Phalanx bone

Scheme human hand bones-en.svg
The phalanges /fəˈlænz/ (singular: phalanx /ˈfælæŋks/) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones.

The phalanges are the bones that make up the fingers of the hand and the toes of the foot. There are 56 phalanges in the human body, with fourteen on each hand and foot. Three phalanges are present on each finger and toe, with the exception of the thumb and large toe, which possess only two. The middle and far phalanges of the fourth and fifth toes are often fused together (symphalangism).[1] The phalanges of the hand are commonly known as the finger bones. The phalanges of the foot differ from the hand in that they are often shorter and more compressed, especially in the proximal phalanges, those closest to the body.

A phalanx is named according to whether is are proximal, middle, or distal and its associated finger or toe. The proximal phalanges are those that are closest to the hand or foot. In the hand, the prominent, knobby ends of the phalanges are known as knuckles. The proximal phalanges join with the metacarpals of the hand or metatarsals of the foot at the metacarpophalangeal joint or metatarsophalangeal joint. The intermediate phalanx is not only intermediate in location, but usually also in size. The thumb and large toe do not possess a middle phalanx. The distal phalanges are the bones at the tips of the fingers or toes. The proximal, intermediate, and distal phalanges articulate with one another through interphalangeal articulations.[2]:708–711:708–711

Each phalanx consists of a central part, called the body, and two extremities.

In the foot, the proximal phalanges have a body that is compressed from side to side, convex above, and concave below. The base is concave, and the head presents a trochlear surface for articulation with the second phalanx. The middle are remarkably small and short, but rather broader than the proximal. The distal phalanges, as compared with the distal phalanges of the finger, are smaller and are flattened from above downward; each presents a broad base for articulation with the corresponding bone of the second row, and an expanded distal extremity for the support of the nail and end of the toe.

In the hand, the distal phalanges are flat on their palmar surface, small, and with a roughened, elevated surface of horseshoe form on the palmar surface, supporting the finger pulp.[3]:6b. 3. The Phalanges of the Hand The flat, wide expansions found at the tips of the distal phalanges are called apical tufts. They support the fingertip pads and nails.[4] The phalanx of the thumb has a pronounced insertion for the flexor pollicis longus (asymmetric towards the radial side), an ungual fossa, and a pair of unequal ungual spines (the ulnar being more prominent). This asymmetry is necessary to ensure that the thumb pulp is always facing the pulps of the other digits, an osteological configuration which provides the maximum contact surface with held objects.[5]

In the foot, the distal phalanges are flat on their dorsal surface. It is largest proximally and tapers to the distal end. The proximal part of the phalnx presents a broad base for articulation with the middle phalanx, and an expanded distal extremity for the support of the nail and end of the toe.[3]:6b. 3. The Phalanges of the Foot The phalanx ends in a crescent-shaped rough cap of bone epiphysis — the apical tuft (or ungual tuberosity/process) which covers a larger portion of the phalanx on the volar side than on the dorsal side. Two lateral ungual spines project proximally from the apical tuft. Near the base of the shaft are two lateral tubercles. Between these a V-shaped ridge extending proximally serves for the insertion of the flexor pollicis longus. Another ridge at the base serves for the insertion of the extensor aponeurosis.[6] The flexor insertion is sided by two fossae — the ungual fossa distally and the proximopalmar fossa proximally.

The number of phalanges in animals is often expressed as a "phalangeal formula" that indicates the numbers of phalanges in digits, beginning from the innermost medial or proximal. For example, humans have a 2-3-3-3-3 formula for the hand, meaning that the thumb has two phalanges, whilst the other fingers each have three.

This page was last edited on 5 April 2018, at 19:17 (UTC).
Reference: under CC BY-SA license.

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