Week 3 Biomechanics of Glenohumeral (shoulder) joint

Question 1

angle of inclination 傾角 of head of humerus

Answer 1

130-150 degrees (coronal plane)

Question 2

angle of torsion 扭轉 of head of humerus

Answer 2

30 degrees posteriorly (transverse plane)

Question 3

degrees of flexion of GH movement

Answer 3

97-120 degrees

Question 4

degrees of extension of GH movement

Answer 4

50 degrees

Question 5

degrees of abduction of GH movement

Answer 5

large variation 90-120 degrees

Question 6

degrees of internal/ external rotation of GH movement

Answer 6

in 0 abduction: arc 60 degrees
in 90 abduction: arc of up to 120 degrees

Question 7

GH joint stability (static)

Answer 7

– Ligaments (especially superior &
coracohumeral in resting position)
– Capsule
– Glenoid labrum
– Negative intra-articular pressure
– LH biceps tendon
– Orientation of glenoid fossa

Question 8

GH joint stability (dynamic)

Answer 8

rotator cuff muscles

Question 9

glenoid labrum

Answer 9

• enhance stability by increasing the depth of the glenoid fossa by 50%
• attachment site for glenohumeral ligaments

Question 10

close packed position of GH joint

Answer 10

abduction and external rotation

Question 11

GH joint movement - abduction

Answer 11

humeral head rolls superiorly and slides inferiorly

Question 12

GH joint movement - flexion/ extension

Answer 12

humeral head tends to spin about relatively fixed point on the glenoid fossa

Question 13

GH joint movement - internal rotation

Answer 13

humeral head slides posteriorly and rolls anteriorly

Question 14

GH joint movement - external rotation

Answer 14

humeral head slides anteriorly and rolls posteriorly

Question 15

functions of the shoulder complex muscles

Answer 15

pivot and stabilise the scapula 樞轉
protect the GH joint
position the humerus at the GH joint
propel the trunk on the humerus

Question 16

scapular pivoters

Answer 16

• the position of scapula is to allow muscles to develop force and move the upper limb efficiently
• no muscles produces scapular rotation (force couples)

Question 17

glenohumeral protectors

Answer 17

rotator cuff muscles - stabilise GH joint
1. supraspinatus - arm abduction
2. infraspinatus - lateral rotates arm
3. teres minor - lateral rotates arm
4. subscapularis - adducts arm

Question 18

factors that may contribute to subacromial impingement

Answer 18

• scapular position
• humeral position
• anatomical structure of acromion
• muscular imbalance/ control
• pain / inhibition of muscular control
• poor mechanics

Question 19

what is the humeral positioners

肱骨定位器 – muscles

Answer 19

deltoid
- powerful abductor, multipennate muscle
- deltoid activity peaks at 90 degrees abduction
- third class lever, mechanical disadvantage

Question 20

why deltoid is mechanical disadvantage through most of range, but it still suited for shoulder abdcution?

Answer 20

• large physiological cross section
• multipennate fibre arrangement
• greater tuberosity acts as an anatomical pulley to improve moment arm

Question 21

angle of pull (rotary force) of deltoid improves throughout range of shoulder abduction, relies on
三角肌的拉角（旋轉力）在肩部外展的整個範圍內得到改善，依賴…

Answer 21

1. scapular movement and stability
   - upward rotation of scapula maintains the distance between proximal and distal attachments of deltoid; therefore, less active insufficiency of deltoid
2. strong rotator cuff muscles

Question 22

what is inferior translation

Answer 22

offsets superior pull of deltoid (force couple) during abduction

Question 23

which three rotator cuff muscles produce an inferior translation

Answer 23

infraspinatus
teres minor
subscapularis

Question 24

propeller muscles

Answer 24

1. pectoralis major (clavicular and sternal head)
   adducts and medially rotates humerus
2. latissimus dorsi
   OKC - adduction, extension, medial rotation of humerus
   CKC - lfit the body towards arm

Question 25

what can latissimus dorsi can do

Answer 25

• weight bearing through hands (crutches, walking stick)
• assist in compensating for Trendlenburg gait