Osteoarthritis is chronic wear of the joint cartilage accompanied by an imbalance between the production and destruction of bone cells. Osteoarthritis is a complex phenomenon involving physical and metabolic factors. In a joint, the cartilage covers the end of the bone and helps to ensure joint mobility with minimum friction. The cells are replaced at the same rate as they are destroyed. The full mobility of the joint is thus preserved. When the cells are renewed more slowly than they are destroyed, and/or if physical stresses (impacts, repeated friction) are too severe, the metabolic balance of the joint is disrupted. Cartilage wear then develops, starting with cracks, which then gradually worsen to form genuine holes (ulcerations). The bone can be left completely bare in places and the bone surfaces are then in direct contact with one another.
The phenomenon tends to be a self-perpetuating process. It culminates in painful restriction of joint mobility, with the joint becoming increasingly stiff. Arthritic pain is triggered by use of the joint and relieved by rest. However, certain inflammatory forms are also painful at night. Osteoarthritis can affect any joint in the body, but it is most common in the knees, hands, spine and hips. It is promoted by physical factors, heredity, age or obesity.
Basal thumb arthritis is chronic wear of the cartilage in the joint at the base of the thumb. It is localised in the trapeziometacarpal joint. It is most common in women over the age of 50. It usually begins with the dominant hand (for example the right hand in a right-handed person) but both hands may also be affected. It progresses by flare-ups, gradually leading to stiffening of the thumb and the development of an "adductus" or, more rarely, "Z" deformity of the thumb. It gradually becomes impossible to grip an object between the thumb and the index or other fingers. Genetic factors, the menopause or the repetition of certain movements appear to promote its development. It is also called "trapeziometacarpal arthritis".
An orthopaedic solution meets two objectives: it reduces pain and prevents loss of joint range of motion (thumb opening). Night-time immobilisation using a standard or made-to-measure heat-moulded wrist and thumb brace reduces muscle tension and alleviates pain. If the pain is not relieved, it tends to gradually worsen, reflecting an acceleration in the inflammatory phenomenon causing the joint deterioration. At night, the brace holds the thumb in an open position maintaining the range of joint motion (prevention of adductus deformity of the thumb). This preserves normal use of the thumb during the day. In the event of more advanced damage, functional braces leaving the wrist free may be worn during the day.
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