Biomechanics Exam #2 (The elbow and forearm) Flashcards

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

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

• Mid-to-distal humerus
• Ulna
• Radius

• 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

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

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

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

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

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

• concave on convex
• SLIDE UP + ROLL UP

• concave on convex
• SLIDE UP + ROLL UP

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

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

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

• 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

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

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

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

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

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

Maximal isometric internal torques (greatest to lowest)

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

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*)

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

• Triceps Brachii
• Anconeus

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

• Flexion: anterior deltoid
• Extension: elbow

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

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

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