorly on the body of the ischium and responsible for the attachment of muscles. The pubic bone is located anteroinferior and consists itself, just as the ischium, of a central body and two rami. The superior ramus is connected to the ilium and identifies the anteroinferior margin of the acetabulum, whereas the inferior ramus is connected to the ischium through the formation of the ischiopubic ramus. On the body of the pubic bone, which lies at the centre, we find the attachment of the adductor muscles of the thigh, and on the anterosuperior aspect of the body there is the pubic crest, instead responsible for the insertion of abdominal muscles. Anterolaterally on the body there are also the pubic tubercles which provide attachment for the inguinal ligament (providing an indirect attachment site for muscles). Remember that the pubic tubercles are oriented laterally with respect to the medial pubic symphysis, as they are still located on the body of the pubic bone, which is more medial with respect to the two rami. The pubic crest is formed through the formation of the pubic symphysis by the medial articulation of the two symphysial surfaces of the body of the pubic bone. On the posterior aspect of the superior ramus of the pubic bone there is the pecten pubis, which is a medial protrusion that forms part of the pelvic rim. The acetabulum is essentially a socket (just as the glenoid cavity) which enables for the formation of a synovial ball and socket joint with the femoral head. It is not entirely spherical however as there is an inferior hole, where the ischium and pubis attach. This little hole is called acetabular notch. The acetabulum itself, above the acetabular notch, is the acetabular fossa proper, which is the articulation site of the head of the femur. The acetabular labrum is the incomplete fibrocartilaginous ring that surrounds the external portion of the acetabulum, providing a deeper acetabular fossa and greater articulating space for the femoral head. The labrum, being an incomplete ring, at the level of the acetabular notch proceeds with the transverse acetabular ligament. Remember that the acetabulum is directed inferiorly, anteriorly, laterally, as the head of the femur is directed medially, superiorly, and posteriorly. The acetabulum forms an angle of 30-40° of elevation on the horizontal axis in order to provide coverage and articulating area for the femoral head. Also, it has an anterior orientation of 15-20° with the frontal axis. The femur is the longest and heaviest bone of our body. It consists of a shaft and two epiphyses, one proximal and one distal. The proximal epiphysis is involved in the hip joint whereas the distal epiphysis in the knee joint. The proximal surface consists of a head, neck, and two trochanters, one greater and one lesser. The head is the articulating portion of the femur with the acetabulum, and is spherical in shape except for a small medial depression, called fovea. The fovea is the site where the ligamentum teres is formed, attaching the femoral head with the acetabulum. The greater and lesser trochanters are found on the proximal end of the shaft of the femur. These constitute the insertion and origin of a series of muscles of the thigh and leg. The greater trochanter is found laterally and faces slightly posterior, whereas the lesser trochanter is located medially and below the neck and head of the femur. Note that the greater trochanter is a large, irregular, quadrilateral eminence of the proximal end of the shaft of the femur.  The intertrochanteric line is a landmark that states the border between the proximal end of the shaft of the femur and its neck. On the greater trochanter insert and originate abductor and rotator muscles of the thigh, whereas on the lesser trochanter insert the tendon of the psoas major and the iliacus. The femoral head makes an angle of 120-125° with the shaft, and of 10-30° with the frontal plane. As we age, the angle decreases. Indeed, newborns have a head-shaft angle of 150°, which then stabilises at around 120-125° in adulthood. The angle of femoral neck anteversion (hence the angle between the neck of the femur and the shaft) is of 14° (between 8-15°), and represents the angle of anterior anteversion with respect to the shaft (where the head is angled slightly forward with respect to the shaft). The ligamentum teres is between the anterosuperior part of the fovea and attaches to the acetabulum by means of two bands, one into each side of the acetabular notch. The ligamentum teres plays a trivial mechanical role in femoral dynamics and provides vascular supply to the femoral head via the artery of the ligamentum teres, a posterior branch of the obturator artery. The hip joint is constituted by the articulation between the acetabulum and the head of the femur. It is maintained highly stable through the presence of a series of ligaments and articular capsules. The hip capsule surrounds entirely the head of the femur, and is formed by interaction medially of the acetabular labrum and transverse acetabular ligament and laterally with the neck of the femur. The hip capsule constitutes of 2 types of fibres, which are longitudinal and circular. The hip capsule and hip joint in general is kept stable through the presence of 3 main ligaments: posteriorly the ischiofemoral ligament, which sends fibres posteriorly from the ischial part of the acetabular labrum to the trochanteric fossa of the femur; anterosuperior the iliofemoral ligaments, which are two and send fibres from the anterior inferior iliac spine of the ilium to the intertrochanteric line and the proximal end of the femur; anterior the pubofemoral ligament, which sends fibres from the obturator crest and superior ramus of the pubic bone to the anterior surface of the trochanteric fossa. In the erect position, these ligaments are under moderate tension. During extension of the hip (from orthostatic position the thigh moves behind, bringing the straight free part of the lower limb posteriorly) all ligaments become stiff, winding around the femoral head. During flexion instead, where the thigh is brought towards the thorax, ligaments relax. Stiffening of ligaments during extension and their relaxation during flexion also explain why the hip joint has a much higher angle of flexion and such limited angle of extension (as extension itself is limited by ligament stiffening). During lateral rotation of the hip, the greater trochanter undergoes medial rotation (as it is located laterally) and becomes more posterior, whereas the lesser trochanter undergoes lateral rotation (as it is located medially) and becomes more anterior. This helps us to understand that when we are laterally rotating our hip the anterior ligaments (iliofemoral and pubofemoral) become tense and stiffen up to limit over ext. rotation, whilst the posterior ischiofemoral ligament relaxes. Inversely, during internal rotation the anterior ligaments relax, as they essentially become shorter as the hip is moving towards their direction (medially) and the posterior ischiofemoral ligament instead tenses up to inhibit over int. rotation. During adduction instead the iliofemoral ligament is tense (including the ischiofemoral ligament) whilst the pubofemoral ligament is relaxed, whilst during abduction the pubofemoral ligament tenses up, and the iliofemoral ligament relaxes (with the ischiofemoral ligament being partially relaxed). This makes sense as during adduction, being the pubofemoral ligament the medial most ligament of the hip, it shortens when the hip moves towards such direction. The iliofemoral ligament instead tenses up during adduction because it originates from the anterior inferior iliac spine, and thus sends fibres vertically towards the intertrochanteric line, which tense up when the hip is stretched medially. Inversely, they relax when the hip abducts, as it moves superiorly and  laterally, relaxing the descending fibres of the iliofemoral ligament and stretching the transverse fibres of the pubofemoral ligament for the same inverse reason. Muscles of the thigh can be organised depending on their location, therefore, either anterior or posterior, and depending on their action. Muscles of anterior and medial thigh o Hip Flexors (5 total): § Pectineus Originates from the superior ramus of the pubis Inserts into the pectineal line of the femur, just below the lesser trochanter Performs flexion and adduction of the hip, and aids in lateral rotation § Psoas major Originates from the transverse process and intervertebral disc of vertebrae from T12 to L5 Inserts into the lesser trochanter of the femur Perform flexion of the hip joint, and flexion + ipsilateral flexion of the trunk § Psoas minor Originates from the side and intervertebral disc of T12 and L1 Inserts into the pectineal line via the iliopectineal arch Performs flexion of the hip joint, and flexion + ipsilateral flexion of the trunk § Iliacus Originates from the iliac crest, iliac fossa, sacral ala, and anterior sacroiliac ligaments Inserts into the lesser trochanter and proximal end of the femur, as well as in the tendon of the psoas major Performs flexion of the hip joint, and flexion + ipsilateral flexion of the trunk § Sartorius Originates from the anterior superior iliac spine Inserts into the pes anserinus of the tibia (medial aspect of the proximal end of the tibia) Performs flexion, abduction, and lateral rotation (when the knee is flexed) of the hip; performs also knee flexion and intra-rotation of the leg when the knee is flexed o Knee Extensors (quadriceps femoris – 4 total): § Rectus femoris Originates from the anterior inferior iliac spine and ilium superior to the acetabulum Inserts into the base of the patella by means of the quadriceps tendon and indirectly into the tibial tuberosity through the patellar ligament Performs knee extension and aids the iliopsoas (psoas major, psoas minor, and iliacus) in hip flexion § Vastus medialis Originates from the intertrochanteric line and medial lip of the linea aspera of the femur Inserts into the base of the patella by means of the common quadriceps femoris tendon, as well as indirectly with the tibial tuberosity via the patellar ligament, and the patella and tibia by means of an aponeurosis  Performs knee extension § Vastus intermedius Originates from the anterior and lateral surfaces of the midshaft of the femur Inserts into the base of the patella by means of the common quadriceps femoris tendon, as well as indirectly with the tibial tuberosity by means of the patellar ligament Performs knee extension § Vastus lateralis Originates from the greater trochanter and lateral lip of the linea aspera of the femur Inserts into the base of the patella by means of the common quadriceps femoris tendon, as well as indirectly with the tibial tuberosity through the patellar ligament. It is also attached to the patella and tibia by means of an aponeurosis (in the same way as the vastus medialis) Performs knee extension o Hip adductors (5 total): § Adductor brevis Originates from the body and the inferior ramus of the pubic bone Inserts into the pectineal line and proximal part of the linea aspera of the femur (just below the lesser trochanter) Performs hip adduction and slight flexion of the thigh § Adductor longus Originates from the body of the pubic bone, inferior to the pubic crest Inserts into the middle third of the linea aspera Performs hip adduction and slight flexion of the thigh § Adductor magnus Adductor component: o Originates from the inferior ramus of the pubic bone and ramus of the ischium o Inserts into the gluteal tuberosity, linea aspera, and medial supracondylar line o Performs hip adduction and slight flexion of the thigh Hamstring component: o Originates from the ischial tuberosity o Inserts into the adductor tubercle of the femur o Performs hip adduction and slight extension of the thigh § Gracilis Originates from the body and inferior ramus of the pubic bone Inserts into the pes anserinus (medial aspect of the proximal end of the tibia) Performs adduction and flexion of the hip, also aiding in medial rotation § Obturator externus Originates from the margin of the obturator foramen and membrane Inserts into the trochanteric fossa of the femur Performs lateral rotation of the hip, and maintains the head of the femur with the acetabulum Muscles of gluteal region o Superficial layer (4 total):  §Gluteus maximus Originates from the posterior gluteal line (posterior surface of the ilium), from the dorsal surface of the sacrum and coccyx, and from the sacrotuberous ligament (which connects the ischial tuberosity to the lateral surface of the lower sacrum and upper coccyx) Inserts into the lateral tibial condyle through the iliotibial tract (composed of the tensor fascia latae and gluteus maximus) and into the gluteal tuberosity of the femur Performs extension of the hip joint (especially from the flexed position – squat position), as well as the trunk. Assists also in lateral rotation of the hip § Gluteus medius Originates from the anterior and posterior gluteal lines of the external surface of the ilium Inserts into the lateral surface of the greater trochanter Performs abduction and extension of the hip joint. It also stabilises the pelvis when the ipsilateral limb is weight bearing § Gluteus minimus Originates between the anterior and posterior gluteal lines of the external surface of the ilium Inserts into the anterior surface of the greater trochanter Performs extension and abduction of the hip joint, and aids stabilisation of the ipsilateral limb during weight bearing § Tensor fascia latae Originates from the anterior superior iliac spine and the anterior part of the iliac crest Inserts into the lateral condyle of the tibia by means of the iliotibial tract tendon (formed with the gluteus maximus) Performs abduction and lateral rotation of the hip joint. It also stabilises the pelvis when the ipsilateral limb is weight bearing o Deep layer (5 total): § Piriformis Originates from the anterior surface of the sacrum and sacrotuberous ligament Inserts into the superior aspect of the greater trochanter Performs lateral rotation of the hip when extended and performs abduction of the flexed thigh. It also stabilises the femoral head in the acetabulum § Obturator internus Originates from the posterior (pelvic) surface of the obturator membrane and adjacent bones Inserts into the medial surface of the greater trochanter Performs lateral rotation of the extended hip and abduction of the flexed thigh. It also stabilises the head of the femur into the acetabulum § Superior gemellus Originate from the ischial spine Inserts into the medial surface of the greater trochanter Performs lateral rotation of the extended hip and abduction of the flexed thigh. It also stabilises the head of the femur into the acetabulum  § Inferior gemellus Originates from the ischial tuberosity Inserts into the medial surface of the greater trochanter Performs lateral rotation of the extended hip and abduction of the flexed thigh. It also stabilises the head of the femur into the acetabulum § Quadratus femoris Originates from the lateral surface of the ischial tuberosity Inserts into the quadrate tubercle of the intertrochanteric line Performs lateral rotation of the hip joint. It also stabilises the head of the femur into the acetabulum Muscles of posterior thigh o Hip extensors and knee flexors (3 total): § Semitendinosus Originates from the ischial tuberosity Inserts into the pes anserinus (superior medial surface of the tibia) Performs hip extension when the knee is flexed, flexes the leg and medially rotates it when the knee is flexed, and slightly extends the trunk § Semimembranosus Originates from the ischial tuberosity Inserts into the posterior surface of the medial condyle of the tibia. Its tendon reflection gives rise to the oblique popliteal ligament Performs hip extension when the knee is flexed, medial rotation and flexion of the leg when the knee is flexed, and slightly extends the trunk § Biceps femoris The long head originates from the ischial tuberosity; the short head originates from the linea aspera of the lateral supracondylar line of the femur Inserts into the lateral surface of the head of the fibula by means of the biceps femoris tendon. The tendon is separated in two at the insertion site by the fibular collateral ligament of the knee Performs leg flexion and rotates it laterally when the knee is flexed. It also extends the thigh and the trunk The hip joint (coxo-femoral joint) is similar in terms of structure to the glenohumeral joint, with the large difference that the glenohumeral joint is very much dislocation prone (as it has greater degrees of movement) with respect to the hip joint. This means that despite having smaller ranges of dynamics, the coxo-femoral joint is much more stable and less prone to dislocation. It is indeed the most stable joint in our body. This makes sense when we think in terms of the great weight bearing that the whole pelvic structure has to sustain. Flexion has a range of motion of 90° when the knee is extended. It increases to 120° and further when the knee is flexed. Clearly, passive flexion has a greater range of flexion compared to active flexion. Extension is the opposite, where when the knee is flexed the range is very small and limited, yet when it is extended, the leg can be extended up to 20° of angle posteriorly. When we tilt forward the pelvis there is a large increase in the available extension angle as a result of lumbar lordosis. The maximum range of abduction is reached when the angle in between the two lower limbs is of 90°. Abduction is restricted by adductor muscles and the pubofemoral ligament. Pure adduction cannot be achieved alone, and has to be paired with either extension, flexion, or abduction of the other lower limb. In any case, the maximum angle of adduction is 30°.  In the prone position (when laying down) when the leg moves medially the range of lateral rotation occurs at a maximum angle of 60°, whereas when the leg moves laterally, the maximum angle of medial rotation is of 30-40°. The knee is an important point of junction in the lower limb between the femur, tibia, and fibula, to develop the lower component of the lower limb itself. It serves a primary purpose of weight bearing and locomotion, primarily through its main axis, allowing for flexion and extension. When the knee is flexed it has an accessory degree of freedom, which is a slight medial and lateral rotation of the long axis of the leg. Again this only occurs when the knee is flexed as when it is instead extended the extensor muscles inserting into the pes anserinus, base of the patella, and tibial tuberosity inhibit individual rotation of the knee in any direction (only allow for entire leg rotation). The femur forms an obtuse angle with the tibia, causing a physiological valgus of the knee. The angle is indeed of 170-175°, hence slightly tilted inwards. The mechanical axis represents the leg and thigh at an exactly 0° difference, where the head of the femur (hip joint) is exactly aligned vertically with the knee joint and the ankle joint. The anatomical axis instead shows a 6° tilt of the hip joint, as the femur is not straight from proximal to distal epiphyses, and for this reason has a 6° acute angle of difference with the mechanical axis (anatomically speaking). The knee joint consists of 3 subjoints: two condyloid joints and one patella-femur joint. Note that the two condyloid joints are between the respective medial and lateral condyles of the tibia and femur and between the menisci (lateral and medial). The knee joint proper is a hinge type of joint. Femoral condyles are large and constitute almost entirely the distal epiphysis of the femur. They are both convex in shape yet are different in terms of size: the lateral condyle has a larger protrusion whereas the medial condyle is smaller and designated more for weight bearing. The two condyles, being large protrusions, form a sulcus posteriorly and inferiorly between them, which is called intercondylar fossa. Anteriorly of the intercondylar fossa, the two condyles merge into a shallow depression which represents the articulating patellar surface (indeed for articulation of the femur with the patella). The lateral condyle has a central projection that is referred to as lateral epicondyle. Same does the medial condyle, yet the projection is larger, and forms the medial epicondyle. Proximal to the medial epicondyle there is also the adductor tubercle, where the hamstring component of the adductor magnus inserts. The lateral and medial epicondyles are crucial as they are the attachment sites of the collateral ligaments of the knee joint. The superior surface of the proximal epiphysis of the tibia is composed of two plateaus (medial and lateral) with an intercondylar eminence between them. These are important articulating surfaces that will form the base of the knee joint, known as the tibial plateau, which will articulate each with their respective femoral condyle (medial tibial plateau will articulate with the medial femoral condyle and the same goes for the lateral side). It is important to note that the medial plateau is concave superiorly with a curvature radius of 80mm, whereas the lateral plateau is convex superiorly with curvature radius of 70mm. The intercondylar eminence located between the two tibial plateaus is given rise by the presence of the medial and lateral intercondylar tubercles. These tubercles fit posteriorly and superiorly into the intercondylar fossa (posterior and inferior on the distal epiphysis of the femur) and provide an attachment site for the menisci and a series of ligaments. The lateral tibial condyle, where the iliotibial tract inserts, is not the precise name of this tendon’s insertion, as it technically inserts into the Gerdy tubercle, which is located laterally of the tibial plateau. Note that the Gerdy tubercle is located within the lateral condyle of the tibia. Below the lateral plateau there is the fibular articular facet, which is indeed articulates posterolaterally with the head of the fibula.  On the anterior surface of the tibia there is the tibial tuberosity, which a rather large area on the proximal end of the tibia where the patellar ligament attaches, extending from the base of the patella. Through this ligament in fact, the quadriceps femoris inserts into the tibial tuberosity, other than inserting into the base of the patella through the quadriceps tendon. Note that the patella lies in front of the anterior intercondylar depression of the femur, and is the largest sesamoid bone of the body. The articulation with the two femoral condyles is enabled by the presence (posteriorly) of a layer of cartilage on the actual patellar structure. The articular capsule of the knee is rather similar to any other articular capsule where indeed the two major areas involved in the formation of the joint (distal femoral epiphysis and proximal tibial epiphysis) are covered by this non-bony wall of articular layer, which is filled in synovium (a synovial membrane of connective tissue that produces and regulates the amount of synovial fluid present within the joint). The capsule attaches to the medial, lateral, and anterior articulating surfaces of the tibia. Posterolaterally the capsule lines the tibial condyle and joins the tibial insertion of the posterior cruciate ligament, whereas posteromedially it blends into the tibial insertion of the posterior cruciate ligament. The infrapatellar pad is a layer of adipose tissue that acts as a protective layer against impingement between the anterior intercondylar fossa of the tibia, the patellar ligament, and the inferior aspect of the patellar surface of the femur. During flexion it is squeezed by the patellar ligament and gets separated on either side of the patellar apex (both laterally and medially). The lack of congruence of the articular surfaces of the knee are corrected by the presence of pads called menisci. Menisci (lateral and medial) have a triangular shape with a concave superior aspect to host the respective femoral condyle, a cylindrical peripheral surface in contact with the articular capsule, and an almost flat inferior surface which is instead in contact with the respective tibial plateau. The central area of the knee on its base (superior surface of the proximal epiphysis of the tibia) is covered anteriorly by the intercondylar fossa and posteriorly by intercondylar eminence. Due to the presence of these two irregular structures (as well as the intercondylar tubercles) the menisci are not circle shaped, and form an anterior and posterior horn. The horns of the lateral meniscus are closer to each other (making almost an entire circle), whereas the horns of the medial meniscus are farther away in a more of C shape. The anterior horns of the two menisci are attached together by means of the transverse ligament of the knee, which is itself connected to the patella by means of the infrapatellar pad. Menisci are also kept in position by fibres running from the lateral surfaces of the patella to the two menisci, forming menisco-patellar fibres. The medial collateral ligament of the knee is indeed attached by means of its deep fibres to the internal border of the medial meniscus. The peripheral one-third of the menisci is vascularised, while the vascularisation decreases as we move deeper into the structure. Consequently, damage to the peripheral region has a better potential for natural healing due to its blood supply. In contrast, injuries to the middle and inner thirds, which lack significant vascularisation, often require surgical intervention for repair or reconstruction. Menisci are very important shock absorbers, where the compression forces applied on the femur are transduced on the tibia. Menisci serve to limit the strength of these forces in order to limit the strength of the impact. During flexion, both menisci move posteriorly, covering the posterior part of the tibial condyle (both medial and lateral). Note that the posterior displacement of the two menisci (medial and lateral) is much different. Indeed, the lateral meniscus recedes twice as far compared to the medial meniscus, where the medial travels posteriorly only by 6mm, whereas the lateral meniscus by 12mm. During lateral rotation instead the lateral meniscus moves towards the anterior aspect of its respective tibial condyle (lateral in this case), and the medial meniscus instead travels posteriorly.  During medial rotation instead the medial meniscus moves anteriorly (forward), whilst the lateral meniscus moves posteriorly (recedes). Collateral ligaments serve to stabilise the articular capsule on the medial and lateral aspects. These are also important as they help stabilising the joint when the knee is extended. The anterior cruciate ligament is attached to the anterior intercondylar fossa of the tibia, along the edge of the medial tibial condyle and between the insertion of the anterior horn of the medial meniscus anteriorly and the insertion of the lateral meniscus posteriorly. It runs obliquely (superiorly and laterally) attaching to the internal aspect of the lateral condyle of the femur. The anterior cruciate ligament consists of two bands, one anteromedial, more prone to injuries due to its length and superficiality, and one posterolateral, shorter, more protected, and less involved in tears. The posterior cruciate ligament inserts into the intercondylar notch of the intercondylar fossa of the femur (behind the attachment of the anterior cruciate ligament). It arises from the posterior intercondylar fossa of the tibia posteriorly (located behind the posterior horns of the lateral and medial menisci). It runs superiorly and medially to insert into the intercondylar notch and partially into the lateral surface of the medial femoral condyle. The posterior cruciate ligament is composed of 4 bands: posteromedial band, inserted most posteriorly into the tibia and most medially into the femur, anterolateral band, inserted most anteriorly into the tibia and most laterally into the femur, anterior band of Humphrey, often absent, and finally the menisco-femoral ligament of Wrisberg which runs from the posterior horn of the lateral meniscus to a common insertion site on the lateral surface of the medial femoral condyle (menisco-femoral ligament for this reason). Sometimes this menisco-femoral ligament of Wrisberg is also present anteriorly with the anterior cruciate ligament where few fibres from this ligament attach to the anterior horn of the medial meniscus, near the site of attachment of the transverse ligament, connecting the two menisci together. Cruciate ligaments do not have the same angle of inclination during flexion and extension. When the knee is fully extended, the anterior cruciate ligament lies more vertically whilst the posterior cruciate ligament lies more horizontally. When the knee is flexed instead, the posterior cruciate ligament rears itself up and forms a vertical angle of 60° with the tibia, whilst the anterior cruciate ligament is raised only slightly. Starting from the neutral position or a slight flexion (30°), both cruciate ligaments are tense. Flexion up to 60° has no to little effect on the tensile force exerted on the ligaments. When flexion increases to 90-120° the posterior cruciate ligament rears up vertically and is more stretched compared to the anterior cruciate ligament. Indeed, the posterior cruciate ligament is more stretched during flexion. The anterior cruciate ligament is instead much more stretched during extension/hyperextension, whilst only the posterosuperior fibres of the posterior cruciate ligament are stretched during extension. In general, the two ligaments serve the primary purpose to limit anteroposterior translation of the tibia on the femur during flexion and extension. The muscles that act on the knee joint are several, and are divided into extensors and flexors. Note that extensor muscles are located on the anterior surface of the thigh, whereas the flexor muscles are located on the posterior surface. Extensor muscles of the knee are the quadriceps femoris (rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis). Flexor muscles the knee are much more and these are the semitendinosus, semimembranosus, gracilis, sartorius, popliteus, gastrocnemius (medial and lateral heads), and biceps femoris (medial and lateral heads). Note that out of these muscles there are 3 that insert in the pes anserinus of the tibia, and these are the semitendinosus, the gracilis, and the sartorius. Also, the sartorius is not part of the posterior surface of flexor muscles, but rather is a flexor muscle located anteriorly.  It is also important to note that flexor muscles of the knee are at the same time rotators of the latter. Depending on their insertion site (either medial or lateral to the central axis of rotation of the knee) they undergo lateral (external) or medial (internal) rotation. Muscles that insert in the pes anserinus (medial surface of the proximal epiphysis of the tibia, medial to the tibial tuberosity) perform in fact medial rotation. These muscles are the sartorius, gracilis, and semitendinosus. Note that also the semimembranosus (which inserts into the posterior aspect of the medial tibial condyle) and the popliteus (which inserts into the posterior surface of the tibia, slightly below the medial tibial condyle) are medial rotator muscles as they insert medially of the axis of rotation of the knee. Flexor muscles that instead insert into the lateral portions of the tibia are lateral rotator muscles, as they are located laterally of the axis of rotation. These muscles include the biceps femoris and the tensor fascia latae. Flexion and extension occur around the transverse axis, on the sagittal plane. In the orthostatic position, the knee is in full extension (as we describe knee extension as the maximal angle from which the posterior aspect of the leg is far away from the posterior aspect of the thigh). It is however possible to reach an angle of 5-10° of extension angle when the leg is passively extended. Relative extension is the combined movement with flexion that enables us to walk and run. Indeed, relative extension is performed whenever the lower limb, once off the ground, is tilted back straight down to allow the foot to make contact with the ground. Knee flexion, as extension, can be absolute (with respect to the initial orthostatic position) or relative, according to any partial flexion position. There are 3 achievable degrees of flexion. The first is when the hip is in full extension, where the maximal angle of knee flexion reaches the 120°. The second degree of flexion occurs when we have both the flexion of the hip and the flexion of the knee. In this situation, the maximal angle of flexion reaches the 140°. The third degree of flexion can be achieved via passive flexion, where the maximal flexion angle achievable is of 160° (where the heel touches the buttock). Femoral condyles roll and slide on the tibial plateaus when, from the orthostatic, fully extended position, we start to flex the knee. Initially, the femoral condyles only roll on the tibial plateaus’ surface, and once reached a certain degree of flexion start to roll and slide. When flexion is terminating, the condyles slide without rolling. Pure rolling is achieved only at the very first degrees of flexion, and these are different for the two condyles. The medial condyle has a smaller degree, where pure rolling is achieved only at around 10-15° of flexion. The lateral condyle instead has a degree of pure rolling up to 20° of flexion. Knee rotation can only be achieved when the knee is flexed, as the proper anatomical structure of the knee does not allow for medial and lateral rotation when the knee is in full extension (as that implies hip rotation rather than knee rotation, due to their axis being the same). Medial rotation sees the foot’s toes facing medially, important in foot adduction, whereas lateral rotation sees the foot’s toes facing laterally, important in foot abduction. It is important to note that the angle of medial rotation is smaller compared to the angle of lateral rotation. Indeed, lateral rotation has a maximal angle of 40° whereas medial rotation a maximal angle of 30°. Passive axial rotation can be measured only when the individual is in the prone position (laying down) and the knee is flexed. The degree of passive rotation is greater compared to the degree of active rotation. Automatic rotation involves the involuntary slight rotation angle of the foot in the final stages of extension and of the leg in the initial stages of flexion. Indeed, when the knee is fully extended there is slight lateral rotation of the foot whereas when we begin the flexion movement, the leg is automatically rotated medially. The extensor apparatus of the knee is responsible for the superior and inferior movement of the patella on the distal epiphysis of the femur, more precisely in the area of the intercondylar notch  (where the patella will deepen when the knee is extended). When the knee is extended, the quadriceps femoris contracts, and thus shortens, and vertically displaces the patella superiorly. During flexion instead, due to relaxation of the quadriceps femoris, the patella is vertically displaced inferiorly, aligning it with the intercondylar notch. The motion of the patella on the distal epiphysis of the femur is like that of a cable on a pulley. The patella also moves in concomitance with the tibia, both during flexion and extension, and during axial rotation. In the orthostatic position the patellar ligament is slightly oblique inferiorly and laterally to attach to the tibial tuberosity. The ligament rotates accordingly with the tibia, hence when the tibia rotates laterally, the patellar ligament tilts laterally, and vice versa in medial rotation. The knee is stabilised laterally and medially by the iliotibial tract and lateral collateral ligament and the pes anserinus muscles and medial collateral ligament, respectively. The presence of the menisci, as well as the articular capsule, and the anterior-posterior cruciate ligaments help prevent anteroposterior translation of the knee. The gastrocnemius and quadriceps femoris also aid in this prevention. Cruciate ligaments prevent rotation of the extended knee. The anterior cruciate ligament is tense during medial rotation, where the posterior cruciate ligament is relaxed, and the latter is tense during lateral rotation, where the anterior cruciate ligament is relaxed. The tibiotarsal joint (ankle joint) is the distal joint of the lower limb. It is a hinge joint and is represented by a total of 3 joints: the talocrucal joint, the subtalar joint, and the inferior tibiofibular joint. This joint only possesses 1 degree of freedom (on the transverse axis and sagittal plane, indeed enabling flexion and extension). The ankle structure is composed of the tibia, fibula, and talus. The tibia is a long bone constituted of a diaphysis (shaft) and two epiphyses, one proximal which articulates with the femoral condyles via the menisci to form the knee joint (clearly with all the relative adjacent structures), and one distal which instead has a longer protrusion medially that extends as the medial malleolus. The distal end of the tibia, as well as the medial malleolus articulates with talus, covered by a layer or articular cartilage. Very similarly to the radius and ulna, also the tibia and fibula have an intraosseous membrane that aids in the articulation between the two bone structures. Additionally, on the lateral aspect inferiorly is the fibular notch, which is an articulation site for the distal end of the fibula. It is important to note that the fibula lies posterolaterally with respect to the tibia. The articulation of the distal end of the fibula on the fibular notch of the tibia forms the lateral malleolus. The two malleoli are important sites of attachment of ligaments of the ankle joint. The lateral malleolus with respect to the medial malleolus protrudes for a longer length (indeed it is 1cm more distal) and is more posterior. The talus can be divided into three parts: head, neck, and body. The head carries the articulate surface of the navicular bone. The neck is instead a small area between the head and body in which there are small vascular channels. The body is the main component of the talus which contains two trochlea tali, which are two articular surfaces for the medial and lateral malleoli. The ankle mortise (superior part of the ankle joint) is responsible for keeping the articular surface of the malleoli in a steady grip, in order to ensure the stability of the ankle proper. The ankle joint is formed inferiorly by the talus, latero-superiorly by the fibula and medio- superiorly by the tibia. It is again a hinge joint that enables for dorsiflexion and plantar flexion. Ankle ligaments are divided in two categories: lateral and medial collateral ligaments, and anterior and posterior ligaments (which are accessory). The bone structure of the foot follows: Tibia, fibula, and talus form the main structure of the ankle joint. The ankle joint itself also involves the navicular bone, located anteriorly of the talus, and the calcaneus, located inferiorly and posteriorly of both the navicular bone and the talus. Also involved in the bone structure of the foot is the cuboid bone, located anteriorly and superiorly of the calcaneus, and laterally of the lateral cuneiform bone. It also articulates medially  with the lateral cuneiform bone and the navicular bone. The lateral cuneiform bone articulates with the intermediate cuneiform bone as well as the anterior aspect (via its posterior surface) of the navicular bone. The intermediate cuneiform is located between the medial and lateral cuneiform bones and posteriorly articulates with the navicular bone. The medial cuneiform bone articulates laterally with the intermediate cuneiform and posteriorly with the navicular bone. The first metatarsal bone articulates posteriorly with the medial cuneiform only, the second metatarsal with the intermediate cuneiform only, and the third metatarsal with the lateral cuneiform only. The fourth and fifth metatarsal bones instead articulate posteriorly with the cuboid bone. The medial collateral ligament is indeed located medially and it consists of 4 ligaments, all originating from the medial malleolus. These are the posterior and anterior tibiotalar ligament, indeed between the medial malleolus of the tibia and the anterior and posterior surface of the talus, the tibionavicular ligament, and the tibiocalcanear ligament. The anterior and posterior tibiotalar ligament fibres are deep. The anterior extends to the anterior surface of the neck of the talus whereas the posterior fibres extend to the deep medial fossa of the talus. Note that the anterior and posterior ligaments travel from the medial malleolus inferiorly, obliquely, and in their respective direction. The superficial fibres of the medial collateral ligament are instead represented by the tibionavicular and the tibiocalcanear ligaments. The lateral collateral ligament instead consists of three ligamentous fibres which all originate from the lateral malleolus. The first component of the ligament is the anterior talofibular ligament, which extends from the anterior lateral surface of the lateral malleolus and travels inferiorly and obliquely anteriorly to insert in between the lateral articular facet and the mouth of the sinus tarsi of the talus. The posterior talofibular ligament instead extends from the medial surface of the lateral malleolus and travels inferiorly and obliquely posteriorly (more horizontally) to insert into the posterior tubercle of the talus. The third ligament is the calcaneofibular ligament which originates from the depression near the apex of the lateral malleolus and travels inferiorly and obliquely posteriorly into the lateral surface of the calcaneus. The inferior tibiofibular joint is a syndesmosis between the distal ends of the fibula and tibia, which serves to maintain their tightness and ensure the overall integrity of the ankle structure. The inferior tibiofibular joint is strengthened by two inferior ligaments, which are the anterior tibiofibular ligament and the posterior tibiofibular ligament. The joint itself is a syndesmosis as there is no articular cartilage between the two bones. Also, the tibia and fibula are held together through the intraosseous membrane and the articular area of the fibular notch of the tibia. The subtalar joint is found between the lower surface of the talus and the superior surface of the calcaneus, which consists of 4 ligaments. The anterior compartment of muscles (also known as extensor compartment) is involved in dorsiflexion of the foot. Here, muscles are located between the lateral surface of the shaft of the tibia and the medial surface of the shaft of the fibula, and are anterior with respect to the intraosseous membrane that connects these bones together. Anterior (dorsal flexor) compartment muscles o Tibialis anterior § Originates from the lateral tibial plateau, lateral condyle, and superior half of the lateral surface of the tibia and intraosseous membrane § Inserts into the medial and inferior surfaces of the intermediate cuneiform bone and the base of the first metatarsal bone § Performs dorsiflexion and inversion of the foot (where the sole of the foot is turned to face medially) o Extensor digitorum longus § Originates from the lateral condyle of the tibia and the superior ¾ of the medial surface of the fibula and intraosseous membrane  § Inserts into the base of the middle and distal phalanges of the second through fifth metatarsal bones § Performs dorsiflexion of the ankle, pronation of the foot, and extension of the second through fifth digits o Extensor hallucis longus § Originates from the middle part of the anterior surface of the fibula and intraosseous membrane § Inserts into the dorsum of the distal phalanx of the hallux § Performs independent extension of the hallux and helps in ankle dorsiflexion o Fibularis tertius § Originates from the inferior third of the anterior surface of the fibula § Inserts into the dorsum of the base of the fifth metatarsal bone § Performs dorsiflexion of the ankle and foot eversion (where the sole of the foot faces laterally) The lateral (evertor) compartment of the leg is the smallest of the leg compartments and is limited by the lateral surface of the fibula and the various septa and fasciae of the leg. Lateral (evertor) compartment muscles o Fibularis longus § Originates from the head and the superior 2/3rds of the lateral surface of the fibula § Inserts into the base of the first metatarsal bone and the intermediate cuneiform bone § Performs eversion of the foot and aids in weak plantarflexion of the ankle o Fibularis brevis § Originates from the inferior 2/3rds of the lateral surface of the fibula § Inserts into the dorsal surface of the tuberosity on the lateral side of the base of the fifth metatarsal bone § Performs foot eversion and slight plantarflexion of the ankle The posterior (plantar flexor) muscle compartment is the largest of the three of the leg. It is separated into a superficial and deep layer by the transverse intermuscular septum. Posterior (plantar flexor) compartment muscles o Superficial layer: § Gastrocnemius It is composed of a lateral head and a medial head. The medial head originates from the popliteal surface of the femur, superior to the medial condyle, whereas the lateral head originates from the lateral aspect of the lateral condyle of the femur Both lateral and medial heads insert by means of the calcaneal tendon into the posterior surface of the calcaneus Performs plantarflexion of the ankle when the knee is extended, and it flexes the leg at the knee joint. Also, the gastrocnemius is responsible for heel elevation during walking. § Soleus Originates from the posterior aspect of the head and the superior quarter of the lateral aspect of the fibula, the soleal line and the middle third of the medial surface of the tibia, and the tendinous arch Inserts into the posterior surface of the calcaneus by means of the calcaneal tendon together with the two heads of the gastrocnemius, forming the triceps surae. Note that the soleus is essentially located anteriorly of the gastrocnemius  Performs plantarflexion independently from the position of the knee (either when flexed or extended) and it stabilises the leg § Plantaris Originates from the inferior end of the lateral supracondylar line of the femur and from the oblique popliteal ligament Inserts into the calcaneus by means of the calcaneal tendon Performs weak plantarflexion of the ankle by aiding the gastrocnemius o Deep layer: § Popliteus Originates from the posterior surface of the tibia, above the soleal line Inserts into the lateral surface of the lateral condyle of the femur and the lateral meniscus Performs slight knee flexion and unlocks it by rotating the femur of 5° on the tibia. It also allows for medial rotation of the tibia § Flexor hallucis longus Originates from the inferior 2/3rds of the posterior surface of the fibula and the inferior part of the intraosseous membrane Inserts into the base of the distal phalanx of the hallux Performs slight plantarflexion of the ankle, fully flexes the hallux at all joints, and supports the medial longitudinal arch of the foot § Flexor digitorum longus Originates from the medial part of the posterior surface of the tibia, inferiorly of the soleal line, and from a broad tendon from the fibula It inserts into the base of the distal and middle phalanges of the second through fifth digits Performs plantarflexion of the ankle, flexion of the digits, and supports the longitudinal arch of the foot § Tibialis posterior Originates from the intraosseous membrane, from the inferior surface of the tibia inferiorly of the soleal line, and from the posterior surface of the fibula Inserts into the tuberosity of the navicular, cuneiform, cuboid, and calcaneus. It also inserts into the base of the second, third, and fourth metatarsal bones Performs plantarflexion of the ankle and foot inversion These above were all the extrinsic muscles that insert into the foot. Find below the intrinsic muscles of the foot which both originate and insert within the foot structure. These can be divided into dorsal intrinsic muscles, plantar intrinsic muscles, and intraossei muscles. Intrinsic foot muscles o Dorsal muscles: § Extensor digitorum brevis Performs extension at the proximal interphalangeal joint § Extensor hallucis brevis Performs extension at the metatarsophalangeal joint of the hallux o Plantar muscles: § Flexor hallucis brevis Performs flexion at the metatarsophalangeal joint of the hallux, as well as allowing for some degree of adduction and abduction of the hallux. Provides support for the medial longitudinal arch of the foot  § Flexor digitorum brevis Performs flexion of the four digits at the metatarsophalangeal and proximal interphalangeal joints, as well as supporting the medial longitudinal arch of the foot § Adductor hallucis Performs adduction at the metatarsophalangeal joint of the hallux, and supports the medial longitudinal arch of the foot § Abductor hallucis Performs abduction at the metatarsophalangeal joint of the hallux, and supports the medial longitudinal arch of the foot § Flexor digiti minimi Performs independent flexion and abduction of the fifth digit at the metatarsophalangeal joint and at the proximal interphalangeal joint § Abductor digiti minimi Performs abduction of the fifth digit at the metatarsophalangeal joint § Lumbrical muscles Perform flexion of the digits at the metatarsophalangeal joint and extension of the interphalangeal joints o Interossei muscles § Divide both in dorsal and plantar. Dorsal interossei are 4 bipennate muscles whereas plantar interossei are 3 unipennate. § Perform flexion, adduction, and abduction of the metatarsal bones Foot dynamics work in such a way that the X axis passes horizontally through the two malleoli, indeed on a transverse axis along the sagittal plane. Here movement is dictated by flexion and extension of the ankle and clearly of the foot. The Y axis controls the movements of foot abduction and adduction, where moving farther from the median line (sagittal axis) indicates abduction and moving closer to the sagittal axis indicates adduction. Movement occurs on the transverse plane. The Z axis indicates, on a sagittal plane, pronation and supination of the foot with respect to axis. It controls the movement of the sole of the foot, allowing it to face either inferiorly (orthostatic position), medially, and laterally. Dorsiflexion (movement of the dorsum of the foot towards the anterior surface of the leg (towards the tibia essentially – foot flexion) has an angle between 20-30°. Plantarflexion (movement of the plantar surface of the foot towards the gastrocnemius, hence the posterior aspect of the leg – foot extension) has a greater angle with respect to dorsiflexion, of around 30-50°. Eversion is a combination between pronation and abduction of the foot where the sole of the foot faces laterally, away from the midline. Inversion is the opposite, hence a combination of supination and adduction of the foot where the sole of the foot faces towards the midline. Extreme dorsiflexion is limited by the neck of the talus moving and impinging against the frontal tibial surface (thus limiting the degree of dorsiflexion) and is also controlled by the tension of the fibres of the articular capsule and those of the posterior collateral ligaments. Also the activation of the soleus and the gastrocnemius are important limiting factors to prevent extreme dorsiflexion as their common calcaneal tendon (which gives rise to the triceps surae) is being stretched. Plantarflexion on the other hand is limited by bony structures almost impinging against one another, especially the posterolateral tubercle of the talus which makes contact with the posterior surface of the tibia. It is also limited by the anterior fibres of the articular capsule and those of the anterior collateral ligament. Extreme plantarflexion is also limited by the tonic activation of  the extensor muscles (gastrocnemius, soleus, fibularis longus, tibialis anterior, and extensor digitorum longus). The Spine The spine is a crucial bone component as it is the protector organ of the spinal cord and nerve routes that afflux and efflux from it. Also, it is the main weight bearing structure of the upper body (including the head), ensuring a great compromise between movement, stability, and integrity. The spine has such a structure that on the base of ligament tension and muscle action it can slightly alter its conformation (allowing for a wide range of degrees of motion) yet still maintaining its integrity. The spine changes its location in the body depending on the segment. The cervical portion is located centrally, between the anterior 2/3rds and posterior 1/3rd of the head and neck. The thoracic portion lies more posteriorly, indeed in the posterior 1/4th of the thorax. The lumbar portion instead lies centrally, together with the sacrum and coccyx. In the neck it is central to maintain a good centre of gravity and balance, in the thorax is located posteriorly due to the presence of internal organs, and in the lumbar region lies centrally mainly for weight bearing purposes. The spine consists of 33 total vertebrae, divided into 5 groups. From top to bottom, there are 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, 5 sacral vertebrae, and finally 4 coccygeal vertebrae. The 5 sacral and 4 coccygeal are fused together into the triangular shaped bone called sacrum, which lines the posterior margin of Elvis the pelvis. From the lateral view, the spine has a specific curvature, which is an alternating lordosis and kyphosis pattern. Cervical lordosis has an angle between 20-40°, thoracic kyphosis an angle of 20-40°, lumbar lordosis an angle of 30-50°. In the sacral area, there is sacral kyphosis. The vertebra is constituted by a body anteriorly and an arch posteriorly. The arch shows 3 main processes, which are the transverse processes and articular processes, located posterolaterally of the body, and the spinous process, located on the medial axis. There are 2 transverse processes, 4 articular processes (2 superior and 2 inferior), and 1 spinous process per vertebra, with a total of 7 processes protruding from each spinous arch. The space between the posterior aspect of the body and the anterior aspect of the vertebral arch is the vertebral foramen. The vertebral body is composed of trabecular bone on the inside and compact bone on the outside. From the T4 downwards bodies become thicker, as they have to sustain more weight.