Middle Phalanx

What is the Central Phalanx

A central phalanx (plural: phalanges) is one of the elongated tubular bones present in the fingers [1, 2]. It may also be denoted as a medial phalanx or intermediate phalanx. Similar to the rest of the phalanges, each central phalanx consists of a head, body/shaft, and base.

What is the Location of the Central Phalanges

As indicated by its name, the central phalanges are situated in the middle tier of finger bones, positioned between the proximal and distal phalanges [3].

Middle Phalanx

How Many Central Phalanges are There in the Hand

Except for the thumb, each finger possesses one central phalanx, resulting in a total of four of these phalanges per hand, and eight altogether in both hands. The thumb contains only one proximal and one distal phalanx [4]. According to the associated finger, the four phalanges can be distinguished as the index finger, middle finger, ring finger, and the little finger central phalanx.

Development and Ossification

The primary ossification center for the body of the central phalanx appears early, around the 8th-9th week of fetal development. Additionally, a secondary center for the base begins to develop around 4-5 years of age. The ossification centers fuse as one reaches 18-20 years of age [5].

Central Phalanges of the Hand X-Ray Image

Structure of the Central Phalanges

Surfaces and Joints of a Central Phalanx

Proximal Interphalangeal (PIP) Joints (between the central and proximal phalanges in each finger [6]) — The base of each central phalanx features two concave facets, along with a smooth ridge dividing them, to articulate with the head of the proximal phalanx [7]. This joint is characterized by the second crease in each finger when descending from the fingertip or fingernail. However, the thumb lacks this joint, as it only consists of two phalanges [8].

Distal Interphalangeal (DIP) Joints (between the central and distal phalanges in each finger) — The central phalanges possess a pulley-shaped facet on their head for articulating with the base of the distal phalanx [7]. Similar to the PIP joints, the thumb does not have a DIP joint [6].

Muscular Attachments

Four flexor digitorum superficialis tendons, as well as the flexor sheath, attach to the central phalanges at their sides [8]. These aid in the flexion of the central phalanges at the PIP joints. Additionally, at the base of their dorsal aspect, these phalanges receive the extensor digitorum tendons [7], which assist in the extension and separation of the fingers [9].

Supply of Blood

The middle phalangeal area is supplied by branches from both the superficial palmar arch and deep palmar arch [10].

Functions of the Central Phalanges

Featuring two interphalangeal joints on each side, the central phalanges play a crucial role in enabling the fingers to bend at two points. This allows for the precise execution of all daily hand and finger movements [3]. Furthermore, it is essential for lateral grip, such as when holding something between your fingers (e.g. smoking a cigarette).

Common Injuries and Related Conditions

Fractures and Dislocations: Fractures and dislocations of the central phalanx are less frequent compared to those of the proximal phalanx [11]. These injuries most commonly result from sports-related incidents, although they can also occur as a result of other types of trauma or accidents.

Arthritis: The PIP and DIP joint arthritis are linked to this bone, with the index finger joints being more susceptible due to their involvement in almost all hand activities, particularly those requiring pinching [12]. Treatment options include splints, anti-inflammatory medication, limited hand movement, and in severe cases, surgical intervention.

Other conditions that commonly affect the DIP joint include jersey finger (a common sports injury), mallet finger (abnormality arising from damage to the extensor tendon responsible for extending the fingers), and mucous cysts (small painless fluid-filled sacs on the fingers) [12].

References

1. 1. https://www.kenhub.com/en/library/anatomy/the-phalanges
   2. http://library.open.oregonstate.edu/aandp/chapter/6-2-bone-classification/
   3. https://www.healthline.com/human-body-maps/middle-phalanges-hand
   4. http://teachmeanatomy.info/upper-limb/bones/bones-of-the-hand-carpals-metacarpals-and-phalanges/
   5. https://prohealthsys.com/central/anatomy/grays-anatomy/index-10/index-10-2/index-10-2/ossificationhand/
   6. https://radiopaedia.org/articles/phalanges-of-the-hands
   7. https://prohealthsys.com/central/anatomy/grays-anatomy/index-10/index-10-2/index-10-2/phalanges_of_the_hand/
   8. http://www.mccc.edu/~behrensb/documents/TheHandbig.pdf?ref=binfind.com/web
   9. https://www.healthline.com/human-body-maps/extensor-digitorum-muscle
   10. https://www.orthobullets.com/hand/6007/blood-supply-to-hand
   11. https://emedicine.medscape.com/article/98322-overview
   12. http://www.assh.org/handcare/Anatomy/Joints