Interesting Facts About Synovial Joints

Synovial joints allow a large range of motion and are surrounded by a joint capsule that is lined by the synovial membrane. The bones are separated from one another by a joint space that is filled with synovial fluid. 

Synovial joints  are also known as diarthroses or real joints. The bones are separated from one another by a gap filled with synovial fluid. They are also surrounded by the joint capsule, which holds the joint bones together. This enables frictionless movement.

Synovial joints: characteristics

Synovial joints: characteristics

Synovial joints  are surrounded by cartilage tissue that protects the surface of the ends of the bones. This makes it possible that the two bone elements, ie the joint socket and the joint head, do not have any direct contact. So when you see an X-ray, you can see the space between the bone elements.

In addition, synovial joints are characterized by a  joint capsule, which consists of an inner synovial skin (membrana synovialis) and an outer fiber layer (membrana fibrosa). 

Synovial joints: the synovial skin (membrana synovialis)

The synovial skin lines the joint cavity between cartilage tissue and bone. It is criss-crossed by many nerve fibers and produces the synovial fluid (synovial fluid),  which fills the joint space and makes it glide. At the same time, it also nourishes the cartilage tissue.

Synovial pouches also occur outside the joints, for example where there are muscles or between ligaments and bones, ligaments and joints or skin and bones. They take on the role of a shock absorber and reduce tissue friction and pressure when moving. The tendon sheaths that surround the tendons also reduce friction.

Synovial joints: the fiber layer (membrana fi brosa)

The outer capsule layer, also called the fiber layer, consists of dense collagen connective tissue. At the base of the joint capsule it merges into the periosteum and has the task of stabilizing the joint and allowing it to move freely.

Other structures characteristic of synovial joints

The following structures can also be found in synovial joints and perform important tasks:

  • Joint discs (Disci): This is fibrous cartilage tissue that normally divides the joint height into two separate chambers. Its job is to act as a shock absorber to buffer the pressure on the joint. They are also important for improving mobility and increasing the contact area between the joint parts.
  • Fat pads:  They are usually located between the synovial skin and the capsule and relieve the pressure. When the joint moves, the fatty tissue can also move.

Synovial joints: different types

Synovial joints: different types
  1. Flat joint (planar joint): It has two flat joint surfaces that can slide against each other. An example of this is the shoulder joint. 
  2. Hinge joint: This shape variant enables movement around a transverse axis. In this way you can bend and stretch your elbow, for example.
  3. Rotary joint:  This consists of a pin in a short joint socket and enables various rotational movements.
  4. Rotary hinge joint:  This enables not only bending and stretching, but also slight rotation when bent. An example of this is the knee joint.
  5. Biaxial egg joint:  This joint with an elliptical joint surface enables extension and flexion as well as adduction and abduction. The wrist, for example, belongs in this category.
  6. Saddle joint:  Here the joint surfaces interlock in a saddle shape. This enables extension, flexion, adduction and abduction. An example is the base joint of the thumb.
  7. Ball joint:  This allows different movements: flexion and extension, adduction and abduction as well as rotation (back and forth). The hip and shoulder joint can be mentioned as an example.


The joints enable us to move our skeleton in different ways:  We can perform a wide variety of activities and move forward through flexion and extension, adduction and abduction, and rotational movements.

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