Chapter 1: The Pathophysiology of frozen shoulder
Frozen shoulder syndrome (FFS) is a condition that causes pain and stiffness of the shoulder in some adults. It is also called adhesive capsulitis because the sack that contains the lubricating fluid in the shoulder joint forms adhesions and this can contribute to the inflammation and stiffness of the joint. There are many underlying pathologies associated with this condition and the muscles, ligaments and bursae of the shoulder all seem to be involved in the condition. However, there are still a lot of things that we do not understand about this condition and patients are frequently misdiagnosed or not diagnosed until they have suffered with the pain for a long time. Nevertheless, patients that have frozen shoulder syndrome feel pain and stiffness that can last weeks or months, causing them a lot of sleepless nights and significantly impacting their quality of life.
The Shoulder Joint
In order to understand the causes of frozen shoulder syndrome, it is necessary to briefly explain the anatomy of the human shoulder and how it normally functions in a healthy person. The shoulder joint is also called the genohumeral joint and is composed of the head of the humerus which moves within the glenoid cavity (or fossa) of the scapula. Both of these moving surfaces are covered with hyaline cartilage which is typical for a synovial type joint. Since the head of the humerus is much larger than the glenoid fossa, it inherently renders the joint unstable, making it easily susceptible to damage caused by physical strain. To reduce the disproportion in the joint surfaces, the glenoid fossa is deepened by a fibrocartilage rim, called the glenoid labrum (have to re-word this).
Frozen Shoulder (FSS): what is it and what do we know about the underlying pathology?
Frozen shoulder syndrome is a painful and debilitating condition that can affect as much as 5% of the population. Sometimes it is called adhesive capsulitis. This name is a clinical diagnosis which means that it is used to describe an array of underlying pathophysiological conditions sometimes referred to as calcifying tendinitis, partial rotator cuff tear or subacromial bursitis. Even though there may be many terms used to describe this condition, the condition is painful and causes restriction in the active and passive use of the shoulder. Most importantly, this means that the shoulder is completely stiff and immovable. Not only can the patient not move his/her arm, even someone else cannot help them move it.
Most physicians will diagnose a case of frozen shoulder syndrome when a patient has a stiff shoulder with less than 50% of normal range of active and passive motion in any direction. Normally, this type of restricted movement must have occurred for about 1 month in order for an FSS diagnosis to be given. There are really two types of frozen shoulder syndrome which were originally defined by physicians. The first type is the primary which means that the frozen shoulder syndrome occurred without any warning signs, such as a trauma or illness. Patients with primary FSS usually have no previous history that would indicate how their FSS occurred. On the other hand, secondary FSS is the result of some sort of injury or trauma to their upper body region.
Thus, the joint capsule of the shoulder joint has ligaments that hold the shoulder bones together and when the capsule becomes inflamed, the shoulder bones are unable to move freely in the joint and this causes a “freezing” or lack of motion.
Who gets frozen shoulder?
Frozen shoulder syndrome usually affects patients aged 40-70 years but the exact number of FSS cases are not precisely known because FSS is often misdiagnosed. However, it is estimated that 3% of people develop the disease over their lifetime, women tend to get FSS more frequently than men, and there is no predilection for race.
The most frustrating part of this condition is that patients that get this condition usually have no prior history or clinical finding to indicate the purpose of their FSS and it is very difficult to predict if someone will get FSS in the future. However, some links to pre-existing conditions, particularly in secondary FSS, have been suggested by some researchers.
Frozen shoulder syndrome occurs more frequently in people who have diabetes (10-20%), especially in those patients with insulin-dependent diabetes (36%), suggesting a possible link between sugar metabolism and this condition. Some researchers have suggested that muscular inactivity increases the risk of developing FSS (DePalma). In a study of neurosurgery patients that immobilized their shoulder for various periods of time, the incidence of frozen shoulder was 5-9 times greater than the general population (Bruckner).
An autoimmune component of FSS has also been proposed by some researchers who have reported that FSS patients tend to express certain types of immunohistocompatibility antigens. Some researchers believe that the reason women are more susceptible to developing FSS is because it is linked to diseases that predominantly affect women. For example, FSS has also been linked with cervical disease, hyperthyroidism and ischemic heart disease.
What does a frozen shoulder feel like?
The symptoms of primary frozen shoulder have been divided into three phases:
(1) painful phase
(2) stiffening phase
(3) thawing phase.
Each of these phases is associated with a specific period of time but it can be different for each patient. In the early painful phase, for some patients there is a gradual build up in the pain over the entire shoulder which can last for weeks or even months. For other patients, there is a very sharp spasm of pain without any apparent cause. In this case, the sharp pain changes into a persistent ache that never goes away, but is usually worse at night. Patients in this phase usually suffer from disturbed sleep and a depletion of energy that further aggravates their quality of life.
The stiffening phase is when the patient experiences a progressive loss of motion that may last up to 1 year. At this point, the pain goes away (for the most part) but the shoulder stiffness increases. Most patients lose rotation in the shoulder and cannot perform the most straightforward tasks such as brushing their teeth or picking up a set of keys.
The final, thawing phase can last weeks or months and can be a period of gradual motion improvement. For some patients this may require up to 9 months before they regain even a small improvement in their range of motion.
The underlying pathology of Frozen Shoulder Syndrome
Originally, when FSS was first described by Dr. Duplay in the late 1800s, it was proposed that the underlying causes of FSS were soft tissue damage. Since then, our understanding of FSS has progressed so that now we know it is mediated by inflammation and results in the formation of scar tissue in the shoulder joint.
More recent research has shown that FSS is caused by inflammation and the body’s inappropriate over-compensation to turn off this inflammatory response. The shoulder ball and socket joint is surrounded by a fluid filled bag with 35-70ml of synovial fluid which helps to lubricate and nourish the joint; with Frozen Shoulder the capsule thickens and becomes tight and the fluid levels drop to an average of 5-10ml. Stiff bands of tissue (referred to as adhesions) may start to develop in and around the capsule. This is due to inflammation. The hallmark sign of a “frozen shoulder” is being unable to move your shoulder – either on your own or with the help of someone else.
FSS begins when the lax capsular sack becomes sticky and can sometimes (though not always) form adhesions; hence the name of the condition. The stickiness is caused by inflammation and research has shown that this occurs in the rotator interval where inflammation often starts in the groove behind the biceps tendon. This can occur after a small injury or can even be brought about by something simple like reaching for something behind the couch. Once established, this inflammation spreads into other soft tissues in the shoulder and this causes swelling in other shoulder sacks (bursae). This happens because the muscles, ligaments and bursae within the shoulder are very much interconnected. Over a period of time, FSS causes the capsule surrounding the shoulder to contract and form scar tissue, further aggravating the motion of the joint.
Therefore, Frozen shoulder syndrome is a painful condition that causes the lack of motion in the shoulder joint. It can last weeks, months or even years and most often occurs in older women between the ages of 40 and 60. No one knows the causes of FSS, but it is believed that certain endocrine conditions (such as Diabetes) can increase the risk of developing FSS. The underlying pathology of FSS is inflammation of the shoulder joint which eventually causes scar formation. Sometimes FSS resolves on its own but often some form of medical intervention is required.