A joint is an articulation, the place where two or more rigid structures unite. Joints occur in a variety of forms according to their function. Joints are classified into fibrous, cartilaginous and synovial.
At a synovial joint, the degree of movement that they allow is the most important feature that characterises them and this concerns the shape of articulation, the amount and location of cartilage, the capsule and ligaments, the synovial membrane and fluid, and the muscles that cross the joint.
Synovial fluid nourishes the articular cartilage and lubricates the joint surfaces. It is an essential component to release friction and smooth the movement.
Accessory ligaments occur very often to reinforce the articulation, providing an extra feature for stability. These are important in preventing any over movement and in guarding against sudden accidental stresses. They might be extrinsic or intrinsic.
The higher the axis of rotation at a joint, the higher the degrees of movement allowed. Movement is directly related with the stability of a joint: the less mobile, the more stable it is. A very mobile joint, as the glenohumeral joint, is very unstable, being easily dislocated.
Movement occurs due to muscle contraction. However, at a joint, movement is hugely dependent on the antagonistic effect of the muscle that opposes the one contracting. For example, flexion of the arm at the elbow joint is done by the contraction of brachialis and biceps brachii, but it is only possible if triceps is extended. The elongation of the muscles at the opposite site is crucial to allow movement of the primary muscles.
It is very important to look after the joints of the body. They can be easily injured through dislocation or subject to painful diseases, such as arthritis or bursitis.
Osteoarthritis, in particular, is the most common joint disorder in the world. It is more prevalent in women than men and usually develops after 50 years of age. It is characterized by inflammation of the joints, loss and damage of cartilage, and bone growth in the edges of the joint. Although astonishingly common, there is no cure available for osteoarthritis yet.
It is important to be aware that osteoarthritis and other types of arthritis may impact severely on the patient daily routine. Pain is constant, mobility may be very reduced and life-long drug treatment is often needed in order to manage the symptoms. Treatments involve physiotherapy, anti-inflammatory and analgesic drugs, and surgery, such as knee and hip replacements.
Patients tend to suffer in silence, take their drugs and await for warmer weather, but it improvements can be achieved through small changes in the routine. Obesity is commonly an underlying cause for arthritis, therefore friendly regular exercise and a balanced diet will most certainly help. Due to the chronic character of the disease, it is also advisable to keep the immune system as strong as possible to prevent a secondary disease, such as an infection.