Impingement Syndrome (Fig, 3-10)
Overhand tennis stroke
Front crawl and butterfly swimming strokes
Side arm and overhand throwing act
The subacromial arch is formed by the acromion, acromioclavicular joint, lateral clavicle, and the coracoacromial ligament.
The strucures in the subacromial space (the supraspinatus tendon, long head of biceps tendon, subscapularis tendon, and the subacromial bursa) can be subject to repeated impingement between the humerus and the acromion (and coracoacromial ligament), as described by Rathburn and McNab, as well as Hawkins and Kennedy.
Repeated abduction (at angles between 70° and 120°), coupled with internal or external rotation and shoulder flexion, can inflame these structures.
This impingement occurs during the tennis serve, the front crawl and butterfly swimming strokes, weight lifting, and overhand and sidearm pitches.
If any of the structures become damaged, inflammation and swelling decreases the subacromial space and impingement discomfort results. This impingement can cause one or all of the following: biceps tendonitis, supraspinatus tendonitis, subacromial bursitis (Rathburn, McNab, Kennedy et al.) (Fig. 3-11).
Because of this impingement an avascular zone can develop in the supraspinatus tendon (1 cm proximal to the insertion) and in the long head of the biceps, where it stretches over the humeral head. This avascular zone can cause necrosis of the tendon cells, calcification, and even tears.
Chronic subacromial bursitis can result if adhesions develop in the bursal wall or if there is a thickening of the muscles in the subacromial space; these adhesions or thickenings will reduce the subacromial space even further.
Neer and Welsh maintain that thickening or a separation of the acromioclavicular joint may cause secondary impingement syndromes. Hawkins and Abrams state that shoulder boney architecture has a role with impingement, from any of the following:
• abnormal shape or thickness of the acromial process
• prominent greater tuberosity
• incompletely fused apophysis
Neer states that an acromion with less slope and a prominent anterior edge may be more susceptible to impingement.
According to Nuber et al., during the front crawl and butterfly strokes the latissimus dorsi and the clavicular head of the pectoralis major muscle were found to be the predominant muscles of propulsion; however, the subscapularis muscle also has a role. The supraspinatus, infraspinatus, and middle fibers of the deltoid were mainly recovery phase muscles. The serratus anterior appeared to have an important role during the recovery phase in the stabilizing of the glenoid cavity. As the inflammation from impingement increases, the rotator cuff muscles may show reflex weakness and may not be able to stabilize the gleno-
humeral head in the glenoid cavity. As a result, the deltoid may overwork to stabilize the head, which in turn leads to greater impingement.
This impingement problem usually develops in the young athlete (swimmer, thrower) but can also occur in the middle-aged athlete who overtrains (squash, tennis). In both cases , the impingement may be aggravated by an imbalance between the internal or external rotator muscle strength. Swimmers and throwers tend to have stronger internal rotators than external rotators.
The anterior glenoid labrum or anterior capsular laxity that may result from a previous dislocation or from repeated subluxation can result in clicking and/or pain during the front crawl or butterfly strokes.
Has the injury occurred before? Anterior glenohumeral dislocations tend to recur.
Biceps tendonitis recurs especially when overtraining in the throwing act. The biceps tendon is an important stabilizer during throwing and when overworked will inflame. It tends to occur more commonly in the athlete with the anterior or forward glenohumeral joint or impingement syndrome. Biceps tendonitis is common from the serve and overhead strokes in tennis and the front crawl in swimmers. Infraspinatus tendonitis is also common in tennis players and throwing athletes because this muscle is important to shoulder stabilization during the deceleration phase or follow-through in both sports.
Subacromial bursitis tends to recur at 2 to 5 year intervals.
Recurrent subluxations of the long head of biceps are common. This problem often occurs in the throwing athlete during the cocking and early acceleration phases, especially in athletes who have a shallow bicipital groove. The tendon subluxes when the humerus goes from external rotation to internal rotation. A subluxing biceps tendon also occurs more easily if the angle of the bicipital groove is less than 30° or there is a supratubercle ridge that forces the tendon against the transverse ligament, making it easier to sublux.
Having the athlete demonstrate the mechanism helps clarify the body position and the stress placed on the involved tissue. This helps determine the damaged structure and injury mechanism.
Reenacting the Mechanism
Can the athlete reenact the mechanism using the opposite limb? Note arm position Note body position Note shoulder position
If it is an overuse injury, ask the athlete to demonstrate the painful action with the opposite limb.
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