The thumb (from the Latin pollex, -icis) is the first finger of the hand and the foot, it allows the movement of the clamp with the fingers, essential for gripping.

The thumb is the larger and shorter of the fingers of the hand [L1] and of the foot, for which it is also called the big toe.

Different from other fingers in its bone structure, the thumb is made up of:

• A metacarpal. The hand has five, they form the palm of the hand. They are numbered from I to V, the thumb being the first (I). It is articulated with the trapezius, a small carpal bone (palm of the hand). The bony heads of the metacarpals stand out when you clench your fist: these are the joints that are generally called joints.
• Two phalanges, one proximal (articulated with the metacarpal) and one distal. The other fingers have three (proximal, middle and distal).

On the fingers are inserted intrinsic muscles which are located in the hand and which allow their precise movements. We can distinguish the interosseous muscles, located between the metacarpals, which allow the fingers to be separated and brought together. The flexion and extension movements of the thumb are provided by the intrinsic (abductor brevis, adductor and flexor digitorum brevis) and extrinsic (extensor digitorum brevis long and short, in the forearm) muscles therein. insert by tendons. On the palmar face, under the thumb, there is a rounded area: this is the thenar eminence, which groups together certain muscles of the thumb. Its movements give it the characteristic of being opposed to other fingers in humans and primates: we speak of a grasping thumb.

The thumb is covered with skin and its tip is covered on its dorsal surface by a fingernail. Its sensitivity is provided by the median nerve, which also innervates the index finger, middle finger, and part of the ring finger.

By being opposable to other fingers in humans and primates, the thumb allows the pincer movement, essential for gripping, handling of objects and food function.

Fracture of the thumb: Joint fracture of the base of the first metacarpal, also called Bennett’s fracture, is a common fracture. It affects the trapeziometacarpal joint, the main joint of the thumb. They are generally the consequence of a voluntary or involuntary blow during a sports shock (combat sport) or of an accidental fall on the thumb. The joint is replaced during surgery.

Thumb sprain: this is the relaxation or rupture of one of the ligaments of the thumb following a trauma. The most frequent accident is the ski fall: the thumb is retained by the strap of the pole which pulls it in an outward movement. The medial lateral ligament is usually the most exposed. This ligament plays an important role in gripping gestures by stabilizing the thumb. In the event of a sprain, the joint therefore becomes unstable and the function of the thumb is impaired. The problem is resolved by immobilization or by surgery if the sprain is serious.

Panaris: infection which is located in two thirds of cases on the periphery or on the underside of the nail. However, it can also be located at the level of the pulp, on the side or on the back of a finger, or even on the palm of the hand. Most often, it is caused by a germ of the Staphylococcus aureus type, but it can also be streptococcus, enterococcus, etc.

Arthritis: Formerly called rheumatism, it literally refers to inflammation of the joints. There are two main forms:

• Osteoarthritis of the thumb or rhizarthrosis: Osteoarthritis is the most common form of arthritis. It is a chronic condition that manifests as persistent pain in the joints caused by abnormal wear and tear of the cartilage and the entire joint. Rhizarthrosis concerns the base of the thumb: it affects the joint between the trapezius and the first metacarpal. This pathology is very common, especially in women;
• Rheumatoid arthritis: an inflammatory disease of the joints that swell, become painful and are limited in their range of motion. Left untreated, these joints tend to gradually deform over time. The joints of the hands (and therefore that of the thumb), wrists and feet are often the first to be affected.

Regarding osteoarthritis, there are several ways that can reduce the risk of its occurrence. Practicing regular physical activity, for example, helps protect your joints. On the other hand, very few means are known to prevent rheumatoid arthritis.

Protecting your joints and fingers during manual activities or sports is beneficial. For gardening, for example, it is advisable to choose the right gloves. For board sports, hand and wrist protections are effective.

Clinical examination: carried out by the doctor, it includes the examination (general then focused on the symptoms that led the patient to consult) followed by the physical examination of the thumb, hand and wrist (skin, blood supply, bone structures, sensitivity and motor skills). This examination makes it possible to make the diagnosis or to confirm it.

Radiography: medical imaging technique that uses X-rays. This is the standard reference examination, the first mandatory step and sometimes sufficient to diagnose a fracture, for example. In the case of rhizarthrosis, it can be used to confirm the diagnosis and see the extent of joint destruction.

MRI (magnetic resonance imaging): medical examination for diagnostic purposes carried out using a large cylindrical device in which a magnetic field and radio waves are produced to generate very precise images, in 2D or 3D, of parts of the body or organs internal (here the hand and the thumb). The MRI is rather a complementary examination of the radiography.

Ultrasound: a medical imaging technique based on the use of ultrasound, inaudible sound waves, which make it possible to “visualize” the interior of the body. It is a standard exam when the metacarpal-phalanx junction of the thumb is affected. It has the advantage of easily studying the tendons.

Scanner: diagnostic imaging technique which consists of “scanning” a given region of the body in order to create cross-sectional images, thanks to the use of an X-ray beam. The term “scanner” is actually the name of the medical device, but it is commonly used to name the exam. We also speak of computed tomography or computed tomography. It is a complementary examination of the x-ray in case of doubt about the diagnosis and which allows, in the case of a fracture, to visualize the involvement of the articular surface.

Thumbing up is a way to express nod or something positive. In arenas, the thumbs up meant the gladiator’s life was spared. Nowadays, it also allows you to hitchhike.

The inch also designates a metric unit, used in particular in the United States and the United Kingdom. It is exactly one twelfth of a foot. Although they do not represent the same value in the two countries (25 mm in the United Kingdom against 25,4 mm in the United States), an industrial agreement has set the official value at 25,4 mm (6).