KIN 301 Chapter 5

glenoid labrum

a cartilaginous ring that surrounds the glenoid fossa just inside its periphery

the shoulder joint (glenohumeral joint) is

a multiaxial ball-and-socket joint classified as enarthrodial

the glenohumeral joint is paired with the shoulder girdle to

accomplish the total shoulder range of motion

the muscles of the shoulder joint are

all innervated by the nerves of the brachial plexus

muscles that originate on the scapula and clavicle and insert on the humerus may be thought of

as muscles intrinsic to the glenohumeral joint

the long head of the triceps brachii

assists in extension and horizontal abduction

the biceps brachii

assists in flexing and horizontally adducting the shoulder

adduction

downward movement of the humerus in the frontal plane medially toward the body from abduction

their point of insertions

enables them to rotate the humerus, an essential movement in this freely movable joint

its stability is

enhanced by the glenoid labrum

muscles originating on the trunk and inserting on the humerus are considered

extrinsic to the glenohumeral joint

GIRD stands for

glenohumeral internal rotation deficit

the biceps brachii and triceps brachii (long head) are also

involved in glenohumeral movements

the shoulder is often injured because of

its anatomical design

horizontal abduction (extension)

movement of the humerus in a horizontal or transverse plane away from the chest

horizontal adduction (flexion)

movement of the humerus in a horizontal or transverse plane toward and across the chest

internal rotation

movement of the humerus in the transverse plane medially around its long axis toward the midline

external rotation

movement of the humerus laterally in the transverse plane around its long axis away from the midline

flexion

movement of the humerus straight anteriorly from any point in the sagittal plane

extension

movement of the humerus straight posteriorly from any point in the sagittal plane, sometimes referred to as hyperextension

the shoulder joint

moves in all planes and is the most movable joint in the body

the price of mobility is

reduced stability

GIRD

represents a difference in internal rotation range of motion between an individual's throwing and nonthrowing shoulders

the scapula, clavicle, and humerus

serve as attachments for most of the muscles of the shoulder joint

the glenohumeral joint is

similar to the hip in its joint; however, the socket provided by the glenoid fossa is much shallower and relatively small in comparison to the rather large humeral head

determining the exact range of movement for the glenohumeral joint is difficult because of

the accompanying shoulder girdle movement

they are small muscles whose tendons cross

the front, top, and rear of the head of the humerus to attach not the lesser and greater tubercles

while the exact number of degrees in one segment compared to another may vary within and between individuals,

the generally accepted ratio is 2 to 1; that is, for every 2 degrees of glenohumeral motion, there is 1 degree of scapula motion

the shoulder joint is also known as

the glenohumeral joint

it is further stabilized by

the glenohumeral ligaments, especially anteriorly and inferiorly

the more stable a joint is,

the less mobile it is

the more mobile a joint is,

the less stable it is

due to the wide range of motion involved in the glenohumeral joint,

the ligaments are quite lax until the extreme ranges of motion are reached

this relative lack of static stability provided by the ligaments emphasizes

the need for optimal dynamic stability to be provided by muscles such as the rotator cuff group

the subscpularis, supraspinatus, infraspinatus, and teres minor muscles make up

the rotator cuff

the only attachment of the shoulder joint to the axial skeleton is via

the scapula and its attachment through the clavicle at the sternoclavicle joint

rotator cuff impingement syndrome occurs when

the tendons of these muscles, particularly the supraspinatus and infraspinatus, become irritated and inflamed as they pass through the subacromial space between the acromion process of the scapula and the head of the humerus

stability is sacrificed

to gain mobility

another frequent injury is

to the rotator cuff

abduction

upward lateral movement of the humerus in the frontal plane out to the side, away from the body

if the shoulder girdle is free to move, then the total range of combined joints is

~170 to 180 degrees of abduction ~170 to 180 degrees of flexion ~140 to 150 degrees of horizontal adduction

if the shoulder girdle is prevented from moving, then the glenohumeral joint movements are generally thought to be in the following ranges:

~90 to 100 degrees of abduction ~0 degrees adduction or 70 degrees anterior of the trunk ~40 to 60 degrees of extension ~90 to 100 degrees of flexion ~70 to 90 degrees of internal and external rotation ~45 degrees of horizontal abduction ~135 degrees of horizontal adduction

shoulder joint muscles - location - superior

~deltoid ~supraspinatus

movements of the shoulder joint (glenohumeral joint)

~flexion ~extension ~abduction ~adduction ~external rotation ~internal rotation ~horizontal abduction (extension) ~horizontal adduction (flexion)

shoulder joint muscles - location - posterior

~latissimus dorsi ~teres major ~infraspinatus ~teres minor

shoulder joint muscles - location -anterior

~pectoralis major ~coracobrachialis ~subscapularis

the rotator cuff group includes

~subscapularis ~supraspinatus ~infraspinatus ~teres minor

scapular landmarks

~supraspinous fossa ~infraspinous fossa ~subscapular fossa ~spine of the scapula ~glenoid cavity ~coracoid process ~acromion process ~inferior angle

the intrinsic muscles include

~the deltoid ~the coracobrachialis ~the teres major ~the rotator cuff group

humeral landmarks

~the head ~greater tubercle ~lesser tubercle ~intertubercular groove ~deltoid tuberosity

extrinsic glenohumeral muscles are

~the latissimus dorsi ~the pectoralis major

a number of factors contribute to its injury rate, including

~the shallowness of the glenoid fossa ~the laxity of the ligamentous structures necessary to accommodate its wide range of motion ~the lack of strength and endurance in the muscles, which are essential in providing dynamic stability to the joint