The Musculus supraspinatus originates at the Fossa supraspinata of the shoulder blade and starts at the large hump (Tuberculum majus) of the humerus. It lies above the spina scapulae. In the shoulder joint, the supraspinatus muscle causes the arm to rotate outwards and moves it away from the body.
The muscle also passes over the capsule of the shoulder joint and is fused with it. This causes the capsule to be tensed and strengthened by the muscle. As a result, the head of humerus is held in the shoulder joint.
Origin/Approach/Innervation
The supraspinatus muscle is one of a total of four muscles of the so-called “rotator cuff“, a special grouping of muscles in the shoulder. It has its origin in the “supraspinous fossa”, a depression in the shoulder blade above the shoulder bone (spina scapulae). The shoulder bones can be easily palpated through the skin at the shoulder blade as a bony projection that rises to the side and ends at the shoulder.
The base of the supraspinatus muscle is the tuberculum majus, a large bony projection on the humerus, which lies approximately laterally below the head of the bone. On the way between the attachment and the origin, the supraspinatus muscle runs through a shoulder narrowing, which is formed by the acromion and the head of the humerus. The origin and insertion of the supraspinatus muscle give the muscle the function of lifting the arm laterally upwards, especially at the beginning of movement.
The innervation of the supraspinatus muscle is ensured by the suprascapular nerve. It is composed of the spinal nerves C4, C5 and C6. Irrespective of the form of the impingement syndrome, the affected patients experience pain, especially when the arm is guided sideways.
If this movement is performed against resistance, the pain increases. The pain occurs mainly in a lateral movement of the arm between 90° and 120° (painful arc). If the arm is lifted even further above the head, the pain subsides again.
The head of humerus is lowered in the subacromial space, leaving more space for the muscles. The diagnosis of the impingement syndrome can be easily made by means of the corresponding symptoms and an X-ray diagnosis. Inflammations of the capsule, calcium deposits or inflammations of the muscle tendons can be visualized by means of ultrasound.
The therapy consists of cooling, pain medication and physiotherapy. If symptoms persist, the impingement syndrome can be corrected by surgery, in which the subacromial space is cleared and thus expanded. However, this therapy option does not always offer an improvement of the symptoms and is therefore only used after the failure of conservative options.
A degenerative process of the supraspinatus tendon is called tendinosis calcarea. This is caused by the deposition of calcium salts on the tendon. Patients suffer from acute, highly restrictive attacks of pain in the shoulder.
The arm is then held close to the body to relieve the muscles and is massively restricted in its mobility due to the pain. Often the tendon below the collarbone is particularly painful due to pressure. If the tendinosis calcarea is chronic, the pain may be less severe and permanent.
Women over the age of 30 are particularly frequently affected by this disease. A rupture of the supraspinatus muscle as part of a rotator cuff tear (rotator cuff rupture) leads to a loss of function and thus to a severe restriction of shoulder elevation (abduction). If the tendon of the supraspinatus muscle is completely torn, active abduction is impossible.
An attempt by the patient to raise the shoulder only results in a shrug of the shoulder. The tendon of the supraspinatus muscle is particularly stressed during life and for this reason often tears spontaneously after the age of 50. This leads to severe pain and a loss of function of the muscle, so that the external rotation and removal of the arm from the body is only difficult or even impossible.
Another important disease of the supraspinatus muscle is the impingement syndrome. In this syndrome, the supraspinatus tendon is trapped under the bony protrusion (acromion) of the shoulder joint and thus causes severe pain. A distinction is made between various causes that lead to the tendon being trapped in the subacromial space.
With so-called outlet impingement, the subacromial space is constricted by the surrounding anatomical structures.These include above all changes in the shape of the bony protrusion (acromion), an acromion spur or bone deposits (osteophytes) in the joint space due to degenerative phenomena. The other form of impingement syndrome is non-outlet impingement. This is caused by inflammation of the shoulder joint capsule, or a lesion of the muscles of the rotator cuff.
These can become inflamed and swollen as a result of the injury, causing the subacromial space to become smaller and the supraspinatus tendon to become trapped. If the rotator cuff tears completely, the entire joint capsule loses stability, which means that the head of humerus can no longer be held in position and slides under the acromion. This case is called instability impingement.
The supraspinatus muscle, but especially its tendon, can cause severe pain due to injury or excessive strain. Most often, a bony constriction, which the supraspinatus muscle passes through in its course, causes problems, as it squeezes the muscle and its tendon, thereby disrupting the blood supply. This pain problem occurs when the bony constriction becomes relatively narrow when the supraspinatus muscle is tensed and the muscle with its tendon no longer fits through it smoothly.
As the muscle becomes more and more constricted as the arm is lifted upwards, the arm position at 60° to 120° is particularly painful for those affected and in some cases cannot be performed at all. Because of the pain it causes, this phenomenon is also called “painful arc”. The clinical picture is called “impingement syndrome”.
Pain of the supraspinatus muscle can also be caused by a rupture of the muscle. This is a common injury. On the one hand, it can occur during sports with powerful and sweeping movements with the arms, or on the other hand due to wear and tear and additional irritation of the tissue, for example, due to impingement syndrome. The pain is usually accompanied by a loss of function of the supraspinatus muscle, which can be compensated for by surrounding muscles in the course of and possibly also with the help of treatment.