Human Anatomy Vol 1

Head of

radius

Fig. 10.19: Radioulnar

Superior radioulnar joint

Radial notch of ulna

Fossa below superior

radioulnar joint

lnterosseous membrane

Axis of movement

I nferior radioulnar joint

Head of ulna

Articular disc of inferior

radioulnar joint

joints

JOINTS OF UPPEH LIMB

elbow, the palm is turned upwards in supination, and

downwards in pronation (kings pronate, beggars

supinate). The movements are permitted at the superior

and inferior radioulnar joints.

The vertical axis of movement of the radius passes

through the centre of the head of the radius above, and

through the ulnar attachment of the articular disc below

(Fig. 10.19). However, this axis is not stationary because

the lower end of the ulna is not fixed: It moves back-

wards and laterally during pronation, and forwards

and medially during supination. As a result of this

movement, the axis (defined above) is displaced

laterally in pronation, and medially in supination.

Supination is more powerful than pronation because

it is an antigravity movement. Supination movements

are responsible for all screwing movements of the hand,

e.g. as in tightening nuts and bolts. Morphologically,

pronation and supination were evolved for picking up

food and taking it to the mouth.

Around 50 degree of supination and 50 degree of

pronation is generally required to perform many of the

routine activities.

Pronation is brought about chiefly by the pronator

quadratus. It is aided by the pronator teres when the

movement is rapid and against resistance. Gravity also

helps (Fi9.70.2t).

Supination is brought aboutby the stpinator muscle and

the biceps brachii. Slow supinatioru with elbow extended,

is done by the supinator. Rapid supination with the

elbow flexed, and when performed against resistance,

is done mainly by the biceps brachii (Fi1.70.22).

Oblique

cord

Triangular fibrocartilaginous disc

Ulnar notch

Radial

styloid

process

Dorsal radioulnar

ligament

Ulnar styloid

process

Head of ulna

t''"1ilJ;."';i'",-

Fig. 10.20: Triangular fibrocartilaginous disc of inferior radio-
ulnar joint

The interosseous membrane performs the following
functions.

a. It binds the radius and ulna to each other.

b. It provides attachments to many muscles.

c. It transmits forces (including weight) applied to

the radius (through the hand) to the ulna. This

transmission is necessary as radius is the main

bone taking part in the wrist joint, while the ulna

is the main bone taking part in the elbow joint

(see Fig.1..2 and Flow chart 1.1).

Supinolion ond Pronolion

Supination and pronation are rotatory movements of the
forearm/hand around a vertical axis. In a semiflexed

Supination and pronation: Drtring supination the

radius and ulna are parallel to each other. During

pronation radius crosses over the ulna (Figs 10.23a

and b). In slmostosis (fusion) of upper end of radius

and ulna, pronation is not possible.

DISSECTION

Cut through the thenar and hypothenar muscles from

their origins and reflect them distally.

Separate the flexor and extensor retinacula of the

wrist from the bones.

Cut through flexor and extensor tendons (if not

already done) and reflect them distally.

Define the capsular attachments and ligaments and

relations of the wrist joint.

o

E

=o

CL

CL

f

c

.9

o0)

a