Humerus abduction

Adduction and abduction are accessory rocking motions of the upper part of the ulna on the trochlea of the humerus. Abduction is an accessory motion of pronation. Adduction is an accessory motion of supination. 

Alternatively if the child remains with their back against the cassette the affected arm is abducted, bent at the elbow and held by a carer with the palm facing cranially. Foam pads are used to support the humerus parallel to the cassette. 

To prevent impingement, the lower end of the humerus has two fossae, one at the front and one at the back. This gives the human elbow a range of 0 -142° of flexion extension with 5 of further passive flexion. About 9 of abduction and adduction exist in the ulno-humeral joint. This range of movement is essential to complete the full arc of pronation and supination. 

The capsule of the glenohumeral joint is loose and pleated. The ligaments, which are merely thickenings in the capsule, provide little support. The major support of the humerus into the fossa is provided by the rotator cuff muscles, which hold the head into the fossa. These muscles include the supraspinatus, infraspinatus, teres minor, and subscapularis. Abduction-adduction and axial and horizontal rotations are coupled in that angular motions are accompanied by translatory slides. The caudal slide of the humeral head with abduction confers increased freedom of motion on the supraspinatus tendon beneath the coracoacromial ligament. 

The two functional joints in the shoulder girdle are the suprahumeral joint and the scapulothoracic joint. As mentioned, both figure prominently in shoulder biomechanics and pathology. The suprahumeral joint is formed by the articulation of the head of the humerus with the coracoacromial arch, composed of the acromion, the coracoid process, and the ligament between them. Articulation occurs during abduction. 

The humerus impinges on the acromial arch at 90 degrees. To prevent impingement and permit abduction to 180 degrees, the scapula must rotate. 

The fibers of the deltoid, attached from the scapula to the humerus, contract to abduct the arm to 90 degrees, at which point they are maximally contracted. As the fossa rotates upward, it maintains the deltoid in position for maximal contraction, allowing the humerus to continue to 180 degrees. 

The scapulohumeral rhythm is a free-flowing and synchronous movement of the scapula and humerus. During abduction, the scapula rotates as the humerus elevates. For every 15 degrees of abduction, humeral elevation accounts for 10 degrees and scapular rotation accounts for 5 degrees. Dysfunction of humeral elevation or of scapular rotation can disturb this rhythm and interfere with shoulder function. Dysfunction of clavicular motion can also interfere with this rhythm. 

Range of motion should be checked actively and passively. Extension is minimal because of bony impingement. Flexion will be limited by the size of the biceps muscle. Besides the gross motions of flexion, extension, supination and pronation, the motion of the head of the radius must be evaluated as it glides on the lateral ulna. The motions of abduction and adduction of the ulna on the humerus should be evaluated. 

Technique The patient s arm is flexed and abducted to 120 degrees. The humerus is markedly externally rotated. The muscle should become very soft in this position (Fig. 86-6). After the 90 seconds, the arm is returned to a neutral position and the tender point is reassessed. 

Techniqne The physician reaches under the affected arm and grasps the abducted humerus. With her other hand, she reaches over the patient s shoulder and places the thumb or hypothenar eminence on the sternal end of the clavicle. The hand holding the humerus applies a lateral traction. The other hand provides a downward force on the clavicle (Fig. 88-9). This may be an articulatory or a high-velocity, low-amplitude force. 

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