Synonyms
Joint head, socket, joint mobility, Medical: Articulatio
Types of joints
Joints are divided into real joints (diarthroses) and fake joints (synarthroses). The real joints are separated from each other by a joint gap. If the joint space is missing and is filled with filling tissue, it is called a fake joint.
In the case of the fake joints, a gap is formed between the
- Banding (syndesmosis),
- Cartilaginous (synchondroses) and
- (synostoses) are differentiated.
Fake joints (synarthroses) usually allow little movement, although this depends on the type of filling tissue. Ligamentous joints are stressed in tension and cartilaginous joints in compression. Fake bony joints are only prevented from ossification (synostosis) by constant movement.
- In banded fake joints (syndesmosis), two bones are connected by tight collagen-fibrous connective tissue, rarely also by elastic connective tissue. These include the interbone membranes between the forearm and lower leg bones (Membranae interossea antebrachii et cruris), the ligamentous apparatus of the distal tibial fibula joint (syndesmosis tibiofibularis) and the ligamentous connections of the spinal column. The connective tissue membranes between the skull bones of a newborn (fontanelles) are also considered syndesmoses.
- In cartilaginous fake joints (synchondroses), the intermediate tissue consists of joint cartilage (hyaline cartilage).
These include the connection between the bony diaphysis and the epiphysis of a young tubular bone, the former connections between the bony parts of the hip bone and the rib cartilage between the ribs and the sternum. The intervertebral disc and the pubic symphysis are also included.
- In the bony fake joints, individual bones are connected secondarily by bone mass. These include the ossified sacrum (Os sacrum), the hip bone (Os pelvis) and also the ossified epiphyseal joints of the long bones in adults.
Real joints
All true joints consist of two bones whose joint surfaces (Facies articularis) are covered with hyaline articular cartilage. This layer differs in thickness between the individual joints and depends on the mechanical load. Hyaline articular cartilage is usually bluish milky.
Due to the absence of the cartilage skin (perichondrium), it has a reduced ability to regenerate and is furthermore only nourished by diffusion and convection via the synovial fluid. In the process, the cartilage becomes thinner at stressed areas through loading and unloading, and when relieved, it absorbs the synovial fluid like a sponge. Within the hyaline joint cartilage, four zones are distinguished in the direction of the bone.
The joint space or joint cavity is located between the two joint partners. The articular cavity is the part within the joint capsule where the two joint partners no longer have direct contact with each other. The shape of the joint cavity changes with the movement of the joint.
It is filled with synovial fluid, which is responsible for feeding the joint cartilage and absorbing mechanical stress. The joint is surrounded by the joint capsule. This membrane consists of two parts.
The membrana fibrosa consists of taut collagen-fibrous connective tissue, which grows in the periosteum of the respective bones involved in the joint. In numerous joints, the Membrana fibrosa is reinforced by internal ligament-like structures (Ligg. capsularia).
They are responsible for the stability and guidance of the joints.
- Zone 1 is the tangential fiber zone . Its main purpose is to reduce shear and friction forces.
- The transition zone is zone 2,
- The Radial Zone is the 3rd zone that is considered the separation zone between the non-mineralized and mineralized cartilage.
- The 4th zone is the mineralization phase that forms the transition between bone and cartilage.
- The Membrana fibrosa and the
- Membrana synovialis.