Upper arm and elbow

The upper arm, or brachium, extends between the shoulder joint and elbow. The shoulder joint connects the upper arm to the torso and the shoulder girdle, while the elbow joint connects it to the forearm. The muscles of the upper arm move the elbow joint (flexion and extension) and the forearm (pronation and supination), as well as stabilize and move the shoulder joint (internal rotation and flexion). This article covers the bones, muscles, vasculature, lymphatics, and innervation of the upper arm and elbow.

See “Forearm, wrist, and hand” and “Shoulder, axilla, and brachial plexus.”

Definition

The humerus is a bone of the arm that articulates proximally with the scapula to form the shoulder joint and distally with the radius and ulna to form the elbow joint.

Head of the humerus

• Spherical proximal portion of the humerus that articulates with the glenoid cavity of the scapula (i.e., the ball of the ball-and-socket glenohumeral joint)

Neck of the humerus

• Anatomical neck of the humerus: constriction that separates the head of the humerus from the tubercles and allows attachment of the ligaments of the glenohumeral joint
• Surgical neck of the humerus
  • Constriction below the tubercles
  • The axillary nerve and posterior humeral circumflex artery pass around the dorsal part of the surgical neck of the humerus together.
• Greater tubercle of the humerus: site of insertion of the supraspinatus, infraspinatus, and teres minor of the rotator cuff
• Lesser tubercle of the humerus: site of insertion of the subscapularis of the rotator cuff
• Bicipital groove (intertubercular sulcus): deep groove between the tubercles in which the tendon of the long head of biceps brachii lie (site of insertion for pectoralis major, teres major, and latissimus dorsi)

Shaft of the humerus

• Deltoid tuberosity: a rough area on the superolateral aspect of the shaft of the humerus into which the deltoid is inserted
• Radial groove: groove on the mid-posterolateral surface of the shaft in which the radial nerve and deep brachial artery run together
• Distal humerus (medial to lateral)
  • Medial epicondyle: medial-most bony prominence of the humerus (site of origin of most forearm flexors and pronator teres)
  • Ulnar groove
    • Deep groove below the medial epicondyle through which the ulnar nerve passes
    • Funny bone: Bumping the ulnar nerve against the medial epicondyle causes pain or a tingling, shock-like sensation and numbness in the distribution of the ulnar nerve (forearm, palm, and palmar sides of digits IV and V).
  • Humeral trochlea; : a dumbbell-shaped bony projection that articulates with the ulna
  • Coronoid fossa; : depression above the trochlea on the ventral humerus that receives the coronoid process of the ulna when the forearm is flexed
  • Capitulum; : spherical bony prominence that articulates with the head of the radius
  • Radial fossa; : depression above the capitulum on the ventral humerus that receives the head of the radius when the forearm is flexed
  • Lateral epicondyle: lateral-most bony prominence (site of origin of most forearm extensors and supinator)
  • Olecranon fossa; : bony depression on the dorsal aspect of the distal humerus (receives the olecranon process of the ulna when the forearm is extended)

“Broken ARM:” the Axillary, Radial, and Median nerves can be injured as a result of a humerus fracture.

Tendinosis at the medial epicondyle (medial epicondylitis) is called golfer's elbow. Tendinosis at the lateral epicondyle (lateral epicondylitis) is called tennis elbow.References:^[1]

The muscles of the arm can be categorized into two groups: flexors and extensors. They lie deep to the brachial fascia and are divided into anterior (flexor) and posterior (extensor) compartments by the medial intermuscular septum and the lateral intermuscular septum.

For specific tests to assess the function of these muscles, see “Motor function” in “Neurological examination.”

Anterior compartment of the arm (flexors)

The anterior compartment contains three muscles that are elbow flexors, all of which are innervated by the musculocutaneous nerve.

The elbow flexors are innervated by the musculocutaneous nerve.

Posterior compartment of the arm (extensors)

The posterior compartment contains two muscles that are elbow extensors, both of which are innervated by the radial nerve.

The elbow extensors are innervated by the radial nerve.

Muscle grooves of the arm

There are two bicipital grooves between the muscle groups of the arm that serve as channels for important neurovascular pathways. They are different from the bicipital groove that lies between the tubercles of the humerus.

Arterial supply

The brachial artery is the main artery of the arm, forearm, and hand.

• Origin: : inferolateral border of the teres major (continuation of the axillary artery)
• Course
  • Lies in the medial aspect of the arm, in close proximity to the median nerve
  • Ends with bifurcation into the radial artery and ulnar artery just below the cubital fossa
• Branches
  • Deep brachial artery; (profunda brachii): supplies the triceps muscle
  • Small branches to the elbow anastomosis (the superior and inferior ulnar collateral arteries)
  • Terminal branches (See “Vasculature and lymphatics” in “Forearm, wrist, and hand”): ulnar artery and radial artery which supply the forearm and hand

The brachial artery can be compressed proximally against the medial humerus to stop bleeding in the distal arm.

Venous drainage

• Superficial veins (See “Veins” in “Forearm, wrist, and hand”)
  • Cephalic vein
  • Basilic vein
• Deep veins: brachial veins (a pair of veins that accompany the brachial artery)
  • Tributaries: ulnar vein and radial vein
  • Unite with the basilic vein at the outer border of teres major to form the axillary vein

Lymphatic drainage

• The lymphatics follow the superficial and deep veins.
• The lateral aspect of the upper limb is drained by lymphatics that follow the cephalic vein and ultimately drain into the lateral and infraclavicular lymph nodes.
• The medial aspect of the upper limb is drained by lymphatics that accompany the basilic vein and ultimately drain into the lateral axillary lymph nodes.

Motor and sensory innervation of the arm and elbow

See “Nerve injuries in the upper body” in “Peripheral nerve injuries” and “Motor function” and “Sensation” in “Neurological examination.”

Dermatomal distribution of the arm

• Proximal shoulder: C4
• Lateral arm: C5
• Posterior arm (elbow): C6
• Inferomedial arm: T1
• Superomedial arm: T2

• Type of joint
  • Complex synovial hinge joint between the distal end of the humerus and the proximal ends of the radius (humeroradial joint) and ulna (humeroulnar joint), as well as between the radius and ulna (radioulnar joint)
  • Connects the arm and forearm
• Composition: consists of three articulations
  • Humeroulnar joint: articulation between the trochlear notch of the ulna and the trochlea of the humerus that allows elbow flexion/extension
  • Humeroradial joint: articulation between the head of the radius and the capitulum of the humerus that allows forearm pronation/supination
  • Proximal radioulnar joint: articulation between the head of the radius and proximal ulna that allows forearm pronation/supination
• Ligaments
  • Radial collateral ligament of the elbow (lateral ligament): from the lateral epicondyle of the humerus to the radial notch of the ulna and the annular ligament of the radius (proximal radioulnar joint)
  • Ulnar collateral ligament of the elbow (internal ligament): from the medial epicondyle of the humerus to the coronoid process and olecranon of the ulna
  • Annular ligament of the radius (ring-shaped ligament): surrounds the head of the radius and anchors the radial head to the radial notch of the ulna
• Carrying angle: : measured using the axis of the humerus and the axis of the fully extended, supinated forearm (normally 5–15°)
• Movements
  • Flexion and extension
  • The concave radial head can pivot on the convex capitulum, which allows forearm pronation and supination at the radioulnar joint.
• Blood supply: elbow anastomosis (an arterial anastomosis between branches of the brachial artery, deep brachial artery, radial artery, ulnar artery)

Radial head subluxation (nursemaid elbow), partial subluxation of the radial head at the radiohumeral joint, is caused by excessive axial traction. It is the most common elbow injury in children < 5 years of age.

References:^[2]

• Definition: triangular space on the anterior aspect of the elbow joint
• Boundaries
  • Laterally: medial border of the brachioradialis
  • Medially: lateral border of the pronator teres
  • Superiorly: imaginary line between the medial and lateral epicondyles of the humerus
  • Inferiorly: brachial artery (dividing into radial artery and ulnar artery)
• Floor: brachialis and supinator muscles
• Roof
  • Bicipital aponeurosis: a fan-shaped connective tissue sheath that connects the biceps tendon to the ulna
  • Median cubital vein: a superficial vein of the cubital fossa that connects the cephalic and basilic veins
  • Medial and lateral cutaneous nerves of the forearm
• Contents
  • From lateral to medial: radial nerve, biceps tendon, brachial artery, and median nerve
  • Epitrochlear lymph nodes (cubital lymph nodes) ^[3]
    • Located in the subcutaneous fat just above the medial epicondyle of the humerus
    • Drains the ulnar side of the forearm and hand

The median cubital vein of the antecubital fossa is one of the most common sites for peripheral venipuncture and intravenous access.

The epitrochlear lymph nodes are classically enlarged in syphilis and/or sarcoidosis.

“Really Need Beer To Be At My Nicest:” the contents of the cubital fossa are (from lateral to medial) Radial Nerve, Biceps Tendon, Brachial Artery, and Median Nerve.

References:^[4]