Chapter 14

Shoulder Pain

with W. Ben Kibler

(The first 11 pages of this chapter are online)

Functional anatomy
Clinical perspective - A practical approach to shoulder pain
Clinical perspective - History
Clinical perspective - Examination
Investigations

Normal shoulder function is essential for many popular sports and shoulder dysfunction causes significant impairment of everyday quality of life. In recent years, there have been many advances in understanding of the pathologies underpinning shoulder pain, and in new treatment for shoulder problems. However, the shoulder remains one of the most challenging regions for all sports medicine practitioners.

The aim of this chapter is to provide a sound background in the functional anatomy and dynamic forces acting around the shoulder joint as without it the pathological processes around the shoulder cannot be understood. After describing the key features of the history, and illustrating the physical examination for this region, we detail the treatment of the various shoulder pathologies. The chapter concludes with a prescription for practical shoulder rehabilitation that is designed to aid the practitioner managing shoulder problems in the office.

Functional anatomy 

The glenohumeral joint is a ball and socket joint (Fig. 14.1). Unlike the hip joint, which has a deep socket, the glenoid cavity is a shallow socket and is inherently unstable. The relationship between the humeral head and the glenoid cavity has been likened to a seal balancing a ball on its nose. This implies that shoulder stability arises from a dynamic ball and socket stability that involves other structures. This additional stability is provided by static constraints - the glenohumeral ligaments, glenoid labrum and capsule - and dynamic constraints, predominantly the rotator cuff muscles.

Fig. 14.1 The anatomy of the shoulder region
(a) Surface from the front

(b) Surface anatomy from behind

The main static stabilizer of the shoulder in the abducted or functional position is the inferior glenohumeral ligament. This is attached to the labrum, which in turn, attaches directly to the margin of the glenoid fossa. The inferior glenohumeral ligament includes the expanded and thickened portions of the anteroinferior, inferior and posteroinferior capsule. The superior margin of this ligament attaches to the glenoid fossa anteriorly at the two o'clock position. When the arm is placed into abduction and external rotation, this broad ligamentous band rotates anteriorly to prevent subluxation of the joint.

Shoulder stability is also enhanced by the glenoid labrum, a ring of fibrous tissue attached to the rim of the glenoid which expands the size and depth of the glenoid cavity. It increases the superior-inferior diameter of the glenoid by 75% and the anterior-posterior diameter by 50%.

(c) Rotator cuff musculature from behind

(d) Ligaments and muscles of the glenoid

The dynamic stabilizers of the glenohumeral joint are the rotator cuff muscles, which serve to control the position of the humeral head in the glenoid fossa. The rotator cuff balances the forces of the deltoid muscle which acts to raise the arm and, in so doing, forces the humeral head superiorly toward the acromion and coracoacromial arch. The rotator cuff muscles, principally the supraspinatus and, to a lesser extent, infraspinatus, teres minor and subscapularis, counteract the action of the deltoid by preventing the head of the humerus from moving superiorly when the arm is raised. An imbalance between the deltoid and the rotator cuff muscle strength may result in excessive superior movement of the humeral head, causing impingement of subacromial structures.

The scapular stabilizers also play an important role in shoulder joint movement. Glenohumeral movement requires the scapulothoracic, acromioclavicular (AC) and sternoclavicular joints to also move. Normal shoulder function requires smooth integration of movement of these joints. This integrated movement is referred to as 'scapulohumeral rhythm'.

Adequate scapulohumeral rhythm is required to achieve full upper limb elevation. Scapular movement ensures that the coracoacromial arch is removed from the path of the upwardly elevating humerus, in particular its greater tuberosity, via upward rotation of the scapula, thus, avoiding potential impingement.

Correct scapulohumeral rhythm also enhances joint stability at greater than 90 degrees of abduction by placing the glenoid fossa under the humeral head, where stability is assisted by the action of the deltoid muscle. A stable scapula provides a base for the muscles arising from the scapula and acting on the humerus, allowing them to maintain their optimal length-tension relationship. Scapulohumeral rhythm should be smooth, co-ordinated and symmetrical.

Disturbed scapulohumeral rhythm may be detected clinically by altered, jerky patterns of scapulohumeral movement. This may indicate injury to the shoulder girdle. Abnormal scapulohumeral rhythm may predispose to the development of a shoulder injury. Abnormalities of scapulohumeral rhythm are most commonly due to weakness of the scapular stablizers (with or without weakness of the rotator cuff muscles), tightness and shortening of the scapulohumeral muscles (infraspinatus, teres minor and subscapularis) or involuntary adaptation to avoid a painful arc.

The muscles controlling scapular rotation are the trapezius (all three portions), serratus anterior (upper and lower portions), rhomboids, levator scapulae and, to a lesser extent, pectoralis minor. For full upper limb extension, upward rotation of the glenoid is required. Following shoulder injury, adequate strengthening and retraining of the scapula stabilizers facilitates rotator cuff strengthening. The muscles primarily involved in the different shoulder movements are shown in Table 14.1.

Table 14.1 Muscles involved in shoulder (glenohumeral and scapular) movements*

*These muscles do not act in isolation. The shoulder relies on force coupling of surrounding muscles for stabilizing and positioning.