General Features and Attachments of the Humerus

Overview

• Humerus is a typical long bone with:
  • Upper end
  • Lower end
  • Intervening shaft
• Shaft has three borders and three surfaces.
• Side determination is discussed in a separate video.

Upper End

• Components:
  • Head: Globular, more than one third of a sphere, smooth, covered by articular cartilage.
  • Neck: Constricted area below the head.
  • Lesser Tubercle: Bony prominence facing anteriorly.
  • Greater Tubercle: Lateral bony prominence.
  • Intertubercular Sulcus: Located between the lesser and greater tubercles.

Articular Features

• The head of the humerus articulates with the glenoid cavity of the scapula to form the glenohumeral articulation (shoulder joint).
• Glenoid cavity is shallower and less extensive compared to the head, allowing for a greater range of movement.
• Articular cartilage is thicker in the center and thinner at the edges.

Angles and Axis

• Angle of Retroversion: Angle between the long axis of the head and the long axis of the lower end.
• Angle of Humeral Torsion: Angle between the articular axis of the head and a perpendicular line to the interepicondylar line.

Muscle Attachments

• Lesser Tubercle: Receives insertion of subscapularis muscle.
• Greater Tubercle: Has three flat muscular impressions for:
  • Supraspinatus
  • Infraspinatus
  • Teres Minor
• Together, these muscles form the rotator cuff, enhancing shoulder stability.

Neck

• **Types of Neck: **
  • Anatomical Neck: Constriction next to the head.
  • Surgical Neck: Constriction associated with the cylindrical shaft, vulnerable to fracture and axillary nerve damage.
  • Morphological Neck: Imaginary line above the surgical neck, indicates epiphyseal plate in young humerus.
• Anatomical neck provides attachment for the capsular ligament of the shoulder joint.

Shaft

• Shape: Upper half cylindrical, lower half triangular.

• Borders:

  • Anterior Border: Extends from greater tubercle to between radial and coronoid fossa.
  • Medial Border: Recognizable from the medial epicondyle, continuous as medial supracondylar ridge.
  • Lateral Border: Recognizable from lateral epicondyle, continuous as lateral supracondylar ridge.

• Surfaces:

  • Anteromedial Surface: Forms intertubercular sulcus, receives muscle insertions (teres major, pectoralis major, latissimus dorsi).
  • Anterolateral Surface: Contains deltoid tuberosity for deltoid insertion; also has origins for brachialis.
  • Posterior Surface: Contains a spiral groove for radial nerve and vessels, provides origin for triceps muscle.

Lower End

• Expanded side-to-side, divided into articular and non-articular areas.

Articular Areas

• Capitulum: Articulates with the head of the radius.
• Trochlea: Asymmetrical pulley articulating with the ulna.

Non-Articular Areas

• Fossas:
  • Radial Fossa: Lodges head of radius during flexion.
  • Coronoid Fossa: Lodges coronoid process of ulna during flexion.
  • Olecranon Fossa: Lodges olecranon process of ulna during extension.
• Epicondyles:
  • Medial Epicondyle: Larger, provides attachment for forearm flexor muscles and ulnar collateral ligament.
  • Lateral Epicondyle: Smaller, provides attachment for forearm extensor muscles and radial collateral ligament.

Conclusion

• Understanding the features and attachments of the humerus is essential for comprehending its function in the shoulder and elbow joints.