Biomechanical And Pathological Considerations of the Shoulder Complex

Question 1

Scapulothoracic Rhythm

Answer 1

2 degrees of GH motion for every 1 degree of scapulothoracic motion

Question 2

Phase I of Scapulothoracic Rhythm

Answer 2

(0-90 degrees of GH ABD)
Humerus glides superior within glenoid
Scapula stabilizes the upwardly rotates 30
Clavicle elevates 20-25

Approx 60 of motion at GHJ
60 GH + 30 at scapula = 90 ABD

Question 3

Phase II Scapulohumeral Rhythm

Answer 3

(90-180)
Scapular upward rotation continues additional 30
Posterior rotation of clavicle 35
GH joint ABD an additional 60
120 degrees GHJ+60 at scapula=180

Question 4

Phase III Scapulohumeral Rhythm

Answer 4

Full GH ABD
Glenoid facing upward
Limited muscle activity
Thoracic extension is accessory motion for full shoulder motion

Question 5

Compressive forces

Answer 5

Phase I

Forces that snug the head of the humerus into the glenoid fossa

Question 6

Concept of “concavity compression”

Answer 6

Interrelationship between dynamic stabilizers and articular geometry
The RTC acting in concert to snug the head of the humerus on the glenoid
Subscapularis and infraspinatus

Question 7

Shear forces

Answer 7

Result of when medially directed forces have a slightly superior or inferior component
Greatest occurs at or around 45 degrees of elevation

Question 8

Muscle functions crossing the GHJ

Answer 8

Move the humerus
Provide intra-articular gliding
Maintain opposition of joint surfaces

Provide arthrokinematics with no impaction of the head on the acromion or the coracoacromial ligament

Question 9

Functions of the scapulothoracic complex

Answer 9

Orient the glenoid for optimal humeral contact
Add ROM for the shoulder
Provide a stable base for maneuvering arm

Question 10

Force Couples

Answer 10

Two muscles working in opposite directions of each other that cause rotation

1. Upper trap and levator scapula-elevates and pulls medially
2. Lower trap and serratus anterior-depress and pulls laterally
3. Result=rotation of the scapula

Question 11

Impingement

Answer 11

Decreased subacromial space or area
Involves the “poorly vascularized” supraspinatus muscle
Classified as primary or secondary

Question 12

Primary Impingement

Answer 12

Degenerative aging
Bone spurs on ACJ
Decreased vascularity to RTC
Decreased strength of RTC and scrap stabilizers
Hypomobility-poor flexibility of pec major, minor, posterior capsule

Question 13

Secondary impingement

Answer 13

Stretched capsule due to trauma or stress
Hypermobility (humeral head destabilized within glenoid)
-subluxation
-impingement
-RTC tear

Question 14

Neer’s Stages of Impingement

Answer 14

Edema & hemorrhage
Fibrosis & tendinitis
AC spur & RTC

Question 15

SICK Scapula

Answer 15

Scapula Infera Coracoid dysKinesia

Question 16

Scapular Function

Answer 16

Dynamically positions glenoid allowing efficient glenohumeral motion
Maintains humeral “center of rotation” throughout ROM