Synonym
Articulatio carpometacarpalis (lat. ), carpometacarpal joint
Definition thumb saddle joint
The thumb saddle joint is located in the area of the wrist, it is largely responsible for the flexible mobility of the thumb and as one of the most stressed joints is often affected by degenerative processes.
Structure
The thumb saddle joint is formed by the large quadrilateral bone (Os trapezium), which belongs to the carpal bones, and by the base of the first metacarpal bone (Os metacarpale I). The joint is therefore not located where the thumb seems to start when looking from the outside, but further down, namely in the area of the wrist. The reason for the name is the saddle-like shape of the Os trapezium in the area of the joint. The capsule surrounding the thumb saddle joint is relatively flaccid, while ligaments ensure that movements are guided safely. Nevertheless, the joint is much less strained by ligaments than the joints between the carpal and metacarpal bones of the other fingers, which explains its large range of motion.
Function of the thumb saddle joint
The thumb saddle joint is mainly responsible for the pronounced mobility of the human thumb. Among other things, this is possible due to the shape of the joint surfaces. These enable different levels of movement: Flexion (flexion) and extension (extension), abduction (spreading) and adduction (approaching) and rotational movements.
An essential movement for humans is the opposition of the thumb. This describes the movement that is performed when the thumb touches the fingertips of the other fingers of the same hand. This movement also takes place in the thumb saddle joint, it is a combination of several of the above mentioned movements. The opposition is essential for fine motor grasping, for example in the form of the tweezer grip.
Clinical significance
The thumb saddle joint is exposed to a variety of stresses and strains and is therefore often the site of degenerative (wear-related) changes. The arthrosis of the thumb saddle joint, the so-called thumb saddle joint arthrosis (rhizarthrosis), is a widespread clinical picture that leads to pain, swelling and restricted movement in the thumb.
Pain in the thumb saddle joint
Pain in the area of the thumb saddle joint can be very unpleasant, since almost every movement of the hand is also accompanied by movement in the thumb saddle joint. Consequently, every movement is perceived as painful. The pain can have a different character.
They can be dull and boring or bright and stabbing. Under certain circumstances the pain extends from the thumb to the forearm. However, it can also manifest itself as pain at points or pressure pain at joint level.
At first, the pain usually occurs only during movement, but if the pain is caused by a progressive disease, the thumb saddle joint often hurts at rest. It is not uncommon for the painful restriction of movement to be accompanied by other symptoms, such as swelling, redness or overheating in the joint area. Everyday movements are often significantly impaired by these complaints, as the thumb plays a major role in all gripping movements of the hand.
The thumb saddle joint allows the thumb to be brought close to the little finger (opposition). This movement is decisive for the human ability to grasp. Pain in the thumb saddle joint therefore interferes with everyday movements, for example when unscrewing or screwing on a screw cap, holding on to heavy objects, squeezing an object with the hand (typically garden shears) or delicate tasks (manual work, playing the piano, picking up small objects, etc.).
The pain in the thumb saddle joint area can have different causes. If arthrosis of the thumb saddle joint is the cause, the pain is caused by the wear and tear of the cartilaginous joint surfaces. The adjacent bones rub directly against each other with every movement and thus cause pain. Over time, smaller cartilage and bone fragments can also recede and cause additional discomfort and inflammation in the joint. If the thumb saddle joint is not arthrotically changed, the cause of the complaints can also lie in a previous trauma (e.g. fall), in which the joint was squeezed/compressed or is broken.
