Scapula

The scapula is raised, as in a shrug of the shoulders, by the trapezius and levator scapulae muscles (figure 28a,b).

Drawing the scapula medially (bracing the shoulders) is by the central fibres of the trapezius and the rhomboid muscles (figure 28c). Downward movement of the scapula is primarily the effects of gravity on the weight of the arm and contributed to by the lower fibres of trapezius and latissimus dorsi. The scapula is drawn forward around the chest and retained on the chest wall by the serratus anterior (figure 28d). Absence, weakness or paralysis of this muscle produces winging of the scapula.

The scapula is closely linked to movements of the shoulder joint (see below). In abduction, the various fibres of the trapezius rotate the bone and, in adduction, the pectoral and lattisimus dorsi muscles pass directly from the trunk to the humerus, as well as to their scapular attachments; the short scapular muscles all contribute to its stability.

The sternoclavicular joint, the clavicle, the acromioclavicular joint, the subacromial bursa, the bicipital groove and the head of the humerus are palpable (figure 29); the clavicle is palpable along its length anteriorly (figure 30).

In figure 31a, the thumbnail lies in the sternoclavicular joint, the sternal head of the sternomastoid muscle lies medially. The joint is injected through an anterior approach (figure 31b).

In figure 32a, the thumbnail lies in the acromioclavicular joint. The joint is injected through an anterior or superior approach (figure 32b).

The coracoid process of the scapula projects forward just below the clavicle and is palpable through the anterior fibres of the deltoid muscle (figure 33a). Injection of the attached tendons is through an anterior approach onto the bone, thus avoiding the axillary vessels and the cords of the brachial plexus that lie below it (figure 33b).

In figure 34a, the thumbnail is inserted beneath the acromion, over the subacromial bursa, and above the supraspinatus tendon and greater tuberosity. The bursa is injected through a lateral approach (figure 34b). The greater tuberosity lies just below this level, where it can be palpated (figure 34c), and the attached tendons injected

The greater and lesser tuberosities of the humerus are separated by the bicipital groove, containing the long tendon of the biceps muscle, its sheath and its bursa (figure 35a). Injections into the sheath are made at this level (figure 35b). Injection into the shoulder joint cavity is through a posterior approach, the needle passing through the fibres of deltoid and teres minor (figure 36).