Humerus Anatomy Overview

Overview

This lecture covers the anatomy of the humerus, including its parts, features, muscle attachments, articulations, relevant nerves, common fractures, and clinical questions.

Humerus Overview & Side Determination

• The humerus is a typical long bone with an upper end, shaft, and lower end.
• The upper end is globular with a rounded head facing medially.
• The lower end is flattened and expanded from side to side.
• The lesser tubercle faces anteriorly; side determination depends on these features.

Upper End Features & Attachments

• The head forms one-third of a sphere and articulates with the glenoid cavity to form the shoulder (glenohumeral) joint.
• The anatomical neck provides shoulder joint capsular ligament attachment except superiorly and medially.
• The surgical neck is the junction between the upper end and shaft, related to the axillary nerve and posterior circumflex humeral vessels.
• The lesser tubercle (anterior) is for subscapularis muscle attachment.
• The greater tubercle (lateral) has three impressions for supraspinatus, infraspinatus, and teres minor insertion.
• The intertubercular sulcus (bicipital groove) lodges the long head of biceps brachii and contains attachments for latissimus dorsi (floor), teres major (medial lip), and pectoralis major (lateral lip).

Shaft Features & Attachments

• The shaft is cylindrical above, triangular below, with three borders (anterior, medial, lateral) and three surfaces (anteromedial, anterolateral, posterior).
• Deltoid tuberosity (anterolateral surface, middle part) is the deltoid muscle insertion site.
• The spiral (radial) groove houses the radial nerve and profunda brachii artery.
• The posterior surface gives origin to lateral and medial heads of triceps brachii.

Lower End Features & Attachments

• The lower end consists of articular (capitulum for radius, trochlea for ulna) and non-articular parts (fossae and epicondyles).
• Medial and lateral epicondyles serve as origins for forearm flexors and extensors, respectively.
• Radial fossa (above capitulum) accommodates the head of radius during elbow flexion; coronoid fossa (above trochlea) receives the coronoid process of ulna.
• Olecranon fossa (posterior) receives the ulna's olecranon process during elbow extension.

Applied Anatomy & Clinical Points

• Common humerus fracture sites: surgical neck, shaft, and supracondylar region.
• Supracondylar fractures risk brachial artery compression, potentially leading to Volkmann's ischemic contracture.
• Elbow alignment: in flexion, epicondyles and olecranon form a triangle; in extension, a straight line.
• Humerus is commonly dislocated inferiorly.
• Three nerves closely related to humerus: axillary (surgical neck), radial (spiral groove), ulnar (behind medial epicondyle).

Key Terms & Definitions

• Humerus — long bone of the upper arm, articulates with scapula and forearm bones.
• Glenohumeral joint — shoulder joint, ball-and-socket.
• Surgical neck — constriction below the humerus head, common fracture site.
• Intertubercular sulcus (bicipital groove) — groove for biceps tendon.
• Deltoid tuberosity — rough area on shaft, deltoid insertion.
• Epicondyle — bony projection for muscle attachment.
• Carrying angle — angle between arm and forearm, normally ~163°, due to trochlea structure.

Action Items / Next Steps

• Review the attachments and relations of the humerus for lab or practical exams.
• Memorize the nerves closely related to the humerus and their clinical significance.
• Prepare for potential exam questions on the anatomical features and fracture implications.