Phalanx [plural phalanges] is a tubular bone present in hand and foot and form digits [fingers and toes].
In this article, we discuss the phalanges of the hand.
There are five digits in each hand – four finger and one thumb.
All fingers have three phalanges distal, middle and proximal.
Thumb has only proximal and distal phalanx.
Distal Phalanx
The distal phalanx consists of the following parts, from proximal to distal.
- Base
- Shaft
- Tuft or ungual tuberosity
These phalanges differ in size, shape, and contour from proximal and middle phalanges.
Distal phalanges of the middle and ring finger are similar in length.
It is followed by an index and little finger. Except for little finger, the width of all the distal phalanges is same.
The shaft of the distal phalanx, in general, is thinner than middle and proximal phalanges.
Base
The base of the distal phalanx generally equals the head of the middle phalanx.
On the dorsal aspect base flares out dorsally and centrally creating a ridge that separates the articular surface from the shaft.
The dorsal base is roughened slightly and forms a raised area called dorsal tubercle.
Shaft
The shaft is wide proximally and narrows distally with the narrowest portion being just proximal to the tuft. The dosral portion of the shaft is slightly convex and rounded and it is slightly concave on the palmar side. Medial and lateral surfaces are rounded.
Tuft
Tuft is the terminal thick roughened crescent-shaped wide portion of the distal phalanx. The tuft provides for attachment of septae that support, stabilize, and anchor the pulp of the digit to the distal phalanx
This tubercle forms the insertion site of the extensor digitorum communis and extensor indicis proprius on index distal phalanx. [extensor pollicis longus on thumb]
A volar tubercle is present on the volar side and two lateral tubercles [one on radial and one on the ulnar side.
The volar tubercle provides attachemnt to flexor digitorum [flexor pollicis longus in thumb] and lateral tubercles provide attachment to lateral collateral ligaments.
Ligaments pass from the distal margin of the widened lateral base to the expanded proximal margins of the tuft. The small branches of the proper digital artery that supply the dorsal arcade just proximal to the nail fold pass under these ligaments very close to the base of the shaft of the distal phalanx.
Digital pulp is a honeycomb structure of fibrous septae containing pockets of fat in each compartment. The proximal part of the pulp is thicker and more mobile than the distal pulp. Tuft is the anchoring point of the architecture of pulp.
The dorsal surface of the distal phalanx is the direct support for the germinal matrix and sterile matrix of the nail. The bone volarly and the nail plate dorsally create a three-layered sandwich with the matrix in the middle.
Middle Phalanx
A middle phalanx [medial phalanx or intermediate phalanx] is a tubular bone that articulates with distal phalanx distally and proximal phalanx proximally.
Each middle phalanx has a head, body[shaft], and a base.
There is one middle phalanx in each finger, except the thumb which has none.
Flexor digitorum superficialis tendons, along with the flexor sheath, are attached to the middle phalanges at their sides. In between the flexor digitorum profundus pass to attach on distal phalanx.
On dorsal aspect, extensor digitorum tendons insert, which help with the extension and separation of the fingers.
Proximal Phalanx
The proximal phalanx is the tubular bone between middle phalanx and metacarpal.
Similar to middle phalanx, proximal phalanx has a head, a body/shaft, and a base.
There is one proximal phalanx in each finger including the thumb.
Proximal phalanges are the longest. The long shafts are flat on the palmar side, but convex dorsally and transversally. Additionally, the medial and lateral borders have distinct sharp edges for attachment.
Proximal phlanx base receives volar and dorsal ossei muscle insertion.
The proximal phalanx of little finger receives insertion of flexor brevis and abductor digitorum quinti on volar aspect.
The proximal phlanax of thumb receives abductor pollicis brevis and flexor pollicis brevis [flexor pollicis longus goes till distal phlanax] insertions on volar side and extensor pollicis brevis [extensor pollicis longus goes till distal phalanx of thumb]
Bones of the hand palmar view
of the fibrous tendon sheaths of the flexor muscles.
Joints of Phalanges
Metacarpophalangeal Joint
- Between proximal phalanges and metacarpal bone
- Located approximately at knuckle levels
Proximal Interphalangeal Joint
- Marked by second finger crease or first bend after knuckles
- Between head of a proximal phalanx and base of middle one
- Thumb doesn’t have a middle phalanx
- Proximal phalanx articulates with the distal phalanx
- Joint is simply called interphalangeal joint
Distal Interphalangeal Joint
The distal interphalangeal joint is the joint between distal phalanx and middle phalanx.
The distal interphalangeal joint is a bicondylar ginglymus joint.
The joint is very well stabilized collateral ligaments on the medial and lateral side and the volar plate
There are two types of collateral ligaments –
– The proper collateral ligaments which insert on the lateral tubercles at the base of the distal phalanx.
– The accessory collateral ligaments attach distally to the lateral margins of the volar plate. Distal interphalangeal joint stability is maintained by articular congruity, the dynamic balance of flexor and extensor tendons and ligaments.
Blood Supply of Phalanges
Branches from the superficial palmar arch and deep palmar arch.
Development and Ossification
Each phalanx has a primary ossification center for the body which appears around 8th-9th week of intrauterine growth. The secondary ossification center is for the base, and it develops at age of 4-5 years old. These centers unite around the age of 18-20 years.
Functions
Phalanges provide the range of motion required for hand functions like precise gripping, grasping and handling of equipment.
Opposition movement of thumb is necessary for fine motor movement like pinching.
So phalanges provide the precision and fineness of the hand movements.
Clinical Significance
Injuries
Injuries to phalanges are common especially distal phalanx.
Following injuries are commonly seen
- Fractures and dislocations
- Fingertip injuries
- Fingernail injuries
- Mallet finger
Arthritis
Metacarpophalangeal and Interphalangeal joints can get involved in rheumatoid arthritis, osteoarthritis and other secondary arthritis like psoriatic arthritis.
Tumors
Enchondroma is common in tubular bones of hand
