Saddle Joints

The saddle joint is a type of synovial joint that allows a wide range of movements. movement in two planes. Joints are characterized by the presence of two reciprocal concave and convex surfaces, that allow movement in two planes. These planes are flexion/extension and abduction/adduction. In the human body, the saddle joint can be found in the carpometacarpal joint of the thumb, the incudomalleolar joint of the middle ear, the sternoclavicular joint of the thorax, and the calcaneocuboid joint of the heel.

What are Saddle Joints?

Saddle joints, also known as a sellar joint, are a type of synovial joint which is one of three types of joints in the body. Saddle joints are highly flexible and are formed between convex and concave articulating surfaces. It allows movements on two planes–flexion or extension and abduction or adduction. In Saddle joints, the articulating surface is covered by articular cartilage which reduces friction between the bones and minimizes the risk of dislocation. The saddle joint provides a balance of stability and mobility that allows fine motor skills and precise movements.

Structure

A saddle joint is a type of synovial joint that connects two bones that are saddle-shaped. One bone is concave on the surface and the other one is convex. The articulating bones fit together like a rider and a saddle. The joint formed is highly flexible.

Diagram of the Saddle Joints

The diagram of the saddle joints is as follows:

Movement of Saddle Joints

Saddle joint allow movement in the two planes, the sagittal and frontal planes. They allow flexion, extension, abduction, adduction, and circumduction, but the axial movement is not allowed. The movement associated with the saddle joints are discussed as follows:

• Flexion: The angle between the bones decreases at the saddle joint.
• Extension: The angle between the bones increases at the saddle joint.
• Abduction: A body part (like arm) moves away from the midline of the body.
• Adduction: A body part (like arm) moves towards the midline of the body.
• Circumduction: It involves circular movement of the joint, like flexion, extension, abduction, and adduction.
• Opposition: This type of movement only occurs in the thumb. The thumb moves toward the other fingers, allowing grasping and manipulation.
• Reposition: The thumb returns from opposition to its anatomical position.

The saddle joint provides wide range of movement that provides balance of stability and mobility which is essential for the fine motor skills and precise movements.

Examples of Saddle Joints

The human body has a few saddle joints. These joints are highly flexible and allow for two degrees of freedom. Examples of Saddle Joints includes:

Carpometacarpal Joint of the Thumb

In humans the most common example of the saddle joint is found at the base of the thumb. The trapezium bone of the wrist forms the convex surface, and the base of the first metacarpal bone forms the concave surface. The movements allowed by this joint includes
opposition and reposition which enables the thumb to touch the tips of the other fingers.

Sternoclavicular Joint

The collarbone or the clavicle articulates with the breastbone or sternum. The joint allow movements in multiple planes, including elevation, depression, protraction, and retraction. The joint is covered by a strong ligament that prevent it from getting injured. This joint enables wide range of activities like raising the arm above head, and also provide support to the shoulder.

Incudomalleolar Joint

The incudomalleolar joint, also known as the incudostapedial joint, is a synovial joint in the middle ear. This joint connects the incus (anvil bone) and the malleus (hammer bone) by small ligament in the middle ear. It enables the transfer of vibrations from the eardrum to the inner ear and contribute to the process of hearing.

Calcaneocuboid Joint of the Heel

The calcaneocuboid joint is a synovial joint present on the lateral side of the foot. It connects the calcaneus (heel bone) and the cuboid bone and contributes to the flexibility and stability of the foot. It allows for limited gliding and rotation movements.

Features of Saddle Joints

Saddle joint has the following features:

• Saddle joints allow for angular movements similar to condyloid joints, but with a greater range of motion.
• A saddle joint includes one concave bone and another convex bone.
• Saddle joints are highly flexible.
• Saddle joints allow for flexion, extension, adduction, abduction, and circumduction. However, axial rotation is not allowed.
• Saddle joints provide a balance of stability and mobility. It contribute to the precise and versatile movements.
• The joint surfaces are covered with articular cartilage which reduces friction. The joint cavity contains synovial fluid for lubrication.
• Saddle joints are similar to condyloid joints in functional appearance.
• The closely placed articulating surfaces reduce the risk of dislocation.
• An example of a saddle joint is the thumb joint.

Location of Saddle Joints

In the human body the saddle joint is present at few locations. These includes:

• Thumb: The joint at the base of the thumb.
• Shoulder: The sternoclavicular joint.
• Ear: The incudomalleolar joint, which is located in the inner ear.

Functions of Saddle Joints

Saddle joint allow the following functions:

• It allows the opposable thumb movement by enabling the thumb to touch other fingers for a precise grip.
• Allows flexion and abduction that is bending and straightening movements of the thumb.
• The incudomalleolar joint, located in the inner ear, connects the incus (anvil) and the malleus (hammer) bones. They are important for hearing and interpreting sounds.
• Saddle joints are biaxial joints, which means movement occurs at two distinct axes at right angles to each other. This allows for bending motions in several directions.
• Saddle joints can perform adduction, abduction, and circumduction movements.

Conclusion – Saddle Joints

In conclusion, the saddle joint is a type of synovial joint that have its appearance similar to the saddle seat. Saddle joints are formed when one bone surface is concave and the other is convex. The structure of saddle joints is a combination of both hinge and ball-and-socket joints. The closely placed articulating surfaces minimize the risk of dislocation. The presence of articular cartilage and synovial fluid lubrication and ensures smooth and efficient joint functioning. They offer greater flexibility and interlocking capabilities compared to other synovial joints.

FAQs on Saddle Joints

What is a Saddle Joint?

Saddle joint is a type of synovial joint that connects two bones. They are formed between convex and concave articulating surfaces, interlocking like two saddles.

Can Saddle Joints Rotate?

Saddle joints allow movement back and forth and from side to side, but do not allow rotation. Saddle joint allow movement in the two planes flexion, extension, abduction, adduction, and circumduction.

Write Two Features of Saddle Joints?

Two features of the saddle joint includes the joints are biaxial and allow movement in the two planes. It is formed between bones that have both concave and convex articulating surfaces.

What are the Examples of Saddle Joints?

Examples of the saddle joint includes the sternoclavicular joint, the incudomalleolar joint, calcaneocuboid joint of the heel, incudomalleolar joint and carpometacarpal Joint of the thumb.

Are Saddle Joints Moveable?

Yes, a saddle joint is a movable joint. It’s a biaxial joint that allows movement on two planes: flexion or extension, and abduction or adduction.

Are Saddle Joints Multiaxial?

No, saddle joints are biaxial joints. This means that they move on two distinct axes that are at right angles to each other.

What Type of Joint is a Saddle Joint?

A saddle joint is a type of synovial joint that allow a wide range of movement. The joints can move up and down and back and forth. There are around 300 joints in human body, and only three are saddle joints, these are present in the thumb, shoulder, and ear.

How many Saddle Joints are Present in the Human Body?

There are only three saddle joints in the human body. These are found in our thumb, shoulder, and ear.

Are Saddle Joints Biaxial?

Yes, saddle joints are biaxial joints and they allow movement on two distinct axes that are at right angles to each other. 

Where the Saddle Joints are Present in Humans?

Saddle joints are present in humans at the base of each thumb, where the trapezium bone articulates with the first metacarpal bone, allowing for a wide range of movement.