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
- Surgical neck:
- Frequent site of fracture
- A fracture here may injure the axillary nerve 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
Proximal end of the humerus
Image by BioDigital, edited by Lecturio
Posterior view of the proximal end of the humerus featuring the surgical neck, a frequent site of fracture. A fracture here may injure the axillary nerve and/or posterior circumflex artery.
Image by BioDigital, edited by Lecturio
Shaft
- Deltoid tuberosity: site of insertion of the deltoid muscle
- Radial or spiral groove: The radial nerve runs in this groove and may be injured secondary to pressure or trauma, with resultant wrist drop.
- Medial and lateral supracondylar ridges
Posterior view of the humerus
Image by BioDigital, edited by Lecturio
Posterior view of the humerus featuring the radial or spiral groove. The radial nerve runs in this groove and may be injured secondary to pressure or trauma, with resultant wrist drop.
Image by BioDigital, edited by Lecturio
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 passes posterior to the medial epicondyle in the ulnar groove
- Lateral epicondyle: common site of pain with “tennis elbow”
- Olecranon, coronoid fossa, and radial fossa: depressions that allow for movement of the elbow during flexion and extension
Anterior view of the distal end of the humerus
Image by BioDigital, edited by LecturioMuscles 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 toward the upper arm.
- Comprises 3 muscles: biceps, brachialis, and coracobrachialis
- All 3 muscles are innervated by the musculocutaneous nerve and supplied by the brachial artery.
- To recall the muscles of the anterior compartment of the arm, remember “BBC”:
- Biceps
- Brachialis
- Coracobrachialis
Cross-section of the arm, featuring the anterior and posterior compartments. Note the brachial fascia enclosing all of the muscles and forming the lateral and medial intermuscular septa.
Image by Lecturio. License: CC BY-NC-SA 4.0| Muscle | Origin | Insertion | Innervation | Function |
|---|---|---|---|---|
| Biceps brachii |
| Radial tuberosity and forearm fascia via bicipital aponeurosis | Musculocutaneous nerve (C6) |
|
| Brachialis | Lateral and medial surface of distal half of humerus | Coronoid process and tuberosity of ulna | Musculocutaneous nerve (C6) | Flexes elbow joint |
| Coracobrachialis | Coracoid process | Middle 3rd of humerus | Musculocutaneous nerve (C6) | Flexes/adducts shoulder joint |
Biceps brachii muscle
Image by BioDigital, edited by Lecturio
Muscles of the anterior compartment of the arm: brachialis and coracobrachialis
Image by BioDigital, edited by Lecturio
Anterior view of the right arm
Image by BioDigital, edited by Lecturio
Anterior view of the right arm, featuring the muscles of the anterior compartment with the biceps brachii removed
Image by BioDigital, edited by Lecturio
Lateral view of the right arm, featuring the deltoid, the muscles of the anterior compartment (biceps brachii, brachialis, brachioradialis), and the posterior compartment (triceps brachii)
Image by BioDigital, edited by Lecturio
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
- Anconeus
- In some sources considered the “fourth head” of the triceps
- In some sources considered part of the posterior compartment of the forearm
- Both muscles are innervated by the radial nerve and supplied by the deep brachial artery.
| Muscle | Origin | Insertion | Innervation | Function |
|---|---|---|---|---|
| Triceps brachii |
| Olecranon | Radial nerve (C7, C8) |
|
| Anconeus | Inserts on the posterior aspect of lateral epicondyle | Lateral surface of the olecranon | Radial nerve (C7, C8) | Assists in extension of the elbow and stabilizes the joint |
Posterior view of the arm featuring the muscles of the posterior compartment: the triceps brachii and the anconeus
Image by BioDigital, edited by Lecturio
Posterior view of the arm
Image by BioDigital, edited by Lecturio
Vessels of the Arm
| Medial bicipital groove | Lateral bicipital groove | |
|---|---|---|
| Location | Between the biceps brachii muscle and the triceps brachii | Between the biceps brachii muscle and the brachial muscle |
| Arteries | Brachial artery | Radial collateral artery |
| Veins |
|
|
| Nerves |
| Radial nerve |
Arterial supply of the arm
The brachial artery:
- Begins at the inferior border of the teres major as a continuation of the axillary artery
- Runs primarily between the biceps and brachialis muscles
- Supplies the anterior compartment
- Has 1 major branch, the deep brachial artery
- Also known as the profunda brachii artery
- Supplies the posterior compartment
- Runs in the radial groove with the radial nerve
Arteries of the arm
Image by BioDigital, edited by LecturioVenous drainage of the arm
- Basilic vein:
- Begins distally in the hand
- Travels on the medial aspect of the upper arm
- Combines with the brachial veins to form the axillary vein
- Cephalic vein:
- Begins distally in the hand
- 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), where it empties into the axillary vein
Veins of the arm
Image by BioDigital, edited by Lecturio
Anteromedial view of the right arm and shoulder joint, featuring the brachial artery and basilic, cephalic, and brachial veins
Image by BioDigital, edited by Lecturio
Nerves of the Arm
| Nerve | Origin | Branches | Functions |
|---|---|---|---|
| Musculo-cutaneous | Terminal branch of lateral cord of brachial plexus (C5–C7) |
|
|
| Median | Unison of medial and lateral roots of brachial plexus (C5–T1) |
|
|
| Ulnar | Terminal branch of the medial cord of the brachial plexus (C8, T1) |
|
|
| Radial | Posterior cord of the brachial plexus (C5–T1) |
|
|
The nerves of the arm, featuring the 5 terminal branches of the brachial plexus: the musculocutaneous, axillary, median, radial, and ulnar nerves
Image by BioDigital, edited by Lecturio
Dermatome map of the nerve roots and superficial innervation of the arm
Image: “Dermatomes and cutaneous nerves” by Mikael Häggström. License: Public Domain, edited by Lecturio
Clinical Relevance
The following injuries are important conditions related to the upper arm:
- Proximal humerus fractures: classic patient is an older woman with osteoporosis who has a low-impact fall onto an outstretched hand (FOOSH). May cause damage to radial nerve 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 within the radial groove. The radial nerve innervates the extensor muscles, and this injury may result in wrist drop.
- Supracondylar humerus fracture: typically from a FOOSH. If the proximal fragment is displaced anterolaterally, then the radial nerve can be damaged; if it is displaced anteromedially, the median nerve and brachial artery can be injured, possibly resulting in inability to flex wrist or pronate the forearm and/or loss of pulses in the radial and ulnar arteries.
- 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, and (rarely) the axillary artery.
- 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: compressive neuropathy of the radial nerve secondary to prolonged pressure on the nerve; may also result in wrist drop.
References
Drake, R.L., Vogl, A.W., & Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA: Churchill Livingstone.
