OSTEOLOGY OF THE HUMERUS
- INTRODUCTION (Shape and position)
- Position : Bone of the arm
- Type : long bone (longest bone of the upper limb )
The humerus articulates with the scapula at the shoulder joint and with the Radius and the ulna at the elbow joint.
2. GENERAL FEATURES OF THE HUMERUS
- It consists of three parts:
- Upper end, lower end, and shaft.
2.1 THE UPPER END :
- The upper end presents the following features:
- The head
- 2 tuberosities ( greater and lesser )
-2 Necks ( anatomical and surgical)
A- The head of the humerus :
- Forms about one-third of a sphere
- Smooth and covered with articular cartilage
- Directed Upwards , medially and backwards
- Articulates with the glenoid cavity of the scapula
A- Necks of humerus :
§ The anatomical Neck :
- It is constriction at the margins of the rounded head separating it from the 2 tuberosities.
- It gives attachment to the capsular ligament of the shoulder joint, except — superiorly where the capsule is deficient, for the passage of tendon of long head of biceps brachii
- Medially the capsule extends down for 1cm to reach the surgical Neck.
§ The surgical Neck :
- It is the junction between the upper end and the shaft
- Lies about one finger breadth below the head and & the 2 tuberosities
- It is related to axillary (circumflex )nerve and posterior and anterior circumflex humeral vessels
A- The 2 tuberosities ( greater and lesser ) :
§ The lesser tuberosity (tubercle ):
- It project forward medial to the inter-tubercle groove (sulcus)
- It shows one facet on the upper part (subscapularis muscle )
- Its lateral edge continuous below with the medial lip of bicipital groove.
§ The greater tuberosity (tubercle):
- Lies on the lateral part of the upper end of the humerus
- Its anterior margin continues downwards as the lateral lip of bicipital groove
- It shows three facets for muscular attachments upper, middle, and lower, which provide attachment to supraspinatus, infraspinatus, and teres minor muscles, respectively.
Intertubercular Sulcus/Bicipital Groove :
- It is a vertical groove between lesser and greater tubercles and extends to the upper one-third of the shaft
- It has a floor and 2lips (med&late) for muscular attachments
- It lodges the tendon of the long head of biceps
2.2 THE LOWER END :
- It is expanded transversely and presents articular and no- articular parts.
- The articular part :
- Capitulum
-Trochlea
- The Non articular part:
-The epicondyles
- The 3 fossae
A- The articular part : The condyle
- It is divided by a faint groove into capitulum laterally and trochlea medially to articulate with the radius and ulna forming the elbow joint
§ The capitulum :
- Small ball-like process lying lateral to the trochlea.
- It covers the anterior and inferior surfaces only of the lateral part of the articular surface of the lower end.
- Articulates with the upper surface of the head of radius.
§ The trochlea :
- Pulley shaped trochlea
- It covers the anterior, inferior and posterior of the medial part of the articular surface of the lower end.
- The medial lip projects more down than the lateral lip.
A- The Non articular part:
-The medial and lateral epicondyles
-The olecranon, coronoid and radial fossa.
§ The epicondyles :
-The medial epicondyle :
- It Projects from the medial side of lower end
- Its more prominent than the lateral epicondyle and is subcutaneous
- Its anterior surface shows a rough impression for muscular attachment
- Its posterior surface may show a shallow groove for the ulnar nerve.
-The lateral epicondyle :
- It projects from the lateral side of the of lower end
- Its less prominent than the medial epicondyle
- Its anterior and posterior surfaces show rough impressions for muscular attachments
§ The 3 fossae :
-olecranon fossa
- deep depression on the posterior surface of the lower end above the trochlea
- It lodges the tip of the olecranon process of the ulna when the elbow is extended.
-Radial fossa
- It is a very shallow depression on the anterior surface of the lower end above the capitulum
- It receives the margin of the head of radius in full flexion of elbow
-Coronoid fossa
- Smaller hollow on the anterior surface of lower end above the trochlea
- It receives the tip of the coronoid process of the ulna in full flexion of the elbow.
2.3 THE SHAFT OF THE HUMERUS
- The upper part of the shaft is cylindrical and
- Its lower part is triangular in cross section
- It has three borders and three surfaces
§ Borders:
-Anterior border:
- It starts from the lateral lip of the intertubercular sulcus
- extends down to the anterior margin of the deltoid tuberosity
- His lower part is smooth and rounded where it ends in the radial fossa.
-Medial border:
- It extends from the medial lip of the intertubercular sulcus down to the medial epicondyle
- Its lower part is sharp and called medial supracondylar ridge. This ridge provides attachment to medial intermuscular septum.
-Lateral border:
- It extends from the back of greater tuberosity above To lateral epicondyle below
- Its lower part is prominent and called lateral supracondylar ridge
- About its middle, this border is crossed by the radial groove from behind
§ Surfaces:
- Anterolateral surface
- It lies between the anterior and lateral borders.
- A little above the middle, this surface presents a characteristic V-shaped tuberosity–the deltoid tuberosity which provides insertion to the deltoid muscle
-Anteromedial surface:
- It lies between the anterior and medial borders.
- The upper part of this surface forms the floor of the intertubercular sulcus.
- About its middle and close to the medial border it presents a nutrient foramen directed downwards.
-Posterior surface:
- It lies between the medial and lateral borders.
- In the upper one-third of this surface, there is an oblique ridge directed downwards and laterally. This ridge provides origin to the lateral head of the triceps brachii.
- Below and medial to the ridge, is the radial/spiral groove, which lodges radial nerve and profound a brachii vessels.
- The entire posterior surface below the spiral groove provides origin to the medial head of the triceps brachii.
