Subacromial impingement is not free of criticism. First, the identification of acromion type shows poor intra- and inter-observer reliability.   Second, a computerized three-dimensional study failed to support impingement by any portion of the acromion on the rotator cuff tendons in different shoulder positions.  Third, most partial-thickness cuff tears do not occur on bursal surface fibers, where mechanical abrasion from the acromion does occur.   Fourth, it has been suggested that bursal surface cuff tears could be responsible for subacromial spurs and not the opposite.     And finally, there is growing evidence that routine acromioplasty may not be required for successful rotator cuff repair, which would be an unexpected finding if acromial shape had a major role in generating tendon lesions.  In summary, despite being a popular theory, the bulk of evidence suggest that subacromial impingement probably does not play a dominant role in many cases of rotator cuff disease. 
Supraspinatus tendinitis is a common source of shoulder pain in athletes that participate in overhead sports (handball, volleyball, tennis, baseball). This tendinitis is in most cases caused by an impingement of the supraspinatus tendon on the acromion as it passes between the acromion and the humeral head. Pain, and a decrease in range of motion, strength and functionality are the main complaints that accompany this injury and should be addressed in the physical therapy. There is enough evidence to prove that physical applications such as ultrasound , cryotherapy, hyperthermia, transcutaneous electrical nerve stimulation and extracorporeal shock wave therapy have a beneficial effect on the recovery of supraspinatus tendinitis. But we have to remember that it is very important to use these methods as an adjunct to physical therapy (increasing ROM, strength training of the rotator cuff muscles and other shoulder stabilizers).
The radiograph shows calcific tendinitis of the supraspinatus tendon. This is the most common structure involved in this disease process.
Uthoff describes stages of calcific tendonosis. The "Pre-calcific" stage shows metaplasia of tenocytes into chondrocytes. The "Calcific" stage has three sub-parts: Formative phase, Resting phase, Resorptive phase. The "Post-calcific" stage is last.
Two types are seen on X-Ray: Type I has as fluffy and fleecy appearance with a poorly defined periphery. This is associated with an acute pain and is usually seen during the formative phase of the calcific stage. Type II is characterized by discrete homogeneous deposits with uniform density and a well defined periphery. This is seen in subacute and chronic cases. Persistent cases may respond to arthroscopic debridement of the deposits with a shaver or spinal needle.
Seyahi et al describes arthroscopic removal of calcifying deposits involving the tendon alone compared to those with additional osseous involvement. The results were similar in both groups.