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ANATOMY OF THE ARM AND FOREARM Mohammed AliLearning Outcomes • Describe and identify the muscles of the anterior compartment of the arm, their actions and innervations • Describe and identify the muscles of the posterior compartment of the arm, their actions and innervations • Describe the cubital fossa, its boundaries and contents • Describe the compartments of the forearm and identify the muscles within them • Apply the anatomy learned to clinical casesTechnical terms • The word “Arm” refers to the humerus and its associated muscles (from shoulder to elbow) • The word “Forearm” refer to the radius and ulnar, and associated muscles (from elbow to wrist) Shoulder joint Elbow joint Muscles will act on the joints which they cross Wrist joint Carpometacarpal joint Proximal interphalangeal joint Metacarpophalangeal joint Distal interphalangeal jointArm: Compartments • 2 compartments in the arm • Anterior: Biceps Brachii, Brachialis, coracobrachialis • Posterior: riceps brachii, anconeus Arm: Anterior compartment Long head Short of head Biceps of biceps Bicipital aponeurosis Biceps tendon Arm: Anterior Compartment • Coracobrachialis lies medial to biceps brachii. Identified as the musculocutaneous nerve pierces it • Brachialis lies deep to Biceps brachii on the distal half of humerus Arm: Anterior compartment Muscle Origin Insertion Innervation Action Biceps Brachii Long head: Radial tuberosity Musculocutaneous Forearm Supraglenoid and fascia of nerve supination, tubercle forearm elbow and Short head: shoulder flexion Coracoid process Coracobrachialis Coracoid process Middle third of Musculocutaneous Shoulder flexion medial humerus nerve and adduction Brachialis Distal half of Ulnar tuberosity Musculocutaneous Elbow flexion anterior humerus and coronoid nerve and partly process radial nerveClinical Anatomy • Bicep tendon rupture • Two types • Proximal: Rupture of the long head tendon from supraglenoid tubercle. Usually occurs in older people. Presents with “Popeye deformity” • Distal:Rupture of distal tendon from radial tuberosity. Occurs due to excessive eccentric load. Diagnosed using “Hook test” Tendon can be surgically reattachedArm: Posterior CompartmentArm: Posterior Compartment Muscle Origin Insertion Innervation Action Triceps Brachii Long head: Olecranon of ulna Radial nerve Long head Infraglenoid and fascia of extends shoulder tubercle forearm joint. Lateral head: All heads extend Posterior surface elbow joint of humerus, superior to radial groove Medial head: Posterior surface of humerus inferior to radial groove Anconeus Lateral epicondyle Olecranon of and Radial nerve Assists in of humerus superior part of extending elbow. ulna Prevents impingement of joint capsuleCubital Fossa • Boundaries • Superior: Imaginary line between epicondyles of humerus Lateral: • Brachioradialis • Medial: Pronator teres • Floor:Brachialis and supinator • Roof: Skin, fascia and bicipital aponeurosis • Contents: Biceps Brachii tendon Brachial Artery Median nerve Order from lateral to medial is TAN (tendon, artery, nerve) Overlying the cubital fossa is the median cubital vein (commonly used for venepuncture)Forearm: Compartments • 5 Compartments: 3 anterior, 2 posterior • Anterior compartments: Superficial, intermediate, deep • Posterior compartments: Superficial and deepForearm: Superficial anterior compartment • 4 muscles sharing a common origination at medial epicondyle: • Pronator teres- pronates forearm • Flexor carpi radialisflexes and abducts the wrist • Palmaris longus - flexes wrist • Flexor carpi ulnari- flexes and adducts the wrist • All muscles innervated by the median nerve EXCEPT flexor carpi ulnaris (innervated by ulnar nerve)Forearm: Intermediate and deep anterior compartments • Intermediate compartment contains 1 muscle: • Flexor digitorum superficialis Flexes up to the proximal IP joint • Deep group contains 3 muscles: • Flexor digitorum profundus - Flexes up to distal IP joint • Flexor pollicus longus- Flexes up to the IP joint of thumb • Pronator quadratus - Pronates forearm All muscles are innervated by the median nerve EXCEPT medial half (to digits 4 & 5) of flexor digitorum profundusForearm: Superficial posterior compartment • 6 muscles commonly originate from lateral epicondyle: • Brachioradialis - flexion of elbow (midpronation) • Extensor carpi radialis longus Extend and • Extensor carpi radialis brevis abduct wrist • Extensor digitorum- Extends up to distal IP joint • Extensor digit minimi- Extends up to distal IP joint of 5 digit • Extensor carpi ulnaris- Extends and adducts wrist • All muscles innervated by radial nerve Forearm: Deep posterior compartment • Supinator-Supinates forearm • 4 “outcropping muscles” • Abductor pollicis longus - Abducts thumb These muscles • Extensor pollicis longus - Extends thumb at IP joint also extend the • Extensor pollicis brevis -Extends thumb at the MCP joint wrist joint • Extensor indicis- Extends second digit • All muscles innervated by the radial nerve • Abductor pollicis longus, Extensor pollicis longus and brevis form boundaries of the anatomical snuffbox Medial Border Latreral BorderMCQ • 60-year-old man presents to the ED with sudden onset shoulder pain which developed while he was lifting boxes to clear out his garage. When asked to flex their elbow a visible deformity can be observed in which the biceps brachii muscle bunches in the middle of the arm. He has no past medical history of note and is on no medications. What tendon is most likely to be ruptured? A. Tendon of coracobrachialis B. Tendon of long head of biceps brachii C. Tendon of short head of biceps brachii D. Tendon of long head of triceps brachiiMCQ • You are a 4 year medical student on placement in the geriatric ward.The junior doctor has asked you to take bloods from a patient.You decide to take blood from the vein overlying the cubital fossa. Which muscle forms the medial border of this fossa? A. Pronator teres B. Brachioradialis C. Brachialis D. Flexor carpi ulnaris