Biomechanics of the Wrist and hand

Question 1

Wrist and hand joint complex

Answer 1

• Distal radioulnar joint (DRUJ)
• Radiocarpal joint
• Midcarpal joint
• Metacarpal-Phalangeal
• Interphalangeal
• = 20 + joints

Question 2

• Radiocarpal joint

Answer 2

• Synovial (condyloid) joint
• Two degrees of freedom:
  p Flexion / extension
  p Abduction (radial deviation) / Adduction (ulnar deviation)
  p Circumduction

Question 3

• Midcarpal joints

Answer 3

• Plane joints
• Small gliding motions
• Increase the range of motion of the radiocarpal joint.

Question 4

Motions of the wrist

Answer 4

• Lot of flexibility

Question 5

Wrist joints

Answer 5

• Distal radio-ulnar joint (DRUJ)
• Facilitate the transmission between the bones.
• Radio-carpal joint
• Flexion/estension, ulnar/radial deviation
• Mid-carpal joint
• Stabilization

Question 6

For the hand to be functional, it requires….

Answer 6

proximal articulations that are both mobile and stable

Question 7

what do we use to access ROM

Answer 7

Goniometry

Question 8

is there more ulnar or radial deviation

Answer 8

• There’s more ulnar deviation

Question 9

Motion of the wrist

Answer 9

1- Flexion, extension
- Proximal row has no tendinous insertions.
- Wrist movement starts at distal row.
- Movement pulls midcarpal ligaments taut and moves proximal row.

Question 10

Proximal carpal movement is changed depending on:

Answer 10

• Tensile force transmits from distal row, compression forces between the radius and the proximal row.

Question 11

Ulnar variance (80% load radius)

Answer 11

• Not everyone has the same angle
• Increase contact = the force can be dispersed over a greater area

Question 12

Negative ulnar variance

Answer 12

2-5mm of ulnar variance:
* 95% of load transmission via radius and 5% through ulna

Question 13

Positive Ulnar Variance

Answer 13

60% of load transmission via radius and 40% via ulna

Question 14

Functional axis of movement

Answer 14

• Dart-throw motion combines all movement of wrist
  “A plane in which wrist functional oblique motion occurs, specifically from radial extension to ulnar flexion.”

Question 15

Moment arm, moment strength, PSCA

Answer 15

• Extensor MA > Flexor
• Flexor PCSA (physical cross-sectional area) (from each muscle) > Extensor
• Flexor moment strength&raquo_space; extensor *determined experimentally

Question 16

Flexor retinaculum

Answer 16

• Prevents bowstringing of flexor tendons
• Maintains carpal arch
• Optimizes flex forces

Question 17

Extensor retinaculum

Answer 17

• Functions as a pulley for the extensor tendons
• Maintains constant moment arm

Question 18

The arches of the hand

Answer 18

• Fixed proximal transverse arch (middle point: capitate bone)
• Mobile distal transverse arch (around the head of the 3rd metacarpal
• Longitudinal arch: connects the two transverse arches

Question 19

Interaction of wrist and hand motions

Answer 19

• Maximal wrist extension: fingers are fully flexed (A)
• Maximal wrist flexion: fingers are fully extended (B)
• Maximal grip power: the wrist is slightly extended and ulnar deviated

Question 20

is the thumb a finger

Answer 20

the growth of the digit of the thumb is similar to the other
- The thumb is a finger

Question 21

Thumb

Answer 21

• 60% of hand function
• Carpometacarpal joint of digit 1 (thumb):
• Articulates with the trapezium
• Synovial: saddle
• Flexion / extension
• Adduction / abduction
• Circumduction
• Opposition

Question 22

• CMC:

Answer 22

saddle joint, flexion/extension, abduction/adduction, circumduction, opposition

Question 23

• IP:

Answer 23

hinge joint, flexion/extension

Question 24

• MCP:

Answer 24

biaxial joint, flexion/extension, abduction/adduction

Question 25

Finger tendon mechanisms

Answer 25

• Intricate and precise system of tendons and sleeves to produce very precise movements

Question 26

Levers:

Answer 26

• Tools used to amplify weak forces of hand