Elbow Complex Biomechanics

Question 1

Proximal Radioulnar Joint

Answer 1

Head of radius in radial notch of ulna

Question 2

Distal Radioulnar Joint

Answer 2

Head of ulna in ulnar notch of radius; TFC is articular disc

Question 3

Proximal Elbow complex

Answer 3

Hinge joint, uniaxial diarthrodial, 1 DF

Question 4

Superior and Inferior RU joint

Answer 4

Pivot Joint, uniaxial diarthrodial, 1 DF

Question 5

Elbow joint capsule

Answer 5

Large, lose, weak anterior and posterior

Cross contamination of infections possible at 3 joints

Question 6

MCL

Answer 6

Anterior, Posterior, and Oblique bands
Anterior protects valgus best at 20-120 flexion
Oblique helps ulnar nn and anchors ant/post bands

Question 7

LCL

Answer 7

Resists varus and distractive forces

Weaker than medial

Question 8

Annular Ligament

Answer 8

Stabilizes head of radius to ulna

Very strong

Question 9

Interosseous membrane

Answer 9

Fibers in all directions for strength

Question 10

Humeroulnar joint kinematics

Answer 10

Concave on convex

Same glides and rolls

Question 11

Humeroradial joint kinematics

Answer 11

Concave on convex

Same glides and rolls

Question 12

Proximal Radioulnar joint Kinematics

Answer 12

Radial Head longer A-P when supinated
Radial Head longer M-L when pronated
Spins on capitulum in relation to radial groove

Question 13

Distal Radioulnar joint Kinematics

Answer 13

Concave radius on convex ulna
Anterior roll and glide pronation
Posterior roll and glide supination

Question 14

Axis of motion at elbow

Answer 14

Carrying angle
5-15 Degrees
Cubital valgus when >15
Cubital Varus when <5

Question 15

Carrying angle disappears when…

Answer 15

Pronation combines with full elbow extension/flexion

Due to position of the lever

Question 16

Open Pack position

Answer 16

Joint capsule and ligaments have greatest laxity

Greatest amount of accessory mobility present

Question 17

Closed Pack position

Answer 17

Joint capsule and ligaments are most taut

Most often position of greatest joint congruency

Question 18

Extension ROM

Answer 18

0 degrees normal
May have 5-10 degrees
Hard end feel
Humeroulnar closed pack
Humeroradial open pack

Question 19

Flexion ROM

Answer 19

135-145 AROM
150-160 PROM
Soft/Hard endfeel
Humeroulnar joint closed pack at 70 degrees
Humeroradial joint closed pack at 90 degrees

Question 20

Active Insufficiency

Answer 20

Agonist muscles too short or too long to produce effective tension

Question 21

Passive insufficiency

Answer 21

Antagonist Muscle is on stretch and is too short to allow further passive ROM

Question 22

Spurt Muscle

Answer 22

Mobility muscle
Increased rotary component and angle of pull
Proximal insertion

Question 23

Shunt Muscle

Answer 23

Decreased rotary component, decreased angle of pull
Increased compressive force
Distal insertion

Question 24

Biceps

Answer 24

Spurt muscle

MA greatest between 80-100

Question 25

Brachioradialis

Answer 25

Shunt muscle | MA greatest between 100-110

Question 26

Brachialis

Answer 26

Spurt muscle MA greatest at 100 Work horse muscle

Question 27

Triceps

Answer 27

Medial head is work horse | Synergistically w/ biceps during resistive forearm supinatoin

Question 28

Anconeus

Answer 28

Initiates elbow extension Active w/ forced finger flexion and extension Draws capsule out to prevent impingement

Question 29

Pronation ROM

Answer 29

85 degrees

Question 30

Supination ROM

Answer 30

90 degrees

Question 31

Proximal RU joint open pack position

Answer 31

35 supination, 70 elbow flexion

Question 32

Proximal RU joint closed pack position

Answer 32

5 supination, extension | good for stabilization

Question 33

Lateral Epicondylitis

Answer 33

Repetitive use, primarily ECRB | Tensile stress leads to microtears

Question 34

Medial Epicondylitis

Answer 34

Repetitive use, primarily pronater teres, FCR, FCU

Question 35

Nursemaids elbow

Answer 35

Longitudinal traction force | Radial head extracted from annular ligament then pinches it

Question 36

Medial Collateral Ligament Sprain

Answer 36

Increased tensile stress leads to increased carrying angle Increased compression of radial head on capitulum Avascular necrosis when prolonged