Mechanics of the Shoulder (Exam 2)

functions of skeletal joints

• provide mobility to the musculoskeletal system

• process a degree of stability

• different joints have different functions

shoulder joint function

the ball-and-socket joint enables the arm to move in all three planes (triaxial motion)

How is higher level of mobility achieved?

achieved at the expense of reduced stability

• also increases the risk to injuries like partial/complete ligament tears and dislocations

elbow joint function

provides movement mainly in one plane (uniaxial motion)

• more stable and less risk of injuries compared to shoulder joint

extremes cases of increased stability

increased stability is achieved at joint that allows no relative motion between the bones making up the joint

• contacting surface of skull bones

main type of human joints

• gliding joint

• hinge joint

• pivot joint

• ellipsoid joint

• saddle joint

• ball-and-socket joint

classification of joint in the skeletal system

• synarthrodial joint

• amphiarthroidal joint

• diarthrodial joint

  • gliding joint

  • hinge joint

  • pivot joint

  • condyloid

  • saddle joints

  • ball-and-socket

synarthrodial joints

joints in the skull that are formed by two tightly fitting bones

• do NOT allow any relative motion

amphiarthrodial joints

joints between vertebrates

• allow slightly relative motion

diarthrodial joints

joints allow varying degrees of relative motion and have articular activity, ligamentous capsules, synovial membrane, and synovial fluid

• gliding joints

• hinge joints

• pivot joints

• condyloid

• saddle joints

• ball-and-socket

ball-and-socket joint

• shoulder

• hip

saddle joints

carpometacarpal of thumb

condyloid joints

wrist

pivot joints

proximal radioulnar

hinge joints

• elbow

• ankle

gliding joints

vertebral facets

clavicle

deltoid muscles

biceps brachii (long head and short head)

triceps brachii (long head, lateral head, and medial head)

brachialis muscle

scapula

humerus

rhomboid major muscle

rhomboid minor muscle

trapezius muscle

supraspinatus muscle

infraspintaus muscle

teres minor muscle

teres major muscle

acromion

deltopectoral muscle

clavicular part of deltoid muscle (anterior fibers)

look at packet diagram

acromial part of deltoid muscle (central fibers)

clavicular part of pectoralis (major)

sternocostal part of pectoralis major

biceps brachii (short head)

biceps brachii (long head)

abdomial part of pectoralis major

manubrium sterni

body of sternum

xiphoid process

rhomboideus major muscle

latissimus dorsi muscle

deltoid muscle

rotator cuff muscles

• subscapularis

• supraspinatus

• infraspinatus

• teres minor

subscapularis

• largest, strongest and most useful of the 4 rotator cuff muscles

• medial rotation of the shoulder/arm

supraspinatus

• abducts the shoulder first 15 degrees 

  • deltoid and trapezius take after

• vertical abduction of shoulder/arm

infraspinatus

lateral/external rotation of the shoulder/arm

teres minor

lateral/external rotation of the shoulder/arm

vertical abduction of shoulder/arm

• middle deltoid

• supraspinatus

horizontal abduction of shoulder/arm

• posterior deltoid

vertical adduction of shoulder/arm

• pectoralis major (sternocostal head)

• coracobrachialis

• latissimus dorsi

horizontal adduction of shoulder/arm

• pectoralis major (clavicle head)

• pectoralis minor

• anterior deltoid

lateral rotators of shoulder/arm

• infraspinatus

• teres minor

• posterior deltoid

medial lateral rotators of shoulder/arm

• subscapularis

• teres major

• latissimus dorsi

• anterior deltoid

what causes the most injuries in the shoulder/arm?

flexion and abduction

bones of human shoulder

• clavicle

• scapula

• humerus

joints of the shoulder

• shoulder joint (glenohumeral joint)

• shoulder girdle (acromioclavicular joint)

acromicalvicular (AC) joint

plantar type joint between lateral portion of the clavicle and the acromion of the scapula

sternoclavicular (SC) joint

stellar joint between the medial end of the clavicle and the manubrium of the sternum

glenohumeral joint

• ball and socket articulation between the head of humerus and gelnoid cavity

• favors mobility over stability

scapulothoracic joint

• scapula suspended on rib cage by muscles

  • highly mobile

• scapula movements increases range of motion at the shoulder joint

type of joint cartilage

• white cartilage

• labrum

white cartilage

• on the end of bones (articular cartilage)

• allows for bones to glide and move on each other

  • when joint is overused, white cartilage starts to wear out, and joint becomes bumpy and painful and stiff

    • osteoarthritis

labrum

• seen in shoulder

  • different form articular cartilage

• fibrous and rigid than the cartilage on the ends of the ball and socket

• only around socket where it is attached

movements of the shoulder

• flexion

• extension

• abduction (vertical/horizontal)

• adduction

• outward rotation

• inward rotation

rotator cuff

• medical term for a group of muscles and their tendons that stabilize the shoulder

• 4 muscles hold the head of humerus in the glenoid fossa

• bursae provide cushion and protect the joint from injuries

brusae

• two filmy sac-like structures that allow smooth gliding between bone, muscle, and tendon

causes of shoulder dislocation

• weakness of rotator cuff tendons and tendonitis, or trauma

• head of humerus subluxes from glenoid cavity

  • usually when humerus is in abduction or flexion

• occurs in the inferior direction and aspect

  • weakest region of capsule

  • humerus pulled either anterior/posterior to shoulder joint upon which rotator cuff muscles are injured

• arm hangs limp at prominent “step deformity” space between acromion and humeral head

review basic mechanisms of shoulder injuries

humeral fractures

humeral neck fractures

proximal humeral fracture

clavicle fracture

scapula fracture