Phalanges of the hand
The phalanges of the hand are the group of small bones that comprise the bony core of the digits (fingers) of the hand. Even though the phalanges are small in size, they are classified as long bones because of their structural characteristics; each phalanx consists of a shaft, distal head and a proximal base.
There are fourteen phalanges in each hand; each of the medial four digits has three phalanges (proximal, middle and distal), while the thumb has only two (proximal and distal). The phalanges are interconnected by interphalangeal joints and vascularized via the nutrient rami to phalanges, which stem from the palmar digital arteries.
The digits have a universal labeling system using the anatomical position of the hand (palm facing anteriorly) as reference. Going from lateral to medial, they are named thumb (digit 1), index finger (digit 2), middle finger (digit 3), ring finger (digit 4) and little finger (digit 5).
This article will describe the anatomy and functions of the phalanges of hand.
|Type||Proximal, middle and distal phalanges|
|Blood supply||Nutrient rami from palmar digital arteries|
Metacarpophalangeal joints connect the metacarpal bones and proximal phalanges
Proximal interphalangeal joints connect the proximal and middle phalanges
Distal interphalangeal joints connect the middle and distal phalanges
Interphalangeal joint of thumb connect the proximal and distal phalanges of the thumb
|Muscles attaching to phalanges||
Flexors: flexor digitorum superficialis, flexor digitorum profundus, lumbricals, dorsal interossei, palmar interossei, flexor digiti minimi, opponens digiti minimi muscles
Extensors: extensor digitorum, extensor digiti minimi, extensor indicis, lumbricals, dorsal interossei, palmar interossei, abductor digiti minimi muscles
Each hand has a total of five proximal phalanges, one in each digit. Compared to the middle and distal phalanges, they are the largest ones. The proximal phalanx of the thumb is an exception because it is shorter and more stout compared to the rest.
Each proximal phalanx consists of three parts;
- The base, which represents the expanded proximal part. It has a concave, oval-shaped articular facet that articulates with the metacarpal head to form the metacarpophalangeal (MCP) joint. The base also contains nonarticular tubercles for the attachment of various soft tissue structures.
- The body, which continues distally from the base. It tapers distally and has two surfaces; dorsal and palmar. The dorsal surface is round and smooth, appearing convex in the transverse plane. The palmar surface is flat and rough, especially on the sides where the flexor fibrous sheaths of digits attach. The surface appears flat in the transverse plane but concave in the sagittal plane.
- The head, which represents the expanded and rounded distal part. It has a pulley-shaped articular surface that articulates with the base of the middle phalanx to form the proximal interphalangeal (PIP) joint. The heads consist of smooth grooves, especially on the palmar aspects. These grooves represent the attachment points of the collateral interphalangeal ligaments of hand.
Various ligaments attach to the proximal phalanges. The most complex one is the digital fascial complex which attaches the surrounding subcutaneous tissue and neurovasculature to the bony phalanges. The collateral and palmar metacarpophalangeal ligaments attach to the bases of the proximal phalanges. They provide strength to the metacarpophalangeal joints. The collateral interphalangeal ligaments of hand attach to the heads, supporting the PIP joints. The proximal phalanges are also covered by the extensor expansion of hand on the dorsal aspect.
The proximal phalanges are very mobile at the MCP joints. They are mainly capable of flexion, extension, adduction and abduction. Circumduction and rotation are also possible, especially at the MCP joint of the thumb. These movements are enabled by the action of several muscles;
- Posterior (extensor) forearm muscles, such as extensor digitorum, extensor pollicis brevis, extensor digiti minimi and extensor indicis.
- Metacarpal muscles, such as the lumbricals, palmar interossei and dorsal interossei.
- Thenar muscles, for example flexor pollicis brevis and adductor pollicis.
- Hypothenar muscles like abductor digiti minimi and flexor digiti minimi.
These muscles carry out their functions via their direct attachments to the bases of the proximal phalanges. In addition, many extensors carry out the movements via the extensor expansion of hand which covers the phalanges.
There are a lot of muscles inserting into the phalanges of the hand. Learn them easily and systematically using Kenhub’s muscle anatomy and reference charts!
There are four middle (intermediate) phalanges in each hand because the thumb is missing one. They have a similar structure to the proximal ones, consisting of a base, body and head. The base of each middle phalanx has two concave-shaped articular facets and matches the head of the corresponding proximal phalanx. Their apposition forms the PIP joint. The heads of the middle phalanges have a pulley-like appearance. They articulate with the bases of the distal phalanges to form the distal interphalangeal (DIP) joints of hand.
The middle phalanges are reinforced by the same ligaments supporting the proximal ones; digital fascial complex, collateral interphalangeal ligaments and extensor expansion of hand. The collateral interphalangeal ligaments attach to the base and heads of the middle phalanges to reinforce the PIP and DIP joints.
The middle phalanges are less mobile compared to the proximal phalanges. They are only capable of flexion and extension at the PIP joints. Only the flexor digitorum superficialis muscle attaches directly to the sides of the middle phalanges, flexing them at the PIP joints. The remaining contributions are provided by the action of the previously mentioned muscles; the forearm extensors, metacarpal, thenar and hypothenar muscle groups. Flexion and extension are transferred to the middle phalanges from the direct action of these muscles on the proximal phalanges or via the extensor expansion of hand.
Each hand has five distal phalanges, which look shorter and slightly thicker compared to the previous two sets. Each distal phalanx has a base, body and head. The base has a double articular facet which matches the shape of the head of the middle phalanx. The distal phalanges have a smooth and round dorsal surface. In contrast, their palmar surface is wrinkled and irregular. The nonarticular heads contain an irregular, curved shaped distal tuberosity. It serves as an anchor point for the pulps of the digits.
The distal phalanges are stabilized by the digital fascial complex, collateral interphalangeal ligaments and extensor expansion of hand. The collateral interphalangeal ligaments attach to the base of the distal phalanges to reinforce the DIP joints.
The distal phalanges are capable of flexion and extension at the DIP joints. Two forearm extensors and one flexor muscle insert directly into the bases of the distal phalanges, permitting these actions. These include flexor digitorum profundus, flexor pollicis longus and extensor pollicis longus. The previously mentioned muscle groups acting on the proximal and middle phalanges also act indirectly on the distal ones via the extensor expansion of hand.
For more details about the phalanges of the hand, take a look at the videos, articles, illustrations and quizzes in the following study unit: