Types of joints

Joint types are the different ways that the bones in the body are attached to each other. Joints are the joints between bones and are part of the bone system.

The most general classification of joints can be established by their function and their structure..

Types of joints		Characteristics	Examples
According to its structure	Fibrous	Immobile No cavity	Skull sutures Union of teeth Syndesmosis: interosseous membrane between the radius and the ulna.
Cartilaginous	Partially mobile	Synchondrosis: union of the diaphysis and epiphysis of bones. Symphysis: union of the manubrium and sternum.
Synovial	Wrapped in a capsule containing synovial fluid	Union of the femur to the hip
According to its function	Synarthrosis	Immobile	Skull sutures
Amphiarthrosis	Partially mobile Fibrous of the syndesmosis type	Union between the tibia and fibula at the ankle.
Diarthrosis	Mobile phones Synovial type	Pivot: between the first and second vertebra. Hinge: flexion and extension of the elbow. Saddle: between 1st metacarpus and trapezius. Spherical: junction of the femur to the hip. Sliding: between the carpal bones. Ellipsoidal: bones in the wrist of the hand.

Types of joints according to their structure

According to the histology of the tissue that holds the bones together, we can classify the joints into three types:

• Fibrous,
• cartilaginous, and
• synovial.

1. Fibrous joints

Fibrous joints are held together by fibrous tissue, composed primarily of collagen, which holds the joints together. They are characterized by being immobile and not presenting a cavity. They are classified into three types: sutures, gonphosis, and syndesmosis..

1.1. Sutures: skull joints

Sutures are the joints between the flat bones of the skull. At birth these regions are represented by fontanelles, slightly flexible areas that allow the baby to pass through the birth canal. Over time, the bones grow and the fontanelles close, forming a layer of fibrous connective tissue. Finally, the bones of the skull fuse to form a synostosis..

1.2. Gonphosis: joints of the teeth

Gonphoses are the joints between the teeth and the jawbones that support them. They are fixed joints where the periodontal ligament is the fibrous tissue that connects the tooth with the dental socket..

1.3. Syndesmosis

Syndesmoses are slightly mobile joints, where two bones are held together by a membrane. For example, the junction between the tibia and fibula (or fibula) in the leg and the junction between the radius and ulna in the arm.

2. Cartilaginous joints

The cartilaginous joints are held together by hyaline tissue or fibrocartilage. There are two types: primary or synchondrosis and secondary or symphysis.

2.1. Synchondrosis

Synchondrosis is a type of joint where only hyaline is found. It can be temporary or permanent, depending on whether the hyaline tissue ossifies, as at the junction between the epiphysis and the shaft of a bone, or permanent, as occurs between the ribs and the sternum..

2.2. Symphysis

Symphyses are fibrocartilage or hyaline tissue joints and can be slightly mobile. An example is the pubic symphysis, the junction of the two bones of the pelvis..

3. Synovial joints

The synovial joints are the most functional joints in the body. Its main function is to prevent friction between the bones. They are characterized by:

• be mobile (diarthrosis);
• possess a cavity surrounded by a joint capsule and filled with synovial fluid.

Synovial fluid or fluid is produced by the synovial membrane (synovium) and the hyaline cartilage covers the entire surface of the bone that is part of the junction.

Synovial joints can be classified according to the movement they allow:

• hinge,
• flat or sliding,
• pivot,
• condyle or ellipsoidal,
• in saddle, and
• spherical.

Types of joints according to their function

The types of joints according to their function refers to the ability to perform some type of movement between the bones that make them up.

1. Synarthrosis: immobile joints

Synarthrosis are those joints where the bones do not move with each other. Examples are in the bones that make up the skull.

2. Amphiarthrosis: semi-mobile joints

Semi-mobile joints are classified within the group of cartilaginous joints. Examples of amphiarthrosis we have it between the vertebrae.

3. Diarthrosis: mobile joints

Diarthroses are the joints that allow movement in one or more axes. Structurally they are of the synovial type, and depending on the movement, we find six types.

3.1. Hinge joint

This type of joint is established between the concave side of one bone and the convex side of the other bone. It only allows movement in one axis, such as flexion and extension. Examples of hinge joints are the elbow and the joints between the phalanges..

3.2. Ellipsoidal or condyloid joint

The ellipsoidal or condyloid joint is established between a slight depression of one bone and the rounded portion of other bone (s). It allows movement in two axes:

• flexion and extension,
• medial / lateral or abduction / adduction.

The metacarpal-phalangeal joint of the hand is a good example.

3.3. Saddle joint

The saddle joint occurs between bones that have a concave and a convex surface. Can be moved in two axes, allowing flexion / extension and abduction / adduction.

This type of joint is found between the first metacarpus (of the thumb) and the trapezius carpal bone. This allows the thumb to be placed perpendicular to the hand and the ability of the human thumb to oppose.

3.4. Sliding joint

The sliding or flat joint occurs between bones with flat surfaces of similar size. It could allow movement in various axes, but due to the ligaments that surround them, movement is restricted. Examples are between the bones that form the carpus in the hand and the tarsus in the foot..

3.5. Pivot joint

The pivot joint occurs between two bones with rounded edges within a ring of ligaments. The clearest example is the union between the first and second vertebrae, which allows the head to move from side to side..

3.6 Ball joint

The spherical or glenoid joint is characterized by having one of the bones with a round head that fits into the concavity of another bone. This joint allows movement in several axes:

• flexion and extension,
• abduction and adduction,
• rotation.

The classic examples of this type of joint are achieved in the union of the humerus in the shoulder and the head of the femur in the pelvis..

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Reference

Juneja, P., Hubbard, J.B. (2019) Anatomy, Joints. StatPearls [Internet]. www.ncbi.nlm.nih.gov/books/NBK507893/