Shoulder Complex Biomechanics

Question 1

The scapula lies on a plane _____ to the back and _____ to the clavicle

Answer 1

30º to the back

60º to the clavicle

Question 2

List the possible morphologies of the acromion process

Answer 2

1. Type 1: flat
2. Type 2: curved
3. Type 3: hooked

Question 3

which morphology of the acromion is a good prognostic indicator for conservative management?

Answer 3

Type 1: Flat

Type 3: Hooked → negative prognositic indicator and also greatest correlation w/subacromial impingement syndrome

Question 4

List the ligaments found at the scapalua

Answer 4

1. coracoacromial ligament
2. superior transverse scapular ligament
3. inferior transverse scapular ligament

Question 5

where is the superior/inferior transverse scapular ligament?

Answer 5

superior → completes scapular notch to make foramen

inferior → arches over suprascapular nerve (entering infraspinatus fossa)

Question 6

what is the glenoid labrum?

Answer 6

ring of fibrocartilage attached to the margin of the glenoid cavity

deepens the glenoid cavity for congruency of articular surfaces

outer surface attaches to capsular ligaments

Question 7

describe the relative position of the head of the humerus

Answer 7

faces superiorly, medially, and posterioly

angle of inclination = 135º

angle of retroversion = 30º

Question 8

what structures stablize the glenohumeral joint?

Answer 8

1. Joint capsule
2. coraco-humeral ligament
3. 3 bands of GH ligament (S/M/I)a
4. rotator cuff muscles

Question 9

where is the weakest portion of the glenohumerual capsule?

Answer 9

Z spread over the anterior aspect of the capsule between the bands of the glenohumeral ligament

Question 10

when are the 3 GH ligaments taut?

Answer 10

during ER

slackened during IR

Question 11

what is the quadrilateral space?

Answer 11

formed by teres major, teres minor, long head of triceps, and surgical neck of humerus

axillary nerve and posterior circumflex humeral artery pass through from anterior to posterior

Question 12

what movements close the quadrilateral space?

Answer 12

Ext, ABD, and ER

Question 13

what is the rotator cuff interval?

Answer 13

a triangular portion of the GH capsule that lies between the supraspinatus and subscapularis tendons

reinforced by S GH and coracohumeral ligaments

Question 14

how would an adhesion at the rotator cuff interval impact the humerus?

Answer 14

it will cause anterior seating of humeral head

pulls the humeral head forward relative to the glenoid

we see this in adhesive capsulitis

Question 15

what is the biceps pulley?

Answer 15

a tendo-ligamentous sling formed by the:

• S GH ligament
• Coracohumeral ligament
• distal attachement of the subscapularis tendon

it stabilizes the long head of the biceps in the biciptal groove and is located at the rotator cuff interval

Question 16

what is the primary stabilizer of the GH joint?

Answer 16

rotator cuff muscles:

infraspinatus

supraspinatus,

teres minor

subscapularis

Question 17

list the kinematic motions of the scapula involved in elevation of the shoulder complex and the muscles that preform them

Answer 17

1. upward rotation = upper trap, lower trap, serratus anterior
2. posterior tipping = serratus anterior
3. internal rotation

Question 18

shoulder abduction can be broken down into how many phases?

Answer 18

3

Question 19

what occurs during phase 1 of shoulder abduction?

Answer 19

0-60º

deltoid and supraspinatus working

“locking” at 90º from greater tuberosity impacting superior margin of glenoid

lateral rotation and flexion of the humerus to delay lock

Question 20

what occurs during phase 2 of shoulder abduction?

Answer 20

60-120º

60º rotation of scapula to orient glenoid superior and anterior, axial rotation of SC and AC joints

traps (upper and lower) and SA acting here

checked by Lats and pec major

Question 21

what occurs during phase 3 of shoulder abduction?

Answer 21

120-180º

lateral flexion of T-spine

deltoid, supraspinatus, inferior traps, SA elevate UE

Question 22

what occurs during phase 1 of shoulder flexion?

Answer 22

0-50/60º

anterior clavicular fibers of deltoid, coracobrachialis, and superior clavicular fibers of the pec major initaite shoulder flexion

Question 23

what checks/opposes the initial shoulder flexion occuring in phase 1?

Answer 23

tension from the teres major/minor, infraspinatus, and coracohumeral ligament

Question 24

what occurs during phase 2 of shoulder flexion?

Answer 24

60-120º

60º rotation of scapula to orient glenoid superior and anterior, axial rotation of SC and AC joints

traps and SA acting

checked/opposed by lats and inferior pec major

Question 25

what occurs during phase 3 of shoulder flexion?

Answer 25

120-180º

Deltoid, supraspinatus, inferior traps, SA elevate UE

Question 26

List the nerves that go to the shoulder complex

Answer 26

1. dorsal scapular
2. long thoracic
3. nerve to subclavius
4. suprascapular
5. lateral and medial pectoral
6. upper subscapular
7. lower subscapular
8. thoracodorsal
9. axillary
10. radial
11. posterior interosseous
12. musculocutaneous
13. median
14. anterior interosseous
15. ulnar