Chapter 6 - Elbow and Forearm complex

Question 1

Elbow joints

Answer 1

1) humero-ulnar joint

2) humeroradial joint

Question 2

forearm joints

Answer 2

1) proximal radio-ulnar joint

2) distal radio-ulnar joint

Question 3

“carrying angle” of the elbow

Answer 3

normal cubitus valgus(elbow medially) = 15 degrees

• excessive cubitus valgus = 30 degrees
• cubitus varus = 0 degrees

Question 4

medial collateral ligament

Answer 4

anterior, posterior, transverse fiber bundles

• anterior fibers = most resistance to valgus force; taut near full extension
• posterior fibers = become taut in extreme flexion

Question 5

Fall on outstretched arm injures which ligament

Answer 5

medial collateral ligament

Question 6

nerve susceptible to injury with valgus stretch

Answer 6

ulnar nerve

Question 7

repetitive, valgus producing forces

Answer 7

pitching baseball, volleyball spike

Question 8

“position of comfort”

Answer 8

80 degrees, capsule most compliant

• ligaments most relaxed
• accomodates swelling and inflammation

Question 9

lateral collateral ligament

Answer 9

resists varus-directed force

- taut in full flexion

Question 10

lack of flexion may be caused by:

Answer 10

• paralysis of flexor muscles
• contracture due to immobilization
• loss of joint integrity from arthritis or fracture

Question 11

lack of extension may be caused by:

Answer 11

• flexion contracture due to immobilization
• spasticity of elbow flexors
• paralysis of triceps
• scarring anterior elbow area
• loss of joint integrity from arthritis or fracture

Question 12

range needed to have full functional ability

Answer 12

30-130 degrees

Question 13

elbow extension requires extensibility:

Answer 13

dermis, flexor muscles(biceps, brachialis), anterior capsule, anterior fibers of MCL

Question 14

elbow flexion requires elongation of:

Answer 14

• posterior capsule
• extensor muscles
• ulnar nerve
• posterior fibers of MCL

Question 15

arthrokinematics of humeroradial joint

Answer 15

• roll and slide(same direction) of concave fovea and convex capitulum

Question 16

function interosseous membrane

Answer 16

dissipates force from radius to ulna to prevent radial fracture

• 80% of compression force through hand transmits through the lateral side of the carpus and the radius
• not aligned to resist distally applied forces on the radius

Question 17

structures preventing “pulled elbow”

Answer 17

• oblique cord
• annular ligament
• brachioradialis

Question 18

necessary AROM at forearm to be functional with most ADL’s

Answer 18

50 degrees in each direction

Question 19

arthrokinematics for supination

Answer 19

• spinning of radial head within fibro-osseous ring of annular ligament/radial notch of ulna
• concave ulnar notch of radius rolls and slides in similar directions on head of ulna

Question 20

arthrokinematics of pronation

Answer 20

• similar to supination

- full pronation exposes articular surface of ulnar head

Question 21

structures preventing supination

Answer 21

• palmar capsular ligament

- pronator teres

Question 22

structures preventing pronation

Answer 22

• dorsal capsular ligament

- biceps on bicipital tuberosity

Question 23

Elbow flexors(biomechanics)

Answer 23

• dominant side shows significantly higher levels for flexion, but not extension, pronation/supination
• flexor torques 70% greater than extension torques
• flexor torques are 20-25% greater with forearm supinated versus pronated(longer moment arm for biceps)
• maximal flexor torque occurs at about 90 degrees of flexion

Question 24

elbow extension

Answer 24

• triceps produces majority of total extensor torque
• anconeus is first to initiate movement
• medial head of triceps is next(workhorse)
• lateral head is active for moderate to high levels of effort
• long head is activated last

Question 25

elbow extensors(biomechanics)

Answer 25

• maximal elbow extension torque at about 90 degrees

- muscle length, not leverage, determines maximal torque in elbow extensors

Question 26

supinator muscles

Answer 26

primary: supinator, biceps(high power - recruited last)
- if biceps contracts, then elbow triceps and posterior deltoid may have to contract to stabilize
- supination torque is greatest around 90 degrees
- supinators produce 25% greater isometric torque than pronators

Question 27

pronator muscles

Answer 27

primary: pronator quadratus, pronator teres
- pronator quadratus = most active and consistently used
- pronator teres = involved with higher power actions