• Elbow/forearm complex: 3 bones, 4 joints
  • Elbow:

• humeroulnar & humeroradial joints
  • Flexion & extension => alter the functional length of the UE

• Elbow/forearm complex: 3 bones, 4 joints
  • Forearm

• proximal & distal radioulnar joints
• Supination & pronation
  • allows the position of the hand to change without altering the glenoid humeral joint position

Osteology

• Mid-to-distal humerus
• Ulna
• Radius

Mid-to-distal humerus

Humerus (inferior/bottom view)

Lateral view of trochlear notch

Radius

Ulna

Elbow Arthrology: General Features

• humeroulnar & humeroradial
  • Tight fit between the trochlea notch provides MOST of the elbow/s structural stability
  • small amounts of axial rotation & side-to-side motion

Normal Valgus

• Asymmetry of trochlea causes frontal deviation (colloquially called “carrying angle”; cubitus valgus)
  • 13 +/- 6 degrees; women have about 2deg
    more

humeroulnar & humeroradial joints

Elbow Arthrology: Connective Tissue

• Articular capsule is relatively thin; reinforced anteriorly by oblique
  bands of fibrous tissue
• Collateral ligaments
• Wrist flexor and pronator group

Collateral ligaments

• provide much (passive) stability
  • Medial collateral ligament => anterior, posterior, and transverse fiber bundles
    • Anterior is the stiffest provide the most resistance to force

Wrist flexor & pronator group

• provide much (active) stability
  • Most notably the flexor carpi ulnaris

Elbow Osteokinematics

• Flexion & extension
• PROM:
  • 5 degrees beyond neutral in extension
  • 145 degrees flexion
    • Often noted as (-5-145)
• AROM
  • 0-145

Arthrokinematics: Humeroulnar Joint (bicep flex)

• concave on convex
• SLIDE UP + ROLL UP

Arthrokinematics: Humeroradial Joint (radius and ulna)

Sagital section=

• concave on convex
• SLIDE UP + ROLL UP

The Interosseus Membrane

• central band binding radius and ulnar together
• site for extrinsic muscles of the hand

The Interosseus Membrane: Compression force

1. radiocarpal joint to radius
2. compression force to ulna (pulls on tight of IMem)
3. across elbow at humero-ulnar joint
4. cross elbow toward shoulder

the IOM with holding an suitecase

• distal-directed distracting force through the radius
• oblique cord, angular ligaments, and brachioradialis support load
• distraction slackens central and of IOM

Forearm Arthrology: General Features

Pronation

Forearm Arthrology: Connective Tissue

• proximal radioulnar joint is within the joint capsule of the elbow
  • radial head is held against the ulnar via: the radial notch & the annular ligament
    
    • ~75% is from the ligament, 25% from the bony notch

Forearm Arthrology: Connective Tissue

Distal radioulnar joint

Forearm Osteokinematics

• Pronation & supination
  • “zero” point is the thumbs-up position

Elbow Arthrokinematics (fixed/no moving ulna!)

SUPINATION

• roll + slide in SAME DIRECTION of supination (down or up)

Elbow Arthrokinematics (fixed ulna)!

PRONATION

• roll + slide in SAME DIRECTION of pronation(down or up)
• RADIUS CROSSES

Full Supination when weight is pushing on one hand

1. Radius is fixed // humerus and ulna can move
2. H and U has rotated 80-90* externally => forearm pronation

Muscular Actions

• Elbow flexion
• Biceps Brachii
• Brachialis
• Brachioradialis
• Pronator Teres

Muscular actions: movmentd

Maximal isometric internal torques (greatest to lowest)

1. FLEXION
2. EXTENSION
3. SUPINATION
4. PRONATION

Muscular actions: peak levels

1. Flexor torque vs elbow join angle (=90*)
2. Flexor force vs elbow joint angle (=80*)
3. Flexor moment arm vs. elbow joint angle (100*)

Synergy: Elbow Flexion + Shoulder Extension

• Contracting biceps(front): elbow flexion (90*) and shoulder flexion (45*)
• Pulling arm back: elbow flextion (90*), shoulder extention (45*)

Muscular Action: Elbow Extension

• Triceps Brachii
• Anconeus

**(recheck) Muscular Actions: Elbow extensor torque

• Largest at 90*
• Internal muscular action @largest point = flexor (90*) // = extensor (near full extension)
• muscle length NOT leverage

Extension Synergy: Shoulder Flexion & Elbow Extension

• Flexion: anterior deltoid
• Extension: elbow

Muscular Actions: Supination

1. Supinators
2. Biceps Brachii
3. brachioradialis(always pulls the forearm into neutral)

Muscular actions: Pronation

1. Pronator Teres
2. Pronator Quadratus
3. brachioradialis(always pulls the forearm into neutral)

Muscular Action: Supination and Pronation

Muscular Action: Pronators (2)

1. Pronator teres
   • 2heads // Median nerve runs between(in most people)
   • Highpower
2. Pronator Quadratus
   • Workhorse
   • On for all pronation
   • compresses distal radioulnar joint