Intrinsic impingement of the shoulder

Unlike other joints, the shoulder lacks stable ligaments or a large socket to hold the humeral head in place. The shoulder is a joint that relies on good muscular stabilization.

The rotator cuff, in particular, has the task of keeping the humeral head centered in the socket through a complex interplay of individual muscles. If the muscles or associated tendons become dysfunctional, this stabilization is lost. The result is a decentration of the humeral head. Displacement of the humeral head can, for example, cause it to move closer to the acromion and narrow the space below it. This is a classic impingement situation.

The most common cause of intrinsic impingement is damage to the tendons of the supraspinatus muscle. An important function of the supraspinatus muscle is to push the humeral head downward when the arm is raised, thereby expanding the space under the acromion. Tendon damage or tears in the supraspinatus tendon mean that the muscle can no longer perform this function. As a result, the humeral head pushes upward when the arm is raised, and the tendons and bursa become trapped under the acromion. This results in impingement.

When planning treatment, it is extremely important to distinguish intrinsic impingement from other forms of impingement. Surgeries that attempt to expand the space by milling or removing bone are unsuccessful and can even exacerbate the problem. The additional space created quickly leads to the humeral head becoming even more decentered, which in turn triggers impingement. In addition, incorrect loading of the joint surfaces, which no longer fit together optimally, can lead to additional problems.

In cases of intrinsic impingement, attempts must be made to repair the muscle or tendon damage. This is the only way to restore stability in the joint. Only this will lead to centering of the humeral head and increased space under the acromion.