forearm

Question 1

radial vs. ulnar sizes

Answer 1

radius is larger distally and humerus larger proximally

Question 2

forearm function

Answer 2

proximal radioulnar joint (PRUJ)
• interosseous membrane / ligament (IOM / IOL)
• distal radioulnar joint (DRUJ)

Question 3

Ligamentous support of the proximal radioulnar joint:

Answer 3

Annular ligament (resists separation
Oblique cord (limits supination)
Interosseous membrane

Question 4

The interosseous membrane

Answer 4

• thin fibrous sheet joining the radius and ulna • starts below the radial tuberosity

Question 5

Roles of the interosseous membrane

Answer 5

Roles:
1. attachment site for muscles
2. hinge for forearm rotation
3. limit separation & rotation of the radius & ulna
4. stabilise proximal & distal radioulnar joints
5. distribute load from radius to the ulna in the
proximal forearm

Question 6

direction of collagen fibres of IOM

Answer 6

The collagen fibres of the interosseous membrane

run inferiorly & medially from radius to ulna.

Question 7

Distal radioulnar joint

Answer 7

“L” shaped joint
Vertical part = between the ulna and the ulnar notch of the radius
Horizontal = between distal end of the ulna and the triangular fibrocartilage disc
• combination - pivot & gliding joint • little bony stability

Question 8

Distal radioulnar joint support

Answer 8

by non-bony passive structures:
• interosseous membrane
• capsule - very loose - distal radius glides and rotates around distal ulnar
• triangular fibrocartilage complex (TFCC)

Question 9

Osseoligamentous force transmission in the forearm

Answer 9

• distal radioulnar joint (DRUJ) > interosseous membrane / ligament (IOM / IOL) > proximal radioulnar joint (PRUJ)
* UL weight baring want to force radius proximally >
tightens interosseous membrane and drag ulnar with it
> transfer some force from radius to ulnar

Question 10

dispersing applied load - Osseoligamentous force transmission in the forearm

Answer 10

when IOL strain increases, RUJ pressures increase in tandem > reduces the load on any individual structure
• Capable of transmitting the greatest loads in neutral - 60˚ supination
• IOL is lax in full pronation!
• Force transmission across the radiohumeral joint is
greatest in full pronation!
Radiohumeral contact area greatest in flexion

Question 11

Colle’s #

Answer 11

# & posterior displacement of the distal radius
- forearm in pronation and elbow flx.

Question 12

Posterior elbow dislocation

Answer 12

usually with # coronoid - generally posterior dislocation

Question 13

2 Compartments of the forearm – antebrachial fascia

Answer 13

anteromedial - flex/pronate - med. epicondyle

posterolateral - ext/sup - lat. epicondyle and supracondylar ridge

Question 14

Anteromedial compartment

Answer 14

4 superficial:
Pronator teres FCR
Palmaris longus FCU
Intermediate = flexor digitorum superficialis digits 2-5
deep:
FDP
Pronator quadratus
Flex. Policus longus

Question 15

Posterolateral compart.

Answer 15

Supraepicondylar ridge: 
brachioradialis & ECRL 
Lateral epicondyle: ECRB, Edigitorum, ECU
Supinator 
APL
EPB
EPL
EI

Question 16

In which range of pronation – supination is the interosseous membrane tautest & the maximum forces are transmitted across the PRUJ & DRUJ?

Answer 16

60˚ supination - distributes force better

Question 17

In which range of pronation – supination is the interosseous membrane lax?
What is the significance of this functionally?

Answer 17

full pronation - little force transmission > more force up radius which results in # coles and radial head

Question 18

Proximal radioulnar (PRUJ)

Answer 18

Synovial pivot

Question 19

Distal radioulnar (DRUJ)

Answer 19

Synovial plane

Question 20

Flexor carpi ulnaris

Answer 20

FCU - largest PCSA and adds stability

Question 21

Identify the bow shape of the radius and comment on its effect on pronation.

Answer 21

The bowing of the radius effectively increases the moment arm of the pronator teres that attaches at the peak of the bow.

Question 22

olecranon process

Answer 22

attachment for Triceps Brachii

Question 23

ulnar tuberosity

Answer 23

attachment for brachialis

Question 24

articular fovea

Answer 24

shallow cup on upper surface of radius

- attaches to capitulum of humerus

Question 25

articular circumference

Answer 25

attaches to radial notch of ulnar