bones + joints of elbow region

Question 1

Elbow + radioulnar joints

Answer 1

1. elbow joint: (including radiohumeral and humeroulnar articulations)
2. proximal (superior) radioulnar joint
3. intermediate radioulnar joint (interosseus membrane)
4. distal (inferior) radioulnar joint

Question 2

Elbow Joint

Answer 2

• Elbow joint includes both humeroulnar and radiohumeral articulations
• Classified as a synovial, uniaxial, hinge joint
• Normal adult range of motion - sagittal plane (transverse axis): extension - straight arm (0°), active flexion approx 145° (can passively flex further)
• Note: elbow hyperextension can be present - defined as when extension range > -10°
• Radius connects w/ capitulum once the elbow is approx 90° flexed + onwards
• The ulnar stays in contact w/ the humerus all through range

Question 3

Carrying angle of the elbow

Answer 3

• Medial humeral articulating surface projects more distally
• Transverse axis of the elbow joint is oblique
• Normal valgus angle is present b/w the arm and the forearm in the anatomical position
• In men: 10-15°, in women: 20-25°

Question 4

Elbow Joint Capsule

Answer 4

• A single fibrous capsule completely surrounds both the elbow AND proximal (superior) radioulnar joints
• Attaches to the trochlear notch and coronoid processes of ulna and annular ligament of the radius and proximally to the epicondyles
• Capsule holds onto the ligament rather than the bone itself because have all this rotation required at this joint
• A synovial membrane lines the capsule and fossae
• Anterior and posterior fat pads are located within the elbow capsule but are extra synovial
• Laterally and medially strengthened by the collateral ligaments (medial + lateral collateral)

Question 5

The elbow joint - ligaments: ulnar collateral ligament (medial)

Answer 5

• Triangular shaped capsular ligament
• 3 bands - anterior, intermediate (transverse), posterior (have 3 bands due to elbow joints large ROM)
• Primary role: limits abduction of distal ulna
• Anterior band: also limits extension
• Posterior: also limits flexion
• Limits valgus deformity occurring from either a medially directed force at distal humerus or a laterally force at the distal forearm

Question 6

The elbow joint - ligaments: radial collateral ligament (lateral)

Answer 6

• Also triangular not as well defined
• Attaches to annular ligament (not radius - as head of radius needs to be able to rotate to give pronation + supination)
• Primary: limits adduction of the forearm
• Anterior: limits extension
• Posterior: limits flexion
• Resists laterally directed force at elbow or medially at forearm = varus deformity

Question 7

Superior (proximal) radioulnar joint

Answer 7

Classification:
- Synovial, uniaxial, pivot
Articular surfaces 
- Radial head 
- Radial notch on ulna
- Annular ligament (80%)

Annular ligament

• Encircles head + neck of radius
• 80% of articular surface sup r/u joint
• Prevents inferior dislocation of radius

Movement

• (functional r/s radius/ulna)
• pronation/supination (radius rotates over ulna)
• Axis of rotation - through centre of radial head (proximal) and head of the ulna (distal)

Question 8

Interosseus membrane

Answer 8

Classification 
- Fibrous - syndesmosis
Function
- Holds radius/ ulna together
- Muscle attachment 
- Passage for blood vessels 
- Transmits forces from the radius to ulna

Question 9

Inferior (distal) radioulnar joint

Answer 9

Classification
- Synovial, uniaxial, pivot

Movement

• pronation/ supination
• note: this radius movt is accompanied by a relative translation of the ulna

Articular surfaces

• Head of ulna
• Ulnar notch of radius
• Intra-articular disc

- Stability at the inferior radioulnar joint is crucial to forearm, wrist stability + grip strength 
Stability maintained by:
- Interosseous membrane
- Intra-articular disc 
- Pronator quadratus

Question 10

Articular disc (Triangular Fibrocartilaginous Complex - TFCC)

Answer 10

• Ulna styloid process to radius

- Held b/w ligaments on both sides that extend from the ulna styloid process to the medial aspect of the distal radius

Question 11

Major bursae of the elbow: subcutaneous, subtendinous, radioulnar, bicipitoradial

Answer 11

• Bursa = a fluid filled sac that reduces friction between a bone and overlying muscles or tendons.
  i) subcutaneous olecranon (between the skin and the olecranon)
  ii) subtendinous olecranon (under distal attachment of the triceps tendon)
  iii) radioulnar (between the extensor digitorum, radiohumeral articulation and the supinator muscle)
  iv) bicipitoradial (between the biceps tendon and the anterior part of the radial tuberosity)
• If compression or friction occurs the bursa will increase its fluid content in response e.g. olecranon bursitis (students elbow)