CHAPTER 17 The shoulder
Functional anatomy
Rotator cuff action
Active abduction of the humerus is accomplished by the supraspinatus and deltoid, acting as the prime movers. With the arm dependent, contraction of the deltoid (particularly the middle fibres) merely approximates the joint (upward translation), because the medial muscle fibres run almost parallel with the humerus. Unopposed, this pull would force the head of the humerus into the coracoacromial arch, resulting in impingement. Contraction of the infraspinatus, subscapularis, and teres minor (Fig. 17.2) causes compression and downward translation to offset the upward translation of deltoid (Culham and Peat, 1993). In an overhead throwing or serving action (Fig. 17.3) the subscapularis moves superiorly because the humerus has externally rotated and the muscle can no longer effectively control the humeral head. The infraspinatus and to a lesser extent the teres minor stabilize the joint anteriorly in this position (Cain, Mutschler and Fu, 1987). For this reason sEMG addresses this muscle in stabilization programmes targeted at throwing sports. By 90° abduction, the pull of the deltoid no longer tends to cause impingement, as shear forces are exceeded by compression, and the humeral head is stabilized into the glenoid (Perry and Glousman, 1995).

Figure 17.3 Muscular restraints to anterior displacement of the humeral head in an overhead throwing action.
Adapted from Reid (1992), with permission.
The abduction cycle
Movement of the arm into abduction may be divided into three overlapping stages (Table 17.1).
Table 17.1 Movement of the arm into abduction
Stage (I)
In stage (I), no movement of the scapula should occur. The scapular stabilizers (serratus anterior especially) should hold the scapula firmly on the ribcage, providing a stable base for the humerus to move upon. As the arm abducts, lateral rotation of the humerus may be detected by palpation of the bicipital groove (intertubercular sulcus). If the humerus is maintained in a neutral position, abduction in the frontal plane is limited to about 90°. Laterally rotating the humerus increases this range to 120° (Lucas, 1973). When the arm is elevated in the sagittal plane, abduction is accompanied by medial rotation due to tightness in the coracohumeral ligament (Gagey, Bonfait and Gillot, 1987). No rotation is required for elevation in the scapular plane (30–45° anterior to the frontal plane). In this position, the joint capsule does not undergo torsion, and the deltoid and supraspinatus are optimally aligned.
Stage (II)

Figure 17.4 Muscle force couples which create scapular rotation. (A) Lateral rotation. (B) Medial rotation.
From Palastanga, Field and Soames (1989), with permission.
The biomechanics of throwing
Screening examination of the shoulder complex

Figure 17.6 Angular displacement of the shoulder during a throwing action.
After Fleisig, Dillman and Andrews (1994), with permission.
Locking test and quadrant test
Should movement apparently be full and painless at the glenohumeral joint, two further procedures are useful to reproduce the patient’s symptoms. These are the locking test and the quadrant position (Maitland, 1991). Both tests refer to the position of the greater tuberosity relevant to acromial arch and glenoid (Corrigan and Maitland, 1994). Each should be assessed for pain and end-feel, and compared with the uninjured side.
Locking test
Keypoint
The locking position compresses the subacromial space and gives pain with an impingement syndrome.
Sternoclavicular joint
Injury
Posterior dislocations, even if successfully reduced, will still require hospital referral and observation. Posterior dislocations usually stay reduced, but anterior dislocations are apt to recur. Surgical fixation of anterior dislocation is possible, but the number of complications makes the procedure undesirable. Migration of a Steinmann pin or Kirchner wire into the heart or major vessels has been reported (Garrick and Webb, 1990). Rockwood and Odor (1989) reported excellent results following conservative management of atraumatic anterior displacement 8 years after initial treatment. Patients treated surgically (not by these authors) in the same study had complications including scarring, instability, pain and limitation of activity.
Acromioclavicular joint
Examination
The cross body test has been shown to gap the AC joint by an average of 6.4 mm measured using ultrasonography compared to a gap of 7.7 mm with passive end range external rotation. However, greater direct stress is placed on the AC joint using the cross body manoeuvre than with humeral rotation (Park, Park and Bae, 2009). The cross body test has been shown to have a sensitivity of 77% compared to 41% for the active compression test (Chronopoulos et al., 2004). This latter test was designed to assist the diagnosis of labral tears and to differentiate them from AC joint involvement depending on the patient’s description of their pain location as ‘on top’ or ‘inside’ the shoulder (Brian et al.: O’, 1998).
Injury
The most common conditions affecting the AC joint are sprains and degeneration. AC joint sprains vary in intensity between minor grade I injuries to grade III ruptures representing complete disruption of the coracoclavicular ligament and AC joint dislocation (sprung shoulder) (Fig. 17.11). The injury may be further classified using weight-lifting radiographs. Here, the anterior deltoid is contracted by having the patient hold a weight with the elbow flexed and arm next to the body. If the clavicular attachment of the deltoid is intact, the joint may reduce as weight is taken (IIIa), or there may be no change in the joint appearance (IIIb). However, if the lateral end of the clavicle becomes more prominent, the clavicular attachment of the deltoid may have been stripped off (Dias and Gregg, 1991). Radiographs are also used to differentiate the condition from fractures of the distal clavicle where this is suspected.
Acromioclavicular taping
Stress may be taken off the AC joint by a simple taping designed to press the clavicle down and take some of the weight of the arm away from the distal shoulder structures (Austin, Gwynn-Brett and Marshall, 1994; Macdonald, 1994). The athlete is positioned in sitting at the side of the couch with the elbow flexed to 90° and the shoulder abducted to 30°. The shoulder is slightly elevated and the arm rests on the couch. The shoulder and chest on the injured side of the body should be shaved of long hair. Spray adhesive is applied, making sure that the athlete turns the head away from the spray and covers the eyes with the unaffected hand. Also, the nipple area must be protected with a non-adhesive pad.
A felt pad is placed over the acromion to protect it from abrasion. Two anchors of 7.5 cm elastic adhesive tape are applied. The first runs horizontally from the sternum to the paravertebral area on the side of injury. The second is placed around the mid-humerus with light tension, ensuring that the limb is not excessively compressed (Fig. 17.12A). Two stirrups of 7.5 cm elastic adhesive tape are placed (pre-stretched) from the front to the back of the chest anchor, passing over the acromion (Fig. 17.12B). These are then reinforced by two strips of 5 cm zinc oxide taping. Two further strips of elastic adhesive tape are placed (pre-stretched) laterally from the arm anchor across the anterior aspect of the shoulder to join the chest stirrups over the acromion, and laterally from the anchor, passing posteriorly over the shoulder to the acromion (Fig. 17.12C). Again, these stirrups are reinforced by 5 cm zinc oxide taping. If the shoulder stirrups have been applied correctly, their tension will tend to lift the arm into abduction slightly. The chest and arm stirrups are closed by reapplying the chest and arm anchors (7.5 cm elastic adhesive tape) to act as fixing strips. Sensation and pulse should be re-tested after tape application.

Figure 17.12 Acromioclavicular joint taping. (A) Anchors. (B) Stirrup applied under tension. (C) Arm stirrups.
Surgical intervention
There is some controversy concerning the treatment of this condition. Both conservative and surgical approaches restore function to a similar degree (Larsen, Bjerg-Nielsen and Christensen, 1986; Dias et al., 1987; Bannister et al., 1989), and some surgical methods have been shown to give long-term functional detriment. Certainly, removal of the distal end of the clavicle (Gurd, 1941) will disrupt the acromioclavicular ligament, a main stabilizer of the joint (Fukuda et al., 1986). In the literature, the main argument for surgery has been the development of degenerative changes in the joint as a result of non-operative management. However, degeneration does not occur in all patients, and when it does occur, it is not necessarily a limitation (Dias et al., 1987). In addition, surgery is often as effective if done in the acute or chronic condition, so there is normally no advantage to operating immediately. Importantly, surgery carries with it a high risk of complications (Ejeskar, 1974; Lancaster, Horowitz and Alonso, 1987; Taft, Wilson and Oglesby, 1987).
In a literature review of 11 papers detailing the long-term results of both surgical and conservative management of this injury, Dias and Gregg (1991) found poor results to have occurred in 13 out of 247 patients treated conservatively (5.3%), and 22 out of 233 managed surgically (9.4%). These authors argued that as comparable results were obtained regardless of the method used, conservative management was the treatment of choice for most AC injuries. Looking at strength testing following grade III AC injuries treated conservatively (average 4.5 year follow-up), Tibone, Sellers and Tonino (1992) found no subjective complaints in patients, all of whom were able to participate in sport. Full motion occurred in all subjects, and no significant differences were found in muscle strength of injured and non-injured sides in rotation, abduction/adduction or flexion/extension.
Winged scapula
Treatment note 17.1 Restoraton of scapulothoracic stability
Taping may be used to give feedback about the position of the scapula and lengthened muscle. A positional box tape may be used to facilitate position of the scapula (Fig. 17.15). The tape has two horizontal strips to draw the medial borders of the scapulae together and two vertical strips to facilitate thoracic extension. Non-elastic taping is used to take up skin tension and act as a feedback system for the patient. Facilitatory taping may be used over the serratus anterior (Fig. 17.16A), lower trapezius (Fig. 17.16B) or to increase patient awareness of body segment position and facilitate underlying muscle action.
Impingement syndrome
The subacromial space (Fig. 17.18) lies beneath the coracoacromial arch formed by the coracoacromial ligament together with the coracoid and acromion the so-called ‘roof of the joint’. The coracoacromial arch is covered by the deltoid, and inferiorly its fascia is continuous with that of the supraspinatus. The arch prevents upward dislocation of the glenohumeral joint. The supraspinatus passes beneath the arch, being separated from it by the subacromial bursa. The subacromial distance (space between the inferior acromion and the head of the humerus) is normally about 1cm (Petersson and Redlund-Johnell, 1984). If the supraspinatus tendon has ruptured, or the muscle is no longer active, this space will reduce by as much as 50% due to the unopposed pull of the deltoid.
Keypoint
The subacromial space may reduce by as much as 50% if the supraspinatus muscle is dysfunctional.
Movement dysfunction
The action of abduction involves a complex series of movements. Impingement is associated with a change in the muscle action involved in the abduction sequence. Most commonly there is a reduction in the stabilizing action of the serratus anterior muscle with other muscles (especially the upper trapezius) compensating. The result is an altered scapular position relative to the humerus during abduction. This movement dysfunction has been termed scapula dyskinesia (Paterson, 2008). EMG studies of patients with impingement pain have shown a reduction in serratus anterior muscle action and a change in scapula position (Ludewig and Cook, 2000). The scapula is more anteriorly tipped drawing it closer to the approaching humeral head, and upward rotation during the early stages of abduction is delayed. Decreased force output in the both the serratus anterior and lower trapezius has also been shown with overhead athletes demonstrating shoulder impingement (Cools et al., 2004).
Examination
The screening examination is used initially, followed by observation of both static and dynamic position of the scapula and humerus. Two further tests are useful which are specific to impingement. In test one (Fig. 17.19A) the arm is fully abducted and overpressure is put onto the internally rotated (thumb forwards) shoulder. For test two (Fig. 17.19B), the glenohumeral joint is flexed and internally rotated (Hawkins test). Overpressure is then added to internal rotation and abduction or horizontal flexion. Resisting flexion by placing pressure over the elbow may also bring on the athlete’s pain (Hawkins and Hobeika, 1983; Reid, 1992).
In addition to a purely mechanical impingement, changes in the microvascular supply to the area have been noted. Pressure exerted by the humeral head on the supraspinatus tendon, has the effect of ‘wringing out’ the tendon vessels and creating an avascular zone (Rathbun and Macnab, 1970). This area, known as the critical zone (Fig. 17.20), is an anastomosis between the osseous vessels and the tendinous vessels (Moseley and Goldie, 1963). Furthermore, repeated microtrauma results in local oedema within the tendon and an increase in tissue volume. This in turn makes the structures more susceptible to impingement by reducing the subacromial space and so perpetuates the problem.
A reduction in the subacromial space may be the result of individual variation in the anatomical architecture of this region, with some individuals more prone to impingement than others (Ticker and Bigliani, 1994). Cadaveric studies of 140 specimens have identified three types of acromion associated with full thickness tears of the rotator cuff (Bigliani, Morrison and April, 1986).
The flat (type I) acromion occurred in 17% of subjects, the curved (type II) acromion was seen in 43%, and the hooked (type III) type in 39% (Fig. 17.21). The hooked acromion was present in 70% of rotator cuff tears whereas the flat type was only seen in 3%. By assessing the supraspinatus outlet view x-ray, Morrison and Bigliani (1987) showed 80% of those with positive arthrograms to have a hooked acromion. The same authors showed that 66% of patients who underwent open subacromial decompression had a hooked acromion.

Figure 17.21 Acromion types. (A) Type I, flat. (B) Type II, curved. (C) Type III, hooked.
After Ticker and Bigliani (1994).