The majority of sports couldn't be played without using the most mobile joint in the body -- the shoulder. Due to its superior flexibility, the shoulder is vulnerable to injury as it contorts through angles and positions during throwing, catching and passing.

Athletes may experience pinching (impingement) of delicate soft tissues between the bones of the shoulder during repetitive movements. As a result, impingement syndrome is one of the most common pathologies that affects the active shoulder.
Impingement syndrome is shoulder pain that's caused by mechanical irritation of the rotator cuff as it passes through the coracoacromial region between the humeral head and the underside of the Acromion. The Supraspinatus tendon is the most commonly pinched structure. But the Subacromial bursa, the long head of the biceps tendon, and the Infraspinatus or subscapularis tendons may also be sources of pain.
Other symptoms include rotator cuff weakness, decreased range of motion and a positive impingement sign. An athlete may also experience a painful arc during shoulder elevation between 60 and 120 degrees of abduction. The most discomfort may occur at 90 degrees.
Shoulder pain may refer down to the deltoid tuberosity or as far as the elbow. It can also reach into the neck as the upper trapezius muscle struggles to help raise the painful shoulder during compensatory "shoulder hunching" maneuvers.
Athletes who participate in sports that involve high-velocity, resisted motions or repetitive overhead movements are predisposed to shoulder impingement. Impingement syndrome is common in athletes, especially among pitchers, swimmers and tennis players.

Squeeze Play
During overhead motion, the tendons of the rotator cuff are protected from compression and friction against surrounding bones by the Subacromial bursal cushion and by the firing of muscles that keep the humeral head centered in the glenoid fossa.
However, structural changes and biomechanical deficits can narrow the Subacromial space, which may lead to impingement. Shoulder overuse with repetitive overhead movements - especially when performed against resistance can repeatedly squeeze the underlying rotator cuff tendons and Subacromial bursa. This leads to friction, soft tissue microtrauma and chronic inflammation. Once the impingement pattern is established, shoulder pain reproduces every time the arm is raised, which impairs freedom of movement and inhibits muscle strength.
In addition to restricting participation in sports, impingement is a major cause of rotator cuff tears, especially in the dominant arm. Studies show that microtrauma causes the death (apoptosis) of Supraspinatus tendon cells, which results in tendon fiber degeneration and increases the risk of a rotator cuff tear.
An impingement pattern begins with a narrowed joint space that compresses, pinches and frays the rotator cuff tendons. However, in certain circumstances, existing rotator cuff tendonitis, a partial rotator cuff tear or Subacromial bursitis may be the origin of impingement pain, since swollen soft tissue structures clog the Subacromial space.
Repetitive, forceful and high velocity overhead movements can provoke early degenerative changes in the distal rotator cuff tendons and cause shoulder impingement in younger athletes. Although rotator cuff tears are infrequent among younger athletes, the incidence progressively increases after the fourth decade and leads to the clinical maxim "gray hair means cuff tear."

Static and Dynamic Control
As a freely moving joint, the shoulder is protected from excessive movement, Subluxation or dislocation by static and dynamic stabilizers. Static stabilizers are inert structures that include bony joints, cartilaginous labrum, glenohumeral ligaments and the joint capsule. Dynamic shoulder stabilizers include the scapular muscles (large stabilizers) and rotator cuff muscles (small stabilizers).
When stabilization mechanisms fail to protect the joint, impingement occurs. Impingement syndromes fall into three subgroups.
Primary impingement is more common in older athletes and people over age 50. It's usually due to structural degenerative changes of the static stabilizers, which create a narrow outlet that squeezes the Supraspinatus tendon against the Acromion as it rides along the humeral head, especially with repetitive shoulder abduction.
Causes include bone spur formation (osteophytes), joint capsule restrictions (adhesive capsulitis), acromioclavicular joint arthritis and calcification of the coracoacromial ligament from a previous trauma.
Primary impingement may also be caused by degenerative, highly curved Acromion. In one study, 93 percent of people over age 50 had a curved or hooked Acromion, which correlated to a higher incidence of rotator cuff tears from overlying impingement.
Pain from primary impingement is typically anterolateral and reflects a decreased range of motion with shoulder elevation. In addition, an athlete may experience pain at night when he attempts to lie on the affected shoulder. Differential diagnosis should rule out calcific tendonitis of the Supraspinatus tendon as an alternate source of pain.
Secondary impingement is common among younger athletes. Although the pathology is similar to primary impingement, it's caused by underlying glenohumeral joint structural instability (laxity in the static stabilizers) or functional instability from scapular and rotator cuff weakness (dysfunctional dynamic stabilizers). Throwing athletes often experience secondary impingement, since repeated overhead movements require excessive range of motion, which is a consequence of stretched shoulder ligaments and increased joint capsule laxity.
Secondary impingement occurs when the unstable humeral head slips in the glenoid fossa and traps rotator cuff tendons within the coracoacromial space. On occasion, the micro-instability of secondary impingement may also promote tears in the glenoid labrum.
Training imbalances may cause the rotator cuff to lose competency via weakness, disuse, injury or fatigue from overuse. Secondary impingement can occur when the dysfunctional rotator cuff can't control the genohumeral joint. This allows the larger deltoid muscle to pull the humeral head superiorly and entrap the rotator cuff tendons in a narrow coracoacromial space. Characteristic anterior or anterolateral pain is reported during athletic activity.
Internal impingement may occur when an unstable humeral head squeezes the suprasinatus and infranspinatus tendons against the posterior glenoid fossa. This may be seen in baseball players during the late cocking phase of pitching, when the arm is in extreme abduction and external rotation (posterior-superior glenoid impingment). Internal impingement may be the cause of pain if previously diagnosed rotator cuff tendonitis fails to respond to treatment.
Another less common form of internal impingement occurs when the subscapularis tendon is pinched between the humeral head and coracoid process during flexion and internal rotation. With internal impingement, look for a positive apprehension sign, restricted internal rotation and posterior shoulder pain.

Taking a Time Out
Once an impingement injury occurs, it's imperative to reduce pain and inflammation of the damaged rotator cuff tendons. Most impingement syndromes resolve by modifying aggravating activities to eliminate further pinching; this may initially require cessation of overhead and cross-body motions.
In the acute phase of treatment, prescribe rest, non-painful range of motion and oral non-steroidal anti-inflammatory medications. You can use anti-inflammatory modalities, such as cryotherapy, interferential stimulation, ultrasound, phonophoresis, lasers and acupuncture, to control swelling and speed healing. Research indicates that lasers may be more effective for adhesive capsulitis and ultrasound can create benefits for calcific tendonitis.
Advise patients to use the shoulder for all activities of daily living, work tasks and sports that don't reproduce the pain. For the recalcitrant painful shoulder, therapeutic cortocosteroid injections may be indicated to decrease inflammation.

Returning to Play
Once initial inflammation decreases, attempt to restore range of motion, mobilize the shoulder joint and implement a strengthening program to improve function and reduce short and long-term pain.
With primary impingement, mobilization techniques to glide the humeral head caudally and posteriorly can help reduce stress on irritated tissues and may increase Subacromial joint space. This measure can correlate with functional symptom improvement.
With secondary impingement, it's critical to restore normal strength and biomechanical patterns to large and small dynamic stabilizers. Insufficiency of the scapulothoracic and subscapular muscles occur when poor posture or pectoral / paraspinal muscle imbalance allows the scapula to protract and the humeral head to sublux closer to the Acromion.
Design a program to increase activation of scapular stabilizers and improve postural awareness. Elongated, weak scapular stabilizers can increase rotator cuff workload. Studies show that athletes who have an impingement syndrome demonstrate a delay in middle and lower trapezius muscles activation, and the postural improvement with scapular taping delays the onset of pain with shoulder elevation.
You must strengthen and retrain the rotator cuff muscles in order to stabilize the humeral head within the glenoid fossa during overhead movements. Isometric exercises, followed by isotonic concentric and eccentric strengthening exercises that emphasize abduction, internal rotation and external rotation, are a priority.
Other manual techniques, such as proprioceptive neuromuscular facilitation, can balance a rotator cuff and enable the gradual return to sport-specific dynamics.
With internal impingement, you should emphasize progressive stretching of the posterior joint capsule, which may be tight despite anterior joint instability. In addition, make sure you retrain the large and small dynamic stabilizers with sport-specific movements.
Also, patient education is an important component of treatment to reduce impingement risk. With a primary or secondary impingement, instruct athletes about correct body mechanics when raising the arm overhead. The rotator cuff tendons should "clear" the underside of the Acromion without pinching.
In the short term, it may be necessary to adjust the mechanics of throwing, a swimming stroke or tennis serve until the dynamic stabilizers are strong enough to improve the biomechanical advantage of the joint.
Optimizing shoulder range of motion, rotator cuff and scapulothoracic strength, dynamic posture, and sport-specific biomechanics can help prevent a recurrence. Analyze and adjust training habits to facilitate a pain-free return to play. Most cases respond to rehabilitative treatment, and surgical options are reserved only for chronically impinged, debilitated shoulders.
Full rehab of an impingement syndrome and related rotator cuff injury has a high success rate, so most athletes can get out of a pinch and back in the game.

Source: Advance Directors in Rehabilitation May 2006 Vol. 15 No. 5