The phalanges are among the bony structures of the upper extremities of the human musculoskeletal system. All fingers, with the exception of the thumb, each consist of three individual bony members (phalanges) that are connected by joints.
What is a phalanx?
The hand is the functionally highly complex grasping apparatus of humans. It is roughly composed of the carpus, the metacarpus, and the fingers. The bony structures, i.e., the eight carpal bones, five metacarpal bones, and 14 phalanges, form the basic framework of the hand. From an anatomical point of view, the fingers connect distally to the metacarpal bones and practically mark the five end links of the hand. The finger bones of the five fingers, i.e. thumb, index finger, middle finger, ring finger and little finger, are each composed of several individual bone links, the so-called phalanges. The cohesion and mobility of the bones are based on the articulated connection of these individual phalanges, including the necessary muscles, tendons and ligaments.
Anatomy and structure
The fingers are composed of two limbs in the case of the thumb, and three limbs in all other fingers. Starting from the metacarpus distally, they are divided conceptually into proximal, middle, and distal phalanx, or first (proximal), second (medial), and third (distal) limbs. The designation is based on their proximity or distance from the trunk of the body. From a structural point of view, the phalanges, i.e. the bony phalanges, belong to the elongated tubular bones, which consist of two joint endings covered with cartilage and a shaft lying between them. Accordingly, they consist of a proximal base, a body, and a distal head. The first phalanx, the proximal phalanx, is generally the longest of the phalanges, although the length varies among the different fingers. The middle phalanx is also intermediate in length between distal and proximal phalanxes. The third phalanx is the shortest compared to the other phalanges. The individual phalanges are connected by small joints. Between the respective metacarpals and the associated proximal phalanges lie the metacarpophalangeal joints, colloquially known as the knuckles. The two rows of joints located between the proximal and middle phalanx and the middle and distal phalanx are called the finger middle joints and finger distal joints. They are also called proximal and distal interphalangeal joints.
Function and tasks
Thus, there are three joints on each of the index, middle, ring, and little fingers: the proximal joint and the two interphalangeal joints. Accordingly, the base joints of fingers 2 to 5 are functionally assigned to the so-called egg joints, which allow two directions of movement: Movements to the right and left side, i.e. abduction and adduction, as well as forward and backward movements, i.e. flexion and extension. The interphalangeal joints are hinge joints and therefore have one degree of freedom with flexion and extension. Compared to the other fingers, there are only two joints on the thumb. The base joint corresponds anatomically and functionally to a saddle joint. As with the egg yolk joint, movements in two directions, i.e. abduction and adduction as well as flexion and extension, can be performed. The main function of the saddle joint is the opposition function, i.e. the opposition of the thumb to the other fingers. The hand’s diverse, precise movement capabilities are based on the articulated, free-moving fingers. The targeted interaction between the thumb and the other fingers forms the basis for the various precision and power grips and thus for fine motor skills, i.e. for complex movement sequences. The fine motor mobility of the fingers is essential for functions such as grasping, touching, supporting or holding and enables them to handle and move objects in a controlled and coordinated manner. In addition, the fingers have a communicative importance, as they are the prerequisite for gestures, writing or even sign languages.
Diseases
Missing fingers or functionally limited fingers can severely hinder the ability to act in everyday life. Causes for the functional restrictions or limited mobility can be different disease patterns, such as rheumatism, gout and arthritis, but also fractures, tumors or genetic malformations.Polyarthrosis refers to degenerative wear and tear of several joints at the same time, especially the finger end and finger middle joints and the thumb saddle joint. The symptoms are usually due to premature wear or progressive destruction of the protective articular cartilage. A distinction is made between Heberden’s arthrosis, when the finger end joints are affected, and Bouchard’s arthrosis, when the finger middle joints are affected. Arthrosis of the thumb saddle joint is called rhizarthrosis. Symptomatically, joint stiffness, joint swelling or palpable protrusions as well as load-dependent pain and later also pain at rest appear. As the disease progresses, the patient usually also develops poor posture, which is associated with a change in the joint structure. The joints have increasingly limited mobility and may even stiffen in pathological positions. Similar symptoms are seen in inflammatory systemic diseases, such as rheumatoid arthritis, which also attacks and destroys the joints. The course is mostly chronic-progressive, but sometimes also with relapses and a very individual clinical picture. Congenital malformations include adactyly, in which all fingers are usually missing on one side, and polydactyly, with an excessive number of fingers. In clinodactyly, laterally bent finger limbs are present, caused by an isolated malformation or as a concomitant of genetic diseases. In the context of a fracture of the fingers, the proximal, middle or distal phalanx may be affected. The cause of the fracture is usually trauma, i.e., direct external force to the bone.
