DIARTHROSIS: DEFINITION, TYPES AND EXAMPLES - ANATOMY AND PHYSIOLOGY - 2025

Joints that allow wide ranges and different directions of movement are called diarthrosis. The word diarthrosis comes from the Greek, in which "dia" means separation, and "arthron" means joint, that is, the bone surfaces are completely separated from each other, and are joined by other structures.

That is why they are also known as synovial or freely mobile joints, since unlike amphiarthrosis and synarthrosis, they have a joint cavity with synovial fluid that serves as a lubricant between the two opposing bone surfaces.

Head of the femur and acetabulum of the hip bone.

Synovial fluid is a fluid whose consistency is similar to that of egg white, with an oily to mucous appearance, with a transparent color. In addition to lubricating, the synovial fluid nourishes the articular cartilage, serving as a transport for the nutrients that the cartilage needs.

It is located within the synovial membrane, which is inserted into the bone surface, from the articular cartilage to the synovial capsule, that is, it is within the joint capsule and is the internal lining of it.

The bony ends of each bone that make up a diarthrosis are covered by a thin layer of hyaline cartilage, which is responsible for reducing friction between bone structures and cushioning blows.

They are the joints that represent the fundamental characteristic of the appendicular skeleton, its mobility.

Types of diarthrosis

Mobile joints can be classified according to the axes in which it allows movement, in this way we have:

-Uiaxial joints

As their name indicates, they are those that allow the mobilization of the joint in a single axis.

Hinge joint

They are those joints where the convex surface of one bone end, articulates with the concave surface of the other bone end.

In this sense, it is understood that it only allows movements in the sagittal axis, that is, flexion and extension movements.

The most characteristic joints of this type of joint are the humerus-ulnar joints of the arms (elbow) or the interphalangeal joints of the fingers.

Pivot joint

They are those joints where one of the bone surfaces is cylindrical, which serves as a pivot, and the other is concave, allowing one to rotate over the other. This type of joint allows movement only in the longitudinal axis.

An example is the joint between the radius and the ulna that allows pronosupination. Another example is the rotation of the head on the neck, due to the joint formed between the atlas and the odontoid process of the axis (1st and 2nd cervical vertebrae).

-Biaxial joints

These are joints that allow mobilization in two axes.

Arthrodia joint

Also called flat joints, their main characteristic is that the articular bone surfaces are flat, therefore, they only allow sliding movements.

A clear example is the joints of the carpal bones.

Saddle joint

In this joint there is a reciprocal fit between both joint surfaces.

An articular surface is convex-concave, which would be the saddle, which articulates with a concave-convex articular surface, which would be the rider.

Allows lateral and frontal movements. An example of these is the sternoclavicular joint.

Condyloid joint

Also called ellipsoids, as one of the bone surfaces culminates in a condyle that articulates with the ellipsoidal or oval surface of another bone.

One of the surfaces is concave and the other convex, but it cannot rotate as it is not a sphere. The surfaces are uneven.

It allows flexion, extension, adduction and abduction movements. An example of it would be the radiocarpal joint.

-Multiaxial joints

It allows joint movements in more than three axes. Flexion, extension, adduction, abduction, circumduction and internal and external rotation movements.

Ball joint or ball and socket

Similarly, one surface is concave and another is convex. In this case, the convex articular surface is in the shape of a ball or sphere, and the concave articular surface is in the shape of a receptacle or cup to house the sphere.

This allows free movement in almost any direction and is the characteristic joint that joins the appendicular skeleton (mobile skeleton) to the axial skeleton (base skeleton), through the glenohumeral and coxofemoral joints.

References

1. Anatomy & Physiology. Unit 4. Skeletal System. Module 11. Articulations: Diarthrosis. Page 87. Recovered from: oli.cmu.edu
2. Encyclopedia Britannica. Joint Skeleton. The Sinovial Fluid. Page 5. Recovered from: britannica.com
3. Matt Quinn. Structures of a synovial joint. December 22, 2017. Recovered from: teachmeanatomy.info
4. Up Health. Health System. What is the synovial membrane and what are its functions. Recovered from: arribasalud.com
5. Anatomy. Joints of the human body. Recovered from: tusintoma.com