Among men and women, joint pain is the main reason for loss of mobility. Beyond the age of 70 the probability of being confronted with joint disorders is estimated at 80%.
The joints seem to be “rusty.” The discomfort is generally located in the neck, lower back, knees, hips, fingers and toes. The origin of these problems is wear on the cartilage.
Once established, it develops gradually, causing pain that is more and more frequent and of increasing intensity.
What is a joint?
A joint is made up of several parts: bone, cartilage, tendons, synovial membrane, capsule, muscles, synovial fluid and ligaments. The major component of a joint is the cartilage. This is what protects the ends of the bones and ensures their movements, while absorbing shocks. It is composed mainly of water (70%), collagen, proteoglycans (glucosamine and chondroitin) and cells specialized in the synthesis of the constituent elements of cartilage, called chondrocytes.
Collagen [ 1 ] and hyaluronic acid [ 2 ] form a mesh network to support the proteoglycans [ 3 ] 1. This structure is impregnated with synovial fluid like “a real sponge,” to ensure the elasticity and compression of the joints. Chondrocytes [ 4 ], are specialized cells that continually ensure the renewal of cartilage to fight against aging.
Integral parts of the skeleton, joints can be compared to the “hinges” between two adjoining bones. These “hinges” are essential for carrying out movements.
Composition of a joint
Joints are composed of a number of more or less fragile elements:
The joint capsule [ A ]
The joint capsule is a fibrous and elastic casing that surrounds a joint. Along with the ligaments, the joint capsule contributes to the maintenance and stability of the joint.
Synovial fluid [ B ]
Synovial fluid (or synovia) is secreted by the synovial membrane. It lubricates and nourishes the cartilage. It contains water, minerals, proteins and hyaluronic acid, which gives it its viscous consistency in particular.
Synovial membrane [ C ]
The synovial membrane lines the inside of the joint capsule. It is a casing that secretes synovial fluid. It has mechanical functions but also a role in defending against external aggressions.
Ligaments [ D ]
A ligament connects two bones in a joint to hold them together during movement or slippage. Thus it protects the joint from sprains and dislocations.
Joint cartilage [ E ]
Cartilage is collagen-based and is found in moving joints, allowing good flexibility of movement. It is elastic and resists the overloading and pressure produced by shocks, thus protecting the underlying bone surfaces. It is a sort of shock absorber.
Muscle tendons [ F ]
A tendon is a fibrous, elastic and resistant strip that connects bone to muscle. The tendon and the muscle to which it is attached, form a dynamic unit that stabilizes the joint and allows movement.
1 Proteoglycans are proteins to which glycosaminoglycan (GAG) chains, the key elements in cartilage structure, are attached. Proteoglycans have a negative charge, which gives them an affinity for water.