DRUJ ARTICULATING SURFACES

PRUJ and DRUJ are mechanically linked, with motion in one joint affecting the other

Maximum torque values for supinators are found in the ________ deg range of pronation

Found posteriorly

The carrying angle disappears at flexion beyond 30 deg, as found by

-15 deg

EMG

Trochlear groove config: in extension, forearm moves _______ to a positional slightly ______ to the axis of the humerus

Isometric testing shows that pronators are stronger than supinators, highlighting the functional distinctions between these muscle groups

Thin, soft, adjacent to the central band

Trochlear groove common configuration: ulna is guided medially from extension to flexion, so in full flexion the forearm aligns with humerus

Connects to the ulna, capsule and collateral ligaments

2 divisions of radioulnar ligament

Joint surface configuration, ligaments and joint capsule all contribute to limiting ROM while providing stability

>15 deg

DRUJ DISC SURFACES

Used to monitor the electrical activity produced by the firing of motor units

Carrying angle is present during

Interosseous membrane structure

<5 deg

Extends from below the ulna’s radial notch to the bicipital tuberosity of radius

DRUJ stability muscular support

Elbow injuries

Valgus resistance in closed pack position

Joints surfaces of radioulnar is optimal in maximal pronation/supination, with minimal contact in neutral position

Limits the extremes of flexion

Helps determine the relative proportion of motor units firing in a muscke during a specific contraction

No direct attachment to the radius

Limits the spin of the radius

its function may be to prevent separation of the radius and ulna

Stabilizes the PRUJ and DRUJ

PRUJ ARTICULATING SURFACES

Cushions compressive forces from the carpal to the ulna and stabilizes the ulnar side, bearing strain based on FA position

Runs from ulna to radius

There is slight increase in the angle in the dominant arm compared to the nondominant arm

Radial head spinning within annular ligament and radial notch

Flexion ROM is greater when the forearm is supinated compared to pronation or a neutral position

Supinator muscle acts alone during unresisted slow supination in any elbow or forearm position. But it cannot act alone during fast supination with the elbow extended

The diarthrodial joint of the radioulnar system allows for pronation and supination, enhancing hand mobility but compromising stability. Muscles like the extensor carpi radialis brevis and extensor carpi ulnaris attach at the distal humerus, creating a functional link between the elbow, wrist, and hand.

Supination torque increaes as the forearm moves into pronation, peaking at about 20 deg of pronation

Encircles the radial head, lined with articular cartilage and attaches to the radial notch’s anterior and posterior edges

Carrying angle is usually about _____ deg in full extension, with a range of ______

The axis of motion for pronation and supination is a longitudinal axis extending from the center of the radial head to the center of the ulnar head

Ulanr head moves proximally and medially

Elbow flexors

Elbow flexion ROM

Concave, located on the lat aspect of proximal ulna and mi ed with articular cartilage

Carrying angle increaes until around age 14 or 15, when epiphyseal ______ occurs, then decrease slightly but becomes more consistent after age ____

Forearm rotation

Active flexion range

Forms 4/5 of ring

Varus resistance in close pack position

Ulnar head moves distally and dorsally

The motion of proximal ulna is less in magnitude compared to that of the radius and is opposite in direction

Pronator teres

Anconeus may also assist in supination and pronation

Tasks requiring stability

EMG can identify muscle activation patterns of agonists and antagonsists

taut in pronation

Closed pack position of humeroulnar jt

Biceps brachii is involved during resisted supination or fast supination with the elbow flexed

Attached to ulna and rotates around the radiak head and attaches back to the ulna

At 90 degrees flexion, the anterior lart of the MCL provides primary resistance to both distraction and valgus stress

Subluxation/dislocation of the radial head from the annular ligament

The carrying angle typically disappears when the forearm is supinated and flexed against the humerus

Uniarticular muscles

Remains taut during rotation, preventing radial-ulnar separation and helps transfer wrist loads to the forearm

Factors affecting motion of elbow joint

Varus stress at 90 deg flexion

In full extension, resistance to joint distraction is provided by soft tissue structures, particularly the

Connects the ulna’s radial notch to the neck of the radius, reinforcing the inferior joint capsule and limiting radial head spin during forearm rot

Muscles crossing both the elbow and shoulder, such as the brachioradialis and brachialis, may restrict elbow motion when both jts attempt full ROM simultaneously

PRUJ DISC SURFACES

Taut in supination

An increased carrying angle beyond the normal range, which may be abnormal, esp if unilateral

Runs from the ulnar notch of the radius to the ulnar fovea and styloid process

Taut in supination

Prevent separation of ulna and radius, allowing about 5 mm of movement before resisting distraction

Pronator quadratus

Stabilizes the DRUJ, taut in pronation and loose in supination, protecting the ulnar head

Radius crosses over ulna

Closed pack position humeroulnar jt:

Runs counter to central band, from the ulna to the middle radius

Primary muscles for pronation and supination

The configuration of the trochlear groove determines the pathway of the forearm during flexion and extension

Elbow stabilization muscles

Ulnar head rests against the palmar aspect of the ulnar notch

Biarticular muscles

Different configurations of the trochlear groove can lead to variations in the forearm’s path during flexion, causing it to rest either medially or laterally to the humerus in full flexion

Passive flexion typically has a smaller range than an active motion due to muscle bulk limiting approximation between the forearm and humerus

Older adults: less type 2 fibers, same type 1 fiber percentage

Encircles four-fifths of the radial head, covered with cartilage, blending with joint capsule and reinforced by LCL

Passive flexion range

Thick, collagen rich, maintains spacing between radius and ulna during rotation

Aging reduces pennation angles and fascicle lengths, leading up to 50% muscle function loss. Passive stretching can counter this by increasing fascicle length

Carrying angle is absent during

Higher BMI may limit elbow ROM. Studies show an increase of 2-3 deg for each z-score increase in BMI

Found anteriorly

Muscle mass and contraction tyoe influence performance loss, with isometric contractions being least affected

Collagen-rich, mostly avascular and articulates with ulnar head and carpal bones