A synovial joint is characterized by a fluid-filled joint cavity that is enclosed within a fibrous capsule.

In addition to being the most common type of joint on earth, it contains a number of structures not found in cartilaginous or fibrous joints.

A synovial joint's anatomy will be discussed in this article - its capsule, its neurovascular structures, and its clinical correlations.


Key Structures of a Synovial Joint

A synovial joint is composed of three main constituent parts: (i) the articular capsule, (ii) the articular cartilage, and (iii) synovial fluid.

Articular Capsule

As the articulating bones are connected by their periosteum, the articular capsule surrounds the joint.

The two layers are:

Outer fibrous layer(Inner) Synovium
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A synovial joint has the following basic structures.


Articular Cartilage

As bones move in a synovial joint, hyaline cartilage covers the surfaces directly in contact with each other.

During joint movement, articular cartilage plays two main roles: (i) reducing friction; and (ii) absorbing shocks.

Synovial Fluid

During synovial joint motion, synovial fluid is released from the joint cavity.It has three main functions:

Avascular cartilage is dependent on passive diffusion of nutrients from the synovial fluid.


Accessory Structures of a Synovial Joint

Accessory Ligaments

A joint capsule or separate ligament is an accessory ligament.

It is composed of bundles of dense regular connective tissue that resist strain well.As a result, extreme movements won't damage the joint.


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FIGURE 2 - The external ligaments of the hip joint; ileofemoral, pubofemoral, and ischiofemoral ligaments.


Bursae

Synovial bursas, lined with synovial membrane and filled with synovial fluid, are small sacs.

Bursae are located at the main points of friction in joints.Joints can move freely, yet friction-induced degeneration of the articular surfaces is prevented.


Innervation

Unlike synovial joints, articular nerves supply synovial joints.

Anatomical nerves transmit afferent impulses, including proprioceptive (joint position) and nociceptive (pain) sensations


Vasculature

.Joint capsule articular arteries are mostly located in synovial membrane.

There is a tendency for the articular arterial supply to have frequent anastomoses (communications) so as to ensure a blood supply to and across the joint regardless of its location.A blood vessel usually travels above and below a joint, curving around both sides of it and interconnecting through smaller vessels.

They are also found within the synovial membrane along with the articular arteries.


Clinical Relevance: Osteoarthritis

The most common form of joint inflammation (arthritis) is osteoarthritis.The condition occurs from the wear and tear on articular cartilage over many years, along with erosion of underlying articular surfaces of bones.

It occurs irreversibly and is degenerative.

This wear and tear can cause joint pain, stiffness, and discomfort as a result of repeated friction.Hips and knees, which support the full body weight, tend to be affected.