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Functions of proximal and distal RU joints - Coggle Diagram
Functions of proximal and distal RU joints
pronation and supination
The axis of motion
For pronation and supination the axis of
motion is
through a longitudinal axis
extending from the center of the radial
head to the center of the ulnar head
In supination radius and ulna is parallel
Ulna head moved proximally and medial
In pronation radius cross over the ulna
Ulna head moves distally and dorsal
ROM
A Total of 150 degrees of motion possible at radioulnar joints
To assess the ROM of supination and pronation,
the elbow joint has to be stabilized at the side of the trunk at 90 degrees of flexion
Pronation in all position is limited by the
bony approximation and by the
dorsal radioulnar ligament and
posterior fibers of the medial collateral ligament
Supination is limited by
Passive tension in the palmar
radioulnar ligament and the oblique cord
The quadrate ligament limits
spin of the radial head in both
supination and pronation
The annular ligament helps
maintain stability of proximal radioulnar joint by holding the radius in close approximation to
the radial notch
Muscle Action
Pronation
Pronators exerts a pull on the radius
Shaft and distal end turns over the ulna
Pronator teres (2 joint muscle)
Major action at Radioulnar joint
Long head can contribute to elbow flexion
Stabilises proximal radioulnar joint
Helps the radial head maintain contact with the capitulum
Pronator quadratus (1 joint muscle)
Active in both unresisted and resited pronation
Active in slow and fast pronation
Deep head is active during resisted supination and resisted pronation and
act as a stabilizer to maintain compression of
the distal radioulnar joint.
Supination
Supinators act by pulling the
shaft and distal end of radius over the ulna
Supinator
Can act alone during unresisted
slow
supination
in all positions of forearm or elbow
Can act alone during usresisted
fast
supination
when the elbow is extended
Biceps brachii
will be active during:
Supination when performed against resistance
Fast supination
when
elbow is flexed in 90 degrees
Supination tourque is greatest at
20 degrees of pronation
Stability at the Distal radioulnar joint
Musculature support
dynamic
stabilisation
provided by Deep head of pronator quadratus
Extensor carpi ulnaris muscle
exerts a depressive force on the dorsal aspect of the ulnar head as the tendon is stretched over the head during supinaton
Tension in the tendon helps to maintain the position
of the ulnar head during supination and pronation
Extensor carpi radialis brevis act as both
Stabilizer to the forearm fro gripping during pronation torques
Prime mover for wrist extension for supination
tourques
Nonmusculatur support
Dorsal radioulnar ligament is taut in pronation
Palmar radioulnar ligament is taut in supination
The radioulnar ligaments,
articular disc
and the pronator quadratus
maintain the ulna within the ulna notch and
prevent the ulna from subluxating or dislocating (dynamic stabilisers)
The interossesous ligaments
binds the radius and ulna together
and provide stability
( horizontal stabilization)
The interosseous ligament and
the triangular fibrocartilaginous complex
provide longitudinal stabilisation
Radioulnar load sharing at the
wrist and elbow positions
Elbow in varus position,
force is transmitted from distal radius
through the interosseous membrane to the proximal ulna
distal radius - interosseous m - proximal ulna
No contact between the
radial head and capitulum
Elbow in valgus position,
force is transmitted through the radius
there is Contact between the
radial head and capitulum
Elbow in neutral position,
force transmitted to the ulna is greater at
the
proximal end
when compared to the distal end
Articular disc and forces
Serves as a cushion between the
carpals and the ulna
allowing compression force transmission and
act as a stabilizer
Assists in transmission of compressive forces from the radius to ulna
in supination
Tension across the entire disc decreased
in pronation
tension increased in the
radial portion of the disc
Compressive forces are transmitted through the central portion of the disc
and
some load is converted to tensile loading within the peripheral margins
table