Anatomy and kinesiology
The bones that can be distinguished at the shoulder are the clavicle, the scapula and the humerus. The clavicle connects the sternoclavicular joint with the acromioclavicular joint. On the dorsal side, the scapula is divided by the protruding spine of the scapula into the supraspinatous fossa and the infraspinatous fossa. Laterally, the spines become the acromion. On the medial side, the scapula is bordered by the medial border, and on the lateral side by the lateral border. Cranially and caudally, there are two protrusions, the superior angle and the inferior angle. At the cranio-lateral side, the scapula has a bony protrusion into the ventral direction: the coracoid process. The coracoid process, the acromion and their connective ligaments (the coracoacromial ligament) form the ‘coracoacromial arch’ [Figure 1].
Figure 1
- coracoid process
- acromion
- clavicle
- coracoacromial ligament
- supraspinatus muscle (tendon attachment not indicated)
- deltoid muscle
- greater tubercle
- lesser tubercle
- intertubercular groove
- subacromiodeltoid bursa
On the cranial part of the humerus (head of the humerus) the lesser tubercle is located ventrally and the greater tubercle is located laterally, divided by the intertubercular groove in which the tendon of the long head of the biceps brachii muscle lies. The space between the coracoacromial arch and head of the humerus is called the ‘subacromial space’. In this lie the subacromiodeltoid bursa and some of the rotator cuff tendons, amongst other structures. The glenohumeral joint is a ball and socket joint. It is a highly mobile joint with a shallow joint socket (glenoid space), a cartilage rim (glenoid labrum) and a very wide joint capsule. The surrounding rotator cuff muscles fulfil an important stabilising function. Lesions of these weak parts can easily result in dislocation of the head of the humerus. In the shoulder girdle, there are three synovial joints (the glenohumeral, the acromioclavicular and the sternoclavicular joints), as well as a ‘functional’ joint (the scapulothoracic joint).
The movement possibilities for each joint are as follows:
glenohumeral joint
- anteflexion
- retroflexion
- abduction
- adduction
- outward rotation
- inward rotation
sternoclavicular joint and acromioclavicular joint
- elevation (of the clavicle)
- depression (of the clavicle)
- protraction (of the clavicle)
- retraction (of the clavicle).
These are angular movements. In addition, the clavicle rotates around the longitudinal axis during the abovementioned movements.
scapulothoracic joint
- outward rotation (lateral displacement of inferior angle) [Figure 2]
- inward rotation (medial displacement of inferior angle) [Figure 2]
Figure 2
- cranial gliding movement (upwards gliding of the scapula along the thoracic wall) [Figure 3]
- caudal gliding movement (downwards gliding of the scapula along the thoracic wall) [Figure 3]
Figure 3
- lateral gliding movement (the scapula glides across the thoracic wall laterally and forwards) [Figure4]
- medial gliding movement (the scapula glides across the thoracic wall medially and backwards) [Figure 4]
Figure 4
Together, these four joints are responsible for six composite movements between arm and torso that are normally covered during the movement examination. These are:
- anteflexion (approximately 180°): raising the arm forwards relative to the torso. During this movement the following should occur as a minimum:
- anteflexion of the humerus
- posterior rotation of the clavicle
- outward rotation and gliding of the scapula laterally
- retroflexion (approximately 45°): raising the arm backwards relative to the torso. This movement is achieved by:
- retroflexion of the humerus
- anterior rotation of the clavicle
- inward rotation and gliding of the scapula medially
- abduction (approximately 180°): raising the arm sideways relative to the torso. During this movement, the following should occur as a minimum:
- abduction of the humerus
- elevation and posterior rotation of the clavicle
- outward rotation of the scapula
- horizontal adduction (approximately 45°): placement of the hand on the opposite shoulder in a horizontal plane. This movement is achieved by:
- adduction/anteflexion of the humerus
- protraction of the clavicle
- outward rotation and lateral gliding of the scapula
- outward rotation (approximately 80°): outward rotation of the lower arm with the elbow in 90° flexion. This movement is achieved by:
- outward rotation of the humerus
- retraction of the clavicle
- inward rotation and gliding of the scapula in a medial direction
- inward rotation (approximately 90°): lower arm is rotated inwards and placed on the back, with the elbow in 90° flexion. This movement is achieved by:
- inward rotation of the humerus
- depression and anterior rotation of the clavicle
- outward rotation and gliding of the scapula in a lateral direction when placing the lower arm on the back, and subsequent inward rotation and gliding movement medially.
Four muscles are considered to be part of the ‘rotator cuff’.
These muscles are:
- supraspinatus muscle [Figure 5]
origin: supraspinatus fossa
insertion: greater tubercle
Figure 5
- infraspinatus muscle [Figure 6]
origin: infraspinatus fossa
insertion: greater tubercle
- teres minor muscle [Figure 6]
origin: lateral border
insertion: greater tubercle
Figure 6
- subscapularis muscle [Figure 7]
origin: subscapular fossa (ventral side of the scapula)
insertion: lesser tubercle
Figure 7
The rotator cuff muscles work very closely together. Their functioning cannot really be assessed individually. The tendon of the supraspinatus muscle is the only tendon of the rotator cuff muscles that runs underneath the shoulder blade. During the abduction movement this tendon is compressed to a certain degree. Another muscle that stabilises the humerus, particularly during the abduction movement, is the long head of the biceps brachii muscle.
- biceps brachii muscle
origin of long head (caput longum): supraglenoid tubercle of the scapula and glenoid labrum
origin of short head (caput brevis): coracoid process
insertion: radial tuberosity and antebrachial fascia (via the bicipital aponeurosis).
The reason that only the aforementioned muscles are discussed in some detail is their clinical relevance, which is also confirmed by epidemiological data.
Based on the origin and insertion of the shoulder muscles, the following classification can also be applied:
- Muscles from the shoulder girdle to the torso, neck and skull
- sternocleidomastoid muscle
- trapezius muscle
- levator scapulae muscle
- rhomboid muscle (major and minor)
- serratus anterior muscle
- pectoralis minor muscle
- subclavius muscle.
- Muscles from the scapula and/or the clavicle to the humerus (or forearm)
- deltoid muscle
- rotator cuff muscles
- pectoralis major (clavicular part)
- teres major muscle
- biceps brachii muscle
- triceps brachii muscle
- Muscles from the torso to the humerus
- pectoralis major (sternocostal part)
- latissimus dorsi muscle.
Terminology
Scapulohumeral rhythm [Figure 8]. This is the movement course of the scapula and humerus in relation to each other and the torso. During abduction the first 45°-90° (differs per individual) of movement is primarily glenohumeral: during this, the scapula can even rotate 5°-10° internally. Only from 45°-90° does the scapula move along to a great degree (outward rotation). If one of the four joints of the shoulder girdle is abnormal, this will almost always become apparent through a change in this rhythm; therefore, assessment of any left-right difference is extremely important in such an instance.
Figure 8
‘Painful arc’. The patient will indicate a painful movement arc, particularly during abduction [Figure 9] and possibly also during anteflexion; these will be preceded and followed by a painless arc of motion. This specifically occurs during active movement examinations but can also occur during a passive movement examination. In the case of a painful arc between approximately 60° – approximately 120° there will often be a rotator cuff disorder and/or subacromial bursitis. In the case of a painful arc between approximately 150° – approximately 180° (so called ‘high painful arc’), there will often be a disorder of the acromioclavicular joint.
Figure 9
‘Painful drop’. This is a sudden painful adduction movement (read ‘drop’) of an anteflexed arm between approximately 60°-120° of adduction. This phenomenon is seen specifically with rotator cuff rupture or other very painful subacromial structures, during which active abduction is barely possible.
‘Impingement’ [Figure 10]. This involves entrapment of the rotator cuff tendons (particularly the tendon of the supraspinatus muscle) and primarily the subacromiodeltoid bursa underneath the acromion process of the scapula during the abduction movement.
Figure 10
‘Referred pain’. The patient will indicate the location of the pain at a different site than the actual source. For the shoulder this means that the patient often indicates pain in dermatome C4 or C5. A disorder of the cervical spinal column or the acromioclavicular joint can express itself as pain in the whole of dermatome C4.
Piano key phenomenon. This is a disorder where the tip of the acromion of the clavicle can be pressed and it will spring back like a piano key. This is a result of cranial dislocation of the clavicle in the case of either a rupture of the acromioclavicular ligament or the coracoclavicular ligament.
‘Thoracic outlet syndrome’. This is the collective term for a number of syndromes, in which mechanical compression of the brachial plexus and the subclavian artery and vein develops in the upper thoracic outlet.
Periarthritis of the shoulder. This is the collective name for painful soft tissue disorders of the shoulder girdle. In essence, this is a pseudodiagnosis.