Upper Limb Bones and Joints

The article Upper Limb Bones and Joints provides a comprehensive understanding of upper limb joints and their movements. The article includes:

Introduction to Upper Limb

The article Upper Limb Bones and Joints explores the intricate framework and seamless mobility of the upper limb through an in-depth study of its bones and joints. The human upper limb is a remarkable structure composed of numerous joints that work together to provide → mobility, strength, and agility. Understanding the upper limb joints is crucial in comprehending how we perform daily activities canv engage in physical tasks. To, understand the joints in the upper limb, we first need to be aware of the bones in the upper limb.

In the upcoming section, we will discuss the bones in the upper limb, which makes us understand the joints better and their associated movements. 

Upper Limb Bones

The upper limb bones, also known as the bones of the upper extremity, refer to the skeletal structures that form the framework of the arms and hands. They include the following bones:

Scapula (Shoulder Blade)

It is a flat, triangular bone that connects the upper arm bone (humerus) to the collarbone (clavicle) and provides attachment points for several muscles involved in shoulder movement.

Clavicle (Collarbone)

It is a long, S-shaped bone that connects the sternum (breastbone) to the scapula (shoulder blade), providing stability to the shoulder joint and acting as a strut to support the upper limb.

Humerus

The humerus is the long bone of the upper arm. It extends from the shoulder to the elbow and is the largest bone in the upper limb.

Radius

The radius is one of the two bones in the forearm, along with the ulna. It runs parallel to the ulna on the thumb side (lateral side) of the forearm.

Ulna

The ulna is the other bone in the forearm, located on the little finger side (medial side) of the forearm. It is slightly longer than the radius.

Carpals

The carpal bones are a group of eight small bones that form the wrist. They are arranged in two rows of four bones each.

Metacarpals

The hand has five metacarpal bones, connecting the wrist to the fingers. Each metacarpal corresponds to one of the five digits (thumb, index finger, middle finger, ring finger, and little finger).

Phalanges

The phalanges are the bones of the fingers. Each finger has three phalanges, except for the thumb, which has two. The phalanges are commonly referred to as the proximal, middle, and distal phalanges.

In the next part, we will discuss the Joints in the Upper Limb, which include → Acromioclavicular Joint, Wrist Joint, Shoulder Joint, Elbow Joint, Radioulnar Joint, Metacarpophalangeal Joint, Proximal Interphalangeal Joint, Sternoclavicular Joint.

Joints in the Upper Limb

The upper limb consists of several joints that facilitate movement and provide stability. Here are the major joints of the upper limb:

Acromioclavicular Joint

The acromioclavicular (AC) joint is a small but significant joint located in the shoulder region. It plays a crucial role in facilitating movements and stabilizing the shoulder girdle. Let’s discuss the structure of these joints.

Structure of the Acromioclavicular Joint

The AC joint is formed by the lateral end of the clavicle (collarbone) and the acromion process of the scapula (shoulder blade). It is a synovial joint surrounded by a joint capsule and supported by ligaments. Let’s delve into the specific structures:

1. Acromion Process

The acromion is a bony projection of the scapula that extends laterally and superiorly. Its flattened upper surface articulates with the clavicle to form the AC joint.

2. Joint Capsule

The AC joint is encapsulated by a fibrous joint capsule, which helps stabilize the joint and contains synovial fluid for lubrication.

3. Ligaments

Several ligaments provide stability and limit excessive movements at the AC joint:

1. Acromioclavicular Ligament: This ligament connects the acromion to the clavicle and resists upward displacement of the clavicle.
2. Coracoclavicular Ligaments: Two ligaments, conoid and trapezoid ligaments, connect the clavicle to the coracoid process of the scapula. Together these ligaments are known as coracoclavicular ligaments. They provide crucial stability to the AC joint and prevent upward and downward displacement of the clavicle.

Now, we will learn about the movements of the acromioclavicular joint.

Movements Associated with the Acromioclavicular Joint

The AC joint allows a limited range of movements, contributing to overall shoulder mobility and stability. Let’s explore the primary movements associated with this joint:

1. Elevation and Depression

The AC joint enables the clavicle to elevate (move upward) and depress (move downward) relative to the acromion. These movements occur during actions such as shrugging the shoulders or carrying heavy loads.

2. Protraction and Retraction

Protraction involves the forward movement of the clavicle, while retraction refers to its backward movement. These movements occur during activities like pushing or pulling movements of the arms

3. Upward and Downward Rotation

The AC joint facilitates the upward and downward rotation of the scapula. These movements contribute to the overall motion of the shoulder joint complex, allowing optimal arm positioning during activities such as reaching overhead or throwing.

Wrist Joint

It is a complex structure that plays a crucial role in the movement and stability of the hand. Let’s discuss the structure of these joints.

Structure of the Wrist Joint

The wrist joint is formed by the articulation between the radius and the proximal row of carpal bones. The carpal bones include the scaphoid (near the base of the thumb) lunate(crescent-shaped bone), triquetrum (small bone), pisiform (pear-shaped bone), trapezium (at the base of the thumb), trapezoid (sits next to trapezium) capitate (near center of wrist joint), and hamate (base of the palm). These bones form two rows: the proximal row (scaphoid, lunate, triquetrum, and pisiform) which is in contact with the radius, and the distal row (trapezium, trapezoid, capitate, and hamate), which articulates with the metacarpal bones of the hand. The following are the anatomical structures:

1. Ligaments

To stabilize the wrist joint, several ligaments are present. The most important ligaments include the radiocarpal ligaments, which connect the radius to the carpal bones, and the ulnocarpal ligaments, which connect the ulna to the carpal bones. Additionally, the collateral ligaments on the sides of the joint provide stability during movements.

2. Articular Surfaces

The articulating surfaces of the wrist joint are covered with hyaline cartilage, which helps reduce friction and allows for smooth movements. The radius has a concave surface, while the carpal bones have convex surfaces, enabling a close fit and enhancing joint stability.

Now, we will talk about the movements of the wrist joint.

Movements Associated with the Wrist Joint

The wrist joint allows a wide range of movements that are essential for hand function. These movements include:

1. Flexion: Bending the wrist forward, reducing the angle between the palm and the forearm.
2. Extension: Straightening the wrist, increasing the angle between the palm and the forearm.
3. Abduction: Moving the wrist away from the midline of the body.
4. Adduction: Bringing the wrist closer to the midline of the body.
5. Circumduction: A combined movement of flexion, extension, abduction, and adduction, creating a circular motion.
6. Limited Rotation: The wrist joint allows limited pronation (palm down) and supination (palm up) movements.

Shoulder Joint

The shoulder joint is a highly mobile joint that connects the upper arm bone (humerus) with the shoulder blade (scapula). It is classified as a ball-and-socket joint, allowing for a wide range of motion in multiple directions.

Structure of the Shoulder Joint

The shoulder joint is also known as the glenohumeral joint. Let’s examine each of these components in detail:

1. Articular Surfaces

They are found in joints, where two or more bones come together. Articular surfaces are covered with a layer of smooth, specialized connective tissue known as articular cartilage. This cartilage reduces friction between the bones, provides shock absorption, and enables smooth movement within the joint. These surfaces are divided into several types:

1. Glenoid cavity: This is a shallow, socket-like depression on the lateral aspect of the scapula where the head of the humerus articulates.
2. Head of the humerus: This is the rounded, ball-like structure at the upper end of the humerus that fits into the glenoid cavity.
3. Glenoid labrum: It is a fibrocartilaginous ring that surrounds the rim of the glenoid cavity, deepening the socket and providing stability to the joint.

2. Joint Capsule

The shoulder joint is surrounded by a flexible, fibrous capsule that encloses the joint and helps maintain its stability.

3. Ligaments and Tendons

The shoulder joint is reinforced by several ligaments and tendons, which play a crucial role in providing stability and preventing excessive movements. And those are:

1. Glenohumeral Ligaments: These ligaments surround the joint capsule and help secure the humerus to the glenoid fossa, providing stability to the joint.
2. Rotator Cuff Tendons: A rotator cuff is a group of four tendons that originate from muscles around the shoulder joint. These tendons blend to form a “cuff” that stabilizes the humeral head within the glenoid fossa.

4. Bursae

Bursae are small fluid-filled sacs located around the shoulder joint. They help reduce friction between tendons, muscles, and bones during movement.

Let’s talk about the various movements, shoulder joints can perform.

Movements associated with the Shoulder Joint

The shoulder joint allows for a remarkable range of movements due to its unique anatomy and the actions of the surrounding muscles. Let’s explore the primary movements enabled by the shoulder joint:

1. Flexion

Flexion refers to bringing the arm forward, such as when throwing a ball. It occurs when the angle between the humerus and the scapula decreases.

2. Extension

An extension is the opposite of flexion, involving moving the arm backwards. It occurs when the angle between the humerus and the scapula increases.

3. Abduction

Abduction involves moving the arm away from the body, such as when raising it to the side. It occurs in the plane parallel to the frontal plane.

4. Adduction

Adduction is the opposite of abduction, where the arm moves toward the body. It brings the arm back to the neutral position from an abducted position.

5. Internal Rotation

Internal rotation refers to rotating the arm inward, towards the body’s midline. It allows activities such as reaching behind the back.

6. External Rotation

External rotation is the opposite of internal rotation, involving rotating the arm outward. It is often involved in actions like throwing a ball.

Elbow Joint

The elbow joint is a vital hinge joint that enables a range of movements involving the arm. Composed of three bones and several supporting structures, it allows us to perform various activities such as lifting, throwing, and gripping objects. Let’s discuss the structure of the elbow joint.

Structure of the Elbow joint

The structure of the elbow joint consists of → articular cartilage, joint capsule, and various ligaments. Here’s an overview of the key components:

1. Articular Cartilage

Articular cartilage covers the articulating surfaces of the bones within the elbow joint. It provides a smooth and low-friction surface that allows for easy movement between the bones.

2. Joint Capsule

The elbow joint is encapsulated by a fibrous joint capsule, which surrounds and stabilizes the joint. The capsule is lined with a synovial membrane that produces synovial fluid, a lubricating fluid that nourishes the joint and reduces friction between the bones during movement.

3. Ligaments

There are several ligaments found in the elbow joints:

1. Medial collateral ligament (MCL): Located on the inner side of the elbow, it helps stabilize the joint and prevents excessive inward (valgus) stress.
2. Lateral collateral ligament (LCL): Located on the outer side of the elbow, it provides stability and prevents excessive outward (varus) stress.
3. Annular ligament: Encircles the head of the radius and holds it in place against the ulna.

Movements associated with the Elbow Joint

1. Flexion: This movement decreases the angle between the humerus and the ulna, bringing the forearm closer to the upper arm. The primary muscles involved in elbow flexion are the biceps brachii (front of the upper arm) and the brachialis (Situated deep to the biceps brachii).
2. Extension: This movement increases the angle between the humerus and the ulna, straightening the arm. The primary muscle involved in elbow extension is the triceps brachii (back of the upper arm).
3. Pronation: This movement involves the rotation of the forearm so that the palm faces downward. It is primarily carried out by the pronator teres and pronator quadratus muscles (both are located in the forearm).
4. Supination: This movement involves the rotation of the forearm so that the palm faces upward. It is primarily carried out by the biceps brachii and supinator muscles (located in the forearm).

Radioulnar Joint

The is an essential component of the forearm that facilitates various movements of the forearm and wrist. Composed of the radius and ulna bones, the joint plays a crucial role in forearm rotation and stability. Let’s talk about the types of Radioulnar Joints.

Types of Radioulnar Joints

There are two primary types of radioulnar joints: 

1. Proximal Radioulnar Joint

The proximal radioulnar joint is located at the elbow, connecting the proximal end of the radius and the radial notch of the ulna. This joint allows for rotational movements of the forearm, enabling pronation (palm-down) and supination (palm-up) of the hand. It consists of the following structures:

1. Radial Head: The rounded end of the radius that articulates with the radial notch of the ulna.
2. Radial Notch: A concave depression on the lateral aspect of the ulna that accommodates the radial head.
3. Annular Ligament: A strong, fibrous band that encircles the radial head, holding it in place and providing stability to the joint.

2. Distal Radioulnar Joint

The distal radioulnar joint is located at the wrist, connecting the distal ends of the radius and ulna. This joint allows for rotation and gliding movements of the radius over the ulna, contributing to forearm pronation and supination. The structures involved in the distal radioulnar joint are as follows:

1. Ulnar Head: The distal end of the ulna that articulates with the ulnar notch of the radius.
2. Ulnar Notch: A concave surface on the medial aspect of the radius that accommodates the ulnar head.
3. Triangular Fibrocartilage Complex (TFCC): A cartilaginous structure that enhances joint stability and provides cushioning between the ulna and radius.

Now, we will talk about the various structural components based on the two types of radioulnar joints.

Structure of the Radioulnar Joint

Both the proximal and distal radioulnar joints are synovial, allowing for smooth movement and the presence of a synovial membrane. The structures contributing to their stability and mobility include ligaments, articular surfaces, and cartilaginous structures, let’s discuss them briefly:

1. Ligaments

Various ligaments are formed in radioulnar joints, we will talk about it separately in each region:

1. Proximal Radioulnar Joint: The annular ligament encircles the radial head, holding it firmly against the radial notch of the ulna, providing stability and allowing rotational movements.
2. Distal Radioulnar Joint: Various ligaments, including the dorsal and palmar radioulnar ligaments reinforce the joint, preventing excessive movement and maintaining proper alignment.

2. Articular Surfaces

The articular surfaces formed in two radioulnar joints are-

1. Proximal Radioulnar Joint: The radial head articulates with the radial notch of the ulna, forming a pivot-like joint that enables rotation.
2. Distal Radioulnar Joint: The ulnar head fits into the ulnar notch of the radius, allowing for rotational and gliding movements.

3. Cartilaginous Structures

The cartilaginous structures formed in these two types of radioulnar joints-

1. Proximal Radioulnar Joint: Hyaline cartilage covers the articular surfaces of the radial head and radial notch, reducing friction and facilitating smooth movement.
2. Distal Radioulnar Joint: The triangular fibrocartilage complex (TFCC) is a cartilaginous structure that cushions the joint and improves stability.

Movements Associated with the Radioulnar Joint

The radioulnar joints contribute to two significant movements of the forearm:

1. Pronation: This movement involves the rotation of the radius across the ulna, causing the palm to face downward. The proximal radioulnar joint primarily facilitates pronation.

2. Supination: Supination involves the rotation of the radius back to its normal position, allowing the palm to face upward. Both the proximal and distal radioulnar joints contribute to supination.

Metacarpophalangeal Joint

It is commonly referred to as the MCP joint and is a crucial component of the human hand. Located between the metacarpal bones of the hand and the proximal phalanges of the fingers, this joint plays a vital role in hand function and dexterity.

Let’s learn about the structure of Metacarpophalangeal joints.

Structure of the Metacarpophalangeal Joint

The MCP joint is a synovial joint, specifically classified as a condyloid joint (an oval-shaped condyle (with rounded prominence), that fits into a concave surface). It is formed by the articulation of the rounded heads of the metacarpal bones with the concave proximal ends of the phalanges. Let’s examine the key components of the MCP joint:

1. Articular Surfaces: The metacarpal heads are rounded and convex, while the proximal phalanges possess concave surfaces. This articular configuration allows for smooth movement and stability within the joint.

2. Articular Capsule: The MCP joint is enveloped by a fibrous joint capsule that encloses the joint cavity. This capsule is reinforced by ligaments, which provide stability and limit excessive movement.

3. Synovial Membrane: The inner lining of the articular capsule is known as the synovial membrane. It secretes synovial fluid, which lubricates the joint surfaces, reduces friction, and nourishes the articular cartilage.

4. Articular Cartilage: The articulating surfaces of the MCP joint are covered with hyaline cartilage. This smooth and resilient cartilage helps in distributing forces and minimizing wear and tear during movement.

Let’s talk about the movements in the metacarpophalangeal joint.

Movements Associated with the Metacarpophalangeal Joint

The metacarpophalangeal joint allows for a variety of movements that are essential for hand function. These movements include:

1. Flexion: Flexion refers to the bending of the finger towards the palm. This movement is crucial for grasping objects and performing activities such as gripping a pen or holding a cup. It is primarily controlled by the flexor muscles located in the forearm, which connect to the fingers through tendons.
2. Extension: Extension is the opposite of flexion and involves straightening the finger. It allows the hand to reach out and grasp objects, as well as perform tasks that require an open hand. Extensor muscles located in the forearm control this movement.
3. Abduction: Abduction refers to the movement of the finger away from the midline of the hand. This movement allows for the spreading of the fingers, as seen when playing a musical instrument or typing on a keyboard. Abductor muscles, situated in the hand itself, control this motion.
4. Adduction: Adduction is the opposite of abduction and involves bringing the finger back toward the midline of the hand. This movement brings the fingers together, enabling activities like grasping a small object or forming a fist. The adductor muscles, located in the hand, control this movement.
5. Circumduction: Circumduction is a combination of flexion, extension, abduction, and adduction, resulting in a circular movement of the finger. This movement allows for a wide range of hand motions, such as tracing a circle in the air or waving goodbye.

Now, let’s talk about Proximal Interphalangeal joints.

Proximal Interphalangeal Joint (

PIP)

It is an essential part of the hand’s intricate structure, allowing for precise finger movements and dexterity. This joint is located between the proximal and middle phalanges of each finger and plays a crucial role in various activities such as → grasping, gripping, and manipulating objects.

Now, let’s learn about the structure of this joint.

Structure of the Proximal Interphalangeal Joint

The proximal interphalangeal joint comprises several important structures that work together to facilitate its function. These structures include:

1. Articular Surfaces

The PIP joint consists of convex articular surfaces on the head of the proximal phalanx and concave articular surfaces on the base of the middle phalanx. These opposing surfaces allow for smooth articulation and mobility of the joint.

2. Collateral Ligaments

The joint is reinforced by collateral ligaments on either side, known as the medial collateral ligament (ulnar collateral ligament) and the lateral collateral ligament (radial collateral ligament). These ligaments provide stability to the joint, preventing excessive side-to-side movement.

3. Flexor Tendons

The flexor tendons, originating from the muscles in the forearm, pass through the PIP joint and attach to the base of the middle phalanx. These tendons are responsible for flexing or bending the finger at the PIP joint.

4. Extensor Tendons

The extensor tendons, located on the back of the hand, pass over the PIP joint and attach to the middle phalanx. These tendons enable the extension or straightening of the finger at the PIP joint.

Now we will discuss the movements in this joint.

Movements Associated with the Proximal Interphalangeal Joint

The PIP joint allows for three primary movements: flexion, extension, and limited lateral movement. Let’s explore each of these movements in detail:

1. Flexion

Flexion at the PIP joint occurs when the finger bends, bringing the middle phalanx closer to the palm. This movement is essential for activities such as gripping objects and typing on a keyboard.

2. Extension

Extension at the PIP joint involves straightening the finger and moving the middle phalanx away from the palm. It allows for the finger to reach a fully extended position, important for tasks like pointing or stretching the hand.

3. Lateral Movement

Although the PIP joint primarily permits flexion and extension, it also allows for limited lateral or side-to-side movement. This slight mobility aids in fine adjustments when gripping objects with different shapes or sizes.

Now, we will talk about the Sternoclavicular Joint.

Sternoclavicular Joint (SC)

It is a crucial connection between the sternum (breastbone) and the clavicle (collarbone). This articulation allows for various movements of the shoulder girdle, contributing to the overall mobility and stability of the upper body. 

Let’s learn about the structure of the sternoclavicular joint.

Structure of the Sternoclavicular Joint

The SC joint is a complex joint with a unique structure that allows for stability and mobility. It consists of three main components:

1. Articular Surfaces

The SC joint is formed by the articulation of two articular surfaces: the medial end of the clavicle and the clavicular notch of the sternum. The clavicular notch is a shallow depression on the superior surface of the manubrium (uppermost part) of the sternum. These articular surfaces are covered by a thin layer of hyaline cartilage, facilitating smooth movement and minimizing friction.

2. Fibrous Capsule

Surrounding the articulating surfaces is a fibrous capsule, which provides stability to the SC joint. Ligaments reinforce the capsule. These ligaments like → anterior (front) sternoclavicular ligament, and posterior (back) sternoclavicular ligament, connect the sternum to the clavicle. While the interclavicular ligament connects the upper ends of the clavicle and the costoclavicular ligament connects clavicles to the first rib. These ligaments prevent excessive movement and maintain the joint’s integrity.

3. Articular Disc

An articular disc, made of fibrocartilage, is situated within the SC joint. It divides the joint into two separate compartments → the medial and lateral compartments. This disc enhances stability by increasing the congruence between the clavicle and sternum, while also absorbing shock and distributing forces across the joint.

Let’s discuss the movements associated with the Sternoclavicular joint.

Movements associated with the Sternoclavicular Joint

The sternoclavicular joint allows for a wide range of movements, making it unique among other joints in the body. The major movements associated with the SC joint include:

1. Elevation and Depression

Elevation refers to raising the shoulder girdle, while depression involves lowering it. These movements occur primarily during activities such as shrugging the shoulders or carrying heavy loads.

2. Protraction and Retraction

Protraction refers to moving the shoulder girdle forward, while retraction involves pulling it backward. These movements are commonly observed when pushing or pulling objects.

3. Anterior and Posterior Rotation

Anterior rotation means the forward movement of the clavicle. While posterior rotation involves moving it backward. These movements are important for activities like throwing or swinging the arms.

4. Circumduction

Circumduction combines multiple movements and describes the circular motion of the shoulder girdle. It involves a combination of elevation, depression, protraction, and retraction, creating a circular path of movement.

Conclusion

In conclusion, The article Upper Limb Bones and Joints discovers the remarkable synergy of bones and joints in the upper limb, essential for its strength, flexibility, and functionality. The upper limb is a complex network of bones and joints. They all work together to provide mobility, strength, and agility. Understanding the anatomy and movements of the upper limb joints is crucial for comprehending how we perform daily activities and engage in physical tasks.

The bones in the upper limb are → scapula, clavicle, humerus, radius, ulna, carpals, metacarpals, and phalanges. These bones form the framework of the arms and hands, providing attachment points for muscles and allowing for a wide range of movements.

The joints in the upper limb play a vital role in facilitating movement and providing stability. Some of the major joints include the → acromioclavicular joint, wrist joint, shoulder joint, elbow joint, radioulnar joint, metacarpophalangeal joint, proximal interphalangeal joint, and sternoclavicular joint. Each joint has a unique structure and is associated with specific movements.

Further Reading

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For more reading, check on the other sources such as:

1. Wikipedia: https://en.wikipedia.org/wiki/Upper_limb
2. NCBI: https://www.ncbi.nlm.nih.gov/books/NBK507841/
3. Wikipedia: https://en.wikipedia.org/wiki/Category:Bones_of_the_upper_limb

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