The pathology of frozen shoulder
Frozen shoulder was first written about by Codman in 1934 and its cause has been unclear ever since. Many suggestions have been made to explain what frozen shoulder really is but none have stood the test of scientific examination.
Frozen shoulder is a difficult and mysterious condition which is often diagnosed when a middle-aged person gets a painful and stiff shoulder.
Many causes have been suggested and this condition has been given various names such as adhesive capsulitis, or assumed to be the result of infection, inflammation, joint bleeds, nerve malfunction, injuries or degeneration of the shoulder muscles.
Studies of tissues from frozen shoulders
Tissue studies on material taken from shoulders at operation have indicated a possible inflammatory or fibrosing condition. Bunker has recently shown that the tissue is made of dense collagen, similar in all respects to the tissue found in Dupuytren’s disease or contracture.
Modern work, such as that of Bunker, shows that frozen shoulder is primarily a fibrosing condition affecting the capsule (fibrous bag around a joint) of the shoulder joint. This leads to a tightening up of the coracohumeral ligament (one of the ligaments attaching the shoulder blade to the arm bone), which then restricts passive movement of the shoulder, especially the outward turning movement.
Pain is a big deal in frozen shoulder. It can be very severe and take over a person’s life, interfering with anything they do and denying them sleep.
But why? It’s not clear, since frozen shoulder is a fibrosing condition, why it should be so painful. Other such conditions do not have severe pain associated with them.
The reason that the shoulder can be so painful maybe because of what also happens when the shoulder begins to become abnormal. The head of the humerus (arm bone) may move upwards and impinge on the underneath of the acromion (part of the shoulder blade) causing what is know as impingement pain. As this problem settles the pain may reduce over time.