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Introduction

The upper limb is designed primarily for mobility and dexterity, allowing a wide range of precise and coordinated movements such as reaching, grasping, lifting, and manipulating objects. Its skeletal framework is light but strong, providing both flexibility and mechanical leverage.
The osteology of the upper limb refers to the study of its bones, which are connected through joints and supported by muscles, tendons, and ligaments. These bones are organized into four main regions: the shoulder girdle, arm, forearm, and hand.

1. General Organization of the Upper Limb Skeleton

The upper limb is divided into four anatomical regions:

Region	Main Bones	Description
Shoulder Girdle (Pectoral Girdle)	Clavicle, Scapula	Attaches the upper limb to the axial skeleton and provides attachment points for muscles.
Arm (Brachium)	Humerus	Extends from the shoulder to the elbow.
Forearm (Antebrachium)	Radius, Ulna	Extends from the elbow to the wrist.
Hand (Manus)	Carpal bones, Metacarpals, Phalanges	Forms the wrist, palm, and fingers.

 

 2. The Shoulder Girdle

The shoulder girdle connects the upper limb to the axial skeleton and provides a wide range of motion for the arm. It consists of the clavicle and the scapula.

2.1. Clavicle

• Shape: S-shaped long bone situated horizontally at the root of the neck.
• Position: Subcutaneous throughout its length, acting as a strut that holds the scapula laterally.
• Features:
• Sternal end: Articulates with the manubrium of the sternum.
• Acromial end: Articulates with the acromion of the scapula.
• Inferior surface: Has the conoid tubercle and trapezoid line for ligament attachments.

Functions:

• Connects the upper limb to the trunk.
• Acts as a support to keep the limb away from the thorax.
• Transmits mechanical forces from the upper limb to the axial skeleton.

 

 

2.2. Scapula

• Shape: Flat triangular bone located on the posterior thoracic wall between the 2nd and 7th ribs.
• Surfaces and Borders:
• Anterior (costal) surface: Contains the subscapular fossa.
• Posterior surface: Divided by the spine of the scapula into supraspinous and infraspinous fossae.
• Lateral angle: Bears the glenoid cavity for articulation with the head of the humerus.

 

Important Processes:

• Acromion: Extends laterally to form the highest point of the shoulder.
• Coracoid process: Projects forward for muscle and ligament attachment.
• Glenoid cavity: Receives the head of the humerus, forming the shoulder joint.

Function:
Provides attachment for muscles that move and stabilize the shoulder joint, maintaining alignment of the humeral head during arm movements.

 

3. The Arm (Brachium)

Humerus

The humerus is the largest and longest bone of the upper limb, forming the skeleton of the arm.

• Proximal End:
• Head: Articulates with the glenoid cavity of the scapula.
• Anatomical neck: Separates the head from the tubercles.
• Greater and lesser tubercles: Serve as attachment sites for rotator cuff muscles.
• Intertubercular sulcus (bicipital groove): Lodges the tendon of the long head of biceps brachii.
• Shaft:
• Deltoid tuberosity: Insertion point for the deltoid muscle.
• Radial (spiral) groove: Accommodates the radial nerve and deep brachial artery.
• Distal End:
• Capitulum: Articulates with the head of the radius.
• Trochlea: Articulates with the ulna.
• Medial and lateral epicondyles: Serve for muscle attachments and ligament anchoring.

 

4. The Forearm (Antebrachium)

The forearm extends from the elbow to the wrist and forms the link between the arm and the hand. It plays a vital role in positioning the hand and performing movements such as pronation, supination, grasping, and manipulation.
It consists of two parallel long bones, the radius and the ulna, which are connected by the interosseous membrane.

General Arrangement

Feature	Radius	Ulna
Position	Lateral (thumb side)	Medial (little finger side)
Length	Shorter	Longer
Wrist Articulation	Directly articulates with carpal bones	Does not articulate with carpal bones
Main Role	Responsible for hand movements	Provides stability and forms elbow hinge

A. The Ulna

The ulna is the medial and longer bone of the forearm. It mainly participates in the elbow joint, providing stability for forearm movements.

Part	Description	Function
Proximal End	- Olecranon process: Prominent projection forming the point of the elbow. - Coronoid process: Anterior projection fitting into the coronoid fossa of the humerus during flexion. - Trochlear notch: Articulates with the trochlea of the humerus. - Radial notch: Articulates with the head of the radius.	Forms the hinge of the elbow joint and provides leverage for triceps.
Shaft	Triangular in cross-section, with an interosseous border facing the radius.	Serves for muscle attachment and stability.
Distal End	Small head with styloid process projecting downward.	Articulates with the radius and provides ligament attachment for the wrist.

 

B. The Radius

The radius is the lateral and shorter bone of the forearm. It is the main bone involved in wrist movements because it articulates directly with the carpal bones.

Part	Description	Function
Proximal End	- Head: Disc-shaped; articulates with the capitulum of the humerus and the radial notch of the ulna. - Neck: Narrow part below the head. - Radial tuberosity: Rough area for insertion of biceps brachii tendon.	Allows rotation at the elbow and transmits biceps force.
Shaft	Slightly curved, with interosseous border facing the ulna.	Provides attachment for pronator and supinator muscles.
Distal End	Broad, articulates with the scaphoid and lunate bones; has a lateral styloid process.	Forms the main articulation for the wrist joint.

 

C. The Interosseous Membrane

The interosseous membrane is a strong fibrous sheet connecting the interosseous borders of the radius and ulna.

 

Functions:

• Maintains the relative position of both bones.
• Serves as an attachment surface for deep forearm muscles.
• Transmits forces from the hand through the radius to the ulna and then to the humerus.

 

D. Functional Movements of the Forearm

Movement	Description	Muscles Involved	Bones’ Relationship
Supination	Palm faces upward or forward.	Biceps brachii, Supinator	Radius and ulna are parallel.
Pronation	Palm faces downward or backward.	Pronator teres, Pronator quadratus	Radius crosses over the ulna.

Summary of the Forearm

• The ulna provides stability and forms the hinge of the elbow.
• The radius provides mobility and is essential for wrist and hand movements.
• The interosseous membrane coordinates their actions, ensuring stability and efficient transmission of forces.
• Together, they give the upper limb its functional versatility and fine control.

 

 

 

 

 

 

 

 

 

 

 

 

 

5. The Hand (Manus)

The hand is the most specialized part of the upper limb. It is adapted for grasping, sensation, and precise manipulation.

Region	Bones	Description
Carpus (Wrist)	8 carpal bones arranged in two rows.	Provides flexibility and movement at the wrist.
Metacarpus (Palm)	5 metacarpal bones (I–V).	Form the skeleton of the palm.
Phalanges (Fingers)	14 bones (3 per finger, 2 for the thumb).	Provide fine mobility and dexterity.

Arrangement of Carpal Bones

Proximal Row (lateral → medial)	Distal Row (lateral → medial)
Scaphoid	Trapezium
Lunate	Trapezoid
Triquetrum	Capitate
Pisiform	Hamate

Mnemonic:“Some Lovers Try Positions That They Can’t Handle.”

 

Together, these features make the human upper limb one of the most adaptable and functional systems in the body, enabling skilled movements essential for daily activities and tool use.