HUMERUS BONE
- Humerus is the arm bone which articulates with the scapula at the shoulder joint and with radius and ulna at elbow joint.
OSSIFICATION:
The humerus ossifies from 1 primary & 7 secondary centers.
Primary center is for shaft (diaphysis), & appears during 8th week of I.U.L.
Upper end ossifies from 3 secondary centers:
- one for head (1st year)
- one for greater tubercle (2nd year)
- one for lesser tubercle (5th year)
→ These three centers fuse together during sixth year to form one epiphysis, which fuses with shaft during 20th year.
The lower end ossifies from 4 secondary centers which form 2 epiphysis. The center includes :
- one for capitulum & lateral flange of trochlea (1st year)
- one for medial flange of trochlea (9th year)
- one for lateral epicondyle (12th year)
→ All three fuse during 14th year to form one epiphysis, which fuses with shaft at 16th year.
- the 4th center for medial epicondyle appears at 4-6 years, forms a separate epiphysis & fuses with shaft during 20th year.
Multiplying factor for estimating stature from humerus in male is 5-6.
PARTS OF HUMERUS:
- It is longest bone of upper limb and has upper end, lower end & shaft.
1. UPPER END (Proximal end):
- HEAD (articulates with glenoid cavity)
- The upper end of humerus has a head, which is separated from greater & lesser tubercle by anatomical neck.
- The upper end of humerus is the growing end.
- Surgical neck separates proximal end from the shaft.
- There is intertubercular sulcus(bicipital groove) which separates lesser tubercle from greater tubercle and also forms the lateral wall of axilla.
- Attachment on proximal end are-
- Greater tubercle (or tuberosity):- Insertion of supraspinatus, Infraspinatous & teres minor.
- Lesser tubercle (or tuberosity):– Insertion of subscapularis.
2. LOWER END (Bony Features):
Articular Part:
- Capitulum
- Trochlea
Nonarticular Part:
- Medial Epicondyle
- Lateral Supracondylar ridge
- Medial Supracondylar ridge
- Coronoid Fossa
- Radial Fossa
- Olecranon Fossa
→ These fossa lie within the joint cavity.
→ Medial epicondyle & lateral epicondyle are outside the capsule.
→ Posterior surface of medial epicondyle has a groove lodging ulnar nerve.
- Medial epicondyle of humerus is sometimes called as “funny bone” becausre gentle tapping of it results in tingling sensation due to stimulation of ulnar nerve.
3. SHAFT:
- The shaft of humerus is cylindrical in the upper half & triangular on cross-section in the lower half.
- Contains three borders & three surfaces.
- Borders:
- Anterior Border
- Lateral Border
- Medial Border
- Surfaces:
- Anterolateral Surface(b/w anterior & lateral borders)
- Anteromedial Surface(b/w anterior & medial border)
- Posterior Surface(b/w medial & lateral borders)
- The upper part has intertubercular sulcus (bicipital groove) anteriorly.
- Bicipital groove contains long head of biceps with its synovial sheath and an ascending branch of anterior circumflex humeral artery.
- Middle third of posterior surface of shaft of the humerous has a spiral groove (radial groove) which contains radial nerve & profunda brachi vessels.
- Side Determination:
- Upper end: Rounded.
- Lower end: Expanded from side to side & flattened from before backwards.
- Head: Directed posterior & medially upwards.
- Lesser Tubercle: Projects from the front of the upper end & is limited laterally by the intertubercular sulcus.
|
Insertion muscles (upper humerus) |
Intertubercular sulcus Greater tubercle |
Pectoratis major, Latissmus dorsi & Teres major Supraspinatus, Infraspinatus & Teres minor |
|
Lesser tubercle |
Subscapularis |
|
|
Origin muscles(lower humerus) |
Medial |
Pronator teres, common flexor origin |
|
Lateral |
Brachioradialis, extensor carpi radialis longus, common extensor origin Et anconeus |
- Rotator cuff (Musculotendinous cuff): Fibrous sheath formed by the four flattened tendons of Subscapularis, Infraspinatus, Teres minor and Supraspinatus (SITS)
- Gives strength to the capsule of shoulder joint all around except inferiorly
- I.m. injections in the deltoid should be given in the lower half of the muscle to avoid injury to axillary nerve
- Nutrient arteries:Humerus – profunda brachii [Brachial artery]
VEINS
- Preaxial vein of upper limb – Cephalic vein
- Postaxial vein of upper limb – Basilic vein
- AXILLARY Nerve at the Surgical neck.
- RADIAL Nerve passes through the Radial groove( spiral groove of humerus)
- ULNAR Nerve behind the medial epicondyle.
- Multiplying factor for estimating stature from humerus in male is 5-6.
- Intertubercular sulcus (bicipital groove) separates lesser tubercle from greater tubercle and also forms the lateral wall of axilla.
- Intertubercular sulcus of humerus gives attachment to pectoralis major, latissmus dorsi & teres major.
- RADIAL Nerve passes through the Radial groove (spiral groove of humerus).
- Nerves of humerus are radial, ulnar & axillary nerve.
- Nerve injured in fracture of medial epicondyle of humerus is Ulnar nerve.
- Axillary nerve is damaged in fracture surgical neck of humerus.
- Most common complication of mid shaft humerus fracture is Radial nerve palsy.
- Distal (lower) end of Humerus ossifies from 4 secondary ossification centers.
- Most common nerve involved in supracondylar fracture of humerus is anterior interosseous branch of median nerve is mostly affected.
