The Biomechanics of the Shoulder

Question 1

Why is the shoulder so important?

Answer 1

The shoulder is the linkage to the hand

Question 2

Name the bony anatomy of the shoulder

Answer 2

Scapula, humerus, clavicle

-joints that link these bones into a functional entity

Question 3

Interdependent linkages 
(Joints of the shoulder)

Answer 3

1. Acromioclavicular joint
2. Sternoclavicular joint
3. Scapulothoracic joint
4. Glenohumeral joint

Question 4

Mobility v Stability

Answer 4

The shoulder is a golf ball resting on a golf tee

• precariously unstable with bony anatomy
• with proper mechanics and timing good results can occur

Question 5

Which bone of the shoulder is most important in rehab?

Answer 5

The scapula is the most important in rehab

Question 6

Static Stability

Answer 6

Bony structures of the true shoulder joint

Question 7

Dynamic Stability

Answer 7

Muscle activity that maintains joint integrity

Question 8

Which joint is the “base of operation” for the scapula? Why?

Answer 8

The sternoclavicular joint.

Only structural attachment of the scapula to the rest of the body?

Question 9

SCJ Movement

Answer 9

Movement of the clavicle at the SCJ produces movement of the scapula
Certain scapular motions must produce motion at the SCJ

Question 10

Name the 3 major ligaments of the SCJ

Answer 10

1. Interclavicular ligament
2. Costoclavicular ligament
3. Sternoclavicular ligament

Question 11

Interclavicular Ligament

Answer 11

Connects clavicle to clavicle spanning the sternum centrally

Checks excessive depression or downward glide of the clavicle

Question 12

Why is the interclavicular ligament crucial?

Answer 12

Protects the brachial plexus and the subclavian artery

Question 13

Costoclavicular ligament

Answer 13

Connects the first rib to the clavicle
Strong ligament that provides substantial stability
Functions to check clavicular elevation and superior glide of the clavicle

Question 14

Sternoclavicular Ligament

Answer 14

Connects clavicle and sternum
Anterior and posterior segments
Checks anterior and posterior movement of the head of the clavicle

Question 15

SC Joint Disk

Answer 15

Fibrocartilaginous disk or meniscus
Located between the superior clavicle, sternum, and first costal cartilage
Diagonally transepts the SC joint space
Maintains mobility and enhances stability by increasing joint congruency and absorbing forces from lateral end of clavicle

Question 16

SC joint

Answer 16

Constitutes only 1% of joint dislocations in the body
Motions: elevation-depression of the clavicle, protraction-retraction of the clavicle, clavicular rotation
(Visualize lateral end movements)

Question 17

SC Motions Described

Answer 17

Elevation-elevation of lateral end results in downward sliding of medial end
Elevation=45 degrees
Depression=15 degrees

Clavicle elevation is associated with elevation and depression of the scapular because of the linkage

Question 18

Shoulder ROM and the SC

Answer 18

During the first 90 degrees of GH elevation, the clavicle elevates 4 degrees for every 10 degrees of GH elevation
Clavicle angularion is negligible after 90 degrees of GH motion

Question 19

ACJ

Answer 19

Primary function: maintain relationship between clavicle and scapula in the early stages of elevation of the UE and to allow the scapula additional range of rotation on thorax

Question 20

3 major ligaments of ACJ

Answer 20

Acromioclavicular
Coracoacromial
Coracoclavicular

Question 21

AC Ligament

Answer 21

Superior and inferior
Assists capsule in stability
Superior fibers reinforced by trap & deltoid muscle fibers
Superior stronger than inferior

Question 22

Coracoacromial ligament

Answer 22

Connects coracoid process to the acromion

Ligament associated with shoulder impingement because of its location

Question 23

Coracoclavicular ligament

Answer 23

Connects clavicle to scapula
Lateral portion=trapezoid
Medial potion=conoid

Question 24

ACJ Stability

Answer 24

Capsule of the AC is inherently weak
Gains Stability from reinforcing ligaments
Joint is susceptible to both trauma and DJD

Question 25

Motion at the ACJ

Answer 25

Articulating surfaces are small and limited in ROM | Clavicle rotation 0-50 degrees in frontal plane

Question 26

Movements of the ACJ

Answer 26

With scapular rotation... the coracoid process is pulled downward the coracoclavicular ligament becomes taut and pulls on the distal clavicle=posterior rotation of the clavicle

Question 27

Angle of Inclination

Answer 27

Humeral head faces medially, superiorly, and posteriorly with respect to shaft of humerus Axis through humeral head and longitudinal axis of the shaft of the humerus forms angle of 130-150 degrees in frontal plane

Question 28

Angle of Torsion

Answer 28

Axis through the humeral head and an axis through the humeral condyles distally forms an angle in the transverse plane of 30 degrees posteriorly aka retrotorsion

Question 29

Functions of glenoid labrum

Answer 29

Attachment for long head of the biceps Makes glenoid deeper Provides attachment for GH ligaments and joint capsule

Question 30

Labrum attachments

Answer 30

Labrum is loosely attached superiorly and firmly attached inferiorly

Question 31

Posterior capsule

Answer 31

Assists in support of GH posteriorly GH area is repositioned on average 7mm anteriorly with active flexion in subjects who suffer from posterior capsule tightness

Question 32

Glenohumeral Capsule

Answer 32

Taut superiorly | Slack anteriorly and inferiorly

Question 33

Open packed v closed packed

Answer 33

Open: 55 ABD, 30 ADD Closed: full ABD and ER

Question 34

3 GH ligaments

Answer 34

1. Superior-prevents anterior and inferior translations of the humeral head with arm at side (0 ABD) 2. Middle-prevents anterior humeral head translation with arm at 0-45 ABD 3. Inferior-provides stability with 3 bands (anterior, axillary, posterior) during ABD beyond 45 degrees or with combined ABD and rotation All tighten with ER and anterior glide

Question 35

Coracohumeral ligament

Answer 35

Originates from coracoid process and blends with superior capsule and the supraspinatus tendon to insert in the greater tubercle Functions to check lateral (ER) rotation of the humerus with arm ADD