Upper Arm Bone
Humerus
location_on Upper arm, between the shoulder and elbow joints
The humerus is the longest and largest bone of the upper limb, articulating with the scapula at the shoulder and the radius and ulna at the elbow. The spiral groove on its posterior shaft carries the radial nerve, making this nerve vulnerable in midshaft fractures. The distal humerus forms the complex hinge-pivot of the elbow with the trochlea and capitulum.
Key Anatomical Features
- Head is a hemisphere that articulates with the glenoid cavity of the scapula
- Greater and lesser tubercles provide attachment for rotator cuff muscles
- Intertubercular (bicipital) groove houses the tendon of the long head of biceps
- Radial (spiral) groove on the posterior shaft carries the radial nerve and profunda brachii artery
- Trochlea articulates with the ulna and capitulum articulates with the radial head
- Medial and lateral epicondyles are palpable landmarks for flexor and extensor muscle origins
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Deltoid | Deltoid tuberosity on lateral midshaft | Abducts, flexes, and extends the arm |
| Supraspinatus | Superior facet of greater tubercle | Initiates abduction of the arm |
| Infraspinatus | Middle facet of greater tubercle | Laterally rotates the arm |
| Teres minor | Inferior facet of greater tubercle | Laterally rotates the arm |
| Subscapularis | Lesser tubercle | Medially rotates the arm |
| Biceps brachii (long head) | Passes through intertubercular groove | Flexes the elbow and supinates the forearm |
| Triceps brachii (lateral head) | Posterior shaft above radial groove | Extends the elbow |
| Brachialis | Anterior distal half of shaft | Flexes the elbow (primary flexor) |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Glenohumeral (shoulder) joint | Synovial ball-and-socket | Scapula |
| Elbow joint (humero-ulnar) | Synovial hinge | Ulna |
| Elbow joint (humero-radial) | Synovial pivot | Radius |
Common Pathologies
Proximal humerus fracture
Common in elderly osteoporotic patients from falls. Classified by the Neer system into parts based on the four segments: head, greater tubercle, lesser tubercle, and shaft.
Midshaft humerus fracture with radial nerve palsy
Fractures at the midshaft commonly injure the radial nerve in the spiral groove, causing wrist drop (inability to extend the wrist and fingers).
Lateral epicondylitis (tennis elbow)
Tendinopathy of the common extensor origin at the lateral epicondyle, causing lateral elbow pain that worsens with gripping and wrist extension.
Supracondylar fracture
The most common elbow fracture in children. Carries risk of brachial artery injury and Volkmann ischemic contracture if compartment syndrome develops.
Clinical Relevance
Midshaft humeral fractures warrant immediate assessment of radial nerve function (wrist and finger extension, sensation on the dorsal first web space). Supracondylar fractures in children require urgent assessment of the brachial artery pulse and anterior interosseous nerve function. The carrying angle (valgus angle of the extended elbow) averages about 13 degrees and is greater in females; alteration suggests a malunited distal humeral fracture.
Development and Ossification
The humerus ossifies from eight centers: one primary center for the shaft (8th fetal week) and seven secondary centers. The proximal epiphysis (head, greater and lesser tubercles) fuses around age 20. The distal epiphysis (capitulum at age 1, medial epicondyle at age 5, trochlea at age 10, lateral epicondyle at age 12) fuses by age 16-17.
Did You Know?
- The humerus gets its name from the Latin umerus meaning shoulder or upper arm, not from humor
- Hitting the funny bone is actually compressing the ulnar nerve against the medial epicondyle of the humerus
- The humerus is one of the three long bones that together allow the huge range of motion of the upper limb
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