There is a region in the shoulder composed of the acromion process, coracoacromial ligament, and coracoid process known as the coracoacromial arch (Figure 1).
Anterior-lateral view of the shoulder showing the coracoacromial arch and tissues at risk of impingement. Impingement might result purely from the structure of the coracoacromial arch, but commonly results from a combination of architecture and repetitive motions, especially those involving flexion and internal rotation of the humerus.
There are three progressive stages of impingement syndrome.2 Stage 1 is more common in patients 25 years old or younger. A further classification of impingement pathologies divides them into primary or secondary. Secondary impingement occurs without any specific alterations in the shape of the acromion process. It is mostly a result of dysfunctional shoulder biomechanics, and is exacerbated by excessive motion or long periods of compression.
Shoulder impingement is a challenging problem to treat because many of the affected tissues lie underneath the acromion process.
Normal wear and tear of the muscles, injury to the rotator cuff, repeated overhead movements, sudden (unused and improper) lifting or poor posture can cause inflammation of the rotator cuff causing impingement. Similarly with age, bone spurs may develop under the end of the collarbone or the spine of the shoulder blade (picture below) resulting in reduced subacromial space.
Shoulder stiffness is possible and hence it is important to follow the physiotherapy rehabilitation after surgery.
Also problematic are activities requiring that the shoulder be held in an elevated position for prolonged periods. Primary impingement is predominantly caused by the architecture of the subacromial region.3 Primary impingement is directly related to the variations in shape of the acromion process. However, in many cases, such as secondary impingement problems, repetitive motion and altered shoulder biomechanics aggravate the condition. One of the adverse effects of repetitive motion or holding the shoulder in a static position for long periods is shoulder impingement.
Shoulder impingement involves compression of soft tissues between the head of the humerus and the underside of the acromion process or coracoacromial ligament.
Impingement might lead to tendinosis, rotator cuff tears, calcific tendinitis, bone spurs or subacromial bursitis. In addition, bone spurs and osteophytes might develop along the underside of the acromion and further contribute to subacromial impingement.
You can imagine it’s a little like a bone spur, except this spur has a tendency to press into the underlying tendon, hence impingement.
Every time you lift your arm up to the side or you scratch your back, this hook presses into the supraspinatus tendon, and pinches causing pain. This shoulder impingement may also be caused by some arthritis under the acromion, including small bony nobules called osteophytes. Then depending on the exact cause of your shoulder impingement, you can use anti-inflammatory drugs, physical therapy such as osteopathy or physio, and ice packs to reduce the inflammation.
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