07 - anatomy final 2

8/11/2019 07 - Anatomy Final 2

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Anatomy

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carpal joint that differentiates the hand of the human of that of lower

primates and gives the human wrist its extreme freedom of

movement. On the other hand, the TFCC is a structure that is very

sensible to trauma and degeneration and can be a source of ulnar

wrist pain that is difficult to treat.[14]

The distal radio-ulnar joint (DRUJ) is of equal importance as

the radio-carpal joint. It is composed of the fixed ulnar head and the

sigmoid notch. This sigmoid notch not only rotates around the ulnar

head, but it makes at the same time a translational movement. In

pronation, the ulnar head moves dorsally in the sigmoid notch. In

supination, it is displaced anteriorly. The most important stabilizer of

the DRUJ is the TFCC, additional stabilizers are the interosseous

membrane of the forearm, pronator quadratus muscle and the

tendons and sheets of the extensor and flexor carpi ulnaris muscles.

As the interaction of all of these structures is of great importance for

stability and motion, deformity after injury or fracture has an

important influence on the function of the entire wrist.[14]

The bony architecture of the distal radius can be viewed in

terms of columns. Rikli and Regazzoni [3] divided the distal forearm

in three columns: the medial column consisting of the ulna, the

TFCC and the DRUJ; the intermediate column made up of the fossalunata and the sigmoid notch and the lateral column including the

fossa scaphoida and the styloid process. Fracture lines often run

between these columns. The intermediate column can also be split in

a sagittal plane, creating the dorsal and the volar intermediate


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Anatomy

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fragment. The surgical reconstruction of the distal radius should be

based on the knowledge of these columns. Almost 80% of the

transmitted forces go over the distal radius by longitudinal loading of

the wrist, if radius and ulna are equally long (ulna neutral).

Lengthening of the ulna shifts force transmission in the direction of

the ulna, whereas ulnar shortening shifts forces towards the radius.[15]

Trabecular pattern of the distal radius

analysing the radiographic trabecular pattern of an area of the

distal radius revealed that the pattern runs along the direction of the

bone, as shown in figure 1 but is not nearly as organised as that

observed in the femoral head since the loading of the radius is not as

consistent.[16]

(Fig. 1) Trabecular pattern of distal radius.[16]


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Radiological anatomy of the distal radius

The normal distal radius articular surface inclines radially

between 22 and 23 degrees in the frontal plane.[17] (Fig 2)

Radial length refers to the distance between the tip of the

radial styloid process and the distal articular surface of the ulnar

head.[18] The average radial length is 11 to 12 mm. Ulnar variance is

the relative length between the head of the ulna and the articular

surface of the distal radius. This measurement must be taken from a

neutral rotation posteroanterior (PA) radiograph because forearm

rotation affects the relative length from the distal radius to the

ulna.[19] The average ulna and radius end within 1 mm of one

another.[20] These anatomic parameters have become well accepted in

the radiographic evaluation of distal radius fractures (Fig. 3).[21]

(Fig. 2) Normal x-ray anatomy. PA view. Measurement of radial height and inclination

and ulnar variance. [13]


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The joint surface slopes palmward between 4 and 22 degrees, with an

average palmar inclination of 10 to 12 degrees. This is best appreciated on a

true lateral radiograph.[17]

(Fig. 3) Normal x-ray anatomy, lateral view. Measurement of palmar inclination. [13]

Blood Supply of the Distal Radius

Blood supply to the distal radius includes the radial, ulnar, anterior

interosseous, and posterior interosseous arteries. Anastomoses between the

anterior branch of the anterior interosseous artery and the palmar carpal arch

and also between the anterior and posterior interosseous arteries and the

dorsal carpal arch are always present. Small vessels coming from the

anterior interosseous artery and the insertion of pronator quadratus over thesigmoid notch of the radius were also present. The intraosseous areas of

vascularization came from these adjacent small branches.[22]

The distal radius is supplied by three main vascular systems:

epiphyseal, metaphyseal, and diaphyseal. The palmar epiphyseal vessels


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Anatomy

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branched from the radial artery, palmar carpal arch, and anterior branch of

the anterior interosseous artery. They entered the bone through three points:

the radial styloid process, Lister's tubercle, and the sigmoid notch.[22]

The intraosseous point of entry to the dorsal epiphyseal vessels is

from the fourth and fifth extensor compartment arteries (ECA). The fourth

ECA is located on the radial aspect of the fourth extensor compartment

floor. It originates from the posterior division of the anterior interosseous

artery or its fifth extensor compartment branch and anastomoses with the

dorsal intercarpal arch and the radiocarpal arch. The fifth ECA is supplied

by the posterior division of the anterior interosseous artery and anastomoses

distally with the dorsal intercarpal arch. It also may make distal connections

to the fourth ECA and the dorsal radiocarpal arch. The fifth ECA provides

direct nutrient branches to the radius.[22]

More proximally, in the metaphyseal area, numerous periosteal and

cortical branches originated from the anterior interosseous artery as it

courses through the pronator quadratus. These branches provided the mainsupply to the distal radius. The vessels perforated the bone-forming and

anastomotic network. The metaphyseal arteries are multiple and enter all the

periosteal surfaces of the proximal and distal metaphyses. They provide the

entire supply of the metaphyses, and their terminal branches anastomose

with the terminal branches of the medullary arterioles at each end of the

medullary cavity.[22]

The nutrient artery provides intraosseous vascularity only to the

diaphyseal part of the distal radius. The principal nutrient artery approaches

the diaphysis under the protection of a fascial attachment. It traverses the full

thickness of the cortex to enter the bone where it divides into the ascending


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and descending branches of the medullary artery. These branches subdivide

into arterioles, which enter the endosteal surface of all portions of the

diaphysis.[22]

(Fig. 4) A. Dorsal and B. palmar views of blood supply of distal radius.[23]

07 - anatomy final 2

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