The adult human body has 206 bones and approximately 300 joints that connect two bones in a body. Among them some joints allow movement and such joints are known as synovial joint, also there are Types of Synovial Joints. It allows smooth movement between two adjacent joints. Synovial Joints of the body are freely mobile and also known as a diarthrosis.
The synovial joints unite bones that are long and they also facilitate greater mobility as well as free bone movements. Such joints are usually filled with synovial fluid. The capsule that is associated with the joint has a fibrous membrane that keeps the bones together. There is an interior or inner layer of the synovial membrane that prevents the synovial fluid from leaking. These joints are the common joint types that are found in mammals. Like most other joints, such joint types facilitate locomotion at the meeting point of long bones.
The bone that is on the adjoining proximal side is known as plafond. The corresponding joint is known as the talocrural joint. Damage to such joints is referred to as the Gosselin fracture. Blood supply to the Synovial joints is done with the help of the arteries that are located in the anastomosis surrounding the joint. The arteries which are located in the anastomosis surrounding the joints help to supply the blood to the Synovial joints.
Synovial Joints vary in structure and have many different types. Let’s discuss the types, structure, function as well as clinical importance of the synovial joints of the body.
Types of Synovial Joints
Types of synovial joints are based on their mobility. Mainly there are six types of synovial joints, that are described in brief below.
1. Plain Joints
Plain Joints are also said to be gliding joints. These joints have bones with articulating surfaces and are found in the tarsal bones of the foot, carpal bones of the hands, and also in between vertebrae.
An example of such a joint type is the wrist carpals. Also, the acromioclavicular joint is yet another example of such joint type. These joints facilitate the sliding and gliding manoeuvres of the body. They also facilitate the articulation between the vertebrae.
2. Pivot joints
Pivot Joints of the body allow rotational joint movements. These joints consist of the rounded end of one bone fitting into a ring formed by the other bone. We can rotate our neck or head just because of pivot joints in the first & second vertebrae of the head & neck.
Examples of pivot joints include the proximal-radioulnar joint, atlantoaxial joint, and distal-radioulnar joint. The pivot joints are such types of joints in the human body that facilitate the rotation of one bone with the help of other bones in the body.
Condyloid Joints are also said to be Ellipsoidal joints of the body. These joints consist of an oval-shaped end of one bone fitting or adjacent to the similar oval-shaped hollow of another bone. Angular movements of two bones can be done through condyloid joints.
The condyloid joint
is a kind of ball & socket joint. Such types of Synovial joints allow primary manoeuvres within axes that are perpendicular to each other. With the ellipsoidal joints, secondary or passive movements can occur on a separate axis. Overall, it can be said that the ellipsoidal joints or the condyloid joints allow extension and flexion manoeuvres within the body.
Hinge Joints are those which help in fitting the rounded end of one bone into the hollow end of another bone in the human body. With the help of hinge joints, one bone can easily move while the other remains constant.
In the human body, the hinge joints are found in the elbow and between the ulna and the humerus. These joints act similar to that of a door hinge. These joints also allow extension and flexion in just a single plane.
5.Ball & socket joints
Ball & socket joint is also referred to as Universal joints. These bones help a rounded shape end of a bone fitting into a cuplike socket of another bone.
The hip and shoulder joints are examples of the ball & socket joints in the human body. These joints facilitate various manoeuvres of the human body except gliding.
Saddle joints in the human body are similar to hinge joints the only difference is that saddle joints are more mobile than hinge joints. Saddle joints help the bone to move in an oval shape. In the human body, the thumb has saddle joints.
Also Read: Most Common Joint Replacement Surgery Myths and Facts
Overview of the Structure and Functions of the Synovial Joints
Every joint in a body has a proper structure and functions. Here are the structure and functions of Synovial joints of the body
The following is the structure that every synovial joint consists of:-
1. Joint capsule:-
The joint capsule is fibrous and it unites bones that are articulating. There are two layers associated with the joint capsule and they are as follows
a. Outer Fibrous Membrane or External membrane which includes adoptive and connective tissues.
b. The inner or interior synovial membrane contains type A and type synovial cells that secrete the synovial fluid.
The synovial fluid is shock-absorbing, joint nourishing, and provides lubrication to the bones. The joint capsule is stimulated and is without lymph or blood vessels.
Diarthrosis has a space between two adjacent bones and this space is known as the Synovial cavity. A synovial cavity that fills with synovial fluid, a modification of plasma containing high levels of hyaluronic acid, which increases articular cartilage viscosity and elasticity, and lubricates the area between the synovial membrane and cartilage.
This is a layer of hyaline cartilages that cover the various bones of the synovial joint. The articular cartilages are smooth and they are slippery. The function of the layer is to absorb shock and diminish friction while moving.
The following is the structure that some synovial joints consist of:-
• Tendons connect skeletal muscle to the periosteum of bone
• Bursae reduces friction in the shoulder and knee
• Articular fat pads help in providing support for the cartilage
• Articular discs are also said to be Menisci. It comprised Fibrocartilage
• Ligaments are both inside or outside of the joint capsule.
Clinical Importance of Synovial Joints
If the joint space narrows down then it is a sign of inflammatory degeneration and osteoarthritis. In this context, it is relevant to comprehend that the normal joint space is about 2 mm in the hip region and it is about 3 mm in the knee region, and about 4-5 mm in the shoulder region. For the temporomandibular joints, joint space in the range of 1.5 to 4 mm is considered normal. In rheumatoid arthritis, the clinical manifestations include inflammations in the synovial region. Sometimes, such medical conditions are characterized by damage to the joint. When the Synovial joints get damaged then the cells in that region (mesenchymal cells that are found in the synovial membrane) get adversely affected. Therapies that aim to correct these cells, and make them healthy are emerging. Such therapies form the basis for the treatment of rheumatoid arthritis.
This write-up on Synovial-joints discusses the various types of joints, it also discusses the structures as well as the functions that are associated with such joints. Finally, the write-up highlights why such joints are significant from the clinical perspective. Many functions are associated with such joints and the most important being extension, flexion, and rotation.
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