Arm: Anatomy

Bones of the Arm: Humerus

The humerus can be divided into 3 parts: the proximal end, the shaft, and the distal end.

Proximal end

• Head of the humerus: articulates with the glenoid
• Anatomical neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess
• Surgical neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess:
  • Frequent site of fracture Fracture A fracture is a disruption of the cortex of any bone and periosteum and is commonly due to mechanical stress after an injury or accident. Open fractures due to trauma can be a medical emergency. Fractures are frequently associated with automobile accidents, workplace injuries, and trauma. Overview of Bone Fractures 
  • A fracture Fracture A fracture is a disruption of the cortex of any bone and periosteum and is commonly due to mechanical stress after an injury or accident. Open fractures due to trauma can be a medical emergency. Fractures are frequently associated with automobile accidents, workplace injuries, and trauma. Overview of Bone Fractures here may injure the axillary nerve Axillary nerve Axilla and Brachial Plexus: Anatomy and/or posterior circumflex artery.
• Greater tubercle: site of attachment of the supraspinatus, infraspinatus, and teres minor rotator cuff tendons
• Lesser tubercle: site of attachment of the subscapularis rotator cuff tendon
• Intertubercular sulcus: separates the tubercles and contains the tendon of the long head of the biceps brachii

Shaft

• Deltoid tuberosity: site of insertion of the deltoid muscle
• Radial or spiral Spiral Computed tomography where there is continuous x-ray exposure to the patient while being transported in a spiral or helical pattern through the beam of irradiation. This provides improved three-dimensional contrast and spatial resolution compared to conventional computed tomography, where data is obtained and computed from individual sequential exposures. Computed Tomography (CT) groove: The radial nerve Radial Nerve A major nerve of the upper extremity. In humans the fibers of the radial nerve originate in the lower cervical and upper thoracic spinal cord (usually C5 to T1), travel via the posterior cord of the brachial plexus, and supply motor innervation to extensor muscles of the arm and cutaneous sensory fibers to extensor regions of the arm and hand. Axilla and Brachial Plexus: Anatomy runs in this groove and may be injured secondary to pressure or trauma, with resultant wrist drop.
• Medial and lateral supracondylar ridges

Distal end

• Trochlea: medial aspect of distal humerus
• Capitulum: lateral to the trochlea and articulates with the radial head
• Medial epicondyle: larger of the epicondyles; the ulnar nerve Ulnar Nerve A major nerve of the upper extremity. In humans, the fibers of the ulnar nerve originate in the lower cervical and upper thoracic spinal cord (usually C7 to T1), travel via the medial cord of the brachial plexus, and supply sensory and motor innervation to parts of the hand and forearm. Axilla and Brachial Plexus: Anatomy passes posterior to the medial epicondyle in the ulnar groove
• Lateral epicondyle: common site of pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways with “ tennis elbow Tennis elbow A condition characterized by pain in or near the lateral humeral epicondyle or in the forearm extensor muscle mass as a result of unusual strain. It occurs due repetitive stresses on the elbow from activities such as tennis playing. Examination of the Upper Limbs”
• Olecranon, coronoid fossa, and radial fossa: depressions that allow for movement of the elbow during flexion Flexion Examination of the Upper Limbs and extension Extension Examination of the Upper Limbs

Muscles of the Anterior Compartment of the Arm

• The anterior compartment of the arm is also called the flexor compartment, because its muscles are in charge of flexing the forearm Forearm The forearm is the region of the upper limb between the elbow and the wrist. The term “forearm” is used in anatomy to distinguish this area from the arm, a term that is commonly used to describe the entire upper limb. The forearm consists of 2 long bones (the radius and the ulna), the interosseous membrane, and multiple arteries, nerves, and muscles. Forearm: Anatomy toward the upper arm.
• Comprises 3 muscles: biceps, brachialis, and coracobrachialis
• All 3 muscles are innervated by the musculocutaneous nerve Musculocutaneous Nerve A major nerve of the upper extremity. The fibers of the musculocutaneous nerve originate in the lower cervical spinal cord (usually C5 to C7), travel via the lateral cord of the brachial plexus, and supply sensory and motor innervation to the upper arm, elbow, and forearm. Axilla and Brachial Plexus: Anatomy and supplied by the brachial artery Brachial Artery The continuation of the axillary artery; it branches into the radial and ulnar arteries. Cubital Fossa: Anatomy.
• To recall the muscles of the anterior compartment of the arm, remember “BBC”:
  1. Biceps
  2. Brachialis
  3. Coracobrachialis

Muscles of the Posterior Compartment of the Arm

• Also called the extensor compartment because its muscles are in charge of extending the elbow
• The posterior compartment of the arm comprises 2 muscles:
  • Triceps brachii Triceps brachii Elbow Joint: Anatomy
  • Anconeus Anconeus Elbow Joint: Anatomy
    • In some sources considered the “fourth head” of the triceps
    • In some sources considered part of the posterior compartment of the forearm Forearm The forearm is the region of the upper limb between the elbow and the wrist. The term “forearm” is used in anatomy to distinguish this area from the arm, a term that is commonly used to describe the entire upper limb. The forearm consists of 2 long bones (the radius and the ulna), the interosseous membrane, and multiple arteries, nerves, and muscles. Forearm: Anatomy
• Both muscles are innervated by the radial nerve Radial Nerve A major nerve of the upper extremity. In humans the fibers of the radial nerve originate in the lower cervical and upper thoracic spinal cord (usually C5 to T1), travel via the posterior cord of the brachial plexus, and supply motor innervation to extensor muscles of the arm and cutaneous sensory fibers to extensor regions of the arm and hand. Axilla and Brachial Plexus: Anatomy and supplied by the deep brachial artery Brachial Artery The continuation of the axillary artery; it branches into the radial and ulnar arteries. Cubital Fossa: Anatomy.

Vessels of the Arm

Arterial supply of the arm

The brachial artery Brachial Artery The continuation of the axillary artery; it branches into the radial and ulnar arteries. Cubital Fossa: Anatomy:

• Begins at the inferior border of the teres major as a continuation of the axillary artery Axillary Artery The continuation of the subclavian artery; it distributes over the upper limb, axilla, chest and shoulder. Axilla and Brachial Plexus: Anatomy
• Runs primarily between the biceps and brachialis muscles
• Supplies the anterior compartment
• Has 1 major branch, the deep brachial artery Brachial Artery The continuation of the axillary artery; it branches into the radial and ulnar arteries. Cubital Fossa: Anatomy
  • Also known as the profunda brachii artery
  • Supplies the posterior compartment
  • Runs in the radial groove with the radial nerve Radial Nerve A major nerve of the upper extremity. In humans the fibers of the radial nerve originate in the lower cervical and upper thoracic spinal cord (usually C5 to T1), travel via the posterior cord of the brachial plexus, and supply motor innervation to extensor muscles of the arm and cutaneous sensory fibers to extensor regions of the arm and hand. Axilla and Brachial Plexus: Anatomy

Venous drainage of the arm

• Basilic vein:
  • Begins distally in the hand Hand The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. Hand: Anatomy
  • Travels on the medial aspect of the upper arm
  • Combines with the brachial veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology to form the axillary vein Axillary Vein The venous trunk of the upper limb; a continuation of the basilar and brachial veins running from the lower border of the teres major muscle to the outer border of the first rib where it becomes the subclavian vein. Axilla and Brachial Plexus: Anatomy
• Cephalic vein:
  • Begins distally in the hand Hand The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. Hand: Anatomy
  • Travels proximally on the antero-lateral aspect of the arm
  • Enters the shoulder through the deltopectoral groove (the groove between the deltoid and pectoralis muscles Pectoralis muscles The pectoralis major and pectoralis minor muscles that make up the upper and fore part of the chest in front of the axilla. Chest Wall: Anatomy), where it empties into the axillary vein Axillary Vein The venous trunk of the upper limb; a continuation of the basilar and brachial veins running from the lower border of the teres major muscle to the outer border of the first rib where it becomes the subclavian vein. Axilla and Brachial Plexus: Anatomy

Nerves of the Arm

Clinical Relevance

The following injuries are important conditions related to the upper arm:

• Proximal humerus fractures: classic patient is an older woman with osteoporosis Osteoporosis Osteoporosis refers to a decrease in bone mass and density leading to an increased number of fractures. There are 2 forms of osteoporosis: primary, which is commonly postmenopausal or senile; and secondary, which is a manifestation of immobilization, underlying medical disorders, or long-term use of certain medications. Osteoporosis who has a low-impact fall onto an outstretched hand Hand The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves. Hand: Anatomy (FOOSH). May cause damage to radial nerve Radial Nerve A major nerve of the upper extremity. In humans the fibers of the radial nerve originate in the lower cervical and upper thoracic spinal cord (usually C5 to T1), travel via the posterior cord of the brachial plexus, and supply motor innervation to extensor muscles of the arm and cutaneous sensory fibers to extensor regions of the arm and hand. Axilla and Brachial Plexus: Anatomy causing decreased function of deltoid and teres minor muscles, with loss of sensation in lateral shoulder.
• Mid-shaft humerus fractures: may result in injury to the radial nerve Radial Nerve A major nerve of the upper extremity. In humans the fibers of the radial nerve originate in the lower cervical and upper thoracic spinal cord (usually C5 to T1), travel via the posterior cord of the brachial plexus, and supply motor innervation to extensor muscles of the arm and cutaneous sensory fibers to extensor regions of the arm and hand. Axilla and Brachial Plexus: Anatomy within the radial groove. The radial nerve Radial Nerve A major nerve of the upper extremity. In humans the fibers of the radial nerve originate in the lower cervical and upper thoracic spinal cord (usually C5 to T1), travel via the posterior cord of the brachial plexus, and supply motor innervation to extensor muscles of the arm and cutaneous sensory fibers to extensor regions of the arm and hand. Axilla and Brachial Plexus: Anatomy innervates the extensor muscles, and this injury may result in wrist drop.
• Supracondylar humerus fracture Fracture A fracture is a disruption of the cortex of any bone and periosteum and is commonly due to mechanical stress after an injury or accident. Open fractures due to trauma can be a medical emergency. Fractures are frequently associated with automobile accidents, workplace injuries, and trauma. Overview of Bone Fractures: typically from a FOOSH. If the proximal fragment is displaced anterolaterally, then the radial nerve Radial Nerve A major nerve of the upper extremity. In humans the fibers of the radial nerve originate in the lower cervical and upper thoracic spinal cord (usually C5 to T1), travel via the posterior cord of the brachial plexus, and supply motor innervation to extensor muscles of the arm and cutaneous sensory fibers to extensor regions of the arm and hand. Axilla and Brachial Plexus: Anatomy can be damaged; if it is displaced anteromedially, the median nerve Median Nerve A major nerve of the upper extremity. In humans, the fibers of the median nerve originate in the lower cervical and upper thoracic spinal cord (usually C6 to T1), travel via the brachial plexus, and supply sensory and motor innervation to parts of the forearm and hand. Cubital Fossa: Anatomy and brachial artery Brachial Artery The continuation of the axillary artery; it branches into the radial and ulnar arteries. Cubital Fossa: Anatomy can be injured, possibly resulting in inability to flex wrist or pronate the forearm Forearm The forearm is the region of the upper limb between the elbow and the wrist. The term “forearm” is used in anatomy to distinguish this area from the arm, a term that is commonly used to describe the entire upper limb. The forearm consists of 2 long bones (the radius and the ulna), the interosseous membrane, and multiple arteries, nerves, and muscles. Forearm: Anatomy and/or loss of pulses in the radial and ulnar arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology.
• Anterior shoulder dislocation: the most common dislocation at the shoulder, where the humeral head has been moved to a position in front of the joint; can damage the axillary nerve Axillary nerve Axilla and Brachial Plexus: Anatomy, and (rarely) the axillary artery Axillary Artery The continuation of the subclavian artery; it distributes over the upper limb, axilla, chest and shoulder. Axilla and Brachial Plexus: Anatomy.
• Tear of the long head of the biceps brachii tendon: Complete tear of the tendon of the long head of the biceps brachii results in a “Popeye muscle” secondary to prominence of the mid-portion of the biceps.
• Saturday night palsy Palsy paralysis of an area of the body, thus incapable of voluntary movement Cranial Nerve Palsies: compressive neuropathy Neuropathy Leprosy of the radial nerve Radial Nerve A major nerve of the upper extremity. In humans the fibers of the radial nerve originate in the lower cervical and upper thoracic spinal cord (usually C5 to T1), travel via the posterior cord of the brachial plexus, and supply motor innervation to extensor muscles of the arm and cutaneous sensory fibers to extensor regions of the arm and hand. Axilla and Brachial Plexus: Anatomy secondary to prolonged pressure on the nerve; may also result in wrist drop.