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Shoulder Impingement Anatomy
The rotator cuff muscles pass below the acromion (part of the shoulder blade) and inserts on the greater tuberosity of the humerus. There is space between the acromion and the greater tuberosity to allow for the thickness of the muscle tendon in this area. Four muscles form this rotator cuff tendon, the subscapularus, supraspinatus, infraspinatus and teros minor muscles. These muscles are the ones that contract during the initial phase of elevating the arm above the head.
For some reason the space between the acromion and the greater tuberosity narrows and the rotator cuff is being pinged between the two bones. This is therefore called shoulder impingement syndrome. The reason for the narrowing of this space is usually caused by an abnormal shape of the acromion, overlaying the tendon. The acromion is normally flat in appearance, but in some cases might be curved. This curved acromion is classified in three types.
Type 1 is a normal flat acromion that would probably not cause impingement. Type 2 is curved and Type 3 is severely curved with a hook in the front part that causes the impingement. There are however other reasons for impingement. As one grows older and the shoulder starts dropping forward and down, the acromion rotates and the tip of the acromion moves downwards. This downward movement of the acromion now causes the impingement.
These patients usually presents with shoulder pain, especially when elevating the arm above their head. The pain is in the front part and top part of the shoulder, and refers down to the upper arm, sometimes down to the elbow, but never to the fore-arm. The pain is usually more prominent during night time. During day time gravity pulls the arm down and the pain is relieved, because the space is opened. During night time the head migrates upwards and compresses and causes severe pain. These patients usually awaken during the night and feel better if they sleep in a sitting position.
The patients can be treated with conservative measures, if the cause is the forward drooping of the shoulder, physiotherapeutic postural reconstruction might help to reposition the shoulder blade in the corrected position. In some cases a cortisone injection might also help into the subacromial space. On the long term however, these condition is usually treated with a removal of the front part of the acromion, to prevent the pressure on the rotator cuff.
The operation is done with keyhole surgery. A video camera is inserted from the back and the front part of the bone is removed with an arthroscopic “Buhr”. This can be done usually through 2 or 3 puncture wounds, with no incision to the skin.
Post Surgery Treatment
These patients do really well, has very little pain and their outcome is usually very good. These patients do not usually wear a sling (only for the initial period of pain) and can start immediately with active movement and elevation of the arm. They usually do very well and the post operative recovery is usually uncomplicated.