Articular cartilage - Hyaline cartilage

A characteristic feature of cartilage is the chondrocytes (cartilage cells) which lie within the cartilage matrix (extracellular matrix ECM) and produce it (as with all connective tissue types). Depending on the type and amount of fibers in the ECM, three types of cartilage are distinguished: hyaline, elastic, and fibrocartilage.

In adults, all types of cartilage are mostly free of blood vessels, and their supply occurs through diffusion processes from the vascular cartilage skin (perichondrium) or, in the case of hyaline joint cartilage, directly through the synovial fluid produced by the joint capsule.

A specific feature common to all three types of cartilage is their high compressive elasticity, viscoelastic deformability (bend-stable), and resistance to shear forces.

The Hyaline Joint Cartilage

Function

Hyaline cartilage forms the covering layer of the very sensitive and well-innervated bones in all synovial joints. It absorbs and disperses shock and compression forces. By minimizing friction forces, it ensures the smooth movement of joints, significantly supported by synovial fluid.

Structure and Components

The morphological structure is arranged within four different zones:

• Zone I: Superficial cartilage zone (approx. 5%), main task: absorb shear forces and reduce friction forces

  It is the thinnest of the four zones; water bonding is the highest; covered with synovial fluid; collagen fibrils are thinnest and run parallel to the joint surface

• Zone II: Middle cartilage zone or transition zone (approx. 15%), main task: specifically unclear

  Collagen fibrils run obliquely to the surface, forming arches (arcades)

• Zone III: Deep or radial cartilage zone (approx. 40–60%), main task: absorption of compression forces

  Thickest layer; collagen fibrils run perpendicular to the joint surface; most active cartilage cells

• Zone IV: Calcified cartilage zone (approx. 30%), main task: connecting joint cartilage to the bone

  Relatively thin layer; boundary between deep and calcified cartilage zone formed by the tidemark; collagen fibrils pass through the tidemark into the calcified zone and connect the softer, more deformable cartilage with the hard, non-deformable joint cartilage; connect and stabilize the joint cartilage with the bone

The fundamental substance of hyaline cartilage can store a lot of water due to its negative charge (60–80%). The strong bonding of water and collagen fibers creates a homogeneous network that can effectively counteract compression loads, the primary task of hyaline joint cartilage.

The cartilage cells (chondrocytes) synthesize the necessary components of the ECM. However, synthesis activities significantly decrease after the growth phase is completed. They are also dependent on the quality and nutrient supply from the synovial fluid, the composition of the matrix, and the subchondral, well-vascularized bone. This presents a problem because cartilage has almost no blood vessels for nutrient supply. Nutrients mainly reach the cells through diffusion and osmosis. During pressure load, water moves not only within the cartilage but also penetrates the synovial fluid and subchondral bone. Upon subsequent release of pressure, the fluid flows back into the cartilage from the underlying bone, bringing necessary nutrients essential for maintaining healthy joint cartilage.

Alternating pressure and relief promote the transport and exchange of needed substances.

What Does Our Joint Cartilage Need?

A healthy joint cartilage requires constant synthesis and renewal of its fibrils and fundamental substance for maintenance. The turnover time of hyaluronic acid is only 2–4 days, but that of fibrils is significantly longer. Bear in mind, the turnover time of collagen fibers is 300 to 500 days, which is a long time. The most damaging thing for good function and high stability of our joint cartilage is chronic underuse, often a consequence of our affluent society's lifestyle.

What Effect Does Training Have on Cartilage Tissue?

Training has a great impact on the structure of the cartilage: the micellar order (micelles: aggregated molecular complexes, called aggregates) is improved after training. This means an increase in tensile strength. Cartilage tissue responds to training stimuli with reversible hypertrophy (the chondrocytes increase). Among other things, this reduces incongruity through an enlargement of contact areas, thereby improving compressive elasticity and shock absorption.

However, training and exercises not only improve the adaptability of the cartilage tissue: stronger skeletal muscles and better technique/coordination also relieve movement sequences under higher loads, sparing tissue and the body!

Arthrosis & Co.

Degenerative manifestations (wear and tear) are referred to as arthroses. Causes include, among other things, reduced changes in load and relief, increasing ossification of the cartilage tissue, and trauma.

Immobilization—due to various causes—leads in a very short time to strong demineralization with a pathophysiological change in our cartilage and bone tissue.

Therapy

The physiotherapists and osteopaths at BodyLab know the anatomical and physiological circumstances and are aware of the therapeutic options available for injuries or complaints/problems. We are pleased to advise and instruct you regarding training possibilities. If this is not yet (after operations or injuries) or no longer possible, the quality and function of the joint cartilage, as well as the entire joint as a functional unit, can be improved using passive joint techniques, sometimes under compression or traction, thereby reducing pain and complaints.

Here again, the motto holds: Life is movement!

If you need us, we are happy to be at your service!

Your BodyLab Team – Your Connective Tissue Specialists

Osteopathy and Physiotherapy | Rehabilitation and Training

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Learn more about our menisci in another blog.