Definition and Location
Phalanges are miniature long bones that form fingers of both hands and feet. There are 14 phalanges in each limb, 56 in total. Each finger has three phalanges: proximal, intermediate and distal. Thumbs of both hand and feet have only two phalanges because intermediate phalanges accreted with distal ones during the development.
The word “phalanx” or “phalanges” was originated from Greek language referring to military formations in which soldiers stand side by side in several rows.
Structure and Anatomy
Each phalanx has a body (shaft), proximal part (base) and a distal part (head). The Body of proximal and intermediate phalanges is convex on dorsal and flat on palmar side, and it tapers from above downward. Sides of the body are rough which gives attachment to the fibrous sheets of the flexor tendons.
The base of proximal phalange is a concave articular surface that create the metacarpophalangeal joint with the distal part of the metacarpal bone. Head of proximal phalanges has a cylinder-shaped articular surface. In the base of intermediate phalange, there is articular surface divided with one median ridge into two concave parts. This articulate surface fits with the cylindrically shaped distal portion of proximal phalanx creating the proximal interphalangeal joint.
Distal phalanges are farthest ones, and they are often called the terminal phalanges. The base of distal phalanges is the same articular surface as in intermediate ones. Their distal part is flat with horseshoe-shaped surface elevation on the palmar side. This elevation supports sensitive pulp of the finger. The main purpose of this part is supporting volar pad and nails on the dorsal surface of the finger.
Distal phalanges also develop apical tufts which are flat, spade-like mediolateral bone expansions. In thumb, distal phalanx has a pronounced place of insertion for the flexor pollicis longus tendon, an ungual fossa and ungual spines. Intermediate and distal phalange create the distal interphalangeal joint. Thumbs have only one interphalangeal joint.
In the foot, phalanges correspond in number and arrangement with those of the hand. The main difference between hand and foot phalanges is in size. Foot phalanges are smaller with a more narrow body that is laterally compressed. Foot phalanges also have a body, proximal and distal part. The body of proximal ones is compressed from side to side, convex above and concave below. In their proximal part, they have a concave articular surface for the metatarsophalangeal joint. In the distal part, there is a cylindrical articular surface with a shallow crease that create the interphalangeal joint with intermediate phalanges. Intermediate phalanges of the foot have a much smaller but broader body than proximal ones.
Distal phalanx of the foot is irregularly shaped, with a body flattened from above downward. Sometimes in the fifth finger, distal phalanx can be absent. Intermediate and distal phalanges of the foot also create interphalangeal joints.
Development
Hand phalanges have two centers of ossification; one is for the body and one for proximal part of the bone. Ossification process begins in the body, around the eighth week of fetal life. Ossification in the proximal part starts between the third and fourth years in proximal phalanges, and a year later in those of intermediate and distal ones. Those two centers become united between eighteenth and twentieth years. In distal phalanges ossification center appears closer to the head of the bone, instead of at the middle of the body as in other phalanges. Distal phalanges are the first ones to ossify of all the bones of the hand.
The phalanges of the foot are also ossified from two centers, one for the body and one for the proximal part. Ossification center appears about the tenth week in the body and between fourth and tenth years in proximal part. The joining of these centers happens around the eighteenth year.
Function of the Phalanges
The function of the phalanges is inseparable from that of fingers. Phalanges are bony basis of fingers and a place of insertions of ligaments and tendons. They create joints that together with corresponding muscles make finger flexion and extension possible.
Opposition and reposition of a thumb, basic and most important thumb and hand moves would not be possible without phalanges. Anatomical arrangement of distal phalanges is necessary for placing the thumb pulp facing the pulps of other fingers which enables maximum contact surface with the object that is held.
Distal phalanges of both hands and feet carry and shape nails and finger pads. Precision holding is completely dependent on distal phalanges.
Clinical Significance
From the clinical aspect, there are variations and disorders of phalanges that are very important to recognize.
Brachymesophalangia is the most common skeletal variation of phalanges. It affects around 20% of Japanese and Native American populations, and it usually affects middle phalanx. In this case, the middle phalanx is shortened and widened. Cases of aplasia and hypoplasia of middle phalanges have also been reported.
Brachyphalangia is shortening of the phalanges often accompanied with shortening of other hand bones. Brachyphalangia is usually part of syndromes (tricho-rhino-phalangeal syndrome), and it is rarely seen apart of them.
Symphalangia is a dysplastic disorder that results in an absent interphalangeal joint. On a clinical examination, this condition will manifest itself as the absence of skin folds over normal finger joint locations.
Syndactyly is a congenital disorder resulting in the fusion of phalanges of separate digits. It occurs bilaterally, most commonly between third and fourth finger, and it mainly affects males.
Axial deviations of the phalanges are congenital variations usually found with different syndromes. There are two variations of this condition: clinodactyly and camptodactyly. Clinodactyly is ulnar or radial deviation of the distal phalanx. Camptodactyly is characterized by a hereditary contracture of individual phalangeal joints.
Polyphalangia is another condition which is defined as the duplication of phalanges within the same finger.
Arachnodactyly is the development of asymmetrically long and slender digits. This condition is usually part of syndromes like Marfan’s syndrome, Ehlers Danlos, and homocystinuria.
Hitchhiker’s thumb is a variation of thumb that manifests as hyperextensibility of thumb that occurs in its interphalangeal joint.
The triphalangeal thumb is an occurrence of all three phalanges in the thumb, and it can happen as a variation or as a part of some syndromes.
Hypoplastic thumb is a condition in which the osseous structures are hypoplastic, the thumb is shortened and malpositioned, and there is often a deficiency of extrinsic and intrinsic muscles. This anomaly is often associated with Holt Oram syndrome, Fanconi syndrome, Cornelia de Lange syndrome, and diastrophic dwarfism.
