Proximal Phalanx

What Does the Distal Phalangeal Bone Refer to

Referring to the tubular, elongated bones [11] situated in the lowermost row of the phalanges or finger bones [1], it can be indicated as a distal phalangeal bone (plural: phalanges). Each distal phalangeal bone consists of a head, a body/shaft, and a base.

Where are the Distal Phalangeal Bones Positioned

Designated by the name, they are located in the lowest row of the phalanges, being the closest to the metacarpals in the human hand [2].

Distal Phalangeal Bone

What is the Quantity of Distal Phalangeal Bones in the Hand

There exists a single distal phalangeal bone in each finger (including the thumb), leading to the presence of five distal phalangeal bones in each hand, making the total count ten in both hands. These are sometimes specifically mentioned as the first (thumb), second (index finger), third (middle finger), fourth (ring finger), and fifth (little finger) distal phalangeal bone.

Growth and Ossification

The ossification center for its body or shaft starts to form around the 8th-9th week of fetal development, while the second center, for the base, ossifies around the age of 3-4 years [3]. The distal phalangeal bones are the first among all the phalanges to begin the process of developing the base.

X-Ray Image of Distal Phalangeal Bones of Hand

Structure of the Distal Phalangeal Bones

Surfaces and Joints of the Distal Phalangeal Bone

Metacarpophalangeal (MCP) Joint (between distal phalangeal bones and metacarpal bones): The bottom end or base of these bones has an oval transverse articular facet for the head of the corresponding metacarpal [1]:

1. Distal phalangeal bone of the thumb articulates with the first metacarpal
2. Distal phalangeal bone of the index finger articulates with the second metacarpal
3. Distal phalangeal bone of the middle finger articulates with the third metacarpal
4. Distal phalangeal bone of the ring finger articulates with the fourth metacarpal
5. Distal phalangeal bone of the little finger articulates with the fifth metacarpal

The two creases on the upper palmar side of the finger, descending from the fingertips, are the MCP joints.

Proximal Interphalangeal (PIP) Joint: On the bottom end, or head of a distal phalangeal bone, there is another articular surface for the base of the middle phalanges [1]. However, the thumb is an exception, as it lacks a middle phalanx, therefore the head of the distal phalangeal bone directly articulates with the distal phalangeal bone [4]. On the palmar side of the hand, the crease in the base of each finger (right where the fingers are connected to the palm) represents the PIP joint.

Locations for Muscular Attachments: Their elongated shafts are relatively flat on the palmar side, but are convex dorsally and transversally. Moreover, the medial and lateral borders have distinct sharp edges. This distinct feature enables the fibrous tendon sheaths of the flexor muscles to attach to the distal phalangeal bones [1].

Blood Supply

Branches stemming from the superficial palmar arch and deep palmar arch are the main blood supply sources in this area [5].

Functions of the Distal Phalangeal Bones

Being the primary row of finger bones, the distal phalangeal bones significantly contribute to connecting the upper parts of the fingers with the palm, enabling us to use our fingers for almost all daily activities. The distal metacarpophalangeal joints are a pivotal part of the knuckles in human hands.

Common Injuries and Related Conditions

Distal Phalangeal Bone Fracture: Distal phalangeal bones are among the most frequently fractured hand bones, and are more prone to injury than the middle phalanges [6]. Furthermore, treating these fractures can be quite challenging due to the presence of the two important joints (MCP and PIP) nearby, along with the passing of vital long tendons [7]. The PIP joints are especially susceptible to injuries. Treatment may involve casting, splints, pain medications, and surgical intervention (in severe cases) [8].

Dislocation of the Distal Phalangeal Bone: The dorsal side of the proximal interphalangeal joint is the most commonly dislocated site in the finger. These can occur due to accidents and any other activity, but are commonly caused by sports injuries. Treatment usually involves splints and medications [9].

Arthritis of the Distal Phalangeal Bone Joints: The MCP joints are primarily affected by arthritis among the two distal phalangeal bone joints, with the index finger and thumb MCP joints experiencing more stress due to activities like pinching. Similar to most other forms of degenerative arthritis, pain is a common symptom of MCP joint arthritis. Treatment typically includes anti-inflammatory medicines, reduced hand activity, splinting, and heat treatment [10].

References

1. https://www.kenhub.com/en/library/anatomy/the-phalanges
2. https://www.healthline.com/human-body-maps/proximal-phalanges-hand
3. https://prohealthsys.com/central/anatomy/grays-anatomy/index-10/index-10-2/index-10-2/ossificationhand/
4. http://www.innerbody.com/image/skel13.html
5. https://www.orthobullets.com/hand/6007/blood-supply-to-hand
6. https://emedicine.medscape.com/article/98322-overview?pa=7exyehU4yVG%2F47L3ieT6XsvQE7ChQbEBG3qgQ7ajFu33cQe26eNMRpaWoWRsYPCk56MI7dGTgNawPfsOtJla9Q%3D%3D
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3360189/
8. https://www.hand.theclinics.com/article/S0749-0712(13)00061-9/pdf
9. https://www.aafp.org/afp/2012/0415/p805.html
10. http://www.assh.org/handcare/hand-arm-conditions/MP-Joint-Arthritis
11. http://library.open.oregonstate.edu/aandp/chapter/6-2-bone-classification/