forearm Flashcards
radial vs. ulnar sizes
radius is larger distally and humerus larger proximally
forearm function
proximal radioulnar joint (PRUJ)
• interosseous membrane / ligament (IOM / IOL)
• distal radioulnar joint (DRUJ)
Ligamentous support of the proximal radioulnar joint:
Annular ligament (resists separation Oblique cord (limits supination) Interosseous membrane
The interosseous membrane
• thin fibrous sheet joining the radius and ulna • starts below the radial tuberosity
Roles of the interosseous membrane
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
direction of collagen fibres of IOM
The collagen fibres of the interosseous membrane
run inferiorly & medially from radius to ulna.
Distal radioulnar joint
“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
Distal radioulnar joint support
by non-bony passive structures:
• interosseous membrane
• capsule - very loose - distal radius glides and rotates around distal ulnar
• triangular fibrocartilage complex (TFCC)
Osseoligamentous force transmission in the forearm
• 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
dispersing applied load - Osseoligamentous force transmission in the forearm
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
Colle’s #
# & posterior displacement of the distal radius - forearm in pronation and elbow flx.
Posterior elbow dislocation
usually with # coronoid - generally posterior dislocation
2 Compartments of the forearm – antebrachial fascia
anteromedial - flex/pronate - med. epicondyle
posterolateral - ext/sup - lat. epicondyle and supracondylar ridge
Anteromedial compartment
4 superficial: Pronator teres FCR Palmaris longus FCU Intermediate = flexor digitorum superficialis digits 2-5 deep: FDP Pronator quadratus Flex. Policus longus
Posterolateral compart.
Supraepicondylar ridge: brachioradialis & ECRL Lateral epicondyle: ECRB, Edigitorum, ECU Supinator APL EPB EPL EI
In which range of pronation – supination is the interosseous membrane tautest & the maximum forces are transmitted across the PRUJ & DRUJ?
60˚ supination - distributes force better
In which range of pronation – supination is the interosseous membrane lax?
What is the significance of this functionally?
full pronation - little force transmission > more force up radius which results in # coles and radial head
Proximal radioulnar (PRUJ)
Synovial pivot
Distal radioulnar (DRUJ)
Synovial plane
Flexor carpi ulnaris
FCU - largest PCSA and adds stability
Identify the bow shape of the radius and comment on its effect on pronation.
The bowing of the radius effectively increases the moment arm of the pronator teres that attaches at the peak of the bow.
olecranon process
attachment for Triceps Brachii
ulnar tuberosity
attachment for brachialis
articular fovea
shallow cup on upper surface of radius
- attaches to capitulum of humerus
articular circumference
attaches to radial notch of ulnar
