Greater Polygonal Leg: Structure, Function & Diseases

The greater polygon bone is one of the bones of the human hand. It is easily palpable when the back of the hand is raised. The polygon bone has a trapezoidal appearance.

What is the great polygon bone?

The greater polygon bone is part of the human skeletal system. It is a bone in the back of the hand. It is also called the Os trapezium or Os carpale primum. Once the back of the hand is pulled upward, the great polygonal bone can be seen and felt under the skin. Due to its trapezoidal shape, it can be easily felt below the thumb. Together with the metacarpal bone, the great polygonal bone forms the thumb saddle joint. Rhizarthrosis, also described as thumb saddle joint arthritis, originates in the thumb saddle joint. In this condition, the visual swelling of the ball of the thumb is very noticeable. The polygonal bone is often affected in hand fractures. It houses several muscles that are located within the palm of the hand. The thumb is subjected to a variety of stresses throughout life. It is used in countless everyday procedures, usually quite unconsciously. As a result, bones of the thumb as well as the ball of the thumb are subjected to a great deal of stress throughout life. If it is defective, simple procedures such as grasping as well as holding onto objects or grasping the door handle can only be done with difficulty.

Anatomy and structure

The human hand consists of a total of eight carpal bones. They include the navicular bone, the lunate bone, the triangular bone, the pea bone, the greater as well as the lesser polygonal bone, the capitate bone and the hook bone. The Os trapezium has a trapezoidal structure. The carpal bone is located thumbward on the radial side of the hand. It is located above the scaphoid bone, the os scaphoideum, and the lesser polygonal bone on the outer side of the hand. Beyond this, it is adjacent to the first metacarpal bone. Various muscles attach to the greater polygon bone. They include the abductor pollicis brevis muscle, also known as the little thumb abductor, the opponens pollicis muscle, and the flexor pollicis brevis muscle, known as the little thumb flexor. The greater polygonal bone has a hump, the tuberculum ossis trapezii. In its center is a groove called the sulcus musculi flexoris carpi radialis. The flexor carpi radialis muscle passes through it. Together with the Os metacarpale, the great polygonal bone forms the thumb saddle joint. This is referred to as the articulatio carpometacarpalis pollicis.

Function and tasks

The great polygonal bone acts as the originating point of several muscles of the hand. They all serve to provide mobility to the fingers and hand. Their respective pathways extend from the polygonal bone to the palm, through the individual fingers and into the fingertips. They enable the movement of the fingers and also the finger joints. The muscles of the thumb and fingers are very delicate. In addition, the muscle fibers of the thumb and the ball of the thumb are very powerful. The great polygonal bone, together with the metacarpal bone, has the function of forming the thumb saddle joint. This is surrounded by several ligaments. The ligaments stabilize the thumb saddle joint as it is subjected to a great deal of stress throughout life. The thumb saddle joint has a saddle-shaped appearance. This allows for rotational movements of the thumb in two axes. The movement structure of the joint is similar to that of a ball and socket joint. Everyday hand movements are made possible by the thumb and thumb joint. These include gripping, grasping or holding objects. The thumb is used for most hand movements, such as writing, feeding or brushing teeth. It is involved in almost all hand movements. The application of pressure by the hand is often performed with the ball of the hand or thumb. The reason for this is the enormous force that is present in the ball of the thumb.

Diseases

The thumb saddle joint, like other ball and socket joints, can be subject to wear and tear. Since this bone wear is irreparable, the damage can only be repaired by inserting a prosthesis. This is done in a surgical procedure with a joint that is modeled after the patient’s individual joint. The prosthesis is molded from stainless steel. The great polygonal bone is often involved in hand fractures or contusions.If injuries to the hand occur after an accident or a fall, X-rays should be taken to check whether the fracture is a straight one or whether there has been chipping of the bone. In the case of a fracture, the hand is usually put in a cast for a few weeks. It must be spared during the healing process so that the fracture can regenerate. If splintering of the bone occurs, further surgical intervention may be required with the aim of removing the splinters. A common disease of the thumb saddle joint is rhizarthrosis. This disease, which is increasingly diagnosed in women, often results in sufferers being unable to perform everyday tasks. Opening a bottle, for example, is not possible for sufferers. Even light objects can no longer be held and severe pain is present in the hand. There is a narrowing of the joint space in this disease. Treatment options include surgical or non-surgical measures. Once the disease is not very advanced, an injection of hyaluronic acid into the joint may already be effective. Muscle inflammation or a torn capsule near the ball of the thumb lead to impaired mobility of the thumb. They are usually experienced as painful.