RADIOULNAR JOINTS

1. Proximal Radioulnar Joint

A. CLASSIFICATION: diarthrodial, pivot
B. ARTICULATING SURFACES

• Proximal: radial notch of ulna on lateral ulna and annular ligament
• Distal: radial head and rim

C. MOVEMENTS: supination ( palm down to palm up)/pronation (palm up to palm down)

• Plane: horizontal
• Axis: longitudinal

(1.) Radial head spins in radial notch of ulna
(2.) ROM: 90 supination/90 pronation
* In supination, the radius & ulna lie parallel to one another. During pronation, the radius crosses over the ulna at the superior radioulnar joint.

D.Supporting structures

• Annular ligament

1. ATTACHMENTS: circles head of radius, around the rim, and attaches to anterior/posterior sides of radial notch of ulna
2. FUNCTIONS: holds head of radius in radial notch
3. OTHER: covered with articular cartilage that is continuous with the radial notch and permits rotation of radial head

• Oblique Cord

1. ATTACHMENTS: inferior radial notch to medial side of radius
2. FUNCTIONS: helps hold the bones together

• Proximal portion of the interosseous membrane

1. ATTACHMENTS: between the radius and the ulna, proximal portion
2. FUNCTIONS: holds the two bones together

2. Middle Radioulnar Joint

A. CLASSIFICATION: synarthrodial, ligamentous
B. ARTICULATING SURFACES: shaft of radius articulates with shaft of ulna and the interosseous membrane supports it.

C. MOVEMENTS: no movement

D. Supporting structures: proximal and distal interosseous membrane that holds the bones together, continuous down the length of the bones

3. Distal Radioulnar Joint

A. CLASSIFICATION: diarthrodial, pivot
B. ARTICULATING SURFACES

• Proximal: head of the ulna
• Distal: ulnar notch, and the articular disc of the radius, which holds the two ends together

C. MOVEMENTS: supination/pronation, ulnar notch of radius slides over ulnar head and the disc follows by twisting at the apex

• Plane: horizontal
• Axis: longitudinal

• Anterior/posterior radioulnar joint capsule: key for joint function
• Interosseous membrane: holds the two bones together

1. triangular shaped disc: base of triangle attaches to ulnar notch and apex attaches to the styloid process of the ulna
2. head of ulna articulates with disc as it spins with radial notch during pronation/supination
3. helps to hold the distal ends of the radius and ulna together
4. separates ulna from carpal bones, reason that ulna never articulates with carpals
   

MOVEMENT OF THE FOREARM in general - all 3 joints work together

1. Pronation- radius crosses over the ulna
2. Supination- radius and ulna are parallel

A. Triceps Brachii

Proximal:

• Lateral: Lateral & Posterior Surfaces of Proximal 1/2 Body of Humerus
  
• Long: Infraglenoid Tubercle of Scapula
  
• Medial: Distal 2/3 of Medial and Posterior Surfaces of Humerus below Radial Groove

• Posterior Surface of Olecranon Process of Ulna

B. Biceps Brachii

Proximal:

• Long: Supraglenoid Tubercle of Scapula
• Short: Apex of Coracoid Process of Scapula

Distal: Tuberosity of Radius; Aponeurosis of Biceps Brachii

C. Brachioradialis

Proximal: Proximal 2/3 Lateral Supracondylar Ridge of Humerus

Distal: Lateral Side of Base of Styloid Process of Radius

D. Pronator Teres

Proximal: Immediately Above Medial epicondyle of Humerus; Medial Side of Coronoid Process of Ulna

Distal: Middle of Lateral Surface of Radius

E. Pronator Quadratus

Proximal: Medial Side; Anterior Surface of Distal 1/4 of Ulna

Distal: Lateral Side; Anterior Surface of Distal 1/4 Radius

F. Supinator

Proximal: Lateral Epicondyle of Humerus; Radial Collateral Ligament of Elbow Joint; Annular Ligament of Radius; Supinator Crest of Ulna

Distal: Lateral Surface of Upper 1/3 of Body of Radius Covering Part of Anterior and Posterior Surfaces

Category: Anatomy Notes