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FOREARM The region of the upper limb between the elbow and the wrist. BAAB 18/04/2016 Introduction: • The forearm is a portion/segment occupying the central part on the distal aspect of the upper limb between the arm and the hand. • It is homologous to the region of the lower limb (leg) that lies between the knee and the ankle joint. • Discussion will involve the following: – – – – – Osteology Joints of Muscles Blood supply Nerves supply OSTEOLOGY • The forearm contains two long bones, the radius and the ulna, forming the radioulnar joints. The interosseous membrane connects these bones to form the fibrous intermediate radioulnar joint. Ultimately, the forearm is covered by skin, the anterior surface usually being less hairy than the posterior surface. • The distal portion of the humerus is reviewed as it contributes in the formation of the elbow joint which is highly involving the radius and ulna. Osteology cont….. Osteology cont…… Osteology cont….. JOINTS • The elbow joint: – Type; synovial ball and socket and hinge joints – Articular bones; the capitulum and trochlea of humerus in the upper arm with the round head of radius and the head of ulna in the forearm respectively. – It is also involving the superior radioulnar joint sharing the joint capsule with the elbow joint but plays no functional role at the elbow. – The elbow region includes prominent landmarks such as the olecranon (the bony prominence at the very tip of the elbow), the elbow pit, and the lateral and medial epicondyles. Elbow joint cont….. Joints cont……. Joint cont….. • The radioulnar joints: i. Superior R/U joint a synovial type of pivot (articular surfaces are head of radius and radial notch of the ulna. ii. Intermediate R/U joint a fibrous syndemosis. ( between the two shafts joined by the interosseous membrane) iii. Inferior R/U joint a synovial type of pivot (articular surfaces are the head of the ulna and the ulnar notch of the radius). Joint cont…… MUSCLES • Muscles of the forearm are mainly extrinsic muscles of the Hand as they are principle flexors and extensors of the hand as well as pronators and supinators of the forearm. • Forearm is divided into two muscular compartments; anterior or flexor/pronator and posterior or extensor/supinator compartments. • There are many muscles in the forearm. • In the anterior compartment, muscles are split into three categories – superficial, intemediate and deep levels. • In general, muscles in the anterior compartment of the forearm perform flexion at the wrist and fingers, and pronation of the forearm. Muscles cont…….. • A crross-section of the forearm to show the muscular compartments Muscles cont…… • Superficial level The superficial muscles in the anterior compartment are the flexor carpi ulnaris, palmaris longus, flexor carpi radialis and pronator teres. They all originate from a common tendon called the common flexor origin. This arises from the medial epicondyle of the humerus. • Intermediate level The flexor digitorum superficialis is the only muscle of the intermediate compartment. It can sometimes be classed as a superficial muscle, but in most cadavers it lies between the deep and superficial muscle layers. • Deep level There are three muscles in the deep anterior forearm; flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. muscles cont…… • Superficial flexor group of muscles Muscles cont…….. • This is a lone intermediate flexor muscle (FDS) Muscles cont…… Muscles cont…… • Important notes: i. Superficial muscles arise from the CFO and some from the ulna, intermediate muscle has two heads – humeral and radial heads, the deep muscles arise from the radial of the forearm and interosseous membrane. ii. Palmaris longus is absent in about 15% of the population. iii. The FDS muscle is a good anatomical landmark in the forearm – the median nerve and ulnar artery pass between its two heads, and then they travel posteriorly. Muscles cont……. iv. FDS and FDP are spliting into four tendons of insertion into the digits. v. The cubital fossa: This is also known as elbow pit which is a triangular area on the anterior view of the elbow of a human or other hominid animal. It is also called the antecubital fossa because it lies anteriorly to the elbow (latin cubitus) when in standard anatomical position. • Boundaries -superior (proximal) boundary — an imaginary horizontal line connecting the medial epicondyle to the lateral epicondyle of the humerus -medial (ulnar) boundary — lateral border of Pronator Teres muscle originating from the medial epicondyle of the humerus. Muscles cont……. -lateral (radial) boundary — medial border of Brachioradialis muscle originating from the lateral supraepicondylar ridge of the humerus. -apex is directed inferiorly, and is formed by the meeting point of the lateral and medial boundaries -superficial boundary (roof)- skin, superficial fascia containing the median cubital vein, the lateral cutaneous nerve of the forearm and the medial cutaneous nerve of the forearm, deep fascia reinforced by the bicipital aponeurosis (a sheet of tendon-like material that arises from the tendon of the biceps brachii) -deep boundary (floor)- brachialis and supinator muscles Muscles cont…. • Contents: The contents of the cubital fossa include vessels, nerves and the biceps tendon (lateral to medial) : Radial nerve – This is not always strictly considered part of the cubital fossa, but is in the vicinity, passing underneath the brachioradialis muscle. As it does so, the radial nerve divides into its deep and superficial branches. Biceps tendon – It runs through the cubital fossa, attaching to the radial tuberosity, just distal to the neck of the radius. Brachial artery – The brachial artery supplies oxygenated blood the forearm. It bifurcates into the radial and ulnar arteries at the apex of the cubital fossa. Muscles cont….. Median nerve – Leaves the cubital between the two heads of the pronator teres. It supplies the majority of the flexor muscles in the forearm. Median cubital vein – the median cubital vein (or median basilic vein) is a superficial vein of the upper limb. It connects the basilic and cephalic vein. The bicipital aponeurosis – a tendon of biceps muscle which inserts into the superficial fascia in the cubital fossa. The aponeurosis reinforces the cubital fossa, and helps to protect the brachial artery and the median nerve running under heath. This protection is important during venipuncture (taking blood) from the median cubital vein. Muscle cont….. Muscles cont….. • Clinical correlates 1. Brachial Pulse and Blood Pressure: The brachial pulse palpation and measuring blood pressure can be done immediately medial to the biceps tendon in the cubital fossa. The stethoscope must be placed there, to hear the korotkoff sounds. 2. Venipuncture The median cubital vein is located superficially within the roof of the cubital fossa. It connects the basilic and cephalic veins, and can be accessed easily – this makes it a common site for venipuncture. Muscles cont….. • Space of Parona. This is a potential space between the pronator quadratus deep and the overlying flexor tendons of the forearm that is continuous through the carpal tunnel with the medial central palmar space. It is also known as the sub-tendinous space of the wrist - Pus in tendinous sheath in the hand can ascend in the radial bursa and eventually rupture into this space; - pus in little finger sheath can ascend in ulnar bursae and rupture into this space of Parona; - pus from thenar abscess or mid-palmar abscess may rupture into space of Parona. -if pus from either the radial or ulnar bursae ruptures into Parona’s space, it can be drained by the same incision used for releasing pus from the proximal end of the ulnar bursae. Mucsle cont….. 3. Supracondylar Fractures A supracondylar fracture of the humerus usually occurs by falling on a flexed elbow. It is a transverse fracture, spanning between the two epicondyles. --The displaced fracture fragments may impinge and damage the content of the cubital fossa. --Direct damage, or post-fracture swelling can cause interference to the blood supply of the forearm from the brachial artery. The resulting ischaemia can cause Volkmann’s ischaemic contracture – uncontrolled flexion of the hand, as flexors muscles become fibrotic and short. --There also can be damage to the median or radial nerves. Muscles cont….. • • Muscles in the Posterior Compartment of the Forearm The muscles in the posterior compartment of the forearm are commonly known as the extensor supinator group of muscles. The general function of these muscles is to produce • • extension at the wrist and fingers and to supinate the forearm. They are all innervated by the radial nerve. Anatomically, the muscles in this compartment can be divided into two layers; deep and superficial. These two layers are separated by a layer of fascia. Superficial layer: contains seven muscles. Four of these muscles – extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris and extensor digiti minimi share a common tendinous origin at the lateral epicondyle. This is a common extensor origin Muscle cont….. •Deep Muscles --There are five muscles in the deep compartment of the posterior forearm – the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus and extensor indicis. --With the exception of the supinator, these muscles act on the thumb and the index finger. Muscle cont…… • Muscles of the Posterior/extensor Compartment of the forearm Muscle cont….. • Important notes: 1. The brachioradialis is a paradoxical muscle. Its origin and innervation are characteristic of a extensor muscle, but it is actually a flexor at the elbow. The muscle is most visible when the forearm is half pronated, and flexing at the elbow against resistance. 2. Retinacular. These are fibrous bands found on both anterior and posterior sides of the forearm. They are special structures which hold down and in place the long flexor and extensor muscles. Extensor retinaculum Extensor retinaculum Muscle cont….. 3. Clinical correlates -- Lateral epicondylitis (or tennis elbow) refers to inflammation of the periosteum of the lateral epicondyle. The peak age of onset is 40-50 years old. It is caused by repeated use of the superficial extensor muscles, which strains their common tendinous attachment to the lateral epicondyle. drop is a sign of radial nerve injury that has occurred proximal • Wrist to the elbow. There are two common characteristic sites of damage: Axilla – injured via humeral dislocations or fractures of the proximal humerus. Radial groove of the humerus – injured via a humeral shaft fracture. radial nerve innervates all muscles in the extensor compartment of • The the forearm. In the event of a radial nerve lesion, these muscles are paralysed. The muscles that flex the wrist are innervated by the median nerve, and thus are unaffected. The tone of the flexor muscles produces unopposed flexion at the wrist joint – wrist drop. BLOOD SUPPLY IN THE FOREARM Arteries • • • • Arteries run from the shoulder down to the wrist with just a few branches given off near the elbow. Superficial and deep veins return blood toward the heart. Following is a brief overview: Brachial artery: This artery stems from the axillary artery. It runs along the anterior part of the arm, enters the cubital fossa, and divides into the radial and ulnar arteries Ulnar artery: This artery runs from the cubital fossa down the anterior and medial portion of the forearm until it enters the wrist. Radial artery: This artery runs from the cubital fossa down the anterior and lateral portion of the forearm until it enters the wrist. Blood supply……… Veins • Cephalic and basilic veins: These veins provide • superficial venous return. Brachial, radial, and ulnar veins: These veins are deeper. They accompany the arteries of the same names. Blood supply • . It also has the following branches that form arterial anastomoses (joined arteries) that supply the elbow: – Deep artery of the arm (profunda brachii artery) – Superior ulnar collateral artery – Inferior ulnar collateral artery Anastomosis around the elbow There are 9 branches; -- 4 descending branches -- 4 ascending branches -- communicating artery Blood supply cont….. • It is constituted by the following branches: 1. Superior ulnar collateral branch of brachial artery 2. Anterior branch of inferior ulnar collateral aa. of brachial artery 3. Anterior and posterior branches of profunda brachii artery. 4. Interosseous recurrent a branch of post. interosseous aa. of ulnar artery 5. Radial recurrent branch of radial artery 6. Superior and inferior ulnar recurrent branches of ulnar artery 7. A communicating aa. between post branch of inf. Ulnar collateral and post radial collateral branch of brachial artery. NERVE SUPPLY OF THE FOREARM nerves branch from the brachial plexus and travel through the The arm to supply the elbow and the forearm. Some of these nerves continue through the forearm to supply the wrist and hand. • Median nerve: This nerve starts from the brachial plexus and runs down alongside the brachial artery. It descends into the cubital fossa. It gives off branches that serve the elbow joint and continues down the anterior part of the forearm and into the hand through the carpal tunnel. • Ulnar nerve: This nerve starts from the brachial plexus, passes through the arm medial to the brachial artery, continues posterior to the medial epicondyle of the humerus, and enters the forearm. It travels along the medial part of the forearm until it enters the hand at the wrist. Nerves cont….. • Radial nerve: This nerve starts from the brachial plexus and runs posterior to the brachial artery and anterior to the long head of the triceps. It curves around the shaft of the humerus and continues toward the cubital fossa. From there it branches into the deep and superficial branches and continues down the lateral part of the forearm to enter the hand. • Musculocutaneous nerve: This nerve runs from the brachial plexus through the anterior part of the arm and becomes the lateral cutaneous nerve of the forearm.