The radius and ulna form two joints between them; one at their upper ends and one at their lower ends. They are called superior and inferior radio-ulnar joints (Fig. 10.12). Both these joints are synovial joints of pivot variety. They are uniaxial joints permitting only rotation. The shafts of radius and ulna are also connected to each other by interosseous membrane. This union between radius and ulna is sometimes termed middle radio-ulnar joint.

Superior And Inferior Radio-Ulnar Joints

Features Superior radio-ulnar joint Inferior radio-ulnar joint
Type Pivot type of synovial joint Pivot type of synovial joint
Articular surfaces
  • Circumference of head of radius
  • Fibro-osseous ring formed by annular ligament and radial notch of ulna
  • Head of ulna
  • Ulnar notch of radius
Joint cavity Communicates with the cavity of elbow joint Does not communicate with the cavity of wrist joint
Prime stabilizing factor Annular ligament Articular disc
Movements Supination and pronation Supination and pronation

Superior (Proximal) Radio-Ulnar Joint

Type    

It is a pivot type of synovial joint.

Articular Surfaces

The articulating surfaces are: (a) circumference of radial head and (b) fibro-osseous ring made by radial notch of ulna and annular ligament.

Ligaments    

1. Capsular ligament (joint capsule): The fibrous capsule surrounds the joint. It is continuous with that of elbow joint and is attached to the annular ligament.

  • Annular ligament: It is a strong fibrous band, which encircles the head of radius and holds it against the radial notch of ulna. It forms about four-fifth of the fibro-osseous ring within which the head of radius rotates. Medially the annular ligament is attached to the margins of radial notch of ulna. The upper margin of the ligament is continuous with the capsule of the shoulder joint and its lower part becomes narrow and embraces the neck of radius. The inner surface of annular ligament is covered by a thin layer of cartilage. Laterally, it blends with the radial collateral ligament.
  • Quadrate ligament: It is thin, fibrous ligament, which extends from neck of radius to the upper part of supinator fossa of ulna just below the radial notch.

     

  • Synovial membrane: It lines the inner aspect of the joint capsule and annular ligament of superior radio-ulnar joint and is continuous with the synovial membrane of the elbow joint. It is prevented from herniation by quadrate ligament.

Relations    

Anteriorly and laterally. Supinator muscle.

Posteriorly: Anconeus muscle.

Blood Supply

By articular branches derived from arterial anastomosis on the lateral side of the elbow joint.

Nerve Supply

By articular branches from musculocutaneous, median, radial, and ulnar nerves.

Movements    

Supination and pronation.

Inferior (Distal) Radio-Ulnar Joint

Type    

Synovial joint of pivot variety.

Articular Surfaces

The articulating surfaces are (a) convex head of ulna, and

(b) concave ulnar notch of radius.

Ligaments    

  • Capsular ligament (joint capsule): It is a fibrous sac which encloses the joint cavity and is attached to the margins of articular surfaces. The inner surface of the joint capsule is lined by synovial membrane. The synovial lining of the joint sends an upward prolongation in front of the lower part of the interosseous membrane called recessus sacciformis. The synovial cavity of joint does not communicate with the synovial cavity of the wrist joint.
  • Articular disc: It is a triangular fibrocartilaginous disc and is sometimes referred to by clinicians as triangular ligament. Its apex is attached to the base of the styloid

    process of ulna and its base to the lower margin of the ulnar notch of radius. The articular disc separates the inferior radio-ulnar joint from the wrist joint.

3. Stability of elbow joint: The main factors providing stability to elbow joint are:

  • Wrench-shaped articular surface of the olecranon process of ulna and pulley-shaped trochlea of humerus.
  • Strong medial and lateral collateral ligaments.

Relations    

Anteriorly: Flexor digitorum profundus.

Posteriorly: Extensor digiti minimi.

Blood Supply

By anterior and posterior interosseous arteries.

Nerve Supply

By anterior and posterior interosseous nerves.

A brief comparison of superior and inferior radio-ulnar joints is presented in Table 10.2.

Movements    

Supination and pronation.

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