What is a frozen shoulder?
The term frozen shoulder is a condition associated with pain and stiffness in the absence of a demonstrable cause. That is, it develops out of the
blue. The term “frozen shoulder” is often overused and applied to any person with a stiff and painful shoulder. It has been described as a “waste can” diagnosis which is very unhelpful. A stiff shoulder can be divided into a primary frozen shoulder and secondary stiff shoulder. The primary frozen shoulder or true frozen shoulder is as defined above with a painful and stiff shoulder joint in the “absence of a known intrinsic shoulder disorder”. There is no significant history of injury or investigations which can explain the pain and stiffness. A secondary stiff shoulder is shoulder pain and stiffness from any other causes such as an injury, for example, a fracture, tendon or cartilage tear. It can also occur due to conditions unrelated to the shoulder such as a whiplash injury or a pinched nerve in the neck.
The precise cause of this condition remains poorly understood despite much research. The condition of frozen shoulder is very common. 2% – 5% of the general population develop a frozen shoulder, while diabetics have a risk of over 10%. Insulin-dependent diabetics have a 40% chance of developing a frozen shoulder. Women are 50% more commonly affected than men. The most striking clinical feature of frozen shoulder is its predilection for people in their 50’s. Frozen shoulders can occur in people in their mid to late 40’s to early 60’s. Women are on average slightly younger: 52 years old as opposed to men: 55 years old. There also appears to be a significant genetic increased risk. The other significant risk factors are diabetes and thyroid disease. Once you have developed a frozen shoulder on one side you are at increased risk of developing it on the other side. 15% of people develop a frozen shoulder on both sides. Rarely it can occur simultaneously (both at the same time) but more typically affects the other shoulder within the next 5 years after the first shoulder. Surprisingly, recurrence in the same shoulder is extremely unusual.
What causes a frozen shoulder?
The shoulder joint is a ball and socket joint similar to the hip joint but with strikingly more mobility. In fact it is the most mobile joint in the body and almost the entire animal kingdom. The surrounding cartilage and “soft tissue capsule” which includes the ligaments provide the shoulder with stability but still allow the enormous range of motion. In a frozen shoulder the soft tissue capsule initially becomes very inflamed causing a deep ache in the shoulder joint radiating down the arm.
After the development of inflammation, the surrounding soft tissue capsule contracts like a scar, which restricts shoulder motion causing increasingly severe stiffness. The underlying cause of the inflammation is still largely unknown. It may be due to underlying degerative changes in the rotator cuff tendons which are not visible on MRI or ultrasound. It seems the body perceives the shoulder as being injured and therefore triggers an inflammatory response to try to heal it. As the inflammatory cascade occurs, healing cells including white blood cells, platelets and fibroblasts migrate towards the shoulder joint. These migrating cells attempt to “heal” the shoulder joint which it perceives as being damaged.
This creates a domino effect. Once the process starts, it keeps ongoing. Often, we are not sure what sets it off, but it can be a minor injury which does. Like dominoes, it doesn’t seem to matter what initiated it, the process keeps on going as more and more inflammatory factors are produced and there is increasing pain and stiffness. Like the falling dominos, eventually, it runs out.
The cells called fibroblasts are responsible for the production of healing/scar tissue which shrinks the capsule and ligaments which line the shoulder joint. Because of this the capsule and ligaments, which are normally extremely thin and elastic, becomes thickened, tough, and inelastic.
How do you know this is what I have?
By definition, in the primary frozen shoulder, there is no known underlying disorder. As x-rays, ultrasounds and even MRI’s are good at picking up damaged tissues, they cannot usually see inflammation. These investigations must therefore be essentially normal. Unfortunately, the reports that come with these investigations very often report something. For example, an ultrasound report will almost always say there is bursitis and often recommend an injection into the bursa.
So how do we diagnose a primary frozen shoulder? There is an old expression “if it looks like a duck and quacks like a duck and walks like a duck, it must be a duck”. So, we therefore rely on typical clinical features to suggest the diagnosis of a frozen shoulder. If, however, features are not typical, we call these red flags. Examples include occurring in both shoulders at once or occurring less than 45 years old or greater than 65 years old. In this situation, further investigations are warranted. Blood tests to exclude thyroid disease raised cholesterol or blood sugars may be of some benefit but will not help confirm the diagnosis. We therefore do not rely exclusively on investigations to confirm the diagnosis. Nevertheless, they are of benefit in excluding other conditions such as an underlying arthritis, tendon tears etc. We call this diagnosis by exclusion.
The only investigation which can really assist in confirming the diagnosis of a frozen shoulder is an MRI arthrogram, in which dye is injected into the shoulder joint and then an MRI is performed. In a normal shoulder joint the surrounding capsule is extremely thin and elastic and one can see distension of the capsule with a fluid called the axillary recess (above figure). In the presence of a frozen shoulder, the MRI looks normal except there is no distension, confirming a tight capsule which is diagnostic of a frozen shoulder.
How does it affect me?
Typically, the condition starts with a very mild subtle onset of shoulder pain which becomes increasingly severe over subsequent weeks. Usually, after some weeks to months of increasing pain, stiffness in the shoulder joint starts to develop. By about 6 months after the onset of symptoms, the pain is at its worst and movement has also deteriorated to its lowest level. This worsening phase is often described as the freezing phase of a frozen shoulder. It then plateaus at approximately 6 months with pain and lack of movement at its worst. This is often referred to as the frozen phase of a frozen shoulder.
Over the subsequent few months, pain gradually starts to settle and some weeks or months after that, movement also starts to improve. We call this the thawing phase of a frozen shoulder. These stages are not however discrete or well-defined. The time span and severity vary enormously. This pattern is typical of a frozen shoulder where we do not see wild fluctuations in pain and stiffness as we do in other conditions. Studies show the symptoms of a frozen shoulder can last typically anywhere between 1-3½ years with an average of 2½ years. Looking at the long-term outcome of frozen shoulder, one study reported at 4½ years following the onset of symptoms they noticed that 60% of people had essentially regained a normal or near-normal shoulder joint with minimal or no pain or stiffness. Nevertheless, 40% of patients still had some degree of ongoing symptoms. Overall, these were usually quite mild. However, 5% (1/20) of patients still had severe long-standing and disabling pain and restriction in their movement. Interestingly they noted that this 5% of patients are usually those with most severe symptoms early on.
How can it be treated?
We described the natural history of the condition as what would occur if there was no intervention. Understanding the natural history of this condition can help determine what can be done about it.
Treatment options include what is referred to as “benign neglect” and clinical interventions. Benign neglect is a term frequently associated with frozen shoulder. It is defined as doing nothing about a problem and hoping that it will solve itself. For many patients whose symptoms are tolerable, a wait and see approach is quite reasonable. An explanation of the condition and simple medications may be all that is required. These include pain medications, anti-inflammatories (which may have only a mild effect) and medications to assist in getting some sleep. Typically, if symptoms are tolerable at 6 months following the onset, no further intervention will be required.
Clinical interventions which I will discuss include Physiotherapy, Cortisone injections and occasionally, arthroscopic capsular release.
Physiotherapy can be helpful. However, especially when the range of movement is pushed beyond the comfortable range, it may exacerbate the pain. This is most noticeable in the first few months following the onset of symptoms (the freezing phase). Nevertheless, in the thawing phase when the inflammation has settled, physiotherapy and stretching exercises might accelerate recovery in range of motion. With physiotherapy, it is all about the timing and the stages.
These are used to reduce the inflammation. The correct site for the injection is critical. Most injections are performed into the bursa. With primary frozen shoulders, the inflammation is usually much more in the joint than the bursa.
Therefore, Injections into the bursa do not usually provide significant benefit. Ultrasound-guided injections into the shoulder joint have been shown to be far more successful in reducing the pain. There is some evidence that a combined injection into both may produce even better results. Hydrodilation, which involves distending the joint with saline, does not provide additional benefit. As with physiotherapy, it is all about the timing and the stages. It does appear that cortisone injections into the joint are more beneficial in the inflammatory/ freezing phases. They can provide 3-4 weeks or longer of relief. As a frozen shoulder is usually only temporary and usually at its worse for a relatively short period, this treatment can be highly effective. The injection may need to be repeated a few times to alleviate the worst of the symptoms until the inflammation has settled (thawing phase).
Arthroscopic capsular release
If the symptoms do not respond well to the above modalities and pain and stiffness are prolonged (typically greater than 6 months) or intolerable, an arthroscopic capsular release can be performed. It is a key-hole day-surgery procedure where the inflamed and thickened capsule is released. It requires typically 3 tiny incisions. After the procedure, you are encouraged to use your shoulder as soon as comfort allows. You do not need to wear a sling and can return to driving and light activities within a few days. Full recovery typically takes from 6 weeks to 3 months. This provides much quicker relief of the severe pain and accelerates recovery of the range of motion by many months or years.
Once the diagnosis of a frozen shoulder has been made, a wait and see approach (benign neglect) may be all that is required. If pain is disturbing sleep, a cortisone injection can be performed but to be effective, it must be into the shoulder joint, not into the bursa. We can go back to a wait and see approach and repeat the injection if necessary. If this does not provide good relief and symptoms are severe or persistent (greater than 6 months) this condition can last years. In this situation, an arthroscopic capsular release is an option which can provide dramatic relief of the pain and stiffness.