Glenohumeral Joint

teres minor

Origin Posteriorly on the upper and middle aspect of the lateral border of the scapula Insertion Posteriorly on the greater tubercle of the humerus Action External rotation of the glenohumeral joint Horizontal abduction of the glenohumeral joint Extension of the glenohumeral joint Stabilization of the humeral head in the glenoid fossa Application, strengthening, and flexibility The teres minor functions very similarly to the infraspinatus in providing dynamic posterior stability to the glenohumeral joint. Both of these muscles perform the same actions together. The teres minor is strengthened with the same exercises that are used in strengthening the infraspinatus. The teres minor is stretched similarly to the infraspinatus by internally rotating the shoulder while moving into extreme horizontal adduction.

What does the acronym SITS refer to?

The acronym SITS may be used in learning the names of the supraspinatus, infraspinatus, teres minor, and subscapularis.

Which muscle of the rotator cuff is most often injured?

The supraspinatus is the most often injured rotator cuff muscle. Acute severe injuries may occur with trauma to the shoulder. However, mild to moderate strains or tears often occur with athletic activity, particularly if the activity involves repetitious overhead movements, such as throwing or swimming. Injury or weakness in the supraspinatus may be detected when the athlete attempts to substitute the scapula elevators and upward rotators to obtain humeral abduction. An inability to smoothly abduct the arm against resistance is indicative of possible rotator cuff injury.

9. What are the landmarks of the proximal humerus? a. What are their functions? b. Where are they located?

head greater tubercle lesser tubercle intertubercular groove deltoid tuberosity

b. What is the typical ranges of motion for the glenohumeral joint actions?

90 to 100 degrees of abduction, 0 degrees adduction (prevented by the trunk) or 75 degrees anterior to 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, and 135 degrees of horizontal adduction. If the shoulder girdle is free to move, then the total range of the combined joints is 170 to 180 degrees of abduction, 170 to 180 degrees of flexion, and 140 to 150 degrees of horizontal adduction.

13. Does the glenohumeral joint have more stability or mobility? Why?

Because the shoulder joint has such a wide range of motion in so many different planes, it also has a significant amount of laxity, which often results in instability problems such as rotator cuff impingement, subluxations, and dislocations. The price of mobility is reduced stability. The concept that the more mobile a joint is, the less stable it is and that the more stable it is, the less mobile it is applies generally throughout the body, but particularly in the shoulder joint.

11. In which planes of motion and about which axes of rotation can the glenohumeral joint move?a. Which glenohumeral movements correspond to which planes/axes of motion?

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 Abduction: Upward lateral movement of the humerus in the frontal plane out to the side, away from the body Adduction: Downward movement of the humerus in the frontal plane medially toward the body from abduction External rotation: Movement of the humerus laterally in the transverse plane around its long axis away from the midline Internal rotation: Movement of the humerus in the transverse plane medially around its long axis toward the midline 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 Diagonal abduction: Movement of the humerus in a diagonal plane away from the midline of the body Diagonal adduction: Movement of the humerus in a diagonal plane toward the midline of the body

15. What is GIRD? What does it affect? Who does it commonly affect?

In recent years the phenomenon of glenohumeral internal rotation deficit, or GIRD, has received attention. GIRD represents a difference in internal rotation range of motion between an individual's throwing and nonthrowing shoulders. Studies have demonstrated that overhead athletes who had a GIRD of greater than 20% had a higher risk of injury than those who did not. Appropriate stretching exercises may be used to regain the amount of internal rotation necessary to improve performance and reduce the likelihood of injury.

14. What structures help to stabilize the glenohumeral joint and keep the humeral head in the glenoid fossa?

Its stability is enhanced slightly by the glenoid labrum (see Fig. 5.5), a cartilaginous ring that surrounds the glenoid fossa just inside its periphery. It is further stabilized by the glenohumeral ligaments, especially anteriorly and inferiorly. The anterior glenohumeral ligaments become taut as external rotation, extension, abduction, and horizontal abduction occur, whereas the very thin posterior capsular ligaments become taut in internal rotation, flexion, and horizontal adduction (See Table 5.2). In recent years the importance of the inferior glenohumeral ligament in providing both anterior and posterior stability has come to light (Figs. 5.3 and 5.4). It is, however, important to note that, 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. Stability is sacrificed to gain mobility.

Deltoid

Origin Anterior fibers: anterior lateral third of the clavicle Middle fibers: lateral aspect of the acromion Posterior fibers: inferior edge of the spine of the scapula Insertion Deltoid tuberosity on the lateral humerus Action Anterior fibers: abduction, flexion, horizontal adduction, and internal rotation of the glenohumeral joint Middle fibers: abduction and horizontal abduction of the glenohumeral joint Posterior fibers: abduction, extension, horizontal abduction, and external rotation of the glenohumeral joint Application, strengthening, and flexibility The deltoid muscle is used in any lifting movement. The trapezius muscle stabilizes the scapula as the deltoid pulls on the humerus. The anterior fibers of the deltoid muscle flex and internally rotate the humerus. The posterior fibers extend and externally rotate the humerus. The anterior fibers also horizontally adduct the humerus, while the posterior fibers horizontally abduct it. Any movement of the humerus on the scapula will involve part or all of the deltoid muscle. Lifting the humerus from the side to the position of abduction is a typical action of the deltoid. Sidearm dumbbell raises are excellent for strengthening the deltoid, especially the middle fibers. By abducting the arm in a slightly horizontally adducted (30 degrees) position, the anterior deltoid fibers can be emphasized. The posterior fibers can be strengthened better by abducting the arm in a slightly horizontally abducted (30 degrees) position. See Appendix 2 for more commonly used exercises for the deltoid and other muscles in this chapter. Stretching the deltoid requires varying positions, depending on the fibers to be stretched. The anterior deltoid is stretched by taking the humerus into extreme horizontal abduction or by extreme extension and adduction. The middle deltoid is stretched by taking the humerus into extreme adduction behind the back. Extreme horizontal adduction stretches the posterior deltoid.

Coracobrachialis

Origin Coracoid process of the scapula Insertion Middle of the medial border of the humeral shaft Action Flexion of the glenohumeral joint Adduction of the glenohumeral joint Horizontal adduction of the glenohumeral joint Application, strengthening, and flexibility The coracobrachialis is not a powerful muscle, but it does assist in flexion and adduction and is most functional in moving the arm horizontally toward and across the chest. It is best strengthened by horizontally adducting the arm against resistance, as in bench pressing. It may also be strengthened by performing lat pulls (defined on p. 134). The coracobrachialis is best stretched in extreme horizontal abduction, although extreme extension also stretches this muscle.

Subscapularis muscle

Origin Entire anterior surface of the subscapular fossa Insertion Lesser tubercle of the humerus Action Internal rotation of the glenohumeral joint Adduction of the glenohumeral joint Extension of the glenohumeral joint Stabilization of the humeral head in the glenoid fossa Application, strengthening, and flexibility The subscapularis muscle, another rotator cuff muscle, holds the head of the humerus in the glenoid fossa from in front and below. It acts with the latissimus dorsi and teres major muscles in its typical movement but is less powerful in its action because of its proximity to the joint. The muscle also requires the help of the rhomboid in stabilizing the scapula to make it effective in the movements described. The subscapularis is relatively hidden behind the rib cage in its location on the anterior aspect of the scapula in the subscapular fossa. It may be strengthened with exercises similar to those used for the latissimus dorsi and teres major, such as rope climbing and lat pulls. A specific exercise for its development is done by internally rotating the arm against resistance in the beside-the-body position at 0 degrees of glenohumeral abduction. External rotation with the arm adducted by the side stretches the subscapularis.

Supraspinatus muscle

Origin Medial two-thirds of the supraspinous fossa Insertion Superiorly on the greater tubercle of the humerus Action Abduction of the glenohumeral joint Stabilization of the humeral head in the glenoid fossa Application, strengthening, and flexibility The supraspinatus muscle holds the head of the humerus in the glenoid fossa. In throwing movements, it provides important dynamic stability by maintaining the proper relationship between the humeral head and the glenoid fossa. In the cocking phase of throwing, there is a tendency for the humeral head to subluxate anteriorly. In the follow-through phase, the humeral head tends to move posteriorly. The supraspinatus, along with the other rotator cuff muscles, must have excellent strength and endurance to prevent abnormal and excessive movement of the humeral head in the fossa. The supraspinatus is the most often injured rotator cuff muscle. Acute severe injuries may occur with trauma to the shoulder. However, mild to moderate strains or tears often occur with athletic activity, particularly if the activity involves repetitious overhead movements, such as throwing or swimming. Injury or weakness in the supraspinatus may be detected when the athlete attempts to substitute the scapula elevators and upward rotators to obtain humeral abduction. An inability to smoothly abduct the arm against resistance is indicative of possible rotator cuff injury. The supraspinatus muscle may be called into play whenever the middle fibers of the deltoid muscle are used. A "full-can exercise" may be used to emphasize supraspinatus action. This is performed by placing the arm in thumbs-up position, followed by abducting the arm to 90 degrees in a 30- to 45-degree horizontally adducted position (scaption), as if one were holding a full can. Adducting the arm behind the back with the shoulder internally rotated and extended stretches the supraspinatus.

Lattisumus Dorsi

Origin Posterior crest of the ilium, back of the sacrum and spinous processes of the lumbar and lower six thoracic vertebrae (T6-T12); slips from the lower three ribs Insertion Medial lip of the intertubercular groove of the humerus, just anterior to the insertion of the teres major Action Adduction of the glenohumeral joint Extension of the glenohumeral joint Internal rotation of the glenohumeral joint Horizontal abduction of the glenohumeral joint Application, strengthening, and flexibility Latissimus dorsi means broadest muscle of the back. This muscle, along with the teres major, forms the posterior axillary fold (see Fig. 5.17). It has a strong action in adduction, extension, and internal rotation of the humerus. Due to the upward rotation of the scapula that accompanies glenohumeral abduction, the latissimus effectively downwardly rotates the scapula by way of its action in pulling the entire shoulder girdle downward in active glenohumeral adduction. It is one of the most important extensor muscles of the humerus and contracts powerfully in chinning. The latissimus dorsi is assisted in all its actions by the teres major and is sometimes referred to as the swimmer's muscle because of its function in pulling the body forward in the water during internal rotation, adduction, and extension. Development of this muscle contributes significantly to what is known as a "swimmer's build." Exercises in which the arms are pulled down bring the latissimus dorsi muscle into powerful contraction. Chinning, rope climbing, and other uprise movements on the horizontal bar are good examples. In barbell exercises, the basic rowing and pullover exercises are good for developing the "lats." Pulling the bar of an overhead pulley system down toward the shoulders, known as "lat pulls," is a common exercise for this muscle. The latissimus dorsi is stretched with the teres major when the shoulder is externally rotated while in a 90-degree abducted position. This stretch may be accentuated further by abducting the shoulder fully while maintaining external rotation and then laterally flexing and rotating the trunk to the opposite side.

Infraspinatus muscle

Origin Posterior surface of scapula below spine Insertion Greater tubercle on posterior side of the humerus Action External rotation of the glenohumeral joint Horizontal abduction of the glenohumeral joint Extension of the glenohumeral joint Stabilization of the humeral head in the glenoid fossa Application, strengthening, and flexibility The infraspinatus and teres minor muscles are effective when the rhomboid muscles stabilize the scapula. When the humerus is rotated outward, the rhomboid muscles flatten the scapula to the back and fixate it so that the humerus may be rotated. An appropriate amount of strength and endurance is critical in both the infraspinatus and teres minor as they are called upon eccentrically to slow down the arm from high velocity internal rotation activities such as baseball pitching and serving in tennis. The infraspinatus is vital to maintaining the posterior stability of the glenohumeral joint. It is the most powerful of the external rotators and is the second most commonly injured rotator cuff muscle. Both the infraspinatus and the teres minor can best be strengthened by externally rotating the arm against resistance in the 15- to 20-degree abducted position and the 90-degree abducted position. Stretching of the infraspinatus is accomplished with internal rotation and extreme horizontal adduction.

teres major

Origin Posteriorly on the inferior third of the lateral border of the scapula and just superior to the inferior angle Insertion Medial lip of the intertubercular groove of the humerus just posterior to the insertion of the latissimus dorsi Action Extension of the glenohumeral joint, particularly from the flexed position to the posteriorly extended position Internal rotation of the glenohumeral joint Adduction of the glenohumeral joint, particularly from the abducted position down to the side and toward the midline of the body Application, strengthening, and flexibility The teres major muscle is effective only when the rhomboid muscles stabilize the scapula or move the scapula in downward rotation. Otherwise, the scapula would move forward to meet the arm. This muscle works effectively with the latissimus dorsi. It assists the latissimus dorsi, pectoralis major, and subscapularis in adducting, internally rotating, and extending the humerus. It is said to be the latissimus dorsi's "little helper." It may be strengthened by lat pulls, rope climbing, and internal rotation exercises against resistance. Externally rotating the shoulder in a 90-degree abducted position stretches the teres major.

pectoralis major

Origin Upper fibers (clavicular head): medial half of the anterior surface of the clavicle Lower fibers (sternal head): anterior surface of the costal cartilages of the first six ribs, and adjacent portion of the sternum Insertion Flat tendon 2 or 3 inches wide to the lateral lip of the intertubercular groove of the humerus Action Upper fibers (clavicular head): internal rotation, horizontal adduction, flexion up to about 60 degrees, abduction (once the arm is abducted 90 degrees, the upper fibers assist in further abduction), and adduction (with the arm below 90 degrees of abduction) of the glenohumeral joint Lower fibers (sternal head): internal rotation, horizontal adduction, and adduction and extension of the glenohumeral joint from a flexed position to the anatomical position Application, strengthening, and flexibility The anterior axillary fold is formed primarily by the pectoralis major (Fig. 5.17). It aids the serratus anterior muscle in drawing the scapula forward as it moves the humerus in flexion and internal rotation. Even though the pectoralis major is not attached to the scapula, it is effective in this scapula protraction because of its anterior pull on the humerus, which joins to the scapula at the glenohumeral joint. Typical action is shown in throwing a baseball. As the glenohumeral joint is flexed, the humerus is internally rotated and the scapula is drawn forward with upward rotation. It also works as a helper of the latissimus dorsi muscle when extending and adducting the humerus from a raised position.

10. What type of joint is the glenohumeral joint?a. How does that affect its function?

The shoulder joint, specifically known as the glenohumeral joint, is a multiaxial ball-and-socket joint classified as enarthrodial (see Fig. 5.1). As such, it moves in all planes and is the most movable joint in the body. It is similar to the hip in its joint classification; however, the socket provided by the glenoid fossa is much shallower and relatively small in comparison to the rather large humeral head. Its stability is enhanced slightly by the glenoid labrum (see Fig. 5.5), a cartilaginous ring that surrounds the glenoid fossa just inside its periphery. It is further stabilized by the glenohumeral ligaments, especially anteriorly and inferiorly. The anterior glenohumeral ligaments become taut as external rotation, extension, abduction, and horizontal abduction occur, whereas the very thin posterior capsular ligaments become taut in internal rotation, flexion, and horizontal adduction

12. What is Scapulohumeral Rhythm and how does it related to the shoulder girdle? a. What glenohumeral joint motions correspond with the shoulder girdle motions?

for every 2 degrees of shoulder movement, the scapula rotates 1 degree shoulder joint abduction: shoulder girdle elevation and upward rotation shoulder joint adduction: shoulder girdle depression and downward roation shoulder joint flexion: shoulder girdle elevation and upward rotation shoulder joint extenstion: shoulder girdle depression and downward rotation Shoulder joint internal rotation: shoulder girdle protration shoulder joint external rotation: shoulder girdle retraction

What bones form the glenohumeral joint?

scapula and humerus