Ball and Socket Joint

Introduction

Movement is essential for every living being, without which a living organism cannot function. Movement varies among different organisms based on its kind and requirements. The human body is composed of 206 bones that give shape to the body, guard the internal organs and enable its movement. Even when the body is resting, it undergoes movements such as breathing, blinking eyes etc. How is the movement possible? It is possible because of the different kinds of joints in the body.

Joints

A Joint is the point of connection between two or more bones. The joint could be rigid like the upper jaw or mobile joints like the knee and elbows. The different kinds of joints are categorized based on their location and degree of body mobility. This tutorial explains the ball and socket joint.

Ball and Socket Joint

This joint falls under the category of synovial joints. Synovial joints permit a large variety of moves easily in the direction the human body desires. The basic structure of this joint is that one bone has a sizeable rounded end that is incorporated into a cavity shaped like a cup or socket of a different bone. Much like the cup and saucer, there is a connection between the two bones. The rounded end of the former bone is merged into the cup-like socket of the latter. However, unlike the cup and saucer, the ball and socket joints are inseparable.

Basic Function of Ball and Socket Joints

Due to their great structure, these joints distinguish themselves from other joints in the human body in terms of spinning and bending in all directions, i.e., forward, backward or sideways.

Features of Ball and Socket Joint

The round surface of one bone is circular or spherical; hence the term "ball"; it is connected to the cavity of another bone, generally known as a "socket". Hence the term "ball and socket joint". This joint is filled with a fluid that acts as a pad to help lubricate, facilitating optimum movement and stability. Ligaments and tendons maintain these joints.

Choice of Motions of Ball and Socket Joints

A wide range of mobility is possible with ball and socket joints. It can move in multiple axes. Therefore, these joints are also referred to as multiaxial joints. Therefore, these joints have more muscles for optimal movement while maintaining stability. The ball and socket joint mobility can be observed in three different ways; these include −

• Extension and flexion − Flexion refer to the body movements that reduce or decline the angle between the two body parts. In contrast, extension lengthens or increases the angle between the two bones.

• Abduction and adduction − These movements are vital to the body as flexion and extension. Abduction is the movement of a body part away from the central point, while the movement which involves drawing a part of the body closer to the central point is adduction. During arm abduction, also referred to as shoulder abduction, the arms move away from the body’s centre. During arm adduction, also referred to as shoulder adduction, the arms are brought back towards the body centre.

• Circumduction and rotation − Circumduction is defined as the circular motion of a joint where one end is fixed while the loose end is free to move in a circle. Rotation is when the limb rotates around its centre.

Examples

The hip and shoulder joints are excellent examples of ball and socket joints.

Hip Joint

In the hip joint, the circular or oval head of the femur, which is the thigh bone (ball), is fused into the cavity of the acetabulum (socket) found in the hip. Solid hip muscles and stiff ligaments protect the joints in the hip. This connection is vital to hold the femur in place and guard against strains in the body. The hip bone's socket is quite deep compared to the shoulder joint's socket, making it relatively stable yet also controlling optimum movement. The hollowness of the socket also protects the hips from dislocating by controlling the movement of the joint. The hip joint is substantial compared to shoulder joints because it carries the entire body's weight resting on the legs. However, in comparison to shoulder joints, it is less mobile.

Shoulder Joint

This joint is also named the glenohumeral joint. Here, the round or oval head of the humerus, resembling the ball that is the upper arm bone, is fused into the cavity of the socket of the scapula bone, which is the shoulder blade. The socket in the shoulder joint is called the glenoid fossa. The cup-shaped glenoid cavity is relatively shallow in the shoulder joint, facilitating the movement of the maximum range and in any desired direction. However, the joint is armoured by cartilage around the cavity to provide flexibility.

Defects of ball and socket joints

Since the ball and socket joint is formed due to the assembly of two bones in a cup and saucer manner, any dislocation due to fracture or accidents could lead to severe defects in these joints. Examples include rheumatoid arthritis and osteoporosis. Rheumatoid arthritis involves bone erosion and distortion of the joint. Osteoporosis is characterised by pain and rigidity in the bone due to the absence of lubricating synovial fluid.

FAQs

Name the various joints in the human body?

Ans − The three kinds of joints in the human body are synovial joints, fibrous joints, and cartilaginous joints.

What are synovial joints?

Ans − The joints that permit maximum movement between the bones are called synovial joints or diarthroses.

How is movement different from locomotion?

Ans − Movement is concerned with a position where the body moves from one position to a different position without changing a place. In comparison, locomotion is the dislocation of the entire body from one place to another.

Name the three planes of motion in humans.

Ans − Frontal plane, transverse plane and sagittal plane.

Name the different kinds of synovial joints present in the human body?

Ans − Condyloid, hinge, pivotal, gliding, saddle and ball and socket joints make up the human body.