Movements of the shoulder joint

NEET PG Anatomy
#1

MOVEMENTS OF THE SHOULDER JOINT

Ø The shoulder joint has more freedom of mobility than any other joint in the body, due to the following factors:

  1. Laxity of joint capsule.

  2. Articulation between relatively large humeral head and smaller and shallow glenoid cavity.

Ø The glenohumeral joint permits four groups of movements:

  1. Flexion and extension.

  2. Abduction and adduction.

  3. Medial and lateral rotation.

  4. Circumduction.

Ø The movements of shoulder joint occur in all the three planes and around all the three axes:

· The flexion and extension/hyperextension occur in sagittal plane around the frontal axis.

· The abduction and adduction occur in frontal plane around the sagittal axis.

· The medial and lateral rotation occur in transverse plane around the vertical axis.

· The circumduction is really only a combination of all above movements.

SPECIAL FEATURES

Ø Plane of the glenohumeral joint: The scapula does not lie in the coronal plane but is so oriented that its glenoid cavity faces forwards and laterally, therefore the plane of this joint lies obliquely at about 45° to the sagittal plane. The movements of shoulder joint are, therefore, described in relation to this plane.

§ The details are as under:

  1. Flexion and extension: During flexion, the arm moves forwards and medially, and during extension it moves backwards and laterally. These movements take place parallel to the plane of glenoid cavity (i.e., midway between the coronal and sagittal plane).

  2. Abduction and adduction: During abduction, the arm moves anterolaterally away from the trunk and during adduction the arm moves posteromedially towards the trunk. These movements occur at right angle to the plane of flexion and extension (i.e., in the plane of the body of the scapula).

  3. Medial and lateral rotation: These movements are best demonstrated in midflexed elbow. In this position, the hand moves medially in medial rotation and laterally in lateral rotation.

  4. Circumduction: The circumduction at glenohumeral joint is an orderly sequence of flexion, abduction, extension and adduction or the reverse. During this movement the upper limb moves along a circle. The muscles producing the various movements at the shoulder joint are listed in Table.

Mechanism of Abduction

Ø The abduction at shoulder is a complex movement, hence student must understand it.

Ø The total range of abduction is 180°. Abduction up to 90° occurs at the glenohumeral joint. Abduction from 90° to 120° can occur only if the humerus is rotated laterally. Abduction from 120° to 180° can occur if the scapula rotates forwards on the chest wall.

§ The detailed analysis is as under:

  1. The articular surface of the head of humerus permits elevation of arm only up to 90°, because when the upper end of humerus is elevated, to 90° its greater tubercle impinges upon the under surface of the acromion and can only be released by lateral rotation of the arm.

  2. Therefore, the arm rotates laterally and carries abduction up to 120°.

  3. Abduction above 120° can occur only if scapula rotates. So that the scapula rotates forwards on the chest wall.

SPECIAL FEATURES

• The humerus and scapula move in the ratio of 2:1 during abduction, i.e., for every 15° elevation, the humerus moves 10° and scapula moves 5°.

• During early and terminal stages of elevation, the sternoclavicular and acromioclavicular joints move maximum, respectively.

Range of motion (ROM) of various movements

During clinical examination, the knowledge of range of motion of various movements is very important. It is given in the box below:

Clinical correlation

Dislocation of the shoulder joint: Dislocation of shoulder joint mostly occurs inferiorly because the joint is least supported on this aspect. It often injures the axillary nerve because of its close relation to the inferior part of the joint capsule. However, clinically, it is described as anterior or posterior dislocation indicating whether the humeral head has descended anterior or posterior or to the infraglenoid tubercle of the scapula and long head of the triceps. The dislocation is usually caused by excessive extension and lateral rotation of the humerus.

Clinically, it presents as:

(a) Hollow in rounded contour of the shoulder

(b) Prominence of shoulder tip

• Frozen shoulder (adhesive capsulitis): It is a clinical condition characterized by pain and uniform limitation of all movements of the shoulder joint, though there are no radiological changes in the joint. It occurs due to shrinkage of the joint capsule, hence the name adhesive capsulitis. This condition is generally seen in individuals with 40–60 years of age.

• Rotator cuff disorders: The rotator cuff disorders include calcific supraspinatus tendinitis, subacromial the rotator cuff represent overall the most common cause of shoulder pain. The rotator cuff is commonly injured during repetitive use of the upper limb above the horizontal level (e.g., in throwing sports, swimming, and weight lifting). The deposition of calcium in the supraspinatus tendon is common. The calcium deposition irritates the overlying subacromial bursa causing subacromial bursitis. Consequently, when the arm is abducted the inflamed bursa is caught between tendon and acromian impingement, which causes severe pain. In most people, pain occurs during 60°–120° of abduction (painful arc syndrome). The rotator cuff disorders usually occur in males after 50 years of age.The pain due to subacromial bursitis is elicited when the deltoid is pressed just below the acromion, when the arm is adducted. The pain cannot be elicited by the pressure on the same point when the arm is abducted because the bursa slips/disappears under the acromian process.