Articular capsule

The joint capsule (Latin: Capsula articular ) is a connective tissue sheath around real joints. It surrounds the joint with fluid ( synovial fluid ) filled joint cavity.

  • 2.1 instabilities
  • 2.2 Irritation
  • 2.3 Inflammatory Diseases

Design and function

The capsule is divided into two layers:

  • Fibrous layer
  • Stratum synovial ( synovial membrane )

Membrana fibrosa

The outward-facing membrane fibrosa consists of taut collagenous connective tissue. She goes on in the periosteum ( periosteal ) at the insertion of the joint capsule. It determines the mechanical strength of the joint, and are characteristic for the joint ranges of motion freely.

In most joints, the membrana fibrosa is strip-shaped reinforced at specific points. These ribbon-like capsular ligaments ( ligaments capsularia ) serve to further stabilize the joint ends and provide as guiding or inhibiting bands that the mobility of the joint is restricted to certain directions of movement or degrees. If loose connective tissue separates the ligaments of the membrana fibrosa, it is called extracapsular ligaments.

In the membrana fibrosa are different receptors: Ruffini 's corpuscles, Pacinian corpuscles and Golgi tendon organs. Register the position of the joint (called proprioceptive perception). In addition, the membrana fibrosa has free nerve endings that receive as nociceptors noxious stimuli. You are responsible for ensuring that capsule strains and tears hurt extremely strong.

Synovial membrane

The synovial membrane forming the inner lining of the joint cavity. It consists of several layers of the so-called Synovialozyten. This layer is not epithelium - the typical cell junctions and a basement membrane lacking.

Composite joints, in which more than two bones are involved (eg, knee, wrist, ankle), have a common membrana fibrosa. Within the common external capsule more delineated, formed by the synovial membrane interior spaces can be. Here, then, the inner skin forms several separate part of joint cavities, which communicate either with one another or can be totally separated.

There are two types of synovial cells:

  • A- Synovialozyten: The A- Synovialozyten are macrophages and are derived from the monocytes of the blood. You are at the service of absorption and phagocytosis, to a lesser extent the synthesis of Synoviabestandteilen.
  • B- Synovialozyten: B- Synovialozyten similar to fibroblasts and form the majority of the synovium.

The interplay of production and absorption of synovial fluid normally causes the joint is cleaned by abrasion products. In osteoarthritis but comes into being as much of it that it overwhelmed this mechanism. A prosthesis used, also of metal abrasion or wear of the bone cement may accumulate in the A Synovialozyten and are then not removed from there.

Pathological changes in the joint capsule

Instabilities

In a sprain or dislocation, the ligaments, part of the joint capsule, hurt and often heals not so far that the joint is again afterwards sufficiently stable. Often this happens at the ankle joint, the metacarpophalangeal joint ( " skier's thumb " ) or at the knee. The poor, little precise guidance of the joint leads to uneven loading of the cartilage layer. An injury-related posttraumatic osteoarthritis is the result.

Irritations

Due to injury, surgery or inflammatory disease can cause swelling of the joint capsule. The swollen ligaments lose their flexibility, the joint loses its mobility more or less a.

Inflammatory diseases

An inflammation of the synovial membrane is called synovitis. In the PCP, the primary chronic polyarthritis, synovial cells change their function, be aggressive and overgrow the cartilage layer from the edges. The cartilage is then eaten literally by these cells.

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