Fragility of the joints. This is a very annoying problem in everyday life and the inconveniences it causes are usually long-lasting.
The structure of joints and their function as natural shock absorbers. Within a joint, cartilage is a substance separating two bone ends and allowing the movement and sliding of these two bones against each other. The property of cartilage is to mechanically absorb and distribute often large loads, while ensuring that the joint parts glide together with very little friction. Think of the impact of the thousands of steps we take every day when walking! Normal articular cartilage is white, shiny and slightly translucent. This non-innervated and non-vascularised tissue is made up of a highly hydrated gel.
This high water content contributes to the mechanical properties of damping and resistance to stretching and compression forces.
The joint is a closed cavity bounded by a capsule to which the synovial membrane, an innervated and vascularised structure, adheres. The synovial membrane produces the synovial fluid (or joint fluid). The viscous consistency of the synovial fluid, rich in hyaluronic acid, gives it a role in lubricating the joint during movement.
1. Collagen fibres :
The collagen fibres are wound into strong triple helices. These fibres form the framework of the cartilage (like the beams of a building)
2. Proteoglycans :
These are long chains, the elementary medallion of which is the glucosamine molecule.
Healthy cartilage is physiologically rich in glucosamine, the basic molecule of many proteoglycans involved in water uptake.
3. Hyaluronic acid :
The "joint lubricant" is a very long molecule made up of thousands of individual glucosamine units. These different types of molecules are attached to each other like a "fisherman's net". The high density of this molecular mesh ensures that the mechanical properties of the cartilage are maintained.
4. Chondrocytes :
They participate in the formation of cartilage by synthesising collagen and proteoglycans.
Articular cartilage is a living tissue that is constantly renewed.
Its cells, the chondrocytes, ensure the destruction of old constituents (chondrolysis) and the elaboration of new constituents (chondroformation).
This primordial regulation is in a fragile balance.
1. Insufficient renewal of basic joint constituents
- insufficient renewal of proteoglycans (long chains of glucosamine)
- Insufficient renewal of "hyaluronic acid" (lubricating role of the joint, based on glucosamine).
2. Overproduction of "metalloproteases", enzymes responsible for the degradation of joint constituents (symbolised here by scissors!)
3. Excessive cartilage degradation: local areas of erosion
4. Triggering of the inflammatory joint component
The debris of degraded constituents leaking into the inter-articular cavity recruits the inflammatory process.
The production of inflammatory signals (IL,TNF-α,COX-2 / Prostaglandins) is at the origin of painful sensations. These signals drive a vicious circle of increased degradation of cartilage constituents.
The cascade of signals controls a vicious circle of increased degradation of cartilage constituents.
