Muscles of the Upper Arm and The Superior Radio-Ulnar Joint

Question 1

Describe the articular surface of the superior radioulnar joint

Answer 1

Head of radius:
= Bevelled circumference of radial head
= coated in hyaline cartilage (continuous with the cartilage on the concave head of radius)
= Wider anterior, medial and posterior than laterally to allow direct angulation with ulna – gives slight oval shape

Radial notch:
= Continuous with trochlear notch of ulna on lateral side – separated by blunt ridge
= Coated in hyaline cartilage
= Forms 1/5th of the articular fibroosseous ring
= Concave AP, flat vertically

Annular Ligament:
= Strong, flexible, well defined band
= Attaches to the anterior and posterior margins of the radial notch of ulnar
= Completes the 4/5ths of fibroosseous arch
= Flexible to allow head of radius to move during pronation and supernation
= Wider posteriorly, narrower on lower borders to prevent downwards displacement of radial head through the ring.
= Upper ligament lined in fibrocartilage
= Lower ligament lined in synovial membrane

Question 2

Classify the superior radioulnar joint

Answer 2

simple, synovial, uniaxial, pivot joint

Question 3

nerve supply to the superior radioulnar joint

Answer 3

posterior interosseous branch of radial nerve, musculocutaneous and medial nerves – C5, 6, 7

Question 4

what factors stabilise the superior radioulnar joint

Answer 4

Articular surfaces relatively incongruent – stability due to annular and quadrate ligament, and interosseous ligament.

Question 5

Shape and DoF of supinator

Answer 5

Downwards and laterally

Wrap around proximal 1/3rd radius

Question 6

attachments of anconeus

Answer 6

O: posterior surface of lateral epicondyle

I: lateral surface of olecranon and upper 1/4 posterior ulna

Question 7

Nerve supply of anconeus

Answer 7

radial nerve C7, C8

Question 8

Action of anconeus

Answer 8

assists extension of elbow

Question 9

Shape and DoF of pronator quadratus

Answer 9

fleshy quadrangular muscle

runs transversely

Question 10

Attachments of pronator quadratus

Answer 10

O: lower 1/4 anterior surface of ulna

I: lower 1/4 anterior surface of radius

Question 11

Nerve supply of pronator quadratus

Answer 11

anterior interosseous branch of median nerve (C8, T1)

Question 12

action of pronator quadratus

Answer 12

initiates pronation