Kinesiology Ch4 Shoulder Complex

Range of motion - Shoulder ABduction

0-180

Range of motion - Shoulder Flexion

0-180

Range of motion - Shoulder Extension

0-60

Range of motion - Shoulder Medial rotation

0-70

Range of motion - Shoulder Lateral rotation

0-90

Glenoid Labrum:

A fibrocartilaginous ring that encircles the rim of the glenoid fossa. The labrum serves to deepen the socket of the GH joint, nearly doubling the functional depth of the glenoid fossa. The labrum also helps seal the joint, thereby contributing to stability by maintaining a suction effect between the humerus and the glenoid fossa.

Rotator Cuff:

A group of four muscles including the supraspinatus, infraspinatus, subscapularis, and teres minor. These muscles surround the humeral head and actively hold the humeral head against the glenoid fossa. These muscles are discussed at length in a subsequent section.

Capsular Ligaments:

A thin fibrous capsule that includes the superior, middle, and inferior glenohumeral ligaments. This relatively loose capsule attaches between the rim of the glenoid fossa and the anatomic neck of the humerus

Kinematics of the Shoulder-Shoulder Abduction

Abduction involves the 2 : 1 ratio of glenohumeral abduction to scapular upward rotation—the scapulohumeral rhythm. • Abduction of the humerus • Upward rotation of the scapula • Clavicular elevation and posterior rotation

Articular Disc:

Acts as a shock absorber between the clavicle and the sternum; helps improve joint congruency

Coracohumeral Ligament:

Attaches between the coracoid process and the anterior side of the greater tubercle. It helps limit the extremes of external rotation, flexion, and extension, as well as inferior displacement of the humeral head

Coracoacromial Ligament:

Attaches the coracoid process to the acromion process; one of the few ligaments of the body that attaches proximally and distally to the same bone. Along with the acromion, the coracoacromial ligament completes the coracoacromial arch—a functional "roof" that protects the head of the humerus.

Biceps Brachii

Because both heads cross anterior to the medial-lateral axis of the shoulder, this muscle is also an effective shoulder flexor. The proximal tendon of the long head courses over the superior aspect of the humeral head, making it vulnerable to damage caused by shoulder impingement.

Coracobrachialis

Because its line of pull is so close to the GH joint's axis of rotation, it is likely more useful as a stabilizer. Such an action may help fixate the head of the humerus on the glenoid fossa as the shoulder moves through various ranges of motion.

Coracoclavicular Ligament:

Composed of the conoid and trapezoid ligaments. Together, these ligaments help suspend the scapula from the clavicle and prevent dislocation.

Sternoclavicular Ligament:

Contains anterior and posterior fibers that firmly join the clavicle to the manubrium

Axial Rotation

During abduction or flexion of the shoulder, the clavicle rotates posteriorly about its longitudinal axis. As the shoulder is abducted, the coracoclavicular ligament becomes taut and spins the clavicle posteriorly. The clavicle rotates anteriorly, back to its rest position, as the shoulder is extended or adducted.

subacromial bursa and subdeltoid bursa

Excessive superior migration of the humeral head will likely impinge, or pinch one or both of these structures. They often develop bursitis as a result of abnormally large forces in certain shoulder dysfunctions

Costoclavicular Ligament:

Firmly attaches the clavicle to the costal cartilage of the first rib and limits the extremes of all clavicular motion except depression

Subscapularis

It provides anterior stability to the GH joint while also balancing the external rotational pull of the other rotator cuff muscles. This synergistic action enables the rotator cuff as a whole to help hold the humeral head firmly on the glenoid fossa.

Acromioclavicular Ligament:

Joins the clavicle to the acromion; helps to prevent dislocations of the scapula and links motion of the scapula to the clavicle

Upper Trapezius

One primary motion is scapular elevation; however, it also plays an important role in the force-couple that produces scapular upward rotation. In addition, with the scapula and the clavicle fixed, it can perform lateral flexion and contralateral rotation of the cervical spine.

Interclavicular Ligament:

Spans the jugular notch, connecting the superior medial aspects of the clavicles

Latissimus Dorsi

The ability to simultaneously adduct/extend the humerus and downwardly rotate the scapula makes it an excellent choice for activities that incorporate pulling motions such as rowing or a wide-grip pull-up.

Kinematics of the Shoulder-Shoulder Extension

The exact kinematics of this joint varies, depending on the range of motion through which the shoulder is being extended. The following movements occur during a pulling motion, beginning at 90 degrees of shoulder flexion and moving to 10 degrees of extension. • Extension of the humerus • Downward rotation and retraction of the scapula • Depression and retraction of the clavicle

Teres Minor

The inferiorly-medially directed line of pull of the this muscle and the infraspinatus plays an important role in the normal arthrokinematic motion of the GH joint. During flexion or abduction of the shoulder, these muscles actively direct the inferior slide of the humerus to avoid GH joint impingement. The two muscles play an important role in abduction by externally rotating the humerus to ensure that the greater tubercle can clear the acromion.

Subclavius

The line of pull of this muscle is nearly parallel with the clavicle, indicating that it primarily functions as a clavicular stabilizer.

Long Head of the Biceps:

The proximal portion of the tendon wraps around the superior aspect of the humeral head, attaching to the superior glenoid tubercle. This tendon helps provide anterior stability because it acts as a partial extension of the glenoid labrum.

dynamic stabilizers of the GH joint

The rotator cuff muscles surround the humeral head anteriorly, superiorly, and posteriorly, each providing a muscular force that pulls the humeral head toward the glenoid fossa.

Pectoralis Major

The sternal head of the is the only GH joint muscle without an attachment to the scapula or clavicle.

Long Head of the Triceps

The two-joint muscle is often described as an elbow extensor. On the basis of the long head's proximal attachment, however, it is a strong shoulder extensor.

Rhomboids

The wide, flat shape of this muscle group provides firm control of the entire medial border of the scapula. Act along with other muscles helping to prevent unwanted scapular motions. They are active during nearly any pulling activity of the upper extremity.

Kinematics of the Shoulder-Shoulder Flexion

This motion involves the typical scapulohumeral rhythm: a 2 : 1 ratio of glenohumeral flexion and scapulothoracic upward rotation. • Flexion of the humerus • Upward rotation of the scapula • Elevation and posterior rotation of the clavicle

Deltoid (anterior)

This muscle is also strongly activated during pushing activities, such as pushing open a heavy door. It assists with shoulder abduction.

Teres Major

This muscle is sometimes referred to as "latissimus dorsi's little helper" because it performs all the same actions as the latissimus dorsi, except scapular depression.

Infraspinatus

Throwing motions such as pitching a baseball or spiking a volleyball generate huge internal rotation torques that must be decelerated, primarily through eccentric activation of this muscle and the teres minor. Often, one or both of these muscles may become injured or torn during attempts to resist these large forces. This injury is often referred to as a rotator cuff tear.

Serratus Anterior

Weakness of this muscle can significantly decrease the effectiveness of pushing activities. Also, because it is the primary upward rotator of the scapula, weakness of this muscle severely compromises motions involving active flexion or abduction of the shoulder.

reverse action

a muscular action that causes the proximal segment of a joint to move toward the relatively fixed distal segment.

impingement

abnormal and excessive contact between two components of the musculoskeletal system. This term often describes shoulder impingement, a pathologic condition that occurs as the humerus collides with the undersurface of the acromion of the scapula during shoulder abduction.

winging

abnormal condition of the scapula in which the medial border flares away from the rib cage, giving the appearance of a bird's wing. Typically, this is an indication of weakness of the serratus anterior muscle.

force-couple

an action at a joint that occurs when two or more muscles produce forces in different linear directions but produce a torque in the same rotary direction.

muscular substitution

an action performed by muscles other than those that would normally produce a particular action.

subluxation

an incomplete or partial dislocation of a joint or organ

AC joint

articulation between the lateral aspect of the clavicle and the acromion process of the scapula, allows motion in all 3 planes

SC joint

articulation of the medial end of clavicle with sternum

Serratus Anterior

courses between the anterior surface of the scapula and the outer surface of the rib cage. The extensive attachments and line of pull of this muscle make it the most powerful upward rotator and protractor of the scapula.

scapulothoracic joint motions

elevation, depression, protraction, retraction, upward rotation, downward rotation

Middle Trapezius

has a favorable line of pull to perform scapular retraction and often plays an essential role in stabilizing the scapula against strong forces produced by other scapulothoracic muscles such as the serratus anterior—a powerful protractor.

Elevation and Depression of AC joint

is a near-frontal plane movement about a near-anterior-posterior axis of rotation, allowing roughly 45 degrees of clavicular elevation and 10 degrees of depression.

Levator Scapulae

is palpable just superior and medial to the superior angle of the scapula. Painful trigger points often develop within this muscle, typically as a result of strain from poor, slouched posture.

Joint Capsule: Surrounds the entire SC joint;

is reinforced by the anterior and posterior SC joint ligaments

Lower Trapezius

is the largest of the three trapezius muscles. Along with being a prime mover of scapular depression, it is integral to performing both scapular upward rotation and scapular retraction.

downward rotation

motion of the scapula in which the glenoid fossa moves from an upward rotated position to a downward rotated position. This motion occurs naturally as the shoulder is adducted or extended from an elevated position.

upward rotation

motion of the scapula in which the glenoid fossa moves upward. This motion occurs naturally as the shoulder is abducted or flexed.

scapulothoracic joint

not a "true" joint, the junction created by the anterior aspect of the scapula on the posterior thorax

Protraction and Retraction of AC joint

occur in the horizontal plane about a vertical axis of rotation, allowing about 15 to 30 degrees of clavicular motion in either direction.

Supraspinatus

one of the rotator cuff muscles; its position over the humeral head provides important superior stability to the GH joint. It is an important initiator of abduction because its horizontal line of pull is perfectly suited to begin the roll of the humeral head during GH abduction.

Pectoralis Minor

plays a significant role in stabilizing the scapula and neutralizing unwanted motions of the scapula produced by other muscles such as the lower trapezius. With the scapula fixed, it may be used to assist with inspiration by elevating the ribs.

static stability

stabilization of a particular bone or body segment that results in no or very little movement.

dynamic stabilization

stabilization of a particular moving bone or body segment.

scapulohumeral rhythm

the natural ratio or rhythm that exists between the humerus and the scapula during abduction of the shoulder; specifically, for every 2 degrees of glenohumeral abduction, the scapula simultaneously and upwardly rotates 1 degree

Throwing motion

this motion occurs with the shoulder abducted to about 90 degrees. A quick concentric contraction of the external rotators cocks the shoulder and is followed by a concentric contraction of the internal rotators, which generates huge amounts of internal rotational torque.

Primary Glenohumeral Joint Flexors

• Anterior deltoid • Pectoralis major (clavicular head) • Coracobrachialis • Biceps brachii

Kinematics of the Shoulder-Horizontal Abduction

• Horizontal abduction of the humerus • Retraction of the scapula • Retraction of the clavicle

Kinematics of the Shoulder-Horizontal Adduction

• Horizontal adduction of the humerus • Protraction of the scapula • Protraction of the clavicle

Primary Glenohumeral Joint Extensors

• Latissimus dorsi • Teres major • Pectoralis major • Posterior deltoid • Long head of the triceps

Primary Scapular Depressors

• Lower trapezius • Latissimus dorsi • Pectoralis minor • Subclavius

Primary Scapular Retractors

• Rhomboids • Middle trapezius

Primary Scapular Downward Rotators

• Rhomboids • Pectoralis minor

Primary Scapular Upward Rotators

• Serratus anterior • Upper trapezius • Lower trapezius

Joints of the Shoulder Complex

• Sternoclavicular • Scapulothoracic • Acromioclavicular • Glenohumeral

Primary Glenohumeral Joint Abductors

• Supraspinatus • Anterior deltoid • Middle deltoid

Rotator Cuff Muscles

• Supraspinatus • Infraspinatus • Teres minor • Subscapularis

Primary Glenohumeral Joint Adductors

• Teres major • Latissimus dorsi • Pectoralis major

Primary Glenohumeral Internal Rotators

• Teres major • Pectoralis major • Subscapularis • Latissimus dorsi • Anterior deltoid

Primary Glenohumeral External Rotators

• Teres minor • Infraspinatus • Posterior deltoid

Primary Scapular Elevators

• Upper trapezius • Levator scapulae • Rhomboids