Latin junctura synovialis FMA 7501 | TA A03.0.00.020 | |
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A synovial joint, also known as diarthrosis, joins bones with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer boundary of a synovial cavity, and surrounds the bones' articulating surfaces. The synovial cavity/joint is filled with synovial fluid. The joint capsule is made up of an outer layer, the articular capsule, which keeps the bones together structurally, and an inner layer, the synovial membrane, which seals in the synovial fluid.
Contents
They are the most common and most movable type of joint in the body of a mammal. As with most other joints, synovial joints achieve movement at the point of contact of the articulating bones.
Structure
Synovial joints contain the following structures:
Many, but not all, synovial joints also contain additional structures:
The bone surrounding the joint on the proximal side is sometimes called the plafond, especially in the talocrural joint. A damage to this occurs in a Gosselin fracture.
Blood supply
The blood supply of a synovial joint is derived from the arteries sharing in the anastomosis around the joint.
Types
There are six types of synovial joints. Some are relatively immobile, but are more stable. Others have multiple degrees of freedom, but at the expense of greater risk of injury. In ascending order of mobility, they are:
Function
The movements possible with synovial joints are:
Clinical significance
The joint space equals the distance between the involved bones of the joint. A joint space narrowing is a sign of either (or both) osteoarthritis and inflammatory degeneration. The normal joint space is at least 2 mm in the hip (at the superior acetabulum), at least 3 mm in the knee, and 4-5 mm in the shoulder joint. Joint space narrowing is therefore a component of several radiographic classifications of osteoarthritis.