Synovial joints

Synovial joints

* Structure :

- The joint is enveloped by fibrous capsule.

- The capsule is thickened in some places forming ligaments.

- The capsule is lined with synovial membrane.

- The articular surface of the bone is covered by articular cartilage.

- The joint cavity contains synovial fluid.

- The joint cavity may contain other additional intracapsular structures like 

   inter-articular disc, labrum, meniscus or tendons of muscles.

* Classification :

( According to the number of axes around which movements occur )

1. Uni-axial joints ( one axis ) :
   1. Hinge joints : transverse axis > flexion and extension > elbow joint
   2. Pivot joints : vertical axis > rotation > radio-ulnar joint
2. Bi-axial joints ( two axes ) :
   1. Ellipsoid joints : flexion, extension, adduction and abduction > wrist joint 
   2. Saddle joints : flexion, extension, adduction, abduction and slight rotation > carpo-metacarpal joint of the thumb.
3. Multi-axial joints ( more than two axes ) :All types of movement are allowed > shoulder and hip joints.
4. Other types :
   1. Plane joints : the articular surface are flat > just gliding > intercarpal joints.
   2. Compound joints : more than one type in the same joint > tempro-mandibular joint.

* Illustrations :

Structure of synovial joints :

 

Inter-articular disc

Labrum

Meniscus

Hinge joint

Pivot joint

Ellipsoid joint

Saddle joint

Multi-axial joint

Plane joint

Compound joint