The Superior radio-ulnar joint and the Inferior radio-ulnar joint are the two joints formed between the radio and ulna. The Superior radio-ulnar joint is formed at the upper end, while the Inferior radio-ulnar joint is formed at the lower end of radius and ulna. Both these joints are synovial joints of pivot variety. Both Superior and Inferior radio-ulnar joints are uniaxial joints that permits only rotation. The interosseous membrane connects the shafts of radius and ulna. This union between radius and ulna is called as 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|
|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
It is a pivot type of synovial joint.
The articulating surfaces are: (a) circumference of radial head and (b) fibro-osseous ring made by radial notch of ulna and annular ligament.
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.
Anteriorly and laterally. Supinator muscle.
Posteriorly: Anconeus muscle.
By articular branches derived from arterial anastomosis on the lateral side of the elbow joint.
By articular branches from musculocutaneous, median, radial, and ulnar nerves.
Supination and pronation.
Inferior (Distal) Radio-Ulnar Joint
Synovial joint of pivot variety.
The articulating surfaces are (a) convex head of ulna, and
(b) concave ulnar notch of radius.
- 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.
Stability of elbow joint: The main factors giving 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.
Anteriorly: Flexor digitorum profundus.
Posteriorly: Extensor digiti minimi.
By anterior and posterior interosseous arteries.
By anterior and posterior interosseous nerves.
Supination and pronation.