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Shoulder Impingement

Key Points

  • In clinical frequency, shoulder pain is exceeded only by low back pain and neck pain. The most common source of shoulder pain originates in the subacromial space, with the most prevalent diagnosis being impingement syndrome.
  • Without treatment, symptoms will persist and usually progress.
  • Shoulder impingement has been described as “symptomatic mechanical irritation of the rotator cuff tendons from direct contact at the anterior edge of the coracoacromial arch.”
  • In the normal shoulder, the coordinated muscle tension within the rotator cuff compresses the humeral head, keeping it centered within the glenoid fossa. By coupling with the force of the deltoid, a fulcrum is created, generating strength through a wide arc of motion.
  • Any process that interferes with the rotator cuff’s capability to keep the humeral head centered or that compromises the normal coracoacromial arch, including calcium deposits, thickened bursae, and an unfused os acromiale, can lead to impingement of the rotator cuff.
  • Functional overload, intrinsic tendonopathy, and internal anatomic impingement have also led to shoulder impingement.
  • It is important to rule out other potential sources of shoulder pain, including: acromioclavicular arthrosis, rotator cuff tear, instability, adhesive capsulitis, biceps tendonitis, labral pathology, and cervical radiculopathy.
  • The x-ray views that are most helpful are anterior-posterior view, supraspinatous outlet view, and axillary lateral. A 15-degree cephalic view of the Acromioclavicular (AC) joint and an anterior posterior (AP) view with humeral internal rotation can also be helpful.
  • Nonoperative care is tried before surgical intervention is considered. The majority of patients can be treated conservatively. Treatment consists of physical therapy, activity modification, anti-inflammatory medications, and steroid injections into the subacromial space.
  • When nonoperative treatment fails, the procedure of choice is arthroscopic subacromial decompressions (ASAD). The advantages of arthroscopy include minimally invasive surgery without detachment of the deltoid.
  • Conventional postoperative pain control can generally be obtained with oral medications. Stiffness can be avoided when early motion is emphasized.
  • Through progressive steps in exercises, full active range of motion can usually be achieved within three to four weeks. Athletes using overhead motions should avoid sports for at least 3 months, and complete recovery can take 6 months.

The concept of mechanical impingement on the rotator cuff was popularized by Neer. He noted that with forward elevation of the arm, the rotator cuff tendons were subject to repeated mechanical insult by the overlying coracoacromial arch. He observed that impingement was a result of bony spurs at the anterior third of the acromion and the coracoacromial ligament. This concept of anterior impingement as opposed to lateral acromial impingement has been generally accepted.

Neer reported the cause of most impingement to be due to an inadequate “outlet” and described this phenomenon as outlet impingement. The outlet is the space beneath the anterior acromion, coracoacromial ligament, and acromioclavicular (AC) joint. Within this space, the rotator cuff tendons pass to their insertions on the tuberosities of the humerus. The superior border of the outlet forms an arch known as the coracoacromial arch.

Any prominence that affects this arch may encroach on the outlet causing outlet impingement. In addition to outlet impingement, the terms subacromial, primary or external impingement are also used. The definition has more recently been described as “symptomatic mechanical irritation of the rotator cuff tendons from direct contact at the anterior edge of the coracoacromial arch”.

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