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AAAC34 21/5/05 10:49 AM Page 79
See Figs 34.1 and 34.2.
(C5,6).
• Type: the shoulder is a synovial ‘ball and socket’ joint which permits
multiaxial movement. It is formed by the articulation of the humeral
Shoulder movements
head with the shallow glenoid fossa of the scapula (see p. 63). The • Nerve supply: from the axillary (C5,6) and suprascapular nerves
glenoid is slightly deepened by a fibrocartilaginous rimathe glenoid The shoulder is a ‘ball and socket’ joint allowing a wide range of move-
labrum. Both articular surfaces are covered with hyaline cartilage. ment. Much of this range is attributed to the articulation of the shallow
• The capsule: of the shoulder joint is lax permitting a wide range of glenoid with a rounded humeral head. The drawback, however, is that
movement. It is attached medially to the margins of the glenoid and lat- of compromised stability of the joint.
erally to the anatomical neck of the humerus except inferiorly where it The principal muscles acting on the shoulder joint are:
extends to the surgical neck. The capsule is significantly strengthened • Flexion (0–90°): pectoralis major, coracobrachialis and deltoid
by slips from the surrounding rotator cuff muscle tendons. (anterior fibres).
• Stability: is afforded by the rotator cuff and the ligaments around the • Extension (0–45°): teres major, latissimus dorsi and deltoid (poster-
shoulder joint. The latter comprise: three gleno-humeral ligaments ior fibres).
which are weak reinforcements of the capsule anteriorly; a coraco- • Internal (medial) rotators (0–40°): pectoralis major, latissimus
humeral ligament which reinforces the capsule superiorly; and a cora- dorsi, teres major, deltoid (anterior fibres) and subscapularis.
coacromial ligament which protects the joint superiorly. The main • External (lateral) rotators (0–55°): infraspinatus, teres minor and
stability of the shoulder is afforded by the rotator cuff. The cuff com- deltoid (posterior fibres).
prises: subscapularis, supraspinatus, infraspinatus and teres minor • Adductors (0–45°): pectoralis major and latissimus dorsi.
(see Muscle index, p. 162) which pass in front of, above and behind the • Abductors (0–180°): supraspinatus, deltoid, trapezius and serratus
joint, respectively. Each of these muscles can perform its own function anterior.
and when all are relaxed free movement is possible, but when all are Abduction at the shoulder joint is initiated by supraspinatus; deltoid
contracted they massively reinforce shoulder stability. continues it as soon as it obtains sufficient leverage. Almost simultan-
• Bursae: two large bursae are associated with the shoulder joint. The eously the scapula is rotated so that the glenoid faces upwards; this
subscapular bursa separates the shoulder capsule from the tendon of action is produced by the lower fibres of serratus anterior which are
subscapularis which passes directly anterior to it. The subscapular inserted into the inferior angle of the scapula and by the trapezius which
bursa communicates with the shoulder joint. The subacromial bursa pulls the lateral end of the spine of the scapula upwards and the medial
separates the shoulder capsule from the coracoacromial ligament end downwards.
above. The subacromial bursa does not communicate with the joint.
The tendon of supraspinatus lies in the floor of the bursa. Inflammation Shoulder dislocation (Fig. 34.3)
of the bursa due to adjacent inflammation of the supraspinatus tendon As has been described above, stability of the shoulder joint is mostly
caused by impingement of the supraspinatus tendon on the coracoacro- afforded anteriorly, superiorly and posteriorly by the rotator cuff.
mial ligament gives rise to severe pain and limitation of shoulder Inferiorly, however, the shoulder is unsupported and strong abduction,
abduction (classically between 60 and 120°) known as the painful arc coupled with external rotation, can force the head of the humerus
syndrome. downwards and forwards (sometimes damaging the axillary nerve) to
• The synovial membrane: lines the capsule and covers the articular the point that the joint dislocates. This is termed the anterior shoulder
surfaces. It surrounds the intracapsular tendon of biceps and extends dislocation as the head usually comes to lie anteriorly in the subcora-
slightly beyond the transverse humeral ligament as a sheath. It forms coid position. Sometimes the force of the injury is sufficient to tear the
the subscapular bursa anteriorly by protruding through the anterior wall glenoid labrum anteriorly thereby facilitating recurrence. A surgical pro-
of the capsule. cedure is always required when the latter has led to repeated dislocations.

The shoulder (gleno-humeral) joint 79