Radioulnar Joints

Describe briefly the radio-ulnar joints .

 There are three radioulnar joints between radius and ulna:

• Superior radio-ulnar joint
• Middle radio-ulnar joint
• Inferior radioulnar joint

Superior radio-ulnar joint

Type: It is a  pivot type of synovial joint .

Articular surfaces: a. Circumference of head of radius, b. radial notch of ulna and annular ligament  (forming fibro-osseous ring).

Joint capsule:The joint capsule is continuous with the capsule of elbow joint and is attached to annular ligament.

Ligaments:

• Annular ligament:
  • It surrounds the head of the radius and forms the 4/5th  ( fibrous part) of the fibro-osseous ring  within which the head of the radius rotates. medially
  • It is attached to the anterior and posterior margins of the radial notch of ulna.
  • Superiorly, it is continuous with the capsule of elbow joint.
  • Inferiorly, it surrounds the neck of radius.
  • laterally it blends with radial collateral ligament.
• Quadrate ligament:
  • It is a thin ligament that extends from the neck of the radius to the lower margin of the radial notch of ulna.

Blood and nerve supply

• Arterial supply is derived from the arterial anastomosis on the lateral side of the elbow joint.
•  Nerve supply is by the musculocutaneous, median, and radial nerves.

Movements: Supination and Pronation.

Inferior radio-ulnar joint

Type: It is a  pivot type of synovial joint .

Articular surfaces: a. head of ulna b. ulnar notch of radius.

Joint capsule:The joint capsule is attached to the articular margins ( the  upper part of the capsule is evaginated by the synovial membrane lining the capsule  to form recessus sacciformis in front of the interosseous membrane.

Blood and nerve supply

• Arterial supply is anterior and posterior interosseous arteries.
• Nerve supply is by anterior and posterior interosseous nerves ( branches of median and radial nerves respectively).

 Movements: Supination and Pronation

Middle radio-ulnar joint

• Type: It is a syndesmosis type of fibrous joint.
• The interosseous membrane connects the shafts of radius and ulna.
• Above the interosseous membrane the oblique cord  that extend from the ulnar tuberosity to the radial tuberosity (direction of fibers is downwards and laterally) connects the two bones.
• Interosseous membrane:
  • It extends from 2-3cm below the radial tuberosity to the capsule of inferior radio-ulnar joint.
  • Direction of fibers is downwards and medially.
  • Posterior interosseous vessels reach extensor compartment of forearm by passing through the gap between the interosseous membrane and oblique cord.
  • Anterior interosseous vessels reach extensor compartment of forearm by piercing the interosseous membrane a little above its lower margin.
  • Its functions are – a. to bind the radius and ulna, b. to provide attachment to the deep muscles of forearm, c. to transmit the force from the radius  (transmitted to radius from hand) to ulna.

 Describe briefly supination and pronation movements at radioulnar joints.

• Supination and pronation are the rotatory movements of forearm that take place at radioulnar joints around a vertical axis.
• The axis of the movement passes through the center of the head of the radius above to the base of styloid process of ulna below. It is nor stationary, it passes forwards and medially during supination and backwards and laterally during pronation.
• In a semiflexed elbow, the palm is turned upwards in supination and downwards in pronation.
• In supination, the radius and ulna are parallel to each other.
• In pronation the of radius crosses in front of the lower end of ulna (due to rotaion of lower end of radius at radioulnar joints).
• Supination is more powerful than the pronation because it is antigravity movement. Therefore, supination movement is used in for tightening the nuts and bolts, whereas, pronation is used for loosening /opening of nuts and bolts.