Topic 2

Question 1

what are the muscles connecting the axial skeleton and the humerus

Answer 1

pectoralis major - sternal head
latissimus dorsi

Question 2

what are the muscles connecting the axial skeleton to the shoulder girdle

Answer 2

trapezius
rhomoidmajor
rhomoid minor
levator scapulae
pectoralis minor
serratus anterior

Question 3

what are the muscles connecting the shoulder girdle and the humerus

Answer 3

pectoralis major - clavicular head
deltoid
coracobrachialis
teres major
teres minor
subscapularis
supraspinatus
infraspinatus
biceps brachii
triceps brachii

Question 4

describe how rotator cuff muscles group provide dynamic stability at the shoulder joint

Answer 4

to provide dynamic stability at the glenohumeral joint, the rotator muscles take up slack in the shoulder joint capsule during movement as well as provide a medial force to the humeral head to accurately position it in the centre of the glenoid fossa during shoulder movement.

Question 5

how do the rotator cuff muscles function in ABDUCTION

Answer 5

mover: deltoid contraction produces ABduction and will cause humeral head to glide superiorly.

synergist: inferior part subscapularus, inferior part of infraspinatus and teres minor cancel rotations and prevents superior glide of humeral head.

medial, inferior force muscles of RCC stabilise.

Question 6

how do the rotator cuff muscles function in upward rotation

specifically the traps and serratus anterior

Answer 6

note - upward rotation accompanies abduction and flexion of shoulder joint. during this the glenoid fossa moves which increases the mobility of the shoulder.

this movement repositions the rotator cuff muscles so that they can provide appropriate stabilising force to the humeral head throughout the range of shoulder movement, and maintain the length-tension relationship.

serratus anterior muscles protract and upwardly rotate scapula.

upper traps elevate and upwardly rotate scapula, middle traps retracts scapula, and lower trapezius depressed and upwardly rotates scapula.

therefore, the movers = upper traps, lower traps and serratus anterior and synergists = upper traps (cancels depression from lower traps), serattus anterior (cancels retraction), lower traps (cancels elevation) and middle traps (cancels protraction from serratus anterior).

Question 7

what is scapulohumeral rhythm

Answer 7

describes the movement relationship between scapula and humerus.

upward rotation and abduction/flexion of humerus occur synchronously - this apparent “rhythm” of movements happens in a reproducible ratio of 2 degrees of glenohumeral to 1 degree of scapulothoracic movement.

Question 8

what is the functional significance of scapulohumeral rhythm

Answer 8

scapulohumeral increases range of movement of the shoulder by allowing the humeral head to roll and glide on a moving glenoid fossa, as the glenoid fossa moves by moving the scapula.

it also maintains muscle at optimal length for effective contraction (such as the deltoid and rotator cuff muscles which increase stability throughout range).

Question 9

what is the purpose of the shoulder girdle

Answer 9

the shoulder girdle increases range of movement at the shoulder joint by changing the position of the glenoid fossa and holding the shoulder away from the trunk (because of how the clavicle acting as a strut).

if there was no girdle then abduction ROM drops from 180 degrees to 120 degrees and flexion drops from 180 to 120 as well.

Question 10

why is the position of the glenoid fossa important

Answer 10

because the head of humerus is 3 x larger than the glenoid fossa articular surface.

Question 11

what provides stability at the glenohumeral joint in pendant position

Answer 11

in pendant position, stability at the shoulder joint is provided by the orientation of gelnoid fossa, tension in the ligaments of shoulder joint and superior capsule.

when the arm is not in pendant position, the orientation of the glenoid fossa is ineffective and tension in the ligaments are reduced. Hence, passive stability is not effective when the arms moves away from anatomical position. therefore dynamic stability is required.

Question 12

what happens if the humeral head was laterally displaced

Answer 12

it would be vulnerable to inferior displacement

Question 13

structures that prevent lateral movement of the humeral head also …

Answer 13

prevent inferior movement of humeral head
and therefore increase stability

Question 14

the scapulothoracic joint

Answer 14

• is not an anatomical joint (because it has no articular surfaces, ligaments or joint capsule) therefore is called a functional joint, which mean sit is heavily involved in contributing to movement.
• the scapular moves on the thoracic cage (ribs), and fascia over the muscles in that area permits gliding and sliding of the scapula.
• major contribution to full ROM at shoulder joint (1/3),

Question 15

describe movements of the scapula and clavicle

Answer 15

during protraction of scapula - clavicle moves posteriorly

during retraction of scapula - clavicle moves anteriorly

during elevation of scapula - clavicle moves superiorly

during depression of scapula - clavicle moves inferiorly.

axial rotation of scapula - clavicle rotates internally and externally.

note - all this movement occurs at acromioclavicular joint.

Question 16

during elevation and depression at sternoclavicular joint

Answer 16

there is large amount of movement laterally and little but of movement medially at this joint.

Question 17

what is the function of the clavicle

Answer 17

acts as strut to hold scapula laterally, increases ROM and holds pectoral girdle.

the crank like shape of the clavicle increase shoulder region mobility.

movements:
- initially scapular upward rotation produces medial clavicle elevation at SC joint.
- tension is costoclavicular ligament pushes the movement laterally
- some elevation at AC joint, but next tension in conoid ligament increases and locks in posterior clavicle
- this causes posterior rotation of clavicle (movement at SC and AC joints).
- this completes final elevation of AC joint to achieve full ROM at shoulder joint.

Question 18

implications of crank -like structure of clavicle

Answer 18

implication = small movement at medial end is amplified into bigger movement at lateral end.

because of bent shape, arc of movement is increased.