The radius and ulnar bones are joined to each other at the superior and inferior ends. They are also connected by interosseous membrane which is sometime said to constitute the middle radiounar joints.
SUPERIOR RADIOULNAR JOINT
It is a uniaxial synovial pivot joint formed between the circumference of the head of radius and the osseofibrous ring formed by the annular ligament and the radial notch of the ulnar. The inner aspect of the annular is lined by hyaline cartilage.
Ligaments:
The annular ligament: It forms 4/5 of the ring within which the head of the radius rotates. It is attached to the margin of the radial notch of the ulnar and it continues with the capsule of the elbow joint.
The quadrate ligament: Extends from the neck of the radius to the lower margin of the radial notch of the ulnar, they share the same synovial membrane with the elbow joint.
Blood supply: Anastomosis along the lateral side of the elbow.
Nerve Supply: Median and radial nerve.
Movements: Pronation and supination.
THE INFERIOR RADIOULNAR JOINT
It is a uniaxial synovial joint between the convex head of the ulnar and the concave ulnar notch of the radius. A triangular cartilaginous articular disc is attached by its base to the lower margin of the ulnar notch of the radius and by its apex to a fossa at the base of the ulnar styloid. The proximal surface of the disc articulates with the ulnar head. The synovial membrane of the joint projects proximally, as the recesses sacciformis, posterior to the pronator quadratus and anterior to the interosseous membrane.
Blood supply: Anterior and posterior interosseous artery.
Nerve supply: Anterior and posterior interosseous nerve
Movement: Supination and pronation.
THE INTEROSSEOUS MEMBRANE
It connects the interosseous border of the radius and ulnar. Its fibers run inferomedially from the radius to the ulnar. The oblique cord is a flat band which connects the two bones it fibers runs obliquely. It extends from the tuberosity of the radius to the tuberosity of the ulnar. The direction of its fibers is opposite to that in the interosseous membrane.
The posterior interosseous vessels pass through the gap between the oblique cord and the upper end of the interosseous membrane. Superiorly the interosseous membrane begins 2-3cm below the radial tuberosity between the oblique cord and the interosseous membrane there is a gap for the passage of the posterior interosseous artery to the back of the forearm, inferior a little above its lower margin there is an aperture for the passage of the anterior and posterior interosseous vessel to the back of the forearm.
The anterior surface is related to the flexor pollicis longus, flexor digitorum profundus and pronator quadratus and the anterior interosseous vessels and nerve. The posterior surface is related to the supinator, the abductor pollicis longus, the extensor pollicis brevis, extensor pollicis longus, extensor indicis, the anterior and posterior interosseous vessels.
FUNCTION
· It binds the radius and ulnar to each other.
· It provides attachment to many muscles.
· It transmits forces (including weigh) applied to the radius to the ulnar, this transmission is necessary as the radius is the main bone taking part in the wrist joint while the ulnar is the main bone taking part in the elbow joint.
RADIOCARPAL JOINTS
It is a biaxial synovial joint of the ellipsoidal variety.
Articular Surface:
Upper: Inferior surface of the lower end of the radius and the articular disc of the inferior radioulnar joint.
Lower: Scaphoid, lunate and triquetral bones.
The joint’s surface projection is a convex upward line obtained by joining the styloid process of the radius and ulnar. The joint neither communicate with the inferior radio-ulnar joint nor with inter-carpal joints.
LIGAMENTS
1. An articular capsule surrounds t-
joint.It is attached above to the lower end of the radius and ulnar and below to the proximal row of carpal bones. A protrusion called the prestyloid recess lies in front of the styloid process of the ulnar and in the front of the articular disc. It is bounded inferior by a small meniscus projecting inward from the ulnar collateral ligament between the styloid process and the triquetral bone. The fibrous capsule is strengthened by the overlying ligaments.
2. On the anterior aspect there are two palmar carpal ligaments: The palmar radiocarpal ligament which is a broad band that begins above from the anterior margin of the lower end of the radius and its styloid process, it then runs downward and medially to be attached to the anterior surface of the scaphoid, the lunate and triquetrum bone. The palmar ulnocarpal ligament is a rounded fasciculus which begins above from the base of the styloid process of the ulnar and the anterior margin of the articular disc runs downward and laterally and is attached to the lunate and triquetral bones. Both the palmar carpal ligaments are considered to be intracapsular.
3. On the dorsal aspect of the joint there is one dorsal radiocarpal ligament. It is weaker than the palmar ligament. It begins above from the posterior margin of the lower end of the radius runs downward and medially and is attached below to the dorsal surface of the scaphoid, lunate, triquetral bones.
4. The radial collateral ligament extends from the tip of the styloid process of the radius to the lateral side of the scaphoid bone. It is related to the radial articular.
5. Ulnar collateral ligament extends from the tip of the styloid process of the ulnar to the triquetrum and pisiform bones.
RELATIONS
Anterior: Long flexor tendons with their synovial sheath and median nerve.
Posterior: Extensor tendons of the wrist and fingers with their synovial sheath.
Blood Supply: Anterior and posterior carpal arch.
Nerve Supply: Anterior and posterior interosseous.
MOVEMENT
1. Flexion: It takes place more at the mid carpal than at the wrist. The main flexors are flexor carpi radialis, flexor carpi ulnaris, and the palmaris longus, the movement is assisted by long flexors of the fingers and thumb and the abductor pollicis longus.
2. Extension: It takes place mainly at the wrist. The main extensors are extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris. Assisted by extensors of the fingers and thumb.
3. Abduction: Occurs mainly in the mid carpal joint the main abductors are flexor carpi radialis, extensor carpi radialis longus, abductor pollicis longus and extensor pollicis brevis. In abduction which occurs up to 150 the scaphoid bone makes most contact to the radius and the lunate contact the articular disk.
4. Adduction: It occurs mainly at the wrist joint. The main adductors are extensor carpi ulnaris and flexor carpi ulnaris. In adduction which occurs up to 450 degree, the lunate bone comes in contact with the radius while the triquetrum contacts the articular disk.
5. Circumduction: This is feasible because the joint perform two degrees of freedom.
APPLIED ANATOMY
1. The wrist joint is commonly involved in rheumatoid arthritis, in which collagen is mostly affected.
2. The wrist joint can be aspirated from the posterior surface between the tendon of extensor pollicis longus and extensor indicis.
3. The joint is immobilized in optimum position of 30o dorsi-flexion.
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