Bones of the Arm: Humerus
The humerus can be divided into 3 parts: the proximal end, the shaft, and the distal 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
- 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
- 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
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 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 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|
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
- 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.
|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|
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|
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
Venous 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
Nerves of the Arm
|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 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.
Drake, R.L., Vogl, A.W., & Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA: Churchill Livingstone.