Phalanges (Finger Bones)

Definition: What are the Finger Phalanges (Digit Bones)

The cylindrical bones shaping the fingers and thumbs in human hands are referred to as digital bones (singular term: digitus) [1]. These are commonly known as finger or manual bones [2].

This article is focused solely on the digit bones of the hands. For information about the toe bones, please refer to the article on the digit bones of the feet.

What Kind of Bones are the Finger Phalanges

The finger phalanges are categorized as lengthy bones [3, 4].

How Many Digit Bones are There in the Hand

Each finger has three digit bones, apart from the thumb which has only two digit bones [5]. Hence, there are a total of fourteen digit bones in each hand, which adds up to twenty-eight in both hands collectively.

Where are the Digital Bones Located

Situated within each digit, above the metacarpals, these form the terminal bones (located farthest from the center of the body) of the upper limbs in humans [6] You can feel the digit bones within your fingers and thumb, with each section of a finger comprising one digit bone.

Nomenclature of the Phalanges According to Location

Proximal Phalanges: Located at the proximal end, where they articulate with the metacarpals [6].

Middle Phalanges: Positioned in the middle, between the proximal phalanges and distal phalanges. The middle digit is absent in the human thumb, which only consists of a proximal and a distal digit bone [7].

Distal Phalanges: The most terminal of all the digit bones, located at the end of the digits in hand [8].

Digital Bones

Structure of a Digit Bone

Components of the Bone

Similar to the metacarpals, each digit bone can be segmented into three parts [9]:

• Base: The articular proximal end of each digit bone [1].
• Body/Shaft: The slender middle part between the head and base [8].
• Head: The distal end with or without articular surfaces (depending on the location of the digit bone) [10].

Articulations

Metacarpophalangeal Joint: The points of connection between the proximal end of the proximal digit bones and the rounded distal heads of their adjacent metacarpals. The metacarpophalangeal joints are examples of condyloid joints that allow the fingers a 360° motion at their base [7].

Proximal Interphalangeal Joint: The connections between the distal end of the proximal digit bones and the proximal end of the middle digit bones. There are only 4 proximal interphalangeal joints in each hand, as the thumb lacks a middle digit bone [1].

Distal Interphalangeal Joint: The articulations between the distal end of the middle digit bones and the proximal end of the distal digit bones. This is the only interphalangeal joint within the thumb [11].

Interphalangeal joints form the knuckles of hand [12] and are a simple form of hinge joint in the human body [13].

X-Ray Image of Finger Digital Bones

Ligament Connections

Both the metacarpophalangeal joints and interphalangeal joints are linked by the robust fibrous bands of the volar plates (also referred to as the palmar ligaments). These are further connected at the metacarpophalangeal joint by the deep transverse metacarpal ligament [1].

Vascular Supply

The superficial palmar arch gives rise to a palmar digital artery to supply the ulnar side of the little finger. There are three common palmar digital arteries that run along the web spaces distally, dividing into proper palmar digital arteries to supply the fingers that are adjacent on either side.

The deep palmar arch gives rise to the princeps pollicis artery to supply the thumb and the radialis indicis artery to supply the radial aspect of the index finger. The dorsal metacarpal arteries have vascular connections with the dorsal, and superficial arch, as well as the common palmar digital arteries [9].

Growth and Ossification

Each digit bone has two ossification centers, the first for the body or shaft, and the second for the base or proximal extremity. The shaft starts to ossify quite early, around the eighth week of fetal growth.

Among the bases or proximal extremities, the base of the proximal row is the first to begin ossifying between 3 and 4 years of age, with those for the middle and distal rows following a year later.

The base and shaft unite with each other when one is eighteen to twenty years old [14].

Functions of the Digit Bones

The digit bones play a vital role in the movement and flexibility of digits, as well as the whole hand. These bones enable us to flex and fold the fingers and thumb to grab or pick something up, and engage in all daily activities like using a phone, typing, eating and so on. They also create insertion points for various muscles that assist with the flexion of the fingers and hand [15, 16].

Common Injuries and Associated Conditions

Fracture and dislocation: These are the most common forms of injury to the digit bones, occurring due to direct stress or a blow to the hand, often during an accident or because of overuse. The knuckles are most frequently hurt. A fractured digit bone may also be associated with an injury to the ligaments, tendons, fingernails, or some other soft tissues [17].

Digititis: A relatively rare condition characterized by infection, and inflammation of these bones, joints, or the surrounding soft tissues. Treatment may include medications, splints, injuries, and surgeries, depending on the severity of the condition [18].

Short, underdeveloped, or hypoplastic digit bones may occur due to some birth deformity or genetic abnormality and are often associated with some multisystem disorder or other serious conditions.

References

1. https://radiopaedia.org/articles/phalanges-of-the-hands
2. https://depts.washington.edu/pku/PDFs2/BoneDiagram.pdf
3. http://library.open.oregonstate.edu/aandp/chapter/6-2-bone-classification/
4. https://www.dartmouth.edu/~humananatomy/part_1/chapter_2.html
5. https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0023111/
6. https://www.kenhub.com/en/library/anatomy/the-phalanges
7. http://www.innerbody.com/image/skel13.html
8. http://anatomyzone.com/anatomy-feed/proximal-phalanx/
9. https://prohealthsys.com/central/anatomy/grays-anatomy/index-10/index-10-2/index-10-2/phalanges_of_the_hand/
10. https://www.earthslab.com/anatomy/bones-of-the-hand-carpals-metacarpals-and-phalanges/
11. http://www.mccc.edu/~behrensb/documents/TheHandbig.pdf?ref=binfind.com/web
12. https://www.medicinenet.com/image-collection/finger_anatomy_picture/picture.htm
13. http://www.innerbody.com/image_skel07/skel31.html
14. https://prohealthsys.com/central/anatomy/grays-anatomy/index-10/index-10-2/index-10-2/ossificationhand/
15. https://www.rightdiagnosis.com/organ/phalanges.htm
16. https://study.com/academy/lesson/phalanges-definition-function.html
17. https://www.emedicinehealth.com/finger_injuries/article_em.htm
18. https://www.rightdiagnosis.com/medical/phalangitis.htm