Topic Overview

Humerus

General Features

• Longest and strongest bone of the upper limb.

• Situated in the arm (brachium), between the scapula and bones of the forearm.

• Proximal end articulates with glenoid cavity of scapula → shoulder joint.

• Distal end articulates with radius and ulna → elbow joint.

Parts of Humerus

1. Upper End

   • Head → rounded, directed medially, upward and backward, articulates with glenoid cavity.

   • Anatomical neck → constriction around head.

   • Greater tubercle → lateral, three facets for supraspinatus, infraspinatus, teres minor.

   • Lesser tubercle → anterior, for subscapularis.

   • Intertubercular sulcus (bicipital groove) → lodging long head of biceps tendon; bounded by lips for pectoralis major (lateral), teres major (medial), latissimus dorsi (floor).

   • Surgical neck → narrow, common fracture site, close relation to axillary nerve.

2. Shaft

   • Cylindrical above, triangular below.

   • Surfaces:

     • Anterolateral → deltoid tuberosity (insertion of deltoid).

     • Anteromedial → nutrient foramen.

     • Posterior → spiral (radial) groove, transmitting radial nerve and profunda brachii vessels.

   • Borders: anterior, medial, lateral.

3. Lower End

   • Expanded, forms condyles of humerus.

   • Capitulum → articulates with head of radius.

   • Trochlea → articulates with ulna.

   • Medial epicondyle → prominent, gives attachment to flexors; ulnar nerve passes behind.

   • Lateral epicondyle → smaller, gives attachment to extensors.

   • Fossae:

     • Radial fossa (above capitulum).

     • Coronoid fossa (above trochlea, anterior).

     • Olecranon fossa (posterior, for olecranon of ulna).

Ossification of Humerus

• Primary center: shaft, appears in 8th week intrauterine life.

• Secondary centers:

  • Head → 1 year.

  • Greater tubercle → 3 years.

  • Lesser tubercle → 5 years.

  • All fuse to form upper epiphysis by 7 years.

  • Capitulum → 1 year.

  • Trochlea → 9–10 years.

  • Lateral epicondyle → 12 years.

  • Medial epicondyle → 5 years.

• Fusion:

  • Upper epiphysis unites with shaft at about 20 years.

  • Lower epiphysis unites with shaft at about 16–17 years.

• Total: 1 primary + 7 secondary centers.

Clinical Anatomy

• Fractures of Humerus

  • Surgical neck → injures axillary nerve.

  • Shaft → injures radial nerve in spiral groove.

  • Supracondylar fracture (children) → dangerous, may injure brachial artery (Volkmann’s ischemic contracture).

  • Medial epicondyle fracture → injures ulnar nerve.

• Dislocations

  • Anterior dislocation of shoulder joint → common, may damage axillary nerve.

• Clinical landmarks

  • Medial epicondyle easily palpable → used in locating ulnar nerve.

  • Surgical neck important for radiology and surgical reference.

• Ossification centers are valuable in forensic age estimation.