The distal phalanx consists of following parts, from proximal to distal.
- Tuft or ungual tuberosity
These phalanges differ in size, shape and contour from proximal and middle phalnges.
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 disal phalanges is same.
Shaft of the distal phalanx, in general, is thinner than middle and proximal phalanges.
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.
Image modified from AO Foundation
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 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 of the extensor digitorum communis and extensor indicis proprius on index distal phalanx.
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 and lateral tubbercles 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.
Anatomy of 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.
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