Shoulder 29. December. 2012 Thursday



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CLINICAL NOTES-SHOULDER

Testing the deltoid muscle

To test the deltoid (or the function of the axillary nerve that supplies it), the arm is abducted, starting from approximately 15°, against resistance. If acting normally, the deltoid can easily be seen and palpated. The influence of gravity is avoided when the person is supine.

Quadrangular Space Syndrome

Quadrilateral space syndrome is a clinical syndrome resulting from compression of the axillary nerve and posterior circumflex humeral artery in the quadrilateral space. The quadrilateral space is an anatomic space in the upper arm bounded by the long head of the triceps, the teres minor and teres major muscles, and the cortex of the humerus. The passage of the axillary nerve backward from the axilla through the quadrangular space makes it particularly vulnerable here to downward displacement of the humeral head in shoulder dislocations or fractures of the surgical neck of the humerus. Paralysis of the deltoid and teres minor muscles results. The cutaneous branches of the axillary nerve, including the upper lateral cutaneous nerve of the arm, are functionless, and consequently there is a loss of skin sensation over the lower half of the deltoid muscle.



Rupture of the Supraspinatus Tendon

In advanced cases of rotator cuff tendinitis, the necrotic supraspinatus tendon can become calcified or rupture. Rupture of the tendon seriously interferes with the normal abduction movement of the shoulder joint. The main function of the supraspinatus muscle is to hold the head of the humerus in the glenoid fossa at

the commencement of abduction. The patient with a ruptured supraspinatus tendon is unable to initiate abduction of the arm. However, if the arm is passively assisted for the first 15° of abduction, the deltoid can then take over and complete the movement to a right angle.

Rotator Cuff Tendinitis

The rotator cuff, consisting of the tendons of the subscapularis,supraspinatus, infraspinatus, and teres minor muscles, which are fused to the underlying capsule of the shoulder joint, plays an important role in stabilizing the shoulder joint. Lesions of the cuff are a common cause of pain in the shoulder region. Excessive overhead activity of the upper limb may be the cause of tendinitis, although many cases appear spontaneously. During abduction of the shoulder joint, the supraspinatus tendon is exposed to friction against the acromion. Under normal conditions, the amount of friction is reduced to a minimum by the large subacromial bursa, which extends laterally beneath the deltoid. Degenerative changes in the bursa are followed by degenerative

changes in the underlying supraspinatus tendon,and these may extend into the other tendons of the rotator

cuff. Clinically, the condition is known as subacromial bursitis, supraspinatus tendinitis, or pericapsulitis. It is characterized by the presence of a spasm of pain in the middle range of abduction, when the diseased area impinges on the acromion.



Movements of the shoulder girdle

The movements of the shoulder joint itself cannot be divorced from those of the whole shoulder girdle. Even if the shoulder joint is fused, a wide range of movement is still possible by elevation, depression, rotation and protraction of the scapula, leverage occuring at the sternoclavicular joint, the pivot being the costoclavicular ligament.

Abduction of the shoulder is initiated by the supraspinatus; the deltoid can then abduct to 90 degrees. Further movement to 180 degrees (elevation) is brought about by rotation of the scapula upwards by the trapezius and serratus anterior. Shoulder and shoulder girdle movements combine into one smooth action. As soon as abduction commences at the shoulder joint, so the rotation of the scapula begins. Movements of the scapula occur with reciprocal movements at the sternoclavicular joint.

Of the rotator cuff musles, the supraspinatus is of the greatest practical importance. It passes over the apex of the shoulder beneath the acromion process and coracoacromial ligament, from which it is separated by the subacromial bursa. This bursa is continued beneath the deltoid as the subdeltoid bursa, forming, together, the largest bursa in the body.

The supraspinatus initiates the abduction of humerus on the scapula; if the tendon is torn as a result of injury, active initation of abduction becomes impossible and the patient has to develop the trick movement of tilting his body towards the injured side so that gravity passively swings the arm from his trunk. Once this occurs, the deltoid and the scapular rotators can then come into play.
Principal muscles acting on the shoulder joint


Abductors

Supraspinatus

Deltoid

Adductors

Pectoralis major

Lattisimus dorsi

Extensors

Teres major

Lattisimus dorsi

Deltoid (posterior fibres)



Flexors

Pectorali major

Coracobrachialis

Deltoid (anterior fibres)



Medial rotators

Pecroralis major

Lattisimus dorsi

Teres major

Deltoid (anterior fibres)

Subscapularis



Lateral rotators

Infraspinatus

Teres minor

Deltoid (posterior fibres)




Quadrangular space syndrome

Hypertrophy of the quadrangular space muscles or fibrosis of the muscle edges may impinge on the axillary nerve. Uncommonly, this produces weakness of the deltoid muscle. Typically it produces atrophy of the teres minor muscle, which may affect the control that the rotator cuff muscles exert upon shoulder movement.



Table 1. Movements of scapula.

Movement of Scapula

Muscles Producing Movementa

Nerve to Muscles

Range of Movement (Angular
Rotation; Linear Displacement)

Elevation

Trapezius, descending part
Levator scapulae
Rhomboids

Spinal accessory (CN XI)
Dorsal scapular

10-12 cm

Depression

Gravity
Pectoralis major, inferior sternocostal head
Latissimus dorsi
Trapezius, ascending part
Serratus anterior, inferior part
Pectoralis minor

Pectoral nerves
Thoracodorsal
Spinal accessory (CN XI)
Long thoracic
Medial pectoral




Protraction

Serratus anterior
Pectoralis major
Pectoralis minor

Long thoracic
Pectoral nerves
Medial pectoral

40-45°; 15 cm

Retraction

Trapezius, middle part
Rhomboids
Latissimus dorsi

Spinal accessory (CN XI)
Dorsal scapular
Thoracodorsal




Upward rotationa

Trapezius, descending part
Trapezius, ascending part
Serratus anterior, inferior part

Spinal accessory (CN XI)
Long thoracic

60°; inferior angle: 10-12 cm, superior angle: 5-6 cm

Downward rotationb

Gravity
Levator scapulae
Rhomboids
Latissimus dorsi
Pectoralis minor
Pectoralis major, inferior sternocostal head

Dorsal scapular
Thoracodorsal
Medial pectoral
Pectoral nerves




Boldface indicates prime or essential mover(s).
aThe glenoid cavity moves superiorly, as in abduction of the arm.
b The glenoid cavity moves inferiorly, as in adduction of the arm

Table 2. Scapulohumeral (Intrinsic) shoulder muscles.



Muscle

Origin

Insertion

Nerve

Function

Deltoid

Lateral third of clavicle; acromion and spine of scapula

Deltoid tuberosity of humerus

Axillary nerve

Clavicular (anterior) part: flexes and medially rotates arm

Acromial (middle) part: abducts arm

Spinal (posterior) part: extends and laterally rotates arm

Supraspinatus

Supraspinous fossa of scapula

Superior facet of greater tubercle of humerus

Suprascapular nerve

Initiates and assists deltoid in abduction of arm and acts with rotator cuff muscles

Infraspinatus

Infraspinous fossa of scapula

Middle facet of greater tubercle of humerus

Suprascapular nerve

Laterally rotates arm; and acts with rotator cuff muscles

Teres minor

Middle part of lateral border of scapula

Inferior facet of greater tubercle of humerus

Axillary nerve

Laterally rotates arm; and acts with rotator cuff muscles

Teres major

Posterior surface of inferior angle of scapula

Medial lip of intertubercular sulcus of humerus

Inferior subscapular nerve

Adducts and medially rotates arm

Subscapularis

Subscapular fossa (most of anterior surface of scapula)

Lesser tubercle of humerus

Sup. & Inf. subscapular nerves

Medially rotates arm; as part of rotator cuff, helps hold head of humerus in glenoid cavity

Supraspinatus

Supraspinous fossa of scapula

Superior facet of greater tubercle of humerus

Suprascapular nerve

Initiates and assists deltoid in abduction of arm and acts with rotator cuff muscles

Collectively, the supraspinatus, infraspinatus, teres minor, and subscapularis muscles are referred to as the rotator cuff, or SITS, muscles. Their primary function during all movements of the glenohumeral (shoulder) joint is to hold the humeral head in the glenoid cavity of the scapula.











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