Biomechanics Elbow

Question 1

joints that comprise the elbow

Answer 1

humero-ulnar joint
humero-radial joint
proximal radio-ulnar joint
distal radio-ulnar joint

Question 2

most of structural stability of elbow comes from which joint

Answer 2

humero-ulnar

Question 3

humero-ulnar joint

• type of joint
• motions allowed

Answer 3

modified hinge joints

mostly flexion/extension

Question 4

cubital valgus

• other name
• normal range
• excessive value
• cubital varus (other name)

Answer 4

carrying angle
normal = 13 +/- 6
excessive > 20
cubital varus = gunstock deformity

Question 5

ligaments of the elbow

Answer 5

ulnar collateral ligament
-anterior and posterior fibers
radial collateral ligament
lateral ulnar collateral ligament
annular ligament

Question 6

UCL anterior fibers

-function

Answer 6

limit

• valgus
• extension
• flexion

Question 7

UCL posterior fibers

-function

Answer 7

limit

• valgus
• flexion

Question 8

radial collateral ligament

-function

Answer 8

limits

• varus
• external rotation (supination)

Question 9

lateral UCL

-function

Answer 9

limits

• varus
• ER (supination)
• flexion

Question 10

annular ligament

-function

Answer 10

limits

• radial distraction
• ER (supination)

Question 11

what type of force can lead to a UCL rupture

Answer 11

valgus force (force to lateral side of elbow)

Question 12

“Tommy John” repair

-what is repaired

Answer 12

UCL

Question 13

what does ORIF stand for?

Answer 13

open reduction, internal fixation

Question 14

humero-ulnar arthrokinematics

-what is the rule (open chain)

Answer 14

concave on convex

Question 15

humero-radial joint arthrokinematics

• ____ sagittal stability
• provides _____ of resistance against valgus forces
• what moves on what?

Answer 15

minimal sagittal stability
provides 50% of resistance
concave fovea of radius rolls and slides across convex capitulum in flexion/extension

Question 16

interosseus membrane

-function

Answer 16

binds radius and ulna together
stable attachment for muscles
transmist force proximally through upper limb

Question 17

radiocarpal joint stability

Answer 17

when load bearing through the hand occurs, muscles contract that are attached to the radius, causing compressing with contraction
-this adds to the stability of the RC joint

Question 18

pronation/supination of forearm

• occurs at which joints
• hand and wrist connect firmly to _____
• how does pronation occur?

Answer 18

occurs at proximal and distal radio-ulnar joints
hand and wrist connect firmly to radius, not ulna
distal end of radius crosses over fixed ulna for pronation

Question 19

triangular fibrocartilage complex

• function
• components

Answer 19

primary stabilizer of the distal radio-ulnar joint
-holds ulnar head firmly against ulnar notch of radius in pronation/supination
components
-articular disc
-capsular ligaments
-ulnar collateral ligament

Question 20

radio-ulnar arthrokinematics of supination and pronation

Answer 20

distal
-concave ulnar notch of radius rolls and slides over convex ulna
-concave on convex
proximal
-radial head rotates in the annular ligament/radial notch of unla
-primarily spin

Question 21

humero-radial arthrokinematics of supination and pronation

Answer 21

concave fovea of radius “spins” against convex capitulum of humerus

Question 22

elbow flexors

• what are they?
• which has greatest force potential
• which has greatest mechanical advantage

Answer 22

biceps brachii
brachialis
brachioradialis
greatest force potential
-brachialis
-greatest PSCA
greatest mechanical advantage
-brachioradialis
-moment arm

Question 23

at what angle do the following occur for elbow flexion

• maximum elbow torque
• maximum force
• maximum moment arm

Answer 23

torque
-80-100
force
-70-85
moment arm
-80-110 (except brachioradialis)

Question 24

synergistic relationship between biceps brachii and posterior deltoid

Answer 24

simultaneous shoulder extension can increase elbow flexion capability

Question 25

elbow extensor muscles - what are they - which has greatest force potential - which has greatest mechanical advantage

Answer 25

``` triceps -long head -medial head -lateral head anconeus greatest force -LH trices -PCSA greatest mechanical advantage -triceps ```

Question 26

unique function of each of the elbow extensors

Answer 26

anconeus -first to initiate, stays on at low level, assists with elbow stabilization medial head -initiates after anconeus, stays on -workhorse muscle lateral and long heads come on last -reserve muscles for maximal extension force

Question 27

which muscles are the primary elbow stabilizers? | -similar to...

Answer 27

elbow extensors | similar to quadriceps in the knee

Question 28

to pronate/supinate, the muscle must attach...

Answer 28

on both sides of axis of rotation -humerus or ulnar attachment proximally --> radius or hand distally must have an internal momemt arm that produces rotation around pronation/supination axis

Question 29

functional association between forearm pronators/supinators and shoulder IR/ER allows...

Answer 29

nearly 360 degree movement of hand in space

Question 30

forearm supination stronger with shoulder in...

Answer 30

ER

Question 31

when is supination strongest - why - function of triceps during supination

Answer 31

strongest in 90 elbow flexion optimizes biceps brachii triceps co-contract to prevent elbow flexion

Question 32

which are stronger: pronators or supinators

Answer 32

supinators produce 25% more torque | left-hand dominant person has a disadvantage with things such as using a screwdriver