Bones of the Upper Limb

The humerus, a long bone in the upper arm, is crucial for both anatomical and physiological functions. It offers structural support for arm movements, acts as a primary attachment site for muscles, and enables a wide range of motion through its joint connections.

1.0Bones of Upper Limb 

• Pectoral Girdle  Arm : Humerus.  
• Forearm: Radius & Ulna.  
• Wrist: Carpal bones.  
• Hand: Metacarpals & Phalanges.

2.0Pectoral Girdle

• It is composed of two bones: Clavicle and Scapula.  
• It is very light, allowing the upper limb to move exceptionally freely.

3.0Clavicle

• It is a long bone lying horizontally across the root of the Neck. 
• It is subcutaneous throughout its length.
• It is considered a long bone with no medullary (bone marrow) cavity. Its medial End, the "Sternal end", is enlarged & triangular. Its lateral End, the "Acromial end", is flattened. 
• The medial 2/3 of the shaft is convex forward. The lateral 1/3 is concave forward. 
• These curves make the clavicle look like an elongated capital (S). 
• It has two surfaces:  Superior and smooth, as it lies deep into the skin. Inferior: rough because strong ligaments bind it to the 1^st rib. 

Functions

• It acts as a stable support, suspending the scapula and upper limb away from the trunk to maximize arm mobility. 
• Additionally, it transmits forces from the upper limb to the axial skeleton, provides anchorage for muscles, and defines the boundary of the cervicoaxillary canal, safeguarding the neurovascular bundle.

Fractures of the Clavicle

• Falling. "Commonly in children"  
• The weakest part of the clavicle is the junction of the middle and lateral thirds.  
• After fracture, the medial fragment is elevated(by the sternomastoid muscle).  
• The lateral fragment drops because of the weight of the upper limb.  
• It may be pulled medially by the adductors of the arm.

4.0Scapula

• It is a triangular flat bone. Extends between the 2nd to 7th ribs, that has:

Forms the (glenoid cavity): a shallow concave oval fossa that receives the head of the humerus 

Functions of the Scapula

• Gives attachment to muscles.  
• Has a considerable degree of movement on the thoracic wall to enable the arm to move freely.  
• The glenoid cavity forms the socket of the shoulder joint.  
• Because most of the scapula is well protected by muscles and by its association with the thoracic wall, most of its fractures involve the protruding subcutaneous acromion. 

5.0Arm (Humerus)

• It is a typical long bone, and it is the largest bone in the upper limb.

• Proximal End comprises "Head, Neck, Greater and Lesser tubercles".
• Head: It is smooth and forms 1/3 of a sphere. It articulates with the glenoid cavity of the scapula. 
• Anatomical Neck: formed by a groove separating the head from the tubercles. 
• Greater tubercle: at the lateral margin of the Humerus. 
• Lesser tubercle: projects anteriorly "The two tubercles are separated by Intertubercular Groove(Bicipital Groove) ". 
• Surgical Neck: a narrow part distal to the tubercles. It is a common fracture site of the Humerus. 

Shaft (Body)

• It has two prominent features.
• Deltoid tuberosity -  A rough elevation laterally for the attachment of a deltoid muscle. 
• Spiral (Radial) groove - Runs obliquely down the posterior aspect of the shaft, and it lodges the important radial nerve and vessels.

Distal End

• Widens as the sharp medial and lateral Supracondylar Ridges form and End in the medial and lateral Epicondyles, providing muscular attachment.
• Trochlea: (medial) for articulation with the ulna.
• Capitulum: (lateral) for articulation with the radius. 
• Coronoid fossa: above the trochlea (anteriorly). 
• Radial fossa: above the capitulum. 
• Olecranon fossa: above the trochlea  (posteriorly).

 Fractures of the Humerus

• The most common fractures of the surgical Neck, especially in elderly people with osteoporosis.  
• The fracture results from falling on the hand (transmission of force through the bones of the forearm of the extended limb).  
• In younger people, fractures of the greater tubercle result from falling on the hand when the arm is abducted.  
• The body of the Humerus can be fractured by a direct blow to the arm or by indirect injury, such as falling on the outstretched hand. 

6.0Articulations of the Humerus

• The head of the Humerus with the glenoid cavity of the scapula forms the shoulder joint.  
• The lower End (Trochlea & Capitulum) with the upper ends of the radius & ulna form the elbow joint. 

7.0Forearm

Ulna: It is the stabilizing bone of the forearm. It is the medial & longer of the two bones of the forearm.

Proximal End

• It has two prominent projections:
• Olecranon process: projects proximally from the posterior aspect (Forms the prominence of the elbow). 
• Coronoid process: projects anteriorly.
• Trochlear notch: articulates with the trochlea of the Humerus. 
• Radial notch: a smooth, rounded concavity lateral to the coronoid process.  
• Tuberosity of ulna: inferior to coronoid process.

Shaft

• Thick & cylindrical superiorly but diminishes in diameter.
• Three surfaces (Anterior, Medial & Posterior).  
• Sharp lateral interosseous border. 

Distal End

• Small rounded Head: Styloid process medial.
• The head lies distally at the wrist.  
• The articulations between the ulna and Humerus at the elbow joint allow primarily only flexion and extension (a small amount of abduction and adduction occurs). 

8.0Radius: It is the shorter and lateral of the two forearm bones.

Proximal End

• Head: small, circular and its upper surface is concave for articulation with the capitulum.  
• Neck  
• Radial Tuberosity: Medially directed and separates the proximal End from the body. 

Shaft

• Has a lateral convexity.  
• It gradually enlarges as it passes distally. 

Distal End

• It is rectangular.  
• Its medial aspect forms a concavity: An ulnar notch to accommodate the head of the ulna.  
• Radial Styloid process: extends from the lateral aspect.  
• Dorsal tubercle: projects dorsally.

Articulations of Radius and Ulna

• The distal End of the Humerus with the proximal ends of the Radius & Ulna Elbow joint.  
• Proximal Radioulnar joint.  
• Distal Radioulnar joint.  
• The flexible interosseous membrane connects the two bones. 

Fractures of Radius and Ulna

• The radius and ulna are tightly connected by the interosseous membrane, so a fracture in one bone often leads to a dislocation in the nearest joint.  
• Colles’ fracture, which occurs at the distal end of the radius, is the most common type of forearm fracture.  
• This injury is particularly prevalent in women after middle age due to osteoporosis.  
• It typically occurs when the hand is forced into dorsiflexion, such as during a fall when the upper limb is instinctively outstretched to break the impact.  
• A common history of this fracture involves slipping. Fortunately, the bony union tends to heal well, thanks to the rich blood supply at the distal end of the radius.  

Hand 

• The skeleton of the hand consists of:
• Carpals: 8 bones
• Metacarpals: 5 bones
• Phalanges: 14 bones

Wrist

• The carpus consists of eight carpal bones organized into two irregular rows of four each. 
• These small bones provide flexibility to the wrist. 
• The carpus is concave on its anterior surface and convex from side to side on its posterior surface.

 Fracture of Scaphoid

• It is the most commonly fractured carpal bone, and it is the most common injury of the wrist.  
• It results from a fall onto the palm when the hand is abducted.  
• Pain occurs along the wrist's lateral side, especially during the hand's dorsiflexion and abduction.  
• Union of the bone may take several months because of poor blood supply to the proximal part of the scaphoid.