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 “” and “ .”
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
- 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
- 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.
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 “.”
Anterior compartment of the arm (flexors)
|Overview of the muscles of the anterior compartment of the arm|
|Muscle||Biceps brachii|| |
Posterior compartment of the arm (extensors)
|Overview of the muscles of the posterior compartment of the arm|
|Muscle||Triceps brachii||Anconeus muscle|
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 humerus.that lies between the tubercles of the
|Medial bicipital groove||Lateral bicipital groove|
Vasculature and lymphatics
The brachial artery is the main artery of the arm, forearm, and hand.
- Origin: : inferolateral border of the teres major (continuation of the )
Superficial veins (See “Veins” in “ ”)
- Deep veins: brachial veins (a pair of veins that accompany the brachial artery)
- 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 .
Motor and sensory innervation of the arm and elbow
|Overview of the innervation of the arm and elbow|
| || |
| || |
See “Nerve injuries in the upper body” in “” and “Motor function” and “Sensation” in “ .”
Dermatomal distribution of the arm
- Proximal shoulder: C4
- Lateral arm: C5
- Posterior arm (elbow): C6
- Inferomedial arm: T1
- Superomedial arm: T2
- Type of joint
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
- 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°)
- 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.
- Definition: triangular space on the anterior aspect of the elbow joint
- Floor: brachialis and supinator muscles