Week 3 Biomechanics of Glenohumeral (shoulder) joint

Question 1

angle of inclination 傾角
and angle of torsion 扭轉
of head of humerus

Answer 1

angle of inclination: 130-150 degrees (coronal plane)
angle of torsion: 30 degrees posteriorly (transverse plane)

Question 2

degrees of flexion, extension, abduction and internal/ external rotation of GH movement

Answer 2

flexion: 97-120 degrees
extension: 50 degrees
abduction: large variation of 90-120 degrees
internal/ external rotation:
- in 0 degrees abduction: arc 60 degrees
- in 90 degrees abduction: arc of up to 120 degrees

Question 3

GH joint stability (static)

Answer 3

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

Question 4

GH joint stability (dynamic)

Answer 4

rotator cuff muscles

Question 5

functions of glenoid labrum

Answer 5

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

Question 6

close packed position of GH joint

Answer 6

abduction and external rotation

Question 7

GH joint movement - abduction

Answer 7

humeral head rolls superiorly and slides inferiorly

Question 8

GH joint movement - flexion/ extension

Answer 8

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

Question 9

GH joint movement - internal rotation

Answer 9

humeral head slides posteriorly and rolls anteriorly

Question 10

GH joint movement - external rotation

Answer 10

humeral head slides anteriorly and rolls posteriorly

Question 11

functions of the shoulder complex muscles

Answer 11

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 12

muscles that influence GH joint
trunk –> shoulder girdle
shoulder girdle –> humerus
trunk –> humerus

Answer 12

trunk –> shoulder girdle (scapula)
- trapezius
- serratus anterior
- levator scapulae
- rhomboids
- pectoralis minor

shoulder girdle –> humerus
- GH protectors: supraspinatus, infraspinatus, subscapularis, teres minor
- humeral positioners: deltoid, teres major, coracobrachialis

trunk –> humerus
- pectoralis major
- latissimus dorsi

Question 13

scapular pivoters

Answer 13

• 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 14

glenohumeral protectors

Answer 14

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 15

factors that may contribute to subacromial impingement

Answer 15

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

Question 16

what is the humeral positioners

Answer 16

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

mechanical disadvantage = imparts speed to end of lever (hand)

Question 17

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

Answer 17

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

Question 18

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 18

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 19

what is inferior translation

Answer 19

offsets superior pull of deltoid (force couple) during abduction

Question 20

which three rotator cuff muscles produce an inferior translation

Answer 20

infraspinatus
teres minor
subscapularis

Question 21

propeller muscles

Answer 21

1. pectoralis major (clavicular and sternal head)
   adducts and medially rotates humerus
2. latissimus dorsi
   OKC - extends, adducts and medially rotates of humerus
   CKC - lift the body towards arm

Question 22

what can latissimus dorsi can do

Answer 22

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