Rotator cuff action

Most joints have a high degree of passive stability provided by their capsules and ligaments (see also Table 17.3). The shoulder, however, depends more on the active stability provided by its muscles to maintain joint integrity. In the anatomical position, the weight of the arm is largely supported by the coracohumeral ligament and superior capsule. When the arm moves away from the side of the body, tension in the superior capsule is immediately lost. Now joint stability is provided by the rotator cuff muscles alone.

The fibres of the joint capsule are angled forwards and slightly medially when the arm is hanging by the side of the body. As abduction progresses, tension within these fibres causes the shoulder to passively externally rotate. This movement prevents the humeral head from being pulled closer to the glenoid and facilitates a greater range of movement. Importantly, the external rotation also allows the greater tuberosity to clear the acromion process (see below).

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 17.2 (A) Deltoid pull at 30° and 90° abduction. (B) Muscles counteracting pull of deltoid. (i) Supraspinatus, (ii) infraspinatus and teres minor. (C) Subscapularis. Resolution of muscle force: S, shear; C, compression.

Figure 17.3 Muscular restraints to anterior displacement of the humeral head in an overhead throwing action.

Adapted from Reid (1992), with permission.

The supraspinatus is better placed to produce a rotatory action and therefore initiates abduction for the first 20°. The line of action of supraspinatus is such that less translation is caused, and its contribution to abduction is to reduce the reliance on deltoid and, as a consequence, reduce translation. After 30° of abduction the scapula starts to rotate to alter the glenoid position.

Scapulohumeral rhythm

Motion of the shoulder girdle as a whole changes the position of the glenoid fossa, placing it in the most favourable location for the maximum range of humeral movement. When the glenoid cavity moves, it does so in an arc, the diameter of which is the length of the clavicle (Palastanga, Field and Soames, 1989). The medial border of the scapula moves in a similar but smaller arc and as a consequence the positions of the shoulder girdle structures change in relation to each other.

As the scapula moves medially and laterally towards and away from the vertebral column, the curvature of the ribcage forces the scapula to change from a frontal to a more sagittal position. This, in turn, alters the direction in which the glenoid cavity faces. With elevation, the scapula is accompanied by some rotation, the glenoid cavity gradually pointing further upwards as the scapula gets higher.

With both shoulder abduction and flexion, the clavicle axially rotates. As the scapula twists, the coracoclavicular ligament ‘winds up’ and tightens, causing the clavicle itself to rotate. As the arm is abducted to 90° (phase I and II, see below) the clavicle elevates by 15° but does not rotate. Above 90° (phase III) further elevation of the clavicle occurs (up to 15°) but marked posterior rotation now occurs to 30–50° (Magee, 2002). For this reason a diminished range of movement at either SC or AC joints which reduces clavicular rotation will also impair scapular and therefore glenohumeral motion.

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.

At the beginning of abduction in the frontal plane, slight approximation of the humerus should occur (maximum 3 mm) to overcome the weight of the arm as the fibres of the joint capsule are taken off stretch and no longer support the arm through elastic recoil. No noticeable elevation of the shoulder should occur, unless the upper fibres of trapezius dominate the movement. The instantaneous axis of rotation in stage (I) is near the root of scapular spine, and moves superiorly and laterally as abduction progresses.

Stage (II)

By the beginning of stage (II), from 30° of abduction, the scapula should be upwardly rotating to maintain clearance between the acromion and the approaching greater tuberosity of the humerus. Scapular rotation in the beginning of stage (I) occurs as a result of elevation of the clavicle on the SC joint. Between 80 and 140° the instantaneous axis of rotation (IAR) migrates towards the AC joint along the upper central scapular area. Movement then occurs as elevation of the clavicle on the SC joint, and rotation of the scapula on the clavicle at the AC joint. More movement occurs at the glenohumeral joint than at the scapulothoracic joint. Ratios of 2 : 1 are normally quoted, giving 120° of movement at the glenohumeral joint and 60° at the scapulothoracic joint in a total abduction range of 180°. However, some authors (Lucas, 1973) have argued that the ratio is closer to 5 : 4 or 3 : 2 after phase (I) of abduction.

Scapular rotation occurs as a result of force-couples between the various muscles attached to the scapula (Fig. 17.4). Upward (lateral) rotation accompanying shoulder joint abduction or flexion is brought about by contraction of the upper and lower fibres of trapezius and the lower portion of serratus anterior. Serratus anterior is probably the most important of the group. It has two sets of fibres. The fibres of the upper portion run horizontally and slightly upwards, while those of the lower portion are aligned downwards. Both sets pull powerfully on the scapula, anchoring it to the ribcage and causing scapular upward rotation as trapezius lifts the lateral end of the clavicle and acromion process. If serratus anterior and the lower fibres of trapezius are ineffective, the upper trapezius will dominate the movement. In this case, these fibres show increased tone and can be tight. As the abduction moves further into stage (II), the moment arm of lower trapezius is lengthened and this portion of the muscle becomes increasingly active in the movement.

Figure 17.4 Muscle force couples which create scapular rotation. (A) Lateral rotation. (B) Medial rotation.

From Palastanga, Field and Soames (1989), with permission.

Downward (medial) rotation frequently occurs as a result of eccentric action of the above muscles. However, in activities such as hanging and chinning a beam, active scapular rotation is accomplished by levator scapulae and the rhomboids pulling upwards on the medial side of the scapula together with pectoralis minor pulling the coracoid process down. In cases where these muscles are tight or overactive, upward rotation of the scapula will be limited during abduction.

As scapular rotation progresses, lateral rotation of the humerus should be apparent as the cubital fossa and thumb orientate towards the ceiling. Ineffective scapular upward rotators, especially lengthening of the lower fibres of trapezius, will prevent correct orientation of the glenoid and increase the risk of impingement. Tightness in the medial rotators, especially the pectoralis major and subscapularis, combined with lengthening and weakness of the lateral rotators, may lead to delayed lateral rotation at the glenohumeral joint, resulting in impingement of the greater tuberosity against the inferior acromion.

During stage (II), as the humerus reaches 90° abduction, its head slides beneath the acromion, and a noticeable dip is formed in the skin. Failure of the shoulder musculature to pull the humerus into this position may result in the head slipping beneath the acromion with a sudden thud as the arm raises above 90° and similarly in this position during descent.

Stage (III)

During stage (III), as the arm approaches 120° abduction, no further movement is available from the glenohumeral joint. Additional range to reach the arm overhead is achieved by sliding the scapula over the thorax into further upward rotation and abduction. To facilitate this movement, the thoracic spine must reverse its kyphosis and flatten. A kyphotic posture and inflexibility in the thoracic spine will therefore limit the final degrees of abduction. As a simple test for this, the patient is asked to stand with the back flat against a wall and the pelvis posteriorly tilted to avoid any possibility of hyperextension at the lumbar spine. Both arms are then abducted, keeping them in full contact with the wall. If thoracic extension is limited, the patient will be unable to perform pure abduction to full range. Instead, the arm moves through flexion–abduction to bring it in front of the forehead. In conditions where abduction is limited, therefore, greater range may often be gained by mobilizing the thoracic spine as well as working on the glenohumeral joint.

As the arm moves into its final overhead position and the scapula rotates maximally, the inferior angle of the scapula juts out through the outer edge of the thorax. However, no more than 1–2 cm of the inferior angle should be visible at this point. During this final phase the IAR moves to the AC joint. Clavicular elevation is limited by tension in the costoclavicular ligament. As the coracoid process moves away from the clavicle, tension in this ligament causes dorsal rotation of the clavicle about its long axis.

Figure 17.5 (A) Stages of throwing. (i) wind-up—athlete positions him- or herself for the throw; (ii) cocking—lead leg moves forwards, arm moves backwards, stretching body; (iii) acceleration—body drives forwards, leaving arm behind; (iv) deceleration—object released. Elbow continues to extend and shoulder to internally rotate; (v) follow through—trunk and lead leg show eccentric activity to dissipate energy. (B) Similarity to tennis serve.

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

The locking position combines internal rotation, extension and abduction of the shoulder with the scapula fixed. In this position the subacromial space is compressed and will give pain should an impingement syndrome be present. Cadaveric studies have shown that in the locking position the posterosuperior tip of the glenoid is in contact with the humeral head (Mullen, Slade and Briggs, 1989).

Keypoint

The locking position compresses the subacromial space and gives pain with an impingement syndrome.

To perform the test, the patient is in a supine position, and the practitioner stands by the patient’s side towards the shoulders. The therapist places the palmar aspect of his or her forearm beneath the patient’s shoulder, and grips the trapezius muscle to stop the shoulder shrugging. The therapist holds the patient’s elbow, slightly medially rotates the arm, and lifts it into abduction.

Figure 17.7 Locking position and quadrant position.

Quadrant test

The quadrant position stresses the anterior and inferior capsule, and combines external rotation, slight flexion and full abduction of the shoulder. The therapist’s forearm grips the patient’s shoulder to prevent shrugging. The action is to hold the elbow and move the patient’s arm into abduction, allowing the humerus to move from medial rotation (palm to chest) to lateral rotation (palm to ceiling). The point at which the humerus begins to change from medial to lateral rotation marks the beginning of the quadrant (Petty and Moore, 2001). From this point horizontal extension is examined by pressing the elbow to the floor, releasing it and then moving into further abduction before pressing again. Both the quality and the range of motion are assessed, as well as the occurrence of muscle spasm. The affected shoulder is compared to the unaffected side.

Keypoint

The quadrant position stresses the joint capsule and indicates capsular tightening.

Figure 17.8 Movement of the clavicle.

After Palastanga, Field and Soames (1994), with permission.

Figure 17.9 Sternoclavicular dislocation. (A) Anteriorly directed force causes posterior dislocation. (B) Posteriorly directed force causes anterior dislocation.

From Garrick and Webb (1990), with permission.

Injury

Injury to the SC joint is unusual, forming about 3% of all shoulder girdle trauma. Anterior dislocations occur more commonly than posterior dislocations in a ratio of 20 : 1 (Zachazewski, Magee and Quillen, 1996). Normally, the clavicle will fracture or the acromioclavicular joint will give way before the SC joint is seriously injured. However, when damage does occur, it is frequently the result of direct lateral compression of the shoulder, such as occurs when falling onto the side of the body. The injury is more common in horse-riding and cycling where sufficient force is produced, but is seen in rugby and wrestling.

The SC joint will dislocate in the opposite direction to the applied force, thus an anterior force (falling onto the back) will dislocate the joint backwards. Several important structures lie in close proximity to the joint including the oesophagus, trachea, lungs, pleurae, brachial plexus and major arteries and veins. Posterior dislocation therefore, if it is severe, may be potentially life-threatening. In contrast, anterior dislocation can occur in the absence of trauma, and frequently results only in slight discomfort.

Initial examination (of posterior dislocation) on the field must obviously be aimed at ruling out life-threatening injury. The presence of stridor, dyspnoea, cyanosis, difficulty with speech, pulsating vessels and neurological signs may all necessitate immediate hospitalization.

If these are not present, joint examination may continue. Pain is generally well localized, and may become progressively more limiting over time. Anterior dislocation leaves a visible step deformity, and with posterior dislocation the usual prominence over the medial clavicle is lost. Local swelling is sometimes present, with crepitus and pain to motion, especially horizontal flexion. The shoulder is frequently held protracted.

Radiographic investigation will rule out clavicular fracture, and may enable differentiation between fracture and epiphyseal injury in the young (below 25 years) athlete. Closed reduction is often possible immediately after injury if pain is not too severe and before muscle spasm sets in. Both anterior and posterior dislocations may be reduced by placing a knee between the scapulae of the seated athlete and gently pulling the shoulders back. The joint often reduces with an audible thud. After reduction the joint is immobilized with a figure-of-eight bandage and ice is used to reduce local swelling.

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.

Even though the joint is frequently hypermobile, joint mobilizations may be used to relieve pain (Maitland, 1991). Anteroposterior gliding may be performed with the therapist placing his or her thumbs over the sternal end of the clavicle.

Examination

The AC joint is examined using the ‘cross body’ or ‘scarf’ test. Here, the patient’s hand is taken across their chest (horizontal adduction) and placed on top of their other shoulder. Where the joint is especially painful this is carried out as a passive movement with the therapist supporting the weight of the patient’s arm. In cases of high irritability, minimal horizontal adduction is all that is required to provoke symptoms.

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.

Figure 17.11 Acromioclavicular joint injuries. Type I (sprain), type II (subluxation), type II (dislocation), type IIIa (reduces as weight taken), type IIIb (no change as weight taken), type IIIc (lateral end of clavicle more prominent as weight taken).

Injury is usually the result of a superiorly directed force as occurs with a fall onto the point of the shoulder or being struck from above. The force drives the scapula downwards, an action resisted by the coracoclavicular ligament.

Examination reveals local tenderness over the AC joint, sometimes with a noticeable step deformity. The deformity may occur later, if initial muscle spasm reduces acromioclavicular separation.

Initial treatment aims to reduce the symptoms. Ice and a sling support to take the weight of the arm are recommended. The joint is immobilized in the sling for 2–3 weeks, and then gradually mobilized within pain-free limits. With grade I injuries, some relief may be provided by taping.

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.

In the acute phase of injury, the forearm weight may also be taken by a collar and cuff sling. With time, when pain-free arm motion to 90° is available, the humeral portion of the tape may be dispensed with.

Specific exercise therapy

As inflammation subsides, exercise therapy is commenced to restore function. This is used initially to maintain muscle tone in the absence of joint movement. Isometric contractions of the scapular and glenohumeral muscles are used, and the athlete maintains general fitness and lower body strength by exercising with the AC joint taped. When pain subsides and movement commences, gentle scapular actions are used, such as shoulder shrugging and bracing within the limits of pain. These may progress to a scapular stabilization programme. Range of motion exercises for the glenohumeral joint are begun, ensuring that correct scapulohumeral rhythm is maintained.

When full pain-free motion is obtained, the athlete may be seen to have a permanent step deformity, and some joint degeneration may occur in later years. The major problem resulting from this injury is lack of confidence when falling in contact sports. The effects of direct trauma may be limited by placing a felt doughnut pad over the joint. Confidence is built using progressive closed chain exercises and rehearsal of falling actions. These may begin with forward rolls onto the outstretched arm on a mat, initially from a kneeling position, progressing to standing and finally a diving forward roll over a bench. Pressure over the point of the shoulder begins with log rolling on the floor, and builds up to shoulder blows on to a rolled mat or punch bag.

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.

AC joint degeneration

Joint degeneration is common in later years following injury, regardless of the grade of damage which occurred, and particularly after repeated trauma. In addition, some sports, such as weight-lifting, have a higher incidence of degenerative changes in the AC joint, even where no incidents of trauma may have occurred. Cahill (1982) reported 46 cases of osteolysis of the distal clavicle, all but one occurring in weight-lifters. He argued that degeneration occurred as a result of subchondral stress fractures resulting from repeated microtrauma. The condition presents as pain, usually dull and aching in nature, brought on by activities such as lifting and throwing. On examination there is point tenderness over the joint, with pain and crepitus to passive horizontal adduction (cross body test).

Where the diagnosis is uncertain, radiographs will frequently reveal degeneration, and injection of local anaesthetic into the joint is helpful to establish if the degeneration is the cause of the patient’s symptoms.

Movements which stress the joint (for example, press-ups, weight training or throwing) should be avoided. Initially, immobilization in a sling may be required in the very acute lesion. Later, joint mobilization provides good results. Anteroposterior gliding may be performed with the patient in a sitting position. The therapist grasps the distal end of the clavicle with his or her thumb and forefingers of one hand, and the acromion process in a similar fashion with the other hand. The hands are worked against each other to glide the joint. Injection of corticosteroid may give many months of relief, a technique made easier if the shoulder is laterally rotated to distract the AC joint.

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.

Figure 17.18 Impingement of the rotator cuff.

During elevation and internal rotation, the greater tuberosity, with the supraspinatus riding on top, may press against the anterior edge of the underside of the acromion (or a spur from a degenerating AC joint) causing impingement pain. During flexion, impingement may also involve the long head of biceps (Peat and Culham, 1994). At the point where the greater tuberosity comes close to the acromion (70–120° abduction), a number of structures may be pinched between the involved bones or the tuberosity and the coracoclavicular ligament. Normally, the structures affected are the suprasinatus tendon, the long head of biceps and the subacromial bursa.

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).

Figure 17.19 Impingement tests. (A) Full abduction with overpressure to the internally rotated shoulder. (B) Hawkin’s sign. Flexion and internal rotation. Overpressure to internal rotation and abduction or horizontal flexion.

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.

Figure 17.20 Vascularity of the critical zone.

From Keirns (1994) with permission.

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).

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