Shoulder biomechanics

Question 1

what are the four bones of the shoulder complex

Answer 1

sternum, clavicle humerus and scapula.

Question 2

what is the function of the shoulder complex

Answer 2

provides mobility for arm positioning, mechanical link in the upper limb, enables greatest range of motion in the human body.

Question 3

4 articulations of the shoulder

Answer 3

sternoclavicular joint- connects sternum to clavicle.
Acromioclavicular joint- acromium to clavicle.
glenohumeral joint- ball and socket joint between humerus and glenoid fossa on the scapula.
scapulothoracic articulation- functional joint.

Question 4

which joint is the primary shoulder joint?
why is it inherently unstable?

Answer 4

glenohumeral joint, ball and socket joint with 3 dof.
The humeral head is much larger than the shallow glenoid fossa, relying on soft tissues for stability.

Question 5

what structurews provide stability to the shoulder

Answer 5

ligaments, joint capsule, rotator cuff muscles, labrum.

Question 6

function of rotator cuff

Answer 6

provides dynamic stability and assists in shoulder rotation and movement.

Question 7

role of the deltoid muscle

Answer 7

primary abductor of the arm after the first 50 degrees of motion (assisted by supraspinatus)

Question 8

what is the scapulohumeral rythm

Answer 8

coordinated movement of the scapula and humerus during shoulder elevation. 2:1 ratio, 2 degrees humeral elevation to 1 degree of scapular upward rotation.

Question 9

force couple in the shoulder, adn the estimated weight on the glenohumeral joint at 90 degrees abduction

Answer 9

two equal but opposite forces that generate rotation, such as the deltoid and rotator cuff muscles during arm abduction.
apprx 90 percent of body weight due to joint reaction forces.

Question 10

shoulder pathologies and injuries
name 3 common shoulder injuries

Answer 10

glenohumeral dislocation
acromioclavicular dislocation
rotator cuff tear

Question 11

how does poor posture contribute to shoulder injuries

Answer 11

leads to abnormal biomechanics, causing stress on soft tissues and cartilage, increasng the risk of conditions like rotator cuff tears and osteoarthritis.

Question 12

How does an arm elevation affect muscle fatigue?

Answer 12

Holding the arm at 90 degree flexion or abduction leads to rapid fatigue, especially upper trapezius and supraspinatus muscles.

Question 13

What factor is more important than weight in determining shoulder muscle load?

Answer 13

degree of arm elevation