Author: Jana Vasković•Reviewer: Francesca Salvador MScLast reviewed: September 23, 2021Reading time: 7 minutes
The proximal radioulnar joint is a synovial joint that connects the proximal ends of the radius and ulna.
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In this joint, the circumferent head of radius is placed within the ring formed by the radial notch of ulna and the annular ligament. This configuration makes this joint a pivot joint.
The proximal radioulnar joint is a uniaxial joint, allowing movements in one degree of freedom; pronation-supination. In humans, this movement is unique for the upper limb.
This article will discuss the anatomy and function of the proximal radioulnar joint.
|Type||Synovial pivot joint; uniaxial|
|Articular surfaces||Head of radius, radial fossa of ulna|
|Ligaments||Annular ligament, quadrate ligament|
|Innervation||Median, musculocutaneous, radial and ulnar nerves|
|Blood supply||Deep brachial, radial and common interosseous arteries|
|Movements||Pronation - supination|
The articular surfaces of the proximal radioulnar joint are the head of radius and the radial fossa of ulna.
Both surfaces are lined with hyaline cartilage. The radial head is circular and convex, while the radial fossa is reciprocally concave.
However, the radial fossa is in touch with only one-fifth of the radial head. For the sake of completeness of this pivot joint, the annular ligament surrounds the radial head and holds it tight against the radial fossa of ulna.
Ligaments and joint capsule
The fibrous capsule of the radioulnar joint attaches to the annular ligament distally, while proximally it is continuous with the capsule of the elbow joint. The synovial membrane attaches to the margins of the articular surfaces and to the annular ligament. It lines the interior surface of the capsule,where it is continuous with the synovial membrane of the elbow joint. Thus, the elbow and proximal radioulnar joints share one continuous synovial cavity.
The proximal radioulnar joint is reinforced by the annular and quadrate ligaments.
The annular ligament extends from the anterior margin of radial fossa of ulna, encircles the radial head and attaches to the posterior margin of the radial fossa. Thus, the annular ligament helps to create a stable ring within which the radial head can rotate.
The proximal margin of the ligament is fused with the joint capsule, while the distal margin attaches to the neck of radius. The internal surface of the annular ligament is covered by a thin layer of cartilage which is in direct contact with the surface of the radius. The superficial surface is fused with the radial collateral ligament and is one of the attachment sites of the supinator muscle.
The quadrate ligament is a short fibrous band that spans from the superior part of the supinator fossa of ulna to the neck of radius, just proximal to the radial tuberosity.
The proximal radioulnar joint is supplied by the branches of median, musculocutaneous, radial and ulnar nerves.
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The blood supply to the proximal radioulnar joint comes from a periarticular network formed by the radial collateral branch of deep brachial artery, radial and recurrent branches of the radial and common interosseous arteries.
The proximal radioulnar joint works in a unit with the distal radioulnar joint to enable rotatory movements of the forearm; pronation and supination. When the arm is in the resting position beside the body, the range of motion for pronation is 61–66°, while for supination it is 70–77°
In the proximal radioulnar joint, the head of radius rotates within the ring formed by the radial fossa and annular ligament. The axis of rotation is dynamic and depends on the position of the forearm. When the forearm is in supination, the axis passes through the center of the head of radius proximally, and through the ulnar attachment of the articular disc in the distal radioulnar joint. When the forearm is pronated, the distal point of the axis moves medially, passing through the head of ulna.
Besides rotation of the radial head, the supination and pronation are followed by a sequence of additional movements in the proximal radioulnar joint;The superior surface of the radial head rotates against the capitulum of humerusThe head of radius tilts laterally and inferiorly in the transverse planeSince the head of radius is ellipsoid on cross-section, its wider axis comes into a transverse, thus displacing the radial head laterally
The proximal radioulnar joint takes a closed packed position at the 5° of supination. The open packed (resting) position occurs when the forearm is flexed at 70° and supinated at 35°. The capsular pattern of the joint is defined and limited by pronation and supination. The proximal radioulnar joint permits the accessory movements of anteroposterior gliding of the radial head against the ulna and the capitulum of humerus.
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References:Cael, C. (2010). Functional anatomy: Musculoskeletal anatomy, kinesiology, and palpation for manual therapists. Philadelphia, PA: Wolters Kluwer Health/Lippincott, Williams & Wilkins.Hall, S. J. (2015). Basic biomechanics (7th ed.). New York, NY: McGraw-Hill EducationMagee, D. J. (2014). Orthopedic physical assessment (6th ed.). St. Louis: Elsevier Saunders.Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.Netter, F. (2019). Atlas of Human Anatomy (7th ed.). Philadelphia, PA: Saunders.Palastanga, N., & Soames, R. (2012). Anatomy and human movement: structure and function (6th ed.). Edinburgh: Churchill Livingstone.Richards, J. (2018). The comprehensive textbook of clinical biomechanics (2nd ed.). Amsterdam, The Netherlands: Elsevier.Standring, S. (2016). Gray"s Anatomy (41tst ed.). Edinburgh: Elsevier Churchill Livingstone.
Illustrations:Proximal radioulnar joint (Articulatio radioulnaris proximalis) - Irina Münstermann