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Brachydactyly (BD) refers to shortening of the fingers or toes due to underdevelopment of the bones in the hands or feet.
The word brachydactyly comes from the Greek terms brachy, meaning "short," and daktylos, meaning "digit." This term is used to describe the hands and feet of people who have shortened digits (fingers or toes). The digits themselves may be shorter than normal, or they may appear small because of shortening of the other bones in the hands or feet. This shortening occurs when one or more of the hand or foot bones fail to develop or grow normally.
BD is usually isolated, meaning that it is not associated with any other medical problems. BD may occur along with other physical differences or health problems, often as part of a "syndrome."
BD occurs in a variety of patterns, depending upon which hand or foot bones are affected and how severely they are shortened. It is important to know some basic information about the bone structure of the hands and feet in order to understand the various patterns of BD. Beyond the wrist and ankle, each hand and foot contains 19 tube-shaped (tubular) bones in a specific arrangement. For purposes of orientation, the fingers and toes are numbered from one (thumb or great toe) to five (little finger or little toe). When a fist is made, the bones in the hand that extend from the wrist to the knuckles are called metacarpals. There are five metacarpals, one for the thumb (first metacarpal) and each finger. Each thumb and finger contains several bones called phalanges. A single one of these bones is called a phalanx. The phalanges are arranged end to end and are separated by joints. The thumb has two phalanges and each finger has three phalanges. The phalanges within a particular finger are named according to their location. The phalanges closest to the metacarpals are called the "proximal" phalanges, those in the middle of the fingers are called the "middle" phalanges, and those at the ends of the fingers are called the "distal" or "terminal" phalanges. The thumbs have only proximal and distal phalanges.
The foot bones are very similar to the hand bones. Like the metacarpals, there are five metatarsal bones that extend from the ankle to each of the toes. The bones in the toes are also called phalanges. There are two phalanges in the great toe and three phalanges in each of the other toes.
BD can involve any of the phalanges, metacarpals, and metatarsals in many different combinations. The shortening of these bones may range from mild to severe. Sometimes certain bones are completely absent. Shortening of the bones may occur in one, several, or all of the digits. For a particular finger or toe, the entire digit may be short or only a particular phalanx may be underdeveloped. When BD involves the distal phalanges, the fingernails or toenails may be small or absent. A digit may also be of normal length but appear short due to shortening of its corresponding metacarpal or metatarsal bone. Reduced length of a metacarpal bone is often easiest to appreciate when the hand is held in a fist.
BD can also occur with other abnormalities of the hands and feet. When a phalanx is abnormally shaped, the finger or toe may be bent to one side (clinodactyly). Sometimes the digits have webbing between them (syndactyly). The phalanges may also be fused together at their ends (symphalangism). This makes it difficult to bend a digit at the joint where the phalanges are fused.
BD frequently occurs in characteristic patterns that can be inherited through families. These patterns are classified as particular types of BD, depending upon which bones and which digits of the hands and/or feet are shortened. There are several classification systems used to describe these different types of BD. The system that is used most frequently was developed by Dr. Julia Bell in 1951 and is called the "Bell Classification."
There are five main types of BD in the Bell Classification, which are designated types A through E. Their major features are as follows:
Author Info: David B. Everman MD, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Genetic Disorders Part I, 2002This feature is for informational purposes only and should not be used to replace the care and information received from your healthcare provider. Please consult a healthcare professional with any health concerns you may have.
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